AN EXPERIMETAL AND NUMERICAL INVESTIGATION OF RESIDUAL STRESSES IN BUTT WELDING OF TWO MILD STEEL PLATES

摘要

Welding is a reliable and efficient joining process in which the coalescence of metals is achieved by fusion. Welding is carried out with a very complex thermal cycle which results in irreversible elastic-plastic deformation and residual stresses in and around fusion zone and heat affected zone (HAZ). A residual stress due to welding arises from the differential heating of the plates due to the weld heat source. Residual stresses may be an advantage or disadvantage in structural components depending on their nature and magnitude. The beneficial effect of these compressive stresses have been widely used in industry as these are believed to increase fatigue strength of the component and reduce stress corrosion cracking and brittle fracture. But due to the presence of residual stresses in and around the weld zone the strength and life of the component is also reduced. To understand the behavior of residual stresses, two 10 mm thick Fe410WC mild steel plates are butt welded using the Metal Active Gas (MAG) process. An experimental method (X-ray diffraction) and numerical analysis (finite element analysis) are carried out to calculate the residual stress values in the welded plates. A three-pass V-butt weld joint is considered in this study. In multi-pass welding operation the residual stress pattern developed in the material changes with each weld pass. In X-ray diffraction method, the residual stresses were derived from the elastic strain measurements using a Young's modulus value of 210 GPa and Poisson's ratio of 0.3. Finite element method based, SolidWorks Simulation software is used to develop a coupled thermal-mechanical three dimension finite element model. The finite element model was evaluated for the transient temperatures and residual stresses during welding. Also variations of the physical and mechanical properties of material with the temperature were taken into account. It can also be concluded that when temperature distribution increases then the residual stress in the weldment also increase. The results obtained by finite element method agree well with those from experimental X-ray diffraction method.