ASTM D7766/D7766M-23

Standard Practice for Damage Resistance Testing of Sandwich Constructions

SIGNIFICANCE AND USE
5.1 This practice provides supplemental instructions that allow Test Methods D6264/D6264M (for quasi-static indentation testing) and D7136/D7136M (for drop-weight impact testing) to determine damage resistance properties of sandwich constructions. Susceptibility to damage from concentrated out-of-plane forces is one of the major design concerns of many structures made using sandwich constructions. Knowledge of the damage resistance properties of a sandwich panel is useful for product development and material selection.  
5.2 Sandwich damage resistance testing can serve the following purposes:  
5.2.1 To establish quantitatively the effects of facing geometry, facing stacking sequence, facing-to-core interface, core geometry (cell size, cell wall thickness, core thickness, etc.), core density, core strength, processing and environmental variables on the damage resistance of a particular sandwich panel to a concentrated quasi-static indentation force, drop-weight impact force, or impact energy.  
5.2.2 To compare quantitatively the relative values of the damage resistance parameters for sandwich constructions with different facing, core or adhesive materials. The damage response parameters can include dent depth, damage dimensions and location(s), indentation or impact force magnitudes, impact energy magnitudes, as well as the force versus time curve.  
5.2.3 To impart damage in a specimen for subsequent damage tolerance tests, such as Test Method D8287/D8287M and Practice D8388/D8388M.  
5.2.4 Quasi-static indentation tests can also be used to identify a specific sequence of damage events (only the final damage state is identifiable after a drop-weight impact test).  
5.3 The properties obtained using these practices can provide guidance in regard to the anticipated damage resistance capability of sandwich structures with similar materials, geometry, stacking sequence, and so forth. However, it must be understood that the damage resistance of a sandwich structu...
SCOPE
1.1 This practice provides instructions for modifying laminate quasi-static indentation and drop-weight impact test methods to determine damage resistance properties of sandwich constructions. 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, truss cores and fiber-reinforced cores).  
1.2 This practice supplements Test Methods D6264/D6264M (for quasi-static indentation testing) and D7136/D7136M (for drop-weight impact testing) with provisions for testing sandwich specimens. Several important test specimen parameters (for example, facing thickness, core thickness and core density) are not mandated by this practice; however, repeatable results require that these parameters be specified and reported.  
1.3 Three test procedures are provided. Procedures A and B correspond to D6264/D6264M test procedures for rigidlybacked and edge-supported test conditions, respectively. Procedure C corresponds to D7136/D7136M test procedures. All three procedures are suitable for imparting damage to a sandwich specimen in preparation for subsequent damage tolerance testing in accordance with Test Method D8287/D8287M (compressive loading) and Practice D8388/D8388M (flexural loading).  
1.4 In general, Procedure A is considered to be the most suitable procedure for comparative damage resistance assessments, due to reduced influence of flexural stiffness and support fixture characteristics upon damage formation. However, the selection of a test procedure and associated support conditions should be done in consideration of the intended structural application, and as such Procedures B and C may be more appropriate for comparative purposes for some applications.  
1.5 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 ...

General Information

• Status: Published
• Publication Date: 30-Apr-2023
• ICS: 83.120 - Reinforced plastics
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.09 - Sandwich Construction

Relations

• 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 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 D3878-18 - Standard Terminology for Composite Materials
• Effective Date: 01-Apr-2018
• Refers: ASTM E456-13A(2017)e3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017

Overview

ASTM D7766/D7766M-23: Standard Practice for Damage Resistance Testing of Sandwich Constructions sets out supplemental procedures for assessing the damage resistance of sandwich structures. Developed by ASTM Committee D30 on Composite Materials, this standard complements existing test methods (ASTM D6264/D6264M and D7136/D7136M) to provide a robust framework for conducting quasi-static indentation and drop-weight impact tests on sandwich constructions. Sandwich composites, featuring various core materials such as foams, honeycomb, and balsa wood, are widely used in aerospace, automotive, marine, and civil infrastructure due to their high strength-to-weight ratios. However, their layered nature makes them susceptible to damage from out-of-plane forces, highlighting the importance of standardized damage resistance testing.

Key Topics

• Supplemental Guidance: Provides detailed instructions to adapt standard indentation and impact testing methods for sandwich structures.

• Test Procedures:

  • Procedure A: Quasi-static indentation, rigidly-backed condition - preferred for comparative studies due to minimized impact from flexural stiffness.
  • Procedure B: Quasi-static indentation, edge-supported condition - reflects damage resistance away from rigid support.
  • Procedure C: Drop-weight impact, edge-supported condition - simulates real-world impact scenarios.

• Core & Facing Material Permissibility: Applies to both continuous-core (e.g. foams, balsa) and discontinuous-core (e.g. honeycomb, truss) structures.

• Important Variables: Test results are impacted by parameters such as facing and core geometry, core density, adhesive properties, environmental factors, and support conditions; these should be specified and reported for accurate data comparison.

• Test Result Metrics: Evaluates dent depth, damage area, force and energy at failure, and force-time relation to comprehensively characterize damage response.

• Test Preparation: Addresses requirements for specimen fabrication, calibration, measuring equipment, and environmental conditioning to ensure reliable, repeatable results.

Applications

The damage resistance testing of sandwich structures is critical for:

• Product Development: Enables manufacturers and designers to compare material systems, panel configurations, and processing methods, accelerating innovation in lightweight structural components.
• Material Selection: Supports objective comparison of competing sandwich panel constructions (different facings, cores, adhesives), guiding optimal choices for specific applications.
• Performance Benchmarking: Quantifies the impact of geometric or environmental variables, such as core thickness or moisture, on the damage resistance of composite panels.
• Residual Strength Assessment: Facilitates preparation of specimens with controlled damage states for subsequent damage tolerance testing (e.g., compressive and flexural residual strength evaluations).
• Quality Control: Ensures consistency in production by establishing repeatable procedures for sandwich panel damage resistance assessment.

Industries where this standard is applied include:

• Aerospace: Aircraft fuselage panels, interior floorboards, structural fairings.
• Automotive: Lightweight vehicle body panels, battery enclosures.
• Marine: Hull sections, bulkheads in boats and ships.
• Civil infrastructure: Building panels, bridge decks.

Related Standards

• ASTM D6264/D6264M: Test Method for Quasi-Static Indentation of Fiber-Reinforced Polymer-Matrix Composites.
• ASTM D7136/D7136M: Test Method for Drop-Weight Impact Testing of Fiber-Reinforced Polymer Matrix Composites.
• ASTM D8287/D8287M: Test Method for Compressive Residual Strength of Damaged Sandwich Composite Panels.
• ASTM D8388/D8388M: Practice for Flexural Residual Strength Testing of Damaged Sandwich Constructions.
• ASTM D792: Test Methods for Density and Specific Gravity of Plastics.
• ASTM D5687/D5687M: Guide for Preparation of Flat Composite Panels.
• ASTM E2533: Guide for Nondestructive Examination of Polymer Matrix Composites in Aerospace Applications.

Summary

ASTM D7766/D7766M-23 is an essential standard for laboratories and manufacturers working with sandwich composite panels. By providing a consistent, rigorous approach to damage resistance testing, it ensures results are reliable, comparable, and valuable for design, manufacturing, and safety assurance. Adhering to this standard helps industry professionals effectively evaluate and improve the performance of advanced sandwich structures in demanding applications.

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: D7766/D7766M − 23
Standard Practice for
Damage Resistance Testing of Sandwich Constructions
This standard is issued under the fixed designation D7766/D7766M; 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 values stated in each system are not necessarily exact equiva-
lents; therefore, to ensure conformance with the standard, each
1.1 This practice provides instructions for modifying lami-
system shall be used independently of the other, and values
nate quasi-static indentation and drop-weight impact test meth-
from the two systems shall not be combined.
ods to determine damage resistance properties of sandwich
1.5.1 Within the text the inch-pound units are shown in
constructions. Permissible core material forms include those
brackets.
with continuous bonding surfaces (such as balsa wood and
1.6 This standard does not purport to address all of the
foams) as well as those with discontinuous bonding surfaces
safety concerns, if any, associated with its use. It is the
(such as honeycomb, truss cores and fiber-reinforced cores).
responsibility of the user of this standard to establish appro-
1.2 This practice supplements Test Methods D6264/
priate safety, health, and environmental practices and deter-
D6264M (for quasi-static indentation testing) and D7136/
mine the applicability of regulatory limitations prior to use.
D7136M (for drop-weight impact testing) with provisions for
1.7 This international standard was developed in accor-
testing sandwich specimens. Several important test specimen
dance with internationally recognized principles on standard-
parameters (for example, facing thickness, core thickness and
ization established in the Decision on Principles for the
core density) are not mandated by this practice; however,
Development of International Standards, Guides and Recom-
repeatable results require that these parameters be specified and
mendations issued by the World Trade Organization Technical
reported.
Barriers to Trade (TBT) Committee.
1.3 Three test procedures are provided. Procedures A and B
correspond to D6264/D6264M test procedures for rigidly-
2. Referenced Documents
backed and edge-supported test conditions, respectively. Pro-
2.1 ASTM Standards:
cedure C corresponds to D7136/D7136M test procedures. All
D792 Test Methods for Density and Specific Gravity (Rela-
three procedures are suitable for imparting damage to a
tive Density) of Plastics by Displacement
sandwich specimen in preparation for subsequent damage
D883 Terminology Relating to Plastics
tolerance testing in accordance with Test Method D8287/
D3171 Test Methods for Constituent Content of Composite
D8287M (compressive loading) and Practice D8388/D8388M
Materials
(flexural loading).
D3878 Terminology for Composite Materials
1.4 In general, Procedure A is considered to be the most
D5229/D5229M Test Method for Moisture Absorption Prop-
suitable procedure for comparative damage resistance
erties and Equilibrium Conditioning of Polymer Matrix
assessments, due to reduced influence of flexural stiffness and
Composite Materials
support fixture characteristics upon damage formation.
D5687/D5687M Guide for Preparation of Flat Composite
However, the selection of a test procedure and associated
Panels with Processing Guidelines for Specimen Prepara-
support conditions should be done in consideration of the
tion
intended structural application, and as such Procedures B and
D6264/D6264M Test Method for Measuring the Damage
C may be more appropriate for comparative purposes for some
Resistance of a Fiber-Reinforced Polymer-Matrix Com-
applications.
posite to a Concentrated Quasi-Static Indentation Force
D7136/D7136M Test Method for Measuring the Damage
1.5 Units—The values stated in either SI units or inch-
Resistance of a Fiber-Reinforced Polymer Matrix Com-
pound units are to be regarded separately as standard. The
posite to a Drop-Weight Impact Event
This practice 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 May 1, 2023. Published June 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2011. Last previous edition approved in 2016 as D7766/D7766M – 16. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D7766_D7766M-23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7766/D7766M − 23
D8287/D8287M Test Method for Compressive Residual event during a drop-weight impact test. The dent depth shall be
Strength Properties of Damaged Sandwich Composite defined as the maximum distance in a direction normal to the
Panels face of the specimen from the lowest point in the dent to the
D8388/D8388M Practice for Flexural Residual Strength plane of the indented or impacted surface that is undisturbed by
Testing of Damaged Sandwich Constructions the dent.
E6 Terminology Relating to Methods of Mechanical Testing
3.2.3 nominal value, n—a value, existing in name only,
E122 Practice for Calculating Sample Size to Estimate, With
assigned to a measurable property for the purpose of conve-
Specified Precision, the Average for a Characteristic of a
nient designation. Tolerances may be applied to a nominal
Lot or Process
value to define an acceptable range for the property.
E177 Practice for Use of the Terms Precision and Bias in
–2
3.2.4 recorded contact force, F [MLT ], n—the force ex-
ASTM Test Methods
erted by the indenter on the specimen during a quasi-static
E456 Terminology Relating to Quality and Statistics
indentation test, or by the impactor on the specimen during a
E2533 Guide for Nondestructive Examination of Polymer
drop-weight impact test, as recorded by a force indicator.
Matrix Composites Used in Aerospace Applications
3.2.5 tip, n—the portion or component of the indenter or
2.2 Other Documents:
CMH-17-3G Composite Materials Handbook, Volume impactor which comes into contact with the test specimen first
during a quasi-static indentation or drop-weight impact test.
3—Polymer Matrix Composites: Materials Usage, Design
and Analysis
3.3 Symbols:
CMH-17-6 Composite Materials Handbook, Volume
3.3.1 E —potential energy of impactor prior to drop
6—Structural Sandwich Composites
3.3.2 t —thickness of impacted sandwich facing
MIL-HDBK-728/1 Nondestructive Testing
MIL-HDBK-731A Nondestructive Testing Methods of
4. Summary of Practices
Composite Materials—Thermography
MIL-HDBK-732A Nondestructive Testing Methods of
4.1 Procedure A—In accordance with Test Method D6264/
Composite Materials—Acoustic Emission
D6264M, but with a sandwich specimen, perform a quasi-static
MIL-HDBK-733A Nondestructive Testing Methods of
indentation test of a rigidly-backed specimen. Damage is
Composite Materials—Radiography
imparted through an out-of-plane, concentrated force applied
MIL-HDBK-787A Nondestructive Testing Methods of
by slowly pressing a displacement-controlled hemispherical
Composite Materials—Ultrasonics
indenter into the face of the specimen. The damage resistance
is quantified in terms of the resulting size, location and type of
3. Terminology
damage in the specimen.
3.1 Definitions—Terminology D3878 defines terms relating
4.2 Procedure B—In accordance with Test Method D6264/
to high-modulus fibers and their composites, as well as terms
D6264M, but with a sandwich specimen, perform a quasi-static
relating to sandwich constructions. Terminology D883 defines
indentation test of an edge-supported specimen. Damage is
terms relating to plastics. Terminology E6 defines terms
imparted through an out-of-plane, concentrated force applied
relating to mechanical testing. Terminology E456 and Practice
by slowly pressing a displacement-controlled hemispherical
E177 define terms relating to statistics. In the event of a
indenter into the face of the specimen. The damage resistance
conflict between terms, Terminology D3878 shall have prece-
is quantified in terms of the resulting size, location and type of
dence over the other terminologies.
damage in the specimen.
3.2 Definitions of Terms Specific to This Standard:
4.3 Procedure C—In accordance with Test Method D7136/
3.2.1 If the term represents a physical quantity, its analytical
D7136M, but with a sandwich specimen, perform a drop-
dimensions are stated immediately following the term (or letter
weight impact test of an edge-supported specimen. Damage is
symbol) in fundamental dimension form, using the following
imparted through an out-of-plane, concentrated impact using a
ASTM standard symbology for fundamental dimensions,
drop weight with a hemispherical striker tip. The damage
shown within square brackets: [M] for mass, [L] for length, [T]
resistance is quantified in terms of the resulting size, location
for time, [θ] for thermodynamic temperature, and [nd ] for
and type of damage in the specimen.
non-dimensional quantities. Use of these symbols is restricted
to analytical dimensions when used with square brackets, as
5. Significance and Use
the symbols may have other definitions when used without the
brackets.
5.1 This practice provides supplemental instructions that
3.2.2 dent depth, d [L], n—residual depth of the depression
allow Test Methods D6264/D6264M (for quasi-static indenta-
formed by an indenter after removal of applied force during a
tion testing) and D7136/D7136M (for drop-weight impact
quasi-static indentation test, or by an impactor after the impact
testing) to determine damage resistance properties of sandwich
constructions. Susceptibility to damage from concentrated
out-of-plane forces is one of the major design concerns of
Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale,
many structures made using sandwich constructions. Knowl-
PA 15096, http://www.sae.org.
edge of the damage resistance properties of a sandwich panel
Available from U.S. Army Materials Technology Laboratory, Watertown, MA
02471. is useful for product development and material selection.
D7766/D7766M − 23
5.2 Sandwich damage resistance testing can serve the fol- edge-supported tests in which the core shear stiffness, core
lowing purposes: shear strength and sandwich panel flexural stiffness have
greater influence upon the test results. Consequently, it is
5.2.1 To establish quantitatively the effects of facing
imperative to consider the intended assessment and structural
geometry, facing stacking sequence, facing-to-core interface,
application when selecting a test procedure for comparative
core geometry (cell size, cell wall thickness, core thickness,
purposes, and as such the use of Procedures B and C may be
etc.), core density, core strength, processing and environmental
more appropriate for some applications.
variables on the damage resistance of a particular sandwich
panel to a concentrated quasi-static indentation force, drop- 5.3.3 For some structural applications, the use of a rigidly-
backed specimen in drop-weight impact testing may be appro-
weight impact force, or impact energy.
priate. Specific procedures for such testing are not included in
5.2.2 To compare quantitatively the relative values of the
this practice, but the general approach detailed for Procedure C
damage resistance parameters for sandwich constructions with
may be useful as guidance material when conducting such
different facing, core or adhesive materials. The damage
assessments. Such tests should be performed in consideration
response parameters can include dent depth, damage dimen-
of the implications of using rigidly-backed support conditions,
sions and location(s), indentation or impact force magnitudes,
such as their effect upon contact forces and sandwich defor-
impact energy magnitudes, as well as the force versus time
mation under impact, as well as the potential for damage to the
curve.
test apparatus.
5.2.3 To impart damage in a specimen for subsequent
damage tolerance tests, such as Test Method D8287/D8287M
5.4 The standard indenter and impactor geometries have
and Practice D8388/D8388M.
blunt, hemispherical tips. Historically, these tip geometries
5.2.4 Quasi-static indentation tests can also be used to have generated a larger amount of internal damage for a given
identify a specific sequence of damage events (only the final
amount of external damage, when compared with that observed
damage state is identifiable after a drop-weight impact test).
for similar indentations or impacts using sharp tips. Alternative
indenter and impactor geometries may be appropriate depend-
5.3 The properties obtained using these practices can pro-
ing upon the damage resistance characteristics being examined.
vide guidance in regard to the anticipated damage resistance
For example, the use of sharp tip geometries may be appropri-
capability of sandwich structures with similar materials,
ate for certain facing penetration resistance assessments.
geometry, stacking sequence, and so forth. However, it must be
understood that the damage resistance of a sandwich structure 5.5 Some testing organizations may desire to use these
is highly dependent upon several factors including geometry, practices in conjunction with a subsequent damage tolerance
thickness, stiffness, mass, support conditions, and so forth. test method (such as Test Method D8287/D8287M or Practice
D8388/D8388M) to assess the residual strength of specimens
5.3.1 Significant differences in the relationships between
force/energy and the resultant damage state can result due to containing a specific damage state, such as a defined dent
depth, damage geometry, damage location, and so forth. In this
differences in these parameters. For example, properties ob-
tained using edge-supported specimens would more likely case, the testing organization should subject several specimens,
or a large panel, to multiple indentations or impacts, or both, at
reflect the damage resistance characteristics of a sandwich
various energy levels using these practices. A relationship
panel away from substructure attachments, whereas rigidly-
between force or energy and the desired damage parameter can
backed specimens would more likely reflect the behavior of a
then be developed. Subsequent residual strength tests in
panel local to substructure which resists out-of-plane deforma-
accordance with Test Method D8287/D8287M or Practice
tion. Similarly, edge-supported impact test specimen properties
D8388/D8388M can then be performed using specimens dam-
would be expected to be similar to those of a sandwich panel
aged using an interpolated energy or force level that is
with equivalent length and width dimensions, in comparison to
expected to produce the desired damage state.
those of a panel significantly larger than the test specimen,
which tends to divert a greater proportion of the impact energy
6. Interferences
into elastic deformation.
5.3.2 Procedure A (quasi-static indentation using a rigidly- 6.1 The response of a sandwich specimen to an out-of-plane
backed specimen) is considered to be the most suitable force or impact is dependent upon many factors, such as facing
procedure for comparison of the damage resistance character- material, facing thickness, facing ply thickness, facing stacking
istics of sandwich panels of varying material, geometry, sequence, facing surface flatness, facing-to-core adhesive
stacking sequence and so forth. This is because the rigid material, adhesive thickness, core material, core geometry (cell
backing plate resists out-of-plane deformation of the specimen, size, cell wall thickness, core thickness, etc.), core density,
such that the sandwich flexural stiffness and support geometry facing void content, adhesive void content, environment, panel
have less influence on damage initiation and growth behavior geometry, impactor mass, tip geometry, ratio of tip diameter to
than in edge-supported tests. However, it should be noted that core cell size, impact velocity, impact energy, and boundary
damage resistance behavior observed using rigidly-backed conditions. Consequently, comparisons cannot be made be-
specimens may not strictly translate to edge-supported appli- tween sandwich constructions unless identical test
cations. For example, sandwich constructions using cores with configurations, test conditions, and sandwich panel configura-
high compression stiffness or strength, or both (for example, tions are used. Damage resistance properties may vary based
balsa wood) may exhibit superior performance in rigidly- upon the processing and build sequence (e.g., precured/bonded
backed tests, but that performance may not strictly translate to versus co-cured facings).
D7766/D7766M − 23
6.2 Material and Specimen Preparation—Poor material fab- indentation tests and in Test Method D7136/D7136M for
rication practices, lack of control of fiber alignment, and drop-weight impact tests.
damage induced by improper specimen machining are known
causes of high data scatter in composites in general. Specific 7. Apparatus
material factors that affect sandwich composites include vari-
7.1 General Apparatus:
ability in core density and degree of cure of resin in both facing
7.1.1 Procedure A—General apparatus shall be in accor-
matrix material and core bonding adhesive. Important aspects
dance with Test Method D6264/D6264M with flat rigid sup-
of sandwich panel specimen preparation that contribute to data
port.
scatter are incomplete or nonuniform core bonding to facings,
7.1.2 Procedure B—General apparatus shall be in accor-
misalignment of core and facing elements, the existence of
dance with Test Method D6264/D6264M, with edge support
joints, voids or other core and facing discontinuities, out-of-
consisting of a single plate with a 125.0 mm 6 3.0 mm
plane curvature, facing thickness variation, and surface rough-
[5.00 in. 6 0.10 in.] diameter opening. Alternative opening
ness.
geometries may be appropriate, depending upon the sandwich
6.3 Support Fixture Characteristics—Results are affected
specimen geometry (especially thickness), flexural stiffness,
by geometry, material, and bending rigidity of the support
through-thickness shear stiffness, etc. It may be necessary to
fixture. Test results are influenced by the rigidity of the support
use alternative geometries to avoid core failure local to the
fixture and its constituents (for example, support plate, re-
edge support if the core has insufficient compression or shear
straints) relative to both the flexural rigidity and the through- strength. Tests conducted using alternative opening geometries
thickness shear rigidity of the sandwich specimen. Edge-
must be designated as such, with the opening geometry
supported test results are affected by the support fixture cut-out reported with any test results.
dimensions. Drop-weight impact tests are affected by the
7.1.3 Procedure C—General apparatus shall be in accor-
rigidity of the surface that the support fixture is located upon,
dance with Test Method D7136/D7136M, with edge support
the location of the support fixture clamps, clamp geometry, and
utilizing a plate with a rectangular cut-out. The cut-out in the
the clamping force.
plate shall be 75 mm 6 1 mm by 125 mm 6 1 mm [3.0 in. 6
0.05 in. by 5.0 in. 6 0.05 in.]. Clamps shall be used to restrain
6.4 Non-Destructive Inspection—Non-destructive inspec-
the specimen during impact. Alternative cut-out geometries
tion (NDI) results are affected by the particular method
and support conditions may be appropriate, depending upon
utilized, the inherent variability of the NDI method, the
the sandwich specimen geometry (especially thickness), flex-
experience of the operator, and so forth. Different NDI methods
ural stiffness, through-thickness shear stiffness, etc. It may be
may be required for assessing the various damage modes that
necessary to use alternative geometries to avoid core failure
may arise during sandwich damage resistance testing. Damage
local to the edge support if the core has insufficient compres-
location may also influence the selection of NDI methods.
sion or shear strength. Tests conducted using alternative cutout
6.5 Environment—Results are affected by the environmental
geometries or support conditions, or both, must be designated
conditions under which the tests are conducted. Critical envi-
as such, with the cut-out geometry and support conditions
ronments must be assessed for each specific combination of
reported with any test results.
core material, facing material and core-to-facing interfacial
NOTE 1—If the measured damage area exceed half the unsupported
adhesive (if used).
specimen width, it is recommended to examine alternative specimen and
6.6 Indentation, Impact and Relaxation Behavior—
fixture designs, which are larger and can accommodate larger damage
areas without significant interaction from edge support conditions.
Different core materials may exhibit different indentation,
impact and dent relaxation characteristics, failure mechanisms
7.2 Indenter or Impactor Tip:
and failure locations. For example, brittle cores (for example,
7.2.1 Procedures A and B—The standard indenter tip shall
fiberglass honeycomb and foam) may shatter upon impact,
be in accordance with Test Method D6264/D6264M.
allowing the facing to spring back to its un-impacted geometry
7.2.2 Procedure C—The standard impactor tip shall be in
with minimal residual indentation. Conversely, other cores (for
accordance with Test Method D7136/D7136M.
example, aramid and aluminum honeycomb) may crush and
7.2.3 Alternative tip geometries may be appropriate depend-
remain bonded to the facing after impact, resulting in measur-
ing upon the core characteristics. For example, it may be
able dent geometry. While dent relaxation begins immediately
necessary to use a tip of larger diameter to ensure that multiple
after impact, both the rate of relaxation and the time to reach an
cells are indented or impacted when testing honeycomb core.
equilibrium state may vary for different core materials and
Conversely, the use of sharp tip geometries may be appropriate
environments. For example, aramid honeycomb cores tend to
for certain facing penetration resistance assessments. Alternate
relax more than aluminum honeycomb cores, and exhibit
tip geometries may also be used to study relationships between
accelerated relaxation at elevated temperatures and humidity
visible damage geometry (for example, dent depth, dent
levels. Similarly, core failure mode and location are influenced
diameter) and the internal damage state. Tests conducted using
by the relative contributions of bending, shear and contact
alternative tip geometries must be designated as such, with the
loadings and associated core properties during indentation or
tip geometry reported with any test results.
impact.
NOTE 2—Damage resistance behavior and failure modes can vary
6.7 Other—Additional sources of potential data scatter are
depending upon the tip diameter utilized. For example, decreasing the
documented in Test Method D6264/D6264M for quasi-static indentation or impactor tip diameter in edge-supported tests can shift the
D7766/D7766M − 23
damage resistance characteristics from being core shear-dominated to
Tests conducted using alternative specimen dimensions must
being core compression-dominated.
be designated as such, with the dimensions reported with any
7.3 Dent Depth Indicator—The dent depth shall be mea- test results.
sured using a dial depth gage to permit concurrent determina-
NOTE 4—It is permissible to impact a panel larger than the specified
tion of the dent periphery. The measuring probe shall have a
dimensions, then to cut out specimens (with the indentation or impact site
spherical tip with a maximum radius of curvature of 8.0 mm
centered) for subsequent residual strength testing in accordance with Test
(0.35 in.). An instrument with an accuracy of 6 25 microm- Method D8287/D828
...

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: D7766/D7766M − 16 D7766/D7766M − 23
Standard Practice for
Damage Resistance Testing of Sandwich Constructions
This standard is issued under the fixed designation D7766/D7766M; 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 provides instructions for modifying laminate quasi-static indentation and drop-weight impact test methods to
determine damage resistance properties of sandwich constructions. 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, truss
cores and fiber-reinforced cores).
1.2 This practice supplements Test Methods D6264/D6264M (for quasi-static indentation testing) and D7136/D7136M (for
drop-weight impact testing) with provisions for testing sandwich specimens. Several important test specimen parameters (for
example, facing thickness, core thickness and core density) are not mandated by this practice; however, repeatable results require
that these parameters be specified and reported.
1.3 Three test procedures are provided. Procedures A and B correspond to D6264/D6264M test procedures for rigidlybacked and
edge-supported test conditions, respectively. Procedure C corresponds to D7136/D7136M test procedures. All three procedures are
suitable for imparting damage to a sandwich specimen in preparation for subsequent damage tolerance testing.testing in accordance
with Test Method D8287/D8287M (compressive loading) and Practice D8388/D8388M (flexural loading).
1.4 In general, Procedure A is considered to be the most suitable procedure for comparative damage resistance assessments, due
to reduced influence of flexural stiffness and support fixture characteristics upon damage formation. However, the selection of a
test procedure and associated support conditions should be done in consideration of the intended structural application, and as such
Procedures B and C may be more appropriate for comparative purposes for some applications.
1.5 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, each system mustto ensure conformance with the standard, each
system shall be used independently of the other. Combiningother, and values from the two systems may result in non-conformance
with the standard.shall not be combined.
1.5.1 Within the text the inch-pound units are shown in brackets.
1.6 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 healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
1.7 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.
This practice 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 May 15, 2016May 1, 2023. Published June 2016June 2023. Originally approved in 2011. Last previous edition approved in 20112016 as
D7766/D7766MD7766/D7766M – 16.–11. DOI: 10.1520/D7766_D7766M-16.10.1520/D7766_D7766M-23.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7766/D7766M − 23
2. Referenced Documents
2.1 ASTM Standards:
D792 Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement
D883 Terminology Relating to 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
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
D8287/D8287M Test Method for Compressive Residual Strength Properties of Damaged Sandwich Composite Panels
D8388/D8388M Practice for Flexural Residual Strength Testing of Damaged Sandwich Constructions
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
E2533 Guide for Nondestructive Examination of Polymer Matrix Composites Used in Aerospace Applications
2.2 Other Documents:
CMH-17-3G Composite Materials Handbook, Volume 3—Polymer Matrix Composites: Materials Usage, Design and Analysis
CMH-17-6 Composite Materials Handbook, Volume 6—Structural Sandwich Composites
MIL-HDBK-728/1 Nondestructive Testing
MIL-HDBK-731A Nondestructive Testing Methods of Composite Materials—Thermography
MIL-HDBK-732A Nondestructive Testing Methods of Composite Materials—Acoustic Emission
MIL-HDBK-733A Nondestructive Testing Methods of Composite Materials—Radiography
MIL-HDBK-787A Nondestructive Testing Methods of Composite Materials—Ultrasonics
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 Definitions of Terms Specific to This Standard:
3.2.1 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.
3.2.2 dent depth, d [L], n—residual depth of the depression formed by an indenter after removal of applied force during a
quasi-static indentation test, or by an impactor after the impact event during a drop-weight impact test. The dent depth shall be
defined as the maximum distance in a direction normal to the face of the specimen from the lowest point in the dent to the plane
of the indented or impacted surface that is undisturbed by the dent.
3.2.3 nominal value, n—a value, existing in name only, assigned to a measurable property for the purpose of convenient
designation. Tolerances may be applied to a nominal value to define an acceptable range for the property.
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.
Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale, PA 15096, http://www.sae.org.
Available from U.S. Army Materials Technology Laboratory, Watertown, MA 02471.
D7766/D7766M − 23
–2
3.2.4 recorded contact force, F [MLT ], n—the force exerted by the indenter on the specimen during a quasi-static indentation
test, or by the impactor on the specimen during a drop-weight impact test, as recorded by a force indicator.
3.2.5 tip, n—the portion or component of the indenter or impactor which comes into contact with the test specimen first during
a quasi-static indentation or drop-weight impact test.
3.3 Symbols:
3.3.1 E —potential energy of impactor prior to drop
3.3.2 t —thickness of impacted sandwich facing
4. Summary of Practices
4.1 Procedure A—In accordance with Test Method D6264/D6264M, but with a sandwich specimen, perform a quasi-static
indentation test of a rigidly-backed specimen. Damage is imparted through an out-of-plane, concentrated force applied by slowly
pressing a displacement-controlled hemispherical indenter into the face of the specimen. The damage resistance is quantified in
terms of the resulting size, location and type of damage in the specimen.
4.2 Procedure B—In accordance with Test Method D6264/D6264M, but with a sandwich specimen, perform a quasi-static
indentation test of an edge-supported specimen. Damage is imparted through an out-of-plane, concentrated force applied by slowly
pressing a displacement-controlled hemispherical indenter into the face of the specimen. The damage resistance is quantified in
terms of the resulting size, location and type of damage in the specimen.
4.3 Procedure C—In accordance with Test Method D7136/D7136M, but with a sandwich specimen, perform a drop-weight impact
test of an edge-supported specimen. Damage is imparted through an out-of-plane, concentrated impact using a drop weight with
a hemispherical striker tip. The damage resistance is quantified in terms of the resulting size, location and type of damage in the
specimen.
5. Significance and Use
5.1 This practice provides supplemental instructions that allow Test Methods D6264/D6264M (for quasi-static indentation testing)
and D7136/D7136M (for drop-weight impact testing) to determine damage resistance properties of sandwich constructions.
Susceptibility to damage from concentrated out-of-plane forces is one of the major design concerns of many structures made using
sandwich constructions. Knowledge of the damage resistance properties of a sandwich panel is useful for product development and
material selection.
5.2 Sandwich damage resistance testing can serve the following purposes:
5.2.1 To establish quantitatively the effects of facing geometry, facing stacking sequence, facing-to-core interface, core geometry
(cell size, cell wall thickness, core thickness, etc.), core density, core strength, processing and environmental variables on the
damage resistance of a particular sandwich panel to a concentrated quasi-static indentation force, drop-weight impact force, or
impact energy.
5.2.2 To compare quantitatively the relative values of the damage resistance parameters for sandwich constructions with different
facing, core or adhesive materials. The damage response parameters can include dent depth, damage dimensions and location(s),
indentation or impact force magnitudes, impact energy magnitudes, as well as the force versus time curve.
5.2.3 To impart damage in a specimen for subsequent damage tolerance tests.tests, such as Test Method D8287/D8287M and
Practice D8388/D8388M.
5.2.4 Quasi-static indentation tests can also be used to identify a specific sequence of damage events (only the final damage state
is identifiable after a drop-weight impact test).
5.3 The properties obtained using these practices can provide guidance in regard to the anticipated damage resistance capability
D7766/D7766M − 23
of sandwich structures with similar materials, geometry, stacking sequence, and so forth. However, it must be understood that the
damage resistance of a sandwich structure is highly dependent upon several factors including geometry, thickness, stiffness, mass,
support conditions, and so forth.
5.3.1 Significant differences in the relationships between force/energy and the resultant damage state can result due to differences
in these parameters. For example, properties obtained using edge-supported specimens would more likely reflect the damage
resistance characteristics of a sandwich panel away from substructure attachments, whereas rigidly-backed specimens would more
likely reflect the behavior of a panel local to substructure which resists out-of-plane deformation. Similarly, edge-supported impact
test specimen properties would be expected to be similar to those of a sandwich panel with equivalent length and width dimensions,
in comparison to those of a panel significantly larger than the test specimen, which tends to divert a greater proportion of the impact
energy into elastic deformation.
5.3.2 Procedure A (quasi-static indentation using a rigidly-backed specimen) is considered to be the most suitable procedure for
comparison of the damage resistance characteristics of sandwich panels of varying material, geometry, stacking sequence and so
forth. This is because the rigid backing plate resists out-of-plane deformation of the specimen, such that the sandwich flexural
stiffness and support geometry have less influence on damage initiation and growth behavior than in edge-supported tests.
However, it should be noted that damage resistance behavior observed using rigidly-backed specimens may not strictly translate
to edge-supported applications. For example, sandwich constructions using cores with high compression stiffness or strength, or
both (e.g., (for example, balsa wood) may exhibit superior performance in rigidly-backed tests, but that performance may not
strictly translate to edge-supported tests in which the core shear stiffness, core shear strength and sandwich panel flexural stiffness
have greater influence upon the test results. Consequently, it is imperative to consider the intended assessment and structural
application when selecting a test procedure for comparative purposes, and as such the use of Procedures B and C may be more
appropriate for some applications.
5.3.3 For some structural applications, the use of a rigidly-backed specimen in drop-weight impact testing may be appropriate.
Specific procedures for such testing are not included in this practice, but the general approach detailed for Procedure C may be
useful as guidance material when conducting such assessments. Such tests should be performed in consideration of the implications
of using rigidly-backed support conditions, such as their effect upon contact forces and sandwich deformation under impact, as well
as the potential for damage to the test apparatus.
5.4 The standard indenter and impactor geometries have blunt, hemispherical tips. Historically, these tip geometries have
generated a larger amount of internal damage for a given amount of external damage, when compared with that observed for
similar indentations or impacts using sharp tips. Alternative indenter and impactor geometries may be appropriate depending upon
the damage resistance characteristics being examined. For example, the use of sharp tip geometries may be appropriate for certain
facing penetration resistance assessments.
5.5 Some testing organizations may desire to use these practices in conjunction with a subsequent damage tolerance test method
(such as Test Method D8287/D8287M or Practice D8388/D8388M) to assess the residual strength of specimens containing a
specific damage state, such as a defined dent depth, damage geometry, damage location, and so forth. In this case, the testing
organization should subject several specimens, or a large panel, to multiple indentations or impacts, or both, at various energy
levels using these practices. A relationship between force or energy and the desired damage parameter can then be developed.
Subsequent residual strength tests in accordance with Test Method D8287/D8287M or Practice D8388/D8388M can then be
performed using specimens damaged using an interpolated energy or force level that is expected to produce the desired damage
state.
6. Interferences
6.1 The response of a sandwich specimen to an out-of-plane force or impact is dependent upon many factors, such as facing
material, facing thickness, facing ply thickness, facing stacking sequence, facing surface flatness, facing-to-core adhesive material,
adhesive thickness, core material, core geometry (cell size, cell wall thickness, core thickness, etc.), core density, facing void
content, adhesive void content, environment, panel geometry, impactor mass, tip geometry, ratio of tip diameter to core cell size,
impact velocity, impact energy, and boundary conditions. Consequently, comparisons cannot be made between sandwich
constructions unless identical test configurations, test conditions, and sandwich panel configurations are used. Damage resistance
properties may vary based upon the processing and build sequence (e.g., precured/bonded versus co-cured facings).
6.2 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
D7766/D7766M − 23
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
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.
6.3 Support Fixture Characteristics—Results are affected by geometry, material, and bending rigidity of the support fixture. Test
results are influenced by the rigidity of the support fixture and its constituents (e.g., (for example, support plate, restraints) relative
to both the flexural rigidity and the through-thickness shear rigidity of the sandwich specimen. Edge-supported test results are
affected by the support fixture cut-out dimensions. Drop-weight impact tests are affected by the rigidity of the surface that the
support fixture is located upon, the location of the support fixture clamps, clamp geometry, and the clamping force.
6.4 Non-Destructive Inspection—Non-destructive inspection (NDI) results are affected by the particular method utilized, the
inherent variability of the NDI method, the experience of the operator, and so forth. Different NDI methods may be required for
assessing the various damage modes that may arise during sandwich damage resistance testing. Damage location may also
influence the selection of NDI methods.
6.5 Environment—Results are affected by the environmental conditions under which the tests are conducted. Critical environments
must be assessed for each specific combination of core material, facing material and core-to-facing interfacial adhesive (if used).
6.6 Indentation, Impact and Relaxation Behavior—Different core materials may exhibit different indentation, impact and dent
relaxation characteristics, failure mechanisms and failure locations. For example, brittle cores (e.g., (for example, fiberglass
honeycomb and foam) may shatter upon impact, allowing the facing to spring back to its un-impacted geometry with minimal
residual indentation. Conversely, other cores (e.g., (for example, aramid and aluminum honeycomb) may crush and remain bonded
to the facing after impact, resulting in measurable dent geometry. While dent relaxation begins immediately after impact, both the
rate of relaxation and the time to reach an equilibrium state may vary for different core materials and environments. For example,
aramid honeycomb cores tend to relax more than aluminum honeycomb cores, and exhibit accelerated relaxation at elevated
temperatures and humidity levels. Similarly, core failure mode and location are influenced by the relative contributions of bending,
shear and contact loadings and associated core properties during indentation or impact.
6.7 Other—Additional sources of potential data scatter are documented in Test Method D6264/D6264M for quasi-static
indentation tests and in Test Method D7136/D7136M for drop-weight impact tests.
7. Apparatus
7.1 General Apparatus:
7.1.1 Procedure A—General apparatus shall be in accordance with Test Method D6264/D6264M with flat rigid support.
7.1.2 Procedure B—General apparatus shall be in accordance with Test Method D6264/D6264M, with edge support consisting of
a single plate with a 125.0 6 3.0 mm [5.00 6 0.10 in.] 125.0 mm 6 3.0 mm [5.00 in. 6 0.10 in.] diameter opening. Alternative
opening geometries may be appropriate, depending upon the sandwich specimen geometry (especially thickness), flexural stiffness,
through-thickness shear stiffness, etc. It may be necessary to use alternative geometries to avoid core failure local to the edge
support if the core has insufficient compression or shear strength. Tests conducted using alternative opening geometries must be
designated as such, with the opening geometry reported with any test results.
7.1.3 Procedure C—General apparatus shall be in accordance with Test Method D7136/D7136M, with edge support utilizing a
plate with a rectangular cut-out. The cut-out in the plate shall be 75 6 1 mm by 125 6 1 mm [3.0 6 0.05 in. by 5.0 6 0.05 in.].
75 mm 6 1 mm by 125 mm 6 1 mm [3.0 in. 6 0.05 in. by 5.0 in. 6 0.05 in.]. Clamps shall be used to restrain the specimen during
impact. Alternative cut-out geometries and support conditions may be appropriate, depending upon the sandwich specimen
geometry (especially thickness), flexural stiffness, through-thickness shear stiffness, etc. It may be necessary to use alternative
geometries to avoid core failure local to the edge support if the core has insufficient compression or shear strength. Tests conducted
using alternative cutout geometries or support conditions, or both, must be designated as such, with the cut-out geometry and
support conditions reported with any test results.
NOTE 1—If the measured damage area exceed half the unsupported specimen width, it is recommended to examine alternative specimen and fixture
designs, which are larger and can accommodate larger damage areas without significant interaction from edge support conditions.
D7766/D7766M − 23
7.2 Indenter or Impactor Tip:
7.2.1 Procedures A and B—The standard indenter tip shall be in accordance with Test Method D6264/D6264M.
7.2.2 Procedure C—The standard impactor tip shall be in accordance with Test Method D7136/D7136M.
7.2.3 Alternative tip geometries may be appropriate depending upon the core characteristics. For example, it may be necessary
to use a tip of larger diameter to ensure that multiple cells are indented or impacted when testing honeycomb core. Conversely,
the use of sharp tip geometries may be appropriate for certain facing penetration resistance assessments. Alternate tip geometries
may also be used to study relationships between visible damage geometry (e.g., (for example, dent depth, dent diameter) and the
internal damage state. Tests conducted using alternative tip geometries must be designated as such, with the tip geometry reported
with any test results.
NOTE 2—Damage resistance behavior and failure modes can vary depending upon the tip diameter utilized. For example, decreasing the indentation or
impactor tip diameter in edge-supported tests can shift the damage resistance characteristics from being core shear-dominated to being core
compression-dominated.
7.3 Dent Depth Indicator—The dent depth shall be measured using a dial depth gage to permit concurrent determination of the
dent periphery. The measuring probe shall have a spherical tip with a maximum radius of curvature of 8.0 mm (0.35 in.). An
instrument with an accuracy of 6 25 micrometers [6 0.001 in.] is desirable for depth measurement.
7.4 Micrometers and Calipers—A micrometer with a 4 to 7 mm [0.16 to 0.28 in.] 4 mm to 8 mm [0.16 in. to 0.32 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 at least one surface is irregular (e.g. (for example, the bag-side of a thin facing face sheet
laminate that is neither smooth nor flat). A micrometer or caliper with a flat anvil interface is recommended for thickness
measurements when both surfaces are smooth (e.g. (for example, tooled surfaces). A micrometer or caliper with a flat anvil
interface shall be used for measuring length and width. The use of alternative measurement devic
...