Papers by Keyword: Welding Residual Stress (WRS)

Abstract: This investigation firstly performs a thermal elasto-plastic analysis using finite element techniques to evaluate residual stresses in monolithic joint weldments, then develops an effective procedure by combining the welding residual stress and dynamic responses by moving train loads , finally calculates the stress history of hot spots in local weldments .The results showed that the stresses of some hot spots in weldments had exceeded the yield stress of steel , so the fatigue of these spots should be categorized into low cycle fatigue; the load application on the welded bridge produces a reassessment of the stress field in the weldments and, in particular, a relaxation of the maximum stress.

Abstract: In this paper, a butt-welded plate with cracks of different sizes and locations was used to analyze the crack propagation in the residual stress field. A two-dimensional finite element model was established to study the distributions of stress intensity factor along crack front in the residual stress field. Several cases with different crack lengths and angles were investigated. It was found that the distributions of stress intensity factor along crack front were very sensitive to residual stress. The methods and results presented in this paper are capable of providing a reference for the efficient assessment of the effect of residual stress field on the crack propagation behavior. It also implies that proper welding procedures are required for acceptable residual stress distributions to ensure prolonged service life of weldments.

Abstract: As a kind of the high strength low alloy steel (HSLA), 30CrMoSi has been used widely in some industrial fields. However, just like some HSLA, this steel also faces some problems when it is welded, especially such problem as cold cracking in the welded joints. In this paper, the cold welding cracks and microstructure of the joints of 30CrMoSi steel were studied by scanning electron microscopy (SEM) and optical microscopy (OM), and a method called welding with trailing impacting and rolling (WTIR) was utilized to solve the problem mentioned above by decreasing the residual welding stress which is one main factor to lead to cold welding crack in the joint of HSLA. The crack-free joints of 30CrMoSi steel were obtained by using proper parameters.

Abstract: The welding processes of steel materials are often accompanied by the occurrence of phase transformation. Volume change caused by phase transformation will affect the history of stress and strain. In this article, taking the welding of Q345 as an example, the effects of solid-state phase transformation on the residual stress were investigated by numerical simulation. The values of thermal strain at different temperatures were set to make the volume change caused by phase transformation equivalent as thermal strain. The simulation contained two cases both considering phase transformation and not. The results show that in both two cases the longitudinal stress distribution in the weld zone has almost the same trend. But in the case without considering phase transformation, there is large longitudinal tensile stress concentrating in the weld and HAZ zone and the maximum value is up to 427MPa in the weld. For transverse stress, phase transformation not only changes the value of the stress, but also alters the sign of the stress in the middle of the weld zone. Experiment was also carried out to measure the residual stress by X-ray diffraction. The result considering phase transformation matched much better with the experimental data. It can be concluded that phase transformation in the process of welding has a significant effect on the residual stress and can not be ignored in the numerical simulation of welding.

Abstract: Aimed at the problems such as welding stress concentration and especially irregular distribution of welding residual stress for anchorage area in cable-stayed bridges, three full-scale beam-anchor-plate connection models of Chongqing Jiangjin Guanyinyan Yangtse Rive bridge were made and the tests were performed. The purposes of the tests and study were to investigate the distribution of welding residual stress in anchorage area and moreover to find a way to reduce and eliminate the welding residual tensile stresses. For this reason ultrasonic impact was imposed on the main welds of the three models. The result of the experiment showed that there were quite considerable welding residual stresses in the anchorage area. It also displayed that the ultrasonic impact was able to effectively decrease and even release the welding residual tensile stress. The ultrasonic impact was able to not only improve the adverse state of the welds stress but also make the distribution of the welds stress smoother. The ultrasonic impact is an effective and feasible method to decrease and eliminate welding residual stress and thereby improve the fatigue strength of welds for the steel bridge.

Abstract: By the finite element analysis codes ABAQUS and the function of RESTART, a sequential coupling calculating program for creep based on welding residual stress has been developed by establishing the model of temperature field, residual field and creep analysis. The welding residual stress and creep of welded joint for Cr5Mo furnace tubes was simulated by the program. This method established the basis for calculating the effects of welding residual stress on the creep of welded joint. A creep comparison between the welded joint tubes with welding residual stress and with internal pressure was made in the paper. The results show that although the residual stress is greatly decreased due to the creep relaxation behavior at high temperature, the initial welding residual stress has a great influence on the tube creep. The research results provide a reference for strength design of high temperature components.

Abstract: The micromagnetic measurement method is a fast and easy to handle alternative for the determination of residual stresses in steel welds. The accuracy is lower in comparison to diffraction techniques but it can be applied faster and under rough conditions however connected with a lower accuracy. Experimental results of investigations with different steel welds show that the method requires an external calibration and the consideration of particular boundary conditions as well as certain limitations must be accepted. Then the method is a good alternative or more a complementary measurement methods which helps to reduce the effort for the analysis of residual stresses in welded components.

Abstract: Residual stress relaxation of butt-welded small scale steel specimens under static and cyclic mechanical loading was investigated. The experiments were carried out on different types of steel with yield strengths between 300 and 1200MPa. The x-ray and neutron diffraction techniques were applied for the residual stresses analysis. The maximum values of initial residual stresses were measured at the weld bead centerline and were not as frequently assumed as high as the yield strength of the material. From fatigue point of view the internal stresses at the weld toe are of importance. It was observed that only a fraction of maximum residual stress accommodated in the weld bead centerline, is available at the weld toe. Under static tensile and compressive loading by increasing the load level the residual stress field relaxes continuously. The relaxation sets in with delay under compression since the tensile residual stresses should be first overcome. Under cyclic loading, once the first relaxation takes place further cyclic relaxation is either not considerable or continues moderately depending on loading conditions. In high cycle fatigue the residual stresses are stable until 2x10⁶ cycles. In low cycle fatigue however the variation of the residual stresses continues until failure. This variation is partly related to crack initiation and propagation. The von Misses failure criterion with the local yield strength as material resistance against plastic deformation was able to describe the relaxation of surface welding residual stresses in low cycle fatigue.

Abstract: The dynamic stress-strain and welding residual stress during welding are the significant factors which lead to welded cracking and debasement of the joint properties. Therefore, the welding residual stresses are still very importang problems.A large number of guyed mast accidents study shows that the welded joints of earplate and shaft were easily to be destroyed. Therefore, the accurate assessment of the guyed maste earplate joint substructure’s welding residual stress is of great significance. The theory and method of simulation of the welding temperature field and welding stress field by finite element method is first introduced, and then the earplate substructure refine model is established which was up to the welding numerical simulation. Based on ANSYS software’s APDL language to apply the welding heat source load, we can get and save the welding temperature field results at each time. Conversing the thermal analysis element into structure element to finish the caculation of the welding stress field. Eventually by adopting the elimination remnant technology to remove the part of welding residual stresses, we can got the final welding residual stress in different relieving proportion.

Abstract: Based on the finite element analysis software ABAQUS, a sequentially coupled fillet welding thermal-stress calculation program was developed to simulate the plate close welding structure. The welding temperature fields and the stress/strain distributions of plate sealing joint of the hydrogenation heat exchanger were obtained. The simulation results showed that there existed higher stress near the fillet weld sealing joint zone and the maximum stress at the start welding point, the plastic strain of the weld joint was lager and a strain mutation occurred on the weld overlay .The analysis of the calculation result provides theory references for controlling the welding residual stress and it’s of great significance to improve the reliability and safety of hydrogenation heat exchanger.