Study On The Evolution Process And Mechanical Behavior Of Multiple Cracks At Weld Toe

At present,welding is the most important connection mode in engineering structure.Welding structures are widely used in various industries.Under the action of alternating load,fatigue failure is one of the main reasons for the failure of welding structure,and the fatigue performance of welding structure is mainly determined by the fatigue performance of welding joint,so it is very necessary to analyze the fatigue of welding joint.In the process of manufacturing,there are inevitable defects in the welding structure,which lead to the stress concentration effect in the local part of the weld,and the most significant is the fatigue crack at the weld toe.In this paper,for the cruciform welded joint,considering the local morphology of the complex weld,combined with the elastic-plastic theory,the influence of the weld morphology on the behavior of multiple cracks initiation is studied.Using the method of finite element simulation and fatigue test,with the aid of fracture inversion technology,multiple cracks of different scales are successively inserted at the weld toe,and the evolution rule and corresponding life change of multiple cracks in the whole process of fatigue are studied The stress distribution at the weld toe is analyzed when there are cracks of different scales.The main research contents are as follows:(1)Taking the cruciform welded joint as the research object,considering the local morphology of the weld,a three-dimensional finite element model was established to calculate the stress and strain distribution in the weld toe area,and compared with the numerical simulation results without considering the local morphology of the weld,the influence of the weld morphology on the initiation position of multiple cracks in the welded joint was studied.The cyclic tensile test under variable amplitude load was carried out on the specimens.The initiation life of multiple cracks was calculated by Manson-coffin strain life curve.The influence of local weld morphology on the fatigue life of welded joints was studied.The initiation behavior of multiple cracks was studied by comparing with the test results.(2)The fatigue fracture morphology obtained from the test is studied by fracture inversion technology.The beach mark is used to represent the instantaneous crack front line,so the information of real multiple cracks is obtained.Combined with the finiteelement simulation technology,the complete cyclic loading process of the crack is simulated by using the method of sub model,and the asynchronous evolution characteristics of the multiple cracks are analyzed.(3)The semi elliptical cracks with the same shape ratio and different depth are respectively inserted into the weld toe of the cross weld joint.Combined with the properties of elastic-plastic materials,the stress and strain state of each point on the whole weld toe line is calculated and analyzed,and the change of the stress field in the weld toe area with the crack size and the distance between the crack tips is studied.