On the validity of LEFM methods to investigate the fracture behavior of angle-ply laminates

Abstract

In this research, an experimental characterization of the interlaminar fracture behavior of unidirectional and multidirectional glass/epoxy laminates is presented under pure mode I loading. The delamination growth resistance curves are obtained by means of two different data reduction methods based on the LEFM and the J-integral approaches. The J-integral approach has great advantages over the standard LEFM approach. It removes the need for measurement of the delamination length. Moreover, it is not subjected to the strictly limited scope of LEFM, the validity of which is not guaranteed in the presence of damage mechanisms. This might be a great concern for multidirectional laminates where distributed damage in the form of matrix cracking is usually anticipated. The current standards do not provide any validity criteria for LEFM assumptions in multidirectional laminates. Any way, these data are often reduced with common standard methods. In this study it has been shown that the LEFM method provides comparable results with the J-based one for unidirectional laminates. However, it may grossly underestimate the fracture resistance of multidirectional laminates.