Flatwise compressive strength and modulus are fundamental mechanical properties of sandwich cores that are used in designing sandwich panels. Deformation data can be obtained, and from a complete force versus deformation curve, it is possible to compute the compressive stress at any applied force (such as compressive stress at proportional limit force or compressive strength at the maximum force) and to compute the effective modulus of the core.

This test method provides a standard method of obtaining the flatwise compressive strength and modulus for sandwich core structural design properties, material specifications, research and development applications, and quality assurance.

In order to prevent local crushing at the edges of some honeycomb cores, it is often desirable to stabilize the edges with a suitable material, such as a thin layer of resin or thin facings. Flatwise compressive strength data may be generated using either stabilized specimens (reported as stabilized compression strength) or non-stabilized specimens (reported as bare compression strength). It is customary aerospace industry practice to determine compression modulus only when using stabilized specimens.

Factors that influence the flatwise compressive strength and shall therefore be reported include the following: core material, methods of material fabrication, core geometry (cell size), core density, specimen geometry, specimen preparation, specimen conditioning, environment of testing, specimen alignment, loading procedure, and speed of testing.