Fatigue life enhancement of additive manufactured 316l stainless steel by LSP using a DPSS laser system

Abstract

Present work aims to study the fatigue life behaviour of additively manufactured (AM) stainless steel 316L in a laser shock peening (LSP) process. The fatigue behaviour of as-built samples and LSPeened sample were studied on the AM samples. A new diode-pumped laser system was utilized as an instrument to perform LSP operations. LSP operation was performed under two different sacrificial layers of different materials i.e. vinyl tape and aluminium tape. The other essential LSP parameters, namely energy, pulse width, spot size, overlap, and number of layers were kept constant based on the previous experimental findings. The characterization was done for analyzing the residual stresses using a hole drilling process, and a 4-point bending machine. A considerable improvement in compressive residual stress and fatigue life was observed in the LSPeened samples. Such improvements in residual stresses and fatigue life may pave a road to establishing diode-pumped lasers for LSP applications.

Evolution, Control, and Mitigation of Residual Stresses in Additively Manufactured Metallic Materials: A Review

“…Besides, some high-energy impact strengthening strategies (e.g., high-energy LSP) may lead to complications such as nonuniform compressive RSs in the treated surface, or they may not be applicable to thin-walled structures. [266,267] As such, a balanced RS mitigation strategy is essential for any particular application, and the RS mitigation strategy should be integrated with AM process optimization for the most promising outcome.…”

Fatigue Behavior of Additively Manufactured Stainless Steel 316L

“…An alternative to machining or polishing operations is represented by surface treatments, which may alter roughness, usually by mechanically reducing heights of peaks and valleys of the profile and/or inducing a compressive stress state. For AM 316L, different approaches were reported in the literature, including Shot Peening (SP) [51,67], Laser Shot Peening (LSP) [68], High-Frequency Mechanical Impact (HFMI) [57], and vibratory finishing process (VF) [43]. A summary of the life curves under these conditions is reported in Figure 5.…”

“…Among the diverse types of heat treatments reported in the literature for AM 316L, the most common is Stress Relief (SR), which is often performed on AM products and samples to release tension in the material at the end of the printing process. For SR, the temperature is relatively low and no changes in the microstructure occur, but maximum temperatures and durations varied quite significantly among the studies, ranging between 350-650 • C [46,70] and 1-9 h [68,98]. The other possible treatments include Annealing (ANN) and Hot Isostatic Pressing (HIP), which involves a combination of high temperature and pressure.…”

Fatigue life assessment of wire arc additively manufactured ER100S-1 steel parts

“…Some industries, such as aerospace and automotive, have already introduced and are widely implementing AM processes. Thus, the majority of reported data on fatigue performance of AM (and WAAM in particular) are for titanium [6,[14][15][16][17] and stainless steel [18,19]. However, only limited information is available on structural steels, which is required for promoting AM techniques in other industrial sectors, including civil engineering and renewable energy and offshore structures.…”