ASTM C394/C394M-16
(Test Method)Standard Test Method for Shear Fatigue of Sandwich Core Materials
Standard Test Method for Shear Fatigue of Sandwich Core Materials
SIGNIFICANCE AND USE
5.1 Often the most critical stress to which a sandwich panel core is subjected is shear. The effect of repeated shear stresses on the core material can be very important, particularly in terms of durability under various environmental conditions.
5.2 This test method provides a standard method of obtaining the sandwich core shear fatigue response. Uses include screening candidate core materials for a specific application, developing a design-specific core shear cyclic stress limit, and core material research and development.
Note 3: This test method may be used as a guide to conduct spectrum loading. This information can be useful in the understanding of fatigue behavior of core under spectrum loading conditions, but is not covered in this standard.
5.3 Factors that influence core fatigue response and shall therefore be reported include the following: core material, core geometry (density, cell size, orientation, etc.), specimen geometry and associated measurement accuracy, specimen preparation, specimen conditioning, environment of testing, specimen alignment, loading procedure, loading frequency, force (stress) ratio and speed of testing (for residual strength tests).
Note 4: If a sandwich panel is tested using the guidance of this standard, the following may also influence the fatigue response and should be reported: facing material, adhesive material, methods of material fabrication, adhesive thickness and adhesive void content. Further, core-to-facing strength may be different between precured/bonded and co-cured facings in sandwich panels with the same core and facing materials.
SCOPE
1.1 This test method determines the effect of repeated shear forces on core material used in sandwich panels. Permissible core material forms include those with continuous bonding surfaces (such as balsa wood and foams) as well as those with discontinuous bonding surfaces (such as honeycomb).
1.2 This test method 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 shear stress or applied force may be used as a constant amplitude fatigue variable.
1.3 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. Within the text, the inch-pound units are shown in brackets.
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 and health practices and determine the applicability of regulatory limitations prior to use.
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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: C394/C394M − 16
Standard Test Method for
Shear Fatigue of Sandwich Core Materials
This standard is issued under the fixed designation C394/C394M; 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 D5229/D5229M TestMethodforMoistureAbsorptionProp-
erties and Equilibrium Conditioning of Polymer Matrix
1.1 This test method determines the effect of repeated shear
Composite Materials
forces on core material used in sandwich panels. Permissible
E6 Terminology Relating to Methods of Mechanical Testing
core material forms include those with continuous bonding
E122 Practice for Calculating Sample Size to Estimate,With
surfaces (such as balsa wood and foams) as well as those with
Specified Precision, the Average for a Characteristic of a
discontinuous bonding surfaces (such as honeycomb).
Lot or Process
1.2 This test method is limited to test specimens subjected
E177 Practice for Use of the Terms Precision and Bias in
to constant amplitude uniaxial loading, where the machine is
ASTM Test Methods
controlled so that the test specimen is subjected to repetitive
E456 Terminology Relating to Quality and Statistics
constant amplitude force (stress) cycles. Either shear stress or
E467 Practice for Verification of Constant Amplitude Dy-
applied force may be used as a constant amplitude fatigue
namic Forces in an Axial Fatigue Testing System
variable.
E739 PracticeforStatisticalAnalysisofLinearorLinearized
Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
1.3 The values stated in either SI units or inch-pound units
are to be regarded separately as standard. The values stated in E1012 Practice for Verification of Testing Frame and Speci-
men Alignment Under Tensile and Compressive Axial
each system may not be exact equivalents; therefore, each
system shall be used independently of the other. Combining Force Application
values from the two systems may result in non-conformance
2.2 ISO Standards
with the standard. Within the text, the inch-pound units are
ISO 13003:2003(E) Fibre-reinforced plastics: Determination
shown in brackets.
of fatigue properties under cyclic loading conditions
1.4 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:
priate safety and health practices and determine the applica-
3.1.1 Terminology D3878 defines terms relating to high-
bility of regulatory limitations prior to use.
modulus fibers and their composites, as well as terms relating
to sandwich constructions. Terminology D883 defines terms
2. Referenced Documents
relating to plastics. Terminology E6 defines terms relating to
2.1 ASTM Standards:
mechanical testing. Terminology E456 and Practice E177
C271/C271M Test Method for Density of Sandwich Core
define terms relating to statistics. In the event of a conflict
Materials
between terms, Terminology D3878 shall have precedence
C273/C273M Test Method for Shear Properties of Sandwich
over the other terminologies.
Core Materials
NOTE 1—If the term represents a physical quantity, its analytical
D883 Terminology Relating to Plastics
dimensionsarestatedimmediatelyfollowingtheterm(orlettersymbol)in
D3878 Terminology for Composite Materials
fundamental dimension form, using the following ASTM standard sym-
bology for fundamental dimensions, shown within square brackets: [M]
for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature,
This test method is under the jurisdiction of ASTM Committee D30 on and[nd]fornon-dimensionalquantities.Useofthesesymbolsisrestricted
Composite Materials and is the direct responsibility of Subcommittee D30.09 on
to analytical dimensions when used with square brackets, as the symbols
Sandwich Construction.
may have other definitions when used without the brackets.
Current edition approved April 1, 2016. Published April 2016. Originally
3.2 Definitions:
approved in 1957. Last previous edition approved in 2013 as C394 – 13. DOI:
10.1520/C0394_C0394M-16.
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 Available from International Organization for Standardization (ISO), 1, ch. de
the ASTM website. la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C394/C394M − 16
3.2.1 constant amplitude loading, n—in fatigue,aloadingin force (stress) cycles at which failure occurs for a specimen
which all of the peak values of force (stress) are equal and all subjected to a specific force (stress) ratio and force (stress)
of the valley values of force (stress) are equal. magnitude is determined.
3.2.2 fatigue loading transition, n—in the beginning of
NOTE 2—This test method may be used as a guide to conduct shear
fatigue loading, the number of cycles before the force (stress) fatigue testing of sandwich panels consisting of facesheets and core with
the Test Method C273/C273M loading plates bonded to the facesheets.
reaches the desired peak and valley values.
4.2 The only acceptable failure modes for shear fatigue of
3.2.3 force (stress) ratio, R [nd], n—in fatigue loading, the
sandwich core materials are those which are internal to the
ratio of the minimum applied force (stress) to the maximum
sandwich core. Failure of the loading plate-to-core bond is not
applied force (stress), where positive force (stress) corresponds
an acceptable failure mode.
to the tension mode of loading.
-1
3.2.4 frequency, f [T ], n—in fatigue loading,thenumberof
5. Significance and Use
force (stress) cycles completed in 1 s (Hz).
5.1 Often the most critical stress to which a sandwich panel
3.2.5 peak, n—in fatigue loading, the occurrence where the
core is subjected is shear. The effect of repeated shear stresses
first derivative of the force (stress) versus time changes from
on the core material can be very important, particularly in
positive to negative sign; the point of maximum force (stress)
terms of durability under various environmental conditions.
in constant amplitude loading.
5.2 This test method provides a standard method of obtain-
-1 -2
3.2.6 residual strength, [ML T ], n—the value of force
ing the sandwich core shear fatigue response. Uses include
(stress) required to cause failure of a specimen under quasi-
screening candidate core materials for a specific application,
static loading conditions after the specimen is subjected to
developing a design-specific core shear cyclic stress limit, and
fatigue loading.
core material research and development.
3.2.7 run-out, n—in fatigue,anupperlimitonthenumberof
NOTE 3—This test method may be used as a guide to conduct spectrum
force cycles to be applied.
loading. This information can be useful in the understanding of fatigue
3.2.8 spectrum loading, n—in fatigue, a loading in which behavior of core under spectrum loading conditions, but is not covered in
this standard.
the peak values of force (stress) are not equal or the valley
values of force (stress) are not equal (also known as variable
5.3 Factors that influence core fatigue response and shall
amplitude loading or irregular loading).
therefore be reported include the following: core material, core
geometry (density, cell size, orientation, etc.), specimen geom-
3.2.9 valley, n—in fatigue loading,theoccurrencewherethe
etry and associated measurement accuracy, specimen
first derivative of the force (stress) versus time changes from
preparation, specimen conditioning, environment of testing,
negative to positive sign; the point of minimum force (stress)
specimen alignment, loading procedure, loading frequency,
in constant amplitude loading.
force (stress) ratio and speed of testing (for residual strength
3.2.10 wave form, n—the shape of the peak-to-peak varia-
tests).
tion of the force (stress) as a function of time.
NOTE 4—If a sandwich panel is tested using the guidance of this
3.3 Symbols—b = width of specimen, mm [in]
standard,thefollowingmayalsoinfluencethefatigueresponseandshould
CV = coefficient of variation statistic of a sample population
be reported: facing material, adhesive material, methods of material
for a given property (in percent)
fabrication, adhesive thickness and adhesive void content. Further, core-
L = length of specimen, mm [in] to-facingstrengthmaybedifferentbetweenprecured/bondedandco-cured
facings in sandwich panels with the same core and facing materials.
N = number of constant amplitude cycles
P = force on specimen, positive for tension mode of loading,
6. Interferences
N [lb]
6.1 Material and Specimen Preparation—Poormaterialfab-
R = fatigue force (stress) ratio, minimum-to-maximum
rication practices and damage induced by improper specimen
cyclic force (stress)
machining are known causes of high data scatter in composites
S = standard deviation statistic of a sample population for
n–1
in general. Specific material factors that affect sandwich core
a given property
include variability in core density and degree of cure of core
x = test result for an individual specimen from the sample
bonding adhesive. For this particular core shear test, thickness
population for a given property
of the adhesive bond to honeycomb core (adhesive-filled depth
x¯ = mean or average (estimate of mean) of a sample
into the honeycomb core cells), core misalignment/distortion/
population for a given property
damage, or bonding surface roughness may affect the core
τ = core shear stress, MPa [psi]
shear strength and fatigue life.
4. Summary of Test Method
6.2 System Alignment—Unintended loading eccentricities
4.1 This test method consists of subjecting a sandwich core will cause premature failure. Every effort should be made to
to cyclic shear force parallel to the plane of its faces.The force eliminate undesirable eccentricities from the test system. Such
is transmitted to the core through loading plates which are eccentricities may occur as a result of misaligned grips, poor
bonded directly to the core (unlike the static core shear test, specimen preparation, or poor alignment of the bonded loading
Test Method C273/C273M, bonding of loading plates to plates and loading fixture. If there is any doubt as to the
facesheets bonded to the core is not permitted). The number of alignment inherent in a given test machine, then the alignment
C394/C394M − 16
should be checked following the general philosophical ap- 7.3.2 Force Indicator—The testing machine force-sensing
proach described in Test Method E1012. device shall be capable of indicating the total force being
carried by the test specimen. This device shall be essentially
6.3 Geometry—Specific geometric factors that affect core
free from inertia lag at the specified rate of testing and shall
shear fatigue response include core cell geometry (shape,
indicate the force with an accuracy over the force range(s) of
density, orientation), core thickness, specimen shape (L/b
interest to within 61 % of the indicated value.
ratio), and adhesive thickness.
7.3.3 Counter—The testing machine shall be capable of
6.4 Environment—Resultsareaffectedbytheenvironmental
counting cycles of applied load.
conditions under which the tests are conducted. Specimens
tested in various environments can exhibit significant differ-
7.4 Conditioning Chamber—When conditioning materials
ences in both fatigue life and failure mode. Critical environ- in non-laboratory environments, a temperature/vapor-level
ments must be assessed independently for each adhesive and
controlledenvironmentalconditioningchamberisrequiredthat
core material tested. If possible, test the specimen under the
shall be capable of maintaining the required temperature to
same fluid exposure level used for conditioning. However,
within 63°C [65°F] and the required relative humidity level
cases such as elevated temperature testing of a moist specimen
to within 63 %. Chamber conditions shall be monitored either
place unrealistic requirements on the capabilities of common
on an automated continuous basis or on a manual basis at
testing machine environmental chambers. In such cases, the
regular intervals.
mechanical test environment may need to be modified, for
7.5 Environmental Test Chamber—An environmental test
example, by testing at elevated temperature with no fluid
chamber is required for test environments other than ambient
exposure control, but with a specified limit on time to failure
testing laboratory conditions. This chamber shall be capable of
from withdrawal from the conditioning chamber.
maintaining the gage section of the test specimen at the
6.5 Loading Frequency—Results may be affected by speci-
required test environment during the mechanical test.
men heating if the test is run at too high a cyclic loading rate.
7.6 Thermocouple and Temperature Recording Devices,
High cyclic rates may induce heating due to material damping,
capable of reading specimen temperature to 60.5°C [61.0°F].
and may cause variations in specimen temperature and prop-
erties of the core. Varying the cyclic frequency during the test
8. Sampling and Test Specimens
is generally not recommended, as the response may be sensi-
tive to the frequency utilized and the resultant thermal history.
8.1 Sampling—For statistically significant data, the proce-
6.6 Force (Stress) Ratio—Results may be affected by the
dures outlined in Practice E122 should be consulted. A
force (stress) ratio under which the tests are conducted.
statistically significant distribution of data should be obtained
for a given core material, environment and loading condition
6.7 Loading Mode—Results may be affected by the mode of
from the number of tests selected.
loading (tension versus compression).
8.1.1 Sample Size for S-N Curve—The recommended mini-
6.8 Failure Mode—In some sandwich applications the ef-
mum number of specimens in the development of S-N data is
fectiveshearstrengthofthecoremaybelimitedbythestrength
three specimens per load level and a minimum of three load
of the core-to-facing interface. In these cases it may be
levels.ForadditionalproceduresconsultPracticeE739.Report
appropriate to test a sandwich
...
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: C394/C394M − 13 C394/C394M − 16
Standard Test Method for
Shear Fatigue of Sandwich Core Materials
This standard is issued under the fixed designation C394/C394M; 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 test method determines the effect of repeated shear forces on core material used in sandwich panels. Permissible core
material forms include those with continuous bonding surfaces (such as balsa wood and foams) as well as those with discontinuous
bonding surfaces (such as honeycomb).
1.2 This test method 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 shear stress or applied
force may be used as a constant amplitude fatigue variable.
1.3 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. Within the text, the inch-pound units are shown in brackets.
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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
C271/C271M Test Method for Density of Sandwich Core Materials
C273/C273M Test Method for Shear Properties of Sandwich Core Materials
C274/C274M Terminology of Structural Sandwich Constructions
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
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
E1012 Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force
Application
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)
E1471 Guide for Identification of Fibers, Fillers, and Core Materials in Computerized Material Property Databases (Withdrawn
2015)
This test method is under the jurisdiction of ASTM Committee D30 on Composite Materials and is the direct responsibility of Subcommittee D30.09 on Sandwich
Construction.
Current edition approved Oct. 1, 2013April 1, 2016. Published October 2013April 2016. Originally approved in 1957. Last previous edition approved in 20002013 as
C394 – 00C394 – 13.(2008). DOI: 10.1520/C0394_C0394M–13.10.1520/C0394_C0394M-16.
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
C394/C394M − 16
2.2 ISO Standards
ISO 13003:2003(E) Fibre-reinforced plastics: Determination of fatigue properties under cyclic loading conditions
3. Terminology
3.1 Definitions:
3.1.1 Terminology D3878 defines terms relating to high-modulus fibers and their composites. Terminologycomposites, as
C274/C274M defineswell as terms relating to structural sandwich constructions. Terminology D883 defines terms relating to
plastics. Terminology E6 defines terms relating to mechanical testing. 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 terminologies.
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:
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 (stress) ratio, R [nd], n—in fatigue loading, the ratio of the minimum applied force (stress) to the maximum applied
force (stress), where positive force (stress) corresponds to the tension mode of loading.
-1
3.2.4 frequency, f [T ], n—in fatigue loading, the number of force (stress) cycles completed in 1 s (Hz).
3.2.5 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
3.2.6 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.
3.2.7 run-out, n—in fatigue, an upper limit on the number of force cycles to be applied.
3.2.8 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).
3.2.9 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.
3.2.10 wave form, n—the shape of the peak-to-peak variation of the force (stress) as a function of time.
3.3 Symbols—b = width of specimen, mm [in]
CV = coefficient of variation statistic of a sample population for a given property (in percent)
L = length of specimen, mm [in]
N = number of constant amplitude cycles
P = force on specimen, positive for tension mode of loading, N [lb]
R = fatigue force (stress) ratio, minimum-to-maximum cyclic force (stress)
S = standard deviation statistic of a sample population for a given property
n–1
x = test result for an individual specimen from the sample population for a given property
x¯ = mean or average (estimate of mean) of a sample population for a given property
τ = core shear stress, MPa [psi]
4. Summary of Test Method
4.1 This test method consists of subjecting a sandwich core to cyclic shear force parallel to the plane of its faces. The force is
transmitted to the core through loading plates which are bonded directly to the core (unlike the static core shear test, Test Method
C273/C273M, bonding of loading plates to facesheets bonded to the core is not permitted). The number of force (stress) cycles
at which failure occurs for a specimen subjected to a specific force (stress) ratio and force (stress) magnitude is determined.
NOTE 2—This test method may be used as a guide to conduct shear fatigue testing of sandwich panels consisting of facesheets and core with the Test
Method C273/C273M loading plates bonded to the facesheets.
4.2 The only acceptable failure modes for shear fatigue of sandwich core materials are those which are internal to the sandwich
core. Failure of the loading plate-to-core bond is not an acceptable failure mode.
Available from International Organization for Standardization (ISO), 1, ch. de la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http://www.iso.org.
C394/C394M − 16
5. Significance and Use
5.1 Often the most critical stress to which a sandwich panel core is subjected is shear. The effect of repeated shear stresses on
the core material can be very important, particularly in terms of durability under various environmental conditions.
5.2 This test method provides a standard method of obtaining the sandwich core shear fatigue response. Uses include screening
candidate core materials for a specific application, developing a design-specific core shear cyclic stress limit, and core material
research and development.
NOTE 3—This test method may be used as a guide to conduct spectrum loading. This information can be useful in the understanding of fatigue behavior
of core under spectrum loading conditions, but is not covered in this standard.
5.3 Factors that influence core fatigue response and shall therefore be reported include the following: core material, core
geometry (density, cell size, orientation, etc.), specimen geometry and associated measurement accuracy, specimen preparation,
specimen conditioning, environment of testing, specimen alignment, loading procedure, loading frequency, force (stress) ratio and
speed of testing (for residual strength tests).
NOTE 4—If a sandwich panel is tested using the guidance of this standard, the following may also influence the fatigue response and should be reported:
facing material, adhesive material, methods of material fabrication, adhesive thickness and adhesive void content. Further, core-to-facing strength may
be different between precured/bonded and co-cured facings in sandwich panels with the same core and facing materials.
6. Interferences
6.1 Material and Specimen Preparation—Poor material fabrication practices and damage induced by improper specimen
machining are known causes of high data scatter in composites in general. Specific material factors that affect sandwich core
include variability in core density and degree of cure of core bonding adhesive. For this particular core shear test, thickness of the
adhesive bond to honeycomb core (adhesive-filled depth into the honeycomb core cells), core misalignment/distortion/damage, or
bonding surface roughness may affect the core shear strength and fatigue life.
6.2 System Alignment—Unintended loading eccentricities will cause premature failure. Every effort should be made to eliminate
undesirable eccentricities from the test system. Such eccentricities may occur as a result of misaligned grips, poor specimen
preparation, or poor alignment of the bonded loading plates and loading fixture. If there is any doubt as to the alignment inherent
in a given test machine, then the alignment should be checked following the general philosophical approach described in Test
Method E1012.
6.3 Geometry—Specific geometric factors that affect core shear fatigue response include core cell geometry (shape, density,
orientation), core thickness, specimen shape (L/b ratio), and adhesive thickness.
6.4 Environment—Results are affected by the environmental conditions under which the tests are conducted. Specimens tested
in various environments can exhibit significant differences in both fatigue life and failure mode. Critical environments must be
assessed independently for each adhesive and core material tested. If possible, test the specimen under the same fluid exposure
level used for conditioning. However, cases such as elevated temperature testing of a moist specimen place unrealistic requirements
on the capabilities of common testing machine environmental chambers. In such cases, the mechanical test environment may need
to be modified, for example, by testing at elevated temperature with no fluid exposure control, but with a specified limit on time
to failure from withdrawal from the conditioning chamber.
6.5 Loading Frequency—Results may be affected by specimen heating if the test is run at too high a cyclic loading rate. High
cyclic rates may induce heating due to material damping, and may cause variations in specimen temperature and properties of the
core. 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.
6.6 Force (Stress) Ratio—Results may be affected by the force (stress) ratio under which the tests are conducted.
6.7 Loading Mode—Results may be affected by the mode of loading (tension versus compression).
6.8 Failure Mode—In some sandwich applications the effective shear strength of the core may be limited by the strength of the
core-to-facing interface. In these cases it may be appropriate to test a sandwich panel representative of the intended application.
7. Apparatus
7.1 Micrometers—The micrometer(s) shall use a flat anvil interface on machined edges or very smooth-tooled surfaces. The
accuracy of the instrument(s) shall be suitable for reading to within 1 % of the sample length, width and thickness. For typical
specimen geometries, an instrument with an accuracy of 625 μm [60.001 in.] is desirable for thickness, length and width
measurement.
7.2 Test Fixtures—Use either the tension or compression tension loading fixture described in Test Method C273/C273M
depending on the specified mode of loading.
7.3 Testing Machine—The testing machine shall be in accordance with Practice E467 and shall satisfy the following
requirements:
C394/C394M − 16
7.3.1 Drive Mechanism—The testing machine drive mechanism shall be capable of imparting to the movable head a controlled
velocity with respect to the stationary head. The velocity of the movable head shall be capable of being regulated in accordance
with 11.7.
...
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: C394/C394M − 16
Standard Test Method for
Shear Fatigue of Sandwich Core Materials
This standard is issued under the fixed designation C394/C394M; 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 D5229/D5229M Test Method for Moisture Absorption Prop-
erties and Equilibrium Conditioning of Polymer Matrix
1.1 This test method determines the effect of repeated shear
Composite Materials
forces on core material used in sandwich panels. Permissible
E6 Terminology Relating to Methods of Mechanical Testing
core material forms include those with continuous bonding
E122 Practice for Calculating Sample Size to Estimate, With
surfaces (such as balsa wood and foams) as well as those with
Specified Precision, the Average for a Characteristic of a
discontinuous bonding surfaces (such as honeycomb).
Lot or Process
1.2 This test method is limited to test specimens subjected
E177 Practice for Use of the Terms Precision and Bias in
to constant amplitude uniaxial loading, where the machine is
ASTM Test Methods
controlled so that the test specimen is subjected to repetitive
E456 Terminology Relating to Quality and Statistics
constant amplitude force (stress) cycles. Either shear stress or
E467 Practice for Verification of Constant Amplitude Dy-
applied force may be used as a constant amplitude fatigue
namic Forces in an Axial Fatigue Testing System
variable.
E739 Practice for Statistical Analysis of Linear or Linearized
1.3 The values stated in either SI units or inch-pound units Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
E1012 Practice for Verification of Testing Frame and Speci-
are to be regarded separately as standard. The values stated in
each system may not be exact equivalents; therefore, each men Alignment Under Tensile and Compressive Axial
Force Application
system shall be used independently of the other. Combining
values from the two systems may result in non-conformance
2.2 ISO Standards
with the standard. Within the text, the inch-pound units are
ISO 13003:2003(E) Fibre-reinforced plastics: Determination
shown in brackets.
of fatigue properties under cyclic loading conditions
1.4 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:
priate safety and health practices and determine the applica-
3.1.1 Terminology D3878 defines terms relating to high-
bility of regulatory limitations prior to use.
modulus fibers and their composites, as well as terms relating
to sandwich constructions. Terminology D883 defines terms
2. Referenced Documents
relating to plastics. Terminology E6 defines terms relating to
2.1 ASTM Standards:
mechanical testing. Terminology E456 and Practice E177
C271/C271M Test Method for Density of Sandwich Core
define terms relating to statistics. In the event of a conflict
Materials
between terms, Terminology D3878 shall have precedence
C273/C273M Test Method for Shear Properties of Sandwich
over the other terminologies.
Core Materials
NOTE 1—If the term represents a physical quantity, its analytical
D883 Terminology Relating to Plastics
dimensions are stated immediately following the term (or letter symbol) in
D3878 Terminology for Composite Materials
fundamental dimension form, using the following ASTM standard sym-
bology for fundamental dimensions, shown within square brackets: [M]
for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature,
This test method is under the jurisdiction of ASTM Committee D30 on and [nd] for non-dimensional quantities. Use of these symbols is restricted
Composite Materials and is the direct responsibility of Subcommittee D30.09 on to analytical dimensions when used with square brackets, as the symbols
Sandwich Construction.
may have other definitions when used without the brackets.
Current edition approved April 1, 2016. Published April 2016. Originally
3.2 Definitions:
approved in 1957. Last previous edition approved in 2013 as C394 – 13. DOI:
10.1520/C0394_C0394M-16.
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 Available from International Organization for Standardization (ISO), 1, ch. de
the ASTM website. la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C394/C394M − 16
3.2.1 constant amplitude loading, n—in fatigue, a loading in force (stress) cycles at which failure occurs for a specimen
which all of the peak values of force (stress) are equal and all subjected to a specific force (stress) ratio and force (stress)
of the valley values of force (stress) are equal. magnitude is determined.
3.2.2 fatigue loading transition, n—in the beginning of
NOTE 2—This test method may be used as a guide to conduct shear
fatigue loading, the number of cycles before the force (stress) fatigue testing of sandwich panels consisting of facesheets and core with
the Test Method C273/C273M loading plates bonded to the facesheets.
reaches the desired peak and valley values.
4.2 The only acceptable failure modes for shear fatigue of
3.2.3 force (stress) ratio, R [nd], n—in fatigue loading, the
sandwich core materials are those which are internal to the
ratio of the minimum applied force (stress) to the maximum
sandwich core. Failure of the loading plate-to-core bond is not
applied force (stress), where positive force (stress) corresponds
an acceptable failure mode.
to the tension mode of loading.
-1
3.2.4 frequency, f [T ], n—in fatigue loading, the number of
5. Significance and Use
force (stress) cycles completed in 1 s (Hz).
5.1 Often the most critical stress to which a sandwich panel
3.2.5 peak, n—in fatigue loading, the occurrence where the
core is subjected is shear. The effect of repeated shear stresses
first derivative of the force (stress) versus time changes from
on the core material can be very important, particularly in
positive to negative sign; the point of maximum force (stress)
terms of durability under various environmental conditions.
in constant amplitude loading.
5.2 This test method provides a standard method of obtain-
-1 -2
3.2.6 residual strength, [ML T ], n—the value of force
ing the sandwich core shear fatigue response. Uses include
(stress) required to cause failure of a specimen under quasi-
screening candidate core materials for a specific application,
static loading conditions after the specimen is subjected to
developing a design-specific core shear cyclic stress limit, and
fatigue loading.
core material research and development.
3.2.7 run-out, n—in fatigue, an upper limit on the number of
NOTE 3—This test method may be used as a guide to conduct spectrum
force cycles to be applied.
loading. This information can be useful in the understanding of fatigue
3.2.8 spectrum loading, n—in fatigue, a loading in which
behavior of core under spectrum loading conditions, but is not covered in
this standard.
the peak values of force (stress) are not equal or the valley
values of force (stress) are not equal (also known as variable
5.3 Factors that influence core fatigue response and shall
amplitude loading or irregular loading).
therefore be reported include the following: core material, core
geometry (density, cell size, orientation, etc.), specimen geom-
3.2.9 valley, n—in fatigue loading, the occurrence where the
etry and associated measurement accuracy, specimen
first derivative of the force (stress) versus time changes from
preparation, specimen conditioning, environment of testing,
negative to positive sign; the point of minimum force (stress)
specimen alignment, loading procedure, loading frequency,
in constant amplitude loading.
force (stress) ratio and speed of testing (for residual strength
3.2.10 wave form, n—the shape of the peak-to-peak varia-
tests).
tion of the force (stress) as a function of time.
NOTE 4—If a sandwich panel is tested using the guidance of this
3.3 Symbols—b = width of specimen, mm [in]
standard, the following may also influence the fatigue response and should
CV = coefficient of variation statistic of a sample population
be reported: facing material, adhesive material, methods of material
for a given property (in percent)
fabrication, adhesive thickness and adhesive void content. Further, core-
L = length of specimen, mm [in] to-facing strength may be different between precured/bonded and co-cured
facings in sandwich panels with the same core and facing materials.
N = number of constant amplitude cycles
P = force on specimen, positive for tension mode of loading,
6. Interferences
N [lb]
6.1 Material and Specimen Preparation—Poor material fab-
R = fatigue force (stress) ratio, minimum-to-maximum
rication practices and damage induced by improper specimen
cyclic force (stress)
machining are known causes of high data scatter in composites
S = standard deviation statistic of a sample population for
n–1
in general. Specific material factors that affect sandwich core
a given property
include variability in core density and degree of cure of core
x = test result for an individual specimen from the sample
bonding adhesive. For this particular core shear test, thickness
population for a given property
of the adhesive bond to honeycomb core (adhesive-filled depth
x¯ = mean or average (estimate of mean) of a sample
into the honeycomb core cells), core misalignment/distortion/
population for a given property
damage, or bonding surface roughness may affect the core
τ = core shear stress, MPa [psi]
shear strength and fatigue life.
4. Summary of Test Method
6.2 System Alignment—Unintended loading eccentricities
4.1 This test method consists of subjecting a sandwich core will cause premature failure. Every effort should be made to
to cyclic shear force parallel to the plane of its faces. The force eliminate undesirable eccentricities from the test system. Such
is transmitted to the core through loading plates which are eccentricities may occur as a result of misaligned grips, poor
bonded directly to the core (unlike the static core shear test, specimen preparation, or poor alignment of the bonded loading
Test Method C273/C273M, bonding of loading plates to plates and loading fixture. If there is any doubt as to the
facesheets bonded to the core is not permitted). The number of alignment inherent in a given test machine, then the alignment
C394/C394M − 16
should be checked following the general philosophical ap- 7.3.2 Force Indicator—The testing machine force-sensing
proach described in Test Method E1012. device shall be capable of indicating the total force being
carried by the test specimen. This device shall be essentially
6.3 Geometry—Specific geometric factors that affect core
free from inertia lag at the specified rate of testing and shall
shear fatigue response include core cell geometry (shape,
indicate the force with an accuracy over the force range(s) of
density, orientation), core thickness, specimen shape (L/b
interest to within 61 % of the indicated value.
ratio), and adhesive thickness.
7.3.3 Counter—The testing machine shall be capable of
6.4 Environment—Results are affected by the environmental
counting cycles of applied load.
conditions under which the tests are conducted. Specimens
tested in various environments can exhibit significant differ- 7.4 Conditioning Chamber—When conditioning materials
ences in both fatigue life and failure mode. Critical environ-
in non-laboratory environments, a temperature/vapor-level
ments must be assessed independently for each adhesive and
controlled environmental conditioning chamber is required that
core material tested. If possible, test the specimen under the
shall be capable of maintaining the required temperature to
same fluid exposure level used for conditioning. However,
within 63°C [65°F] and the required relative humidity level
cases such as elevated temperature testing of a moist specimen
to within 63 %. Chamber conditions shall be monitored either
place unrealistic requirements on the capabilities of common
on an automated continuous basis or on a manual basis at
testing machine environmental chambers. In such cases, the
regular intervals.
mechanical test environment may need to be modified, for
7.5 Environmental Test Chamber—An environmental test
example, by testing at elevated temperature with no fluid
chamber is required for test environments other than ambient
exposure control, but with a specified limit on time to failure
testing laboratory conditions. This chamber shall be capable of
from withdrawal from the conditioning chamber.
maintaining the gage section of the test specimen at the
6.5 Loading Frequency—Results may be affected by speci-
required test environment during the mechanical test.
men heating if the test is run at too high a cyclic loading rate.
7.6 Thermocouple and Temperature Recording Devices,
High cyclic rates may induce heating due to material damping,
capable of reading specimen temperature to 60.5°C [61.0°F].
and may cause variations in specimen temperature and prop-
erties of the core. Varying the cyclic frequency during the test
8. Sampling and Test Specimens
is generally not recommended, as the response may be sensi-
tive to the frequency utilized and the resultant thermal history.
8.1 Sampling—For statistically significant data, the proce-
6.6 Force (Stress) Ratio—Results may be affected by the
dures outlined in Practice E122 should be consulted. A
force (stress) ratio under which the tests are conducted.
statistically significant distribution of data should be obtained
for a given core material, environment and loading condition
6.7 Loading Mode—Results may be affected by the mode of
from the number of tests selected.
loading (tension versus compression).
8.1.1 Sample Size for S-N Curve—The recommended mini-
6.8 Failure Mode—In some sandwich applications the ef-
mum number of specimens in the development of S-N data is
fective shear strength of the core may be limited by the strength
three specimens per load level and a minimum of three load
of the core-to-facing interface. In these cases it may be
levels. For additional procedures consult Practice E739. Report
appropriate to test a sandwich panel representative of
...
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