Predictions of Fatigue Crack Growth and Fatigue Life for Riveted Lap Joints
Fatigue is a process in which a crack initiates at a particular location and grows slowly and progressively under service loading to a size at which the residual strength of a structure is insufficient to sustain the prevailing loads, and rapid failure occurs. Aircraft manufacturers were the first industrial branch to place reliance on damage tolerance designs. It was assumed that initial imperfections and flaws inherent in the material or introduced during manufacturing pre-exist in the structure and can become sources of cracking. Consequently, in recent years the main focus of the research related to fatigue of aircraft fuselage lap joints has been on modelling the crack growth stage rather than the crack initiation stage. Most crack growth prediction models are based on linear elastic fracture mechanics (LEFM) concepts and correlate crack growth using the stress intensity factor (SIF). It is well known that due to the anomalous behaviour of small cracks such predictions can be unreliable and lead to unconservative results in the early stage of crack growth from the initial defect. A concept of the equivalent initial flaw size (EIFS) developed by Rudd and Gray (1976, 1978) and Manning and Yang (1986) was conceived to cope with the lack of analytical means to deal with the crack initiation phase and small crack growth. The EIFS approach enables one to model the entire crack growth process using the LEFM methodology.