Thermo-elastic Plastic Finite Element Method Research Articles

A Multipath Process-Based Inherent Strain Method for Prediction of Deformation of Hull Plate for Integrated Heating and Mechanical Rolling Forming Process

Integrated heating and mechanical rolling forming (IHMRF) has recently been introduced for manufacturing complex curvature hull plates. It fabricates the target curved plate by sequential loading along the multipath. Accurate and efficient prediction of the deformation of the plate is the basis for developing the process planning and ensuring the quality of the forming. The inherent-strain method is ideal for this purpose, but its prediction accuracy needs to be improved. This paper proposes a multipath process-based inherent-strain method (MPISM), which considers the effect of the sequential loading process of the multipath on plate deformation. First, the effect of loading paths near the plate edge was investigated, which in turn clarified the rationale for obtaining the inherent strain only in the plate center. Secondly, a strain correction strategy was established by analyzing the variation pattern of the inherent strain caused by the crossing or proximity of the previous path and the subsequent path. This allowed the effects of the loading process to be taken into account in the elastic analysis. Based on the plate-and-shell theory, the idea of an equivalent inherent strain distribution is also presented. This makes the loading of inherent strains more accurate in the elastic finite-element model. MPISM predictions and experimental results show good agreement. Compared with the thermo-elastic–plastic finite element method, the MPISM substantially improves efficiency while maintaining accuracy. Compared with the original inherent-strain method, the MPISM is more accurate in terms of deformation magnitude prediction.

The Effect of TIG Welding Heat Input on the Deformation of a Thin Bending Plate and Its Weld Zone

Heat input is a crucial parameter in the process of welding thin plates. It has a direct impact on the quality of the weld and the degree of deformation caused during welding. This study investigates the impact of heat input on the deformation of a thin bending plate and its weld zone using the thermoelastic–plastic finite element method. The accuracy of the model is ascertained using the non-contact inspection method utilizing digital image correlation technology. The welding deformation patterns of thin bending plates with a radius of 500 mm were analyzed at various welding heat inputs ranging from 173 J/mm to 435 J/mm. The results indicate that the finite element prediction model proposed in this paper is highly accurate. It has been observed that, under this range of thermal input, the thin bent plates undergo saddle deformation. By examining the correlation between heat input and the maximum deformation outside of the plane, it has been determined that a heat input of at least 50 J/mm is required for the thin bending plate to experience out-of-plane deformation. Additionally, as the level of heat input increases, so too does the out-of-plane deformation of the thin bending plate. After the completion of the welding cooling process, the transverse shrinkage at the weld seam of the thin bend plate is twice that of the longitudinal shrinkage. However, the transverse deformation of the bend plate is not significantly different from the longitudinal deformation.

Fatigue crack growth and life assessment of full penetration U-rib welded joints considering residual stresses

The combination of cyclic stresses and welding residual stresses (WRS) can significantly contribute to fatigue cracking in steel bridge decks. This study aims to investigate the effect of WRS on the fatigue life and crack propagation of single-sided and full penetration double-sided U-rib welded joints through experimental and numerical methods. Fatigue tests were conducted to study fatigue crack initiation and propagation behavior. Utilizing the ABAQUS software, a thermoelastic-plastic finite element method was employed to determine the residual stress distribution. Subsequently, based on linear elastic fracture mechanics (LEFM), fatigue crack propagation and life assessment were performed using ABAQUS and FRANC3D software under the coupling of residual stresses and external cyclic stresses. Findings reveal that WRS play a crucial role in fatigue life by altering the effective stress ratio during fatigue crack growth. The effective stress ratio ranges from 0.15 to 0.57, while the changing trends differ between single-sided and double-sided U-rib welded joints. The fatigue crack growth rate of double-sided U-rib welded joints is lower compared to single-sided U-rib welded joints with the same deck thickness. Furthermore, the introduction of WRS induces a mixed mode I, II, and III fracture at the outer weld toe of the U rib, with mode I fracture predominating, which leads to a deviation in the crack propagation path. The fatigue life prediction results agree well with experimental findings when considering WRS. Importantly, these predictions tend to be conservative, thereby ensuring safety and reliability in engineering applications.

Welding Distortion Prediction for Multi-Seam Welded Pipe Structures using Equivalent Thermal Strain Method

Distortion prediction of a welded structure is an important way to improve work efficiency and ensure product quality during the fabrication process. Recently, the widely used approaches for evaluating residual deformation include the thermo-elastic-plastic finite element method (TEP-FEM) and the inherent strain method (ISM). The former can accurately simulate the entire welding process with excessive computational time, whereas the latter has great potential in the fast prediction of residual distortion in complex welded components. In this study, an equivalent thermal strain method based on inherent strain theory was proposed to predict residual deformation of the multi-seam welded pipe structures. Moreover, a full 3D TEP-FEM model was also developed to estimate the distributions of inherent strain in longitudinal (L-seam) and circumferential (C-seam) welds. To validate the accuracy of the proposed ISM, the welding distortion predicted by the proposed ISM is compared with the experimental data and TEP-FEM simulation results. It is discovered that the proposed ISM can be used to accurately predict welding-induced deformation in multi-seam welded pipe structures. Furthermore, compared with TEP-FEM simulation, the significant advantage of this approach is that the computing efficiency can be increased by about 50 times.

An algorithm for prediction of bending deformation induced by multi-seam welding of a steel-pipe structure

A previous study has demonstrated that welding distortion can be accurately predicted by using the thermo-elastic-plastic finite element method (TEP-FEM) in a steel-pipe joint. Nevertheless, this method still requires excessive computational time. In this study, to overcome this aforementioned limitation, a deformation computing algorithm is developed to estimate welding distortion rapidly and effectively. This algorithm solution process has three main steps. The first step is to collect the weld information. The second step is to calculate bending deformation caused by each weld according to the function of the bending angle. The last step is to make a summation for total welding distortion. However, due to the interaction between adjacent welds, it has a significant influence on the accuracy of prediction results. To improve the performance of this algorithm, a compensation factor has been introduced. Comparing the results of this algorithm with the TEP-FEM analysis, it is discovered that there is a good coincidence. Therefore, it was verified that the proposed algorithm can accurately predict the bending deformation induced by multi-seam welding of a pipe structure.

Numerical prediction of deformation in thin-plate welded joints using equivalent thermal strain method

Large welding-induced distortions are inevitably generated in a thin-plate welded joint due to its weak stiffness. In this study, an equivalent thermal strain method based on inherent strain theory is proposed to predict the welding deformation of thin plates. An artificial temperature and an orthotropic thermal expansion coefficient are adopted to directly simulate the welding shrinkage and bending behavior of the cooling phase in all directions. To describe the distribution of transverse inherent strain through thickness more accurately, a composite shell element is employed, which can divide the thickness into multiple layers and set different material properties. A three-dimensional (3D) thermo–elastic–plastic finite element method (TEP-FEM) model is also developed to simulate the welding process of a thin plate and compute the inherent strain. Moreover, an experiment was performed to verify the accuracy of the numerical model. Comparing the results from experimental data, TEP-FEM, and the proposed method, it is discovered that the new method can predict the deformation of a thin-plate welded joint with good computational accuracy.

Analysis of Forming Regularity in Line Heating Process for Curved Hull Plate by Considering the Plate Deflection

Nowadays in most shipyards, line heating techniques are widely used in the forming process of hull plates. The precision and efficiency of the process are greatly influenced by the determination of technical parameters, including heating length, heating velocity, and the arrangement of heating line. Previous studies on this, which considered only local shrinkage, produced large errors in the calculation of thick and large curvature plates because the whole deformation was ignored. In this article, new mathematical formulas are proposed to indicate the relationship between the whole deflection and shrinkage during the plate-forming process by line heating. The numerical models were established based on the thermoelastic plastic finite element method considering the deflection. The reliability of the numerical models was verified by the comparison of temperature fields and displacement. Based on the analysis of forming regularity, a new concept named influence factor of deflection (IFD) was proposed from the analysis between deflection and shrinkage. The formulas were derived, which establishes the relation between the IFD and technical parameters. Finally, the experimental results showed that the relative percentage error is 5.13% for IFD, and the forming formulas were verified. The research lays a foundation for the technique of parameter prediction of thick and big curvature plates considering the deflection. 1. Introduction The procedure of lofting, marking-off, pretreatment of steel plates, cutting, and welding has been automated in shipbuilding. Hull plate forming is the bottleneck of shipbuilding. There are numerous curved hull plates that need to be formed within the shipbuilding industry. Precision and efficiency are the technical difficulties in hull plate forming. It is very important to realize the automatic forming of curved hull plate. Line heating is an important method in hull plate forming, which mainly relies on the experience of the workers (Seong et al. 2013). The general processes are as follows. First, the technical parameters of hull plate forming are obtained based on the workers' experience. Then, hull plate forming is carried out manually by the workers. Last, plate forming quality is detected by using detection templates or a detection box. If plate forming cannot meet the requirements of the standards, the workers need to reform the plate, until it can meet the requirements. These procedures cause low efficiency and great fluctuation in forming quality. Therefore, it is essential to perform automatic line heating research.

Prediction of welding distortion and residual stress in a thin plate butt-welded joint

In automotive industry, thin plate parts are commonly used. During assembling process, welding technology is usually employed because of high productivity. Welding distortion often occurs in thin plate welded structures due to relatively low stiffness. The distortion causes problems not only in the assembling process but also in the final product quality. Therefore, prediction and reduction of welding deformation have become of critical importance. In this study, three-dimensional, thermo-elastic–plastic, large deformation finite element method (FEM) is used to simulate welding distortion in a low carbon steel butt-welded joint with 1 mm thickness. To compare with the large deformation theory, the small deformation theory is also used to simulate the welding deformation and welding residuals stress. Meanwhile, the characteristics of welding temperature field, plastic strain distribution and welding residual stress in thin welded plates are also examined numerically. Experiments are also carried out to measure the welding distortion in the thin plate butt-welded joint. By comparing the simulation results with the measurements, it is found that the results predicted by the thermo-elastic–plastic, large deformation FEM match the experimental values well. Moreover, using the inherent strains obtained by the thermo-elastic–plastic FEM, an elastic FEM is also employed to estimate welding deformation in the same butt-welded joint. Comparing the results simulated by the elastic FEM with those predicted by the thermo-elastic–plastic FEM, it is verified that the inherent strain method can effectively predict the welding deformation in the thin plate butt-welded joint with 1 mm thickness.

A study on fatigue crack initiation point of load-carrying fillet welded cruciform joints

Load-carrying fillet welded cruciform joints have two fatigue crack initiating points. These are located at the weld toes and weld roots, where high stress concentrations occur. The location of the fatigue crack initiation depends on the weld size, plate thickness and weld penetration. These mechanisms are easily understood. Previous experimental results have indicated that the fatigue crack originating point is also influenced by the magnitude of the stress range, but the reason for this phenomenon is not yet clear. To better understand this phenomenon, fatigue tests on welded joint specimens were performed in this study. In addition, the welding residual stresses were analyzed with a thermo-elastic–plastic finite element method. Finally, a fatigue crack propagation analysis that considered the residual stresses was performed.

Finite element analysis for the mechanical features of resistance spot welding process

In this paper, a 2D axisymmetric model of thermo-elastic–plastic finite element method (FEM) is developed to analyze the mechanical behavior of resistance spot welding (RSW) process using commercial software ANSYS. A transient temperature field obtained from a prior performed thermal–electrical simulation of RSW process is applied as nodal load on the model. The temperature-dependent properties and plastic behavior of materials are taken into account during the simulation. The distributions and changes of the contact pressure at both the faying surface and the electrode–workpiece interface are obtained through the analysis. The stress and strain distributions in the weldment and their changes during the RSW process are determined. The deformation of the weldment and the electrode displacement are also calculated.

103 Inconel718のエンドミル切削のFEMシミュレーション(OS12 最新切削加工)

A finite element analysis of end milling a nickel-base superalloy is presented for aiming at understanding its cutting performances, and improving cutting conditions, cutting efficiency and machined surface integrity. A formulation coupled with radial return method for thermo-elastic plastic finite element method, penalty methods, mass scaling, subcycling gave chip formation and cuttig processes of Inconel718. Calculated and experimental results on. end milling of S45C with HSS tool agreed well in cutting forces and shapes of chip. From calculated results on end milling of Inconel718, it was found that cutting speed had a great influence on the cutting temperature on the rake face.

Cutting Mechanism on Ultrasonic Vibration Cutting (1st Report)

In this report, the remarkable features in the ultrasonic vibration cutting was extracted from the view point of relative cutting speed between the tool and the work piece, then the chip forming process considering this feature was simulated by using the finite element method. As first, the existence of the transitional cutting speed was shown. When the steady cutting speed is lower than the transitional cutting speed, the maximum relative speed, which is the sum of the steady feed speed and the maximum vibration speed of tool, cannot be obtained in the real cutting term. In this case, the relative cutting speed is the highest at the moment of tool-chip contact in the cycle of vibration, and then it becomes lower in the cutting term. Secondly the deformation process in the ultrasonic vibration cutting, which is an interrupted cutting process and the relative cutting speed varied largely during the 1 period of vibration, was analyzed by thermo elastic-plastic finite element method. The chip forming process was shown from the strain rate distribution in the deformation zone. It was also shown that the cutting force acting between tool-chip and the temperature rise are almost same in vibration cutting and conventional cutting, if we assume that the frictional characteristic and the flow stress are the same in conventional cutting and vibration cutting.

切削シミュレーションによるニッケル基超耐熱合金の被削性評価

A finite element modeling of machining of a nickel-base superalloy is presented for aiming at understanding its cutting performances and improving cutting conditions, cutting efficiency and machined surface integrity. A formulation with a dynamic explicit thermo-elastic plastic finite element method, penalty methods dealing with mechanical and thermal boundary conditions on the tool-chip contact area, and mass scaling for efficient calculation gave chip formation and cutting processes of Inconel X750 under a wide range of cutting conditions. Calculated and experimental results agreed well in cutting forces, shear angle, tool-chip contact length and stress distribution on the rake face. It was found that the rake angle had a great influence on the predicted thickness of affected layer for constant undeformed chip thickness while the cutting speed had a little. The instantaneous ratio of heat into the tool to the energy consumption due to friction on the rake face was calculated. At the beginning of cutting the ratio was greater than 100%, then decreased to 100% and less. From the results it was suggested that for better interrupted cutting with good tool cooling, cutting length per tooth may be taken as one at the ratio of 100%.

An investigation of sticking behavior on the chip–tool interface using thermo-elastic–plastic finite element method

This paper presents a high-speed orthogonal cutting model and also establishes a finite element method to analyze the mechanics of steady state in the high-speed orthogonal precision cutting process of oxygen-free high conductivity copper. The paper proposes a variant pseudo-friction coefficient concept to modify the large-deformation finite element formulation and to develop a stress analysis model of the chip–tool interface to solve the problems of the shear stress, normal stress and variant pseudo-friction coefficient on the chip–tool interface. In spite of the high-speed micro-cutting, the effect of high strain rate and high temperature will produce the sticking phenomenon on the rake face of the tool. Not only will the sticking phenomenon shorten tool life, but also will have an effect on the machining accuracy in precision diamond cutting. Therefore, the results in this study can be considered as acceptable consideration during the procedure of high-speed precision cutting.

Chip breaking analysis from the viewpoint of the optimum cutting tool geometry design

The chip breaking process mechanism of the grooved rake face tools is simulated by thermo-elastic plastic finite element method. The shape, temperature and flow stress of the deformed chip in the initial model of this simulation are obtained from the finite element analysis of the steady state metal cutting mechanism. In this chip breaking simulation, a stress-dependent fracture criterion is used. The chip breakability and the force change at the chip breaker edge are obtained. The simulated results are in good agreement with experimental results for various cutting conditions and various tool geometries. It is verified that this simulation is effective as an analytical approach to the optimum metal cutting tool geometry design.

チップブレーカによる切りくず破断過程の熟弾塑性有限要素法シミュレーシヨン

Chip breaking processes of the grooved rake face tools are simulated to predict the chip breakability and forces change at the chip breaker edge in detail. This simulation is focused on the deformed chip and is carried out by elastic plastic finite element method with non-steady state heat conduction analysis. The initial model is made using the results of the steady state metal cutting analysis by thermo-elastic plastic finite element method with iterative convergence method. It is assumed that cracks develop on the chip surface when the maximum principal stress criterion or the maximum shear stress criterion are satisfied. These cracks propagate in the direction of the minimum principal stress for the former case or in the direction of the maximum shear rate for the latter case. The crack propagation is considered as node separation. The broken chip shapes simulated are in good agreement with those experimentally obtained. There is very good correlation between the simulated and measured cutting force changes. It is found that the breakability can be changed dramatically by rather changing the tool geometry than changing the other cutting conditions.

FEM Analysis on Cyclic Fatigue of Ceramic/Metal Joints.

Cyclic fatigue of Si3N4/SUS304 joints with copper interlayer was analyzed using the thermoelastic-plastic finite-element method (FEM). It is found that the equivalent plastic strain (ε^-p) is concentrated on the copper interlayer near the interface of the ceramic side due to the joining process. The equivalent plastic strain range (Δε^-p) is increased and the residual stresses (σx, σy) of the ceramic side are relaxed due to cyclic fatigue. Stress singularity near the interface of the ceramic side was also studied. The exponent of stress singularity (λ) and intensity of stress singularity (K) are decreased due to cyclic fatigue. Therefore, fracture originates in the copper interlayer near the interface of the ceramic side due to cyclic fatigue. It is concluded that the cyclic fatigue strength and fracture mechanism of the ceramic/metal joints are influenced by the elastic-plastic behavior of the copper interlayer.

Thermal stress analysis of joints of ceramics and metals. (1st Report: Variation of stress concentration and plastic region by modifying size of joints.)

The bonding of ceramics and metals is an effective method for applying ceramics to structural materials. In the previous paper, it was shown that high stress concentrations are induced only in the vicinity of the interface edge of the joint near the outer surface of a ceramic, and that the stress concentration can be reduced by modifying the shape of the ceramic. Using the thermoelastic-plastic finite element method, the authors investigate in the present paper how the thermal stress concentration and the shape of the plastic region in the metal are influenced by the size of both materials. It is found that the values of the stress concentration in the axial direction and the shape of the plastic region in the metal are changed by modifying the size of both materials, and that the plastic region in the metal develops from the bonding interface.

Reliability evaluation of joints of ceramics and metals. 2nd Report. The influence of changing the shape of a joint on the thermal stress of joined dissimilar materials.

The bonding of ceramics and metals is an effective method for the use of ceramics as structural materials .Generally, there is a serious problem that a significant thermal stress concentration occurs in the ceramics owing to the different thermal properties of both materials. In the previous work, it was found that high axial stress is induced only in the very narrow region near the outer surface of the ceramics. In the present paper, the authors investigate how the thermal stress concentration is influenced by shape of the ceramics of a joint, using the thermoelastic-plastic finite element method. It is found that the stress concentration can be reduced by changing the shape of the ceramics, and that the maximum value of the axial stress as well as the principal stress in the joints with various shapes is estimated by a simplified theoretical analysis.