Friction Stir Surface Modification Approach for Enhanced Fatigue Allowable

Fatigue life critically depends on the microstructural distribution and surface conditions. Friction stir processing (FSP) is a solid-state process that refines the microstructure very significantly. This leads to enhanced fatigue life for aluminum and magnesium alloys. Overall fatigue life of defect-free microstructure is usually divided into, (a) cycles to crack nucleation, and (b) crack growth life. The microstructural refinement by FSP influences both these stages. Discussion will be presented for how design allowable can be increased by taking advantage of microstructural refinement. A framework of optimum grain size range where crack initiation and growth is retarded will be presented. Reliability of high performance components can be treated by connecting the microstructural distribution with fatigue life distribution, a probabilistic-deterministic linkage approach.