ASTM D8387/D8387M-23

Standard Test Method for High Bypass – Low Bearing Interaction Response of Polymer Matrix Composite Laminates

SIGNIFICANCE AND USE
5.1 Refer to Guide D8509.
SCOPE
1.1 This test method determines the uniaxial high bypass - low bearing interaction response of multi-directional polymer matrix composite laminates reinforced by high-modulus fibers using a two-fastener hard point joint specimen. The scope of this test method is limited to net section (bypass) failure modes. Standard specimen configurations using fixed values of test parameters are described for this procedure. A number of test parameters may be varied within the scope of the standard, provided that the parameters are fully documented in the test report. The composite material forms are limited to continuous-fiber or discontinuous-fiber (tape or fabric, or both) reinforced composites for which the laminate is balanced and symmetric with respect to the test direction. The range of acceptable test laminates and thicknesses are described in 8.2.1. This test method was previously published under Test Method D7248/D7248M-17 Procedure C.  
1.2 This test method is consistent with the recommendations of Composite Materials Handbook, CMH-17, which describes the desirable attributes of a bearing/bypass interaction response test method.  
1.3 The two-fastener test configurations described in this test method are intended to provide data in the relatively high bypass, low bearing part of the composite bolted joint bearing-bypass interaction diagram. This data complements the data from filled hole tension and compression (Practice D6742/D6742M), bearing (Test Method D5961/D5961M), and low bypass/high bearing interaction (Test Method D7248/D7248M) tests.  
1.4 This test method requires careful specimen design, instrumentation, data measurement, and data analysis. The use of this test method requires close coordination between the test requestor and the test lab personnel. Test requestors need to be familiar with the data analysis procedures of this test method and should not expect test labs who are unfamiliar with this test method to be able to produce acceptable results without close coordination.  
1.5 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.  
1.5.1 Within the text, the inch-pound units are shown in brackets.  
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Aug-2023
• ICS: 83.120 - Reinforced plastics
• ICS: 83.140.20 - Laminated sheets
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.05 - Structural Test Methods

Relations

• Replaces: ASTM D8387/D8387M-21 - Standard Test Method for High Bypass – Low Bearing Interaction Response of Polymer Matrix Composite Laminates
• Effective Date: 01-Sep-2023
• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM D2734-23 - Standard Test Methods for Void Content of Reinforced Plastics
• Effective Date: 01-Oct-2023
• Refers: ASTM D7248/D7248M-23 - Standard Test Method for High Bearing - Low Bypass Interaction Response of Polymer Matrix Composite Laminates Using 2-Fastener Specimens
• Effective Date: 01-Sep-2023
• Refers: ASTM D6484/D6484M-23 - Standard Test Method for Open-Hole Compressive Strength of Polymer Matrix Composite Laminates
• Effective Date: 01-Sep-2023
• Refers: ASTM D6742/D6742M-23 - Standard Practice for Filled-Hole Tension and Compression Testing of Polymer Matrix Composite Laminates
• Effective Date: 01-Sep-2023
• Refers: ASTM D883-22 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2022
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM E456-13a(2022) - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM D7248/D7248M-21 - Standard Test Method for High Bearing - Low Bypass Interaction Response of Polymer Matrix Composite Laminates Using 2-Fastener Specimens
• Effective Date: 15-May-2021
• Refers: ASTM D6484/D6484M-20 - Standard Test Method for Open-Hole Compressive Strength of Polymer Matrix Composite Laminates
• Effective Date: 01-Oct-2020
• Refers: ASTM D6742/D6742M-17 - Standard Practice for Filled-Hole Tension and Compression Testing of Polymer Matrix Composite Laminates
• Effective Date: 15-Oct-2017
• Refers: ASTM D2734-16 - Standard Test Methods for Void Content of Reinforced Plastics
• Effective Date: 01-Sep-2016
• Referred By: ASTM D4762-23 - Standard Guide for Testing Polymer Matrix Composite Materials
• Effective Date: 01-Sep-2023

Overview

ASTM D8387/D8387M-23 is the internationally recognized standard test method for assessing the high bypass - low bearing interaction response of multi-directional polymer matrix composite laminates reinforced with high-modulus fibers. Developed by ASTM Committee D30 on Composite Materials, this standard provides precise guidance for evaluating the structural performance of composite laminates subjected to complex load interactions through a two-fastener hard point joint specimen. This method is specifically designed to assess net section (bypass) failure modes using well-defined specimen and test configurations, supporting material qualification, design, and structural analysis across aerospace, automotive, civil, and defense applications.

Key Topics

• Scope and Purpose: This standard establishes procedures for measuring the response of composite laminates under simultaneous high bypass (net section force) and low bearing (localized fastener load) conditions using uniaxial loading, complementary to other bolted joint test methods.
• Material and Specimen Requirements: Applicable to continuous- or discontinuous-fiber reinforced, balanced, and symmetric polymer matrix composites, with detailed stacking sequence and thickness guidelines.
• Test Configurations: Uses a two-fastener configuration to ensure test results represent the high bypass/low bearing region of the composite bolted joint interaction diagram. Both tensile and compressive loading methods are described.
• Instrumentation and Precision: Emphasizes the importance of accurate specimen design, instrumentation, and data measurement, including micrometers, torque wrenches, extensometers, and environmental chambers.
• Failure Mode Assessment: Focuses on net section (bypass) failure rather than bearing failures, promoting industry-standard definitions of gross and net bypass strength.
• Data Reporting: Requires thorough documentation of material properties, specimen preparation, geometry, environmental conditioning, and testing parameters to ensure reproducibility and comparability of results.

Applications

The ASTM D8387/D8387M-23 standard is essential for:

• Aerospace and Automotive Engineering: Supports qualification and comparative evaluation of advanced composite materials used in primary and secondary structural components, where bolted joints and complex load-paths are prevalent.
• R&D and Material Development: Provides a robust test protocol for generating design allowable data, optimizing composite layups, and assessing new resin/fiber systems under realistic joint loading scenarios.
• Structural Design and Analysis: Supplies critical input for numerical modeling, finite element analysis (FEA) validation, and failure prediction in structures where bearing and bypass load interactions govern laminate performance.
• Quality Assurance and Certification: Offers standardized assessment criteria for regulatory compliance, safety validation, and supplier qualification in the composites industry.

Related Standards

ASTM D8387/D8387M-23 works in conjunction with several related ASTM standards and international guidelines:

• ASTM D8509: Guide for test method selection and specimen design for bolted joint related properties.
• ASTM D7248/D7248M: Test method for high bearing - low bypass interaction response of polymer matrix composite laminates.
• ASTM D5961/D5961M: Test method for bearing response of polymer matrix composite laminates.
• ASTM D6742/D6742M: Practice for filled-hole tension and compression testing.
• Composite Materials Handbook (CMH-17): Outlines best practices for composite material testing and structural performance assessment.

Implementing ASTM D8387/D8387M-23 facilitates informed design decisions, improves joint reliability, and advances composite technology by providing a comprehensive, standardized approach to evaluating high bypass - low bearing interaction responses in polymer matrix composite laminates.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D8387/D8387M − 23
Standard Test Method for
High Bypass – Low Bearing Interaction Response of
Polymer Matrix Composite Laminates
This standard is issued under the fixed designation D8387/D8387M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope and should not expect test labs who are unfamiliar with this test
method to be able to produce acceptable results without close
1.1 This test method determines the uniaxial high bypass -
coordination.
low bearing interaction response of multi-directional polymer
1.5 Units—The values stated in either SI units or inch-
matrix composite laminates reinforced by high-modulus fibers
pound units are to be regarded separately as standard. The
using a two-fastener hard point joint specimen. The scope of
values stated in each system are not necessarily exact equiva-
this test method is limited to net section (bypass) failure
lents; therefore, to ensure conformance with the standard, each
modes. Standard specimen configurations using fixed values of
system shall be used independently of the other, and values
test parameters are described for this procedure. A number of
test parameters may be varied within the scope of the standard, from the two systems shall not be combined.
1.5.1 Within the text, the inch-pound units are shown in
provided that the parameters are fully documented in the test
report. The composite material forms are limited to brackets.
continuous-fiber or discontinuous-fiber (tape or fabric, or both)
1.6 This standard does not purport to address all of the
reinforced composites for which the laminate is balanced and
safety concerns, if any, associated with its use. It is the
symmetric with respect to the test direction. The range of
responsibility of the user of this standard to establish appro-
acceptable test laminates and thicknesses are described in
priate safety, health, and environmental practices and deter-
8.2.1. This test method was previously published under Test
mine the applicability of regulatory limitations prior to use.
Method D7248/D7248M-17 Procedure C.
1.7 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.2 This test method is consistent with the recommendations
ization established in the Decision on Principles for the
of Composite Materials Handbook, CMH-17, which describes
Development of International Standards, Guides and Recom-
the desirable attributes of a bearing/bypass interaction response
mendations issued by the World Trade Organization Technical
test method.
Barriers to Trade (TBT) Committee.
1.3 The two-fastener test configurations described in this
test method are intended to provide data in the relatively high
2. Referenced Documents
bypass, low bearing part of the composite bolted joint bearing-
2.1 ASTM Standards:
bypass interaction diagram. This data complements the data
D792 Test Methods for Density and Specific Gravity (Rela-
from filled hole tension and compression (Practice D6742/
tive Density) of Plastics by Displacement
D6742M), bearing (Test Method D5961/D5961M), and low
D883 Terminology Relating to Plastics
bypass/high bearing interaction (Test Method D7248/D7248M)
D2584 Test Method for Ignition Loss of Cured Reinforced
tests.
Resins
1.4 This test method requires careful specimen design,
D2734 Test Methods for Void Content of Reinforced Plastics
instrumentation, data measurement, and data analysis. The use
D3171 Test Methods for Constituent Content of Composite
of this test method requires close coordination between the test
Materials
requestor and the test lab personnel. Test requestors need to be
D3878 Terminology for Composite Materials
familiar with the data analysis procedures of this test method
D5229/D5229M Test Method for Moisture Absorption Prop-
erties and Equilibrium Conditioning of Polymer Matrix
Composite Materials
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.05 on
Structural Test Methods. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Sept. 1, 2023. Published October 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2021. Last previous edition approved in 2021 as D8387/D8387M – 21. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D8387_D8387M-23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8387/D8387M − 23
D5687/D5687M Guide for Preparation of Flat Composite C = fastener flexibility (Ref 1)
F
Panels with Processing Guidelines for Specimen Prepara- C = plate (specimen) flexibility
P
tion C = doubler plate flexibility
S
D5766/D5766M Test Method for Open-Hole Tensile CV = sample coefficient of variation, %
Strength of Polymer Matrix Composite Laminates d = fastener diameter, mm [in.]
D5961/D5961M Test Method for Bearing Response of Poly- D = hole diameter, mm [in.]
mer Matrix Composite Laminates e/D = actual edge distance ratio
D6484/D6484M Test Method for Open-Hole Compressive E = fastener modulus, MPa [psi]
F
Strength of Polymer Matrix Composite Laminates E = test specimen laminate modulus, MPa [psi]
xP
D6742/D6742M Practice for Filled-Hole Tension and Com- E = doubler plate modulus in axial (x) direction, MPa [psi]
xS
gr_byp_t
pression Testing of Polymer Matrix Composite Laminates F = ultimate tensile gross bypass strength, MPa [psi].
x
net_byp_t
D7248/D7248M Test Method for High Bearing - Low By- F = ultimate tensile net bypass strength, MPa [psi]
x
gr_byp_c
pass Interaction Response of Polymer Matrix Composite F = ultimate compressive gross bypass strength,
x
Laminates Using 2-Fastener Specimens MPa [psi]
net_byp_c
D8509 Guide for Test Method Selection and Test Specimen F = ultimate compressive net bypass strength, MPa
x
Design for Bolted Joint Related Properties [psi]
br_byp
E4 Practices for Force Calibration and Verification of Test- F = bearing stress at ultimate bypass strength, MPa
ing Machines [psi]
E6 Terminology Relating to Methods of Mechanical Testing g = distance from hole edge to specimen end, mm [in.]
E83 Practice for Verification and Classification of Exten- h = specimen thickness near hole (nominal or actual, as
someter Systems specified), mm [in.]
E122 Practice for Calculating Sample Size to Estimate, With k = proportion of total force transferred through doubler
D
Specified Precision, the Average for a Characteristic of a plates
Lot or Process k = estimate of proportion of total force transferred through
E
E177 Practice for Use of the Terms Precision and Bias in fasteners to doubler plates
ASTM Test Methods k = proportion of total force transferred through specimen
S
E251 Test Methods for Performance Characteristics of Me- L = distance between fastener centerlines, mm [in.]
tallic Bonded Resistance Strain Gages n = number of strain gages on the doubler plate
E456 Terminology Relating to Quality and Statistics n = number of tested specimens
E1237 Guide for Installing Bonded Resistance Strain Gages P = total force applied to specimen, N [lbf]
P , P = force in doubler plates, N [lbf]
D1 D2
2.2 Other Document:
P = force at i-th data point, N [lbf]
i
CMH-17 Composite Materials Handbook-17, Polymer Ma-
P = maximum force prior to failure, N [lbf]
max
trix Composites, Vol 1, Section 7
P = force in specimen between fasteners, N [lbf]
S
s = sample standard deviation
n-1
3. Terminology
t = test specimen laminate thickness, mm [in.]
P
3.1 Definitions—Terminology D3878 defines terms relating
t = doubler plate thickness, mm [in.]
S
to high-modulus fibers and their composites. Terminology
v = fastener Poisson’s ratio
F
D883 defines terms relating to plastics. Terminology E6 defines
w = width of specimen across hole, mm [in.]
terms relating to mechanical testing. Terminology E456 and
w = test specimen width, mm [in.]
P
Practice E177 define terms relating to statistics. In the event of
w = doubler plate width, mm [in.]
S
a conflict between terms, Terminology D3878 shall have
¯
X = sample mean (average)
precedence over the other documents.
x = measured or derived property
i
δ = extensometer-1 displacement at i-th data point, mm
NOTE 1—If the term represents a physical quantity, its analytical 1i
[in.]
dimensions are stated immediately following the term (or letter symbol) in
fundamental dimension form, using the following ASTM standard sym-
δ = extensometer-2 displacement at i-th data point, mm
2i
bology for fundamental dimensions, shown within square brackets: [M]
[in.]
for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature,
br
ɛ = bearing strain, microstrain
i
and [nd] for non-dimensional quantities. Use of these symbols is restricted
br
σ = bearing stress at i-th data point, MPa [psi]
to analytical dimensions when used with square brackets, as the symbols i
may have other definitions when used without the brackets.
4. Summary of Test Method
3.2 Definitions of Terms Specific to This Standard—Refer to
Guide D8509.
4.1 Refer to Guide D8509 for discussion of bearing/bypass
test procedures.
3.3 Symbols:
2 2
A = gross cross-sectional area (disregarding hole) mm [in. ]
4.2 High Bypass/Low Bearing Double Shear:
3 4
Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale, The boldface numbers in parentheses refer to the list of references at the end of
PA 15096, http://www.sae.org. this standard.
D8387/D8387M − 23
4.2.1 A flat, constant rectangular cross-section test specimen ends of the test specimen are gripped in the jaws of a test
with two centerline holes located in the middle of the machine and loaded in tension or compression.
specimen, as shown in the test specimen drawing of Fig. 1, is
4.2.1.1 Unstabilized Configuration (No Support Fixture)—
axially loaded. Two doubler plates, Fig. 2, are attached to the
The ends of the test specimen are gripped in the jaws of a test
specimen as shown in Fig. 3 to act as a “hardpoint” which
machine and loaded in tension.
induces bearing forces in the test specimen and plates. The
FIG. 1 Double-Shear, 2-Fastener Hardpoint Test Specimen Drawing
D8387/D8387M − 23
FIG. 2 Doubler Plate Drawing
D8387/D8387M − 23
FIG. 3 (a) Tensile Loading—Test Specimen and Doubler Plate Assembly
4.2.1.2 Stabilized Configuration (Using Support Fixture)— 4.2.2 Refer to Guide D8509 for additional test details and
The test specimen is face-supported in a multi-piece bolted for the standard test configuration.
support fixture, as shown in Fig. 4. The test specimen/fixture
5. Significance and Use
assembly is clamped in hydraulic wedge grips and the force is
sheared into the support fixture and then sheared into the 5.1 Refer to Guide D8509.
specimen. Tensile or compressive force is applied. The stabi-
6. Interferences
lization fixture is required for compressive loading and is
optional for tensile loading. 6.1 Refer to Guide D8509.
D8387/D8387M − 23
FIG. 3 (b) Compressive Loading—Test Specimen and Doubler Plate Assembly (continued)
7. Apparatus reading to within 1% of the sample dimensions. For typical
specimen geometries, an instrument with an accuracy of
7.1 Micrometers—A micrometer with a 4 mm to 8 mm
60.0025 mm [60.0001 in.] is adequate for the thickness
[0.16 in. to 0.32 in.] nominal diameter ball interface shall be
measurement, while an instrument with an accuracy of 60.025
used to measure the specimen thickness when at least one
mm [60.001 in.] is adequate for the width measurement.
surface is irregular (such as the bag-side of a laminate). A
Additionally, a micrometer or gage capable of determining the
micrometer with a 4 mm to 8 mm [0.16 in. to 0.32 in.] nominal
hole diameters to 60.025 mm [60.001 in.] shall be used.
diameter ball interface or with a flat anvil interface shall be
NOTE 2—The accuracies given above are based on achieving measure-
used to measure the specimen thickness when both surfaces are
ments that are within 1 % of the sample width and thickness.
smooth (such as tooled surfaces). A micrometer or caliper, with
a flat anvil interface, shall be used to measure the width of the 7.2 Loading Fasteners or Pins—The fastener (or pin) type
specimen. The accuracy of the instruments shall be suitable for shall be specified as an initial test parameter and reported. The
D8387/D8387M − 23
FIG. 4 Support Fixture Assembly (for Details of the Support Fixture, See Test Method D5961/D5961M)
assembly torque (if applicable) shall be specified as an initial 7.4.2 For test laminates that are narrower than the standard
test parameter and reported. This value may be a measured specimen width, which may be required in some cases to
torque or a specification torque for fasteners with lock-setting obtain a bypass failure mode, the standard doubler plate widths
features. If washers are utilized, the washer type, number of may be used. Actual widths shall be used in the force
washers, and washer location(s) shall be specified as initial test proportion estimate calculations in 8.2.2.
parameters and reported. The reuse of fasteners is not recom-
7.4.3 Strain Gages—For tensile tests, two axial strain gages
mended due to potential differences in through-thickness
shall be mounted on each doubler plate at the locations shown
clamp-up for a given torque level, caused by wear of the
in Fig. 3a. For compressive tests, one axial strain gage shall be
threads or deformation of the locking features.
mounted on each doubler plate at the location shown in Fig. 3b.
7.4.4 Machining Precision—Doubler plates and calibration
7.3 Torque Wrench—If using a torqued fastener, a torque
loading plates require high machining quality, hole diameter
wrench used to tighten the fastener shall be capable of
tolerances, hole positioning, hole perpendicularity, flatness,
determining the applied torque to within 610 % of the desired
etc.
value.
7.4.5 For compressive tests, an alternate to doublers that fit
7.4 Fixture—Doubler plates, Fig. 2, are attached to the test
within the support fixture window is to use full width doublers
specimen using two fasteners. In some cases, it may be
(same as for tensile tests). In this case, shims (4 total) equal to
desirable to use doubler plates that are more closely matched in
the doubler plate thickness will be required at each end of the
stiffness to the test laminate, particularly when testing soft
specimen to provide a flat surface to interface with the support
laminate materials or layups. These plates may typically be
fixture. In some cases, test laminate failure may then occur at
reused, as the force transferred into the plates should be
the gap between the doubler and shim; a mitigation for this
relatively small. The holes in the plates should be examined for
situation is to modify the doublers and shims to have a chevron
bearing deformation after each use and replaced if deformation
shape similar to the support fixture such that there is no
is observed. If the doubler plates are replaced, the new plates
unsupported laminate area across the specimen width.
shall be calibrated in accordance with 11.3.
7.4.1 For compressive tests, the doubler plates must be sized 7.5 Support Fixture (Compressive Loading)—If compres-
to fit into the support fixture window. See alternate described in sive loads are applied or if requested in the test plan, a support
7.4.5. fixture shall be used to stabilize the specimen. The fixture is a
D8387/D8387M − 23
face-supported test fixture as shown in Fig. 4. The fixture the indicator device must fit within the stabilization fixture
consists of two short-grip/long-grip assemblies, two support when a specimen with a width less than 36 mm [1.5 in.] is
plates, and stainless steel shims as required to maintain a tested in the standard fixture. Transducer gage lengths on the
nominally zero (0.00-mm to 0.12-mm [0.000-in. to 0.005-in.] order of 50 mm [2.0 in.] are typically used. The transducers of
tolerance) gap between the support plates and the long grips. If the bearing deformation indicator may provide either indi-
this gap does not meet the minimum requirement, shim the vidual signals to be externally averaged or an electronically
contact area between the support plate and the short grip with averaged signal. The indicator may consist of two matched
stainless steel shim stock. If the gap is too large, shim between strain-gage extensometers or displacement transducers such as
the support plate and the long grip, holding the shim stock on LVDTs or DCDTs. Attachment of the bearing deformation
the support plate with tape. The fixture should be checked for indicator to the specimen shall not cause damage to the
conformity to engineering drawings. Each short-grip/long-grip specimen surface. Transducers shall satisfy, at a minimum,
assembly is line-drilled and must be used as a matched set. The Practice E83, Class B-2 requirements for the displacement
threading of the support plate is optional. The fixture is range of interest, and shall be calibrated over that range in
hydraulically gripped on each end and the force is sheared by accordance with Practice E83. The transducers shall be essen-
means of friction through the fixture and into the test specimen. tially free of inertia-lag at the specified speed of testing.
A cutout exists on both faces of the fixture for a thermocouple,
7.8 Conditioning Chamber—When conditioning materials
fastener(s), and surface-mounted extensometer. The long and
at non-laboratory environments, a temperature-/vapor-level
short fixtures have an undercut along the corner of the
controlled environmental conditioning chamber is required that
specimen grip area so that specimens are not required to be
shall be capable of maintaining the required temperature to
chamfered and to avoid damage caused by the radius. The
within 63 °C [65 °F] and the required relative humidity level
fixtures also allow a slight clearance between the fixture and
to within 63 %. Chamber conditions shall be monitored either
the gage section of the specimen, in order to minimize grip
on an automated continuous basis or on a manual basis at
failures and friction effects. This fixture does not allow
regular intervals.
specimens to be end loaded.
7.9 Environmental Test Chamber—An environmental test
7.5.1 Support Fixture Details—The detailed drawings for
manufacturing the support fixture are contained in Test Method chamber is required for test environments other than ambient
testing laboratory conditions. This chamber shall be capable of
D5961/D5961M. Other fixtures that meet the requirements of
this section may be used. maintaining the gage section of the test specimen at the
required test environment during the mechanical test within
NOTE 3—Experience has shown that fixtures may be damaged in use;
63 °C or 65 °F.
thus, periodic re-inspection of the fixture dimensions and tolerances is
important.
7.10 Strain-Indicating Device—Strain data, when required,
7.6 Testing Machine—The testing machine shall be in con- shall be determined by means of bonded resistance strain
formance with Practices E4, and shall satisfy the following gages.
requirements:
7.10.1 Bonded Resistance Strain Gage Selection—Strain
7.6.1 Testing Machine Configuration—The testing machine
gage selection is based on the type of material to be tested. A
shall have both an essentially stationary head and a movable
minimum active gage length of 3 mm [0.125 in.] is recom-
head. A short loading train and rigidly mounted hydraulic grips
mended for composite laminates fabricated from unidirectional
shall be used for Procedure B when using the support fixture.
layers. Larger strain gage sizes may be more suitable for some
7.6.2 Drive Mechanism—The testing machine drive mecha-
textile fabrics. Gage calibration certification shall comply with
nism shall be capable of imparting to the movable head a
Test Method E251. Strain gages with a minimum normal strain
controlled velocity with respect to the stationary head. The
range of approximately 3 % are recommended. When testing
velocity of the movable head shall be capable of being
textile fabric laminates, gage selection should consider the use
regulated as specified in 11.4.
of an active gage length that is at least as great as the
7.6.3 Force Indicator—The testing machine force-sensing
characteristic repeating unit of the fabric. Some guidelines on
device shall be capable of indicating the total force being
the use of strain gages on composite materials follow.
carried by the test specimen. This device shall be essentially
7.10.1.1 Surface preparation of fiber-reinforced composites
free from inertia-lag at the specified rate of testing and shall
in accordance with Guide E1237 can penetrate the matrix
indicate the force with an accuracy over the force range(s) of
material and cause damage to the reinforcing fibers, resulting
interest of within 61 % of the indicated value.
in improper coupon failures. Reinforcing fibers should not be
7.6.4 Grips—Each head of the testing machine shall be
exposed or damaged during the surface preparation process.
capable of holding one end of the test assembly so that the
The strain gage manufacturer should be consulted regarding
direction of force applied to the specimen is coincident with the
surface preparation guidelines and recommended bonding
longitudinal axis of the specimen. Wedge grips shall apply
agents for composites, pending the development of a set of
sufficient lateral pressure to prevent slippage between the grip
standard practices for strain gage installation surface prepara-
face and the test specimen or support fixture.
tion of fiber-reinforced composite materials.
7.7 Bearing Deformation Indicator—Bearing deformation 7.10.1.2 Consideration should be given to the selection of
data shall be determined by an indicator device able to measure gages having larger resistances to reduce heating effects on low
longitudinal hole deformation, as shown in Fig. 5. The arms of conductivity materials. Resistances of 350 Ω or higher are
D8387/D8387M − 23
FIG. 5 Transducer Gage Length and Location
(such as a tabbed mechanical specimen), then use a traveler specimen of
preferred. Additional consideration should be given to the use
the same nominal thickness and appropriate size (but without tabs) to
of the minimum possible gage excitation voltage consistent
determine when equilibrium has been reached for the specimens being
with the desired accuracy (1 V to 2 V is recommended) to
conditioned.
reduce the power consumed by the gage. Heating of the coupon
8.2 Geometry:
by the gage may affect the performance of the material directly
or it may affect the indicated strain as a result of a difference
8.2.1 Stacking Sequence—The standard laminate shall have
between the gage temperature compensation factor and the multidirectional fiber orientations (fibers shall be oriented in a
coefficient of thermal expansion of the coupon material.
minimum of two directions), and balanced and symmetric
7.10.1.3 Consideration of some form of temperature com- stacking sequences. For tensile loaded specimens, nominal
pensation is recommended, even when testing at standard
thickness shall be 2.5 mm [0.10 in.], with a permissible range
laboratory atmosphere. Temperature compensation may be
of 2 mm to 5 mm [0.080 in. to 0.208 in.], inclusive. For
required when testing in non-ambient temperature environ-
compressive loaded specimens, nominal thickness shall be 4
ments.
mm [0.160 in.], with a permissible range of 2.5 mm to 5 mm
7.10.1.4 Consideration should be given to the transverse
[0.100 in. to 0.208 in.], inclusive. Fabric laminates containing
sensitivity of the selected strain gage. The strain gage manu-
satin-type weaves shall have symmetric warp surfaces, unless
facturer should be consulted for recommendations on trans-
otherwise specified and noted in the report.
verse sensitivity corrections and effects on composites.
NOTE 5—Typically, a [45 /0 /–45 /90 ] tape or [45 /0 ] fabric lami-
i j i k ms i j ms
nate should be selected such that a minimum of 5 % of the fibers lay in
8. Sampling and Test Specimens
each of the four principal orientations. This laminate design has been
8.1 Sampling—Test at least five specimens per test condi-
found to yield the highest likelihood of acceptable failure modes.
tion unless valid results can be gained through the use of fewer
8.2.2 Configuration—The geometry of the specimen is
specimens, as in the case of a designed experiment. For
shown in Fig. 1. Strain gages as shown in Fig. 3 are
statistically significant data, the procedures outlined in Practice
recommended to provide additional data to determine the
E122 should be consulted. The method of sampling shall be
proportion of force transferred to the doubler plates. The
reported.
following equations may be used to estimate the proportion of
NOTE 4—If specimens are to undergo environmental conditioning to
force transferred to the doubler plates for test specimen design
equilibrium, and are of such type or geometry that the weight change of
the material cannot be properly measured by weighing the specimen itself purposes. These equations assume the two fasteners and the
D8387/D8387M − 23
two doubler plates are identical. The fastener flexibility equa- 8.3.4 Labeling—Label the specimens so that they will be
tion is obtained from Ref (2). These equations shall not be used distinct from each other and traceable back to the raw material,
and in a manner that will both be unaffected by the test and not
for test data calculations.
influence the test.
2C
P
k 5 (1)
~2C 1 C 1 2C !
P S F
9. Calibration
L
9.1 The accuracy of all measuring equipment shall have
C 5 (2)
P
t w E
P P xP
certified calibrations that are current at the time of use of the
L
equipment.
C 5 (3)
S
t w E
S S xS
10. Conditioning
3 2 2 3
8 2t 1 t 1 1 v 64 8t 1 16t t 1 8t t 1 t
~ !~ ! ~ !~ !
S P F S S P S P P
C 5 1
F 2 4
3πE d 192πE d 10.1 Unless explicitly specified by the test requestor, no
F F
pre-test conditioning shall be performed and the test specimens
2t 1t 1 2
S P
1 1 1 (4)
shall be tested as prepared.
t t E t E t E
S P F S xS P xP
10.2 The pre-test specimen conditioning process, to include
where:
specified environmental exposure levels and resulting moisture
k = estimate of proportion of total force transferred
E
content, shall be reported with the test data.
through fasteners to doubler plates,
NOTE 6—The recommended pre-test specimen condition is effective
C = plate (specimen) flexibility,
P moisture equilibrium at a specific relative humidity per Test Method
C = doubler plate flexibility,
D5229/D5229M.
S
C = fastener flexibility (Ref 1), NOTE 7—The term moisture, as used in Test Method D5229/D5229M,
F
includes not only the vapor of a liquid and its condensate, but the liquid
t = test specimen laminate thickness, mm [in.],
P
itself in large quantities, as for immersion.
t = doubler plate thickness, mm [in.],
S
w = test specimen width, mm [in.],
10.3 If no explicit conditioning process is performed, the
P
w = doubler plate width, mm [in.],
specimen conditioning process shall be reported as “uncondi-
S
E = test specimen laminate modulus, MPa [psi],
xP
tioned” and the moisture content as “unknown.”
E = doubler plate modulus in axial (x) direction, MPa
xS
[psi],
11. Procedure
E = fastener modulus, MPa [psi],
F
11.1 Parameters to Be Specified Prior to Test:
v = fastener Poisson’s ratio,
F
11.1.1 The specimen sampling method, specimen type and
d = fastener diameter, mm [in.], and
geometry, fastener type and material, fastener torque (if
L = distance between fastener centerlines, mm [in.].
appropriate), type of loading (tensile or compressive), support
8.3 Specimen Preparation—Guide D5687/D5687M pro-
fixture (if appropriate), cleaning process, and conditioning
vides recommended specimen preparation practices and should
travelers (if required).
be followed where practical.
11.1.2 The properties to report and data reporting format
desired.
8.3.1 Panel Fabrication—Control of fiber alignment is criti-
cal. Improper fiber alignment will reduce the measured prop-
NOTE 8—Determine specific material property, accuracy, and data
erties. The panel(s) must be flat and of uniform thickness to
reporting requirements prior to test for proper selection of instrumentation
and data recording equipment. Estimate specimen failure stress and
ensure even loading. Erratic fiber alignment will also increase
bearing strain levels to aid in transducer selection, calibration of
the coefficient of variation. Report the panel fabrication
equipment, and determination of equipment settings.
method.
11.1.3 The environmental conditioning test parameters.
8.3.2 Machining Methods—Specimen preparation is ex-
11.1.4 If performed, extensometer requirements and related
tremely important for this specimen. Take precautions when
calculations.
cutting specimens from plates to avoid notches, undercuts,
11.1.5 If performed, the sampling method, specimen
rough or uneven surfaces, or delaminations due to inappropri-
geometry, and test parameters used to determine density and
ate machining methods. Obtain final dimensions by water-
reinforcement volume.
lubricated precision sawing, milling, or grinding. The use of
11.2 Before Test:
diamond tooling has been found to be extremely effective for
11.2.1 Report any deviations from this test method, whether
many material systems. Edges should be flat and parallel
intentional or inadvertent.
within the specified tolerances. Record and report the specimen
11.2.2 If specific gravity, density, reinforcement volume, or
cutting and hole preparation methods.
void volume are to be reported, then obtain these samples from
8.3.3 Hole Drilling—Holes should be drilled undersized and
the same panels being bearing tested. Specific gravity and
reamed to final dimensions. Special care shall be taken to
density may be evaluated by means of Test Methods D792.
ensure that creation of the specimen hole does not delaminate
Volume percent of the constituents may be evaluated by one of
or otherwise damage the material surrounding the hole. Speci-
the matrix digestion procedures of Test Method D3171, or, for
mens should be match drilled with the doubler straps to ensure
certain reinforcement materials such as glass and ceramics, by
that the fasteners can be installed. the matrix burn-off technique of Test Method D2584. The void
D8387/D8387M − 23
content equations of Test Method D2734 are applicable to both individually. Torque the fasteners to 0.6-1.2 N·m [5-10 lbf-in.].
Test Method D2584 and the matrix digestion procedures. Test each of the doubler plates as follows:
11.2.3 Condition the specimens as required. Store the speci-
11.3.2 Assign a unique identification number to each dou-
mens in the conditioned environment until test time, if the test
bler plate and mark the number on the plate. Assign a unique
environment is different than the conditioning environment.
strain gage number to each gage on each doubler plate and
11.2.4 Following final specimen machining, but before any
mark the gage numbers on the plate.
conditioning and testing, measure the specimen width, w, and
11.3.3 Speed of Testing—A standard head displacement rate
the specimen thickness, h, in the vicinity of each hole. Measure
of 2 mm/min [0.05 in./min] is recommended.
each hole diameter, D. Measure the fastener or pin diameter, d,
11.3.4 Test Environment—Test the doubler assembly at the
at the bearing contact location. The accuracy of all measure-
same temperature as the test specimen will be tested.
ments shall be within 1 % of the dimension, unless otherwise
specified in this test method. Record the dimensions to three
11.3.5 Insert the specimen into the test machine, attaching
significant figures in units of millimeters [inches].
loading interfaces or tightening grips as required.
11.3 Test Procedure Step 1 – Doubler Plate Force-Strain 11.3.6 Attach the strain gages to the recording instrumenta-
Calibration:
tion. Remove any remaining pre-load and zero the strain gages.
11.3.1 For purposes of accurately determining the force
Record the doubler and strain gage numbers. Record a unique
transferred into the doubler plates, a calibration of the force
calibration loading run identification number.
applied by the fastener to the doubler and the strain measured
11.3.7 Apply the force to the doubler assembly at the
by the strain gages on the doubler must be determined using a
specified rate while recording data. Load the assembly to a
determinant loading setup. Assemble each of the doubler plates
maximum force equal to:
with two or four loading straps, as shown in Fig. 6. For doubler
P 5 1.1 Expected Bearing / Bypass Specimen Failure Load
~ ! ~ !
plates with the recess for strain gages on the specimen, max
k from Eq. 1 # plates ⁄ 2
~ ! ~ !
assemble the two doubler plates back-to-back to avoid exces- E
sive bending which could occur if the plates are tested (5)
FIG. 6 Doubler Plate Force-Strain Calibration Setup
D8387/D8387M − 23
where: (install a nut to prevent loss of the fastener pin during test;
torqueing of collars/nuts is not required), as shown in Fig. 7a;
(# plates) = the number of double plates in the doubler
for compressive loaded tests, install fasteners into the specimen
calibration assembly, Fig. 6.
holes (install a nut to prevent loss of the fastener pin during
NOTE 9—Take care when selecting the maximum force for the doubler
plate calibration that bearing deformation or damage is not introduced in
test; torqueing of collars/nuts is not required) and assemble the
the doubler during the calibration test.
test laminate with the Fig. 5 support fixture, as shown in Fig.
NOTE 10—Every doubler plate used for testing shall be calibrated.
7b. Torque the fixture fasteners to 0.6-1.2 N·m [5-10 lbf-in.].
Traceability of the calibration load-strain data for each doubler strain gage
Test the laminate plate as follows:
must be maintained.
11.4.2 Assign a unique strain gage number to each gage on
11.3.8 Record force versus strain continuously, or at inter-
each test laminate and mark the gage numbers on the plate.
vals of 2-3 data recordings per second with a target minimum
11.4.3 Speed of Testing—A standard head displacement rate
of 100 data points per test.
of 2 mm/min [0.05 in./min] is recommended.
11.4 Test Procedure Step 2 – Test Laminate Force-Strain
11.4.4 Test Environment—Test the laminate at the same
Calibration:
temperature as the test specimen that will be tested.
11.4.1 While the strain data from the doubler plates can be
11.4.5 Insert the specimen into the test machine, attaching
used to determine the force transferred into the doubler plates,
loading interfaces or tightening grips as required.
it is recommended that the strain in the test laminate also be
measured during the bearing/bypass tests. To use this strain 11.4.6 Attach the strain gages to the recording instrumenta-
data, a force-strain calibration of the strain measured by the tion. Remove any remaining pre-load and zero the strain gages.
strain gages on the test laminate must be determined. For Record the specimen and strain gage numbers. Record a unique
tensile loaded tests, install fasteners into the specimen holes calibration loading run identification number.
FIG. 7 Test Laminate Force-Strain Calibration Setup
D8387/D8387M − 23
11.4.7 Apply the force to the laminate at the specified rate fixture halves. This should result in the specimen hole(s)/
while recording data. Load the laminate to a maximum force fastener(s) being centered in the fixture cutout. Tighten the four
equal to P from Eq 5; however, P should not be greater bolts just enough to hold the specimen in place during fixture
max max
than 80 % of the expected bearing 2 % offset strength for the installation.
laminate.
11.6.4.1 Place the fixture in the grips of the testing machine,
11.4.8 Record force versus strain continuously, or at inter-
taking care to align the long axis of the gripped fixture with the
vals of 2-3 data recordings per second with a target minimum test direction. When inserting the fixture into the grip-jaws,
of 100 data points per test.
grip the outer portion of the fixture up to the bolts, approxi-
mately 80 mm [3 in.].
NOTE 11—For a group of identical test specimens (same material,
11.6.4.2 Tighten the grips, recording the pressure used on
layup, thickness, geometry, test environment, etc.), it is acceptable to only
perform the force-strain calibration procedure for one of the test the hydraulic grips. The ends of the grip-jaws on wedge-type
specimens, provided that the strain gage types and locations are identical
grips should be even with each other following insertion to
for all of the specimens.
avoid inducing a bending moment which could result in
NOTE 12—Traceability of the calibration load-strain data for each test
premature failure of the specimen.
laminate gage must be maintained.
11.6.4.3 Re-torque the four bolts to approximately 7 N-m
11.5 Test Procedure Step 3 – Specimen Assembly:
[60 lbf-in.] after hydraulic gripping pressure is applied.
11.5.1 Cleaning—Clean the specimen hole, surrounding
11.6.4.4 Check the gaps between the support plates and the
clamping area, and fastener or pin shank. If the fastener threads
long grip portion of the support fixture using a feeler gage, and
are required to be lubricated, apply the lubricant to the nut
shim as required (see Test Method D5961/D5961M).
threads instead of the fastener threads and take extreme care
11.6.4.5 Check that the gap between the gage section of the
not to accidentally transfer any of the lubricant to the fastener
specimen and the long grip portion of the support fixture is
shank, the specimen hole, or to the clamping area during
0.05 6 0.05 mm [0.002 6 0.002 in.] using a feeler gage. A gap
assembly and torqueing. Record and report cleaning method
outside of this tolerance range is indicative of one of the
and lubricant used, if any.
following: improper assembly, an out-of-tolerance specimen,
11.5.2 Specimen Assembly—Assemble the test specimen to
damaged fixtures, or a combination thereof.
the doubler plates with the specified fasteners or pins (and
11.6.5 Bearing Deformation Indicator Installation—Attach
washers if specified).
the bearing deformation indicator to the edges of the specimen
11.5.3 Fastener Torqueing—If using torqued fasteners,
as shown in Fig. 5 to provide the average displacement across
tighten the fasteners to the required value using a calibrated
the loaded hole(s) at the edge of the specimen. Attach the
torque wrench. Record and report the actual torque value.
recording instrumentation to the indicator. Remove any re-
11.6 Test Procedure Step 4 – Specimen Test Procedure:
maining pre-load and zero the indicator.
11.6.1 Speed of Testing—Set the speed of testing so as to
11.6.6 Strain Gages—Attach the strain gages to the record-
produce failure within 1 to 10 min. If the ultimate failure stress
ing instrumentation. Remove any remaining preload and zero
and bearing strain of the material cannot be reasonably
the strain gages. Record the doubler plate identification num-
estimated, initial trials should be conducted using standard
bers. Record the doubler plate and test laminate strain gage
speeds until the ultimate bearing strain of the material and the
numbers.
compliance of the system are known, and speed of testing can
11.6.7 Loading—Apply the force to the specimen at the
be adjusted. The suggested standard speeds are:
specified rate while recording data. The specimen is loaded
11.6.1.1 Bearing Strain-Controlled Tests—A standard
until the force has dropped off at least 30 % from a previously
-1
bearing-strain rate of 0.01 min .
attained maximum force value. Unless specimen rupture is
11.6.1.2 Constant Head-Speed Tests—A standard head dis-
specifically desired, the test is terminated so as to prevent
placement rate of 2 mm/min [0.05 in./min].
masking of the true failure mode by large-scale hole distortion,
11.6.2 Test Environment—If possible, test the specimen in order to provide a more representative failure mode assess-
under the same fluid exposure level used for conditioning. ment and to prevent support fixture damage (if used). In
However, cases such as elevated temperature testing of a moist compressive loading, care should be taken to ensure that the
specimen place unrealistic requirements on the capabilities of stabilization plates do not self-contact by terminating compres-
common testing machine environmental chambers. In such sive test loading when head displacement has reached a
cases, the mechanical test environment may need to be maximum of 4.5 mm [0.18 in.] (90 % of nominal end gap
modified, for example, by testing at elevated temperature with
distance) to prevent support fixture damage.
no fluid exposure control, but with a specified limit on time to
11.6.8 Data Recording—Record force versus bearing defor-
failure from withdrawal from the conditioning chamber. Re-
mation (or hole displacement) and force versus strain
cord any modifications to the test environment.
continuously, or at intervals of 2-3 data recordings per second
11.6.3 Specimen Installation with No Support Fixture—
with a target minimum of 100 data points per test. If a
Insert the specimen into the test machine, attaching loading transition region or initial ply failures are noted, record the
interfaces or tightening grips as required.
load, bearing deformation, and mode of damage at such points.
11.6.4 Specimen Installation With Support Fixture—Install If the specimen is to be failed, record the maximum load, the
the test specimen into the support fixture such that the failure load, and the bearing deformation (or hole displace-
machined ends of the specimen are flush with the ends of the ment) at, or as near as possible to, the moment of rupture.
D8387/D8387M − 23
NOTE 13—Other valuable data that can be useful in understanding
13.1.1 Plot the force-strain data for each doubler strain
testing anomalies and gripping or specimen slipping problems includes
gage.
force versus head displacement data and force versus time data.
13.1.2 For each strain gage, determine a linear portion of the
11.6.9 Failure Mode—Record the mode and location of
force-strain curve towards the upper range of applied force. Fit
failure of the specimen. Note that the intention of this test
a linear regression line to this range, to obtain the slope, m, and
method is to determine the effect of bearing stress on the net
intercept, b, for the equation: P = m*strain + b.
section bypass strength of the material. In some cases, speci-
13.2 Step 2—Test Laminate Force-Strain Calibration:
mens that fail in a net section mode will also exhibit bearing
13.2.1 Plot the force-strain data for each test laminate strain
damage at the fastener holes; this combined mode is within the
gage.
scope of this method. The evaluation of specimens that
13.2.2 For each strain gage, determine a linear portion of the
produce only bearing failure modes is beyond the scope of this
force-strain curve towards the upper range of applied force. Fit
test method. Net section stress results shall not be reported
a linear regression line to this range, to obtain the slope, m, and
under this test method for specimens exhibiting primary
intercept, b, for the equation: P = m*strain + b.
bearing failure modes. Choose, if possible, a standard descrip-
tion using the five-part failure mode code shown in Table 1. A
13.3 Step 3—Specimen Measurements:
multimode failure can be described by including each of the
13.3.1 Width to Diameter Ratio—Calculate the actual speci-
appropriate failure-type codes between the parentheses of the
men width to diameter ratio using measured values with Eq 6,
M failure-typ
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D8387/D8387M − 21 D8387/D8387M − 23
Standard Test Method for
High Bypass – Low Bearing Interaction Response of
Polymer Matrix Composite Laminates
This standard is issued under the fixed designation D8387/D8387M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method determines the uniaxial high bypass - low bearing interaction response of multi-directional polymer matrix
composite laminates reinforced by high-modulus fibers using a two-fastener hard point joint specimen. The scope of this test
method is limited to net section (bypass) failure modes. Standard specimen configurations using fixed values of test parameters
are described for this procedure. A number of test parameters may be varied within the scope of the standard, provided that the
parameters are fully documented in the test report. The composite material forms are limited to continuous-fiber or
discontinuous-fiber (tape or fabric, or both) reinforced composites for which the laminate is balanced and symmetric with respect
to the test direction. The range of acceptable test laminates and thicknesses are described in 8.2.1. This test method was previously
published under Test Method D7248/D7248M-17 Procedure C.
1.2 This test method is consistent with the recommendations of Composite Materials Handbook, CMH-17, which describes the
desirable attributes of a bearing/bypass interaction response test method.
1.3 The two-fastener test configurations described in this test method are intended to provide data in the relatively high bypass,
low bearing part of the composite bolted joint bearing-bypass interaction diagram. This data complements the data from filled hole
tension and compression (Practice D6742/D6742M), bearing (Test Method D5961/D5961M), and low bypass/high bearing
interaction (Test Method D7248/D7248M) tests.
1.4 This test method requires careful specimen design, instrumentation, data measurement, and data analysis. The use of this test
method requires close coordination between the test requestor and the test lab personnel. Test requestors need to be familiar with
the data analysis procedures of this test method and should not expect test labs who are unfamiliar with this test method to be able
to produce acceptable results without close coordination.
1.5 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in
each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used
independently of the other, and values from the two systems shall not be combined.
1.5.1 Within the text, the inch-pound units are shown in brackets.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
This test method is under the jurisdiction of ASTM Committee D30 on Composite Materials and is the direct responsibility of Subcommittee D30.05 on Structural Test
Methods.
Current edition approved April 1, 2021Sept. 1, 2023. Published June 2021October 2023. Originally approved in 2021. Last previous edition approved in 2021 as
D8387/D8387MDOI: 10.1520/D8387_D8387M-21. – 21. DOI: 10.1520/D8387_D8387M-23.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8387/D8387M − 23
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D792 Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement
D883 Terminology Relating to Plastics
D2584 Test Method for Ignition Loss of Cured Reinforced Resins
D2734 Test Methods for Void Content of Reinforced Plastics
D3171 Test Methods for Constituent Content of Composite Materials
D3878 Terminology for Composite Materials
D5229/D5229M Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite
Materials
D5687/D5687M Guide for Preparation of Flat Composite Panels with Processing Guidelines for Specimen Preparation
D5766/D5766M Test Method for Open-Hole Tensile Strength of Polymer Matrix Composite Laminates
D5961/D5961M Test Method for Bearing Response of Polymer Matrix Composite Laminates
D6484/D6484M Test Method for Open-Hole Compressive Strength of Polymer Matrix Composite Laminates
D6742/D6742M Practice for Filled-Hole Tension and Compression Testing of Polymer Matrix Composite Laminates
D7248/D7248M Test Method for High Bearing - Low Bypass Interaction Response of Polymer Matrix Composite Laminates
Using 2-Fastener Specimens
D8509 Guide for Test Method Selection and Test Specimen Design for Bolted Joint Related Properties
E4 Practices for Force Calibration and Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E83 Practice for Verification and Classification of Extensometer Systems
E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or
Process
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E251 Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages
E456 Terminology Relating to Quality and Statistics
E1237 Guide for Installing Bonded Resistance Strain Gages
2.2 Other Document:
CMH-17 Composite Materials Handbook-17, Polymer Matrix Composites, Vol 1, Section 7
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating to high-modulus fibers and their composites. Terminology D883
defines terms relating to plastics. Terminology E6 defines terms relating to mechanical testing. Terminology E456 and Practice
E177 define terms relating to statistics. In the event of a conflict between terms, Terminology D3878 shall have precedence over
the other documents.
NOTE 1—If the term represents a physical quantity, its analytical dimensions are stated immediately following the term (or letter symbol) in fundamental
dimension form, using the following ASTM standard symbology for fundamental dimensions, shown within square brackets: [M] for mass, [L] for length,
[T] for time, [θ] for thermodynamic temperature, and [nd] for non-dimensional quantities. Use of these symbols is restricted to analytical dimensions when
used with square brackets, as the symbols may have other definitions when used without the brackets.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 bearing area, [L ],n—the area of that portion of a specimen used to normalize applied loading into an effective bearing
stress; equal to the diameter of the fastener multiplied by the thickness of the specimen.
–2
3.2.2 bearing force, P [MLT ],n—the in-plane force transmitted by a fastener to a specimen at the fastener hole.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale, PA 15096, http://www.sae.org.
D8387/D8387M − 23
br
3.2.3 bearing strain, ε, [nd],n—the normalized hole deformation in a specimen, equal to the deformation of the bearing hole in
the direction of the bearing force, divided by the diameter of the hole.
br_byp -1 -2
3.2.4 bearing strength, F [ML T ],n—the value of bearing stress occurring at the point of bypass (net section) failure.
x
br -1 -2
3.2.5 bearing stress, σ [ML T ],n—the bearing force divided by the bearing area.
3.2.6 diameter to thickness ratio, D/h [nd],n—in a bearing specimen, the ratio of the hole diameter to the specimen thickness.
3.2.6.1 Discussion—
The diameter to thickness ratio may be either a nominal value determined from nominal dimensions or an actual value determined
from measured dimensions.
3.2.7 edge distance ratio, e/D [nd],n—in a bearing specimen, the ratio of the distance between the center of the hole and the
specimen end to the hole diameter.
3.2.7.1 Discussion—
The edge distance ratio may be either a nominal value determined from nominal dimensions or an actual value determined from
measured dimensions.
gr_byp -1 -2
3.2.8 gross bypass stress, f [ML T ],n—the gross bypass stress for tensile loadings is calculated from the total force
bypassing the fastener hole.
net_byp -1 -2
3.2.9 net bypass stress, f [ML T ],n—the net bypass stress for tensile loading is calculated from the force bypassing the
fastener hole minus the force reacted in bearing at the fastener.
3.2.9.1 Discussion—
For compressive loadings, the gross and net bypass stresses are equal and are calculated using the force that bypasses the fastener
hole (since for the compressive loading case, the bearing stress reaction is on the same side of the fastener as the applied force,
the force reacted in bearing does not bypass the fastener hole).
3.2.9.2 Discussion—
Several alternate definitions for gross and net bypass stress have been used historically in the aerospace industry. Comparison of
data from tests conforming to this test method with historical data may need to account for differences in the bypass definitions.
3.2.10 nominal value, n—a value, existing in name only, assigned to a measurable quantity for the purpose of convenient
designation. Tolerances may be applied to a nominal value to define an acceptable range for the quantity.
bru -1 -2
3.2.11 ultimate bearing strength, F [ML T ],n—the value of bearing stress, in the direction specified by the subscript, at the
x
maximum force capability of a bearing specimen.
gr_byp -1 -2
3.2.12 ultimate gross bypass strength, F [ML T ],n—the value of gross bypass stress, in the direction specified by the
x
subscript, at the maximum force capability of the specimen.
net_byp -1 -2
3.2.13 ultimate net bypass strength, F [ML T ],n—the value of net bypass stress, in the direction specified by the subscript,
x
at the maximum force capability of the specimen.
3.2.14 width to diameter ratio, w/D [nd],n—in a bearing specimen, the ratio of specimen width to hole diameter.
3.2.14.1 Discussion—
The width to diameter ratio may be either a nominal value determined from nominal dimensions or an actual value, determined
as the ratio of the actual specimen width to the actual hole diameter.
3.2 Definitions of Terms Specific to This Standard—Refer to Guide D8509.
3.3 Symbols:
2 2
A = gross cross-sectional area (disregarding hole) mm [in. ]
D8387/D8387M − 23
C = fastener flexibility (Ref 1)
F
C = plate (specimen) flexibility
P
C = doubler plate flexibility
S
CV = sample coefficient of variation, %
d = fastener diameter, mm [in.]
D = hole diameter, mm [in.]
e/D = actual edge distance ratio
E = fastener modulus, MPa [psi]
F
E = test specimen laminate modulus, MPa [psi]
xP
E = doubler plate modulus in axial (x) direction, MPa [psi]
xS
gr_byp_t
F = ultimate tensile gross bypass strength, MPa [psi].
x
net_byp_t
F = ultimate tensile net bypass strength, MPa [psi]
x
gr_byp_c
F = ultimate compressive gross bypass strength, MPa [psi]
x
net_byp_c
F = ultimate compressive net bypass strength, MPa [psi]
x
br_byp
F = bearing stress at ultimate bypass strength, MPa [psi]
g = distance from hole edge to specimen end, mm [in.]
h = specimen thickness near hole (nominal or actual, as specified), mm [in.]
k = proportion of total force transferred through doubler plates
D
k = estimate of proportion of total force transferred through fasteners to doubler plates
E
k = proportion of total force transferred through specimen
S
L = distance between fastener centerlines, mm [in.]
n = number of strain gages on the doubler plate
n = number of tested specimens
P = total force applied to specimen, N [lbf]
P , P = force in doubler plates, N [lbf]
D1 D2
P = force at i-th data point, N [lbf]
i
P = maximum force prior to failure, N [lbf]
max
P = force in specimen between fasteners, N [lbf]
S
s = sample standard deviation
n-1
t = test specimen laminate thickness, mm [in.]
P
t = doubler plate thickness, mm [in.]
S
v = fastener Poisson’s ratio
F
w = width of specimen across hole, mm [in.]
w = test specimen width, mm [in.]
P
w = doubler plate width, mm [in.]
S
X¯ = sample mean (average)
x = measured or derived property
i
δ = extensometer-1 displacement at i-th data point, mm [in.]
1i
δ = extensometer-2 displacement at i-th data point, mm [in.]
2i
br
ɛ = bearing strain, microstrain
i
br
σ = bearing stress at i-th data point, MPa [psi]
i
4. Summary of Test Method
4.1 Bearing/Bypass Test Procedures—Definition of the uniaxial bearing/bypass interaction response requires data for varying
amounts of bearing and bypass forces at a fastener hole. Refer to Guide Fig. 1 shows a typical composite laminate bearing/bypass
interaction diagram (Refs 1-3), along with illustrative data from various test types. Data from Practice D6742/D6742MD8509 and
Test Method D5961/D5961M define the 100 % bypass and bearing ends of the interaction diagram. Test Method D7248/D7248M
Procedures A and B provide data in the low bypass/high bearing region. This test method provides data in the high bypass/low
bearing region. More complicated test setups have been used to develop data across the full range of bearing/bypass interaction.
This test method is limited to cases where the bearing and bypass loads are aligned in the same direction. It is also limited to
uniaxial tensile or compressive bypass loads. Test procedures for cases where the bearing and bypass loads act at different
directions, or cases with biaxial or shear bypass loads are outside the scope of this test method.for discussion of bearing/bypass
test procedures.
4.1.1 Ultimate strength for all procedures is calculated based on the specimen gross cross-sectional area, disregarding the presence
The boldface numbers in parentheses refer to the list of references at the end of this standard.
D8387/D8387M − 23
of the hole. While the hole causes a stress concentration and reduced net section, it is common industry practice to develop notched
design allowable strengths based on gross section stress to account for various stress concentrations (fastener holes, free edges,
flaws, damage, and so forth) not explicitly modeled in the stress analysis. This is consistent with the ASTM D30 test methods for
open and filled hole tension and compression strength (Test Methods D5766/D5766M, D6484/D6484M, and Practice
D6742/D6742M).
4.2 High Bypass/Low Bearing Double Shear:
4.2.1 A flat, constant rectangular cross-section test specimen with two centerline holes located in the middle of the specimen, as
shown in the test specimen drawing of Fig. 21, is axially loaded. Two doubler plates, Fig. 32, are attached to the specimen as shown
FIG. 21 Double-Shear, 2-Fastener Hardpoint Test Specimen Drawing
D8387/D8387M − 23
FIG. 32 Doubler Plate Drawing
D8387/D8387M − 23
in Fig. 43 to act as a “hardpoint” which induces bearing forces in the test specimen and plates. The ends of the test specimen are
gripped in the jaws of a test machine and loaded in tension or compression.
4.2.1.1 Unstabilized Configuration (No Support Fixture)—The ends of the test specimen are gripped in the jaws of a test machine
and loaded in tension.
FIG. 43 (a) Tensile Loading—Test Specimen and Doubler Plate Assembly
D8387/D8387M − 23
FIG. 43 (b) Compressive Loading—Test Specimen and Doubler Plate Assembly (continued)
4.2.1.2 Stabilized Configuration (Using Support Fixture)—The test specimen is face-supported in a multi-piece bolted support
fixture, as shown in Fig. 54. The test specimen/fixture assembly is clamped in hydraulic wedge grips and the force is sheared into
the support fixture and then sheared into the specimen. Tensile or compressive force is applied. The stabilization fixture is required
for compressive loading and is optional for tensile loading.
4.2.2 The amount of force that is transferred through the doubler plates is determined from the measurement of strain in the plates
and test specimen. The force-strain response of the doubler plates and test specimen must be determined using a determinant test
setup prior to the bearing/bypassRefer to Guide D8509 test. Due to uncertainties in the hole tolerances and fastener flexibilities,
calculation of the doubler plate forces is not sufficiently reliable for data reduction (equations are provided in this test method for
estimating the fastener loads for the purposes of specimen design).for additional test details and for the standard test configuration.
D8387/D8387M − 23
FIG. 54 Support Fixture Assembly (for Details of the Support Fixture, See Test Method D5961/D5961M)
4.2.3 Both the applied force and the associated deformation of the hole(s) are monitored. The applied force is normalized by the
projected hole area to yield an effective bearing stress. The specimen is loaded until a two part failure is achieved.
4.2.4 The standard test configuration for this procedure has defined values for the major test parameters. However, the following
variations in configuration are allowed and can be considered as being in accordance with this test method as long as the values
of all variant test parameters are prominently documented with the results. The standard specimen width has a w/d = 6, as bearing
failures for this specimen configuration are not common, unlike that for the 2-fastener Test Method D7248/D7248M bypass
specimen. This avoids having to put spacers into the support fixture for narrow specimens.
Parameter Standard Variation
Loading condition double-shear none
Loading type tensile compressive
Doubler plate material steel yes, if documented
Number of holes 2 none
Countersunk holes no none
Hole fit tight any, if documented
Fastener torque 9.0-10.7 N·m [80-95 lbf- any, if documented
in.] for tensile load 2.2-
3.4 N·m [20-30 lbf-in.] for
compressive load
Laminate quasi-isotropic any, if documented
Fastener diameter 6 mm [0.250 in.] any, if documented
w/D ratio 6 any, if documented
D/h ratio 1.2-2 any, if documented
5. Significance and Use
5.1 This test method is designed to produceRefer to Guide D8509low bearing / high bypass interaction response data for research
and development, and for structural design and analysis. The standard configuration for this procedure is very specific and is
intended as a baseline configuration for developing structural design data. The high bypass/low bearing double-shear hardpoint
D8387/D8387M − 23
configuration is recommended for determining the effect of low bearing stress levels on bypass strength. While a similar
single-shear configuration could be tested, there is insufficient experience with a single-shear configuration to recommend its use
at this time.
5.2 General factors that influence the mechanical response of composite laminates and should therefore be reported include the
following: material, methods of material preparation and lay-up, specimen stacking sequence, specimen preparation, specimen
conditioning, environment of testing, specimen alignment and gripping, speed of testing, time held at test temperature, void
content, and volume percent reinforcement.
5.3 Specific factors that influence the bearing/bypass interaction response of composite laminates and should therefore be reported
include not only loading type (tension or compression) but the following: edge distance ratio, width to diameter ratio, diameter
to thickness ratio, fastener torque, fastener or pin material, fastener or pin clearance. Properties, in the test direction, which may
be obtained from this test method include the following:
5.3.1 Filled hole tensile bearing/bypass strength.
5.3.2 Filled hole compressive bearing/bypass strength.
5.3.3 Bearing stress/bypass strain curve.
6. Interferences
6.1 Refer to Test Method Guide D7248/D7248MD8509 for discussion of interferences with bolted joint bearing/bypass testing.
D8387/D8387M − 23
7. Apparatus
7.1 Micrometers—A micrometer with a 4 to 8 mm [0.16 to 0.32 in.] 4 mm to 8 mm [0.16 in. to 0.32 in.] nominal diameter ball
interface shall be used to measure the specimen thickness when at least one surface is irregular (such as the bag-side of a laminate).
A micrometer with a 4 to 8 mm [0.16 to 0.32 in.] 4 mm to 8 mm [0.16 in. to 0.32 in.] nominal diameter ball interface or with a
flat anvil interface shall be used to measure the specimen thickness when both surfaces are smooth (such as tooled surfaces). A
micrometer or caliper, with a flat anvil interface, shall be used to measure the width of the specimen. The accuracy of the
instruments shall be suitable for reading to within 1% of the sample dimensions. For typical specimen geometries, an instrument
with an accuracy of 60.0025 mm [60.0001 in.] is adequate for the thickness measurement, while an instrument with an accuracy
of 60.025 mm [60.001 in.] is adequate for the width measurement. Additionally, a micrometer or gage capable of determining
the hole diameters to 60.025 mm [60.001 in.] shall be used.
NOTE 2—The accuracies given above are based on achieving measurements that are within 1 % of the sample width and thickness.
7.2 Loading Fasteners or Pins—The fastener (or pin) type shall be specified as an initial test parameter and reported. The assembly
torque (if applicable) shall be specified as an initial test parameter and reported. This value may be a measured torque or a
specification torque for fasteners with lock-setting features. If washers are utilized, the washer type, number of washers, and
washer location(s) shall be specified as initial test parameters and reported. The reuse of fasteners is not recommended due to
potential differences in through-thickness clamp-up for a given torque level, caused by wear of the threads or deformation of the
locking features.
7.3 Torque Wrench—If using a torqued fastener, a torque wrench used to tighten the fastener shall be capable of determining the
applied torque to within 610 % of the desired value.
7.4 Fixture—Doubler plates, Fig. 32, are attached to the test specimen using two fasteners. In some cases, it may be desirable to
use doubler plates that are more closely matched in stiffness to the test laminate, particularly when testing soft laminate materials
or layups. These plates may typically be reused, as the force transferred into the plates should be relatively small. The holes in the
plates should be examined for bearing deformation after each use and replaced if deformation is observed. If the doubler plates
are replaced, the new plates shall be calibrated in accordance with 11.3.
7.4.1 For compressive tests, the doubler plates must be sized to fit into the support fixture window. See alternate described in 7.4.5.
7.4.2 For test laminates that are narrower than the standard specimen width, which may be required in some cases to obtain a
bypass failure mode, the standard doubler plate widths may be used. Actual widths shall be used in the force proportion estimate
calculations in 8.2.2.
7.4.3 Strain Gages—For tensile tests, two axial strain gages shall be mounted on each doubler plate at the locations shown in Fig.
43a. For compressive tests, one axial strain gage shall be mounted on each doubler plate at the location shown in Fig. 43b.
7.4.4 Machining Precision—Doubler plates and calibration loading plates require high machining quality, hole diameter
tolerances, hole positioning, hole perpendicularity, flatness, etc.
7.4.5 For compressive tests, an alternate to doublers that fit within the support fixture window is to use full width doublers (same
as for tensile tests). In this case, shims (4 total) equal to the doubler plate thickness will be required at each end of the specimen
to provide a flat surface to interface with the support fixture. In some cases, test laminate failure may then occur at the gap between
the doubler and shim; a mitigation for this situation is to modify the doublers and shims to have a chevron shape similar to the
support fixture such that there is no unsupported laminate area across the specimen width.
7.5 Support Fixture (Compressive Loading)—If compressive loads are applied or if requested in the test plan, a support fixture
shall be used to stabilize the specimen. The fixture is a face-supported test fixture as shown in Fig. 54. The fixture consists of two
short-grip/long-grip assemblies, two support plates, and stainless steel shims as required to maintain a nominally zero
(0.00(0.00-mm to 0.12-mm [0.000[0.000-in. to 0.005-in.] tolerance) gap between the support plates and the long grips. If this gap
does not meet the minimum requirement, shim the contact area between the support plate and the short grip with stainless steel
shim stock. If the gap is too large, shim between the support plate and the long grip, holding the shim stock on the support plate
with tape. The fixture should be checked for conformity to engineering drawings. Each short-grip/long-grip assembly is line-drilled
and must be used as a matched set. The threading of the support plate is optional. The fixture is hydraulically gripped on each end
and the force is sheared by means of friction through the fixture and into the test specimen. A cutout exists on both faces of the
D8387/D8387M − 23
fixture for a thermocouple, fastener(s), and surface-mounted extensometer. The long and short fixtures have an undercut along the
corner of the specimen grip area so that specimens are not required to be chamfered and to avoid damage caused by the radius.
The fixtures also allow a slight clearance between the fixture and the gage section of the specimen, in order to minimize grip
failures and friction effects. This fixture does not allow specimens to be end loaded.
7.5.1 Support Fixture Details—The detailed drawings for manufacturing the support fixture are contained in Test Method
D5961/D5961M. Other fixtures that meet the requirements of this section may be used.
NOTE 3—Experience has shown that fixtures may be damaged in use; thus, periodic re-inspection of the fixture dimensions and tolerances is important.
7.6 Testing Machine—The testing machine shall be in conformance with Practices E4, and shall satisfy the following
requirements:
7.6.1 Testing Machine Configuration—The testing machine shall have both an essentially stationary head and a movable head. A
short loading train and rigidly mounted hydraulic grips shall be used for Procedure B when using the support fixture.
7.6.2 Drive Mechanism—The testing machine drive mechanism shall be capable of imparting to the movable head a controlled
velocity with respect to the stationary head. The velocity of the movable head shall be capable of being regulated as specified in
11.4.
7.6.3 Force Indicator—The testing machine force-sensing device shall be capable of indicating the total force being carried by the
test specimen. This device shall be essentially free from inertia-lag at the specified rate of testing and shall indicate the force with
an accuracy over the force range(s) of interest of within 61 % of the indicated value.
7.6.4 Grips—Each head of the testing machine shall be capable of holding one end of the test assembly so that the direction of
force applied to the specimen is coincident with the longitudinal axis of the specimen. Wedge grips shall apply sufficient lateral
pressure to prevent slippage between the grip face and the test specimen or support fixture.
7.7 Bearing Deformation Indicator—Bearing deformation data shall be determined by an indicator device able to measure
longitudinal hole deformation, as shown in Fig. 65. The arms of the indicator device must fit within the stabilization fixture when
a specimen with a width less than 36 mm [1.5 in.] is tested in the standard fixture. Transducer gage lengths on the order of 50 mm
[2.0 in.] are typically used. The transducers of the bearing deformation indicator may provide either individual signals to be
externally averaged or an electronically averaged signal. The indicator may consist of two matched strain-gage extensometers or
displacement transducers such as LVDTs or DCDTs. Attachment of the bearing deformation indicator to the specimen shall not
cause damage to the specimen surface. Transducers shall satisfy, at a minimum, Practice E83, Class B-2 requirements for the
displacement range of interest, and shall be calibrated over that range in accordance with Practice E83. The transducers shall be
essentially free of inertia-lag at the specified speed of testing.
7.8 Conditioning Chamber—When conditioning materials at non-laboratory environments, a temperature-/vapor-level controlled
environmental conditioning chamber is required that shall be capable of maintaining the required temperature to within 63 °C
[65 °F] and the required relative humidity level to within 63 %. Chamber conditions shall be monitored either on an automated
continuous basis or on a manual basis at regular intervals.
7.9 Environmental Test Chamber—An environmental test chamber is required for test environments other than ambient testing
laboratory conditions. This chamber shall be capable of maintaining the gage section of the test specimen at the required test
environment during the mechanical test within 63 °C or 65 °F.
7.10 Strain-Indicating Device—Strain data, when required, shall be determined by means of bonded resistance strain gages.
7.10.1 Bonded Resistance Strain Gage Selection—Strain gage selection is based on the type of material to be tested. A minimum
active gage length of 3 mm [0.125 in.] is recommended for composite laminates fabricated from unidirectional layers. Larger strain
gage sizes may be more suitable for some textile fabrics. Gage calibration certification shall comply with Test Method E251. Strain
gages with a minimum normal strain range of approximately 3 % are recommended. When testing textile fabric laminates, gage
selection should consider the use of an active gage length that is at least as great as the characteristic repeating unit of the fabric.
Some guidelines on the use of strain gages on composite materials follow.
D8387/D8387M − 23
FIG. 65 Transducer Gage Length and Location
7.10.1.1 Surface preparation of fiber-reinforced composites in accordance with Guide E1237 can penetrate the matrix material and
cause damage to the reinforcing fibers, resulting in improper coupon failures. Reinforcing fibers should not be exposed or damaged
during the surface preparation process. The strain gage manufacturer should be consulted regarding surface preparation guidelines
and recommended bonding agents for composites, pending the development of a set of standard practices for strain gage
installation surface preparation of fiber-reinforced composite materials.
7.10.1.2 Consideration should be given to the selection of gages having larger resistances to reduce heating effects on low
conductivity materials. Resistances of 350 Ω 350 Ω or higher are preferred. Additional consideration should be given to the use
of the minimum possible gage excitation voltage consistent with the desired accuracy (1 to 2 V (1 V to 2 V is recommended) to
reduce the power consumed by the gage. Heating of the coupon by the gage may affect the performance of the material directly
or it may affect the indicated strain as a result of a difference between the gage temperature compensation factor and the coefficient
of thermal expansion of the coupon material.
7.10.1.3 Consideration of some form of temperature compensation is recommended, even when testing at standard laboratory
atmosphere. Temperature compensation may be required when testing in non-ambient temperature environments.
7.10.1.4 Consideration should be given to the transverse sensitivity of the selected strain gage. The strain gage manufacturer
should be consulted for recommendations on transverse sensitivity corrections and effects on composites.
8. Sampling and Test Specimens
8.1 Sampling—Test at least five specimens per test condition unless valid results can be gained through the use of fewer specimens,
as in the case of a designed experiment. For statistically significant data, the procedures outlined in Practice E122 should be
consulted. The method of sampling shall be reported.
NOTE 4—If specimens are to undergo environmental conditioning to equilibrium, and are of such type or geometry that the weight change of the material
cannot be properly measured by weighing the specimen itself (such as a tabbed mechanical specimen), then use a traveler specimen of the same nominal
D8387/D8387M − 23
thickness and appropriate size (but without tabs) to determine when equilibrium has been reached for the specimens being conditioned.
8.2 Geometry:
8.2.1 Stacking Sequence—The standard laminate shall have multidirectional fiber orientations (fibers shall be oriented in a
minimum of two directions), and balanced and symmetric stacking sequences. For tensile loaded specimens, nominal thickness
shall be 2.5 mm [0.10 in.], with a permissible range of 2 to 5 mm [0.080 to 0.208 in.], 2 mm to 5 mm [0.080 in. to 0.208 in.],
inclusive. For compressive loaded specimens, nominal thickness shall be 4 mm [0.160 in.], with a permissible range of 2.5 to 5
mm [0.100 to 0.208 in.], 2.5 mm to 5 mm [0.100 in. to 0.208 in.], inclusive. Fabric laminates containing satin-type weaves shall
have symmetric warp surfaces, unless otherwise specified and noted in the report.
NOTE 5—Typically, a [45 /0 /–45 /90 ] tape or [45 /0 ] fabric laminate should be selected such that a minimum of 5 % of the fibers lay in each of the
i j i k ms i j ms
four principal orientations. This laminate design has been found to yield the highest likelihood of acceptable failure modes.
8.2.2 Configuration—The geometry of the specimen is shown in Fig. 21. Strain gages as shown in Fig. 43 are recommended to
provide additional data to determine the proportion of force transferred to the doubler plates. The following equations may be used
to estimate the proportion of force transferred to the doubler plates for test specimen design purposes. These equations assume the
two fasteners and the two doubler plates are identical. The fastener flexibility equation is obtained from Ref (42). These equations
shall not be used for test data calculations.
2C
P
k 5 (1)
~2C 1 C 1 2C !
P S F
L
C 5 (2)
P
t w E
P P xP
L
C 5 (3)
S
t w E
S S xS
3 2 2 3
8 2t 1 t 1 1 v 64 8t 1 16t t 1 8t t 1 t 2t 1t 1 2
~ !~ ! ~ !~ !
S P F S S P S P P S P
C 5 1 1 1 1 (4)
F 2 4
3πE d 192πE d t t E t E t E
F F S P F S xS P xP
where:
k = estimate of proportion of total force transferred through fasteners to doubler plates,
E
C = plate (specimen) flexibility,
P
C = doubler plate flexibility,
S
C = fastener flexibility (Ref 1),
F
t = test specimen laminate thickness, mm [in.],
P
t = doubler plate thickness, mm [in.],
S
w = test specimen width, mm [in.],
P
w = doubler plate width, mm [in.],
S
E = test specimen laminate modulus, MPa [psi],
xP
E = doubler plate modulus in axial (x) direction, MPa [psi],
xS
E = fastener modulus, MPa [psi],
F
v = fastener Poisson’s ratio,
F
d = fastener diameter, mm [in.], and
L = distance between fastener centerlines, mm [in.].
8.3 Specimen Preparation—Guide D5687/D5687M provides recommended specimen preparation practices and should be
followed where practical.
8.3.1 Panel Fabrication—Control of fiber alignment is critical. Improper fiber alignment will reduce the measured properties. The
panel(s) must be flat and of uniform thickness to ensure even loading. Erratic fiber alignment will also increase the coefficient of
variation. Report the panel fabrication method.
8.3.2 Machining Methods—Specimen preparation is extremely important for this specimen. Take precautions when cutting
specimens from plates to avoid notches, undercuts, rough or uneven surfaces, or delaminations due to inappropriate machining
methods. Obtain final dimensions by water-lubricated precision sawing, milling, or grinding. The use of diamond tooling has been
found to be extremely effective for many material systems. Edges should be flat and parallel within the specified tolerances. Record
and report the specimen cutting and hole preparation methods.
D8387/D8387M − 23
8.3.3 Hole Drilling—Holes should be drilled undersized and reamed to final dimensions. Special care shall be taken to ensure that
creation of the specimen hole does not delaminate or otherwise damage the material surrounding the hole. Specimens should be
match drilled with the doubler straps to ensure that the fasteners can be installed.
8.3.4 Labeling—Label the specimens so that they will be distinct from each other and traceable back to the raw material, and in
a manner that will both be unaffected by the test and not influence the test.
9. Calibration
9.1 The accuracy of all measuring equipment shall have certified calibrations that are current at the time of use of the equipment.
10. Conditioning
10.1 Unless explicitly specified by the test requestor, no pre-test conditioning shall be performed and the test specimens shall be
tested as prepared.
10.2 The pre-test specimen conditioning process, to include specified environmental exposure levels and resulting moisture
content, shall be reported with the test data.
NOTE 6—The recommended pre-test specimen condition is effective moisture equilibrium at a specific relative humidity per Test Method D5229/D5229M.
NOTE 7—The term moisture, as used in Test Method D5229/D5229M, includes not only the vapor of a liquid and its condensate, but the liquid itself in
large quantities, as for immersion.
10.3 If no explicit conditioning process is performed, the specimen conditioning process shall be reported as “unconditioned” and
the moisture content as “unknown.”
11. Procedure
11.1 Parameters to Be Specified Prior to Test:
11.1.1 The specimen sampling method, specimen type and geometry, fastener type and material, fastener torque (if appropriate),
type of loading (tensile or compressive), support fixture (if appropriate), cleaning process, and conditioning travelers (if required).
11.1.2 The properties to report and data reporting format desired.
NOTE 8—Determine specific material property, accuracy, and data reporting requirements prior to test for proper selection of instrumentation and data
recording equipment. Estimate specimen failure stress and bearing strain levels to aid in transducer selection, calibration of equipment, and determination
of equipment settings.
11.1.3 The environmental conditioning test parameters.
11.1.4 If performed, extensometer requirements and related calculations.
11.1.5 If performed, the sampling method, specimen geometry, and test parameters used to determine density and reinforcement
volume.
11.2 Before Test:
11.2.1 Report any deviations from this test method, whether intentional or inadvertent.
11.2.2 If specific gravity, density, reinforcement volume, or void volume are to be reported, then obtain these samples from the
same panels being bearing tested. Specific gravity and density may be evaluated by means of Test Methods D792. Volume percent
of the constituents may be evaluated by one of the matrix digestion procedures of Test Method D3171, or, for certain reinforcement
materials such as glass and ceramics, by the matrix burn-off technique of Test Method D2584. The void content equations of Test
Method D2734 are applicable to both Test Method D2584 and the matrix digestion procedures.
D8387/D8387M − 23
11.2.3 Condition the specimens as required. Store the specimens in the conditioned environment until test time, if the test
environment is different than the conditioning environment.
11.2.4 Following final specimen machining, but before any conditioning and testing, measure the specimen width, w, and the
specimen thickness, h, in the vicinity of each hole. Measure each hole diameter, D. Measure the fastener or pin diameter, d, at the
bearing contact location. The accuracy of all measurements shall be within 1 % of the dimension, unless otherwise specified in this
test method. Record the dimensions to three significant figures in units of millimeters [inches].
11.3 Test Procedure Step 1 – Doubler Plate Force-Strain Calibration:
11.3.1 For purposes of accurately determining the force transferred into the doubler plates, a calibration of the force applied by
the fastener to the doubler and the strain measured by the strain gages on the doubler must be determined using a determinant
loading setup. Assemble each of the doubler plates with two or four loading straps, as shown in Fig. 76. For doubler plates with
the recess for strain gages on the specimen, assemble the two doubler plates back-to-back to avoid excessive bending which could
occur if the plates are tested individually. Torque the fasteners to 0.6-1.2 N·m [5-10 lbf-in.]. Test each of the doubler plates as
follows:
11.3.2 Assign a unique identification number to each doubler plate and mark the number on the plate. Assign a unique strain gage
number to each gage on each doubler plate and mark the gage numbers on the plate.
11.3.3 Speed of Testing—A standard head displacement rate of 2 mm/min [0.05 in./min] is recommended.
11.3.4 Test Environment—Test the doubler assembly at the same temperature as the test specimen will be tested.
FIG. 76 Doubler Plate Force-Strain Calibration Setup
D8387/D8387M − 23
11.3.5 Insert the specimen into the test machine, attaching loading interfaces or tightening grips as required.
11.3.6 Attach the strain gages to the recording instrumentation. Remove any remaining pre-load and zero the strain gages. Record
the doubler and strain gage numbers. Record a unique calibration loading run identification number.
11.3.7 Apply the force to the doubler assembly at the specified rate while recording data. Load the assembly to a maximum force
equal to:
P 5 1.1 Expected Bearing / Bypass Specimen Failure Load
~ !~ !
max
(5)
k from Eq. 1 # plates ⁄2
~ !~ !
E
where:
(# plates) = the number of double plates in the doubler calibration assembly, Fig. 7.
(# plates) = the number of double plates in the doubler calibration assembly, Fig. 6.
NOTE 9—Take care when selecting the maximum force for the doubler plate calibration that bearing deformation or damage is not introduced in the
doubler during the calibration test.
NOTE 10—Every doubler plate used for testing shall be calibrated. Traceability of the calibration load-strain data for each doubler strain gage must be
maintained.
11.3.8 Record force versus strain continuously, or at intervals of 2-3 data recordings per second with a target minimum of 100 data
points per test.
11.4 Test Procedure Step 2 – Test Laminate Force-Strain Calibration:
11.4.1 While the strain data from the doubler plates can be used to determine the force transferred into the doubler plates, it is
recommended that the strain in the test laminate also be measured during the bearing/bypass tests. To use this strain data, a
force-strain calibration of the strain measured by the strain gages on the test laminate must be determined. For tensile loaded tests,
install fasteners into the specimen holes (install a nut to prevent loss of the fast
...