Mode II interlaminar fracture of filament wound angle-ply specimens

This paper presents a study of the interlaminar fracture of filament wound composites. Mode II end notched flexure (ENF) tests were performed on flat glass/polyester specimens. The tested specimens had asymmetric [+/-theta](4) angle-ply stacking-sequences, with theta values from 0.8degrees (hoop winding) to 30degrees. Due to the low stiffness and probable high toughness, it was not possible to propagate the crack in [+/-60degrees](4) specimens before they suffered considerable permanent deformations. A short support span had to be employed for [+/-30degrees](4) specimens in order to obtain crack propagation. Nevertheless, the results for those specimens should be viewed with caution, as some nonlinear behaviour and small permanent deformations were detected. No other unusual features, such as crack jumping to other interface, were observed. The scatter in the critical strain energy release rate values (G(IIc)) was higher for [+/-10degrees](4) and [+/-30degrees](4) specimens than for the quasi-unidirectional ones. G(IIc) values from the insert were generally lower than those from mode II pre-cracks, except for quasi-unidirectional specimens. A plot of average G(IIc) values against theta showed a minimum at theta=5degrees.