Prediction of Fatigue Life and Crack Path in Generic 2d Structural Components under Complex Loading

A reliable and cost effective two-phase methodology is proposed to predict crack propagation in generic two-dimensional structural components under complex fatigue loading. First, the fatigue crack path and its stress intensity factors are calculated in a specialized finite element software, using small crack increments. At each crack propagation step, the mesh is automatically redefined based on a self-adaptive strategy that takes into account the estimation of the stress analysis numerical errors of the previous step. Numerical methods are used to calculate the crack propagation path, based on the computation of the crack incremental direction, and the stress-intensity factors KI and KII, from the finite element response. An application example presents a comparison between numerical simulation results and those measured in physical experiments. Then, an analytical expression is adjusted to the calculated KI(a) values, where a is the length along the crack path. This KI(a) expression is used as input to a powerful general purpose fatigue design software based in the local approach. This software has been developed to predict both initiation and propagation fatigue lives under complex loading by all classical design methods, including the SN, the εN and the IIW (for welded structures) to deal with crack initiation, and the da/dN to treat propagation problems. In particular, its crack propagation module accepts any KI expression and any da/dN rule, using the ∆Krms or the cycle-by-cycle propagation methods to deal with one and two-dimensional crack propagation under complex loading, considering overload-induced crack retardation.