Thermal Elastic-plastic Finite Element Method Research Articles

Prediction of Welding Deformation Using the Thermal Elastic-Plastic Finite Element Method by Considering Welding Interpass Temperature.

In this study, we propose a method for predicting welding deformation caused by multi-pass welding using the thermal elastic-plastic finite element method (TEP-FEM) by considering the interpass temperature. This method increases the interpass temperature, which has not been considered in the existing TEP-FEM, from 200 °C to 1000 °C, and simultaneously performs thermal and mechanical analyses. In addition, this method can also evaluate temperature history and the time it takes to weld. By predicting the welding deformation using this method, angular distortion prediction was reduced from 16.75 mm to 10.9 mm compared to the case where the interpass temperature was cooled to room temperature. Additionally, the deformation error was significantly reduced from 6.14% to 2.92% compared to that of the strain as directed boundary method used in a previous study. Additionally, our research demonstrated that interpass temperatures above 800 °C can result in increased deformation errors. In conclusion, it is essential to select an appropriate temperature to minimize deformation error.

Numerical Simulations and Experimental Verification of T-Structure Welding Deformation Using the Step-by-Step Loading Inherent Strain Method

The existing inherent strain method is improved in this paper to address the shortcomings of the existing inherent strain method in the process of loading inherent strain. Unlike the traditional inherent strain method, which uses one-step loading inherent strain for each weld seam for one-time elastic calculation, the improved inherent strain method uses step-by-step loading inherent strain for each weld seam for multiple elastic calculations to predict welding deformation. The step-by-step loading inherent strain method (SBS-ISM) is more in line with the actual welding deformation generation process. Firstly, the local finite element model of the T-joint was used to analyze the welding deformation and extract the inherent strain by using the thermal elastic–plastic finite element method (TEP-FEM). Subsequently, the one-step loading inherent strain method (OS-ISM) and the step-by-step loading inherent strain method (SBS-ISM) were used to predict the welding deformation for the same local finite element model, respectively. The comparative results showed that the trend and magnitude of welding deformation calculated using SBS-ISM was much closer to those calculated using TEP-FEM. The OS-ISM and SBS-ISM were used to predict the welding deformation of the backward centrifugal fan impeller under different welding sequences, respectively. By comparing the welding deformation results calculated using the two inherent strain methods with the experimental results, it was demonstrated that the step-by-step loading inherent strain method (SBS-ISM) provides more accurate and reliable predictions of welding deformation for large and complex thin-walled T-shaped structural components compared to the one-step loading inherent strain method (OS-ISM).

Influence of welding method on residual stress and metallography of a mild steel welded butt-joint plate

During welding process and cooling process after welding, residual stress will be generated and the microstructure of the weld joint will be changed inevitably, which will be harmful for mechanical performance of welded structures. Hence, it is necessary to study welding-induced residual stress and metallic phase transformation, so as to provide guidance for optimization of welding process. In this paper, three butt-joint plates were fabricated by using different welding methods including shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and submerged arc welding (SAW). Secondly, welding residual stress was measured through blind-hole method. Thirdly, the microstructure of the welded joint was analyzed. Fourthly, thermal elastic-plastic finite element method (FEM) was used to numerically simulate the welding process. Finally, heat cycling curves of typical gauged points were extracted, the mechanism of how welding induces residual stress and phase transformation was analyzed from the perspective of cooling rate. Experimental and numerical results show that compared with longitudinal stress, the influence of welding method on transverse stress is more significant. When SMAW is used for welding process, the distribution of transverse residual stress is more uniform than that using GMAW and SAW. Under the three welding methods, the welded joints show similar metallographic compositions. However, the content and distribution of different metallographic compositions are quite different.

Investigating influence of external restraint on welding distortion in LAHS steel thin-plate structures by means of integrated computational approach

In order to ensure the dimensional accuracy during welding assembly, external restraints are often used to control welding-induced distortion. The objective of this study is to investigate the effectiveness of external restraints on the reduction of welding distortion in low alloy high strength (LAHS) steel thin-plate panel structures with different plate thickness by means of an integrated computational approach. In the current study, the total deformation of LAHS steel thin-plate welded structure was computed by a two-step integrated computational approach which combines the thermal elastic plastic finite element method (FEM) with the elastic FEM based on inherent strain theory. In the integrated computational approach, the thermal elastic plastic FEM was employed to obtain the inherent deformations of each typical joint involved in the thin-plate welded structure at the first step, and then the elastic FEM based on the inherent strain theory was used to estimate the total deformation of the whole thin-plate welded structure. Firstly, the integrated computational approach was used to simulate the buckling distortion in a thin-plate panel structure, and the corresponding experiment was carried out to verify its computational accuracy. Then, two finite element models with plate thickness of 5 and 12 mm were established to clarify the effectiveness of external restraint on the reduction of welding distortion of the thin-plate welded structures. The simulated results suggest that external restraint could not effectively prevent the occurrence of buckling distortion for the thin-plate structure with 5 mm thickness, while it can reduce the out-of-plane deformation to a large extent for the thin-plate welded structure with 12 mm thickness.

Numerical calculation on the seismic performance of a steel frame beam-to-column joint with welding residual stress

ABSTRACT Residual stress has almost always been an essential issue associated with welded structural steel. In this paper, thermal elastic–plastic finite element method (FEM) is adopted to calculate the welding residual stress of a steel frame beam-to-column, and then the calculated residual stress is applied to the subject as an initial condition to calculate its mechanical behaviour. Both monotonic loading and cyclic loading are designed to simulate the seismic behaviour of the structure. Bonora damage model [41–44] is used to calculate the initiation and propagation of the crack. Finally, the hysteretic curve of the structure under cyclic loading is obtained. The results show that the main component of the welding residual stress along weld fillers of the steel frame beam-to-column is longitudinal tensile stress, and the magnitude of the residual tensile stress in welding stable zone is about 1.2 times of the material yield stress. Welding residual stress mainly affects the ductility and fracture behaviour of the steel frame beam-to-column. Under monotonic loading, the drift ratio of crack initiation with welding residual stress is reduced by 9% compared with that without welding residual stress. Under cyclic loading, when welding residual stress is taken into account, the crack initiates a little earlier than when welding residual stress is not considered. Compared with monotonic loading, crack initiates much easier when the structure is subjected to cyclic loading.

Influence of Material Randomness on Welding Residual Stress in Dissimilar Metal Welded Joints of Nuclear Power Plants

The welding residual stress is one of the main factors that lead to Stress Corrosion Cracking (SCC) in dissimilar metal welded (DMW) joints of the safe-end in nuclear power plants. Based on ABAQUS software, a thermal-elastic plastic finite element method is developed to simulate residual stress for DMW joints of the safe-end. Considering the randomness of material parameters of the welding metal, the neural network response surface method is applied to calculate the change of welding residual stress distribution. Meanwhile, to improve the efficiency of numerical analysis, MATLAB is employed in the secondary development for ABAQUS. With the help of existing experimental data, the effect of random parameters of the welding metal on the residual stress in DMW joints is simulated and analyzed in this study. The results show that the residual stress distribution of the DMW joints is significantly affected by the random parameters. Among the parameters, the randomness of Yield strength and Module of Elasticity has the most significant influence on the uncertainty of the distribution of welding residual stress.

Numerical Simulation and Measurement of Welding Residual Stresses in Orthotropic Steel Decks Stiffened with U-Shaped Ribs

This study aims to investigate the magnitude and distribution of welding residual stresses in orthotropic steel decks stiffened with U-shaped ribs. Numerical simulation of the welding residual stresses is performed using the thermal elastic–plastic finite element method. The residual stresses are subsequently measured using the hole-drilling strain-gage method. Based on the results of this study, it can be determined that: (1) The longitudinal welding residual stresses (σz) in the weld zones are tensile stresses, where the peak value exceeds the minimum yield strength (fyl); however, relatively low compressive stresses exist in the areas located far away from the welds; (2) The stress gradient in the weld zone is steep, and the widths of the areas experiencing tensile stress are narrow; (3) In the case of the upper surface of the deck, the weld that is first deposited has the highest peak stress, while similar stresses are determined for the remaining welds. In the case of the lower surface of the deck, the peak stress in the weld zones is greater than that on the upper surface; (4) In the case of the weld zone of the U-shaped ribs, the tensile stresses reach up to 1.15fyl; however, at locations a short distance away from the welds, the σz varies from tensile to compressive, and finally transforms into a small tensile stress at the base of the U-shaped ribs. In addition, the simulated and measured σz are compared, and the deviation between them is analyzed.

Estimation of residual stresses in gear form grinding using finite element analysis and experimental study based on grinding force and heat flux distribution models

Form grinding is one of the most important finishing methods to produce precision gears with high surface quality; however, the generation of high temperatures in the ground zone due to very high energy density induces a complex residual stress field during this process. In the present research, temperature distributions in the workpiece were examined using the finite element method (FEM). The heat generation process was assumed as a three-dimensional distribution of moving heat flux, and different grinding factors, including nonlinear distribution of tangential grinding force, grinding parameters, heat partition ratio along the tooth profile, and triangularly distributed heat source along the contact arc, were considered for thermal analysis. The workpiece temperature field was used as thermal loading in stress calculations, and thermal stresses were determined by thermal elastic–plastic FEM with temperature-dependent material properties and a bilinear kinematic hardening model. Further, grinding forces along the tooth profile were measured using a force dynamometer; surface temperatures were estimated by thermocouples pre-embedded along tooth profile; and surface residual stresses in both grinding direction and tooth profile direction were measured by X-ray diffraction (XRD) analysis. Experimental results of temperatures and residual stresses were utilized to validate the FEM results, and the comparison between numerical and experimental results suggests that the proposed model can be adopted to estimate residual stresses in gear form grinding.

The influence of welding mechanical boundary condition on the residual stress and distortion of a stiffened-panel

Stiffened panel structure is one of the most commonly used structure type in ship and offshore engineering, aeronautics and astronautics and other fields. The basic joint type of stiffened panel structure is welding. One important factor affecting welding quality is mechanical boundary condition. The present work aims to obtain the influence of welding mechanical boundary condition on the residual stress and distortion of a stiffened-panel. Thermal elastic-plastic finite element method (FEM) is used to calculate the welding distortion and residual stress of a stiffened-panel under different mechanical boundary conditions. Welding distortion and residual stress at typical positions of the stiffened-panel are calculated. The results show that mechanical boundary conditions mainly affect the welding deformation and have little influence on the residual stress of stiffened-panels. Symmetric boundary condition can not only refrain localized deformation effectively but also decrease the overall bending magnitude of stiffened panels middle cross-section.

Finite Element Analysis and In-Situ Measurement of Out-of-Plane Distortion in Thin Plate TIG Welding.

Transient distortion of thin plate in the welding process usually has a complicated mode and large magnitude. Quantitative measurement and prediction of full-field distortion are challenging and rarely reported up to now. In this study, the out-of-plane distortion of a thin plate during the Tungsten Inert Gas (TIG) welding process was measured using the digital image correlation (DIC) method. A simulation model based on thermal elastic–plastic finite element method (FEM) and DIC measured geometric imperfection were developed for accurate prediction of the transient welding distortion. The numerical results and experimental data agreed very well in both out-of-plane deformation modes and magnitudes of the plate at different stages of welding. The maximum out-of-plane distortion was larger than 4 mm during welding which can cause instability of arc length and heat input. The distance change between welding torch and plate surface was investigated under different initial deflections of the plate before welding. The plate with flat geometry shows the minimum transient and final gap change. In addition, the relationship between heat input and welding distortion was clarified through a series of numerical analyses. Optimization of welding heat input can be performed based on numerical results to avoid excessive welding distortion.

Welding distortion prediction based on local displacement in the weld plastic zone

For a welding procedure with grooves or filler materials, to avoid underestimating the welding distortion in predictions based on the residual plastic strain, a prediction approach is proposed to estimate the welding distortion based on the local displacement in the weld plastic zone, and the proposed method is verified using the thermal elastic–plastic finite element method. Additionally, the welding distortions of an orthotropic deck are estimated using the proposed method and compared with the experimental measurements. The results show that the proposed method can be used to predict the welding distortion with a high accuracy, and in addition to the welding procedures with grooves or filler materials, the proposed method is also applicable to procedures without them.

Release and redistribution of residual stress in the welded turbine rotor under service-type loadings

Welding residual stress relaxation and migration behavior in the welded turbine rotor was studied by using thermal elastic–plastic finite element method under the fatigue and creep loadings. The effect of solid-state phase transformation on the generation of residual stress during welding process was involved. Results reveal that the increase of welding pass number will reduce the peak of residual stress and the width of heat affected zone (HAZ). Under the repeated loadings, the welding residual stress is largely released after the first cycle of start-up and shut-down with a residence time. In addition, such a relaxation mainly depends on the temperature, the initial level of residual stress and the residence time of steady operation. Compared to the contribution of alternating load induced during the start-up and shut-down operation, the relaxation of residual stress is mainly ascribed to the creep mechanism.

Prediction of residual stresses induced by low transformation temperature weld wires and its validation using the contour method

Welding residual stresses are one of the main factors influencing the engineering properties of welded structures, and should be taken into account during designing and manufacturing products such as ships, bridges, etc. Recently, both computational and experimental methods play a significant role for providing residual stresses. The contour method (CM) became one of the most powerful techniques that can provide measurement of residual stresses normal to a plane of interest. In this method a component is cut at any plane of interest. Displacements normal to the cut surface are measured and then processed. Using the Thermal–Elastic–Plastic Finite Element Method (TEP-FEM), residual stresses after welding can be predicted. As well as, the elastic FEM can be used to reproduce residual stresses from measured longitudinal displacements in the CM.The main objective of this paper is to evaluate the effectiveness of different low transformation temperature (LTT) weld wires using TEP-FEM and the CM. In the simulation part, a computational approach is developed to numerically simulate both of welding and the CM. In the TEP-FEM, phase transformation is considered for LTT welds, additionally volume change and variation of mechanical properties with temperature are considered. In the simulated CM, welded specimens to be measured are replaced by TEP-FE models. Then the procedure of the CM is examined before applying it to real measurements. The simulated CM successfully predicted how the CM would reconstruct the residual stresses if applied experimentally. In the experimental part, welding is conducted using conventional and various LTT weld wires. Longitudinal residual stresses produced due to welding are measured using the CM. The results of TEP-FE simulation and the CM show the effectiveness of the different LTT weld wires in introducing compressive stresses in the weld. It is also observed that the applied LTT weld wires, which have almost the same martensitic transformation start temperatures, do not show big difference in the induced compressive residual stresses in the weld metal.

3-D numerical evaluation of residual stress and deformation due welding process using simplified heat source models

Thermal elastic-plastic finite element method has been employed to predict residual stress and deformation in a T-Fillet welded joint. An uncoupled thermal-mechanical three-dimensional (3-D) model has been developed. A nonlinear-transient heat flow analysis was used to obtain the temperature distribution; then by applying thermal results in the three dimensional elastic-plastic model, residual stress and deformation distribution were obtained. Experiments were carried out to find fusion zone dimensions and displacement. Two heat source models with infinite speed are proposed and the mechanical result of the mentioned models and normal moving heat source are compared.

Predicting welding distortion in a panel structure with longitudinal stiffeners using inherent deformations obtained by inverse analysis method.

Welding-induced deformation not only negatively affects dimension accuracy but also degrades the performance of product. If welding deformation can be accurately predicted beforehand, the predictions will be helpful for finding effective methods to improve manufacturing accuracy. Till now, there are two kinds of finite element method (FEM) which can be used to simulate welding deformation. One is the thermal elastic plastic FEM and the other is elastic FEM based on inherent strain theory. The former only can be used to calculate welding deformation for small or medium scale welded structures due to the limitation of computing speed. On the other hand, the latter is an effective method to estimate the total welding distortion for large and complex welded structures even though it neglects the detailed welding process. When the elastic FEM is used to calculate the welding-induced deformation for a large structure, the inherent deformations in each typical joint should be obtained beforehand. In this paper, a new method based on inverse analysis was proposed to obtain the inherent deformations for weld joints. Through introducing the inherent deformations obtained by the proposed method into the elastic FEM based on inherent strain theory, we predicted the welding deformation of a panel structure with two longitudinal stiffeners. In addition, experiments were carried out to verify the simulation results.

Welding Residual Stress Numerical Simulation of Guyed Mast Earplate Welded Joint

Fatigue damage of guyed mast earplate welded joint is one of the main failure forms of guyed mast under wind load, and the welding residual stress is a important influence on fatigue performance of the welded joints, therefore, accurate welding residual stresses assessment of earplate welded joint is of great significance to the research on fatigue performance of guyed mast earplate welded joint under wind load. In this paper, welding temperature field of earplate welded joint was simulated by using thermal finite element method and the gauss heat source was used as thermal input. Then, welding residual stress of earplate welded joint was simulated by using thermal elastic-plastic finite element method and the temperature field results were used as the load. The welding temperature field simulation results better reflect the locality of heating, mobility of heat source and instantaneity of heating and cooling process during the welding process. The welding residual stress simulation results show that the residual stress peak of earplate welded joint reaches the yield strength of material, and appears at the dangerous point of earplate welded joint under structural external load. This point under influence of the welding residual stress and structure load is likely to be fatigue crack initiation location.

Fatigue Life Numerical Prediction of Butt Welded Plate under Cyclic Loading

Fatigue failure of welded structure has been highly concerned in structural engineering field. At present, the numerical simulation method has been actively applied on fatigue life prediction of welded structures. In this paper, welding residual stress of a butt welded plate was simulated by thermal elastic-plastic finite element method, and welding residual stress relaxation behavior under overload was analyzed. Then, the fatigue life of the welding plate under cyclic loading was numerically predicted with considering the welding residual stress and welding residual stress relaxation, and the result was compared with that calculated according to current steel structures design code of China. The results show that, considering fatigue reliability, the fatigue life calculated based on design formulas of the steel design code is more conservative, and numerical method for fatigue life prediction of welded structures, considering the welding residual stress and welding residual stress relaxation, is a feasible method.

Research on Residual Stress of Engineering Ceramic Grinding Surface

As a kind of special hard and brittle engineering materials, in the grinding process, ceramic parts are prone to product cracks which affect seriously on the strength of the parts, and the residual stress is the main reason for cracks producting. Grinding parameters, grinding force and grinding temperature have a certain impact on the residual stress, and the residual stress effects on the fracture strength and fatigue strength of parts. ceramic grinding surface residual stress are caused by the combined effect, like plastic deformation, phase change, the microscopic plastic deformation of the material and the cold burnishing. The residual stress test several methods have X-ray diffraction method, perturbation degree method, indentation fracture. thermal elastic-plastic finite element method can be used to calculate grinding surface residual stress on ceramic and other hard and brittle materials.

Development of Thermal Elastic-plastic FEM for Line Heating with Remeshing Technique

In order to predict deformation during line heating accurately, thermal elastic-plastic FEM with remeshing technique is developed. The model is represented by a fine mesh near the heat source and much coarser mesh around the fine area. Mesh of the model is updated with the movement of heat source, and solution variables are mapping from the old mesh to the new mesh. The analysis procedure after each remeshing step is the same as conventional method. Results of a typical line heating example show that the remeshing technique ensures the accuracy and accelerates computing speed greatly. Ship hull is formed by many plates with complex geometrical shape which are usually made by skillful workers with line heating. The decrease of these people and lack of new workers specializing in this area will be a problem for shipbuilding. Research on computer aided process dates back to the last decade of 20th century and automation system for line heating has now been employed in some shipbuilding companies. It is recognized to be a much more efficient way compared with that operated by human hand. So it is necessary to predict the distortion quantitatively before performing line heating. Inherent strain method proposed by Ueda and Murakawa is employed currently for analysis of plate distortion under line heating 1) . Stretching strain component and bending strain component are firstly computed based on the initial surface and target surface. And then heating paths can be determined by the distribution of the strain components. Since inherent strain method is an elastic FEM and there are usually some iterative procedures required to obtain the final target shape. Thermal elastic-plastic finite element method (TEP-FEM) is a

Study on Influencing Factors of Tooth Forming Quality for Gear Shaft with Cross Wedge Rolling

The feature of the gear shaft with Cross wedge rolling technology is high efficiency, low material loss and higher strength of the gear shaft forming. A research model of cross wedge rolling plastic forming adopting tri-dimensional thermal elastic-plastic finite element method is put forward. Forming mold divided into two parts as the wedge-shaped molds and tooth mold is designed. Depending on orthogonal test program, applying Deform-3D to numerical simulate for the gear shaft with cross wedge rolling, the influence of temperature, number of teeth, module and feet rate for gear shaft tooth forming quality is studied. The results are analyzed with the temperature of the workpiece, number of teeth, module and feet rate of the die movement during CWR and the best combination of produce conditions is reached.