ASTM C393-00

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
Designation:C393–00
Standard Test Method for
Flexural Properties of Sandwich Constructions
This standard is issued under the fixed designation C 393; 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 (e) 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 in two ways, and the flexural stiffness and shear modulus can
be determined by simultaneous solution of the complete
1.1 This test method covers determination of the properties
deflection equations for each spanor each loading.Ifthefacing
of flat sandwich constructions subjected to flatwise flexure in
modulusvaluesareknown,ashortspanbeamcanbetestedand
such a manner that the applied moments produce curvature of
the calculated bending deflection subtracted from the beam’s
the sandwich facing planes.
total deflection. This gives the shear deflection from which the
1.2 The values stated in SI units are to be regarded as the
core shear modulus can be determined (Notes 1-3).
standard. The inch-pound units given may be approximate.
1.3 This standard does not purport to address all of the
NOTE 1—For cores with high shear modulus, the shear deflection will
safety concerns, if any, associated with its use. It is the be quite small and ordinary errors in deflection measurements will cause
considerable variations in the calculated shear modulus.
responsibility of the user of this standard to establish appro-
NOTE 2—Concentrated loads on beams with thin facings and low
priate safety and health practices and determine the applica-
density cores can produce results that are difficult to interpret, especially
bility of regulatory limitations prior to use.
close to the failure point. Wider load pads with rubber pads may assist in
distributing the loads.
2. Referenced Documents
NOTE 3—To insure that simple sandwich beam theory is valid, a good
2.1 ASTM Standards:
rule of thumb for the four-point bending test is the span length divided by
C 273 Test Method for Shear Properties of Sandwich Core the sandwich thickness should be greater than 20 (L/d > 20) with the ratio
of facing thickness to core thickness less than 0.1 (t/c < 0.1).
Materials
C 480 Test Method for Flexure Creep of Sandwich Con-
4. Apparatus
structions
4.1 Testing Machine, capable of maintaining a controlled
E4 Practices for Force Verification of Testing Machines
loading rate and indicating the load with an accuracy of 61%
3. Significance and Use
of the indicated value. The accuracy of the test machine shall
be verified in accordance with PracticesE4.
3.1 Flexure tests on flat sandwich construction may be
4.2 Loading Fixtures,
conductedtodeterminethesandwichflexuralstiffness,thecore
4.3 Transducer, Deflectometer, Dial Gage, capable of mea-
shear strength and shear modulus, or the facings compressive
suring the displacement with a precision of at least 61%.
and tensile strengths. Tests to evaluate core shear strength may
4.4 Micrometer, Gage, or Caliper, capable of measuring
also be used to evaluate core-to-facing bonds.
accurately to 0.025 mm (0.001 in.).
3.2 These test methods provide a standard method of
obtaining the sandwich panel flexural strengths and stiffness.
5. Test Specimen
3.3 Core shear strength and shear modulus are best deter-
5.1 The test specimen shall be rectangular in cross section.
mined in accordance with Test Method C 273.
The depth of the specimen shall be equal to the thickness of the
3.4 The sandwich stiffness and core shear modulus may be
sandwich construction, and the width shall be not less than
determined by calculations involving measured deflections of
twice the total thickness, not less than three times the dimen-
sandwich flexure specimens. Tests can be conducted on short
sion of a core cell, nor greater than one half the span length.
specimens and on long specimens or on one specimen loaded
The specimen length shall be equal to the span length plus 50
mm (2 in.) or plus one half the sandwich thickness whichever
1 is the greater.
This specification is under the jurisdiction of ASTM Committee D30 on
5.2 To determine core shear strength, it is necessary to
Composite Materials and is the direct responsibility of Subcommittee D30.09 on
Sandwich Construction.
design the test specimen so that the moments produced at core
Current edition approved Jan. 10, 2000. Published April 2000. Originally
failure do not stress the facings beyond the compressive or
published as C 393 – 57 T. Last previous edition C 393 –94.
2 tensile proportional limit stress of the facing material. This
Annual Book of ASTM Standards, Vol 15.03.
Annual Book of ASTM Standards, Vol 03.01. requires thicker facings and shorter support spans. If the
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
C393–00
facings are too thick, the shear load will be carried to a
considerable extent by the facings, thus leading to a high
apparent core shear strength as computed by the usual approxi-
mate methods.
5.3 Proper design of a test specimen for determining com-
pressive or tensile strength of the facings is obtained by a
reverse of considerations for determining core shear strength.
The facings are thinner and the span is lengthened so that
FIG. 2 Two-Point Load
greater moments are produced at loads low enough so that the
allowable core shear stress will not be exceeded. Tensile
failures rarely occur unless the tensile facing is thinner or of
different material than the compression facing. Failure in the
compression facing may occur by actual crushing, yielding
causing unduly large deflection, wrinkling of the facing into
the core or the facing popping off the core, or the facing
dimpling into the honeycomb cells.
6. Conditioning
6.1 When the physical properties of the component materi-
alsareaffectedbymoisture,thetestspecimensshallbebrought
to constant weight (61 %) before testing, prefera
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