Fatigue life extension in existing steel bridges. High-Frequency Mechanical Impact treatment and Tungsten Inert Gas remelting in life extension and fatigue crack repair of welded steel structures
Licentiate thesis, 2020
Complimentary studies showed that the investigated methods induced compressive residual stress, increased the smoothness of the weld toe, increased the local hardness and changed the angular distortion status locally. Moreover, TIG-remelting changed the microstructure in both the fusion zone and the heat-affected zone. HFMI-treatment changed the crack orientation, induced compressive plasticity at the crack tip and caused crack narrowing or even closure. However, these effects were less significant for deeper cracks. Moreover, some practical aspects of the treatment application were investigated. Unlike treating new structures, TIG-electrode should be placed at the weld toe to secure that the maximum fusion depth corresponds to the crack plane. On the other hand, HFMI-indentor should be slanted more toward the base metal than the weld to avoid unintentional crack opening. Moreover, the IIW recommendations for both HFMI-treatment inclination and indentation depth could be extended to cracked structures.
The aforementioned investigated parameters (i.e. residual stress, distortions, local hardness and toe's smoothness) were incorporated in fatigue life predictions for both treatment methods. The base metal S-N curve was used to predict the life of specimens treated via TIG-remelting, while Paris law was used to track the crack propagation of HFMI-treated details. The results corresponded well with fatigue test results. Combining TIG-remelting with HFMI-treatment resulted in welds with higher fatigue strength because of the combined effects of crack closure via TIG-remelting and compressive plasticity via HFMI-treatment.
Post weld treatment
Linear elastic fracture mechanics
Chalmers, Architecture and Civil Engineering, Structural Engineering
Fatigue crack repair in welded structures via tungsten inert gas remelting and high frequency mechanical impact
Journal of Constructional Steel Research,; Vol. 172(2020)
Fatigue life extension of existing welded structures via High Frequency Mechanical Impact treatment, Hassan Al-Karawi, R.U.Franz von Bock und Polach, Mohammad Al-Emrani
The effciency of high frequency mechanical impact treatment and tungsten inert gas remelting in fatigue life extension of existing welded structures, Hassan Al-Karawi, Mohammad Al-Emrani
Crack behaviour after High Frequency Mechanical Impact treatment in welded S355 structural steel, Hassan Al-Karawi, Joakim Hedegård, Mohammad Al-Emrani
LifeExt - Livslängdsförlängning för befintliga stålbroar
Swedish Transport Administration, 2018-05-15 -- 2020-11-30.
VINNOVA, 2017-06-08 -- 2019-12-31.
Areas of Advance
Manufacturing, Surface and Joining Technology
Other Materials Engineering
Lic / Architecture and Civil Engineering / Chalmers University of Technology
Chalmers University of Technology
Opponent: Assoc. Prof. Martin Leitner Chair of Mechanical Engineering Montanuniversität Leoben, Austria