Multiple analyses of factors influencing fatigue life of linear friction welded low carbon steel

Fatigue is an important property from the standpoint of structural reliability. It is very complex because it is affected by several factors. Many studies focus on a specific factor affecting fatigue life; few studies consider multiple factors. This study investigated the factors influencing the fatigue life of linear friction welded (LFWed) low carbon steel SM490A. The LFWed joints were fabricated by varying the applied pressure after oscillation. Joints with higher post oscillation pressure had a longer fatigue life than those with lower applied pressure. The factors affecting fatigue were primarily residual stress, hardness distribution, microstructure, crack propagation path, and local stress concentration. The results showed that for joints with a longer fatigue life, a reduced local stress concentration had a positive effect, whereas the other factors had a negative effect. Thus, it can be concluded that the most effective way to improve the fatigue life of LFWed joints is to reduce the local stress concentration by controlling the weld toe shape. The linear friction welding (LFW) method of changing the weld toe shape by increasing the applied pressure after oscillation can produce excellent joints.