Issue 35

R. Citarella, Frattura ed Integrità Strutturale, 35 (2015) 523-533; DOI: 10.3221/IGF-ESIS.35.58 526 a b c x y x y Crack tip N. 1  Crack tip N. 2  Crack tip N. 3  Crack tip N. 4  Hole N. 6  Hole N. 10  Internal springs  J‐path  Figure 3 : DBEM model of lap-joint in the proposed initial cracked configuration, with highlight of: hole numbering on the cracked raw (a) ; main crack (b) ; hole constraints, rivets, J-path around the crack tip and “internal springs” (c) . Figure 4 : Secondary bending phenomena. Gap elements have also been introduced to better tackle contact conditions [12] but the solution improvement has been judged quite negligible (less than 2% variation on SIFs), except in case of very short cracks initiated from the holes, more sensitive to pin-hole contact conditions. For this reason, and due to the computational effort of a non-linear analysis, they have no longer been used. The J-integral technique is adopted for SIF’s evaluation, being more stable than Crack Opening Displacement method against crack mesh variations [13].