ABSTRACT

The free-edge problem has attracted considerable attention during the past three decades. The proliferation of analytical investigations is a direct result of experimental observations indicating that laminate strength and failures at free edges can be influenced significantly by the stacking sequence of the individual layers. Free-edge stresses exist in a boundary-layer region and they are not accounted for by classical lamination theory. Singular behaviour is exhibited by some of these stresses, making laminates susceptible to delamination at the free edge. A fundamental understanding of the interlaminar stress field associated with the free edge in laminated composites is critical in order to develop delamination prediction models. Consequently, numerous analytical and numerical approaches are described in the literature. For straight free edges, these include finite-difference and finite-element techniques, boundary-layer approaches, force balance methods, stress potentials, sub-structuring and others. As can be seen from figure 5.3.1, discrepancies exist between different solutions even to the extent if the sign of the local stress field [1].