ASSESSMENT OF DELAMINATION CRACK GROWTH RATE OF CO-CURED STEPPED LAP JOINTS IN COMPOSITE MATERIALS

In this paper the fatigue behavior of co-cured stepped-lap joints in composite materials is discussed in terms of Strain Energy Release Rate. Previous works showed that the fatigue life of those joints is characterized by an early nucleation phase of transversal matrix cracks followed by a propagation phase. In this paper 2D finite element models were developed and the mode I and mode II component of the SERR were calculated by using the Virtual Crack Closure Technique. It was found that the propagation phase is under mixed mode (mode I + mode II) loading with a mode I predominance. Therefore the range of the mode I SERR was adopted to define a suitable Paris-like curve able to rationalize in a single scatter band the Delamination Growth Rate data.