Determination of interlaminar shear strength for glass/epoxy and carbon/epoxy laminates at impact rates of strain

Abstract

A brief review is given of some of the techniques which have been used to determine the interlaminar shear strength of laminated composites under impact loading. A new technique employing a double-lap shear specimen, where failure occurs on predetermined interfaces, is then described and results are presented for tests on this design of specimen at both a quasi-static and an impact rate of strain. The strain distribution along the failure plane is determined by using a finite element analysis. Large variations in both the shear strain and the normal strain were observed, the magnitude of this variation being sensitive both to the elastic properties of the different reinforcing plies and to the chosen stacking sequence. Results are presented for the interlaminar shear strength at the interface between (a) two plain-weave glass/epoxy plies, (b) two plain-weave carbon/epoxy plies, and (c) a plain-weave glass/epoxy and a plain-weave carbon/epoxy ply. In each case the mean value of the interlaminar shear stress at failure was found to increase significantly as the loading rate was raised from quasi-static to impact.