ASTM D6873/D6873M-08(2014)
(Practice)Standard Practice for Bearing Fatigue Response of Polymer Matrix Composite Laminates
Standard Practice for Bearing Fatigue Response of Polymer Matrix Composite Laminates
SIGNIFICANCE AND USE
5.1 This practice provides supplemental instructions for using Test Method D5961/D5961M to 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 E739.
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 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 fati...
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. Within the text the inch-pound units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D6873/D6873M − 08 (Reapproved 2014)
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 and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 This practice provides instructions for modifying static
bearing test methods to determine the fatigue behavior of
2. Referenced Documents
composite materials subjected to cyclic bearing forces. The
2.1 ASTM Standards:
composite material forms are limited to continuous-fiber rein-
D883Terminology Relating to Plastics
forced polymer matrix composites in which the laminate is
D3878Terminology for Composite Materials
both symmetric and balanced with respect to the test direction.
D5229/D5229MTestMethodforMoistureAbsorptionProp-
The range of acceptable test laminates and thicknesses are
erties and Equilibrium Conditioning of Polymer Matrix
described in 8.2.
Composite Materials
1.2 ThispracticesupplementsTestMethodD5961/D5961M
D5961/D5961MTestMethodforBearingResponseofPoly-
with provisions for testing specimens under cyclic loading.
mer Matrix Composite Laminates
Several important test specimen parameters (for example,
E4Practices for Force Verification of Testing Machines
fastener selection, fastener installation method, and fatigue
E6Terminology Relating to Methods of MechanicalTesting
force/stress ratio) are not mandated by this practice; however,
E122PracticeforCalculatingSampleSizetoEstimate,With
repeatableresultsrequirethattheseparametersbespecifiedand
Specified Precision, the Average for a Characteristic of a
reported.
Lot or Process
1.3 This practice is limited to test specimens subjected to
E177Practice for Use of the Terms Precision and Bias in
constant amplitude uniaxial loading, where the machine is
ASTM Test Methods
controlled so that the test specimen is subjected to repetitive
E456Terminology Relating to Quality and Statistics
constant amplitude force (stress) cycles. Either engineering
E467Practice for Verification of Constant Amplitude Dy-
stress or applied force may be used as a constant amplitude
namic Forces in an Axial Fatigue Testing System
fatigue variable. The repetitive loadings may be tensile,
E739PracticeforStatisticalAnalysisofLinearorLinearized
compressive, or reversed, depending upon the test specimen
Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
and procedure utilized.
E1309 Guide for Identification of Fiber-Reinforced
Polymer-Matrix Composite Materials in Databases
1.4 The values stated in either SI units or inch-pound units
E1434Guide for Recording Mechanical Test Data of Fiber-
are to be regarded separately as standard. Within the text the
Reinforced Composite Materials in Databases
inch-pound units are shown in brackets. The values stated in
E1823TerminologyRelatingtoFatigueandFractureTesting
each system are not exact equivalents; therefore, each system
must be used independently of the other. Combining values
3. Terminology
from the two systems may result in nonconformance with the
standard.
3.1 Definitions—Terminology D3878 defines terms relating
to high-modulus fibers and their composites. Terminology
1.5 This standard does not purport to address all of the
D883definestermsrelatingtoplastics.TerminologyE6defines
safety concerns, if any, associated with its use. It is the
terms relating to mechanical testing. Terminology E1823
responsibility of the user of this standard to establish appro-
defines terms relating to fatigue. Terminology E456 and
Practice E177 define terms relating to statistics. In the event of
This practice is under the jurisdiction ofASTM Committee D30 on Composite
MaterialsandisthedirectresponsibilityofSubcommitteeD30.05onStructuralTest
Methods. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Aug. 1, 2014. Published September 2014. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2003. Last previous edition approved in 2008 as D6873/D6873M–08. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D6873_D6873M-08R14. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6873/D6873M − 08 (2014)
a conflict between terms, Terminology D3878 shall have
d = fastener or pin diameter
precedence over the other standards.
D = specimen hole diameter
h = specimen thickness
NOTE 1—If the term represents a physical quantity, its analytical
k = calculation factor used in bearing equations to dis-
dimensionsarestatedimmediatelyfollowingtheterm(orlettersymbol)in
tinguish single-fastener tests from double-fastener
fundamental dimension form, using the following ASTM standard sym-
tests
bology for fundamental dimensions, shown within square brackets: [M]
for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature, L = extensometer gage length
g
and[nd]fornon-dimensionalquantities.Useofthesesymbolsisrestricted
N = number of constant amplitude cycles
to analytical dimensions when used with square brackets, as the symbols
P = force carried by specimen
may have other definitions when used without the brackets.
δ = crosshead translation
3.2 Definitions of Terms Specific to This Standard:
∆ = hole elongation
alt
-2
σ = alternating bearing stress during fatigue loading
3.2.1 bearing force, P [MLT ], n—thetotalforcecarriedby
brm
σ = maximum cyclic bearing stress magnitude, given by
a bearing coupon.
max min
the greater of the absolute values of σ and σ
3.2.2 constant amplitude loading, n—in fatigue,aloadingin max
σ = value of stress corresponding to the peak value of
which all of the peak values of force (stress) are equal and all
force (stress) under constant amplitude loading
maxq
of the valley values of force (stress) are equal.
σ = value of stress corresponding to the peak value of
force(stress)underquasi-staticloadingformeasure-
3.2.3 fatigue loading transition, n—in the beginning of
ment of hole elongation, given by the greater of the
fatigue loading, the number of cycles before the force (stress)
max min
absolute values of σ and 0.5 × σ
reaches the desired peak and valley values.
mean
σ = mean bearing stress during fatigue loading
3.2.4 force (stress) ratio, R [nd], n—in fatigue loading, the
min
σ = value of stress corresponding to the valley value of
ratio of the minimum applied force (stress) to the maximum
force (stress) under constant amplitude loading
applied force (stress). minq
σ = value of stress corresponding to the valley value of
-1
3.2.5 frequency,f[T ],n—infatigueloading,thenumberof force(stress)underquasi-staticloadingformeasure-
ment of hole elongation, given by the greater of the
force (stress) cycles completed in 1 s (Hz).
min max
absolute values of σ and 0.5 × σ
3.2.6 hole elongation, ∆ [L], n—the permanent change in
hole diameter in a bearing coupon caused by damage
4. Summary of Practice
formation,equaltothedifferencebetweentheholediameterin
4.1 In accordance with Test Method D5961/D5961M, but
thedirectionofthebearingforceafteraprescribedloadingand
under constant amplitude fatigue loading, perform a uniaxial
the hole diameter prior to loading.
test of a bearing specimen. Cycle the specimen between
3.2.7 nominal value, n—a value, existing in name only,
minimum and maximum axial forces (stresses) at a specified
assigned to a measurable property for the purpose of conve-
frequency. At selected cyclic intervals, determine the hole
nient designation. Tolerances may be applied to a nominal
elongation either through direct measurement or from a force
value to define an acceptable range for the property.
(stress) versus deformation curve obtained by quasi-statically
loading the specimen through one tension-compression cycle.
3.2.8 peak, n—in fatigue loading, the occurrence where the
first derivative of the force (stress) versus time changes from Determine the number of force cycles at which failure occurs,
or at which a predetermined hole elongation is achieved, for a
positive to negative sign; the point of maximum force (stress)
specimensubjectedtoaspecificforce(stress)ratioandbearing
in constant amplitude loading.
stress magnitude.
-1 -2
3.2.9 residual strength, [ML T ], n—the value of force
(stress) required to cause failure of a specimen under quasi-
5. Significance and Use
static loading conditions after the specimen is subjected to
5.1 This practice provides supplemental instructions for
fatigue loading.
using Test Method D5961/D5961M to obtain bearing fatigue
3.2.10 run-out, n—in fatigue, an upper limit on the number
data for material specifications, research and development,
of force cycles to be applied.
materialdesignallowables,andqualityassurance.Theprimary
property that results is the fatigue life of the test specimen
3.2.11 spectrum loading, n—in fatigue, a loading in which
under a specific loading and environmental condition. Repli-
the peak values of force (stress) are not equal or the valley
catetestsmaybeusedtoobtainadistributionoffatiguelifefor
values of force (stress) are not equal (also known as variable
specific material types, laminate stacking sequences,
amplitude loading or irregular loading).
environments, and loading conditions. Guidance in statistical
3.2.12 valley, n—in fatigue loading, the occurrence where
analysis of fatigue data, such as determination of linearized
the first derivative of the force (stress) versus time changes
stress life (S-N) curves, can be found in Practice E739.
from negative to positive sign; the point of minimum force
5.2 This practice can be utilized in the study of fatigue
(stress) in constant amplitude loading.
damage in a polymer matrix composite bearing specimen. The
3.2.13 wave form, n—the shape of the peak-to-peak varia-
loss in strength associated with fatigue damage may be
tion of the force (stress) as a function of time.
determined by discontinuing cyclic loading to obtain the static
3.3 Symbols: strength using Test Method D5961/D5961M.
D6873/D6873M − 08 (2014)
NOTE 2—This practice may be used as a guide to conduct spectrum
6.4 Debris Buildup—Results are affected by the buildup of
loading. This information can be useful in the understanding of fatigue
fiber-matrix debris resulting from damage associated with hole
behaviorofcompositestructuresunderspectrumloadingconditions,butis
elongation.Thepresenceofdebrismaymasktheactualdegree
not covered in this standard.
of hole elongation, and can increase both the friction force
5.3 Factorsthatinfluencebearingfatigueresponseandshall
transfer and temperature within the specimen under fatigue
therefore be reported include the following: material, methods
loading. Experience has demonstrated that non-reversed force
of material fabrication, accuracy of lay-up, laminate stacking
ratios (especially compression-compression force ratios) ex-
sequence and overall thickness, specimen geometry, specimen
hibit greater debris buildup than reversed force ratios, and that
preparation (especially of the hole), fastener-hole clearance,
hole elongation can be most accurately determined if debris is
fastener type, fastener geometry, fastener installation method,
removed prior to hole elongation measurement (1, 2, 4).
fastener torque (if appropriate), countersink depth (if
Therefore,cleaningthespecimenhole(s)priortomeasurement
appropriate), specimen conditioning, environment of testing,
is recommended to ensure conservatism of hole elongation
time at temperature, type of mating material, number of
data.
fasteners, type of support fixture, specimen alignment and
6.5 Environment—Resultsareaffectedbytheenvironmental
gripping, test frequency, force (stress) ratio, bearing stress
conditions under which the tests are conducted. Laminates
magnitude, void content, and volume percent reinforcement.
tested in various environments can exhibit significant differ-
Properties that result include the following:
ences in both hole elongation behavior and failure mode.
5.3.1 Hole elongation versus fatigue life curves for selected
Experience has demonstrated that elevated temperature, humid
bearing stress values.
environments are generally critical for bearing fatigue-induced
5.3.2 Bearing stress versus hole elongation curves at se-
hole elongation (1-4). However, critical environments must be
lected cyclic intervals.
assessed independently for each material system, stacking
5.3.3 Bearing stress versus fatigue life curves for selected
sequence, and torque condition tested.
hole elongation values.
6.6 Fastener-Hole Clearance—Bearing fatigue test results
6. Interferences
are affected by the clearance arising from the difference
between hole and fastener diameters. Small changes in clear-
6.1 Force (Stress) Ratio—Results are affected by the force
ancecanchangethenumberofcyclesatwhichholeelongation
(stress) ratio under which the tests are conducted. Specimens
initiates, and can affect damage propagation behavior (1). For
loaded under tension-tension or compression-compression
this reason, both the hole and fastener diameters must be
force (stress) ratios develop hole elongation damage on one
accurately measured and recorded. A typical aerospace toler-
side of the fastener hole, whereas specimens loaded under
ance on fastener-hole clearance is +75/-0 µm [+0.003/-0.000
tension-compression force (stress) ratios can develop damage
in.] for structural fastener holes.
onbothsidesofthefastenerhole.Experiencehasdemonstrated
that reversed (tension-compression) force ratios are critical for
6.7 Fastener Type/Hole Preparation—Results are affected
bearing fatigue-induced hole elongation, with fully reversed
by the geometry and type of fastener utilized (for example,
tension-compression (R = −1) being the most critical force
lockbolt, blind bolt) and the fastener installation procedures.
ratio (1-3).
Results are also affected by the hole preparation procedures.
6.2 Loading Frequency—Resultsareaffectedbytheloading
6.8 Method of Hole Elongation Measurement—Results are
frequencyatwhichthetestisconducted.Highcyclicratesmay
affected by the method used to monitor hole elongation. Direct
induce heating due to friction within the joint, and may cause
measurement permits an accurate examination of the extent of
variations in specimen temperature and properties of the
damage and elongation local to the hole surface. However, th
...
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 − 08 D6873/D6873M − 08 (Reapproved 2014)
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. Within the text the
inch-pound units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must
be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
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
E4 Practices for Force 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 Practice for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
E1309 Guide for Identification of Fiber-Reinforced Polymer-Matrix Composite Materials in Databases
E1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in Databases
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 March 1, 2008Aug. 1, 2014. Published April 2008September 2014. Originally approved in 2003. Last previous edition approved in 20032008
as D6873D6873/D6873M – 08.-03. DOI: 10.1520/D6873_D6873M-08.10.1520/D6873_D6873M-08R14.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. 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 − 08 (2014)
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, Δ [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.
-1 -2
3.2.9 residual strength, [ML T ], 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.
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.
3.3 Symbols:
d = fastener or pin diameter
D = specimen hole diameter
h = specimen thickness
k = calculation factor used in bearing equations to distinguish single-fastener tests from double-fastener tests
L = extensometer gage length
g
N = number of constant amplitude cycles
P = force carried by specimen
δ = crosshead translation
Δ = hole elongation
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, 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, given by the greater of the absolute values of σ and 0.5 × σ
D6873/D6873M − 08 (2014)
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. Determine the
number of force cycles at which failure occurs, or at which a predetermined hole elongation is achieved, for a specimen subjected
to a specific force (stress) ratio and bearing stress magnitude.
5. Significance and Use
5.1 This practice provides supplemental instructions for using Test Method D5961/D5961M to 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 E739.
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 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 Bearing stress versus hole elongation curves at selected cyclic intervals.
5.3.3 Bearing stress versus fatigue life curves for selected hole elongation 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).
6.2 Loading Frequency—Results are affected by the loading frequency at which the test is conducted. High cyclic rates may
induce heating due to friction within 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—Results are affected by the buildup of fiber-matrix debris resulting from damage associated with hole
elongation. 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, and that hole elongation can be
most accurately determined if debris is removed prior to hole elongation measurement (1, 2, 4). Therefore, cleaning the specimen
hole(s) prior to measurement is recommended to ensure conservatism of hole elongation data.
6.5 Environment—Results are affected by the environmental conditions under which the tests are conducted. Laminates tested
in vario
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