ASTM C393 Shear Properties of Sandwich Constructions by Beam Flexure Testing Machine

5.1 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.

5.2 This test method is limited to obtaining the core shear strength or core-to-facing shear strength and the stiffness of the sandwich beam, and to obtaining load-deflection data for use in calculating sandwich beam flexural and shear stiffness using Practice D7250/D7250M.

5.3 Facing strength is best determined in accordance with Test Method D7249/D7249M.

5.4 Practice D7250/D7250M covers the determination of sandwich flexural and shear stiffness and core shear modulus using calculations involving measured deflections of sandwich flexure specimens.

5.5 This test method can be used to produce core shear strength and core-to-facing shear strength data for structural design allowables, material specifications, and research and development applications; it may also be used as a quality control test for bonded sandwich panels.

5.6 Factors that influence the shear strength and shall therefore be reported include the following: facing material, core material, adhesive material, methods of material fabrication, core geometry (cell size), core density, adhesive thickness, specimen geometry, specimen preparation, specimen conditioning, environment of testing, specimen alignment, loading procedure, speed of testing, and adhesive void content. Further, core-to-facing strength may be different between precured/bonded and co-cured facings in sandwich panels with the same core and facing material.