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Fatigue life extension of existing welded structures via high frequency mechanical impact (HFMI) treatment
Highlights The paper presents fatigue test results and other investigations on HFMI treatment. Crack sizes, residual stresses, weld radii, distortions and hardness are measured. HFMI-treatment shows high capability in life extension of cracked structures. HFMI-treatment affects the existing crack width and changes the crack orientation. Fatigue life is estimated with good precision using fracture mechanics calculations.
Abstract High Frequency Mechanical Impact (HFMI) is one of the post-weld treatment methods. In this study, comparative axial fatigue tests were conducted on as-welded and HFMI-treated welded transverse attachment details. The test results demonstrated the efficiency of HFMI-treatment in fatigue life extension of cracked welded structures, providing that the existing crack size is less than 1.2 mm. Cracks were created in some specimens through fatigue testing before HFMI-treatment, while other specimens were not subjected to any fatigue loading prior to treatment. Many of the treated specimens ran-out after 10 million cycles of loading when tested at a stress range of 150 MPa. Therefore, the stress range was increased to 180 MPa or 210 MPa. No remarkable difference was found between the fatigue strength of the crack-free and the cracked treated specimens. It was found that the induced compressive residual stress can exceed the material yield limit, and reach a depth larger than 1.5 mm in most of the cases. The induced compressive residual stress, the local material hardening, the increase in weld toe radius, the change in crack orientation and the shallowness of the crack size were the causatives of the obtained long fatigue lives of the HFMI-treated specimens. Besides, linear elastic fracture mechanics calculations were conducted to predict the fatigue lives of as-welded and HFMI-treated details. The results were in agreement with the experiment. Moreover, the calculations showed that the initial crack size, the clamping stress and the induced compressive residual stress were the main factors behind the scatter in fatigue lives.
Fatigue life extension of existing welded structures via high frequency mechanical impact (HFMI) treatment
Highlights The paper presents fatigue test results and other investigations on HFMI treatment. Crack sizes, residual stresses, weld radii, distortions and hardness are measured. HFMI-treatment shows high capability in life extension of cracked structures. HFMI-treatment affects the existing crack width and changes the crack orientation. Fatigue life is estimated with good precision using fracture mechanics calculations.
Abstract High Frequency Mechanical Impact (HFMI) is one of the post-weld treatment methods. In this study, comparative axial fatigue tests were conducted on as-welded and HFMI-treated welded transverse attachment details. The test results demonstrated the efficiency of HFMI-treatment in fatigue life extension of cracked welded structures, providing that the existing crack size is less than 1.2 mm. Cracks were created in some specimens through fatigue testing before HFMI-treatment, while other specimens were not subjected to any fatigue loading prior to treatment. Many of the treated specimens ran-out after 10 million cycles of loading when tested at a stress range of 150 MPa. Therefore, the stress range was increased to 180 MPa or 210 MPa. No remarkable difference was found between the fatigue strength of the crack-free and the cracked treated specimens. It was found that the induced compressive residual stress can exceed the material yield limit, and reach a depth larger than 1.5 mm in most of the cases. The induced compressive residual stress, the local material hardening, the increase in weld toe radius, the change in crack orientation and the shallowness of the crack size were the causatives of the obtained long fatigue lives of the HFMI-treated specimens. Besides, linear elastic fracture mechanics calculations were conducted to predict the fatigue lives of as-welded and HFMI-treated details. The results were in agreement with the experiment. Moreover, the calculations showed that the initial crack size, the clamping stress and the induced compressive residual stress were the main factors behind the scatter in fatigue lives.
Fatigue life extension of existing welded structures via high frequency mechanical impact (HFMI) treatment
Al-Karawi, Hassan (author) / von Bock und Polach, Rüdiger U. Franz (author) / Al-Emrani, Mohammad (author)
Engineering Structures ; 239
2021-03-08
Article (Journal)
Electronic Resource
English
INCREASING FATIGUE LIFE OF NEW WELDED AND REPAIRED JOINTS BY HFMI TREATMENT
| Wiley | 2024