ASTM D6873/D6873M-23

Standard Practice for Bearing Fatigue Response of Polymer Matrix Composite Laminates

SIGNIFICANCE AND USE
5.1 Refer to Guide D8509.
SCOPE
1.1 This practice provides instructions for modifying static bearing test methods to determine the fatigue behavior of composite materials subjected to cyclic bearing forces. The composite material forms are limited to continuous-fiber reinforced polymer matrix composites in which the laminate is both symmetric and balanced with respect to the test direction. The range of acceptable test laminates and thicknesses are described in 8.2.  
1.2 This practice supplements Test Method D5961/D5961M with provisions for testing specimens under cyclic loading. Several important test specimen parameters (for example, fastener selection, fastener installation method, and fatigue force/stress ratio) are not mandated by this practice; however, repeatable results require that these parameters be specified and reported.  
1.3 This practice is limited to test specimens subjected to constant amplitude uniaxial loading, where the machine is controlled so that the test specimen is subjected to repetitive constant amplitude force (stress) cycles. Either engineering stress or applied force may be used as a constant amplitude fatigue variable. The repetitive loadings may be tensile, compressive, or reversed, depending upon the test specimen and procedure utilized.  
1.4 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.  
1.4.1 Within the text the inch-pound units are shown in brackets.  
1.5 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.  
1.6 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: 83.140.20 - Laminated sheets
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.05 - Structural Test Methods

Relations

• Refers: ASTM E1823-24a - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Feb-2024
• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM E1823-24 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• 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 E1823-20 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-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 D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM D3878-19 - Standard Terminology for Composite Materials
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018

Overview

ASTM D6873/D6873M-23: Standard Practice for Bearing Fatigue Response of Polymer Matrix Composite Laminates is a key ASTM standard for assessing the fatigue behavior of continuous-fiber reinforced polymer matrix composites under cyclic bearing loads. This practice outlines procedures for modifying static bearing test methods (notably ASTM D5961/D5961M) to evaluate fatigue responses. The method accommodates specimens with symmetric and balanced laminates, subjecting them to cyclic, constant amplitude uniaxial loading.

This standard is critical for quality control, research and development, and establishing material performance for composite structural components, particularly in industries such as aerospace and automotive where bearing fatigue can be a critical design and safety consideration.

Key Topics

• Test Methodology: Provides a detailed procedure for adapting static bearing tests to cyclic fatigue testing conditions. Emphasizes the importance of maintaining constant amplitude loading and clearly defines criteria for specimen configuration and test preparation.
• Scope and Limitations:
  • Focuses on continuous-fiber, symmetric, and balanced polymer matrix composites.
  • Applicable to both tensile and compressive cyclic loads, determined via engineering stress or applied force.
  • Procedures use either SI or inch-pound units, which cannot be mixed within a test.
• Parameters and Reporting:
  • Stresses the need to specify and document key variables: specimen geometry, fastener type, installation methods, force/stress ratios, loading frequency, and environmental conditions.
  • Repeatable results require consistent test setup and thorough reporting, particularly regarding fastener clearance, torque, and hole preparation.
• Measurement and Evaluation:
  • Monitors changes in hole elongation and joint stiffness as indicators of fatigue progression.
  • Joint stiffness and hole elongation data are critical for determining fatigue-induced damage.
  • Recommends use of extensometers for accurate stiffness measurement.
• Environmental and Operational Factors:
  • Recognizes the influence of temperature, humidity, and debris on fatigue results.
  • Notes how fastener reuse, torque levels, and fixture wear can introduce test variability.

Applications

• Materials R&D: Enables material scientists and engineers to evaluate and compare the fatigue lives of candidate composite laminates, supporting material selection in high-performance applications.
• Design Allowables: Generates data (such as S-N curves) needed to define design limits for composite-material structures subjected to bearing loads.
• Structural Integrity: Used by industries like aerospace, wind energy, and automotive to ensure the long-term reliability and safety of composites in service environments where cyclic loading is prevalent.
• Quality Assurance: Provides standardized testing to meet quality control criteria for manufactured composite components, ensuring reproducibility and compliance with engineering specifications.
• Failure Analysis: Supports the understanding of fatigue failure modes, guiding improvements in composite joint design and assembly practices.

Related Standards

• ASTM D5961/D5961M: Test Method for Bearing Response of Polymer Matrix Composite Laminates (the principal standard supplemented by D6873/D6873M).
• ASTM D8509: Guide for Test Method Selection and Test Specimen Design for Bolted Joint Related Properties.
• ASTM D5229/D5229M: Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Composites.
• ASTM E467: Practices for Verification of Constant Amplitude Dynamic Forces in an Axial Fatigue Testing System.
• ASTM E4: Practices for Force Calibration and Verification of Testing Machines.
• ASTM E739: Guide for Statistical Analysis of Stress-Life and Strain-Life Fatigue Data.

By following ASTM D6873/D6873M-23, users achieve standardized, reliable fatigue data for composite laminates, essential for safe and efficient composite material design and usage in high-stress, cyclically loaded applications.

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: D6873/D6873M − 23
Standard Practice for
Bearing Fatigue Response of Polymer Matrix Composite
Laminates
This standard is issued under the fixed designation D6873/D6873M; 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 priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.1 This practice provides instructions for modifying static
1.6 This international standard was developed in accor-
bearing test methods to determine the fatigue behavior of
dance with internationally recognized principles on standard-
composite materials subjected to cyclic bearing forces. The
ization established in the Decision on Principles for the
composite material forms are limited to continuous-fiber rein-
Development of International Standards, Guides and Recom-
forced polymer matrix composites in which the laminate is
mendations issued by the World Trade Organization Technical
both symmetric and balanced with respect to the test direction.
Barriers to Trade (TBT) Committee.
The range of acceptable test laminates and thicknesses are
described in 8.2.
2. Referenced Documents
1.2 This practice supplements Test Method D5961/D5961M 2
2.1 ASTM Standards:
with provisions for testing specimens under cyclic loading.
D883 Terminology Relating to Plastics
Several important test specimen parameters (for example,
D3878 Terminology for Composite Materials
fastener selection, fastener installation method, and fatigue
D5229/D5229M Test Method for Moisture Absorption Prop-
force/stress ratio) are not mandated by this practice; however,
erties and Equilibrium Conditioning of Polymer Matrix
repeatable results require that these parameters be specified and
Composite Materials
reported.
D5961/D5961M Test Method for Bearing Response of Poly-
1.3 This practice is limited to test specimens subjected to mer Matrix Composite Laminates
constant amplitude uniaxial loading, where the machine is D8509 Guide for Test Method Selection and Test Specimen
controlled so that the test specimen is subjected to repetitive Design for Bolted Joint Related Properties
constant amplitude force (stress) cycles. Either engineering E4 Practices for Force Calibration and Verification of Test-
stress or applied force may be used as a constant amplitude
ing Machines
fatigue variable. The repetitive loadings may be tensile, E6 Terminology Relating to Methods of Mechanical Testing
compressive, or reversed, depending upon the test specimen
E122 Practice for Calculating Sample Size to Estimate, With
and procedure utilized. Specified Precision, the Average for a Characteristic of a
Lot or Process
1.4 The values stated in either SI units or inch-pound units
E177 Practice for Use of the Terms Precision and Bias in
are to be regarded separately as standard. The values stated in
ASTM Test Methods
each system are not necessarily exact equivalents; therefore, to
E456 Terminology Relating to Quality and Statistics
ensure conformance with the standard, each system shall be
E467 Practice for Verification of Constant Amplitude Dy-
used independently of the other, and values from the two
namic Forces in an Axial Fatigue Testing System
systems shall not be combined.
E739 Guide for Statistical Analysis of Linear or Linearized
1.4.1 Within the text the inch-pound units are shown in
Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
brackets.
E1823 Terminology Relating to Fatigue and Fracture Testing
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
responsibility of the user of this standard to establish appro-
3.1 Definitions—Terminology D3878 defines terms relating
to high-modulus fibers and their composites. Terminology
This practice 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 September 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2003. Last previous edition approved in 2019 as D6873/D6873M – 19. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D6873_D6873M-23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6873/D6873M − 23
min
D883 defines terms relating to plastics. Terminology E6 defines
σ = value of stress corresponding to the valley value of
terms relating to mechanical testing. Terminology E1823
force (stress) under constant amplitude loading
minq
defines terms relating to fatigue. Terminology E456 and
σ = value of stress corresponding to the valley value of
Practice E177 define terms relating to statistics. In the event of
force (stress) under quasi-static loading for measure-
a conflict between terms, Terminology D3878 shall have
ment of hole elongation and joint stiffness, given by
min
precedence over the other standards.
the greater of the absolute values of σ and 0.5 ×
max
σ
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 sym-
4. Summary of Practice
bology for fundamental dimensions, shown within square brackets: [M]
4.1 In accordance with Test Method D5961/D5961M, but
for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature,
under constant amplitude fatigue loading, perform a uniaxial
and [nd] for non-dimensional quantities. Use of these symbols is restricted
to analytical dimensions when used with square brackets, as the symbols
test of a bearing specimen. Refer to Guide D8509 for addi-
may have other definitions when used without the brackets.
tional test details.
3.2 Definitions of Terms Specific to This Standard—Refer to
Guide D8509.
5. Significance and Use
3.3 Symbols: 5.1 Refer to Guide D8509.
d = fastener or pin diameter
6. Interferences
D = specimen hole diameter
6.1 Refer to Guide D8509.
D = measured hole diameter prior to fatigue loading
i
D = measured hole diameter after N fatigue cycles
N
h = specimen thickness
7. Apparatus
k = calculation factor used in bearing equations to dis-
7.1 General Apparatus—General apparatus shall be in ac-
tinguish single-fastener tests from double-fastener
cordance with Test Method D5961/D5961M. The micrometer
tests
or gauge used shall be capable of determining the hole and
K = joint stiffness prior to fatigue loading
i
fastener diameters to 68 μm [60.0003 in.].
K = joint stiffness after N fatigue cycles
N
N = number of constant amplitude cycles 7.2 Testing Machine—In addition to the requirements de-
P = force carried by specimen scribed in Test Method D5961/D5961M, the testing machine
max
P = greater of the absolute values of the peak and valley
shall be in conformance with Practice E467 and shall satisfy
values of force
the following requirements:
min
P = lesser of the absolute values of the peak and valley
7.2.1 Drive Mechanism and Controller—The velocity of the
values of force
movable head shall be capable of being regulated under cyclic
δ = crosshead or extensometer translation
force (stress) conditions. The drive mechanism and controller
δ = fastener translation prior to fatigue loading
i
shall be capable of imparting a continuous sinusoidal loading
δ = fastener translation after N fatigue cycles
N
wave form to the specimen. It is important to minimize drift of
δ = crosshead or extensometer displacement at zero
Nc
the fatigue loading away from the maximum and minimum
force after quasi-static compressive loading
values. Achieving such accuracy is critical in the development
δ = crosshead or extensometer displacement at zero
Nt
of reliable fatigue life data since small errors in loading may
force after quasi-static tensile loading
result in significant errors in fatigue life. It is recommended
ΔD = hole elongation after N fatigue cycles
N
that the test controller be equipped with a Test Amplitude
ΔK = percent reduction in joint stiffness after N fatigue
N
controller, capable of monitoring the fatigue forces at least
cycles
once every three cycles.
ΔP = change in force over joint stiffness range under
7.2.2 Force Indicator—The force indicator shall be in com-
quasi-static loading
pliance with Practices E4. The fatigue rating of the force
Δδ = change in crosshead or extensometer displacement
indicator shall exceed the forces at which testing will take
over joint stiffness range under quasi-static loading
alt
place. Additionally, this practice recommends compliance with
σ = alternating bearing stress during fatigue loading
brm
Practice E467 for the development of a system dynamic
σ = maximum cyclic bearing stress magnitude, given by
max min
conversion for the verification of specimen forces to within
the greater of the absolute values of σ and σ
max
1 % of true forces.
σ = value of stress corresponding to the peak value of
force (stress) under constant amplitude loading 7.2.3 Grips—The grips shall have sufficient fatigue rating
maxq
σ = value of stress corresponding to the peak value of for forces at which testing will take place.
force (stress) under quasi-static loading for measure-
7.3 Support Fixture—If compressive forces are applied,
ment of hole elongation and joint stiffness, given by
either during fatigue loading or during quasi-static loading to
max
the greater of the absolute values of σ and 0.5 ×
determine hole elongation, a support fixture shall be used to
min
σ
stabilize the specimen. The support fixture shall be in accor-
mean
σ = mean bearing stress during fatigue loading
dance with that described in Test Method D5961/D5961M
D6873/D6873M − 23
Procedure B for single shear specimens, and with that de- 8.3 Specimen Preparation—Specimens shall be prepared in
scribed in Test Method D5961/D5961M Procedure D for accordance with Test Method D5961/D5961M. Special care
double shear specimens. should be taken to ensure that specimen edges are sufficiently
free of obvious flaws as determined by visual inspection. Such
7.4 Thermocouple and Temperature Recording Devices,
flaws may lead to premature failure due to edge delamination.
capable of reading specimen temperature to 60.5 °C
[61.0 °F].
9. Calibration
8. Sampling and Test Specimens
9.1 The accuracy of all measuring equipment shall have
certified calibrations that are current at the time of use of the
8.1 Sampling—For statistically significant data, the proce-
equipment.
dures outlined in Practice E122 should be consulted. From the
number of tests selected a statistically significant distribution
10. Conditioning
of data should be obtained for a given material, stacking
sequence, environment, and loading condition.
10.1 The recommended pre-test condition is effective mois-
8.1.1 Sample Size for S-N Curve—The recommended mini- ture equilibrium at a specific relative humidity as established
mum number of specimens in the development of S-N data is
by Test Method D5229/D5229M; however, if the test requestor
described in Table 1. A minimum of three different force does not explicitly specify a pre-test conditioning environment,
(stress) levels is recommended in development of S-N data.
no conditioning is required and the test specimens may be
For additional procedures consult Practice E739. tested as prepared.
8.2 Geometry—In addition to the requirements described in
10.2 The pre-test specimen conditioning process, to include
Test Method D5961/D5961M, the specimen geometry shall specified environmental exposure levels and resulting moisture
satisfy the following requirements:
content, shall be reported with the test data.
NOTE 2—The term moisture, as used in Test Method D5229/D5229M,
8.2.1 Stacking Sequence—The stacking sequence should be
includes not only the vapor of a liquid and its condensate, but the liquid
evaluated for free edge effects to minimize the likelihood of
itself in large quantities, as for immersion.
edge delamination initiation.
10.3 If no explicit conditioning process is performed, the
8.2.2 Specimen Configuration—The test specimen configu-
specimen conditioning process shall be reported as “uncondi-
ration shall be in accordance with Test Method D5961/
tioned” and the moisture content as “unknown.”
D5961M with the following restrictions:
8.2.2.1 Tensile Loadings Only—Procedure A (double shear),
10.4 Maintaining testing environment is critical to obtaining
Procedure B (single shear, two-piece specimen), and Procedure
consistent fatigue data since testing for long periods of time
C (single shear, one-piece specimen) configurations may be
(days or weeks) is not uncommon. For unattended tests, the test
utilized. For Procedure B, both the single fastener joint and the
environment shall be monitored so that unintended changes in
double fastener joint geometries may be utilized. If the support
the test environment result in suspension of the test. Report the
fixture is used, the length of each specimen half and doubler
testing environment for the duration of the test.
must be adjusted to accommodate loading with the fixture.
Direct measurement of hole diameter(s) is required to deter- 11. Procedure
mine hole elongation.
11.1 Parameters to Be Specified Prior to Test:
8.2.2.2 Compressive Loadings Applied—Both the Procedure
11.1.1 The specimen sampling method, specimen type and
B (single shear) and Procedure D (double shear) configurations min
geometry, minimum and maximum test forces (stresses) σ
and corresponding support fixtures may be utilized. For Pro- max
and σ for each test, force (stress) ratio for each test, test
cedure B, both the single fastener joint and the double fastener
frequency and wave form of the fatigue loading. For the
joint geometries may be utilized; the length of each specimen
purpose of development of an S-N curve, all specimens shall
half and doubler must be adjusted to accommodate loading
be tested at the same frequency and wave form unless that is a
with the support fixture. Hole elongation may be determined
factor to be studied in the test.
through either direct measurement or quasi-static loadings;
11.1.2 Fatigue cycle counts at which hole elongation (and
joint stiffness may also be determined.
joint stiffness if applicable) is to be measured, method of
8.2.3 Adhesive—For specimens with bonded doublers, the
measuring hole elongation, fastener and debris removal
adhesive should have sufficient durability as to withstand
requirements, quasi-static peak and valley forces for hole
fatigue loading for the duration of the test.
elongation and joint stiffness measurement (if applicable), hole
elongation level or percent joint stiffness reduction at which
TABLE 1 Number of Specimens Required for Each S-N Curve
fatigue loading shall cease, and run-out cycles. Historically,
Minimum Number of Test
Type of Test
bearing fatigue testing has ceased after the hole elongation
Specimens
level has reached 10 % to 25 % of the initial hole diameter, or
Preliminary and exploratory 6
Research and development 12 after joint stiffness has been reduced by 10 % to 25 % from the
testing
initial stiffness.
Design allowables data 24
11.1.3 All other parameters documented in Test Method
Reliability data 24
D5961/D5961M.
D6873/D6873M − 23
NOTE 4—Monitor the specimen for the occurrence of slippage or
11.2 General Instructions:
crushing as a result of the grips or fixture. Should either slippage or
11.2.1 Any deviations from these procedures, whether in-
crushing occur and lead to premature specimen failure, this data should
tentional or inadvertent, shall be reported.
not be reported as valid.
11.2.2 Perform general instructions for conditioning,
11.3.4 Extensometer Installation—Attach extensometer(s)
measurement, cleaning, assembly, and fastener torquing in
to the edges of the specimen in accordance with Test Method
accordance with Test Method D5961/D5961M.
D5961/D5961M.
11.3 Test Procedure:
NOTE 5—It is recommended that joint stiffness changes be monitored
11.3.1 Supported Specimen Installation—If the specimen is
using an extensometer. Crosshead deflection data may be used if it is first
to be tested with support fixture, install the test specimen into
demonstrated that percent joint stiffness reduction measurements are
the support fixture as described in Test Method D5961/
consistent with those obtained from extensometer data.
D5961M.
11.3.5 Quasi-Static Loading—If force versus deformation
11.3.2 Temperature Monitoring—Attach temperature re-
data is being used to determine hole elongation and joint
cording device in a manner not to influence the dynamic
stiffness, perform an initial quasi-static loading cycle.
response of the specimen. It is recommended to attach the
11.3.5.1 Quasi-Static Forces—The quasi-static tension and
device to a fastener, as fatigue loading will typically cause a
maxq
greater increase in fastener temperature than in laminate compression forces shall be those corresponding to σ and
minq
σ as defined in 3.3.
temperature. The device may be attached to the fastener using
adhesive, tape, or a spring clip; when utilizing a spring clip, use
11.3.5.2 Loading—From zero force, apply tensile force to
insulating material to isolate the temperature recording device
the specimen quasi-statically up to the force (stress) corre-
maxq
from the spring clip. The temperature of the specimen shall be
sponding to σ , then return to zero force. Apply compres-
monitored, and the frequency should be kept low enough to sive force to the specimen up to the force (stress) correspond-
minq
avoid significant temperature variations, unless that is a factor
ing to σ , then return to zero force. Force (stress) versus
to be studied in the test. Caution is recommended when crosshead deflection and extensometer deflection shall be
selecting loading frequencies; high cyclic rates may cause
recorded during the quasi-static force cycle. A hysteresis curve,
variations in specimen temperature and properties of the similar to those shown in Fig. 1, should be observed after
composite. For some material systems a change in 10 °C
graphically plotting the force (stress) versus deflection data.
[18 °F] has demonstrated measurable degradation of material The quasi-static loading should be conducted under force
properties.
control with a low loading rate (such that a typical hysteresis
cycle takes approximately 20 s to 30
...

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: D6873/D6873M − 19 D6873/D6873M − 23
Standard Practice for
Bearing Fatigue Response of Polymer Matrix Composite
Laminates
This standard is issued under the fixed designation D6873/D6873M; 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 practice provides instructions for modifying static bearing test methods to determine the fatigue behavior of composite
materials subjected to cyclic bearing forces. The composite material forms are limited to continuous-fiber reinforced polymer
matrix composites in which the laminate is both symmetric and balanced with respect to the test direction. The range of acceptable
test laminates and thicknesses are described in 8.2.
1.2 This practice supplements Test Method D5961/D5961M with provisions for testing specimens under cyclic loading. Several
important test specimen parameters (for example, fastener selection, fastener installation method, and fatigue force/stress ratio) are
not mandated by this practice; however, repeatable results require that these parameters be specified and reported.
1.3 This practice is limited to test specimens subjected to constant amplitude uniaxial loading, where the machine is controlled
so that the test specimen is subjected to repetitive constant amplitude force (stress) cycles. Either engineering stress or applied force
may be used as a constant amplitude fatigue variable. The repetitive loadings may be tensile, compressive, or reversed, depending
upon the test specimen and procedure utilized.
1.4 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.
1.4.1 Within the text the inch-pound units are shown in brackets.
1.5 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.
1.6 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:
This practice 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, 2019Sept. 1, 2023. Published May 2019September 2023. Originally approved in 2003. Last previous edition approved in 20172019 as
D6873/D6873M – 17.D6873/D6873M – 19. DOI: 10.1520/D6873_D6873M-19.10.1520/D6873_D6873M-23.
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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6873/D6873M − 23
D883 Terminology Relating to Plastics
D3878 Terminology for Composite Materials
D5229/D5229M Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite
Materials
D5961/D5961M Test Method for Bearing Response of Polymer Matrix Composite Laminates
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
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
E456 Terminology Relating to Quality and Statistics
E467 Practice for Verification of Constant Amplitude Dynamic Forces in an Axial Fatigue Testing System
E739 Guide for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
E1823 Terminology Relating to Fatigue and Fracture Testing
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 E1823 defines terms
relating to fatigue. 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 standards.
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:
-2
3.2.1 bearing force, P [MLT ], n—the total force carried by a bearing coupon.
3.2.2 constant amplitude loading, n—in fatigue, a loading in which all of the peak values of force (stress) are equal and all of the
valley values of force (stress) are equal.
3.2.3 fatigue loading transition, n—in the beginning of fatigue loading, the number of cycles before the force (stress) reaches the
desired peak and valley values.
3.2.4 force (stress) ratio, R [nd], n—in fatigue loading, the ratio of the minimum applied force (stress) to the maximum applied
force (stress).
-1
3.2.5 frequency, f [T ], n—in fatigue loading, the number of force (stress) cycles completed in 1 s (Hz).
3.2.6 hole elongation, ΔD [L], n—the permanent change in hole diameter in a bearing coupon caused by damage formation, equal
to the difference between the hole diameter in the direction of the bearing force after a prescribed loading and the hole diameter
prior to loading.
3.2.7 nominal value, n—a value, existing in name only, assigned to a measurable property for the purpose of convenient
designation. Tolerances may be applied to a nominal value to define an acceptable range for the property.
3.2.8 peak, n—in fatigue loading, the occurrence where the first derivative of the force (stress) versus time changes from positive
to negative sign; the point of maximum force (stress) in constant amplitude loading.
-2
3.2.9 residual strength, [MLT ], n—the value of force (stress) required to cause failure of a specimen under quasi-static loading
conditions after the specimen is subjected to fatigue loading.
3.2.10 run-out, n—in fatigue, an upper limit on the number of force cycles to be applied.
D6873/D6873M − 23
3.2.11 spectrum loading, n—in fatigue, a loading in which the peak values of force (stress) are not equal or the valley values of
force (stress) are not equal (also known as variable amplitude loading or irregular loading).
3.2.12 valley, n—in fatigue loading, the occurrence where the first derivative of the force (stress) versus time changes from
negative to positive sign; the point of minimum force (stress) in constant amplitude loading.
3.2.13 wave form, n—the shape of the peak-to-peak variation of the force (stress) as a function of time.
3.2 Definitions of Terms Specific to This Standard—Refer to Guide D8509.
D6873/D6873M − 23
3.3 Symbols:
d = fastener or pin diameter
D = specimen hole diameter
D = measured hole diameter prior to fatigue loading
i
D = measured hole diameter after N fatigue cycles
N
h = specimen thickness
k = calculation factor used in bearing equations to distinguish single-fastener tests from double-fastener tests
K = joint stiffness prior to fatigue loading
i
K = joint stiffness after N fatigue cycles
N
N = number of constant amplitude cycles
P = force carried by specimen
max
P = greater of the absolute values of the peak and valley values of force
min
P = lesser of the absolute values of the peak and valley values of force
δ = crosshead or extensometer translation
δ = fastener translation prior to fatigue loading
i
δ = fastener translation after N fatigue cycles
N
δ = crosshead or extensometer displacement at zero force after quasi-static compressive loading
Nc
δ = crosshead or extensometer displacement at zero force after quasi-static tensile loading
Nt
ΔD = hole elongation after N fatigue cycles
N
ΔK = percent reduction in joint stiffness after N fatigue cycles
N
ΔP = change in force over joint stiffness range under quasi-static loading
Δδ = change in crosshead or extensometer displacement over joint stiffness range under quasi-static loading
alt
σ = alternating bearing stress during fatigue loading
brm max min
σ = maximum cyclic bearing stress magnitude, given by the greater of the absolute values of σ and σ
max
σ = value of stress corresponding to the peak value of force (stress) under constant amplitude loading
maxq
σ = value of stress corresponding to the peak value of force (stress) under quasi-static loading for measurement of hole
max min
elongation and joint stiffness, given by the greater of the absolute values of σ and 0.5 × σ
mean
σ = mean bearing stress during fatigue loading
min
σ = value of stress corresponding to the valley value of force (stress) under constant amplitude loading
minq
σ = value of stress corresponding to the valley value of force (stress) under quasi-static loading for measurement of hole
min max
elongation and joint stiffness, given by the greater of the absolute values of σ and 0.5 × σ
4. Summary of Practice
4.1 In accordance with Test Method D5961/D5961M, but under constant amplitude fatigue loading, perform a uniaxial test of a
bearing specimen. Cycle the specimen between minimum and maximum axial forces (stresses) at a specified frequency. At selected
cyclic intervals, determine the hole elongation either through direct measurement or from a force (stress) versus deformation curve
obtained by quasi-statically loading the specimen through one tension-compression cycle. If hole elongation is determined from
a force (stress) versus deformation curve, also determine the percent joint stiffness reduction using the force versus deformation
data. Determine the number of force cycles at which failure occurs, or at which a predetermined hole elongation or percent joint
stiffness reduction is achieved, for a specimen subjected to a specificRefer to Guide D8509 force (stress) ratio and bearing stress
magnitude.for additional test details.
5. Significance and Use
5.1 This practice provides supplemental instructions for using Test Method Refer D5961/D5961Mto obtain bearing fatigue data
for material specifications, research and development, material design allowables, and quality assurance. The primary property that
results is the fatigue life of the test specimen under a specific loading and environmental condition. Replicate tests may be used
to obtain a distribution of fatigue life for specific material types, laminate stacking sequences, environments, and loading
conditions. Guidance in statistical analysis of fatigue data, such as determination of linearized stress life (S-N) curves, can be found
in Practice Guide E739D8509.
5.2 This practice can be utilized in the study of fatigue damage in a polymer matrix composite bearing specimen. The loss in
strength associated with fatigue damage may be determined by discontinuing cyclic loading to obtain the static strength using Test
Method D5961/D5961M.
NOTE 2—This practice may be used as a guide to conduct spectrum loading. This information can be useful in the understanding of fatigue behavior of
D6873/D6873M − 23
composite structures under spectrum loading conditions, but is not covered in this standard.
5.3 Factors that influence bearing fatigue response and shall therefore be reported include the following: material, methods of
material fabrication, accuracy of lay-up, laminate stacking sequence and overall thickness, specimen geometry, specimen
preparation (especially of the hole), fastener-hole clearance, fastener type, fastener geometry, fastener installation method, fastener
torque (if appropriate), countersink depth (if appropriate), specimen conditioning, environment of testing, time at temperature, type
of mating material, number of fasteners, type of support fixture, specimen alignment and gripping, test frequency, force (stress)
ratio, bearing stress magnitude, void content, and volume percent reinforcement. Properties that result include the following:
5.3.1 Hole elongation versus fatigue life curves for selected bearing stress values.
5.3.2 Percent joint stiffness reduction versus fatigue life curves for selected bearing stress values.
5.3.3 Bearing stress versus hole elongation curves at selected cyclic intervals.
5.3.4 Bearing stress versus percent joint stiffness reduction curves at selected cyclic intervals.
5.3.5 Bearing stress versus fatigue life curves for selected hole elongation values.
5.3.6 Bearing stress versus fatigue life curves for selected percent joint stiffness reduction values.
6. Interferences
6.1 Force (Stress) Ratio—Results are affected by the force (stress) ratio under which the tests are conducted. Specimens loaded
under tension-tension or compression-compression force (stress) ratios develop hole elongation damage on one side of the fastener
hole, whereas specimens loaded under tension-compression force (stress) ratios can develop damage on both sides of the fastener
hole. Experience has demonstrated that reversed (tension-compression) force ratios are critical for bearing fatigue-induced hole
elongation, with fully reversed tension-compression (R = −1) being the most critical force ratio (1-3).
6.1 Loading Frequency—Results are affected by the loading frequency at which the test is conducted. High cyclic rates may induce
heating due to frictionRefer to Guide D8509within the joint, and may cause variations in specimen temperature and properties of
the composite. Varying the cyclic frequency during the test is generally not recommended, as the response may be sensitive to the
frequency utilized and the resultant thermal history.
6.3 Fastener Torque/Pre-load—Results are affected by the installed fastener pre-load (clamping pressure). Laminates can exhibit
significant differences in hole elongation behavior and failure mode due to changes in fastener pre-load under both tensile and
compressive loading. Experience has demonstrated that low fastener torque/clamp-up is generally critical for bearing
fatigue-induced hole elongation (1, 2, 4). It should be noted that in some instances, low torque testing of single shear specimens
has proven unsuccessful due to loosening of the fastener nut/collar during fatigue loading caused by deformation of the pin/bolt.
6.4 Debris Buildup and Removal—Results are affected by the buildup of fiber-matrix debris resulting from damage associated with
hole elongation, and whether such debris is removed during the test. The presence of debris may mask the actual degree of hole
elongation, and can increase both the friction force transfer and temperature within the specimen under fatigue loading. Experience
has demonstrated that non-reversed force ratios (especially compression-compression force ratios) exhibit greater debris buildup
than reversed force ratios. Fastener and debris removal can facilitate a more accurate measurement of hole elongation (1, 2, 4).
In general, removing fastener(s) and cleaning the specimen hole(s) prior to measurement is recommended to ensure conservatism
of hole elongation data to account for the potential removal of debris over time (due to fluid exposure, for example). However,
fastener and debris removal during the test may result in an unrepresentative measurement of hole elongation growth behavior;
thus, fastener and debris removal requirements shall be specified by the test requestor. Fasteners such as blind bolts and lockbolts
are not practical to remove during fatigue testing; use of such fasteners may preclude cleaning of the specimen hole(s).
6.5 Environment—Results are affected by the environmental conditions under which the tests are conducted. Laminates tested in
various environments can exhibit significant differences in hole elongation behavior, joint stiffness response, and failure mode.
Experience has demonstrated that elevated temperature, humid environments are generally critical for bearing fatigue-induced hole
elongation (1-4). However, critical environments must be assessed independently for each material system, stacking sequence, and
torque condition tested.
D6873/D6873M − 23
6.6 Fastener-Hole Clearance—Bearing fatigue test results are affected by the clearance arising from the difference between hole
and fastener diameters. Small changes in clearance can change the number of cycles at which hole elongation initiates, and can
affect damage propagation behavior (1). For this reason, both the hole and fastener diameters must be accurately measured and
recorded. A typical aerospace tolerance on fastener-hole clearance is +75/-0 μm [+0.003 ⁄-0.000 in.] for structural fastener holes.
6.7 Fastener Type/Hole Preparation—Results are affected by the geometry and type of fastener utilized (for example, lockbolt,
blind bolt) and the fastener installation procedures. Results are also affected by the hole preparation procedures.
6.8 Method of Hole Elongation and Joint Stiffness Measurement—Results are affected by the method used to monitor hole
elongation and joint stiffness. Direct measurement of hole elongation permits an accurate examination of the extent of damage and
elongation local to the hole surface. However, the measured elongation may not be uniform through the thickness of the laminate
and may be uneven along the surface of the hole. Additionally, fasteners such as blind bolts and lockbolts are not practical to
remove during fatigue testing; use of such fasteners precludes direct measurement of hole elongation. Force versus deformation
data provide an “average” through-thickness measurement of hole elongation, as well as an indication of joint stiffness degradation
due to damage formation. However, the accuracy of such measurements for hole elongation is affected by factors such as strain
indicator accuracy, signal noise and slippage, grip slippage (for crosshead deflection data), friction within the joint specimen,
fastener deformation, bearing deformation of load plates, and so forth. In some circumstances, it may be more useful and
appropriate to monitor joint stiffness rather than hole elongation, for example when fatigue damage to both the composite
laminate(s) and fastener(s) may be expected, or when testing joints with fasteners with high clamp-up forces (for example,
lockbolts) which tend to exhibit low levels of hole elongation. It is recommended that joint stiffness changes be monitored using
an extensometer unless it is demonstrated that changes measured using crosshead deflection data are consistent with those obtained
from extensometer data. This is due to the additional sources of stiffness measurement error inherent to crosshead deflection data
(grip slippage, support fixture deformation, and friction).
6.9 Reuse or Replacement of Fastener(s)—Results are affected by whether fastener(s) are reused after hole cleaning and elongation
measurement, or whether they are replaced. Both techniques have been used in industry, with reuse being the more common
practice. Reuse requires less hardware and ensures a constant fastener diameter (and fastener-hole clearance) is maintained. The
removal of thread lubricant during repeated torquing can decrease preload for a given torque level; as lower preload produces more
hole elongation, reuse should produce conservative results. Also, fastener degradation is part of the fatigue process, and
replacement could be considered non-conservative. However, if the fastener(s) deforms during test, reuse requires that it be
replaced in the same “deformed” position as it was prior to removal. Also, replacement ensures that consistent torque and preload
levels are used throughout the test. The technique used during fastener re-installation (reuse or replacement) shall be recorded. It
is recommended to vary hole inspection intervals to aid in assessing whether fastener removal and reinstallation affects hole
elongation behavior.
6.10 Support Fixture Wear—Results can be affected by wear and degradation of the holes, fasteners, and pins of the support fixture
(when utilized) under repeated use. This is especially important for specimens tested using the Procedure B and Procedure D
configurations when compressive loadings are applied, as fixture wear can result in reduced specimen support and stabilization.
Ensure the support fixture pins and fasteners are tight tolerance in accordance with Test Method D5961/D5961M requirements.
6.11 Other—Additional sources of potential data scatter are documented in Test Method D5961/D5961M.
7. Apparatus
7.1 General Apparatus—General apparatus shall be in accordance with Test Method D5961/D5961M. The micrometer or gauge
used shall be capable of determining the hole and fastener diameters to 68 μm [60.0003 in.].
7.2 Testing Machine—In addition to the requirements described in Test Method D5961/D5961M, the testing machine shall be in
conformance with Practice E467 and shall satisfy the following requirements:
7.2.1 Drive Mechanism and Controller—The velocity of the movable head shall be capable of being regulated under cyclic force
(stress) conditions. The drive mechanism and controller shall be capable of imparting a continuous sinusoidal loading wave form
to the specimen. It is important to minimize drift of the fatigue loading away from the maximum and minimum values. Achieving
such accuracy is critical in the development of reliable fatigue life data since small errors in loading may result in significant errors
D6873/D6873M − 23
in fatigue life. It is recommended that the test controller be equipped with a Test Amplitude controller, capable of monitoring the
fatigue forces at least once every three cycles.
7.2.2 Force Indicator—The force indicator shall be in compliance with Practices E4. The fatigue rating of the force indicator shall
exceed the forces at which testing will take place. Additionally, this practice recommends compliance with Practice E467 for the
development of a system dynamic conversion for the verification of specimen forces to within 1 % of true forces.
7.2.3 Grips—The grips shall have sufficient fatigue rating for forces at which testing will take place.
7.3 Support Fixture—If compressive forces are applied, either during fatigue loading or during quasi-static loading to determine
hole elongation, a support fixture shall be used to stabilize the specimen. The support fixture shall be in accordance with that
described in Test Method D5961/D5961M Procedure B for single shear specimens, and with that described in Test Method
D5961/D5961M Procedure D for double shear specimens.
7.4 Thermocouple and Temperature Recording Devices, capable of reading specimen temperature to 60.5 °C [61.0 °F].
8. Sampling and Test Specimens
8.1 Sampling—For statistically significant data, the procedures outlined in Practice E122 should be consulted. From the number
of tests selected a statistically significant distribution of data should be obtained for a given material, stacking sequence,
environment, and loading condition.
8.1.1 Sample Size for S-N Curve—The recommended minimum number of specimens in the development of S-N data is described
in Table 1. A minimum of three different force (stress) levels is recommended in development of S-N data. For additional
procedures consult Practice E739.
8.2 Geometry—In addition to the requirements described in Test Method D5961/D5961M, the specimen geometry shall satisfy the
following requirements:
8.2.1 Stacking Sequence—The stacking sequence should be evaluated for free edge effects to minimize the likelihood of edge
delamination initiation.
8.2.2 Specimen Configuration—The test specimen configuration shall be in accordance with Test Method D5961/D5961M with
the following restrictions:
8.2.2.1 Tensile Loadings Only—Procedure A (double shear), Procedure B (single shear, two-piece specimen), and Procedure C
(single shear, one-piece specimen) configurations may be utilized. For Procedure B, both the single fastener joint and the double
fastener joint geometries may be utilized. If the support fixture is used, the length of each specimen half and doubler must be
adjusted to accommodate loading with the fixture. Direct measurement of hole diameter(s) is required to determine hole elongation.
8.2.2.2 Compressive Loadings Applied—Both the Procedure B (single shear) and Procedure D (double shear) configurations and
corresponding support fixtures may be utilized. F
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