ASTM D8454/D8454M-22

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: D8454/D8454M − 22
Standard Test Method for
Open-Hole Compressive Strength of Sandwich
Constructions
This standard is issued under the fixed designation D8454/D8454M; 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 1.7 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method determines the open-hole compressive
responsibility of the user of this standard to establish appro-
strength of sandwich constructions in a direction parallel to the
priate safety, health, and environmental practices and deter-
sandwich facesheet plane. Permissible core material forms
mine the applicability of regulatory limitations prior to use.
include those with continuous bonding surfaces (such as balsa
1.8 This international standard was developed in accor-
wood and foams) as well as those with discontinuous bonding
dance with internationally recognized principles on standard-
surfaces (such as honeycomb).
ization established in the Decision on Principles for the
1.2 Several important test specimen parameters (for
Development of International Standards, Guides and Recom-
example, facesheet thickness, core thickness, and core density)
mendations issued by the World Trade Organization Technical
are not mandated by this test method; however, repeatable
Barriers to Trade (TBT) Committee.
results require that these parameters be specified and reported.
1.3 The method utilizes a flat, rectangular specimen, with a 2. Referenced Documents
centrally located open through-hole, which is tested under
2.1 ASTM Standards:
edgewise compressive loading using a stabilization fixture.
C364 Test Method for Edgewise Compressive Strength of
Sandwich Constructions
1.4 The properties generated by this test method are highly
D792 Test Methods for Density and Specific Gravity (Rela-
dependent upon several factors, which include: specimen
tive Density) of Plastics by Displacement
geometry, sandwich component materials and dimensions
D883 Terminology Relating to Plastics
(facesheet, core, and adhesive), methods of fabrication, and
D3171 Test Methods for Constituent Content of Composite
boundary conditions.Thus, results are generally not scalable to
Materials
other sandwich constructions, and are particular to the combi-
nation of geometric and physical conditions tested. D3878 Terminology for Composite Materials
D5229/D5229M Test Method for MoistureAbsorption Prop-
1.5 This test method can be used to test unnotched
erties and Equilibrium Conditioning of Polymer Matrix
specimens, but care should be taken to prevent undesirable
Composite Materials
failure modes such as end crushing.ASTMTest Methods C364
D5687/D5687M Guide for Preparation of Flat Composite
or D7249/D7249M are the recommended test methods for
Panels with Processing Guidelines for Specimen Prepara-
unnotched sandwich panel compression strength or long beam
tion
flexure, respectively.
D6484 Test Method for Open-Hole Compressive Strength of
1.6 Units—The values stated in either SI units or inch-
Polymer Matrix Composite Laminates
pound units are to be regarded separately as standard. The
D7249/D7249M Test Method for Facesheet Properties of
values stated in each system are not necessarily exact equiva-
Sandwich Constructions by Long Beam Flexure
lents; therefore, to ensure conformance with the standard, each
D8453/D8453M Practice for Open-Hole Flexural Strength
system shall be used independently of the other, and values
of Sandwich Constructions
from the two systems shall not be combined.
E4 Practices for Force Calibration and Verification of Test-
1.6.1 Within the text, the inch-pound units are shown in
ing Machines
brackets.
E6 Terminology Relating to Methods of Mechanical Testing
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.09 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Sandwich Construction. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Nov. 1, 2022. Published January 2023. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D8454_D8454M-22. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8454/D8454M − 22
E122 Practice for Calculating Sample Size to Estimate,With x—test result for an individual specimen from the sample
i
Specified Precision, the Average for a Characteristic of a population for a given property
Lot or Process x¯—mean or average (estimate of mean) of a sample popu-
E177 Practice for Use of the Terms Precision and Bias in lation for a given property
ASTM Test Methods w—width of specimen across hole
E456 Terminology Relating to Quality and Statistics ∆—percent difference
σ—facesheet compressive stress
3. Terminology ε—indicated strain from gage
3.1 Definitions—Terminology D3878 defines terms relating
4. Summary of Test Method
to high-modulus fibers and their composites, as well as terms
4.1 This test method consists of subjecting a sandwich
relating to sandwich constructions. Terminology D883 defines
panel, with a centrally located through-hole, to a uniaxial
terms relating to plastics. Terminology E6 defines terms
compressive force parallel to the plane of its faces. The
relating to mechanical testing. Terminology E456 and Practice
specimen is installed in a multi-piece support fixture that has
E177 define terms relating to statistics. In the event of conflict
been aligned to minimize loading eccentricities and induced
between terms, Terminology D3878 shall have precedence
specimen bending. The specimen/fixture assembly is placed
over the other terminology standards.
between flat platens and end-loaded under compressive force
NOTE 1—If the term represents a physical quantity, its analytical
until failure.Applied force, crosshead displacement, and strain
dimensionsarestatedimmediatelyfollowingtheterm(orlettersymbol)in
data are recorded while loading. Ultimate strength is calculated
fundamental dimension form, using the following ASTM standard sym-
based on the nominal cross-sectional area of the two
bology for fundamental dimensions, shown within square brackets: [M]
for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature, facesheets, disregarding the presence of the hole. While the
and [nd] for nondimensional quantities. Use of these symbols is restricted
hole causes a stress concentration and reduced net section, it is
to analytical dimensions when used with square brackets, as the symbols
common aerospace practice to develop notched design allow-
may have other definitions when used without the brackets.
able strengths based on gross section stress to account for
3.2 Definitions of Terms Specific to This Standard:
various stress concentrations (flaws, damage, and so forth) not
3.2.1 diameter-to-facesheet thickness ratio, D/t [nd], n—in
explicitly modeled in the stress analysis.
an open-hole specimen, the ratio of the hole diameter to the
4.2 The only acceptable failure modes for ultimate open-
facesheet thickness.
hole sandwich compressive strength are ones which pass
3.2.1.1 Discussion—The diameter-to-thickness ratio may be
through the hole in the test specimen.
either a nominal value determined from nominal dimensions or
an actual value determined from measured dimensions.
5. Significance and Use
3.2.2 length-to-diameter ratio, L/D [nd], n—in an open-
5.1 This test method provides a standard method of deter-
hole specimen, the ratio of the specimen length to the hole
mining the open-hole (notched) strength of the sandwich panel
diameter.
for structural design allowables, material specifications, and
3.2.2.1 Discussion—The length-to-diameter ratio may be
research and development.
either a nominal value determined from nominal dimensions or
5.2 The reporting section requires items that tend to influ-
an actual value determined from measured dimensions.
ence notched sandwich compressive strength to be reported;
3.2.3 width-to-diameter ratio, w/D [nd], n—in an open-hole
these include the following: facesheet and core materials, core
specimen, the ratio of the specimen width to the hole diameter.
density, cell size and wall thickness if applicable, film
3.2.3.1 Discussion—The width-to-diameter ratio may be
adhesive, methods of material fabrication, accuracy of lay-up
either a nominal value determined from nominal dimensions or
orientation, facesheet stacking sequence and thickness, core
an actual value determined from measured dimensions.
thickness, overall specimen thickness, specimen geometry
(including hole diameter, diameter-to-thickness ratio, and
3.3 Symbols:
CV—coefficient of variation statistic of a sample population width-to-diameter ratio), specimen preparation (especially of
the hole), specimen conditioning, environment of testing, type,
for a given property (in percent)
specimen/fixture alignment, time at temperature, and speed of
d—sandwich total thickness
testing. Further, notched sandwich compressive strength may
D—diameter of hole
ohcu
be different between precured/bonded and co-cured facesheets
F —facesheet ultimate open-hole (notched) compressive
of the same material.
strength
L—length of specimen
5.3 The compression strength from this test may not be
n—number of specimens equivalent to the compression strength of sandwich structures
P—applied force subjected to flexural compression testing.
P —maximum force carried by test specimen before
max
6. Interferences
failure
S —standard deviation statistic of a sample population for
6.1 Hole Preparation—Because of the dominating presence
n–1
a given property
of the notch, and the lack of need to measure the material
t—nominal facesheet thickness response,resultsfromthistestmethodarerelativelyinsensitive
D8454/D8454M − 22
to parameters that would be of concern in an unnotched to local out-of-plane rotation due to the fixture geometry. The
compressive property test. However, since the notch has a knife-edge side supports provide resistance to out-of-plane
dominant effect on the strength, consistent preparation of the movement at the edges, which increases the compressive force
hole, without damage to the sandwich specimen, is important that would result in global buckling of the specimen. Edge
to meaningful results. Damage caused by hole preparation will supports must be co-planar. Results may be affected by the
affect strength results. Some types of damage, such as longi- geometry of the various slide plates local to the specimen.
tudinal splitting and delamination, can blunt the stress concen- Results may also be affected by the presence of gaps between
tration caused by the hole, increasing the force-carrying the slide plates and the specimen, which can reduce the
capacity of the specimen and the calculated strength. Other effective edge support and can result in concentrated load
types of damage can reduce the calculated strength. introduction conditions at the top and bottom specimen sur-
faces. Additionally, results may be affected by variations in
6.2 Material and Specimen Preparation—Poormaterialfab-
torque applied to the slide plate fasteners; loose fasteners may
rication practices, lack of control of fiber alignment, and
also reduce the effective edge support.
damage induced by improper specimen machining are known
6.8 System Alignment—Errors can result if the test fixture is
causes of high material data scatter in composites in general.
not centered with respect to the loading axis of the test
Important aspects of sandwich construction preparation that
machine, and aligned or shimmed to apply an essentially
contribute to data scatter include incomplete or nonuniform
uniaxial displacement to the loaded end of the specimen.
core bonding to facesheets, misalignment of core and facesheet
elements, the existence of joints, voids or other core and
6.9 Facesheet Load Distribution—This test method effec-
facesheet discontinuities, out-of-plane curvature, facesheet
tively applies a uniform axial displacement to the test speci-
thickness variation, surface roughness, and failure to meet the
men. If the stiffness of the two facesheets is different, due to
dimensional and squareness tolerances (parallelism and per-
one facesheet having more dimpling due to cocuring (bagside
pendicularity) specified in 8.2.
versus toolside effects), then accurate calculation of the
facesheet stress in the facesheets requires the use of strain
6.3 Geometry—Results are affected by the ratio of specimen
gages on both facesheets to determine the load distribution.
width to hole diameter (w/D); a ratio of 6 is recommended if
Where there is a significant difference in facesheet stiffnesses,
the notch sensitivity is unknown. Results may also be affected
use of the Practice D8453/D8453M test method may be more
by the ratio of hole diameter to facesheet thickness (D/t).
useful and appropriate.
Results may also be affected by facesheet thickness. Further,
6.10 Potting—Potting is commonly used to avoid facesheet
due to the hole size effect, notched strength from this test may
separation and end brooming prior to specimen failure. Potting
not be equivalent to results obtained from Test Method D6484.
of the core may occur during or prior to bonding to the
6.4 Environment—Resultsareaffectedbytheenvironmental
facesheets if the potting material is compatible with the
conditions under which specimens are conditioned, as well as
facesheet cure cycle. Potting may also occur after the specimen
the conditions under which the tests are conducted. Specimens
is cured by removing the core at the ends and inserting potting
tested in various environments can exhibit significant differ-
material.
ences in both strength behavior and failure mode. Experience
7. Apparatus
has demonstrated that elevated temperature, humid environ-
ments are generally critical for notched compressive strength.
7.1 Micrometers and Calipers—A micrometer with a 4 mm
However, critical environments must be assessed indepen-
to 8 mm [0.16 in. to 0.32 in.] nominal diameter ball-interface
dentlyforeachspecificcombinationofcorematerial,facesheet
or a flat anvil interface shall be used to measure the specimen
material, facesheet stacking sequence, and core-to-facesheet
thickness. A ball interface is recommended for thickness
interfacial adhesive (if used) that is tested.
measurements when at least one surface is irregular (for
example, bag-side of a facesheet laminate). A micrometer or
6.5 Material Orthotropy—The degree of facesheet orthot-
caliper with a flat anvil interface is recommended for thickness
ropy strongly affects the failure mode and measured notched
measurements when both surfaces are smooth (for example,
strength.Valid notched strength results should only be reported
tooled surfaces). A micrometer or caliper with a flat anvil
when appropriate failure modes are observed, in accordance
interface shall be used for measuring length, width other than
with 11.13.
machined surface dimensions, and hole diameter. The use of
6.6 Facesheet Thickness Scaling—Thick facesheet sand-
alternative measurement devices is permitted if specified (or
wich structures do not necessarily fail at the same strengths as
agreed to) by the test requestor and reported by the testing
thin facesheet sandwich structures with the same facesheet
laboratory.Theaccuracyoftheinstrumentsshallbesuitablefor
orientation (that is, strength does not always scale linearly with
reading to within1%ofthe sample dimensions. For typical
facesheetthickness).Thus,datagatheredusingthistestmethod
specimen geometries, an instrument with an accuracy of
may not translate directly into equivalent thick-structure prop-
60.0025 mm [60.0001 in.] is adequate for thickness
erties.
measurement, whereas an instrument with an accuracy of
60.025 mm [60.001 in.] is adequate for length, width, other
6.7 Test Fixture Characteristics—The configuration of the
machined surface dimensions, and hole diameter.
panel edge-constraint structure can have a significant effect on
test results. In the standard test fixture, the top and bottom 7.2 Support Fixture—Thecompressivetestfixture,shownin
supports provide no clamp-up force, but provide some restraint Fig. 1 and Fig. 2, utilizes adjustable retention plates to support
D8454/D8454M − 22
FIG. 1 Schematic of Support Fixture with Specimen in Place
FIG. 2 Assembled Support Fixture
the specimen edges and inhibit buckling when the specimen is geometry and overlap the specimen by 8 mm [0.30 in.]). The
end-loaded. The side supports are knife edges that overlap the fixture is adjustable to accommodate small variations in
specimen by 8 mm [0.30 in.] and provide resistance to specimen length, width, and thickness. The top plate and slide
out-of-plane movement at the edges which increases the plates, which are not directly attached to the lower portion of
compressive force that would result in global buckling of the the fixture, slip over the top edge of the specimen. The side
specimen.The fixture consists of one base plate, two base slide plates are sufficiently short to ensure that a gap between the
plates, two angles, four side plates, one top plate, and two top side rails and the top plate is maintained during the test.
slide plates. Alternate fixtures with angles integrated into the 7.2.1 Support Fixture Details—A suitable support fixture is
base plate are permissible. The top and bottom supports shown in Figs. 1-3, but other designs that perform the
provide no clamp-up, but provide some rotational restraint due necessary functions are acceptable. The fixture shall be con-
to the fixture geometry (the slide plates have a squared structed of sufficient stiffness and precision as to satisfy the
D8454/D8454M − 22
FIG. 3 Support Fixture Base Assembly and Top Assembly
loading uniformity requirements of this test method. The 7.3.3 Drive Mechanism—The testing machine drive mecha-
following general notes apply to these figures: nism shall be capable of imparting to the movable head a
controlled velocity with respect to the stationary head. The
NOTE 2—Experience has shown that fixtures may be damaged due to
velocity of the movable head shall be capable of being
handling in use, thus periodic re-inspection of the fixture dimensions and
tolerances is important.
regulated as specified in 11.4.
NOTE 3—Ensure that the fixture design is sufficient that if using shims
7.3.4 Force Indicator—The testing machine force-sensing
to align that the fixture does not deflect at the shims.
device shall be capable of indicating the total force being
7.3 Testing Machine—The testing machine shall be in con-
carried by the test specimen. This device shall be essentially
formance with Practices E4, and shall satisfy the following
free from inertia-lag at the specified rate of testing and shall
requirements:
indicate the force with an accuracy over the force range(s) of
7.3.1 Testing Machine Configuration—The testing machine
interest of within 61 % of the indicated value.
shall have both an essentially stationary head and a movable
7.3.5 Crosshead Displacement Indicator—The testing ma-
head.Ashort loading train and flat end-loading platens shall be
chine shall be capable of monitoring and recording the cross-
used.
head displacement (stroke) with a precision of at least 61%.
7.3.2 Flat Platens—The test machine shall be mounted with
If machine compliance is significant, it is acceptable to
well-alignedflatplatenscapableofprovidingafixedsurface.If
the platens are not sufficiently hardened, or simply to protect measure the displacement of the movable head using a LVDT
the platen surfaces, a hardened plate (with parallel surfaces)
or similar device with 61 % precision on displacement.
can be inserted between each end of the fixture and the
7.4 Conditioning Chamber—When conditioning materials
corresponding platen. The lower platen should be marked to
at non-laboratory environments, a temperature-/vapor-level
help center the test fixture between the platens.
controlledenvironmentalconditioningchamberisrequiredthat
7.3.2.1 The use of a spherical seat platen that includes a
shall be capable of maintaining the required temperature to
position locking feature is encouraged; however, the use of
within 63°C[65 °F] and the required relative humidity level
fixed flat platens is acceptable. When using fixed flat platens,
to within 63 %. Chamber conditions shall be monitored either
the platen surfaces shall be parallel within 0.025 mm [0.001
on an automated continuous basis or on a manual basis at
in.] across the test fixture top plate length of 72 mm [3 in.].
regular intervals.
When using a spherical seat platen, it must be locked into a
fixed position after either aligning it with the fixed platen or
7.5 Environmental Test Chamber—An environmental test
aligning the specimen through the use of strain gages bonded
chamber is required for test environments other than ambient
to the specimen surface. The spherical seat platen may be
testing laboratory conditions. This chamber shall be capable of
placed either below or above the support fixture.
maintaining the test specimen and fixture at the required test
NOTE 4—While the use of a spherical seat platen is preferred for
environment during the mechanical test. The test temperature
specimen alignment, the use of thin metallic shims placed between the
shall be maintained within 63°C [65 °F] of the required
fixture and the fixed flat platens is permissible for specimen alignment.
temperature, and the relative humidity level shall be main-
NOTE5—Whenusingasphericalseatplaten,itispreferabletoplacethe
platen above the loading fixture for specimen alignment. tained to within 63 % of the required humidity level.
D8454/D8454M − 22
days of moisture conditioning.
7.6 Strain-Indicating Device—Strain measurement of the
specimens is required. The longitudinal strain should be
7.7 Data Acquisition Equipment—Equipment capable of
measured simultaneously at four locations (two locations on
recording force, crosshead displacement, and strain data is
opposite faces of the specimen as shown in Fig. 4 and Fig. 5)
required.
to aid in ensuring application of pure compressive loading and
to detect bending or buckling, or both, if any. If the ends of the
8. Sampling and Test Specimens
specimens are potted, the vertical location of the strain gages
shall be either 25 mm [1.0 in.] below the top of the specimen 8.1 Sampling—Test at least five specimens per test condi-
or 12 mm [0.5 in.] below the bottom of the potting, whichever tion unless valid results can be gained through the use of fewer
is greater. The same type of strain transducer shall be used for specimens, as in the case of a designed experiment. For
all strain measurements on any single specimen. The gages,
statistically significant data, the procedures outlined in Practice
surface preparation, and bonding agents should be chosen to E122 should be consulted. The method of sampling shall be
provide for optimal performance on the subject material for the
reported.
prescribed test environment. Attachment of the strain-
8.2 Standard Specimen Configuration—The test specimen
indicatingdevicetothespecimenshallnotcausedamagetothe
shall be a uniform specimen with a constant thickness. The
specimen surface.
core and facesheet thickness should be representative of the
NOTE 6—Although the compression test may be performed without the
intended use. The standard width is 72 mm [3.0 in.], length of
use of strain-indicating devices, lack of instrumentation for the notched
144 mm [6 in.], and a hole diameter of 12 mm [0.50 in.]. The
specimens makes the detection of poor alignment, undesirable specimen
hole shall be machined through both facesheets and the core.
instability, or both, much more difficult. For this reason, strain measure-
ment of the specimens during compressive loading is required. The geometry of the specimen is shown in Fig. 4 and Fig. 5.
NOTE 7—Moisture proofing of the strain gage installations on the
8.3 Non-Standard Specimen Configuration—For non-
specimen needs to be done very carefully with multiple layers of
protective coatings (such as microfined wax, high temperature polytetra-
standard specimen geometries, the length and width must be
fluoroethylene (PTFE) tape, adhesively-bonded aluminum foil, and room
sufficient so that strain gages can be placed in the far field
temperature curing vulcanizing (RTV) compound) before subjecting them
strain field. The width-to-diameter (w/D) ratio should be large
to moisture conditioning inside the environmental conditioning chamber.
enough to produce a statistically significant reduction in
Foil strain gages, protected simply with RTV compound, are likely to
strength from the unnotched configuration, and small enough
become corroded and unfit for hot-wet testing after approximately 100
to minimize finite width effects.Aratio of 6 is recommended if
the notch sensitivity is unknown. The specimen length should
Vijayaraju, K., Mangalgiri, P. D., and Parida B. K., “Hot-Wet Compression
be at least 12 times the hole diameter to minimize finite length
Testing of Impact Damaged Composite Laminates,” Proceedings of the Ninth
effects.
InternationalConferenceonFracture(ICF-9),Sydney,Australia,1997,pp.909-916.
FIG. 4 Open-Hole Compressive Strength Specimen (Inch-Pound Version)
D8454/D8454M − 22
FIG. 5 Open-Hole Compressive Strength Specimen (SI Version)
8.4 Specimen Preparation—Guide D5687/D5687M pro- facesheets and core. The test requestor is responsible for
vides recommended specimen preparation practices and should
specifying the facesheet thicknesses to be used for the calcu-
be followed where practical.
lations in this test method. For metallic or precured composite
8.4.1 Facesheets:
facesheets which are secondarily bonded to the core, the
8.4.1.1 Fabrication—Control of fiber alignment is critical.
facesheet thickness should be measured prior to bonding. In
Improper fiber alignment as well as intra-cell facesheet dim-
these cases, the test requestor m
...