Perpustakaan Digital ITB

Military aircraft are subjected to complex operational loading, while structural discontinuities such as rivet holes create local stress concentrations that can accelerate the propagation of pre-existing flaws. The wing-rib lower flange is a critical structural region containing multiple fastener holes and is therefore susceptible to fatigue-crack propagation. This study develops a numerical procedure based on linear elastic fracture mechanics (LEFM) to analyse multiplecrack propagation and the transition between different crack geometries. The loadrange exceedance data were derived from Flight Data Recorder (FDR) measurements obtained during trainer-aircraft operations. The data were discretized into twelve blocks and converted into a Paris–Walker equivalent constant-amplitude load. The resulting equivalent load factor was 1.3743 g, corresponding to a nominal maximum stress of 36.25 MPa at . Stress-intensity factors were determined using compounded geometry correction factors, while crack propagation was calculated using a thresholded Paris law. The model represents the transition from three collinear cracks at adjacent rivet holes to a single eccentric crack. Three asymmetric initial-flaw cases and load sensitivities from 1 to 9.2 g were evaluated. Under the equivalent loading, only the 1.27 mm primary flaw was initially active, while the 0.127 mm flaws remained below the crack-growth threshold. Initial-flaw location affected the governing crack tip and propagation duration, with Case A producing the shortest numerical life. Increasing load caused a nonlinear reduction in propagation cycles. The model is limited to deterministic, two-dimensional Mode-I loading and excludes loadsequence effects, crack closure, fastener contact, three-dimensional crack geometry, and experimental validation.