Elastic-plastic Finite Element Method Research Articles

Influence of Initial Structural Dimensions of Plates on Welding Distortion

Aiming at the complex full-field deformation problem that easily occurs when welding plates, this paper adopts the elastic–plastic finite element method with heat-force coupling to study the deformation law of plates in different initial states. First, a rectangular plate finite element model with an initial radius and Gaussian heat source model was established to obtain the welding temperature field and deformation field of the plate; then, the method based on digital image correlation technology was used to detect the full-field dynamic deformation of the plate to verify the accuracy of the finite element model; finally, the influence of the initial structural dimensions of the plate on the weld deformation was investigated. The study shows the following: the thermoelastic–plastic finite element model proposed in this paper has high accuracy in both static and dynamic deformation; plates with the same curvature, and different lengths and widths of the initial structure of the plate welding deformation are saddle-shaped, and the edge effect of the welding of the plate is evident, independent of the length of the plate; and the maximum out-of-face deformation of the welding of the plate is linearly related to the length and the closer the aspect ratio of the plate is to 1, the smaller the out-of-face deformation is.

Study on valley deformation of high arch dams based on nonlinear rheological damage model

The scale of the high arch dam project is large, and the water level is high. The construction and water storage effect will significantly impact the rock mass of the high slopes on both sides, especially on the structural planes such as internal faults. Based on the Jinping Ⅰ high arch dam, an improved Nishihara rheological damage model was established to address the phenomenon of valley shrinkage deformation. The stress and deformation states of the rock mass and dam in the reservoir area were calculated, and the results were compared with the conventional elastic–plastic finite element method. The results indicate that the improved parallel Nishihara rheological damage model can better conform to the deformation properties of the internal structural planes of the rock mass, and the calculation results using this model are closer to the actual deformation situation. When considering the structural plane's rheological characteristics, the valley shrinkage deformation law is consistent with the conventional elastic–plastic finite element calculation results, but the magnitude is too large. In addition, when considering the rheological characteristics of the structural plane, the increase in valley shrinkage deformation value further increases the stress and deformation of the high arch dam, which can better reflect the dam's working behavior and ensure the dam's safe operation.

Review of Wind-Induced Effects Estimation through Nonlinear Analysis of Tall Buildings, High-Rise Structures, Flexible Bridges and Transmission Lines

The nonlinear effects exhibited by structures under the action of wind loads have gradually stepped into the vision of wind-resistant researchers. By summarizing the prominent wind-induced nonlinear problems of four types of wind-sensitive structures, namely tall buildings, high-rise structures, flexible bridges, and transmission lines, the occurrence mechanism of their nonlinear effects is revealed, providing cutting-edge research progress in theoretical studies, experimental methods and vibration control. Aerodynamic admittance provides insights into the aerodynamic nonlinearity (AN) between the wind pressure spectrum and wind speed spectrum of tall building surfaces. The equivalent nonlinear equation method is used to solve nonlinear vibration equations with generalized van-der-Pol-type aerodynamic damping terms. The elastic–plastic finite element method and multiscale modeling method are widely employed to analyze the effects of geometric nonlinearity (GN) and material nonlinearity (MN) at local nodes on the wind-induced response of latticed tall structures. The AN in blunt sections of bridges arises from the amplitude dependence of the aerodynamic derivative and the higher-order term of the self-excited force. Volterra series aerodynamic models are more suitable for the nonlinear aerodynamic modeling of bridges than the polynomial models studied more in the past. The improved Lindstedt–Poincare perturbation method, which considers the strong GN in the response of ice-covered transmission lines, offers high accuracy. The complex numerical calculations and nonlinear analyses involved in wind-induced nonlinear effects continue to consume significant computational resources and time, especially for complex wind field conditions and flexible and variable structural forms. It is necessary to further develop analytical, modeling and identification tools to facilitate the modeling of nonlinear features in the future.

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).

The efficiency of advanced polymeric composite sleeves in the rehabilitation of cracked pipelines under combined loadings

The main objective of the present work was to numerically study the effect of loading conditions on the progressive damage of initial defects in steel pipelines. The adhesively-bonded composite sleeve repair technique was utilized to extend the lifetime of such cracked pipelines with different inclination angles (θ) under combined loads (i.e., internal and axial pressure) with different values. Three different glass fiber-reinforced polymer sleeves (GFRPs; [0°]8s, [90°]8s, and [0°/90°]4s) were simulated to study the effect of fiber orientation on the efficiency of composite sleeves in reducing the crack driving force. A three-dimensional (3D) elastic-plastic finite element method was utilized in the present study. The numerical results showed that the loading sequence has a great effect on the development of the crack-tip plastic zone size when the internal pressure is applied first. In the following two cases, if the internal pressure and the tensile stress were applied simultaneously or the tensile stress was applied in the first step followed by internal pressure, the loading sequence has little effect. In the case of the presence of internal pressure, the crack path is mainly dependent on it, and axial pressure has a marginal effect on its value. In such cases, applying [0°]8s sleeves is the best way to arrest cracks in steel pipelines. However, in the absence of pressure within the pipelines, [90°]8s sleeves are the appropriate ones to use to arrest the cracks due to axial pressure. Therefore, [0°/90°]4s sleeves may be recommended for repairing cracked steel pipelines to prevent crack growth in both situations.

Geometric deformation prediction of a centrifugal impeller considering welding distortion and fluid-structure interaction

An impeller serves in a centrifugal fan, pushes the surrounding air and in turn reacts on itself. The fluid-to-structure response and part welding distortion during the fabrication and working processes will cause the impeller to deform and reduce fan performance. This work develops a numerical simulation approach and focuses on two essential factors: welding distortion and distortion induced by fluid to structure interaction. The research target was an impeller comprising five thin-plate curved fillet joints, and its total distortion was predicted using the proposed approach. First, the structure of the impeller was modeled with solid elements, and each welded local joint's welding distortion was measured with a modified inherent strain method. A one-way fluid-structure coupling analysis carefully examined the distortion induced by Fluid-Structure Interaction (FSI) from the fluid medium and coupling surfaces. Then, an interpolation method was conducted to compute the welding and FSI distortion contours using a simple structural analysis. To determine the inherent strain in a curved and non-curved fillet joint, a detailed transient analysis by the Thermal Elastic Plastic (TEP) Finite Element Method (FEM) and their welding distortion, plastic strain distribution, and inherent deformation are discussed. The welding and flow field tests both agree with the simulation results, confirming the modified inherent strain method and relevant FSI results. Thus, the developed approach can provide a suitable reference for controlling distortion in welded fans and related fluid machinery.

Study on Analysis Method and Control Index for Deformation of Super-High Arch Dam Suffering Alkali-Aggregate Reaction

Alkali-aggregate reaction can not only cause uneven expansion of concrete but also lead to cracking and even destruction and consequently affect the working behavior and long-term safety of hydraulic concrete structures. Present researches on alkali-aggregate reaction focus on improving the composition ratio of concrete materials through experimental study to inhibit the reaction, whereas there is a lack of quantitative calculation and analysis. In the present study, the problem of alkali-aggregate reaction in the super-high arch dam of Jinping I Hydropower Station was taken as an example. The expansion of concrete suffering the alkali-aggregate reaction was simulated by means of the overall temperature rise in the dam. Similarly, the yield zone, the expansion process, and the deformation change law with the development of concrete expansive deformation under various load combinations were analyzed by using the elastic–plastic finite element method. Finally, a control index of allowable alkali-aggregate expansion of dam concrete under various load combinations was put forward. The research results demonstrated that the control index was 400~800 με. Since the arch dam has a low safety reserve when operating at a low water level, the lowest reservoir level should be raised as much as possible in dam operation to reduce its drawdown rate, thus restraining the adverse impact of alkali-aggregate reaction in concrete on the dam.

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.

Effect of Material Inhomogeneity on the Crack Tip Mechanical Field and SCC Growth Rate of 52M/316L Dissimilar Metal Welded Joints

The stress–strain conditions at the crack tip in dissimilar metal welded joints (DMWJ) are a critical factor influencing stress corrosion cracking (SCC) behavior. The processing technology and working environment of DMWJ lead to a randomly inhomogeneous distribution of material mechanical properties, making the crack tip mechanical field more complex. An inhomogeneous model was obtained using a combination of physical experiments and the elastic–plastic finite element method to understand the effect of this inhomogeneous distribution of mechanical properties on the direction of SCC growth and the growth rate in DMWJ and the impact of inhomogeneity on the SCC growth behavior was compared and analyzed. The findings demonstrate that Type I (opening mode) cracks are more likely to form due to the inhomogeneity of mechanical properties and are more likely to deflect toward the Alloy 52M region at the interface between Alloy 52M and 316L stainless steel. Additionally, the strain gradient at the crack tip increases with the degree of inhomogeneity, which has a bigger impact on the accuracy of SCC growth rate predictions.

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 prediction of welding deformation in ship block subassemblies via the inhomogeneous inherent strain method

The weld length of ship block subassemblies is several meters even tens of meters long, mainly welded by arc welding. The inherent strain method, applying the same inherent strain value in the welding direction, is typically used in the welding deformation prediction of ship block subassemblies with high efficiency. However, the inherent strain is inhomogeneously distributed in the welding direction, especially for welds with large lengths, causing the accuracy of the inherent strain method cannot meet the need for welding deformation prediction of ship block subassemblies. This paper proposes an inhomogeneous inherent strain method (IHISM) by considering the tensile effect of the solidified zone of the weld on the melted zone. In IHISM, the magnitude of the inherent strain is related to the length of the weld. The inhomogeneous inherent strain value is obtained from a thermal elastic-plastic (TEP) finite element method and experiments. Moreover, different experiments are performed to verify the accuracy and efficiency of the IHISM. Compared with the TEP analysis, the IHISM can reach a similar accuracy while greatly improving computational efficiency. Compared with the conventional inherent strain method, the accuracy of IHISM is higher in terms of deformation trend prediction and relative deviation.

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.

Effect of Material Heterogeneity on Environmentally Assisted Cracking Growth Rate of Alloy 600 for Safe-End Welded Joints.

Environmentally assisted cracking (EAC) is essential in predicting light water reactors’ structural integrity and service life. Alloy 600 (equivalent to Inconel 600) has excellent corrosion resistance and is often used as a welding material in welded joints, but material properties of the alloy are heterogeneous in the welded zone due to the complex welding process. To investigate the EAC crack growth behavior of Alloy 600 for safe-end welded joints, the method taken in this paper concerns the probability prediction of the EAC crack growth rate. It considers the material heterogeneity, combining the film slip-dissolution/oxidation model, and the elastic-plastic finite element method. The strain rate at the crack tip is a unique factor to describe the mechanical state. Still, it is challenging to accurately predict it because of the complicated and heterogeneous material microstructure. In this study, the effects of material heterogeneity on the EAC crack growth behavior are statistically analyzed. The results show that the material heterogeneity of Alloy 600 can not be ignored because it affects the prediction accuracy of the crack growth rate. The randomness of yield strength has the most influence on the EAC growth rate, while Poisson’s ratio has the smallest.

A modular methodology for time-domain stochastic seismic wave propagation

Presented here is a modular methodology for time-domain stochastic seismic wave propagation analysis. Presented methodology is designed to analyse uncertain seismic motions as an input, propagating through uncertain material. Traditional approach for uncertain wave propagation relies on models that include deep bedrock, local soil site, and their random process and random field information. Such models can become quite large and computationally intractable. The modular approach proposed herein features two step approach that allows separate consideration of the deep bedrock and local site along with corresponding random field information. The first step considers an auxiliary stochastic motions problem in the bedrock. Stochastic local site response can then be simulated in a reduced domain within certain depth from the surface. Application of uncertain seismic motions at depth, for local uncertain site response is done using stochastic effective forces developed through the Domain Reduction Method. By using Hermite polynomial chaos expansion to represent the non-Gaussian random field of material parameters and non-stationary random process of seismic motion, the proposed modular methodology is formulated using intrusive stochastic Galerkin approach, as seen in the Stochastic Elastic–Plastic Finite Element Method (SEPFEM).Developed modular methodology is illustrated using a 1-D stochastic seismic wave propagation analysis with three cases, and simulation results are also verified with results from conventional approach.

A stress amplification model to evaluate the stress concentration of tool joint under complex loads

The more and more severe drilling conditions make the load conditions of tool joint extremely complex. Under the complex load conditions, the stress concentration of tool joint is serious, so failure of tool joint often occur in the oilfield. However, few researchers have studied the stress concentration of tool joint under complex loads. In this paper, the stress distribution of an API tool joint, NC38, was analyzed with 3D elastic-plastic finite element method under complex loads. The stress concentration factors of the tool joint were calculated, and the influence of tensile and bending load on it was analyzed in detail. The results show that the existing model cannot effectively reflect the fact that the stress concentration of tool joint will increase with large tensile load in the crooked hole section. Based on the 3D finite element analysis, a stress amplification model is proposed and used to reflect the failure risk of tool joints under the combined action of axial tension and bending moment. The results show that this model is consistent with the fact that the failure risk of tool joint will increase with large tensile load in the crooked hole section.

EFFECTS OF INTERFACE FRACTAL PARAMETERS ON NORMAL CONTACT STIFFNESS

In this study, the complex rough surface is simplified as the superposition of a series of trigonometric curves based on the least square method. In order to calculate the interface contact stiffness, the optimal substrate modeling thickness is determined by the elastic-plastic finite element method. The relationship between normal contact pressure and normal contact deformation and normal contact stiffness is quantitatively investigated. The mechanism of fractal dimension and characteristic scale parameters of rough surface on normal contact stiffness is revealed. The results show that there is an optimal thickness of the substrate, which can effectively improve the calculation efficiency of the contact stiffness of the rough surface. The normal contact stiffness increases nonlinearly with the increase of normal contact deformation and normal contact pressure. The surface fractal dimension and characteristic scale parameters have significant effects on the normal contact stiffness, and the normal contact stiffness increases with the increase of the fractal dimension. However, the normal contact stiffness decreases with the increase of characteristic scale parameters.

Influence of thickness reduction on the forming results in the three-dimensional surface rolling process with rigid arc-shaped rollers

Three-dimensional surface rolling with rigid arc-shaped rollers (TSRRAR), a new method for manufacturing double-curved metal sheets, can be used to realize the rapid forming of 3D surface sheets. The non-uniform roll gap is generated by a pair of rollers with different axial radii with appropriately reduced sheet thickness. After passing through the roll gap, a flat sheet is bent in the rolling direction. Meanwhile, it deforms perpendicular to the rolling direction, resulting in a three-dimensional surface part with curvatures in both directions. The work adopted the elastic-plastic finite element (FE) method to simulate aluminum alloy sheets with different maximum thickness reductions. The results showed that the longitudinal curvature of sheets rose as the reduction increased. Moreover, a slightly increased reduction caused a significant variation in the longitudinal curvature radius of sheets. Different bending curvatures of sheets could be obtained by changing the reduction, indicating the flexible forming of three-dimensional curved surface metal sheets. Also, the changing trend of longitudinal curvatures of testing parts obtained by rolling experiments was substantially in agreement with the FE simulation results. Therefore, the established FE models can be used for exploring the manufacturing process of TSRRAR.

Investigating Welding Distortion of Thin-Plate Stiffened Panel Steel Structures by Means of Thermal Elastic Plastic Finite Element Method

In the past decades, thin-plate weldments have been increasingly used in various engineering structures to meet the requirements of lightweight. However, deformation induced by welding process has a negative effect on assembly accuracy and structural integrity. Therefore, it is critical to predict welding deformation and then to control or reduce the total deformation. Because the thermal elastic plastic FEM has the advantage of high computational accuracy, an attempt was made to predict the welding deformation of a large-scale thin-plate welded structure in this study. Based on the commercial software MSC. Marc, a thermal elastic plastic FEM with the consideration of material nonlinearity, geometrical nonlinearity, and boundary nonlinearity was developed to simulate the welding deformation of large-scale welded structures. The effectiveness of the developed computational approach was verified by the experimental measurements. Moreover, the mechanism of buckling distortion in a large-scale stiffened panel structure was investigated based on the simulated results. In addition, the influences of heat input, welding procedures, and constraint condition on welding deformation were also examined numerically.

Role of the mandrel in the variable curvature local-induction-heating bending process of B1500HS thin-walled rectangular tubes

The variable curvature local-induction-heating bending forming (VC-LIHBF) technology is commonly used in the automotive industry to lighten and stiffen the structure parts. This technology allows the simultaneously bending forming and hardening of ultrahigh strength steel tubes, and allows the tensile strength of B1500HS steel to reach 1500 MPa. By adjusting the bending curvature parameters of the experimental facility through the numerical control system, the production of the tubes with variable curvatures could be achieved without changing dies. However, the more major problem of wrinkling occurs when a small-radius bending is applied on thin-walled rectangular tubes. This paper focuses on improving of forming quality and forming limit of the thin-walled rectangular steel tube (TWRST) with mandrel supported. In this study, an analytical model of the mandrel is established and some reference formulas for the selection of the mandrel parameters are deduced. Based on the above analysis, a three-dimensional elastic-plastic finite element method (FEM) model of the LIHBF process of the B1500HS TWRST is developed using the dynamic explicit FEM code ABAQUS/Temp-disp/Explicit, and key technological problems are solved. Experiments are carried out to verify the accuracy of the analytical model and confirm the reliability of the FEM model. The influences of the mandrel on stress distribution during the local-induction-heating bending process are also investigated. The influence mechanism of the mandrel parameters on the minimum radius of the LIHBF without wrinkling and the forming quality is revealed. The appropriate process parameters for the B1500HS TWRST are obtained through experiments and simulations.

Failure Analysis of Ductile Iron Crankshaft in Four-Cylinder Diesel Engine

Spheroidal graphite cast iron is widely used in automobile crankshafts due to features such as high strength, high toughness, good machinability, low cost, and ductility. The purpose of this paper is first to analyze the fatigue failure in fractured truck crankshafts between 400,000 and 1,350,000 km and then to predict the stress field under the influence of the mechanical loads caused by gas combustion. Several experimental studies including chemical composition, material strength, hardness, and microstructure are performed to evaluate the failure analysis. A nonlinear three-dimensional stress analysis model by the elastic–plastic finite element method is used to estimate the crankshaft stress field under cyclic bending combined with steady torsion. Failure analysis showed that the fracture surface consisted of three zones: fatigue crack initiation, fatigue crack propagation, and static fracture; therefore, the failure is in fatigue. Also, the microstructure results showed that the crankshaft nodularity is about 70%, which crankshaft structures are usually acceptable greater than 80% of nodularity. Besides, hardness gradient showed that the crankshaft crankpin had no hardened surface layer. Finally, numerical stress analysis indicated that the highest stress is in the crankpin–web fillet zone that it is in good agreement with those obtained in the experimental field measurements.