ASTM C393– This test method covers determination of the properties of flat sandwich constructions subjected to flatwise flexure in such a manner

that the applied moments produce curvature of the sandwich facing planes.

ASTM C393–Significance and Use

Flexure tests on flat sandwich construction may be conducted to determine the sandwich flexural stiffness, the core shear strength and shear modulus,

or the facings compressive and tensile strengths.

Tests to evaluate core shear strength may also be used to evaluate core-to-facing bonds.

These test methods provide a standard method of obtaining the sandwich panel flexural strengths and stiffness.

Core shear strength and shear modulus are best determined in accordance with Test Method C 273.

The sandwich stiffness and core shear modulus may be determined by calculations involving measured deflections of sandwich flexure specimens.

Tests can be conducted on short specimens and on long specimens or on one specimen loaded in two ways, and the flexural stiffness and shear modulus

can be determined by simultaneous solution of the complete deflection equations for each span or each loading.

If the facing modulus values are known, a short span beam can be tested and the calculated bending deflection subtracted from the beam’s total deflection.

This gives the shear deflection from which the core shear modulus can be determined

To determine core shear strength, it is necessary to design the test specimen so that the moments produced at core failure do not stress the facings beyond

the compressive or tensile proportional limit stress of the facing material.

This requires thicker facings and shorter support spans.

If the 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 approximate methods