Bending Fatigue Strength of WAAM AISI 316L with Severe Shot Peening Applied to as-Built Surface

This study investigates the surface roughness, hardness, and fatigue performance of AISI 316L walls produced via wire arc additive manufacturing (WAAM) under three different surface conditions: as-built, severe shot peened (SSP), and machined. The WAAM-printed walls exhibit typical layered structures with some surface irregularities due to thermal cycling. Surface roughness measurements show that the machined surface has the lowest roughness values (Ra = 0.43 µm), while the as-built surface displays significant roughness (Ra = 37.56 µm), which is decreased by SSP (Ra = 34.67 µm). SSP slightly improves overall smoothness but does not eliminate major surface irregularities. Hardness measurements indicate that the base material has uniform hardness across the wall, ranging from 200 to 220 HV, while SSP significantly increases surface hardness to 450 HV near the edges due to localized work hardening. SSP-treated surfaces improve fatigue resistance by inducing compressive residual stresses, with a fatigue limit of 198 MPa, compared to 75 MPa for the as-built surface. However, machined surfaces exhibit the best fatigue performance, with a fatigue limit of 223 MPa, owing to the elimination of surface defects and stress concentrators. While SSP enhances surface hardness and fatigue performance over the as-built condition, machining remains essential for achieving superior fatigue life and surface quality.