Thermal and residual stress anlayses of a welded stainless steel plate

In this study, a welding simulation was analyzed numerically by using finite element method. Two-dimensional model of butt welded plate was conducted in ANSYS finite element package software. Transient thermal distribution on ST-37 plate was obtained for all time intervals until it reaches environment temperature. The initial temperature of ST-37 was considered 300 K, whilst the temperature of welded zone was assumed to be 1773 K. The enthalpy and density of the welded zone material were assumed to have temperature dependent values, although the non-welded zone of the steel was considered to have constant values. In accordance to this, plastic stresses were presented base on the elasto-plastic bilinear material behavior using structural analysis. Finally, residual stresses were found out by removing loads on the butt welded plate. Changing of residual stresses and spread of plastic zones according to cooling time were investigated. INTRODUCTION Nowadays, there is wide application area of metallurgical joints made by welding in fabrication industry due to their advanced properties such as high joint efficiency, water and air tightness and low manufacturing cost. The types of welded joint can be classified into five basic categories; butt, fillet, corners, lap and edge [1]. Butt welds are commonly used in joining metal plates either to same metal or to different metal. Problem associated with welded joints is residual stress near the weld zone on the metal plate due to localized heating by the welding process. If residual stresses reach high values, this situation causes a reduction of load capacity and complex failure modes. Because of this reason, it is wanted more detailed design knowledge and production techniques about welded joints. For the prediction of the temperature and residual stress distribution, numerical studies on thermomechanical behaviour of welded structures have increased with the development of finite element method in addition to the experimental studies [2-4]. Teng et al. [1] described the thermal elasto-plastic analysis using finite element techniques to analyze the thermomechanical behavior and evaluate the residual stresses and angular distortions of the T-joints in fillet welds. The effects of flange thickness, welding penetration depth and restraint condition of welding on the residual stresses and distortions were discussed. Barsoum and Lundback [5] carried out two and three dimensional finite element welding simulations in order to study the formation of the residual stresses due to 3D effect of the welding process. Residual stress measurements were carried out using X-ray diffraction technique on the manufactured Twelded structure. The 2D residual stress predictions showed good agreement with measurements. Barsoum and Barsoum [6] developed a welding simulation procedure using the finite element software ANSYS in order to predict residual stresses. The procedure was verified with temperature and residual stress measurements found in the literature on multi-pass butt welded plates and T-fillet welds. The predictions showed qualitative good agreement with experiments. The welding simulation procedure was then employed on a welded ship engine frame box at MAN B&W. A subroutine for LEFM analysis was developed in 2D in order to predict the crack path of propagating fatigue cracks. Teng et al. [7] analyzed the thermo-mechanical behaviour and evaluated the residual stresses with various types of welding sequence in single-pass, multi-pass butt-welded plates and circular patch welds. This was achieved by performing thermal elasto-plastic analysis using finite element techniques. Lindgren [8-10] used finite element simulation in order to predict temperature fields, residual stresses and deformation due to welding in 2D and 3D. Kong et al. [11] developed a model based on a doubleellipsoidal volume heat source to simulate the gas metal arc welding (GMAW) heat input and a cylindrical volume heat source to simulate the laser beam heat input to predict the temperature field and thermally induced residual stress in the hybrid laser–gas metal arc (GMA) welding process. Numerical simulation showed that higher residual stress distributed in the weld bead and surrounding heat-affected zone (HAZ). Zain-ul-abdein et al [12] investigated the effect of metallurgical phase transformations upon the residual stresses and distortions induced by laser beam welding in a T-joint