Thermal Elastic-plastic Finite Element Research Articles

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.

Numerical study of welding simulation and residual stress on butt welding of dissimilar thickness of austenitic stainless steel

Weld-induced residual stress inevitably exists in the vicinity of the weld bead and may have a deleterious effect on the weld joint. In the shipyard industry, butt welds of dissimilar thickness plates are a widely used welding geometry type. Predicting the magnitude and distribution of residual stress and distortion are of significance in the design of structural components. In this work, a fusion welding simulation is studied and verified by coupling thermal-mechanical analysis, and the ‘full-elastic element’ technique is introduced in simulation model to improve the convergence of nonlinear calculations The prediction of weld-induced residual stress on the butt weld between similar and dissimilar thicknesses of steel plates is performed by thermal elastic-plastic finite element (FE) analysis. This exploration predicts the process of thermal cycle loads acting on the weld components as well as residual stress states. The results conclude that the geometry of weld joints significantly affects the residual stress distribution and magnitude, which presents some challenges to tolerance in structural design.

Study on deformation and residual stress of laser welding 316L T-joint using 3D/shell finite element analysis and experiment verification

In this paper, T-joint of 316L steel is obtained by subsection laser welding method without jig, while a thermal elastic-plastic finite element model considering multi-linear yield stress curves and multi-point constraint equations is developed to estimate welding deformation and residual stress. A simplified heat source model with the actual bead geometry is proposed to reduce the number of finite element meshes. Prediction errors between the simulation and experimental measurement results of angular distortions of three reference lines are −11.0, 0.9, and 7.9 % respectively, and the maximum residual stress is 396 MPa. Meanwhile by microstructure analysis, austenite and ferrite are consisted in weld, segregation and dendritic structures are also observed, while the heat-affected zone is very narrow. In a word, weld line with large travel can be welded by subsection laser welding method without jig, while the finite element method proposed in this paper is effective to predict welding deformation and residual stress.

Welding distortion and inherent deformation under temporary tacking and its released states

In the present study, the detailed welding distortion of bead welded plates under temporary tacking state and released state was predicted by thermal elastic-plastic finite element model (FEM) and also measured by the digital image correlation (DIC) method. It was found that the residual welding angular distortion can be reduced to about 50–60% by temporary tacking, while the residual transverse shrinkage and longitudinal shrinkage are less affected. Further, the welding distortion with different ratios of temporary tacking length to weld length for various dimensions of bead welded plates was quantitatively investigated by FEM. The inherent deformations which are described by the integrated values of residual plastic strains were proved to be the same before and after releasing the temporary tacking. The effect of temporary tacking on the welding distortion and inherent deformation were analysed in details.

Finite element analysis of deformation in early stage of multi-pass circumferential dissimilar welding of thick-walled pipes with narrow gap

Three-dimensional thermal elastic-plastic finite element analyses were conducted in order to reveal the mechanism of gap shrinkage in early stage of multi-pass narrow gap welding of thick-walled dissimilar pipes and thick plates. The gap shrinkage up to the 8th pass indicates that the shrinkage of plates becomes to be much larger than that of pipes with increasing the weld passes. In addition, through the decomposition of gap shrinkage to transverse shrinkage and angular distortion, it is found that the gap shrinkage of pipes is mainly governed by the transverse shrinkage, while the shrinkage of plates is influenced by both the transverse shrinkage and angular distortion. Moreover, the serial computational results with various groove shapes suggest that the transverse shrinkage of pipes almost linearly increases with increasing the weld pass, and its increment can be predicted by a linear approximation function obtained by the transverse shrinkage of plates regardless of the groove shape.

Analysis of influence of initial gap of laser-arc hybrid butt welds on inherent strain and welding deformation of a pipe structure

Although the laser-arc hybrid welding process has the advantages of smaller deformation and wide freedoms using different energy ratios, some initial dimension errors such as initial gap or initial mismatch before welding assembly have a significant influence on the final shape of welded structures. In this paper, a thermal elastic-plastic finite element model was developed to investigate the temperature fields and plastic strains in butt joints of steel plates with three different initial gaps (0.2 mm, 0.5 mm, and 1.0 mm). Four inherent deformation parameters, longitudinal inherent shrinkage, transverse inherent shrinkage, longitudinal inherent bending, and transverse inherent bending, were calculated and compared with different initial gaps. Finally, welding deformation in a steel pipe structure with five weld lines was predicted by the inherent strain theory.

Numerical investigation on welding residual stress and out-of-plane displacement during the heat sink welding process of thin stainless Steel Sheets

The effect of trailing heat sinks on welding-induced deformation and residual stress was numerically simulated using the finite element analysis (FEA) in this study. A 3-D thermal elastic plastic finite element model using a 2 mm-thick 304 stainless steel sheet was developed to simulate heat sink welding. In the numerical simulations, the parameters of the heat sink welding, such as the distance between the welding heat source and the heat sink, and the size of the heat sink are varied to compare the variation of out-of-plane displacement and residual stress. This numerical simulation indicated that compared to conventional welding, trailing heat sink welding showed, first, smaller deformation and residual stress, second, a significantly reduced out-of-plane displacement under optimal heat sink welding conditions, and third, a reduced overall residual stress developed although no significant differences were seen in the maximum values of welding residual stress.

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.

Out-of-plane welding distortion prediction and mitigation in stiffened welded structures

A holistic investigation on out-of-plane welding distortion in fabrication of several stiffened welded structures with considering prediction and mitigation is presented. Experiments of typical fillet welded joints and its assembled stiffened welded structures are conducted first, and out-of-plane welding distortion is systematically measured. Different welding distortion patterns, so-called bending distortion and welding buckling, are obviously obtained from the measurements of the examined parallel and cross stiffened welded structures, respectively. A combined computational approach, which involves thermal elastic plastic (TEP) finite element (FE) analysis, eigenvalue analysis, and elastic FE analysis, is then employed to predict the out-of-plane welding distortion and clarify the generation mechanism for different welding distortion patterns. In particular, eigenvalue analysis can support the critical condition for welding buckling occurrence. Since the bending and welding buckling are caused by different reasons, the mitigation processes with flame heating are carried out individually. In detail, line heating is implemented in the opposite side of welded joint to produce inverse bending, and spot heating is employed to heat the region far away from welding line to eliminate effect of inherent deformation on welding buckling generation.

Numerical simulation and experimental validation of angular distortion and residual stresses in a T-joint

Abstract Welding is the most important method in modern industry. However, welding distortion and residual stress after welding are inevitable. In this paper, experiments were performed to obtain the angular distortion, temperature field and longitudinal residual stress in two T plate structures after welding and post-weld heat treatment, respectively. Then, a three-dimensional thermal elastic-plastic finite element analysis using internal heat generation was carried out to simulate the deformation and stress. The FE analysis results were in good agreement with the measurements. The results showed that both, the thickness of the plates and the heat treatment, could influence the angular distortion and residual stress distribution. Finally, the welding process at a bogie was also simulated by using the same heat source model as for the T-joint. The deformation and stresses were shown and explained.

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.

Prediction of welding deformation in stiffened structure by introducing thermo-mechanical interface element

A thermo-mechanical interface element was developed to describe the effective penetration, the fillet weld size and the contact relationship between the skin plate and the stiffener during welding distortion simulation. Based on the interface element formulation, welding distortion in stiffened structures was predicted by means of thermal elastic–plastic finite element analysis. Comparisons between the traditional model and the interface element model were conducted. The results indicate that the calculated data of the interface element model are in better agreement with the experimental measurements. The influences of the welding sequence were discussed numerically based on these two models. The interface element model is more suitable for describing the effect of the welding sequence, which are of great importance on accurately predicting distortion in large scale structure welding. Simulations and experiments upon large scale structures were also carried out to verify the effectiveness of the developed numerical analysis procedure.

Investigation of Bulging Behavior of Coke Drum—A Practical Analysis of Bulging Under Complex Quench Conditions

Coke drums undergo cyclic operations typically in the temperature range from room temperature to about 500 °C (930 °F). During quenching, the coke drum is inevitably subjected to a rapid drop in temperature because cooling water is injected directly into the coke drum through the bottom inlet nozzle. The temperature profile on the shell surface is uneven during quenching, and can vary in each cycle of the quenching operation. Such a complicated thermal profile induces large strains in the shell portion of the coke drum, and eventually causes damage like bulging and/or cracking. The authors have investigated the bulging behavior of the coke drum by the thermal elastic-plastic finite element (FE)-analysis, considering the existence of the overmatch welds and uneven temperature field during quenching (Ohata et al., 2011, “Investigation of Bulging Behavior of Coke Drum—Feasible Study on Causes of Bulging,” ASME PVP2011-57276, Baltimore). In this paper, a practical FE-analysis is developed to estimate the complex strain that leads to bulging under uneven temperature fields during quenching. The actual temperature and strain data during operation are collected by thermocouples and high temperature strain gauges. A thermal analysis model, including an evaluation of boiling heat transfer on the shell's inner surface, is established to simulate the measured shell behavior of the coke drum. By utilizing this FE-analysis model, several parameters thought of as causal factors in bulging can be examined under the uneven temperature profile that is likely to occur during actual operation. This analytical approach can also provide effective technique for improvements in shell durability.

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.

Reduction of Welding Distortion for an Improved Assembly Process for Hatch Coaming Production

The alignment between the hatch coaming top surface and hatch cover is essential to maintain hatch cover water tightness and smooth mechanical operation. An improved assembly process for hatch coaming production is proposed, in which the complete hatch coaming is assembled on the shop floor and then lifted as one part, fitted, and welded to the deck. When this complete hatch coaming is assembled to a ship deck, an irregularly distributed gap is usually found between the lower side of the hatch coaming and the deck. Fitting and welding distortion, in particular longitudinal and transverse shrinkage, influence the dimensional accuracy and consequently the production schedule. In this research, welding pass sequence of a fillet welded joint is improved using thermal elastic plastic analysis and welding distortion of the hatch coaming top surface is predicted using elastic analysis. First, three specimens with different gaps that model the welded joint between the hatch coaming and deck were welded and the changed distance between the measuring equipment and the flange was measured. A three-dimensional thermal elastic plastic finite element analysis was carried out for the same specimens and the computed welding distortion was shown to have good agreement with the measurements. As a result of the possible significant influence of welding pass sequence on transverse shrinkage of a fillet welded joint, the influence of welding pass sequence is studied using the computational approach and improved welding pass sequences are proposed to reduce transverse shrinkage. Finally, elastic analysis using inherent longitudinal and transverse shrinkage deformations evaluated by thermal elastic plastic analysis is used to predict welding distortion of the hatch coaming. In this elastic analysis, the influence of different gaps at different locations between the hatch coaming and the deck is considered.

Reduction of Welding Distortion for an Improved Assembly Process for Hatch Coaming Production

The alignment between the hatch coaming top surface and hatch cover is essential to maintain hatch cover water tightness and smooth mechanical operation. An improved assembly process for hatch coaming production is proposed, in which the complete hatch coaming is assembled on the shop floor and then lifted as one part, fitted, and welded to the deck. When this complete hatch coaming is assembled to a ship deck, an irregularly distributed gap is usually found between the lower side of the hatch coaming and the deck. Fitting and welding distortion, in particular longitudinal and transverse shrinkage, influence the dimensional accuracy and consequently the production schedule. In this research, welding pass sequence of a fillet welded joint is improved using thermal elastic plastic analysis and welding distortion of the hatch coaming top surface is predicted using elastic analysis. First, three specimens with different gaps that model the welded joint between the hatch coaming and deck were welded and the changed distance between the measuring equipment and the flange was measured. A three-dimensional thermal elastic plastic finite element analysis was carried out for the same specimens and the computed welding distortion was shown to have good agreement with the measurements. As a result of the possible significant influence of welding pass sequence on transverse shrinkage of a fillet welded joint, the influence of welding pass sequence is studied using the computational approach and improved welding pass sequences are proposed to reduce transverse shrinkage. Finally, elastic analysis using inherent longitudinal and transverse shrinkage deformations evaluated by thermal elastic plastic analysis is used to predict welding distortion of the hatch coaming. In this elastic analysis, the influence of different gaps at different locations between the hatch coaming and the deck is considered.

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.

Prediction of the residual welding stress in 2.25Cr-1Mo steel by taking into account the effect of the solid-state phase transformations

A computational approach based on the thermal elastic plastic finite element method was developed for predicting welding residual stress in low carbon alloyed steel welds by taking into account the effect of the solid-state phase transformations. The kinetics of phase transformations was described by Johnson Mehl Avrami Kolmogrov (JMAK) equation for bainitic transition and by Koistinen-Marburger (K-M) relationship for martensitic transition. Moreover, an additive rule depending on volumetric phase fraction was adopted to represent the material property changes during heating and cooling. Consequently, the residual welding stresses in a 2.25Cr1Mo steel TIG welded plate were computed. Early calculation results suggest that the bainitic and martensitic transformations took place in the weld the heat-affected zone drastically reduce the residual longitudinal tensile stress in the region.