Retardation of fatigue crack growth in aircraft aluminium alloys via laser heating – Simulation based design optimisation

Abstract

Purpose – While normally the formation of thermally induced residual stresses is seen mainly as detrimental side effect from production processes like welding or casting, the well-directed introduction of thermal residual stresses can also be used as tool to retard fatigue crack growth (FCG). In the presented paper, the use of a defocused laser to modify the residual stress state, and by that to retard the FCG, is examined. The focus lies on the simulation-based optimisation of the heating line position for achieving a maximum fatigue life. The paper aims to discuss these issues. Design/methodology/approach – In the presented work, the developed prediction methodology for the FCG coupling process simulation and subsequent fracture mechanics analysis is used to identify the optimum positioning of either one or two heating lines on a C(T)100 specimen that leads to a maximised total lifetime. Afterwards, the prediction results are validated experimentally for selected cases. Findings – The predictions match the experiments within the experimental scatter indicating the correct identification of the optimum heating line positions. This demonstrates the large potential for reducing the experimental effort needed for design optimisation using the proposed strategy. Originality/value – The used methodology of coupling of welding simulation with subsequent fracture mechanics analysis in order to optimise the FCG behaviour of structures is innovative and only very few published studies addressed parts of similar approaches.