ASTM D6115-97(2019)
(Test Method)Standard Test Method for Mode I Fatigue Delamination Growth Onset of Unidirectional Fiber-Reinforced Polymer Matrix Composites
Standard Test Method for Mode I Fatigue Delamination Growth Onset of Unidirectional Fiber-Reinforced Polymer Matrix Composites
SIGNIFICANCE AND USE
5.1 Susceptibility to delamination is one of the major weaknesses of many advanced laminated composite structures. Knowledge of a laminated composite material's resistance to interlaminar fracture under fatigue loads is useful for product development and material selection. Furthermore, a measurement of the relationship of the mode I cyclic strain energy release rate and the number of cycles to delamination growth onset, G–N, that is independent of specimen geometry or method of load introduction, is useful for establishing design allowables used in damage tolerance analyses of composite structures made from these materials.
5.2 This test method can serve the following purposes:
5.2.1 To establish quantitatively the effects of fiber surface treatment, local variations in fiber volume fraction, and processing and environmental variables on G–N of a particular composite material.
5.2.2 To compare quantitatively the relative values of G–N for composite materials with different constituents.
5.2.3 To develop criteria for avoiding the onset of delamination growth under fatigue loading for composite damage tolerance and durability analyses.
SCOPE
1.1 This test method determines the number of cycles (N) for the onset of delamination growth based on the opening mode I cyclic strain energy release rate (G), using the Double Cantilever Beam (DCB) specimen shown in Fig. 1. This test method applies to constant amplitude, tension-tension fatigue loading of continuous fiber-reinforced composite materials. When this test method is applied to multiple specimens at various G-levels, the results may be shown as a G–N curve, as illustrated in Fig. 2.
FIG. 1 DCB Specimen with Piano Hinges
FIG. 2 G–N Curve
1.2 This test method is limited to use with composites consisting of unidirectional carbon fiber tape laminates with single-phase polymer matrices. This limited scope reflects the experience gained in round robin testing. This test method may prove useful for other types and classes of composite materials, however, certain interferences have been noted (see Section 6.5 of Test Method D5528).
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3.1 Exception—The values provided in parentheses are for information only.
1.4 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.
1.5 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
Relations
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: D6115 − 97 (Reapproved 2019)
Standard Test Method for
Mode I Fatigue Delamination Growth Onset of Unidirectional
Fiber-Reinforced Polymer Matrix Composites
This standard is issued under the fixed designation D6115; 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 2. Referenced Documents
1.1 This test method determines the number of cycles (N) 2.1 ASTM Standards:
for the onset of delamination growth based on the opening
D883 Terminology Relating to Plastics
mode I cyclic strain energy release rate (G), using the Double
D2584 Test Method for Ignition Loss of Cured Reinforced
Cantilever Beam (DCB) specimen shown in Fig. 1. This test
Resins
method applies to constant amplitude, tension-tension fatigue
D2651 GuideforPreparationofMetalSurfacesforAdhesive
loading of continuous fiber-reinforced composite materials.
Bonding
When this test method is applied to multiple specimens at
D2734 TestMethodsforVoidContentofReinforcedPlastics
various G-levels, the results may be shown as a G–N curve, as
D3171 Test Methods for Constituent Content of Composite
illustrated in Fig. 2.
Materials
D3878 Terminology for Composite Materials
1.2 This test method is limited to use with composites
D5229/D5229M TestMethodforMoistureAbsorptionProp-
consisting of unidirectional carbon fiber tape laminates with
erties and Equilibrium Conditioning of Polymer Matrix
single-phase polymer matrices. This limited scope reflects the
Composite Materials
experience gained in round robin testing.This test method may
D5528 TestMethodforModeIInterlaminarFractureTough-
proveusefulforothertypesandclassesofcompositematerials,
ness of Unidirectional Fiber-Reinforced Polymer Matrix
however,certaininterferenceshavebeennoted(seeSection6.5
Composites
of Test Method D5528).
E4 Practices for Force Verification of Testing Machines
1.3 The values stated in SI units are to be regarded as
E6 Terminology Relating to Methods of Mechanical Testing
standard. No other units of measurement are included in this
E122 Practice for Calculating Sample Size to Estimate,With
standard.
Specified Precision, the Average for a Characteristic of a
1.3.1 Exception—Thevaluesprovidedinparenthesesarefor
Lot or Process
information only.
E177 Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the E456 Terminology Relating to Quality and Statistics
responsibility of the user of this standard to establish appro- E467 Practice for Verification of Constant Amplitude Dy-
priate safety, health, and environmental practices and deter-
namic Forces in an Axial Fatigue Testing System
mine the applicability of regulatory limitations prior to use.
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
1.5 This international standard was developed in accor-
E739 PracticeforStatisticalAnalysisofLinearorLinearized
dance with internationally recognized principles on standard-
Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom- E1049 Practices for Cycle Counting in Fatigue Analysis
mendations issued by the World Trade Organization Technical E1150 Definitions of Terms Relating to Fatigue (Withdrawn
Barriers to Trade (TBT) Committee. 1996)
1 2
This test method is under the jurisdiction of ASTM Committee D30 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Composite Materials and is the direct responsibility of Subcommittee D30.06 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Interlaminar Properties. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved March 15, 2019. Published March 2019. Originally the ASTM website.
approved in 1997. Last previous edition approved in 2011 as D6115 – 97(2011). The last approved version of this historical standard is referenced on
DOI: 10.1520/D6115-97R19. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6115 − 97 (2019)
3.3.5 CV—coefficient of variation, %.
3.3.6 da—infinitesimal increase in delamination length.
3.3.7 dU—infinitesimal increase in strain energy.
3.3.8 E —modulus of elasticity in the fiber direction.
II
3.3.9 G—strain energy release rate.
3.3.10 G —opening mode I interlaminar fracture tough-
Ic
ness.
3.3.11 [G ] —average values of G from the quasi-static
Ic av Ic
tests.
3.3.12 G —maximum or peak cyclic mode I strain en-
Imax
ergy release rate.
FIG. 1 DCB Specimen with Piano Hinges 3.3.13 G–N—relationship between the cyclic strain energy
release rate and the number of cycles to onset of delamination
growth.
3. Terminology
3.3.14 h—thickness of DCB specimen.
3.1 Terminology D3878 defines terms relating to high-
3.3.15 N—number of elapsed fatigue cycles.
modulus fibers and their composites. Terminology D883 de-
3.3.16 N —application dependent value of N at which
a
fines terms relating to plastics. Terminology E6 defines terms
delamination growth onset will occur.
relating to mechanical testing. Terminology E456 and Practice
1 %
3.3.17 N —number of fatigue cycles for the value of P
a max
E177 define terms relating to statistics. Definitions E1150
at N = 1 to decrease by 1 %.
defines terms relating to fatigue. In the event of conflict
ViS
between terms, Terminology D3878 shall have precedence 3.3.18 N —numberoffatiguecyclesatwhichtheonsetof
a
delamination growth is observed.
over the other terminology standards.
5 %
3.3.19 N —number of fatigue cycles for the value of P
3.2 Definitions of Terms Specific to This Standard:
a max
at N = 1 to decrease by 5 %.
3.2.1 crack opening mode (Mode I)—fracture mode in
which the delamination faces open away from each other and
3.3.20 P—applied load.
in which these faces do not undergo any relative sliding.
3.3.21 P —value of load at the onset of delamination
cr
3.2.2 cycles to onset of delamination growth, N —the num-
a growth from the insert in the quasi-static tests.
ber of fatigue cycles elapsed until the onset of delamination
3.3.22 P —maximum cyclic load.
max
growth from an implanted thin insert.
3.3.23 R—ratio of minimum and peak loads P /P .
min max
3.2.3 fatigue delamination growth onset relationship,
3.3.24 SD—standard deviation.
G–N—the relationship between the peak cyclic value of strain
energy release rate to the number of fatigue cycles until the 3.3.25 U—strain energy.
onset of delamination growth, N .
a
3.3.26 V —fiber volume fraction, %.
f
3.2.4 mode I interlaminar fracture toughness, G —thecriti-
Ic
3.3.27 δ—load point deflection.
cal value of G for delamination growth because of an opening
3.3.28 δ —value of displacement at the onset of delamina-
cr
load or displacement.
tion growth from the insert in a quasi-static test.
3.2.5 strain energy release rate, G—the loss of strain
3.3.29 δ —maximum value of cyclic displacement.
max
energy, dU, in the test specimen per unit of specimen width for
3.3.30 δ —mean value of cyclic displacement.
mean
an infinitesimal increase in delamination length, da, for a
3.3.31 δ —minimum value of cyclic displacement.
mm
delamination growing under a constant displacement. In math-
3.3.32 ∆—effective delamination extension to correct for
ematical form:
rotation of DCB arms at delamination front.
3.3.33 [∆] —average value of∆ from the quasi-static tests.
1 dU
av
G52 (1)
b da
4. Summary of Test Method
where:
4.1 The Double Cantilever Beam (DCB) shown in Fig. 2 is
U = total elastic strain energy in the test specimen,
described in Test Method D5528.
b = specimen width, and
a = delamination length.
4.2 The DCB specimen is cycled between a minimum and
maximum displacement, δ , and δ , at a specified fre-
3.3 Symbols: min max
quency. For linear elasticity and small deflections (δ/a < 0.4)
3.3.1 a—delamination length.
the displacement ratio, δ / δ , is identical to the R-ratio.
min max
3.3.2 a —initial delamination length.
The number of displacement cycles at which the onset of
3.3.3 b—width of DCB specimen.
delaminationgrowthoccurs, N ,isrecorded.ThemodeIcyclic
a
3.3.4 C—compliance, δ/P, of DCB specimen. strain energy release rate, for example the maximum value,
D6115 − 97 (2019)
the delamination ceases to grow or grows very slowly. In
addition, the rate of change of the delamination growth rate
versus the peak cyclic strain energy release rate for the DCB is
very high. Therefore, small variations in the peak cyclic strain
energy release rate will result in large changes in the delami-
nationgrowthrate.Forthesetworeasons,thistestmethoddoes
not monitor the fatigue delamination growth rate. Instead, this
test method monitors the number of cycles until the onset of
delamination growth from the end of a thin insert. A value of
G may be defined such that delamination growth will not occur
until N cycles have elapsed, where N is defined by the
a a
application, Fig. 1.
6.3 Three definitions to determine the number of cycles
until the onset of delamination growth were used during an
FIG. 2 G–N Curve
investigative round robin. These include: (1) the number of
cycles until the delamination was visually observed to grow at
ViS
the edge, N ;(2) the number of cycles until the compliance
a
1%
hadincreasedby1 %, N (thisisapproximatelyequivalentto
G is calculated using a modified beam theory or other
a
Imax
a 1 % decrease in the maximum cyclic load); and (3) the
methods described in Test Method D5528. By testing several
number of cycles until the compliance has increased by 5 %,
specimens a relationship is developed between G and N
Imax a
5%
N (this is approximately equivalent to a 5 % decrease in the
for the chosen frequency.
a
maximum cyclic load). The three techniques gave different
1%
results, but the N value is typically the lowest of the three
5. Significance and Use
a
values and is recommended for generating a conservative
5.1 Susceptibility to delamination is one of the major
criterion for avoiding onset of fatigue delamination growth in
weaknesses of many advanced laminated composite structures.
durability and damage tolerance analyses of laminated com-
Knowledge of a laminated composite material’s resistance to
posite structures. Because of the difficulties in visually moni-
interlaminar fracture under fatigue loads is useful for product
toringtheendofadelaminationduringafatiguetest,thevisual
development and material selection. Furthermore, a measure-
method is not included in this test method.
ment of the relationship of the mode I cyclic strain energy
6.4 The test frequency may affect results. If the test fre-
release rate and the number of cycles to delamination growth
quency is high, heating effects may occur in the composite. To
onset, G–N, that is independent of specimen geometry or
avoid these effects, frequency should be chosen to be between
method of load introduction, is useful for establishing design
1and10cyclespersecond(Hz)andshouldbechosensuchthat
allowables used in damage tolerance analyses of composite
there is no temperature change of the specimen. Other test
structures made from these materials.
frequencies may be used if they are more appropriate for the
5.2 This test method can serve the following purposes:
application. The test frequency shall be reported.
5.2.1 To establish quantitatively the effects of fiber surface
6.5 The displacement ratio, δ / δ , may have a large
treatment, local variations in fiber volume fraction, and pro-
min max
effect on the results. Because the DCB specimen cannot be
cessing and environmental variables on G–N of a particular
tested in compression the displacement ratio must remain
composite material.
withinthefollowingrange:0≤δ /δ <1.Thedisplacement
5.2.2 To compare quantitatively the relative values of G–N
min max
ratio shall be reported. Large deflections may be considered by
for composite materials with different constituents.
using the corrections given in the Annex of Test Method
5.2.3 To develop criteria for avoiding the onset of delami-
D5528.
nation growth under fatigue loading for composite damage
tolerance and durability analyses.
6.6 The application to other materials, lay-ups, and archi-
tectures is described in Test Method D5528.
6. Interferences
7. Apparatus
6.1 Linear elastic behavior is assumed in the calculation of
G used in this test method. This assumption is valid when the
7.1 Testing Machine—A properly calibrated test machine
zone of damage or non-linear deformation at the delamination
shall be used that can be operated in a displacement control
front, or both, is small relative to the smallest specimen
mode. The testing machine shall conform to the requirements
dimension, which is typically the specimen thickness for the
of Practices E4 and E467. The testing machine shall be
DCB test.
6.2 As the delamination grows under fatigue, fiber bridging
Martin, R. H., and Murri, G. B., “Characterization of Mode I and Mode II
observed in quasi-static testing (see Test Method D5528) may
Delamination Growth and Thresholds in AS4/PEEK Composites,” Composite
also occur. Fiber bridging inhibits the fatigue delamination
Materials: Testing and Design (9th Volume), ASTM STP 1059, S. P. Garbo, Ed.,
growth resulting in slower growth rates than if there was no
1990, pp. 251 –270.
bridging.Thisresultsinartificiallyhighthresholdvalueswhere Preliminary data from D30.06 round robin.
D6115 − 97 (2019)
equipped with grips to hold the loading hinges, or pins to hold
Minimum Number of
Type of Test
Specimens
the loading blocks, that are bonded to the specimen.
Preliminary and exploratory 6 to 12
7.2 Load Indicator—The testing machine load sensing de-
Research and development testing of components 6to12
vice shall be capable of indicating the total load carried by the
and structures
Design allowables 12 to 24
test specimen. This device shall be essentially free from
Reliability data 12 to 24
inertia-lag at the specified rate of testing and shall indicate the
For statistically significant data, the procedures outlined in
load with an accuracy over the load range(s) of interest of
Practice E122 should be consulted. The method of sampling
within 61 % of
...
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