ASTM D7615/D7615M-11(2018)
(Practice)Standard Practice for Open-Hole Fatigue Response of Polymer Matrix Composite Laminates
Standard Practice for Open-Hole Fatigue Response of Polymer Matrix Composite Laminates
SIGNIFICANCE AND USE
5.1 This practice provides supplemental instructions for using Test Methods D5766/D5766M or D6484/D6484M to obtain open-hole 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 open-hole specimen such as the occurrence of microscopic cracks, fiber fractures, or delaminations. The change in strength associated with fatigue damage may be determined by discontinuing cyclic loading to obtain the static strength using Test Methods D5766/D5766M or D6484/D6484M.
Note 2: This practice may be used as a guide to conduct variable amplitude 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 open-hole 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), specimen conditioning, environment of testing, type of support fixture, specimen alignment and gripping, test frequency, force (stress) ratio, normal stress magnitude, void content, and volume percent reinforcement. Properties that result include the following:
5.3.1 Specimen stiffness versus fatigue life curves for selected normal stress values.
5.3.2 Normal stress versus specimen st...
SCOPE
1.1 This practice provides instructions for modifying static open-hole tensile and compressive strength test methods to determine the fatigue behavior of composite materials subjected to cyclic tensile or compressive forces, or both. 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 Methods D5766/D5766M and D6484/D6484M with provisions for testing specimens under cyclic loading. Several important test specimen parameters (for example, 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 may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.
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 regulato...
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Designation: D7615/D7615M − 11 (Reapproved 2018)
Standard Practice for
Open-Hole Fatigue Response of Polymer Matrix Composite
Laminates
This standard is issued under the fixed designation D7615/D7615M; 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 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice provides instructions for modifying static
responsibility of the user of this standard to establish appro-
open-hole tensile and compressive strength test methods to
priate safety, health, and environmental practices and deter-
determine the fatigue behavior of composite materials sub-
mine the applicability of regulatory limitations prior to use.
jected to cyclic tensile or compressive forces, or both. The
1.6 This international standard was developed in accor-
composite material forms are limited to continuous-fiber rein-
dance with internationally recognized principles on standard-
forced polymer matrix composites in which the laminate is
ization established in the Decision on Principles for the
both symmetric and balanced with respect to the test direction.
Development of International Standards, Guides and Recom-
The range of acceptable test laminates and thicknesses are
mendations issued by the World Trade Organization Technical
described in 8.2.
Barriers to Trade (TBT) Committee.
1.2 This practice supplements Test Methods D5766/
D5766M and D6484/D6484M with provisions for testing 2. Referenced Documents
specimens under cyclic loading. Several important test speci-
2.1 ASTM Standards:
men parameters (for example, fatigue force(stress) ratio) are
D883Terminology Relating to Plastics
not mandated by this practice; however, repeatable results
D3878Terminology for Composite Materials
require that these parameters be specified and reported.
D5229/D5229MTestMethodforMoistureAbsorptionProp-
1.3 This practice is limited to test specimens subjected to erties and Equilibrium Conditioning of Polymer Matrix
constant amplitude uniaxial loading, where the machine is Composite Materials
controlled so that the test specimen is subjected to repetitive D5766/D5766M Test Method for Open-Hole Tensile
constant amplitude force (stress) cycles. Either engineering Strength of Polymer Matrix Composite Laminates
stress or applied force may be used as a constant amplitude D6484/D6484MTest Method for Open-Hole Compressive
fatigue variable. The repetitive loadings may be tensile, Strength of Polymer Matrix Composite Laminates
compressive, or reversed, depending upon the test specimen E4Practices for Force Verification of Testing Machines
and procedure utilized. E6Terminology Relating to Methods of Mechanical Testing
E83Practice for Verification and Classification of Exten-
1.4 The values stated in either SI units or inch-pound units
someter Systems
are to be regarded separately as standard. The values stated in
E122PracticeforCalculatingSampleSizetoEstimate,With
each system may not be exact equivalents; therefore, each
Specified Precision, the Average for a Characteristic of a
system shall be used independently of the other. Combining
Lot or Process
values from the two systems may result in non-conformance
E177Practice for Use of the Terms Precision and Bias in
with the standard.
ASTM Test Methods
1.4.1 Within the text the inch-pound units are shown in
E456Terminology Relating to Quality and Statistics
brackets.
E467Practice for Verification of Constant Amplitude Dy-
namic Forces in an Axial Fatigue Testing System
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 April 1, 2018. Published May 2018. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2011. Last previous edition approved in 2011 as D7615/D7615M–11. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D7615_D7615M-11R18. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7615/D7615M − 11 (2018)
E739PracticeforStatisticalAnalysisofLinearorLinearized 3.2.9 run-out, n—in fatigue,anupperlimitonthenumberof
Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data force cycles to be applied.
E1309 Guide for Identification of Fiber-Reinforced
3.2.10 spectrum loading, n—in fatigue, a loading in which
Polymer-Matrix Composite Materials in Databases (With-
the peak values of force (stress) are not equal or the valley
drawn 2015)
values of force (stress) are not equal (also known as variable
E1434Guide for Recording Mechanical Test Data of Fiber-
amplitude loading or irregular loading).
ReinforcedCompositeMaterialsinDatabases(Withdrawn
3.2.11 valley, n—in fatigue loading, the occurrence where
2015)
the first derivative of the force (stress) versus time changes
E1823TerminologyRelatingtoFatigueandFractureTesting
from negative to positive sign; the point of minimum force
(stress) in constant amplitude loading.
3. Terminology
3.2.12 wave form, n—the shape of the peak-to-peak varia-
3.1 Definitions—Terminology D3878 defines terms relating
tion of the force (stress) as a function of time.
to high-modulus fibers and their composites. Terminology
3.3 Symbols:
D883definestermsrelatingtoplastics.TerminologyE6defines
terms relating to mechanical testing. Terminology E1823
A = Cross-sectional area of a specimen
defines terms relating to fatigue. Terminology E456 and
K = specimen chord stiffness, P/δ
Practice E177 define terms relating to statistics. In the event of
K = specimen chord stiffness prior to fatigue cycles
i
a conflict between terms, Terminology D3878 shall have
K = specimen chord stiffness after N fatigue cycles
N
precedence over the other standards.
D = specimen hole diameter
h = specimen thickness
NOTE 1—If the term represents a physical quantity, its analytical
N = number of constant amplitude cycles
dimensionsarestatedimmediatelyfollowingtheterm(orlettersymbol)in
∆ = change in chord stiffness after N fatigue cycles
fundamental dimension form, using the following ASTM standard sym-
N
bology for fundamental dimensions, shown within square brackets: [M] P = force carried by specimen
maxq
for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature,
P = peak force under quasi-static loading for measure-
and[nd]fornon-dimensionalquantities.Useofthesesymbolsisrestricted
ment of stiffness
to analytical dimensions when used with square brackets, as the symbols minq
P = valley force under quasi-static loading for measure-
may have other definitions when used without the brackets.
ment of stiffness
3.2 Definitions of Terms Specific to This Standard:
w = specimen width
3.2.1 constant amplitude loading, n—in fatigue,aloadingin
δ = crosshead or extensometer translation
alt
which all of the peak values of force (stress) are equal and all
σ = alternating open hole stress during fatigue loading
ohm
of the valley values of force (stress) are equal.
σ = maximum cyclic open hole stress magnitude, given
max min
bythegreateroftheabsolutevaluesofσ andσ
3.2.2 fatigue loading transition, n—in the beginning of
max
σ = value of stress corresponding to the peak value of
fatigue loading, the number of cycles before the force (stress)
force (stress) under constant amplitude loading
reaches the desired peak and valley values.
maxq
σ = value of stress corresponding to the peak value of
3.2.3 force, P [MLT ], n—the total force carried by a test
force(stress)underquasi-staticloadingformeasure-
specimen.
ment of stiffness, given by the greater of the
max min
3.2.4 force (stress) ratio, R [nd], n—in fatigue loading, the
absolute values of σ and 0.5 × σ
mean
ratio of the minimum applied force (stress) to the maximum
σ = mean normal stress during fatigue loading
min
applied force (stress). σ = value of stress corresponding to the valley value of
force (stress) under constant amplitude loading
3.2.5 frequency, f [T ], n—in fatigue loading,thenumberof
minq
σ = value of stress corresponding to the valley value of
force (stress) cycles completed in 1 s (Hz).
force(stress)underquasi-staticloadingformeasure-
3.2.6 nominal value, n—a value, existing in name only,
ment of stiffness, given by the greater of the
assigned to a measurable property for the purpose of conve- min max
absolute values of σ and 0.5 × σ
nient designation. Tolerances may be applied to a nominal
value to define an acceptable range for the property.
4. Summary of Practice
3.2.7 peak, n—in fatigue loading, the occurrence where the
4.1 In accordance with Test Methods D5766/D5766M or
first derivative of the force (stress) versus time changes from
D6484/D6484M,butunderconstantamplitudefatigueloading,
positive to negative sign; the point of maximum force (stress)
perform a uniaxial test of an open-hole specimen. Cycle the
in constant amplitude loading.
specimen between minimum and maximum axial forces
-1 -2
3.2.8 residual strength, [ML T ], n—the value of force
(stresses) at a specified frequency.At selected cyclic intervals,
(stress) required to cause failure of a specimen under quasi-
determine the specimen stiffness from a force versus deforma-
static loading conditions after the specimen is subjected to
tion curve obtained by quasi-statically loading the specimen
fatigue loading.
through one tension, compression or tension-compression
cycle as applicable. Determine the number of force cycles at
which failure occurs (or at which a predetermined change in
specimen stiffness is observed), for a specimen subjected to a
The last approved version of this historical standard is referenced on
www.astm.org. specific force (stress) ratio and stress magnitude.
D7615/D7615M − 11 (2018)
5. Significance and Use avoid significant temperature variations, unless that is a factor
to be studied during the test. For example, loading frequencies
5.1 This practice provides supplemental instructions for
up to 5Hz have been used successfully. Varying the cyclic
using Test Methods D5766/D5766M or D6484/D6484M to
frequency during the test is generally not recommended, as the
obtain open-hole fatigue data for material specifications, re-
response may be sensitive to the frequency utilized and the
search and development, material design allowables, and
resultant thermal history.
quality assurance. The primary property that results is the
fatigue life of the test specimen under a specific loading and 6.3 Environment—Resultsareaffectedbytheenvironmental
environmental condition. Replicate tests may be used to obtain conditions under which the tests are conducted. Laminates
a distribution of fatigue life for specific material types, lami- tested in various environments can exhibit significant differ-
natestackingsequences,environments,andloadingconditions. ences in both strength and failure mode. Experience has
Guidance in statistical analysis of fatigue data, such as deter- demonstrated that elevated temperature, humid environments
mination of linearized stress life (S-N) curves, can be found in aregenerallycriticalforopenholefatigue-induceddamage (1).
Practice E739. However, critical environments must be assessed indepen-
dentlyforeachmaterialsystem,stackingsequenceandloading
5.2 This practice can be utilized in the study of fatigue
condition tested.
damage in a polymer matrix composite open-hole specimen
suchastheoccurrenceofmicroscopiccracks,fiberfractures,or 6.4 Method of Stiffness Measurement—Results are affected
delaminations. The change in strength associated with fatigue bythemethodusedtomonitorspecimenstiffness.Forceversus
damage may be determined by discontinuing cyclic loading to deformation data provide an indication of specimen stiffness
obtain the static strength using Test Methods D5766/D5766M change due to damage formation. However, the accuracy of
or D6484/D6484M. such measurements is affected by factors such as strain
NOTE 2—This practice may be used as a guide to conduct variable
indicator accuracy, signal noise, gage length and extensometer
amplitude loading.This information can be useful in the understanding of
slippage, extensometer placement/location, grip slippage, and
fatigue behavior of composite structures under spectrum loading
load frame stiffness (for crosshead deflection data), and so
conditions, but is not covered in this standard.
forth.
5.3 Factors that influence open-hole fatigue response and
6.5 Hole Preparation—Results are affected by the hole
shall therefore be reported include the following: material,
preparation procedures.
methods of material fabrication, accuracy of lay-up, laminate
stacking sequence and overall thickness, specimen geometry,
6.6 Other—Additional sources of potential data scatter are
specimen preparation (especially of the hole), specimen documented in Test Methods D5766/D5766M and D6484/
conditioning, environment of testing, type of support fixture,
D6484M.
specimen alignment and gripping, test frequency, force (stress)
7. Apparatus
ratio, normal stress magnitude, void content, and volume
percent reinforcement. Properties that result include the fol-
7.1 General Apparatus—General apparatus shall be in ac-
lowing:
cordance with Test Method D5766/D5766M Configuration A
5.3.1 Specimen stiffness versus fatigue life curves for se-
fortension-tensionfatigueloading,andinaccordancewithTest
lected normal stress values.
Method D6484/D6484M ProcedureAfor tension-compression
5.3.2 Normal stress versus specimen stiffness curves at
andcompression-compressionfatigueloading.Themicrometer
selected cyclic intervals.
or gage used shall be capable of determining the hole diameter
5.3.3 Normal stress versus fatigue life curves for selected
to 6 0.025 mm [6 0.001 in.].
stress ratio values.
7.2 Testing Machine—In addition to the requirements de-
scribed in Test Methods D5766/D5766M or D6484/D6484M,
6. Interferences
thetestingmachineshallbeinconformancewithPracticeE467
6.1 Force (Stress) Ratio—Results are affected by the force
and shall satisfy the following requirements:
(stress) ratio under which the tests are conducted. Experience
7.2.1 Drive Mechanism and Controller—Thevelocityofthe
has demonstrated that reversed (tension-compression) force
movable head shall be capable of being regulated under cyclic
ratios are critical for fatigue-induced damage in open hole
force (stress)
...
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: D7615/D7615M − 11 D7615/D7615M − 11 (Reapproved 2018)
Standard Practice for
Open-Hole Fatigue Response of Polymer Matrix Composite
Laminates
This standard is issued under the fixed designation D7615/D7615M; 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 open-hole tensile and compressive strength test methods to
determine the fatigue behavior of composite materials subjected to cyclic tensile or compressive forces, or both. 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 Methods D5766/D5766M and D6484/D6484M with provisions for testing specimens under
cyclic loading. Several important test specimen parameters (for example, 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 may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
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 safety, health, and healthenvironmental 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:
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
D5766/D5766M Test Method for Open-Hole Tensile Strength of Polymer Matrix Composite Laminates
D6484/D6484M Test Method for Open-Hole Compressive Strength of Polymer Matrix Composite Laminates
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E83 Practice for Verification and Classification of Extensometer Systems
E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or
Process
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 Jan. 1, 2011April 1, 2018. Published February 2011May 2018.DOI: 10.1520/D7615_D7615M-11. Originally approved in 2011. Last previous
edition approved in 2011 as D7615/D7615M–11. DOI: 10.1520/D7615_D7615M-11R18.
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
D7615/D7615M − 11 (2018)
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 (Withdrawn 2015)
E1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in Databases (Withdrawn 2015)
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:
3.2.1 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.
3.2.2 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.
3.2.3 force, P [MLT ], n—the total force carried by a test specimen.
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).
3.2.5 frequency, f [T ], n—in fatigue loading, the number of force (stress) cycles completed in 1 s (Hz).
3.2.6 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.
3.2.7 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
3.2.8 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.
3.2.9 run-out, n—in fatigue, an upper limit on the number of force cycles to be applied.
3.2.10 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).
3.2.11 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.
3.2.12 wave form, n—the shape of the peak-to-peak variation of the force (stress) as a function of time.
3.3 Symbols:
A = Cross-sectional area of a specimen
K = specimen chord stiffness, P/δ
K = specimen chord stiffness prior to fatigue cycles
i
K = specimen chord stiffness after N fatigue cycles
N
D = specimen hole diameter
h = specimen thickness
N = number of constant amplitude cycles
Δ = change in chord stiffness after N fatigue cycles
N
P = force carried by specimen
maxq
P = peak force under quasi-static loading for measurement of stiffness
minq
P = valley force under quasi-static loading for measurement of stiffness
w = specimen width
δ = crosshead or extensometer translation
The last approved version of this historical standard is referenced on www.astm.org.
D7615/D7615M − 11 (2018)
alt
σ = alternating open hole stress during fatigue loading
ohm max min
σ = maximum cyclic open hole 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 stiffness,
max min
given by the greater of the absolute values of σ and 0.5 × σ
mean
σ = mean normal 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 stiffness,
min max
given by the greater of the absolute values of σ and 0.5 × σ
4. Summary of Practice
4.1 In accordance with Test Methods D5766/D5766M or D6484/D6484M, but under constant amplitude fatigue loading,
perform a uniaxial test of an open-hole specimen. Cycle the specimen between minimum and maximum axial forces (stresses) at
a specified frequency. At selected cyclic intervals, determine the specimen stiffness from a force versus deformation curve obtained
by quasi-statically loading the specimen through one tension, compression or tension-compression cycle as applicable. Determine
the number of force cycles at which failure occurs (or at which a predetermined change in specimen stiffness is observed), for a
specimen subjected to a specific force (stress) ratio and stress magnitude.
5. Significance and Use
5.1 This practice provides supplemental instructions for using Test Methods D5766/D5766M or D6484/D6484M to obtain
open-hole 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 open-hole specimen such as the
occurrence of microscopic cracks, fiber fractures, or delaminations. The change in strength associated with fatigue damage may
be determined by discontinuing cyclic loading to obtain the static strength using Test Methods D5766/D5766M or D6484/
D6484M.
NOTE 2—This practice may be used as a guide to conduct variable amplitude 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 open-hole 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), specimen conditioning, environment of testing, type of support fixture, specimen alignment
and gripping, test frequency, force (stress) ratio, normal stress magnitude, void content, and volume percent reinforcement.
Properties that result include the following:
5.3.1 Specimen stiffness versus fatigue life curves for selected normal stress values.
5.3.2 Normal stress versus specimen stiffness curves at selected cyclic intervals.
5.3.3 Normal stress versus fatigue life curves for selected stress ratio values.
6. Interferences
6.1 Force (Stress) Ratio—Results are affected by the force (stress) ratio under which the tests are conducted. Experience has
demonstrated that reversed (tension-compression) force ratios are critical for fatigue-induced damage in open hole specimens, with
fully reversed tension-compression (R = –1) being the most critical force ratio (1) .
6.2 Loading Frequency—Results are affected by the loading frequency at which the test is conducted. High cyclic rates may
induce heating within the specimen that may cause variations in specimen temperature and properties of the composite as discussed
in 11.3.2. The temperature of the specimen should be monitored, and the frequency should be kept low enough to avoid significant
temperature variations, unless that is a factor to be studied during the test. For example, loading frequencies up to 5Hz have been
used successfully. 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 Environment—Results are affected by the environmental conditions under which the tests are conducted. Laminates tested
in various environments can exhibit significant differences in both strength and failure mode. Experience has demonstrated that
elevated temperature, humid environments are generally critical for open hole fatigue-induced damage (1). However, critical
environments must be assessed independently for each material system, stacking sequence and loading condition tested.
The boldface numbers in parentheses refer to a list of references at the end of this standard.
D7615/D7615M − 11 (2018)
6.4 Method of Stiffness Measurement—Results are affected by the method used to monitor specimen stiffness. Force versus
deformation data provide an indication of specimen stiffness change due to damage formation. However, the accuracy of such
measurements is affected by fact
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