ASTM D8453/D8453M-22

Standard Practice for Open-Hole Flexural Strength of Sandwich Constructions

SIGNIFICANCE AND USE
5.1 This practice provides supplemental instructions that allow the use of Test Method D7249/D7249M to determine the open-hole (notched) strength of the sandwich panel facesheets for structural design allowables, material specifications, and research and development. Due to the curvature of the flexural test specimen when loaded, the open-hole sandwich facesheet strength from this test may not be equivalent to the open-hole sandwich facesheet strength of sandwich structures subjected to pure edgewise (in-plane) tension or compression.  
5.2 Factors that influence the notched facesheet strength and shall therefore be reported include the following: facesheet material, core material, adhesive material, methods of material fabrication, facesheet stacking sequence and overall thickness, core geometry (cell size), core density, adhesive thickness, specimen geometry (including hole diameter, diameter-to-thickness ratio, and width-to-diameter ratio), specimen preparation (especially of the hole), specimen conditioning, environment of testing, specimen alignment, loading procedure, speed of testing, facesheet void content, adhesive void content, and facesheet volume percent reinforcement. Further, notched facesheet strength may be different between precured/bonded and co-cured facesheets of the same material.
SCOPE
1.1 This practice provides instructions for modifying the long beam flexure test method to determine open-hole facesheet properties of flat sandwich constructions subjected to flexure in such a manner that the applied moments produce curvature of the sandwich facesheet planes and result in compressive and tensile forces in the facesheets. 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). This practice supplements Test Method D7249/D7249M with provisions for testing specimens that contain a centrally located through-hole.  
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 may not be exact equivalents; therefore, to enforce 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: 31-Oct-2022
• ICS: 91.080.99 - Other structures
• ICS: 91.100.99 - Other construction materials
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.09 - Sandwich Construction

Relations

• 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 D3878-19a - Standard Terminology for Composite Materials
• Effective Date: 15-Oct-2019
• Refers: ASTM D3878-19 - Standard Terminology for Composite Materials
• Effective Date: 15-Apr-2019
• 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
• 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
• Refers: ASTM D3878-16 - Standard Terminology for Composite Materials
• Effective Date: 01-Aug-2016
• Refers: ASTM D7249/D7249M-16e1 - Standard Test Method for Facing Properties of Sandwich Constructions by Long Beam Flexure
• Effective Date: 01-Jul-2016
• Refers: ASTM D7249/D7249M-16 - Standard Test Method for Facing Properties of Sandwich Constructions by Long Beam Flexure
• Effective Date: 01-Jul-2016
• Refers: ASTM D3878-15 - Standard Terminology for Composite Materials
• Effective Date: 01-Jul-2015
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM E456-13ae3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM E456-13ae1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013

Overview

ASTM D8453/D8453M-22 is the standard practice for determining the open-hole flexural strength of sandwich constructions. Developed by ASTM International, this practice provides instructions to modify the long beam flexure test method for evaluating the properties of sandwich panel facesheets with a centrally located through-hole, under flexural loading. This information is critical for structural design allowables, material specifications, and research and development related to composite sandwich constructions. The standard applies to both continuous (e.g., balsa wood, foam) and discontinuous (e.g., honeycomb) core materials.

Key Topics

• Test Modification: Supplements ASTM D7249/D7249M by enabling evaluation of facesheets with open-holes, simulating notched or damaged conditions as seen in real-world applications.
• Flexural Testing: Involves 4-point bending to produce compressive and tensile forces in the facesheet planes, focusing on the influence of an open-hole on failure strength.
• Specimen Requirements: Details the geometry, hole size, and facesheet properties-which can influence test results, including diameter-to-thickness ratio and width-to-diameter ratio.
• Material Factors: Strength is affected by facesheet and core material, adhesive type, layup sequence, overall thickness, core density, adhesive thickness, and environmental conditioning.
• Failure Modes: Only failures occurring at/through the open-hole in one or both facesheets are considered valid for ultimate strength characterization.
• Data Reporting: Stresses the importance of documenting hole preparation, material fabrication methods, and failure modes for reproducibility and traceability.

Applications

The open-hole flexural strength test for sandwich constructions is especially relevant in industries and research areas that employ composite sandwich structures, including:

• Aerospace: Widely used for aircraft panels and structural elements where notches or holes are present for fasteners or system integration. Understanding open-hole flexural strength helps define structural design allowables and anticipate behavior under service conditions.
• Marine and Automotive: Useful for lightweight panels and hulls that require holes for fixtures or to accommodate design features.
• Civil Construction: Applicable for sandwich panels in buildings and infrastructure, providing insights into durability and safety when modifications or penetrations are necessary.
• Research & Development: Supports development of new composite materials and optimization of sandwich construction design, especially when durability around discontinuities is a concern.

Related Standards

ASTM D8453/D8453M-22 is part of a suite of sandwich construction test standards. Key related standards include:

• ASTM D7249/D7249M: Test method for facesheet properties of sandwich constructions by long beam flexure.
• ASTM D3410/D3410M: Test method for compressive properties of polymer matrix composites.
• ASTM D3878: Terminology for composite materials, providing definitions relevant to sandwich structures.
• ASTM D5687/D5687M: Guide for preparation of flat composite panels and specimen preparation guidelines.
• ASTM E6, E122, and E177: Standards relating to mechanical testing terminology, sample size calculation, and use of precision/bias in ASTM test methods.

Practical Value

By following ASTM D8453/D8453M-22, engineers and researchers can:

• Ensure Consistency: Utilize standardized procedures for generating reliable open-hole flexural strength data.
• Support Design Decisions: Establish accurate material allowables for structures with necessary discontinuities such as holes or notches.
• Enhance Safety: Predict and mitigate failure risks around openings in critical sandwich panels.
• Facilitate Material Comparison: Benchmark and validate new composite sandwich configurations under realistic, notched conditions.

This standard, developed according to internationally recognized guidelines, provides a robust framework for evaluating the mechanical performance of sandwich constructions with open-holes-filling a crucial test gap for advanced composite engineering.

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: D8453/D8453M − 22
Standard Practice for
Open-Hole Flexural Strength of Sandwich Constructions
This standard is issued under the fixed designation D8453/D8453M; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice provides instructions for modifying the
D3410/D3410M Test Method for Compressive Properties of
long beam flexure test method to determine open-hole
Polymer Matrix Composite Materials with Unsupported
facesheet properties of flat sandwich constructions subjected to
Gage Section by Shear Loading
flexure in such a manner that the applied moments produce
D3878 Terminology for Composite Materials
curvature of the sandwich facesheet planes and result in
D5687/D5687M Guide for Preparation of Flat Composite
compressive and tensile forces in the facesheets. Permissible
Panels with Processing Guidelines for Specimen Prepara-
core material forms include those with continuous bonding
tion
surfaces (such as balsa wood and foams) as well as those with
D7249/D7249M Test Method for Facesheet Properties of
discontinuous bonding surfaces (such as honeycomb). This
Sandwich Constructions by Long Beam Flexure
practice supplements Test Method D7249/D7249M with pro-
E6 Terminology Relating to Methods of Mechanical Testing
visions for testing specimens that contain a centrally located
E122 Practice for Calculating Sample Size to Estimate,With
through-hole.
Specified Precision, the Average for a Characteristic of a
1.2 Units—The values stated in either SI units or inch- Lot or Process
E177 Practice for Use of the Terms Precision and Bias in
pound units are to be regarded separately as standard. The
ASTM Test Methods
values stated in each system may not be exact equivalents;
E456 Terminology Relating to Quality and Statistics
therefore, to enforce conformance with the standard, each
system shall be used independently of the other, and values
3. Terminology
from the two systems shall not be combined.
3.1 Definitions—Terminology D3878 defines terms relating
1.2.1 Within the text, the inch-pound units are shown in
to high-modulus fibers and their composites, as well as terms
brackets.
relating to sandwich constructions. Terminology E6 defines
1.3 This standard does not purport to address all of the
terms relating to mechanical testing. Terminology E456 and
safety concerns, if any, associated with its use. It is the
Practice E177 define terms relating to statistics. In the event of
responsibility of the user of this standard to establish appro-
a conflict between terms, Terminology D3878 shall have
priate safety, health, and environmental practices and deter-
precedence over the other standards.
mine the applicability of regulatory limitations prior to use.
3.2 Definitions of Terms Specific to This Standard:
1.4 This international standard was developed in accor-
NOTE 1—If the term represents a physical quantity, its analytical
dance with internationally recognized principles on standard-
dimensionsarestatedimmediatelyfollowingtheterm(orlettersymbol)in
ization established in the Decision on Principles for the
fundamental dimension form, using the following ASTM standard sym-
Development of International Standards, Guides and Recom-
bology for fundamental dimensions, shown within square brackets: [M]
mendations issued by the World Trade Organization Technical for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature,
and [nd] for nondimensional quantities. Use of these symbols is restricted
Barriers to Trade (TBT) Committee.
to analytical dimensions when used with square brackets, as the symbols
may have other definitions when used without the brackets.
This practice is under the jurisdiction ofASTM Committee D30 on Composite
Materials and is the direct responsibility of Subcommittee D30.09 on Sandwich For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Construction. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Current edition approved Nov. 1, 2022. Published December 2022. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D8453_D8453M-22. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8453/D8453M − 22
3.2.1 diameter-to-facesheet thickness ratio, D/t [nd], n—in thickness ratio, and width-to-diameter ratio), specimen prepa-
an open-hole specimen, the ratio of the hole diameter to the ration (especially of the hole), specimen conditioning, environ-
facesheet thickness. ment of testing, specimen alignment, loading procedure, speed
3.2.1.1 Discussion—The diameter-to-thickness ratio may be of testing, facesheet void content, adhesive void content, and
either a nominal value determined from nominal dimensions or facesheet volume percent reinforcement. Further, notched
an actual value determined from measured dimensions. facesheet strength may be different between precured/bonded
3.2.2 width-to-diameter ratio, b/D [nd], n—in an open-hole and co-cured facesheets of the same material.
specimen, the ratio of the specimen width to the hole diameter.
3.2.2.1 Discussion—The width-to-diameter ratio may be
6. Interferences
either a nominal value determined from nominal dimensions or
6.1 Hole Preparation—Because of the dominating presence
an actual value determined from measured dimensions.
of the notch, and the lack of need to measure the material
3.3 Symbols: response,resultsfromthistestmethodarerelativelyinsensitive
b—width of specimen across hole
to parameters that would be of concern in an unnotched tensile
D—hole diameter orcompressivepropertytest,suchasnotches,undercuts,rough
ohu
F —facesheet ultimate open-hole (notched) strength (ten-
or uneven surfaces, and delaminations due to inappropriate
sile or compressive)
machining methods. However, since the notch has a dominant
L—length of loading span effect on the strength, consistent preparation of the hole,
P—applied force
without damage to the sandwich specimen, is important to
S—length of support span meaningful results. Damage caused by hole preparation may
t—facesheet thickness
affect strength results. Some types of facesheet damage, such
as longitudinal splitting and delamination, can blunt the stress
4. Summary of Practice
concentration caused by the hole, increasing the force-carrying
capacity of the specimen and the calculated strength. Other
4.1 This practice consists of subjecting a long beam of
types of damage can reduce the calculated strength.
sandwich construction, with a centrally located through-hole,
to a bending moment normal to the plane of the sandwich,
6.2 Material and Specimen Preparation—Poormaterialfab-
using a 4-point loading fixture in accordance withTest Method
rication practices, lack of control of fiber alignment, and
D7249/D7249M. Ultimate strength is calculated based on the
damage induced by improper specimen machining are known
gross cross-sectional area, disregarding the presence of the
causes of high material data scatter in composites in general.
hole. While the hole causes a stress concentration and reduced
Specific material factors that affect sandwich constructions
net section, it is common aerospace practice to develop
include variability in core density and degree of cure of resin
notched design allowable strengths based on gross section
in both the facesheet matrix material and core bonding adhe-
stress to account for various stress concentrations (flaws,
sive. Important aspects of sandwich core specimen preparation
damage, and so forth) not explicitly modeled in the stress
that contribute to data scatter include the existence of joints,
analysis.
voids or other core discontinuities, out-of-plane curvature, and
surface roughness.
4.2 The only acceptable failure modes for ultimate open-
hole sandwich facesheet strength are those that occur at/
6.3 Geometry—Results are affected by the ratio of specimen
through the hole in one or both of the facesheets.
widthtoholediameter(b/D);aratioof6isrecommendedifthe
notch sensitivity is unknown. Results may also be affected by
4.3 Theopen-holestrengthisdeterminedineithertensionor
the ratio of hole diameter to facesheet thickness (D/t). Results
compression dependent upon the facesheet of the sandwich
may also be affected by facesheet thickness, and facesheet
panel in which the failure occurs through the hole.
surface flatness (toolside or bagside surface in compression).
5. Significance and Use
6.4 Core Material—If the core material has insufficient
5.1 This practice provides supplemental instructions that shear or compressive strength, it is possible that the core may
allow the use ofTest Method D7249/D7249M to determine the locally crush at or near the loading points, thereby resulting in
open-hole (notched) strength of the sandwich panel facesheets facesheet failure due to local stresses. In other cases, facesheet
for structural design allowables, material specifications, and failure can cause local core crushing. When there is both
research and development. Due to the curvature of the flexural facesheet and core failure in the vicinity of one of the loading
test specimen when loaded, the open-hole sandwich facesheet points, it can be difficult to determine the failure sequence in a
strength from this test may not be equivalent to the open-hole postmortem inspection of the specimen as the failed specimens
sandwich facesheet strength of sandwich structures subjected look very similar for both sequences.
to pure edgewise (in-plane) tension or compression.
6.5 Environment—Resultsareaffectedbytheenvironmental
5.2 Factorsthatinfluencethenotchedfacesheetstrengthand conditions under which specimens are conditioned, as well as
shall therefore be reported include the following: facesheet the conditions under which the tests are conducted. Specimens
material, core material, adhesive material, methods of material tested in various environments can exhibit significant differ-
fabrication, facesheet stacking sequence and overall thickness, ences in both strength behavior and failure mode. Experience
core geometry (cell size), core density, adhesive thickness, has demonstrated that cold temperature environments are
specimen geometry (including hole diameter, diameter-to- generally critical for notched tensile strength, while elevated
D8453/D8453M − 22
temperature, humid environments are generally critical for 8.2 Geometry—Thestandardspecimenconfigurationshould
notched compressive strength. However, critical environments be used whenever the specimen design equations in Test
must be assessed independently for each specific combination Method D7249/D7249M indicate that the specimen will pro-
of core material, facesheet material, facesheet stacking duce the desired facesheet failure mode. In cases where the
sequence, and core-to-facesheet interfacial adhesive (if used) standard specimen configuration will not produce a facesheet
that is tested. failure, a non-standard specimen shall be designed to produce
a facesheet failure mode.
6.6 Material Orthotropy—The degree of facesheet orthot-
8.2.1 Standard Specimen Configuration—The standard test
ropy strongly affects the failure mode and measured notched
specimen shall be rectangular in cross section, with a width of
strength.Valid notched strength results should only be reported
72 mm [3.0 in.], length of 600 mm [24.0 in.], and a centrally
when appropriate failure modes are observed, in accordance
located through hole with a diameter of 12 mm [0.50 in.]. The
with 11.5.
depth of the specimen shall be equal to the thickness of the
6.7 Facesheet Thickness Scaling—Thick facesheet sand-
sandwich construction.
wich structures do not necessarily produce the same facesheet
8.2.2 Non-Standard Specimen Configurations—For non-
notched strength as thin facesheet sandwich structures with the
standard specimen geometries (see Fig. 3), the width shall be
same facesheet orientation (that is, facesheet notched strength
not less than twice the total thickness nor more than six times
does not always scale linearly with facesheet thickness). Thus,
the total thickness, not less than three times the dimension of a
data gathered using this test method may not translate directly
core cell, nor greater than one quarter the span length. The
into equivalent thick-facesheet properties.
specimen length shall be equal to the support span length plus
50 mm [2 in.] or plus one half the sandwich thickness, which-
7. Apparatus
ever is the greater. Limitations on the maximum specimen
7.1 Loading Fixtures:
width are intended to allow for the use of simplified sandwich
7.1.1 Standard Fixture Configuration—The standard load-
beam calculations; plate flexure effects must be considered for
ing fixture shall consist of a 4-point loading configuration with
specimens that are wider than the restrictions specified above.
two support bars that span the specimen width located below
The hole diameter should be large enough to produce a
the specimen, and two loading bars that span the specimen
statistically significant reduction in strength but small enough
width located on the top of the specimen (Fig. 1). The force
to minimize finite width effects.Aspecimen width-to-diameter
shall be applied vertically through the loading bars, with the
(b/D) of 6 is recommended.
support bars fixed in place in the test machine. The standard
8.2.3 Specimen Design—Proper design of the sandwich
loading fixture shall have the centerlines of the support bars
flexure test specimen for determining compressive or tensile
separated by a distance of 560 mm [22.0 in.] and the center-
strength of the facesheets is required to avoid core crushing,
lines of the lo
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