ASTM D7956/D7956M-16

Standard Practice for Compressive Testing of Thin Damaged Laminates Using a Sandwich Long Beam Flexure Specimen

SIGNIFICANCE AND USE
5.1 This practice provides a standard method of testing damaged composite laminates which are too thin to be tested using typical anti-buckling fixtures, such as those used in Test Method D7137/D7137M. The laminate is first impacted or indented in order to produce a damage state representative of actual monolithic solid laminate structure. Impacting or static indentation is not performed on an assembled sandwich panel, as the damage state is altered by energy absorption in the core and by support of the core during the impact or indentation event. After damaging, the laminate is bonded onto the core with the impacted or indentation side of the laminate against the core, and with a localized un-bonded area encompassing the damage site. Fig. 1 illustrates the adhesive removal to avoid the damaged area and the assembly of the sandwich specimen with the impacted damaged laminate flipped over from the impacting or indentation orientation. The final assembled sandwich specimen is then tested using a long beam flexure setup with the damaged laminate being on the compression side. The sandwich panel configuration is used as a form of anti-buckling support for the thin damaged laminate.  
5.2 Susceptibility to damage from concentrated out-of-plane forces is one of the major design concerns of many structures made of advanced composite laminates. Knowledge of the damage resistance and damage tolerance properties of a laminated composite plate is useful for product development and material selection.  
5.3 The residual strength data obtained using this test method is used in research and development activities as well as for design allowables; however the results are specific to the geometry and physical conditions tested and are generally not scalable to other configurations.  
5.4 The properties obtained using this test method can provide guidance in regard to the anticipated damage tolerance capability of composite structures of similar material, thickness, stacking sequ...
SCOPE
1.1 This practice covers an approach for compressive testing thin damaged multidirectional polymer matrix composite laminates reinforced by high-modulus fibers using a sandwich long beam flexure specimen. It provides a test configuration in which the core does not constrain any protruding back side damage. It is limited to testing of monolithic solid laminates which are too thin to be tested using typical anti-buckling fixtures. It does not cover compressive testing of damaged sandwich panel facings. The composite material forms are limited to continuous-fiber or discontinuous-fiber (tape or fabric, or both) reinforced composites in which the laminate is balanced and symmetric with respect to the test direction  
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.  
1.2.1 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 and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Published
• Publication Date: 31-Aug-2016
• ICS: 83.140.20 - Laminated sheets
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.09 - Sandwich Construction

Relations

• Replaces: ASTM D7956/D7956M-14 - Standard Practice for Compressive Testing of Thin Damaged Laminates Using a Sandwich Long Beam Fixture Specimen
• Effective Date: 01-Sep-2016
• 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 E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM D7249/D7249M-20 - Standard Test Method for Facesheet Properties of Sandwich Constructions by Long Beam Flexure
• Effective Date: 01-Feb-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 D3878-19 - Standard Terminology for Composite Materials
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• 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 D7249/D7249M-18 - Standard Test Method for Facesheet Properties of Sandwich Constructions by Long Beam Flexure
• Effective Date: 01-Apr-2018
• Refers: ASTM D3878-18 - Standard Terminology for Composite Materials
• Effective Date: 01-Apr-2018

Overview

ASTM D7956/D7956M-16 - Standard Practice for Compressive Testing of Thin Damaged Laminates Using a Sandwich Long Beam Flexure Specimen establishes a recognized method for evaluating the residual compressive strength of thin, damaged composite laminates that are unsuitable for traditional anti-buckling testing fixtures. This standard is essential for manufacturers, engineers, and researchers working with advanced polymer matrix composite materials reinforced with high-modulus fibers, such as those used in aerospace, automotive, and other critical infrastructure sectors.

By bonding a previously impacted or indented laminate to a core (with a deliberate unbonded region at the damage site), a sandwich panel is created and tested in long beam flexure. This setup provides anti-buckling support and allows for accurate measurement of compressive strength after impact or indentation damage, supporting informed decisions on material selection and structural design.

Key Topics

• Purpose and Significance

  • Provides a standardized approach to compressive testing for thin, damaged composite laminates
  • Addresses limitations of traditional anti-buckling fixtures for very thin monolithic laminates
  • Enables testing of composites damaged by drop-weight impact or quasi-static indentation

• Test Specimen Preparation

  • Damaged laminate is bonded to a core and back-side facing, forming a sandwich specimen
  • Localized unbonded adhesive area ensures the damage site is not supported by the core, preserving the authentic damage state
  • Testing is performed with the damaged laminate under compression, using a long beam flexure configuration

• Data and Reporting

  • Measures compressive residual strength and deformation response after impact or indentation
  • Results provide insights into damage tolerance, but are specific to the material form, geometry, and test configuration
  • Reporting requirements include full details on specimen preparation, material type, damage size and location, and test environment

• Scope Limitations

  • Applies only to thin, balanced, and symmetric monolithic laminates with continuous or discontinuous fiber reinforcement
  • Not intended for testing sandwich panel facings or thick laminates
  • Each test configuration and environmental condition must be reported due to sensitivity to these factors

Applications

• Aerospace and Automotive

  • Used to determine the damage resistance and residual compressive strength of thin structural components, such as skins and webs, after impact
  • Critical for evaluating safety margins and certifying new material systems for primary and secondary structures

• Material Development

  • Assists in the selection and optimization of composite materials by providing data on damage tolerance and post-damage performance
  • Supports R&D for products requiring lightweight, high-performance materials

• Quality Control

  • Guides manufacturing process improvement and assessment of damage impacts during fabrication
  • Used for comparative studies between different material systems and layups, provided the specimens are prepared and tested under identical conditions

Related Standards

This practice references and complements several other key ASTM standards for composite testing and terminology:

• ASTM D7136/D7136M - Drop-weight impact resistance testing of polymer matrix composites
• ASTM D7137/D7137M - Compressive residual strength after impact on composite plates
• ASTM D6264/D6264M - Quasi-static indentation damage resistance testing
• ASTM D7249/D7249M - Facing properties of sandwich constructions by long beam flexure
• ASTM D3410 - Compressive properties of polymer matrix composites by shear loading
• ASTM D3878 - Terminology for composite materials
• ASTM D883 - Terminology relating to plastics

ASTM D7956/D7956M-16 is an essential standard in the composite materials sector, enabling reliable compressive strength testing of thin damaged laminates for enhanced safety, product development, and quality assurance across transportation and high-performance engineering industries.

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: D7956/D7956M − 16
Standard Practice for
Compressive Testing of Thin Damaged Laminates Using a
Sandwich Long Beam Flexure Specimen
This standard is issued under the fixed designation D7956/D7956M; 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 Matrix Composite Materials with Unsupported Gage Sec-
tion by Shear Loading
1.1 This practice covers an approach for compressive test-
D6264/D6264M Test Method for Measuring the Damage
ing thin damaged multidirectional polymer matrix composite
Resistance of a Fiber-Reinforced Polymer-Matrix Com-
laminates reinforced by high-modulus fibers using a sandwich
posite to a Concentrated Quasi-Static Indentation Force
long beam flexure specimen. It provides a test configuration in
D7136/D7136M Test Method for Measuring the Damage
which the core does not constrain any protruding back side
Resistance of a Fiber-Reinforced Polymer Matrix Com-
damage. It is limited to testing of monolithic solid laminates
posite to a Drop-Weight Impact Event
which are too thin to be tested using typical anti-buckling
D7137/D7137M Test Method for Compressive Residual
fixtures. It does not cover compressive testing of damaged
StrengthPropertiesofDamagedPolymerMatrixCompos-
sandwich panel facings. The composite material forms are
ite Plates
limited to continuous-fiber or discontinuous-fiber (tape or
D7249/D7249M Test Method for Facing Properties of Sand-
fabric, or both) reinforced composites in which the laminate is
wich Constructions by Long Beam Flexure
balanced and symmetric with respect to the test direction
E6 Terminology Relating to Methods of Mechanical Testing
1.2 The values stated in either SI units or inch-pound units
E122 Practice for Calculating Sample Size to Estimate,With
are to be regarded separately as standard. The values stated in
Specified Precision, the Average for a Characteristic of a
each system may not be exact equivalents; therefore, each
Lot or Process
system shall be used independently of the other. Combining
E177 Practice for Use of the Terms Precision and Bias in
values from the two systems may result in non-conformance
ASTM Test Methods
with the standard.
E456 Terminology Relating to Quality and Statistics
1.2.1 Within the text the inch-pound units are shown in
brackets.
3. Terminology
1.3 This standard does not purport to address all of the
3.1 Definitions—Terminology D3878 defines terms relating
safety concerns, if any, associated with its use. It is the
to high-modulus fibers and their composites, as well as terms
responsibility of the user of this standard to establish appro-
relating to sandwich constructions. Terminology D883 defines
priate safety and health practices and determine the applica-
terms relating to plastics. Terminology E6 defines terms
bility of regulatory limitations prior to use.
relating to mechanical testing. Terminology E456 and Practice
E177 define terms relating to statistics. In the event of a
2. Referenced Documents
conflict between terms, Terminology D3878 shall have prece-
2.1 ASTM Standards:
dence over the other terminologies.
D883 Terminology Relating to Plastics
D3878 Terminology for Composite Materials
4. Summary of Practice
D3410 Test Method for Compressive Properties of Polymer
4.1 This practice consists of fabricating a composite
laminate, damaging the laminate using either Test Method
D6264/D6264M or Test Method D7136/D7136M, bonding the
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.09 on impacted or indented side of the laminate onto core and a back
Sandwich Construction.
side facing to form a sandwich panel, and testing the damaged
Current edition approved Sept. 1, 2016. Published September 2016. Originally
laminate in compression using Test Method D7249/D7249M.
approved in 2014. Last previous edition approved in 2014 as -14. DOI: 10.1520/
D7956_D7956M-16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 5. Significance and Use
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
5.1 This practice provides a standard method of testing
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. damaged composite laminates which are too thin to be tested
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7956/D7956M − 16
using typical anti-buckling fixtures, such as those used in Test geometry and physical conditions tested and are generally not
Method D7137/D7137M. The laminate is first impacted or scalable to other configurations.
indented in order to produce a damage state representative of
5.4 The properties obtained using this test method can
actual monolithic solid laminate structure. Impacting or static
provide guidance in regard to the anticipated damage tolerance
indentation is not performed on an assembled sandwich panel,
capability of composite structures of similar material,
as the damage state is altered by energy absorption in the core
thickness,stackingsequence,andsoforth.However,itmustbe
and by support of the core during the impact or indentation
understood that the damage tolerance of a composite structure
event. After damaging, the laminate is bonded onto the core
is highly dependent upon several factors including geometry,
with the impacted or indentation side of the laminate against
stiffness, support conditions, and so forth. Significant differ-
the core, and with a localized un-bonded area encompassing
ences in the relationships between the existent damage state
thedamagesite.Fig.1illustratestheadhesiveremovaltoavoid
and the residual compressive strength can result due to
the damaged area and the assembly of the sandwich specimen
differences in these parameters. For example, residual strength
with the impacted damaged laminate flipped over from the
and stiffness properties obtained using this test method would
impacting or indentation orientation. The final assembled
more likely reflect the damage tolerance characteristics of an
sandwich specimen is then tested using a long beam flexure
un-stiffened monolithic skin or web than that of a skin attached
setup with the damaged laminate being on the compression
to substructure which resists out-of-plane deformation.
side. The sandwich panel configuration is used as a form of
anti-buckling support for the thin damaged laminate.
5.5 The reporting section requires items that tend to influ-
5.2 Susceptibilitytodamagefromconcentratedout-of-plane
ence residual compressive strength to be reported; these
forces is one of the major design concerns of many structures
include the following: material, methods of material
made of advanced composite laminates. Knowledge of the
fabrication, accuracy of lay-up orientation, laminate stacking
damage resistance and damage tolerance properties of a
sequence and overall thickness, specimen geometry, specimen
laminated composite plate is useful for product development
preparation, specimen conditioning, environment of testing,
and material selection.
void content, volume percent reinforcement, type, size and
location of damage (including method of non-destructive
5.3 The residual strength data obtained using this test
method is used in research and development activities as well inspection (NDI)), fixture geometry, time at temperature, and
as for design allowables; however the results are specific to the speed of testing.
FIG. 1 Sandwich Specimen Assembly
D7956/D7956M − 16
5.6 Properties that result from the residual strength assess- 7. Sampling and Test Specimens
ment include the following: compressive residual strength
7.1 Sampling—Test at least five specimens per test condi-
CAI
F .
tion unless valid results can be gained through the use of fewer
specimens, as in the case of a designed experiment. For
6. Interferences
statistically significant data, consult the procedures outlined in
Practice E122. Report the method of sampling.
6.1 The response of a damaged specimen is dependent upon
many factors, such as laminate thickness, ply thickness, stack-
7.2 Specimen and Fixture Geometry—The test requestor
ing sequence, environment, damage type, damage geometry, shall specify all specimen dimensions and materials along with
damage location, and loading/support conditions. the loading fixture dimensions. Refer to Test Method D7249/
Consequently, comparisons cannot be made between materials D7249Mforsandwichbeamspecimensizingrequirementsand
unless identical test configurations, test conditions, and lami- guidelines.
nate configurations are used. Therefore, all details of the test 7.2.1 Specimen—The test specimens shall be rectangular in
cross section. The width of the specimen shall be at least three
configurationshallbereportedintheresults.Specificstructural
(3)timesthewidthofthemajordamagearea(asdeterminedby
configurations and boundary conditions must be considered
NDI).Themajordamageareaisdefinedastheregionofimpact
when applying the data generated using this test method to
damage that generally extends through the entire laminate
design applications.
thickness; generally it does not include splitting or delamina-
6.2 Material Orthotropy—The degree of laminate orthot-
tion of the surface ply on the opposite side from the impact
ropy strongly affects the failure mode and measured compres-
(typically, the major damage area is approximately circular on
sive residual strength.
the NDI scan image). Any such backside damage that is not
included in the major damage area should not be greater than
6.3 Thickness Scaling—Thick composite structures do not
one-half ( ⁄2) the specimen width nor extend to near the edges
necessarily fail at the same strengths as thin structures with the
of the specimen. If there is uncertainty over the damage area to
same laminate orientation (that is, strength does not always
use for specimen sizing, the
...

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: D7956/D7956M − 14 D7956/D7956M − 16
Standard Practice for
Compressive Testing of Thin Damaged Laminates Using a
Sandwich Long Beam FixtureFlexure Specimen
This standard is issued under the fixed designation D7956/D7956M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers an approach for compressive testing thin damaged multidirectional polymer matrix composite
laminates reinforced by high-modulus fibers using a sandwich long beam flexure specimen. It provides a test configuration in
which the core does not constrain any protruding back side damage. It is limited to testing of monolithic solid laminates which
are too thin to be tested using typical anti-buckling fixtures. It does not cover compressive testing of damaged sandwich panel
facings. The composite material forms are limited to continuous-fiber or discontinuous-fiber (tape or fabric, or both) reinforced
composites in which the laminate is balanced and symmetric with respect to the test direction
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.2.1 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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
C274 Terminology of Structural Sandwich Constructions (Withdrawn 2016)
D883 Terminology Relating to Plastics
D3878 Terminology for Composite Materials
D3410 Test Method for Compressive Properties of Polymer Matrix Composite Materials with Unsupported Gage Section by
Shear Loading
D6264/D6264M Test Method for Measuring the Damage Resistance of a Fiber-Reinforced Polymer-Matrix Composite to a
Concentrated Quasi-Static Indentation Force
D7136/D7136M Test Method for Measuring the Damage Resistance of a Fiber-Reinforced Polymer Matrix Composite to a
Drop-Weight Impact Event
D7137/D7137M Test Method for Compressive Residual Strength Properties of Damaged Polymer Matrix Composite Plates
D7249/D7249M Test Method for Facing Properties of Sandwich Constructions by Long Beam Flexure
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
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)
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 Aug. 1, 2014Sept. 1, 2016. Published September 2014September 2016. Originally approved in 2014. Last previous edition approved in 2014
as -14. DOI: 10.1520/D7956_D7956M-14.10.1520/D7956_D7956M-16.
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
D7956/D7956M − 16
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating to high-modulus fibers and their composites.
Terminologycomposites, as C274 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.
4. Summary of Practice
4.1 This practice consists of fabricating a composite laminate, damaging the laminate using either Test Method D6264/D6264M
or Test Method D7136/D7136M, bonding the impacted or indented side of the laminate onto core and a back side facing to form
a sandwich panel, and testing the damaged laminate in compression using Test Method D7249/D7249M.
5. Significance and Use
5.1 This practice provides a standard method of testing damaged composite laminates which are too thin to be tested using
typical anti-buckling fixtures, such as those used in Test Method D7137/D7137M. The laminate is first impacted or indented in
order to produce a damage state representative of actual monolithic solid laminate structure. Impacting or static indentation is not
performed on an assembled sandwich panel, as the damage state is altered by energy absorption in the core and by support of the
core during the impact or indentation event. After damaging, the laminate is bonded onto the core with the impacted or indentation
side of the laminate against the core, and with a localized un-bonded area encompassing the damage site. Fig. 1 illustrates the
adhesive removal to avoid the damaged area and the assembly of the sandwich specimen with the impacted damaged laminate
flipped over from the impacting or indentation orientation. The final assembled sandwich specimen is then tested using a long beam
flexure setup with the damaged laminate being on the compression side. The sandwich panel configuration is used as a form of
anti-buckling support for the thin damaged laminate.
5.2 Susceptibility to damage from concentrated out-of-plane forces is one of the major design concerns of many structures made
of advanced composite laminates. Knowledge of the damage resistance and damage tolerance properties of a laminated composite
plate is useful for product development and material selection.
5.3 The residual strength data obtained using this test method is used in research and development activities as well as for design
allowables; however the results are specific to the geometry and physical conditions tested and are generally not scalable to other
configurations.
FIG. 1 Sandwich Specimen Assembly
D7956/D7956M − 16
5.4 The properties obtained using this test method can provide guidance in regard to the anticipated damage tolerance capability
of composite structures of similar material, thickness, stacking sequence, and so forth. However, it must be understood that the
damage tolerance of a composite structure is highly dependent upon several factors including geometry, stiffness, support
conditions, and so forth. Significant differences in the relationships between the existent damage state and the residual compressive
strength can result due to differences in these parameters. For example, residual strength and stiffness properties obtained using
this test method would more likely reflect the damage tolerance characteristics of an un-stiffened monolithic skin or web than that
of a skin attached to substructure which resists out-of-plane deformation.
5.5 The reporting section requires items that tend to influence residual compressive strength to be reported; these include the
following: material, methods of material fabrication, accuracy of lay-up orientation, laminate stacking sequence and overall
thickness, specimen geometry, specimen preparation, specimen conditioning, environment of testing, void content, volume percent
reinforcement, type, size and location of damage (including method of non-destructive inspection (NDI)), fixture geometry, time
at temperature, and speed of testing.
CAI
5.6 Properties that result from the residual strength assessment include the following: compressive residual strength F .
6. Interferences
6.1 The response of a damaged specimen is dependent upon many factors, such as laminate thickness, ply thickness, stacking
sequence, environment, damage type, damage geometry, damage location, and loading/support conditions. Consequently,
comparisons cannot be made between materials unless identical test configurations, test conditions, and laminate configurations
are used. Therefore, all details of the test configuration shall be reported in the results. Specific structural configurations and
boundary conditions must be considered when applying the data generated using this test method to design applications.
6.2 Material Orthotropy—The degree of laminate orthotropy strongly affects the failure mode and measured compressive
residual strength.
6.3 Thickness Scaling—Thick composite structures do not necessarily fail at the same strengths as thin structures with the same
laminate orientation (that is, strength does not always scale linearly with thickness). Further, the damage state for a given level of
impact or indentation energy or measured surface dent depth varies with laminate thickness. Thus, data gathered using this test
method may not translate directly into equivalent thick-structure properties.
6.4 Damage Geometry and Location—The size, shape, and location of damage (both within the plane of the plate and
through-the-thickness) can significantly affect the deformation and strength behavior of the specimen. Edge effects, boundary
constraints, and the damaged stress/strain field can interact if the damage size becomes too large relative to the length and width
dimensions of the specimen.
6.5 Environment—Results are affected by the environmental conditions under which specimens are conditioned, as well as the
conditions under which the tests are conducted. Specimens tested in various environments can exhibit significant differences in
stiffness. Critical environments must be assessed independently for each specific combination of core material, facing material, and
core-to-facing interfacial adhesive (if used) that is tested.
6.6 Core Material—If the core material has insufficient shear or compressive strength, it
...