Mehrdad Sarafrazi
Published: 2021
Total Pages: 0
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Welding joints are the most used joining method to fabricate engineering structures due to their low cost, structural strength, and geometric flexibility. Irregular geometries, micro cracks, defects, high stress concentration and tensile residual stresses are some of the results of a highly metallurgical process considered as welding. Thus, an important subject of growing concern in product design is to consider some of the critical factors caused from the weld process including high tensile residual stresses and stress concentrations to properly evaluate the fatigue life of the structures. Lightweight design of welded steel and aluminum structures in cyclic service requires the use of post-treatment approaches like Ultrasonic Impact Treatment (UIT). In this thesis, an evaluation of fatigue tests carried out recently on welded specimens exposed to UIT under the effect of the constant amplitude (CA) loading on the fatigue strength is described. First, the effects of the various fatigue damage parameters on the as-welded (AW) condition and the impact treated welds are described in the literature review. Furthermore, fatigue test data have been taken from literature for both conditions under CA loading for several different stress ranges for each material. Following the tests, residual stress distributions below the weld toe surface have been specified by x-ray diffraction of untested specimens. More importantly, the test data obtained from the literature were analyzed through out the thesis and were used to define input parameter values for fracture mechanics analyses of the welded joint specimens. After that, the crack growth assessment of welded structures is provided. For comparison purposes, both Walker and Forman fatigue crack growth models are thoroughly reviewed and their advantages as invaluable tools for predicting the effects of UIT on fatigue performance for welded joints are examined. Subsequently, the benefit of the models in predicting fatigue crack growth behaviors for nine distinct materials are examined and the effects of the various material strength parameters on the impact treatment performance are assessed. Then, fatigue crack propagation life of the materials is displayed. In the end, the crack shape evolution of the materials is depicted. In conclusion, the outcomes of this investigation accompanied by proposed future work are mentioned.