Further studies into interacting 3D cracks

The phenomenon of ageing structures has focused attention on the problem of multiple-site damage (MSD) and wide spread fatigue damage (WFD). In isolation each ̄aw or crack may be safe. However, the cumulative e€ect of multiple, interacting cracks may signi®cantly degrade the damage tolerance of the structure. This paper presents an overview of a new ®nite element alternating technique algorithm suitable for calculating mode I stress-intensity factors for an arbitrary number of coplanar interacting three dimensional cracks. This new algorithm has been evaluated for a variety of crack aspect ratios and crack separation ratios for fully embedded elliptical cracks, semielliptical surface ̄aws and for quarter elliptical cracks. In each instance, test cases have been studied for both ®nite and in®nite geometries. Results of three of these cases are presented in this paper. These results indicate an agreement to within 4% for all cases checked. # 1999 Published by Elsevier Science Ltd. All rights reserved.