ASTM D4255/D4255M-20e1

Standard Test Method for In-Plane Shear Properties of Polymer Matrix Composite Materials by the Rail Shear Method

SIGNIFICANCE AND USE
5.1 These shear tests are designed to produce in-plane shear property data for material specifications, research and development, and design. Factors that influence the shear response and should therefore be reported include: 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 at temperature, void content, and fiber volume reinforcement content. Properties that may be measured by this test method include:  
5.1.1 In-plane shear stress versus engineering shear strain response,  
5.1.2 In-plane shear chord modulus of elasticity,  
5.1.3 Offset shear stress, and  
5.1.4 Maximum in-plane shear stress. In cases in which the engineering shear strain at failure is greater than 5 %, the shear stress corresponding to 5 % engineering shear strain should be reported.
SCOPE
1.1 This test method determines the in-plane shear properties of high-modulus fiber-reinforced composite materials by either of two procedures. In Procedure A, laminates clamped between two pairs of loading rails are tested. When loaded in tension, the rails introduce shear forces in the specimen. In Procedure B, laminates clamped on opposite edges with a tensile or compressive force applied to a third pair of rails in the center are tested.  
1.2 Application of this test method is limited to continuous-fiber or discontinuous-fiber-reinforced polymer matrix composites in the following material forms:  
1.2.1 Laminates composed only of unidirectional fibrous laminae, with the fiber direction oriented either parallel or perpendicular to the fixture rails.  
1.2.2 Laminates composed only of woven fabric filamentary laminae with the warp direction oriented either parallel or perpendicular to the fixture rails.  
1.2.3 Laminates of balanced and symmetric construction, with the 0° direction oriented either parallel or perpendicular to the fixture rails.  
1.2.4 Short-fiber-reinforced composites with a majority of the fibers being randomly distributed.
Note 1: Additional test methods for determining in-plane shear properties of polymer matrix composites may be found in Test Methods D3518/D3518M, D5379/D5379M, D5448/D5448M, and D7078/D7078M.  
1.3 The reproducibility of this test method can be affected by the presence of shear stress gradients in the gage section and stress concentrations at the gripping areas. Test Methods D5379/D5379M and D7078/D7078M provide superior shear response in comparison to this test method, as their specimen configurations produce a relatively pure and uniform shear stress state in the gage section.  
1.4 The technical content of this standard has been stable since 2001 without significant objection from its stakeholders. As there is limited technical support for the maintenance of this standard, changes since that date have been limited to items required to retain consistency with other ASTM D30 Committee standards, including editorial changes and incorporation of updated guidance on micrometers and calipers, strain gage requirements, speed of testing, specimen preconditioning and environmental testing. Future maintenance of the standard will only be in response to specific requests and performed only as technical support allows.  
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-pounds 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 envi...

General Information

• Status: Published
• Publication Date: 30-Sep-2020
• ICS: 83.140.20 - Laminated sheets
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.04 - Lamina and Laminate Test Methods

Relations

• 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 E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM E1237-20 - Standard Guide for Installing Bonded Resistance Strain Gages
• Effective Date: 15-Aug-2020
• Refers: ASTM E251-20a - Standard Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages
• Effective Date: 01-Jun-2020
• Refers: ASTM E251-20 - Standard Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages
• Effective Date: 01-May-2020
• Refers: ASTM D5229/D5229M-20 - Standard Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite Materials
• Effective Date: 01-Mar-2020
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM D3878-19a - Standard Terminology for Composite Materials
• Effective Date: 15-Oct-2019
• Refers: ASTM D7078/D7078M-19 - Standard Test Method for Shear Properties of Composite Materials by V-Notched Rail Shear Method
• Effective Date: 15-Aug-2019
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D3878-19 - Standard Terminology for Composite Materials
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019

Overview

ASTM D4255/D4255M-20e1 is an internationally recognized standard developed by ASTM for determining the in-plane shear properties of polymer matrix composite materials, using the rail shear method. This test method is essential for characterizing high-modulus fiber-reinforced composites, which are widely utilized in aerospace, automotive, marine, and various high-performance engineering applications. The standard provides two test procedures (two-rail and three-rail methods) to measure and report key in-plane shear properties, supporting material specifications, research and development, and structural design efforts.

Key Topics

• Test Purpose and Scope:
  ASTM D4255/D4255M-20e1 is designed to assess the in-plane shear performance of continuous or discontinuous fiber-reinforced polymer matrix composites. It is applicable to unidirectional laminates, woven fabric laminates, symmetric and balanced laminates, and short-fiber-reinforced composites.

• Procedures:

  • Procedure A (Two-Rail Method): Laminates are clamped between two sets of rails and loaded to induce shear forces.
  • Procedure B (Three-Rail Method): The specimen is clamped on opposite edges, with a force applied through a third, central pair of rails.

• Measured Properties:

  • In-plane shear stress versus engineering shear strain response
  • In-plane shear chord modulus of elasticity
  • Offset shear stress
  • Maximum in-plane shear stress

• Influencing Factors:
  Material type, specimen lay-up, stacking sequence, specimen preparation, conditioning, test environment, alignment, gripping technique, test rate, and material composition (e.g., void and fiber content) can all affect test results and should be reported.

• Test Limitations & Reproducibility:
  The standard notes possible stress gradients in the gage section and concentrations at gripping areas, potentially influencing reproducibility. For more uniform shear stress states, referenced alternatives include ASTM D5379/D5379M and D7078/D7078M.

Applications

• Material Specification:
  The test method provides reliable data for the development and approval of composite materials meeting specific in-plane shear strength and modulus requirements.

• Structural Design:
  Designers use this standard to obtain validated shear property data, enabling safer and more efficient composite structure designs, especially in fields where weight, strength, and durability are critical.

• Quality Control:
  Manufacturers use ASTM D4255/D4255M-20e1 during production runs for quality assurance, ensuring that composite materials meet established mechanical property benchmarks.

• Research and Development:
  Researchers employ the rail shear method to compare new matrix systems, reinforcements, or processing techniques, and to validate predictive modeling for composite behavior under shear loading.

• Multi-Environment Testing:
  The standard allows testing across various environmental conditions (humidity, temperature) for real-world performance assessment.

Related Standards

For users requiring different specimen configurations, stress states, or complementary data, ASTM D4255/D4255M-20e1 references several related ASTM standards:

• ASTM D3518/D3518M: In-plane shear response by tensile test of ±45° laminates
• ASTM D5379/D5379M: Shear properties by the V-notched beam method
• ASTM D5448/D5448M: In-plane shear properties for hoop wound composites
• ASTM D7078/D7078M: Shear properties by the V-notched rail shear method
• ASTM D2734, D3171, D792: Methods for determining void content, constituent content, and density of composites

Practical Value

The ASTM D4255/D4255M-20e1 standard is a foundational method for the composite industry, providing a consistent approach for obtaining critical in-plane shear properties of advanced materials. Compliance ensures materials are accurately characterized and quality assured, supporting innovation and safety in high-performance structural applications.

For laboratories, material engineers, and designers, following ASTM D4255/D4255M-20e1 guarantees reliable, comparable, and internationally accepted results-supporting product development, certification, and regulatory compliance across global markets.

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.
´1
Designation: D4255/D4255M − 20
Standard Test Method for
In-Plane Shear Properties of Polymer Matrix Composite
Materials by the Rail Shear Method
This standard is issued under the fixed designation D4255/D4255M; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
ε NOTE—Adjunct stock code was updated editorially to reflect its digital code in February 2023.
1. Scope stress concentrations at the gripping areas. Test Methods
D5379/D5379M and D7078/D7078M provide superior shear
1.1 This test method determines the in-plane shear proper-
response in comparison to this test method, as their specimen
ties of high-modulus fiber-reinforced composite materials by
configurations produce a relatively pure and uniform shear
either of two procedures. In Procedure A, laminates clamped
stress state in the gage section.
between two pairs of loading rails are tested. When loaded in
tension, the rails introduce shear forces in the specimen. In 1.4 The technical content of this standard has been stable
Procedure B, laminates clamped on opposite edges with a since 2001 without significant objection from its stakeholders.
tensile or compressive force applied to a third pair of rails in As there is limited technical support for the maintenance of this
the center are tested. standard, changes since that date have been limited to items
required to retain consistency with other ASTM D30 Commit-
1.2 Application of this test method is limited to continuous-
tee standards, including editorial changes and incorporation of
fiber or discontinuous-fiber-reinforced polymer matrix com-
updated guidance on micrometers and calipers, strain gage
posites in the following material forms:
requirements, speed of testing, specimen preconditioning and
1.2.1 Laminates composed only of unidirectional fibrous
environmental testing. Future maintenance of the standard will
laminae, with the fiber direction oriented either parallel or
only be in response to specific requests and performed only as
perpendicular to the fixture rails.
technical support allows.
1.2.2 Laminates composed only of woven fabric filamentary
laminae with the warp direction oriented either parallel or 1.5 Units—The values stated in either SI units or inch-
perpendicular to the fixture rails.
pound units are to be regarded separately as standard. The
1.2.3 Laminates of balanced and symmetric construction, values stated in each system are not necessarily exact equiva-
with the 0° direction oriented either parallel or perpendicular to
lents; therefore, to ensure conformance with the standard, each
the fixture rails. system shall be used independently of the other, and values
1.2.4 Short-fiber-reinforced composites with a majority of
from the two systems shall not be combined.
the fibers being randomly distributed. 1.5.1 Within the text the inch-pounds units are shown in
brackets.
NOTE 1—Additional test methods for determining in-plane shear
properties of polymer matrix composites may be found in Test Methods
1.6 This standard does not purport to address all of the
D3518/D3518M, D5379/D5379M, D5448/D5448M, and D7078/
safety concerns, if any, associated with its use. It is the
D7078M.
responsibility of the user of this standard to establish appro-
1.3 The reproducibility of this test method can be affected
priate safety, health, and environmental practices and deter-
by the presence of shear stress gradients in the gage section and
mine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accor-
dance with internationally recognized principles on standard-
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.04 on
ization established in the Decision on Principles for the
Lamina and Laminate Test Methods.
Development of International Standards, Guides and Recom-
Current edition approved Oct. 1, 2020. Published October 2020. Originally
mendations issued by the World Trade Organization Technical
approved in 1983. Last previous edition approved in 2015 as D4255/D4255M – 15a.
DOI: 10.1520/D4255_D4255M-20E01. Barriers to Trade (TBT) Committee.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D4255/D4255M − 20
2. Referenced Documents
2.1 ASTM Standards:
D792 Test Methods for Density and Specific Gravity (Rela-
tive 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
D3518/D3518M Test Method for In-Plane Shear Response
of Polymer Matrix Composite Materials by Tensile Test of
a 645° Laminate
D3878 Terminology for Composite Materials
D5229/D5229M Test Method for Moisture Absorption Prop-
erties and Equilibrium Conditioning of Polymer Matrix
Composite Materials
D5379/D5379M Test Method for Shear Properties of Com-
posite Materials by the V-Notched Beam Method
D5448/D5448M Test Method for Inplane Shear Properties
of Hoop Wound Polymer Matrix Composite Cylinders
D7078/D7078M Test Method for Shear Properties of Com-
posite Materials by V-Notched Rail Shear Method
E4 Practices for Force Calibration and Verification of Test-
ing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E111 Test Method for Young’s Modulus, Tangent Modulus,
FIG. 1 Procedure A Assembly Rail Shear Apparatus
and Chord Modulus
E122 Practice for Calculating Sample Size to Estimate, With
Specified Precision, the Average for a Characteristic of a fundamental dimension form, using the following ASTM standard sym-
bology for fundamental dimensions, shown within square brackets: [M]
Lot or Process
for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature,
E177 Practice for Use of the Terms Precision and Bias in
and [nd] for nondimensional quantities. Use of these symbols is restricted
ASTM Test Methods
to analytical dimensions when used with square brackets, as the symbols
E251 Test Methods for Performance Characteristics of Me-
may have other definitions when used without the brackets.
tallic Bonded Resistance Strain Gages
3.2 Definitions of Terms Specific to This Standard:
E456 Terminology Relating to Quality and Statistics
3.2.1 in-plane shear, n—shear associated with shear forces
E1237 Guide for Installing Bonded Resistance Strain Gages
applied to the edges of the laminate so that the resulting shear
2.2 ASTM Adjunct:
deformations occur in the plane of the laminate rather than
Adjunct No. ADJD4255-E-PDF Rail Shear Fixtures Ma-
through the thickness.
chining Drawings
3.2.2 offset shear stress [M/(LT )], n—the shear stress
3. Terminology associated with an offset of the shear chord modulus of
elasticity line along the strain axis (see 13.5).
3.1 Terminology D3878 defines terms relating to high-
3.2.3 shear strength [M/(LT )], n—the shear stress carried
modulus fibers and their composites. Terminology D883 de-
by a material at failure under a pure shear condition.
fines terms relating to plastics. Terminology E6 defines terms
relating to mechanical testing. Terminology E456 and Practice
3.2.4 transition region, n—a strain region of a stress-strain
E177 define terms relating to statistics. In the event of a
or strain-strain curve over which a significant change in the
conflict between terms, Terminology D3878 shall have prece-
slope of the curve occurs within a small strain range.
dence over the other terminology standards.
3.2.4.1 Discussion—Many filamentary composite materials
exhibit a nonlinear response during loading, such as seen in
NOTE 2—If the term represents a physical quantity, its analytical
plots of either longitudinal stress versus longitudinal strain or
dimensions are stated immediately following the term (or letter symbol) in
transverse strain versus longitudinal strain. In certain cases, the
nonlinear response may be conveniently approximated by a
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
bilinear fit. There are several physical reasons for the existence
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
of a transition region. Common examples include matrix
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
cracking under tensile loading and ply delamination.
A copy of the detailed drawing for the construction of the fixtures shown in
3.2.5 traveler, n—a small piece of the same material as, and
Figs. 1 and 2 is available at a nominal cost from ASTM Headquarters. Request
Adjunct No. ADJD4255-E-PDF. processed similarly to, the test specimen, used for example to
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D4255/D4255M − 20
FIG. 2 Procedure A Partially Assembled Typical Test Fixture
measure moisture content as a result of conditioning. This is usable. The two-rail shear fixtures can also be compression
also sometimes termed as a reference sample. loaded. The force may be applied to failure.
4.1.1 If force-strain data are required, the specimen may be
3.3 Symbols:
instrumented with strain gages. Biaxial strain gage rosettes are
A = cross-sectional area of test specimen
installed at corresponding locations on each face of the
B = percent bending of specimen
y
specimen.
CV = coefficient of variation statistic of a sample population
4.2 Procedure B: Three-Rail Shear Test—A flat panel,
for a given property, %
o
F = offset shear stress, the value of the shear stress at the clamped securely between pairs of rails on opposite edges and
in its center, is loaded by supporting the side rails while loading
intersection of the stress-strain plot with a line passing through
the offset strain value at zero stress and with a slope equal to the center rails. See Figs. 3-5. A force on the center rail of
either tension or compression produces a shear force in each
the shear chord modulus of elasticity
u
F = ultimate shear stress section of the specimen. The force may be applied to failure.
4.2.1 The test fixture consists of three pairs of parallel rails
G = shear modulus of elasticity
h = specimen thickness usually bolted to the test specimen by through bolts. The two
outside pairs of rails are attached to a base plate which rests on
l = specimen length, the dimension parallel to the rails in the
gage section the test machine. A third pair (middle rails) is guided through
a slot in the top of the base fixture. The unit is normally loaded
n = number of specimens
P = force carried by test specimen at ith data point in compression. It is also permissible to load the middle rails in
i
max
tension, but this requires attaching the base fixture to the test
P = force carried by a test specimen that is the lesser of
(1) the maximum force before failure, (2) the force at 5 % machine.
4.2.2 If force-strain data are required, the specimen may be
engineering shear strain, or (3) the force at the bending limit
(see 11.8.1) instrumented with strain gages. Biaxial strain gages are to be
S = sample standard deviation installed at corresponding locations on opposite faces of the
n–1
specimen.
x = measured or derived property for an individual specimen
i
from the sample population
4.3 Detailed fixture drawings are available as ASTM Ad-
χ¯ = sample mean (average)
junct No. ADJD4255-E-PDF.
γ = engineering shear strain
5. Significance and Use
ε = indicated normal strain from strain transducer
-6 -6
µε = 10 m/m (10 in./in.)
5.1 These shear tests are designed to produce in-plane shear
τ = shear stress at ith data point
property data for material specifications, research and
i
development, and design. Factors that influence the shear
4. Summary of Test Method
response and should therefore be reported include: material,
4.1 Procedure A: Two-Rail Shear Test—A flat panel with methods of material preparation and lay-up, specimen stacking
holes along opposing edges is clamped, usually by through sequence, specimen preparation, specimen conditioning, envi-
bolts, between two pairs of parallel steel loading rails; see Figs. ronment of testing, specimen alignment and gripping, speed of
1 and 2. When loaded in tension, this fixture introduces shear testing, time at temperature, void content, and fiber volume
forces in the specimen that produce failures across the panel. reinforcement content. Properties that may be measured by this
This test method is typical but not the only configuration test method include:
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D4255/D4255M − 20
FIG. 3 Procedure B Assembly Rail Shear Fixture
5.1.1 In-plane shear stress versus engineering shear strain
response,
FIG. 4 Procedure B Assembled Typical Test Fixture
5.1.2 In-plane shear chord modulus of elasticity,
5.1.3 Offset shear stress, and
confirm that shear strength has not been influenced by speci-
5.1.4 Maximum in-plane shear stress. In cases in which the
men buckling. Failure by buckling should not be interpreted as
engineering shear strain at failure is greater than 5 %, the shear
indicating the maximum shear strength.
stress corresponding to 5 % engineering shear strain should be
reported. 6.3.1 Ply delamination is another possible failure mode for
laminates containing a large number of 45° plies. This failure
6. Interferences
reflects instability of 45° plies loaded in compression as
contrasted to the overall buckling failure previously described.
6.1 There are no standard test methods capable of producing
Differences in strain gage readings will not be noticeable, but
a perfectly pure and uniform shear stress condition to failure
the failure can be identified by delaminated plies in contrast to
for every material, although some test methods can come
fiber breakage.
acceptably close for a specific material for a given engineering
purpose. The off-axis force of the two-rail method introduces a
6.4 Gripping—Failure through bolt holes indicates inad-
comparatively small tensile force in the panel.
equate gripping. Alternate gripping methods are discussed in
7.2.3.
6.2 Material and Specimen Preparation—Poor material fab-
rication practices, lack of control of fiber alignment, and
6.5 End Effects—This test method assumes a state of pure
damage induced by improper specimen machining are known
shear throughout the length of the specimen gage section.
causes of high material data scatter in composites.
However, the gage section ends have zero shear stress because
no traction and no constraints are applied there. A stress
6.3 Determination of Failure—Rail shear specimens, espe-
transition region exists between the ends and interior portions
cially thin ones, can buckle during force application. Buckling
of the gage section. The length of this transition region
can be detected by measuring surface strains on opposite faces
determines the error induced in the material shear data.
of the specimens with biaxial strain gages. Data measured with
the specimen in a buckled state are not representative of the
material shear properties. Modulus data must be checked to
Hussain, A. K., and Adams, D. F. “The Wyoming-Modified Two-Rail Shear
confirm that buckling has not occurred in the modulus mea-
Test Fixture for Composite Materials,” Journal of Composites Technology and
surement range. Strength measurements must be checked to Research, Vol 21, No. 4, October 1999, pp. 215-223.
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D4255/D4255M − 20
FIG. 5 Procedure B Disassembled Typical Test Fixture
7. Apparatus Adjunct ADJD4255-E-PDF. The test fixture consists of three
pairs of rails that clamp the test specimen with through bolts.
7.1 Micrometers and Calipers—A micrometer with a 4 to
The two outside pairs of rails are attached to a base plate that
8 mm [0.16 to 0.32 in.] nominal diameter ball interface or a flat
rests on the test machine. The third (middle) pair of rails are
anvil interface shall be used to measure the specimen thick-
guided through a slot in the top of the base fixture. The unit
ness. A ball interface is recommended for thickness measure-
shown is loaded in compression. The middle rails can be tensile
ments when at least one surface is irregular (for example, a
loaded, which requires fastening the base fixture to the test
course peel ply surface, which is neither smooth nor flat). A
machine. This equipment is typical but not the only configu-
micrometer or caliper with a flat anvil interface shall be used
ration that is usable. Also see 7.2.3 for rail modifications.
for measuring length, width, and other machined surface
7.2.3 Rail Modifications—The following list is not inclusive
dimensions. The use of alternative measurement devices is
but is typical of methods used by various laboratories to meet
permitted if specified (or agreed to) by the test requestor and
the requirements of specific materials. Techniques that work
reported by the testing laboratory. The accuracy of the instru-
for one material may be unacceptable for another. If these
ment(s) shall be suitable for reading to within 1 % of the
modifications are to be used as part of a specification, the rail
specimen dimensions. For typical specimen geometries, an
grip system shall be completely specified and these modifica-
instrument with an accuracy of 60.0025 mm [60.0001 in.] is
tions noted in the test report. These modifications have been
adequate for thickness measurements, while an instrument with
used to grip the following specimens:
an accuracy of 60.025 mm [60.001 in.] is adequate for
7.2.3.1 Abrasive paper or cloth bonded to the rails,
measurement of length, width, and other machined surface
7.2.3.2 Machining V grooves in the rails,
dimensions.
7.2.3.3 Center punching rails in a random pattern,
7.2 Rail Shear Fixtures
7.2.3.4 Changing the number of bolt holes from three up to
7.2.1 Two-Rail Shear—A two-rail shear fixture is shown in
eight per rail and using smaller holes,
Figs. 1 and 2. Detailed fixture drawings are available as ASTM
7.2.3.5 Soft metal shims,
Adjunct No. ADJD4255-E-PDF. The test fixture consists of
7.2.3.6 Tabbing specimens in rail areas, and
two pairs of rails which can clamp the test specimen with
7.2.3.7 Thermal spray surfaces.
through bolts. The rails are then attached to the test machine
7.3 Testing Machine—The testing machine shall conform
through pins, a load plate that also aligns the rails with each
with Practices E4 and shall satisfy these requirements:
other, and a clevis that connects directly to the test machine.
7.3.1 Testing Machine Heads—The testing machine shall
This equipment is typical but not the only configuration usable.
The two-rail shear fixture can be compression loaded. Also see have two loading heads with at least one movable head along
the testing axis.
7.2.3 for rail modifications.
7.2.2 Three-Rail Shear—A three-rail shear fixture is shown 7.3.2 Platens/Adapter—One of the testing machine heads
in Figs. 3-5. Detailed fixture drawings are available as ASTM shall be capable of being attached to the lower half of the
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D4255/D4255M − 20
two-rail shear test fixture (described in 7.2.1) or of supporting Figs. 6-9. The biaxial gage elements are to be oriented at 645°
the base of the three-rail fixture (described in 7.2.2) using an relative to the direction of the applied force.
adapter or platen interface as required. The other head shall be
NOTE 4—Three-element strain gage rosettes may be used in lieu of
capable of being attached to the upper half of the fixture or of
biaxial strain gages, but are not required. If utilized, two gage elements
loading the center rail of the fixture. If required, one of the
shall be oriented at 645° relative to the direction of the applied force for
each rosette.
interfaces may be capable of relieving minor misalignments
between heads, such as with a universal or a hemispherical ball
7.4.1 Bonded Resistance Strain Gages—Strain gage selec-
joint.
tion is a compromise based on the type of material. An active
7.3.3 Drive Mechanism—The testing machine drive mecha-
gage length of 3 mm [0.125 in.] is recommended for most
nism shall be capable of imparting to the movable head a
materials, although larger gages may be more suitable for some
controlled displacement rate with respect to the stationary
woven fabrics. The gage should not be so large that it lies
head. The displacement of the movable head shall be capable
within four specimen thicknesses of a rail. Gage calibration
of regulation as specified in 11.3.
certification shall comply with Test Methods E251. Biaxial
7.3.4 Force Indicator—The testing machine force-sensing
strain gages with a minimum normal strain range of approxi-
device shall be capable of indicating the total force applied to
mately 3 % (measuring 6 % engineering shear strain) are
the test specimen. This device shall be essentially free from
recommended. When testing woven fabric laminates, gage
response lag at the specified testing rate and shall indicate the
selection should consider the use of an active gage length that
force with an accuracy over the force range(s) of interest of
is at least as large as the characteristic repeating unit of the
within 61 % of the indicated value, as specified by Practices
weave. Some guidelines on strain gage use on composites
E4. The force range(s) of interest may be fairly low for
follow. Additional general information can be found in the
5,6
modulus evaluation or much higher for strength evaluation, or
literature.
both, as required.
7.4.1.1 Surface preparation of fiber-reinforced composites
in accordance with Guide E1237 can penetrate the matrix
NOTE 3—Obtaining precision force data over a large range of interest in
material and cause damage to the reinforcing fibers, resulting
the same test, such as when both elastic modulus and maximum force are
being determined, places extreme requirements on the load cell and its
in improper specimen failures. Reinforcing fibers should not be
calibration. For some equipment, a special calibration may be required.
exposed or damaged during the surface preparation process.
For some combinations of material and load cell, simultaneous precision
Consult the strain gage manufacturer regarding surface prepa-
measurement of both elastic modulus and maximum strength may not be
ration guidelines and recommended bonding agents for
possible, and measurement of modulus and strength may have to be
composites, pending the development of a set of standard
performed in separate tests using a different load cell range for each test.
7.4 Strain-Indicating Device—Bonded resistance strain
gages shall be used to measure strain. The number and position
Tuttle, M. E., and Brinson, H. F., “Resistance-Foil Strain Gage Technology as
Applied to Composite Materials,” Experimental Mechanics , Vol 24, No. 1, 1984,
of strain gages shall be specified by the test requestor. A
pp. 54-65, Errata noted in Vol. 26, No. 2, June 1986, pp. 153-154.
minimum of two biaxial strain gages are required, at corre-
Manual on Experimental Methods of Mechanical Testing of Composites, C. H.
sponding locations on opposite faces of the specimen at the
Jenkins, Ed., second edition, Society for Experimental Mechanics, Section II, Strain
center of the gage section, as illustrated in Fig. 1, Fig. 3, and Measurement, 1998, pp. 25-84.
FIG. 6 Procedure A, Two-Rail Shear Specimen, SI Units
´1
D4255/D4255M − 20
FIG. 7 Procedure A, Two-Rail Shear Specimen, Inch-Pound Units
FIG. 8 Procedure B, Three-Rail Shear Specimen, SI Units
practices for strain gage installation surface preparation of temperature compensation factor and the coefficient of thermal
fiber-reinforced composite materials.
expansion of the specimen material.
7.4.1.2 Select gages having higher resistances to reduce
7.4.1.3 Temperature compensation is recommended when
heating effects on low-conductivity materials. Resistances of
testing at Standard Laboratory Atmosphere. Temperature com-
350 Ω or higher are preferred. Use the minimum possible gage
pensation is required when testing in nonambient temperature
excitation voltage consistent with the desired accuracy (1 to
environments. When appropriate, use a traveler with identical
2 V is recommended) to reduce the power consumed by the
lay-up and strain gage orientations for thermal strain compen-
gage further. Heating of the specimen by the gage may affect
sation.
the performance of the material directly, or it may affect the
7.4.1.4 Correct for strain gage transverse sensitivity when
indicated strain as a result of a difference between the gage
the error caused by strain gage transverse sensitivity is greater
than 1 %. Strain measurements using strain gages mounted to
Adams, D. F., and Lewis, E. Q., “Influence of Specimen Gage Length and
composite materials are susceptible to transverse sensitivity
Loading Method on the Axial Compression Strength of a Unidirectional Composite
Material,” Experimental Mechanics, Vol 31, No. 1, 1991, pp. 14-20. errors because of the highly orthotropic behavior of composite
´1
D4255/D4255M − 20
FIG. 9 Procedure B, Three-Rail Shear Specimen, Inch-Pound Units
materials. Unidirectional composites are especially susceptible 0.13 in.] thick. Thin laminates buckle at low forces, while
to strain gage transverse sensitivity errors. thicker laminates can have shear strengths exceeding the
7.4.1.5 Biaxial strain gages are required on opposite faces of rail-clamping capacity. Thicker specimens are preferred for
the test specimen to detect buckling deformation. When the strength measurements because of their higher buckling stabil-
specimen bends as a result of buckling, strains on one face of ity. However, thicker specimens may not permit spacing of
the specimen exceed strains on the opposite face. strain gage rosettes four specimen thicknesses from the rail
edges, as specified in 7.4.1. The mandatory specimen require-
7.5 Conditioning Chamber—When conditioning materials
ments are described in 8.2.1 and 8.2.2.
in other than ambient laboratory environments, a temperature/
8.2.1 Two-Rail Shear Procedure—The recommended test
vapor-level-controlled environmental conditioning chamber is
specimen shall conform to the dimensions shown in Fig. 6 (SI
required that shall be capable of maintaining the required
units) or Fig. 7 (inch-pound units) and ASTM Adjunct
relative temperature to within 63 °C [65 °F] and the required
ADJD4255-E-PDF. Specimen flatness is essential to minimize
relative vapor level to within 63 %. Chamber conditions shall
the likelihood of buckling. Note that while the sample outer
be monitored either on an automated continuous basis or on a
dimensions are uniform, many variations of hole patterns and
manual basis at regular intervals.
tabbed edges have been used. See 8.3 and 8.4.
7.6 Environmental Test Chamber—An environmental test
8.2.2 Three-Rail Shear Procedure—The test specimen shall
chamber is required for test environments other than ambient
conform to the dimensions shown in Fig. 8 (SI units) or Fig. 9
testing laboratory conditions. This chamber shall be capable of
(inch-pound units) and ASTM Adjunct ADJD4255-E-PDF.
maintaining the gage section of the test specimen within 63 °C
Specimen flatness is essential to minimize the likelihood of
[65 °F] of the required test temperature during the mechanical
buckling.
test. In addition, the chamber may have to be capable of
8.3 Use of Tabs—Tabs are not required. The key factor in
maintaining environmental conditions such as fluid exposure or
the selection of specimen tolerances and gripping methods is
relative humidity during the test (see 11.4).
the successful introduction of force in the specimen and the
NOTE 5—If specimens are to undergo environmental conditioning to
prevention of premature failure as a result of slipping.
equilibrium, and are of such type or geometry that the weight change of
Therefore, the need to use tabs and specification of tab design
the material cannot be properly measured by weighing the specimen itself
parameters shall be determined by the end result: acceptable
(such as a tabbed mechanical specimen), then another traveler specimen
(reference sample) of the same nominal thickness and appropriate size failure mode and location. If acceptable failure modes occur
(but without tabs) shall be used to determine when equilibrium has been
with reasonable frequency, then there is no reason to change a
reached for the specimens being conditioned.
given gripping method.
8.3.1 Tab Geometry—Tab thickness may vary, but is com-
8. Sampling and Test Specimens
monly 1.5 mm [0.06 in.]. The selection of a tab configuration
8.1 Sampling—
...