Solovei S. Increasing fatigue life of the t-shaped welded joints with accumulation of fatigue damages by High-Frequency Peening

Thesis for candidate of engineering sciences degree in specialty 05.03.06 - "Welding and allied processes and technologies". The E.O. Paton Electrical Welding Institute of NAS of Ukraine. Kyiv- 2010. The thesis is dedicated to investigating extension of fatigue life of the t-shaped welded joints from low alloy steels treated by High-Frequency Mechanical Peening (HFMP) in initial state and after accumulation of fatigue damage under regular and variable-spectrum loading. Based on the hypothesis of the linear summation of fatigue damages, the failure criteria of the t-shaped as-welded joints and joints treated by HFMP under variable-spectrum of loading (increasing, decreasing and quasi-random) are defined. It is confirmed that accumulation of fatigue damage of joints treated by HFMP did not depend on sequence of loading. Residual fatigue life of t-shaped welded joints treated by HFMP after the accumulation of 50% fatigue damages under regular and variable-spectrum of loading is investigated. The rule of summation of fatigue damages of the as-welded joints to account for residual stress and stress concentration factor (that decrease scattering of total damage) is substantiated. The effectiveness of HFMP treatment of the t-shaped welded joints, which contain incomplete fusion or surface fatigue cracks, for extension of fatigue life is experimentally proved.