PSI - Issue 36

157 5

Robert Kosturek et al. / Procedia Structural Integrity 36 (2022) 153–158 Robert Kosturek, Janusz Mierzyński, Marcin Wachowski et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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Fig. 3. Fracture surfaces: M1 sample, 0.25% strain amplitude (a,c), M2 sample, 0.5% strain amplitude (b,d). The photos in the lower row are magnifications of the areas marked with yellow squares.

In all tested samples the failures occurred in the heat-affected zones. For both selected fracture surfaces we can observe a couple of dimples and tear ridges characterized by ductile fracture mode indicating plastic deformation capacity (Fig. 3 c,d). The only major difference is in the occurrence of a larger number of crack initiation sides for the sample tested at higher total strain amplitude (Fig. 3b). 4. Conclusions The performed research showed that all joints obtained with parameters of 1600 rpm and 150 – 900 mm/min have very high values of joint efficiency, about 90%. The highest value has been reported for 600 mm/min welding velocity (98%). Low-cycle fatigue test revealed that the AZ31 FSW joint is characterized by three stages of fatigue life: a very short period of cyclic hardening (up to 100 cycles), cyclic stabilization, and a relatively long period of cyclic softening until failure. Both tensile and LCF tests result in a failure in the heat-affected zone for all tested samples. No significant differences between used FSW parameters have been reported in terms of LCF properties.