Investigation on the mode of failures and fatigue life of laser-based powder bed fusion produced stainless steel parts under variable amplitude loading conditions

Additive Manufacturing (AM) is a method of joining metal/non-metals or composites layer by layer using different energy sources. Among the various AM processes, laser-based powder bed fusion (LPBF) is very popular, in which geometrically complex structures can be manufactured directly from CAD models. One of the least investigated areas in LPBF is the fatigue property of LPBF produced stainless steel parts, which find a variety of engineering and medical applications. In actual service conditions, many engineering components undergo variable cyclic loadings. Therefore, in order to widen industrial applications of LPBF process, effects of variable amplitude loading under both zero and tensile mean stresses on the fatigue life of LPBF produced 15-5 precipitation hardened stainless steel parts have been examined in the present study. Further, different modes of failure, effects of load sequences on fatigue life and the cumulative damage during the process have also been studied. For a typical case under tensile mean stress, results showed that the number of cycles to failure with low to high loading sequence was almost double of that with the sequence reversed. Also, the cumulative damage was more in the first case than that of the second case. Fracture surfaces were studied using Scanning Electron Microscopy to investigate the mode of failures and completely different fracture surface morphologies for these two cases explain the observed difference in number of cycles to failure with the reversal of the load sequence.