Four-point bend interlaminar shear testing of uni- and multi-directional carbon/epoxy composite systems

Purpose of the paper is to investigate the possibility of extending the interlaminar shear strength (ILSS) results obtained by four-point bend testing of unidirectional laminates to multidirectional laminates, such as cross-ply and quasi-isotropic, the testing of which is a common practice in the industry but has not been previously validated in the literature. An experimental database is gathered through the known modified version of the ASTM D2344 short beam test and the results show a surprising proximity of results for the three different fiber architectures for the same composite system. Various finite element analyses were developed using ANSYS(R) software, allowing for better insight on the mechanics of delamination in four-point bending, and showed extremely good agreement with the experimental values. The final and most accurate model partially confirmed observations made by other authors, and includes the 'skewed' profile of the shear stress through the thickness and its variation along the length, the distribution of the shear stress across the width, the location of delamination initiation and propagation and maximum ILSS and the shear stress contour. (C) 2003 Elsevier Ltd. All rights reserved.