چكيده به لاتين
Magnetically impelled arc butt welding (MIAB) as a brilliant method for welding tubular components was subject of this research. In this method the arc is impelled to rotate between the gap of weldments and after uniform heating of them the components are forced together to form solid state weld. Residual stress as a major contributing factor for mechanical-metallurgical behaviour of welded joints has been thoroughly investigated in the welding methods. However, it has not been investigated in this type of welded joints. While, the knowledge of residual stresses affected by welding parameters can help us in better selection of welding conditions among feasible ones. To conduct this research MIAB welding machine was constructed and the welding of A335 grade P 11 pipes were performed on different welding conditions to obtain a well welded joint. By the thermal-metallurgical and mechanical experimentally obtained results from the welding condituion were used to verify the accuracy of numerical model to predict distribution of residual stress in this type of joints. Numerical modeling of multi-physic manufacturing processes such as welding has been always a complex task when it involves phase changes. In this regard, a finite element model for simulation of the heat transfer, phase transformation, and mechanical analysis of magnetically impelled arc butt welding of low alloy steels is presented. Both effects of volumetric dilatation and transformation-induced plasticity were considered in the mechanical analysis. Series of welded joints were prepared in various welding conditions by using magnetically impelled arc welding machine. Microstructure and residual stresses of a sample were used to verify numerical results. To highlight the importance of volumetric dilatation and transformation-induced plasticity effects, the numerical results were compared with and without the mentioned effects. Transformation induced plasticity (TRIP) have been subject of many researches for predicting distortion and residual stresses in thermo-mechanical processes which involve phase transformation. Currently available methods range from simplified methods in which yield stresses are only reduced during phase transformation, to sophisticated ones which consider fully coupled thermal-metallurgical and mechanical fields. In this work, modification of classical plasticity for implementation of TRIP is investigated. Using ABAQUS tool, the obtained equations were incorporated in numerical model via developed user subroutines. The accuracy of the adopted model was verified experimentally using measured data of residual stresses in samples welded by magnetically impelled arc butt welding method. The results reveal that the values obtained from the developed model are in good accordance with those of the experiments. In this study, the influence of welding parameters on the distribution of residual stress in magnetically impelled arc butt welded joints was investigated. As major contributing factors to the quality of weldments and residual stress, welding time and welding upsetting pressure were focal points of this work. Experimentally verified thermal-metallurgical and mechanical finite element model was used for conducting this purpose. The effects of phase change including volumetric phase change and transformation plasticity were considered in the numerical model. Based on the numerical simulation it was observed that for instance by increasing upset pressure and decreasing welding time, these stresses have reduced on the outer surface of the weld line. Based on the numerical simulation it was observed that for instance by increasing upset pressure from 0 to 130 MPa, axial residual stresses have reduced from -210 MPa to -109 MPa, while by increasing welding time from 4 to 6 s, these stresses have increased from -109 MPa to -138 MPa on the outer surface of the weld line.
