Prospects in fracture mechanics of “engineering” laminates

The test method development for inter-laminar fracture toughness testing of fibre-reinforced composites has yielded one international standard for Mode I opening loading of unidirectionally fibre-reinforced laminates so far. However, the bulk of composite materials in technical applications, summarily labelled “engineering laminates”, mostly consists of laminates with optimised fibre-orientations, frequently varying from ply to ply, i.e., so-called multi-directional laminates. Increasingly, so-called “three-dimensional” laminates are also being developed and being put to use in engineering applications. The present paper explores some of the problems that arise when the standard Mode I test method is applied to engineering laminates in the form of cross-ply (0°/90°) lay-up or z-pin reinforced, three-dimensional composites.