Short/Small crack model development for aircraft structural life assessment

This paper presents the testing and modeling results from an NRC project on short/small1 crack model development for aircraft structures. Fatigue tests were conducted for 7075-T73 hand forging aluminium material using precracked compact tension (C(T)) and naturally cracked single edge-notch tension (SENT) coupons, under various stress ratios. The adjusted compliance ratio (ACR) method was used for the C(T) coupon tests aiming to quantify remote closure due to plasticity and forging-induced residual stresses. For the SENT coupons, three-dimensional StressCheck finite element (FE) models were developed to accurately calculate the stress intensity factors of surface and corner cracks. Both C(T) and SENT test data were combined to develop short-long fatigue crack growth rate models. These models were then used in crack growth life analyses for coupon and component cases, taken from transport aircraft under spectrum loadings. It was shown that the newly developed models resulted in more accurate fatigue life estimations.Peer reviewed: YesNRC publication: Ye