Thermoelasticity for the Evaluation of Fatigue Behaviour of 6061/AL

In this study, the effect of Friction Stir Welding on a 6061 aluminium alloy reinforced with 20% of alumina particles metal matrix composite was analysed. The sheets were joined by employing a tool rotating speed of 700 RPM and a welding speed of 250 mm/min. The optical and scanning electron microscopy observations performed on the different zones of FSW joints cross section revealed the different structures of the nugget, the thermo‐mechanical affected zone and the heat affected zones thanks to the difference in reinforcing particles dimensions as a consequence of friction process. After FSW the material was aged in a 3.5% NaCl solution for 1, 10 and 90 days. The aim of this work is to apply thermoelastic stress analysis to the study of crack formation and propagation of friction stir welded MMC sheets, during cyclic fatigue tests. Fatigue tests were carried out under the axial total stress‐amplitude control mode with R=omin/omax = 0.1 using a resonant electro‐mechanical testing machine (TESTRONICTM 50 25 KN by RUMUL (SUI)). All the mechanical tests were performed on as‐FSW and aged samples up to failure. The TSA measurement system allowed the crack evolution to be observed in real‐time during fatigue cycles and stress fields to be derived on the specimens from the temperature variation measured.