Influence of initial delamination length on the interlaminar fracture toughness energy – Mode I – of unidirectional GFRP

Abstract When testing double cantilever beam (DCB) specimens, the distance between the load line and the crack tip corresponds to the lever arm, thereby affecting the load necessary to propagate the crack. While ASTM D5528 defines an initial delamination length (IDL) from this load line to the end of the inserted release film, there is no such specification in DIN EN 6033. The question, therefore, arises as to whether the IDL affects the interlaminar fracture toughness energy – Mode I – G IC determined from DCB specimens. This is especially important to know for the positioning and application of the hinges. In the present work, the influence of two different IDL (5 and 20 mm) on the G IC of vacuum-infused quasi-unidirectional glass fiber reinforced plastic is studied according to DIN EN 6033. It is shown that there are significant differences in the load–displacement curves. After evaluation, however, the results of the two series are quite comparable because the differences even out in the course of the tests.