DAMAGE MAPPING OF FATIGUED SKIN-STRINGER SPECIMENS IN THREE DIMENSIONS

摘要

This paper presents the three dimensional fatigue damage observed in two skin-stringer specimens subjected to fatigue cycles. The fatigue specimens were dissected and micrographs of the polished section edges were taken to reveal internal damage. The entire internal damage was mapped in three dimensions and results revealed a reoccurring damage pattern common to both specimens. The damage mechanism initiated in most part by a 45 degree crack at the tip of the bond line between the skin and stringer flange, which then propagated through the bond line to create the first of two delaminations. Damage at the outer edges was identical at diagonally opposite corners of the stringer flange and was dominated by the presence of a single delamination. Damage was most complex in the center of the specimens where delaminations were observed to grow along two distinct planes. Results further revealed an almost systematic transition between the two delaminations, stemmed by a 45 degree transverse matrix crack. The second delamination originated from this transverse crack and propagated in both directions along the length of the specimen. The results will help understand whether the Virtual Crack Closure Technique (VCCT) for Abaqus can be used to model the propagation of damage in skinstringer configurations.