Characterization of the shear/compression failure envelope of Rohacell foam

Abstract

Four-point flexural testing of sandwich structures is often used for the determination of the shear strength of the core material. The accuracy of this test was evaluated using finite-element modeling. The model results show that the measured average shear stress may be inaccurate due to shear stress variations within the sample and the presence of supermiposed compressive stresses. A modified experimental test method was developed to ensure a more homogeneous shear stress field. Using this test method, controlled combinations of shear and compressive stress can be generated within the polymeric foam, allowing evaluation of the shear/compression failure envelope. Results for a Rohacell polymeric foam show that, at the temperatures evaluated, the compression/shear failure envelope is elliptical. On a normalized plot of the failure envelope, the data for all temperatures coincide on a circular plot. Use of this failure envelope approach can reduce the amount of testing required to acquire design data.