Sandwich panels are a composite material created by attaching two thin skins to a lightweight but thick core. They are preferred for their high bending stiffness and overall low density, but tend to be weaker materials in regard to tensile strength. Therefore, they can be tested for their flatwise tensile strength using ASTM C297.


Flatwise tensile strength of sandwich panels is a measure of the strength between the substrate and the core material, or the bond between core and facings of an assembled sandwich panel. Core material forms included in ASTM C297 can include those with continuous bonding surfaces (such as balsa wood and foams) as well as those with discontinuous bonding surfaces (such as honeycomb).

In general, poor material fabrication practices, lack of control of fiber alignment, and damage induced by improper specimen machining are known causes of high data scatter in composites. When it comes to preparing sandwich composite specimens in particular, watch out for incomplete or nonuniform core bonding to facings, misalignment of core and facing elements, the existence of joints, voids or other core and facing discontinuities, out-ofplane curvature, facing thickness variation, and surface roughness.

Testing procedure

The test consists of subjecting a sandwich construction to a tensile load normal to the plane of the sandwich, such load being transmitted to the sandwich through thick loading blocks bonded to the sandwich facings or directly to the core. When watching for a rupture, the only acceptable failure modes for flatwise tensile strength are those which are in the internal sandwich construction. Failure of the loading block-to-sandwich bond is not an acceptable failure mode.

A universal testing machine can be used for testing sandwich panels in ASTM C297. Consider our tensile bond fixtures made specifically for ASTM C297. By means of our testing expertise and modular product design, we will help find the testing solution that is right for you. Give one of our application engineers a call today for help with creating the best budget and testing plan according to ASTM C297.

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