ASTM C297/C297M-04(2010)
(Test Method)Standard Test Method for Flatwise Tensile Strength of Sandwich Constructions
Standard Test Method for Flatwise Tensile Strength of Sandwich Constructions
SIGNIFICANCE AND USE
In a sandwich panel, core-to-facing bond integrity is necessary to maintain facing stability and permit load transfer between the facings and core. This test method can be used to provide information on the strength and quality of core-to-facing bonds. It can also be used to produce flatwise tensile strength data for the core material. While it is primarily used as a quality control test for bonded sandwich panels, it can also be used to produce flatwise tensile strength data for structural design properties, material specifications, and research and development applications.
Factors that influence the flatwise tensile strength and shall therefore be reported include the following: facing material, core material, adhesive material, methods of material fabrication, facing stacking sequence and overall thickness, core geometry (cell size), core density, adhesive thickness, specimen geometry, specimen preparation, specimen conditioning, environment of testing, specimen alignment, loading procedure, speed of testing, facing void content, adhesive void content, and facing volume percent reinforcement. Properties that may be derived from this test method include flatwise tensile strength.
SCOPE
1.1 This test method determines the flatwise tensile strength of the core, the core-to-facing bond, or the facing of an assembled sandwich panel. Permissible core material forms include those with continuous bonding surfaces (such as balsa wood and foams) as well as those with discontinuous bonding surfaces (such as honeycomb).
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text the inch-pound units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: C297/C297M − 04(Reapproved 2010)
Standard Test Method for
Flatwise Tensile Strength of Sandwich Constructions
This standard is issued under the fixed designation C297/C297M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope D3878 Terminology for Composite Materials
D5229/D5229M TestMethodforMoistureAbsorptionProp-
1.1 This test method determines the flatwise tensile strength
erties and Equilibrium Conditioning of Polymer Matrix
of the core, the core-to-facing bond, or the facing of an
Composite Materials
assembled sandwich panel. Permissible core material forms
E4 Practices for Force Verification of Testing Machines
include those with continuous bonding surfaces (such as balsa
E6 Terminology Relating to Methods of Mechanical Testing
wood and foams) as well as those with discontinuous bonding
E122 Practice for Calculating Sample Size to Estimate,With
surfaces (such as honeycomb).
Specified Precision, the Average for a Characteristic of a
1.2 The values stated in either SI units or inch-pound units
Lot or Process
are to be regarded separately as standard. Within the text the
E177 Practice for Use of the Terms Precision and Bias in
inch-pound units are shown in brackets. The values stated in
ASTM Test Methods
each system are not exact equivalents; therefore, each system
E456 Terminology Relating to Quality and Statistics
must be used independently of the other. Combining values
E1309 Guide for Identification of Fiber-Reinforced
from the two systems may result in nonconformance with the
Polymer-Matrix Composite Materials in Databases
standard.
E1434 Guide for Recording Mechanical Test Data of Fiber-
1.3 This standard does not purport to address all of the Reinforced Composite Materials in Databases
safety concerns, if any, associated with its use. It is the
E1471 Guide for Identification of Fibers, Fillers, and Core
responsibility of the user of this standard to establish appro- Materials in Computerized Material Property Databases
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
3. Terminology
2. Referenced Documents 3.1 Definitions—Terminology D3878 defines terms relating
2 to high-modulus fibers and their composites. Terminology
2.1 ASTM Standards:
C274 defines terms relating to structural sandwich construc-
C274 Terminology of Structural Sandwich Constructions
tions. Terminology D883 defines terms relating to plastics.
D792 Test Methods for Density and Specific Gravity (Rela-
Terminology E6 defines terms relating to mechanical testing.
tive Density) of Plastics by Displacement
Terminology E456 and Practice E177 define terms relating to
D883 Terminology Relating to Plastics
statistics.Intheeventofaconflictbetweenterms,Terminology
D2584 Test Method for Ignition Loss of Cured Reinforced
D3878 shall have precedence over the other terminologies.
Resins
D2734 TestMethodsforVoidContentofReinforcedPlastics
3.2 Symbols:
D3039/D3039M Test Method for Tensile Properties of Poly-
A = cross-sectional area of a test specimen
mer Matrix Composite Materials
CV = coefficient of variation statistic of a sample population
D3171 Test Methods for Constituent Content of Composite
for a given property (in percent)
Materials
ftu
F = ultimate flatwise tensile strength
z
P = maximum force carried by test specimen before
max
This test method is under the jurisdiction of ASTM Committee D30 on
failure
Composite Materials and is the direct responsibility of Subcommittee D30.09 on
Sandwich Construction.
S = standard deviation statistic of a sample population for
n-1
Current edition approved Oct. 1, 2010. Published December 2010. Originally
a given property
approved in 1952. Last previous edition approved in 2004 as C297/C297M – 04.
DOI: 10.1520/C0297_C0297M-04R10. x = test result for an individual specimen from the sample
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
population for a given property
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
x¯ = mean or average (estimate of mean) of a sample popu-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. lation for a given property
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C297/C297M − 04 (2010)
4. Summary of Test Method 6.3 Geometry—Specific geometric factors that affect sand-
wich flatwise tensile strength include core cell geometry, core
4.1 This test method consists of subjecting a sandwich
thickness, specimen shape (square or circular), adhesive
construction to a uniaxial tensile force normal to the plane of
thickness, facing thickness, and facing per-ply thickness.
the sandwich. The force is transmitted to the sandwich through
6.4 Environment—Resultsareaffectedbytheenvironmental
thickloadingblocks,whicharebondedtothesandwichfacings
conditions under which the tests are conducted. Specimens
or directly to the core.
tested in various environments can exhibit significant differ-
4.2 The only acceptable failure modes for flatwise tensile
ences in both strength behavior and failure mode. Critical
strength are those which are internal to the sandwich construc-
environments must be assessed independently for each facing,
tion. Failure of the loading block-to-sandwich bond is not an
adhesive and core material tested.
acceptable failure mode.
6.5 Conditioning—Asitisinappropriatetobondamoisture-
conditioned specimen to the bonding blocks, it is necessary to
5. Significance and Use
perform the bonding operation prior to such conditioning. The
5.1 In a sandwich panel, core-to-facing bond integrity is
presence of the bonding blocks will affect the degree of
necessary to maintain facing stability and permit load transfer
moisture intake into the specimen, in comparison to a non-
between the facings and core. This test method can be used to
bonded sample.
provide information on the strength and quality of core-to-
facing bonds. It can also be used to produce flatwise tensile
7. Apparatus
strength data for the core material.While it is primarily used as
7.1 Micrometers—Themicrometer(s)shallusea4-to5-mm
aqualitycontroltestforbondedsandwichpanels,itcanalsobe
[0.16- to 0.20-in.] nominal diameter ball-interface on irregular
used to produce flatwise tensile strength data for structural
surfaces such as the bag-side of a facing laminate, and a flat
design properties, material specifications, and research and
anvil interface on machined edges or very smooth-tooled
development applications.
surfaces.Theaccuracyoftheinstrument(s)shallbesuitablefor
reading to within 1 % of the sample length, width and
5.2 Factors that influence the flatwise tensile strength and
thickness. For typical specimen geometries, an instrument with
shall therefore be reported include the following: facing
anaccuracyof 625mm[60.001in.]isdesirableforthickness,
material, core material, adhesive material, methods of material
length and width measurement.
fabrication, facing stacking sequence and overall thickness,
core geometry (cell size), core density, adhesive thickness,
7.2 Loading Fixtures—The loading fixtures shall be self-
specimen geometry, specimen preparation, specimen
aligning and shall not apply eccentric loads.Asatisfactory type
conditioning, environment of testing, specimen alignment,
of apparatus is shown in Fig. 1. The loading blocks shall be
loading procedure, speed of testing, facing void content,
sufficiently stiff to keep the bonded core or facings essentially
adhesive void content, and facing volume percent reinforce-
flat under load. Loading blocks 40 to 50 mm [1.5 to 2.0 in.]
ment. Properties that may be derived from this test method
thick have been found to perform satisfactorily. Permissible
include flatwise tensile strength.
tolerances for the loading blocks (along with alignment re-
quirements) are provided in Fig. 2.
6. Interferences
7.3 Testing Machine—The testing machine shall be in ac-
6.1 Material and Specimen Preparation—Poormaterialfab-
cordance with Practices E4 and shall satisfy the following
rication practices, lack of control of fiber alignment, and
requirements:
damage induced by improper specimen machining are known
7.3.1 Testing Machine Configuration—The testing machine
causes of high data scatter in composites in general. Specific
shall have both an essentially stationary head and a movable
material factors that affect sandwich composites include vari-
head.
abilityincoredensityanddegreeofcureofresininbothfacing
7.3.2 Drive Mechanism—The testing machine drive mecha-
matrix material and core bonding adhesive. Important aspects
nism shall be capable of imparting to the movable head a
of sandwich panel specimen preparation that contribute to data
controlled velocity with respect to the stationary head. The
scatter are incomplete or nonuniform core bonding to facings,
velocity of the movable head shall be capable of being
misalignment of core and facing elements, the existence of
regulated in accordance with 11.6.
joints, voids or other core and facing discontinuities, out-of-
7.3.3 Load Indicator—The testing machine load-sensing
plane curvature, facing thickness variation, and surface rough-
device shall be capable of indicating the total force being
ness.
carried by the test specimen. This device shall be essentially
free from inertia lag at the specified rate of testing and shall
6.2 System Alignment—Excessive bending will cause pre-
indicate the force with an accuracy over the force range(s) of
maturefailure.Everyeffortshouldbemadetoeliminateexcess
interest of within 61 % of the indicated value.
bending from the test system. Bending may occur as a result of
misaligned grips, poor specimen preparation, or poor align- 7.4 Conditioning Chamber—When conditioning materials
ment of the bonding blocks and loading fixture. If there is any at non-laboratory environments, a temperature/vapor-level
doubt as to the alignment inherent in a given test machine, then controlledenvironmentalconditioningchamberisrequiredthat
the alignment should be checked as discussed in Test Method shall be capable of maintaining the required temperature to
D3039/D3039M. within 63°C [65°F] and the required relative humidity level
C297/C297M − 04 (2010)
specimen. The largest facing area listed in the table (5625
2 2
mm [9.0 in. ]) is a practical maximum for this test method.
Cores with cell sizes larger than 9 mm [0.375 in.] may require
a smaller number of cells to be tested in the specimen.
8.3 Specimen Preparation and Machining—Specimen
preparation is extremely important for this test method. Take
precautions when cutting specimens from large panels to avoid
notches, undercuts, rough or uneven surfaces, or delaminations
due to inappropriate machining methods. Obtain final dimen-
sions by water-lubricated precision sawing, milling, or grind-
ing. The use of diamond tooling has been found to be
extremely effective for many material systems. Edges should
be flat and parallel within the specified tolerances. Record and
report the specimen cutting preparation method.
8.4 Labeling—Label the test specimens so that they will be
distinct from each other and traceable back to the panel of
origin, and will neither influence the test nor be affected by it.
8.5 Loading Fixture Bonding—The loading blocks shall be
bonded to the core or facings of the test specimen using a
suitable adhesive. To minimize thermal exposure effects upon
the existing core-to-facing bonds, it is recommended that the
assembly bonding temperature be at room temperature, or at
least 28°C [50°F] lower than that at which the sandwich was
originally bonded. Similarly, the assembly bonding pressure
shall not be greater than the original facing-to-core bonding
pressure. Permissible tolerances for the bonded assembly
(along with alignment requirements) are provided in Fig. 2.
FIG. 1 Flatwise Tension Test Setup
9. Calibration
to within 63 %. Chamber conditions shall be monitored either
9.1 The accuracy of all measuring equipment shall have
on an automated continuous basis or on a manual basis at
certified calibrations that are current at the time of use of the
regular intervals.
equipment.
7.5 Environmental Test Chamber—An environmental test
chamber is required for test environments other than ambient
10. Conditioning
testing laboratory conditions. This chamber shall be capable of
10.1 Standard Conditioning Procedure—Unless a different
maintaining the gage section of the test specimen at the
environment is specified as part of the experiment, condition
required test environment during the mechanical test.
the test specimens in accordance with Procedure C of Test
Method D5229/D5229M, and store and test at standard labo-
8. Sampling and Test Specimens
ratoryatmosphere(23 63°C[73 65°F]and50 65 %relative
8.1 Sampling—Test at least five specimens per test condi-
humidity).
tion unless valid results can be gained through the use of fewer
specimens, as in the case of a designed experiment. For
11. Procedure
statistically significant data, consult the procedures outlined in
11.1 Parameters to Be Specified Before Test:
Practice E122. Report the method of sampling.
11.1.1 The specimen sampling method, specimen geometry,
8.2 Geometry—Test specimens shall have a square or cir-
and conditioning travelers (if required).
cular cross-section, and shall be equal in thickness to the
11.1.2 The properties and data reporting format desired.
sandwich panel thickness. Minimum specimen facing areas for
various types of core materials are as follows: NOTE 1—Determine specific material property, accuracy, and data
reporting requirements prior to test for proper selection of instrumentation
8.2.1 Continuous Bonding Surfaces (for example, balsa
and data recording equipment. Estimate the specimen strength to aid in
wood, foams)—Theminimumfacingareaofthespecimenshall
transducer selection, calibration of equipment, and determination of
2 2
be 625 mm [1.0 in. ].
equipment settings.
8.2.2 Discontinuous Cellular Bonding Surfaces (for
11.1.3 The environmental conditioning test parameters.
example, honeycomb)—The required facing area of the speci-
11.1.4 If performed, sampling method, specimen geometry,
men is dependent upon the cell size, to ensure a minimum
and test parameters used to determine facing density and
number of cells are tested. Minimum facing areas are recom-
reinforcement volume.
m
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