Finite element modelling of fatigue crack growth in multi-layered architectures

Crack growth analyses in multi-layered architectures used in the automotive industry for plain bearings, displaying elastic and plastic mismatches, were developed through automated meshing processes based on the Finite Element Method in the commercial code ANSYS. Two-dimensional FE analyses studied the effect of shielding and anti-shielding on crack growth in flat strip specimens subjected to three-point bending tests experiencing severe yielding and path deflections. This study was based on Crack Tip Opening Displacement estimates, the maximum tangential strain criterion and automatic step by step extensions to account for crack growth. The analysis of forecasted paths for deflected and bifurcated cracks showed the tendency of the crack to grow parallel to the layers orientation within the compliant interlayer, as observed experimentally, and following a path which maximised the crack driving force. The interaction of two-dimensional width-through cracks in co-linear, parallel-dominant and oblique arrangements was studied to compare their behaviour to independent growing cracks. The development of three-dimensional models was aimed to study the crack front evolution when more compliant or stiffer layers were placed ahead of the crack in flat strip specimens subjected to three-point bending tests experiencing severe yielding. The crack front growth was estimated according to the local values of the Crack Tip Opening Displacement and a fitted crack growth law, which accounted for the short fatigue crack behaviour observed experimentally. The comparison of Crack Tip Opening Displacements obtained with two-dimensional and three-dimensional models showed that the estimates obtained with the latter were affected to a lesser extent by shielding and anti-shielding. The estimation of cycles to propagate a crack to the interlayer, in addition to the initiation life obtained in previous experimental work at the University of Southampton, estimated that less than 40% of the total life was required for such a process and demonstrating the damage tolerance of the layered architecture. A detailed stress and strain analysis of the service conditions, based on the Elasto-Hydrodynamic Lubrication pressure, and manufacturing processes, mainly related to the forming of a concave shell, was developed for plain bearings as the initial step of a damage tolerance analysis.