ASTM C394/C394M-16(2024)

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 are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined. 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, 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

• Status: Published
• Publication Date: 30-Apr-2024
• ICS: 83.120 - Reinforced plastics
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.09 - Sandwich Construction

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: C394/C394M − 16 (Reapproved 2024)
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 C271/C271M Test Method for Density of Sandwich Core
Materials
1.1 This test method determines the effect of repeated shear
C273/C273M Test Method for Shear Properties of Sandwich
forces on core material used in sandwich panels. Permissible
Core Materials
core material forms include those with continuous bonding
D883 Terminology Relating to Plastics
surfaces (such as balsa wood and foams) as well as those with
D3878 Terminology for Composite Materials
discontinuous bonding surfaces (such as honeycomb).
D5229/D5229M Test Method for Moisture Absorption Prop-
1.2 This test method is limited to test specimens subjected
erties and Equilibrium Conditioning of Polymer Matrix
to constant amplitude uniaxial loading, where the machine is
Composite Materials
controlled so that the test specimen is subjected to repetitive
E6 Terminology Relating to Methods of Mechanical Testing
constant amplitude force (stress) cycles. Either shear stress or
E122 Practice for Calculating Sample Size to Estimate, With
applied force may be used as a constant amplitude fatigue
Specified Precision, the Average for a Characteristic of a
variable.
Lot or Process
E177 Practice for Use of the Terms Precision and Bias in
1.3 The values stated in either SI units or inch-pound units
are to be regarded separately as standard. The values stated in ASTM Test Methods
E456 Terminology Relating to Quality and Statistics
each system are not necessarily exact equivalents; therefore, to
ensure conformance with the standard, each system shall be E467 Practice for Verification of Constant Amplitude Dy-
namic Forces in an Axial Fatigue Testing System
used independently of the other, and values from the two
systems shall not be combined. Within the text, the inch-pound E739 Guide for Statistical Analysis of Linear or Linearized
Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
units are shown in brackets.
(Withdrawn 2024)
1.4 This standard does not purport to address all of the
E1012 Practice for Verification of Testing Frame and Speci-
safety concerns, if any, associated with its use. It is the
men Alignment Under Tensile and Compressive Axial
responsibility of the user of this standard to establish appro-
Force Application
priate safety, health, and environmental practices and deter-
2.2 ISO Standards
mine the applicability of regulatory limitations prior to use.
ISO 13003:2003(E) Fibre-reinforced plastics: Determination
1.5 This international standard was developed in accor-
of fatigue properties under cyclic loading conditions
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
3. Terminology
Development of International Standards, Guides and Recom-
3.1 Definitions:
mendations issued by the World Trade Organization Technical
3.1.1 Terminology D3878 defines terms relating to high-
Barriers to Trade (TBT) Committee.
modulus fibers and their composites, as well as terms relating
to sandwich constructions. Terminology D883 defines terms
2. Referenced Documents
2 relating to plastics. Terminology E6 defines terms relating to
2.1 ASTM Standards:
mechanical testing. Terminology E456 and Practice E177
define terms relating to statistics. In the event of a conflict
1 between terms, Terminology D3878 shall have precedence
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.09 on
over the other terminologies.
Sandwich Construction.
NOTE 1—If the term represents a physical quantity, its analytical
Current edition approved May 1, 2024. Published May 2024. Originally
approved in 1957. Last previous edition approved in 2016 as C394 – 16. DOI:
10.1520/C0394_C0394M-16R24.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or The last approved version of this historical standard is referenced on
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM www.astm.org.
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 (2024)
dimensions are stated immediately following the term (or letter symbol) in
4. Summary of Test Method
fundamental dimension form, using the following ASTM standard sym-
4.1 This test method consists of subjecting a sandwich core
bology for fundamental dimensions, shown within square brackets: [M]
to cyclic shear force parallel to the plane of its faces. The force
for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature,
and [nd] for non-dimensional quantities. Use of these symbols is restricted
is transmitted to the core through loading plates which are
to analytical dimensions when used with square brackets, as the symbols
bonded directly to the core (unlike the static core shear test,
may have other definitions when used without the brackets.
Test Method C273/C273M, bonding of loading plates to
3.2 Definitions:
facesheets bonded to the core is not permitted). The number of
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
behavior of core under spectrum loading conditions, but is not covered in
3.2.8 spectrum loading, n—in fatigue, a loading in which
this standard.
the peak values of force (stress) are not equal or the valley
5.3 Factors that influence core fatigue response and shall
values of force (stress) are not equal (also known as variable
therefore be reported include the following: core material, core
amplitude loading or irregular loading).
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
be reported: facing material, adhesive material, methods of material
CV = coefficient of variation statistic of a sample population
fabrication, adhesive thickness and adhesive void content. Further, core-
for a given property (in percent)
to-facing strength may be different between precured/bonded and co-cured
L = length of specimen, mm [in]
facings in sandwich panels with the same core and facing materials.
N = number of constant amplitude cycles
6. Interferences
P = force on specimen, positive for tension mode of loading,
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
in general. Specific material factors that affect sandwich core
n–1
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.
C394/C394M − 16 (2024)
6.2 System Alignment—Unintended loading eccentricities 7.3 Testing Machine—The testing machine shall be in ac-
will cause premature failure. Every effort should be made to cordance with Practice E467 and shall satisfy the following
eliminate undesirable eccentricities from the test system. Such requirements:
eccentricities may occur as a result of misaligned grips, poor 7.3.1 Drive Mechanism—The testing machine drive mecha-
specimen preparation, or poor alignment of the bonded loading nism shall be capable of imparting to the movable head a
plates and loading fixture. If there is any doubt as to the controlled velocity with respect to the stationary head. The
alignment inherent in a given test machine, then the alignment velocity of the movable head shall be capable of being
should be checked following the general philosophical ap- regulated in accordance with 11.7.
proach described in Test Method E1012. 7.3.2 Force Indicator—The testing machine force-sensing
device shall be capable of indicating the total force being
6.3 Geometry—Specific geometric factors that affect core
carried by the test specimen. This device shall be essentially
shear fatigue response include core cell geometry (shape,
free from inertia lag at the specified rate of testing and shall
density, orientation), core thickness, specimen shape (L/b
indicate the force with an accuracy over the force range(s) of
ratio), and adhesive thickness.
interest to within 61 % of the indicated value.
6.4 Environment—Results are affected by the environmental
7.3.3 Counter—The testing machine shall be capable of
conditions under which the tests are conducted. Specimens counting cycles of applied load.
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
and may cause variations in specimen temperature and prop-
[61.0 °F].
erties of the core. Varying the cyclic frequency during the test
is generally not recommended, as the response may be sensi-
8. Sampling and Test Specimens
...