ASTM C273/C273M-20

Standard Test Method for Shear Properties of Sandwich Core Materials

SIGNIFICANCE AND USE
5.1 The core shear properties are fundamental properties that are used in the design of sandwich panels. This test method provides information on the force-deflection behavior of sandwich constructions or cores when loaded in shear parallel to the plane of the facings. From a complete force-deflection curve, it is possible to compute core shear stress at any force (such as the shear stress at proportional limit, at yield, or at maximum force) and to compute an effective core shear modulus.  
5.2 The test does not produce pure shear, but the specimen length is prescribed so that secondary stresses have a minimum effect. Approximate shear properties can also be obtained from a sandwich flexure test (see Test Method C393).  
5.3 This test method provides a standard method of obtaining sandwich core shear data for material specifications, sandwich panel design, research and development applications, and quality assurance.  
5.4 Factors that influence core shear strength and shall therefore be reported include the following: facing material, core material, adhesive material, methods of material fabrication, core geometry (density, cell size, orientation, and so forth), adhesive thickness, specimen geometry and associated measurement accuracy, specimen preparation, specimen conditioning, environment of testing, specimen alignment, loading procedure, speed of testing, 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 material.
SCOPE
1.1 This test method covers the determination of shear properties of sandwich construction core materials associated with shear distortion of planes parallel to the facings. It covers the determination of shear strength parallel to the plane of the sandwich, and the shear modulus associated with strains in a plane normal to the facings. The test may be conducted on core materials bonded directly to the loading plates or the sandwich facings bonded to the plates. 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 Units—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.  
1.2.1 Within the text, the inch-pound units are shown in brackets.  
1.3 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.  
1.4 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: 14-Feb-2020
• ICS: 83.120 - Reinforced plastics
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.09 - Sandwich Construction

Relations

• Replaces: ASTM C273/C273M-19 - Standard Test Method for Shear Properties of Sandwich Core Materials
• Effective Date: 15-Feb-2020
• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM D2734-23 - Standard Test Methods for Void Content of Reinforced Plastics
• Effective Date: 01-Oct-2023
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM D5229/D5229M-20 - Standard Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite Materials
• Effective Date: 01-Mar-2020
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM D3878-19a - Standard Terminology for Composite Materials
• Effective Date: 15-Oct-2019
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D3878-19 - Standard Terminology for Composite Materials
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018
• Refers: ASTM D2584-18 - Standard Test Method for Ignition Loss of Cured Reinforced Resins
• Effective Date: 15-Sep-2018

Overview

ASTM C273/C273M-20 sets out the standard test method for determining the shear properties of sandwich core materials. These core shear properties are essential for the engineering and design of sandwich panels, which are widely used in aerospace, automotive, marine, and construction industries for their high strength-to-weight ratio. This standard provides a consistent approach to evaluating the force-deflection behavior and shear modulus of core materials used in sandwich constructions, ensuring reliable performance and quality assurance of final products.

Key Topics

• Purpose of the Test

  • Measures shear properties of sandwich construction core materials.
  • Evaluates shear strength and shear modulus based on force-deflection behavior.
  • Application of force parallel to the facings' plane.

• Core Material Types

  • Applies to both continuous (e.g., balsa wood, foam) and discontinuous (e.g., honeycomb) core materials.
  • Testing can be done directly on the core or on the sandwich panel with facings bonded to the core.

• Testing Approaches

  • Shear force is applied through bonded loading plates in either compression or tension.
  • The only valid failure mode is shear failure of the core; interface or adhesive failures are not acceptable.

• Reporting and Influencing Factors

  • Reports must include facing material, core material, adhesive, fabrication method, core geometry, adhesive thickness, specimen conditioning, and test environment.
  • Geometry, system alignment, environmental conditions, and loading procedures can significantly impact results.

• Test Validity and Precision

  • At least five specimens per test condition are recommended for statistical significance.
  • Precision and bias statements are not provided due to the lack of reference standards.

Applications

• Design and Engineering

  • Used for the qualification and design of sandwich panels in structural applications where shear strength and modulus are critical.
  • Guides material selection and panel fabrication processes to meet structural performance requirements.

• Material Specification

  • Supports specification of core materials and adhesives in manufacturing and procurement documents.
  • Enables comparison between competing materials and offers a basis for quality assurance programs.

• Research and Development

  • Valuable for R&D to evaluate new sandwich constructions, core geometries, or bonding methods.
  • Used for failure analysis and to optimize sandwich panel designs for specific applications.

• Quality Assurance

  • Provides a standardized method for acceptance testing of core materials in manufacturing.
  • Ensures consistent material properties across production batches, reducing the risk of structural failure in service.

Related Standards

• ASTM C393 - Test Method for Core Shear Properties of Sandwich Constructions by Beam Flexure; offers an alternative means to estimate shear properties.
• ASTM C271/C271M - Test Method for Density of Sandwich Core Materials.
• ASTM D792 - Test Methods for Density and Specific Gravity of Plastics by Displacement.
• ASTM D883 - Terminology Relating to Plastics.
• ASTM D2584, D2734, D3171 - Methods for measuring void content and constituent amounts in composite materials.
• ASTM D5229/D5229M - Test Method for Moisture Absorption and Conditioning of Polymer Matrix Composites.
• ASTM D5687/D5687M - Guide for Specimen Preparation of Flat Composite Panels.

---

Keywords: ASTM C273, sandwich core materials, shear properties, shear modulus, sandwich panels, force-deflection, honeycomb core, core strength, material testing, quality assurance, 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: C273/C273M − 20
Standard Test Method for
Shear Properties of Sandwich Core Materials
This standard is issued under the fixed designation C273/C273M; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the determination of shear
C271/C271M Test Method for Density of Sandwich Core
properties of sandwich construction core materials associated
Materials
with shear distortion of planes parallel to the facings. It covers
C393 Test Method for Core Shear Properties of Sandwich
the determination of shear strength parallel to the plane of the
Constructions by Beam Flexure
sandwich, and the shear modulus associated with strains in a
D792 Test Methods for Density and Specific Gravity (Rela-
plane normal to the facings.The test may be conducted on core
tive Density) of Plastics by Displacement
materials bonded directly to the loading plates or the sandwich
D883 Terminology Relating to Plastics
facings bonded to the plates. Permissible core material forms
D2584 Test Method for Ignition Loss of Cured Reinforced
include those with continuous bonding surfaces (such as balsa
Resins
wood and foams) as well as those with discontinuous bonding
D2734 TestMethodsforVoidContentofReinforcedPlastics
surfaces (such as honeycomb).
D3171 Test Methods for Constituent Content of Composite
1.2 Units—The values stated in either SI units or inch-
Materials
pound units are to be regarded separately as standard. The
D3878 Terminology for Composite Materials
values stated in each system are not necessarily exact equiva-
D5229/D5229M Test Method for MoistureAbsorption Prop-
lents; therefore, to ensure conformance with the standard, each
erties and Equilibrium Conditioning of Polymer Matrix
system shall be used independently of the other, and values
Composite Materials
from the two systems shall not be combined.
D5687/D5687M Guide for Preparation of Flat Composite
1.2.1 Within the text, the inch-pound units are shown in
Panels with Processing Guidelines for Specimen Prepara-
brackets.
tion
D5961/D5961M Test Method for Bearing Response of Poly-
1.3 This standard does not purport to address all of the
mer Matrix Composite Laminates
safety concerns, if any, associated with its use. It is the
E4 Practices for Force Verification of Testing Machines
responsibility of the user of this standard to establish appro-
E6 Terminology Relating to Methods of Mechanical Testing
priate safety, health, and environmental practices and deter-
E122 Practice for Calculating Sample Size to Estimate,With
mine the applicability of regulatory limitations prior to use.
Specified Precision, the Average for a Characteristic of a
1.4 This international standard was developed in accor-
Lot or Process
dance with internationally recognized principles on standard-
E177 Practice for Use of the Terms Precision and Bias in
ization established in the Decision on Principles for the
ASTM Test Methods
Development of International Standards, Guides and Recom-
E456 Terminology Relating to Quality and Statistics
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating
to high-modulus fibers and their composites, as well as terms
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. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Feb. 15, 2020. Published March 2020. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1951. Last previous edition approved in 2019 as C273/C273M – 19. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/C0273_C0273M-20. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C273/C273M − 20
relating to sandwich constructions. Terminology D883 defines effect.Approximate shear properties can also be obtained from
terms relating to plastics. Terminology E6 defines terms a sandwich flexure test (see Test Method C393).
relating to mechanical testing. Terminology E456 and Practice
5.3 This test method provides a standard method of obtain-
E177 define terms relating to statistics. In the event of a
ing sandwich core shear data for material specifications,
conflict between terms, Terminology D3878 shall have prece-
sandwichpaneldesign,researchanddevelopmentapplications,
dence over the other terminologies.
and quality assurance.
3.2 Symbols:
5.4 Factors that influence core shear strength and shall
therefore be reported include the following: facing material,
γ = core engineering shear strain
core material, adhesive material, methods of material
τ = core shear stress
fabrication, core geometry (density, cell size, orientation, and
b = width of specimen
so forth), adhesive thickness, specimen geometry and associ-
c = thickness of the core
CV = coefficientofvariationstatisticofasamplepopulation ated measurement accuracy, specimen preparation, specimen
conditioning, environment of testing, specimen alignment,
for a given property (in percent)
d = overall specimen thickness loading procedure, speed of testing, and adhesive void content.
G = core shear modulus
Further, core-to-facing strength may be different between
L = length of specimen
precured/bonded and co-cured facings in sandwich panels with
L' = length of fixture overhang
the same core and facing material.
P = force on specimen
S = ∆P/ ∆u, slope of initial portion of force-deflection
6. Interferences
curve
6.1 Material and Specimen Preparation—Poormaterialfab-
S = standard deviation statistic of a sample population for
n-1
rication practices, lack of control of fiber alignment, and
a given property
damage induced by improper specimen machining are known
t = first facesheet thickness (measured or nominal)
t = second facesheet thickness (measured or nominal) causes of high data scatter in composites in general. Specific
u = displacement of loading plates material factors that affect sandwich composites include vari-
x = fixture line of loading offset distance
abilityincoredensityanddegreeofcureofresininbothfacing
x¯ = mean or average (estimate of mean) of a sample
matrix material and core bonding adhesive. Important aspects
population for a given property
of sandwich panel specimen preparation that contribute to data
x = test result for an individual specimen from the sample
1 scatter are incomplete or nonuniform core bonding to facings;
population for a given property
misalignment of core and facing elements; the existence of
joints, voids, or other core and facing discontinuities; out-of-
4. Summary of Test Method
plane curvature; facing thickness variation; and surface rough-
ness. For this particular core shear test, thickness of the
4.1 This test method consists of subjecting a sandwich core
adhesive bond to honeycomb core (adhesive-filled depth into
or sandwich panel to monotonically increasing shear force
the honeycomb core cells) may affect the core shear strength
parallel to the plane of its faces. The force is transmitted to the
and modulus values depending on the core thickness.
specimen through bonded loading plates that are subjected to
opposing tensile or compressive displacements that result in a
6.2 System Alignment—Unintended loading eccentricities
shear force on the sandwich core. Core shear modulus, stress,
will cause premature failure. Every effort should be made to
and strength are reported in terms of the nominal shear area of
eliminate undesirable eccentricities from the test system. Such
the core.
eccentricities may occur as a result of misaligned grips, poor
specimen preparation, or poor alignment of the bonded loading
4.2 The only acceptable failure mode is shear failure of the
plates.
core material. Adhesive or cohesive failures, or both, at the
core-to-facesheet, facesheet-to-load-plate, or (if no facesheets
6.3 Geometry—Specific geometric factors that affect core
are used) core-to-load-plate interface are not acceptable failure
shear behavior of sandwich panels include core cell geometry
modes.
(shape, density, orientation), core thickness, and adhesive
thickness.
5. Significance and Use
6.4 Environment—Resultsareaffectedbytheenvironmental
5.1 The core shear properties are fundamental properties conditions under which the tests are conducted. Specimens
thatareusedinthedesignofsandwichpanels.Thistestmethod
tested in various environments can exhibit significant differ-
provides information on the force-deflection behavior of sand- ences in both static strength and failure mode. Critical envi-
wichconstructionsorcoreswhenloadedinshearparalleltothe
ronments must be assessed independently for each sandwich
plane of the facings. From a complete force-deflection curve, it construction tested.
is possible to compute core shear stress at any force (such as
6.5 Loading Direction—FEA analysis of the Test Method
the shear stress at proportional limit, at yield, or at maximum
C273/C273M test configurations shows that both compressive
force) and to compute an effective core shear modulus.
andtensilenormalstressconcentrationsoccurattheendsofthe
5.2 The test does not produce pure shear, but the specimen core surfaces; the highest stress concentration is of the same
length is prescribed so that secondary stresses have a minimum sense as the loading mode (that is, the tension loading mode
C273/C273M − 20
produces higher through-thickenss tensile stress concentrations
than the compression loading mode). Core shear strengths tend
to be more influenced by tensile normal stress concentrations
thancompressivenormalstresses.Theresultis,forsomecores,
the core shear strength using the Test Method C273/C273M
compression loading mode agrees well with strength results
from the Test Method C393 short beam bending test method,
whereas the Test Method C273/C273M tension loading mode
can produce a lower strength result.
7. Apparatus
7.1 Micrometers and Calipers—A micrometer witha4to
8 mm[0.16to0.32in.]nominaldiameterball-interfaceoraflat
anvil interface shall be used to measure the specimen thick-
ness. A ball interface is recommended for thickness measure-
ments when facings are bonded to the core and at least one
surface is irregular (for example, the bag-side of a thin facing
laminate that is neither smooth nor flat). A micrometer or
caliper with a flat anvil interface is recommended for thickness
measurements when facings are bonded to the core and both
surfaces are smooth (for example, tooled surfaces).Amicrom-
eter or caliper with a flat anvil interface shall be used for
measuring length and width, as well as the specimen thickness
when no facings are present. The use of alternative measure-
ment devices is permitted if specified (or agreed to) by the test
requestor and reported by the testing laboratory. The accuracy
of the instruments shall be suitable for reading to within 1 % of
the sample dimensions. For typical specimen geometries, an
FIG. 1 Plate Shear Specimens, Force Line of Action
instrument with an accuracy of 60.025 mm [60.001 in.] is
adequate for the length, width, and thickness measurements.
7.3 Testing Machine—The testing machine shall be in ac-
7.2 Test Fixtures—Either a tensile or compressive loading
cordance with Practices E4 and shall satisfy the following
mode may be used. In either case, the test specimen shall be
requirements:
rigidlysupportedbymeansofsteelplatesbondedtothefacings
7.3.1 Testing Machine Configuration—The testing machine
(seeNote1)asshowninFig.1.Thethicknessoftheplatesmay
shall have both an essentially stationary head and a movable
be varied in accordance with the strength of the sandwich (see
head.
Note2),buttheplatelengthshallbesuchthatthelineofaction
7.3.2 Drive Mechanism—The testing machine drive mecha-
of the direct tensile or compressive force shall pass through the
nism shall be capable of imparting to the movable head a
diagonallyoppositecornersofthesandwichasshowninFig.1,
controlled velocity with respect to the stationary head. The
and as calculated per Fig. 2.Acorrect line of force action may
velocity of the movable head shall be capable of being
also be obtained by modifying the core length to thickness
regulated in accordance with 11.7.
ratio, provided the specimen dimensional requirements noted
7.3.3 Force Indicator—The testing machine force-sensing
in 8.2 are fulfilled.
device shall be capable of indicating the total force being
NOTE 1—To ensure a core shear failure on some honeycomb cores, two
carried by the test specimen. This device shall be essentially
plies of adhesive must be used to bond the honeycomb to the steel plates.
free from inertia lag at the specified rate of testing and shall
This provides deeper adhesive fillets on the honeycomb cell walls.
indicate the force with an accuracy over the force range(s) of
NOTE 2—It has been found that loading plates having a bending
interest of within 61 % of the indicated value.
stiffnessperunitwidth, D= EI/ b,notlessthan2.67MN-mm /mmwidth
7.3.4 Deflectometer, Compressometer, or Extensometer—
per millimeter of core thickness (600 000 lb-in. /in. per inch of core
thickness) have performed satisfactorily.
The deflection measurement device shall be capable of mea-
suring the displacement with a precision of at least 61%.
7.2.1 Tension Loading—Either pinned or bolted load plate-
to-universal-jointtestfixtures,asshowninFig.3,maybeused.
7.4 Conditioning Chamber—When conditioning materials
The overall load-train shall be of the suspended, self-aligning
at non-laboratory environments, a temperature/vapor-level
type.
controlledenvironmentalconditioningchamberisrequiredthat
7.2.2 Compression Loading—Load plates shall taper to a shall be capable of maintaining the required temperature to
knife-edgeandfitintoV-notchloadingblocks,asshowninFig. within 63°C[65 °F] and the required relative humidity level
4. V-notch loading blocks shall be rigidly attached to the test to within 63 %. Chamber conditions shall be monitored either
machine and aligned flat and parallel to within 60.02 mm on an automated continuous basis or on a manual basis at
[60.001 in.]. regular intervals.
C273/C273M − 20
FIG. 2 Plate Shear Specimens, Fixture Length Calculations
7.5 Environmental Test Chamber—An environmental test statistically significant data, consult the procedures outlined in
chamber is required for test environments other than ambient Practice E122. Report the method of sampling.
testing laboratory conditions. This chamber shall be capable of
8.2 Geometry—The test specimens shall have a thickness
maintaining the entire test specimen at the required test
equal to the thickness of the sandwich, a width not less than
environment during the mechanical test.
50 mm [2.0 in.], and a length not less than twelve times the
thickness.
8. Sampling and Test Specimens
8.1 Sampling—Test at least five specimens per test condi- 8.3 Facesheet Thickness—Accurate measurement of
tion unless valid results can be gained through the use of fewer facesheet thicknesses is difficult after secondary bonding or
specimens, as in the case of a designed experiment. For co-bonding of facesheets and core. If direct measurement of
C273/C273M − 20
FIG. 2 Plate Shear Specimens, Fixture Length Calculations (continued)
the facesheets is not feasible, the test requestor is responsible calculations in this test method. For metallic or precured
for specifying the facesheet thicknesses to be used for the compositefacesheetswhicharesecondarilybondedtothecore,
...

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: C273/C273M − 19 C273/C273M − 20
Standard Test Method for
Shear Properties of Sandwich Core Materials
This standard is issued under the fixed designation C273/C273M; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This test method covers the determination of shear properties of sandwich construction core materials associated with shear
distortion of planes parallel to the facings. It covers the determination of shear strength parallel to the plane of the sandwich, and
the shear modulus associated with strains in a plane normal to the facings. The test may be conducted on core materials bonded
directly to the loading plates or the sandwich facings bonded to the plates. 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 Units—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.
1.2.1 Within the text, the inch-pound units are shown in brackets.
1.3 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.
1.4 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:
C271/C271M Test Method for Density of Sandwich Core Materials
C393 Test Method for Core Shear Properties of Sandwich Constructions by Beam Flexure
D792 Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement
D883 Terminology Relating to Plastics
D2584 Test Method for Ignition Loss of Cured Reinforced Resins
D2734 Test Methods for Void Content of Reinforced Plastics
D3171 Test Methods for Constituent Content of Composite Materials
D3878 Terminology for Composite Materials
D5229/D5229M Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite
Materials
D5687/D5687M Guide for Preparation of Flat Composite Panels with Processing Guidelines for Specimen Preparation
D5961/D5961M Test Method for Bearing Response of Polymer Matrix Composite Laminates
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or
Process
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 Sept. 1, 2019Feb. 15, 2020. Published September 2019March 2020. Originally approved in 1951. Last previous edition approved in 20182019
as C273/C273M – 18.C273/C273M – 19. DOI: 10.1520/C0273_C0273M-19.10.1520/C0273_C0273M-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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
C273/C273M − 20
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E456 Terminology Relating to Quality and Statistics
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating to high-modulus fibers and their composites, as well as terms
relating to 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.
3.2 Symbols:
γ = core engineering shear strain
τ = core shear stress
b = width of specimen
c = thickness of the core
CV = coefficient of variation statistic of a sample population for a given property (in percent)
d = overall specimen thickness
G = core shear modulus
L = length of specimen
L' = length of fixture overhang
P = force on specimen
S = ΔP / Δu, slope of initial portion of force-deflection curve
S = standard deviation statistic of a sample population for a given property
n-1
t = first facesheet thickness (measured or nominal)
t = second facesheet thickness (measured or nominal)
u = displacement of loading plates
x = fixture line of loading offset distance
x¯ = mean or average (estimate of mean) of a sample population for a given property
x = test result for an individual specimen from the sample population for a given property
4. Summary of Test Method
4.1 This test method consists of subjecting a sandwich core or sandwich panel to monotonically increasing shear force parallel
to the plane of its faces. The force is transmitted to the specimen through bonded loading plates that are subjected to opposing
tensile or compressive displacements that result in a shear force on the sandwich core. Core shear modulus, stress, and strength
are reported in terms of the nominal shear area of the core.
4.2 The only acceptable failure mode is shear failure of the core material. Adhesive or cohesive failures, or both, at the
core-to-facesheet, facesheet-to-load-plate, or (if no facesheets are used) core-to-load-plate interface are not acceptable failure
modes.
5. Significance and Use
5.1 The core shear properties are fundamental properties that are used in the design of sandwich panels. This test method
provides information on the force-deflection behavior of sandwich constructions or cores when loaded in shear parallel to the plane
of the facings. From a complete force-deflection curve, it is possible to compute core shear stress at any force (such as the shear
stress at proportional limit, at yield, or at maximum force) and to compute an effective core shear modulus.
5.2 The test does not produce pure shear, but the specimen length is prescribed so that secondary stresses have a minimum
effect. Approximate shear properties can also be obtained from a sandwich flexure test (see Test Method C393).
5.3 This test method provides a standard method of obtaining sandwich core shear data for material specifications, sandwich
panel design, research and development applications, and quality assurance.
5.4 Factors that influence core shear strength and shall therefore be reported include the following: facing material, core
material, adhesive material, methods of material fabrication, core geometry (density, cell size, orientation, and so forth), adhesive
thickness, specimen geometry and associated measurement accuracy, specimen preparation, specimen conditioning, environment
of testing, specimen alignment, loading procedure, speed of testing, 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 material.
6. Interferences
6.1 Material and Specimen Preparation—Poor material fabrication practices, lack of control of fiber alignment, and damage
induced by improper specimen machining are known causes of high data scatter in composites in general. Specific material factors
that affect sandwich composites include variability in core density and degree of cure of resin in both facing matrix material and
core bonding adhesive. Important aspects of sandwich panel specimen preparation that contribute to data scatter are incomplete
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or nonuniform core bonding to facings; misalignment of core and facing elements; the existence of joints, voids, or other core and
facing discontinuities; out-of-plane curvature; facing thickness variation; and surface roughness. For this particular core shear test,
thickness of the adhesive bond to honeycomb core (adhesive-filled depth into the honeycomb core cells) may affect the core shear
strength and modulus values depending on the core thickness.
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.
6.3 Geometry—Specific geometric factors that affect core shear behavior of sandwich panels include core cell geometry (shape,
density, orientation), core thickness, 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 static strength and failure mode. Critical environments must be
assessed independently for each sandwich construction tested.
6.5 Loading Direction—FEA analysis of the Test Method C273/C273M test configurations shows that both compressive and
tensile normal stress concentrations occur at the ends of the core surfaces; the highest stress concentration is of the same sense as
the loading mode (that is, the tension loading mode produces higher through-thickenss tensile stress concentrations than the
compression loading mode). Core shear strengths tend to be more influenced by tensile normal stress concentrations than
compressive normal stresses. The result is, for some cores, the core shear strength using the Test Method C273/C273M
compression loading mode agrees well with strength results from the Test Method C393 short beam bending test method, whereas
the Test Method C273/C273M tension loading mode can produce a lower strength result.
7. Apparatus
7.1 Micrometers and Calipers—A micrometer with a 4 to 7 mm8 mm [0.16 to 0.280.32 in.] nominal diameter ball-interface or
a flat anvil interface shall be used to measure the specimen thickness. A ball interface is recommended for thickness measurements
when facings are bonded to the core and at least one surface is irregular (for example, the bag-side of a thin facing laminate that
is neither smooth nor flat). A micrometer or caliper with a flat anvil interface is recommended for thickness measurements when
facings are bonded to the core and both surfaces are smooth (for example, tooled surfaces). A micrometer or caliper with a flat anvil
interface shall be used for measuring length and width, as well as the specimen thickness when no facings are present. The use
of alternative measurement devices is permitted if specified (or agreed to) by the test requestor and reported by the testing
laboratory. The accuracy of the instruments shall be suitable for reading to within 1 % of the sample dimensions. For typical
specimen geometries, an instrument with an accuracy of 60.025 mm [60.001 in.] is adequate for the length, width, and thickness
measurements.
7.2 Test Fixtures—Either a tensile or compressive loading mode may be used. In either case, the test specimen shall be rigidly
supported by means of steel plates bonded to the facings (see Note 1) as shown in Fig. 1. The thickness of the plates may be varied
in accordance with the strength of the sandwich (see Note 2), but the plate length shall be such that the line of action of the direct
tensile or compressive force shall pass through the diagonally opposite corners of the sandwich as shown in Fig. 1, and as
calculated per Fig. 2. A correct line of loadforce action may also be obtained by modifying the core length to thickness ratio,
provided the specimen dimensional requirements noted in 8.2 are fulfilled.
NOTE 1—To ensure a core shear failure on some honeycomb cores, two plies of adhesive must be used to bond the honeycomb to the steel plates. This
provides deeper adhesive fillets on the honeycomb cell walls.
NOTE 2—It has been found that loading plates having a bending stiffness per unit width, D = EI / b, not less than 2.67 MN - mm /mm width per
millimeter of core thickness (600 000 lb-in. /in. per inch of core thickness) have performed satisfactorily.
7.2.1 Tension Loading—Either pinned or bolted load plate-to-universal-joint test fixtures, as shown in Fig. 3, may be used. The
overall load-train shall be of the suspended, self-aligning type.
7.2.2 Compression Loading—Load plates shall taper to a knife-edge and fit into V-notch loading blocks, as shown in Fig. 4.
V-notch loading blocks shall be rigidly attached to the test machine and aligned flat and parallel to within 60.02 mm [60.001 in.].
7.3 Testing Machine—The testing machine shall be in accordance with Practices E4 and shall satisfy the following
requirements:
7.3.1 Testing Machine Configuration—The testing machine shall have both an essentially stationary head and a movable head.
7.3.2 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.
7.3.3 Force Indicator—The testing machine force-sensing device shall be capable of indicating the total force being carried by
the test specimen. This device shall be essentially free from inertia lag at the specified rate of testing and shall indicate the force
with an accuracy over the force range(s) of interest of within 61 % of the indicated value.
7.3.4 Deflectometer, Compressometer, or Extensometer—The deflection measurement device shall be capable of measuring the
displacement with a precision of at least 61 %.
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FIG. 1 Plate Shear Specimens, Force Line of Action
7.4 Conditioning Chamber—When conditioning materials at non-laboratory environments, a temperature/vapor-level controlled
environmental conditioning chamber is required that shall be capable of maintaining the required temperature to within 63 °C
[65 °F] and the required relative humidity level to within 63 %. Chamber conditions shall be monitored either on an automated
continuous basis or on a manual basis at regular intervals.
7.5 Environmental Test Chamber—An environmental test chamber is required for test environments other than ambient testing
laboratory conditions. This chamber shall be capable of maintaining the entire test specimen at the required test environment during
the mechanical test.
8. Sampling and Test Specimens
8.1 Sampling—Test at least five specimens per test condition unless valid results can be gained through the use of fewer
specimens, as in the case of a designed experiment. For statistically significant data, consult the procedures outlined in Practice
E122. Report the method of sampling.
8.2 Geometry—The test specimens shall have a thickness equal to the thickness of the sandwich, a width not less than 50 mm
[2.0 in.], and a length not less than twelve times the thickness.
8.3 Facesheet Thickness—Accurate measurement of facesheet thicknesses is difficult after secondary bonding or co-bonding of
facesheets and core. If direct measurement of the facesheets is not feasible, the test requestor is responsible for specifying the
facesheet thicknesses to be used for the calculations in this test method. For metallic or precured composite facesheets which are
secondarily bonded to the core, the facesheet thickness should be measured prior to bonding. In these cases, the test requestor may
specify that either or both measured and nominal thicknesses be used in the calculations. For co-bonded composite
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