Elastic-plastic Finite Element Model Research Articles

Numerical Study on Mechanical Behavior and Electromechanical Properties of Solder-Jointed REBCO-Coated Conductors.

As the second-generation high-temperature superconducting conductors, rare earth-barium-copper-oxide (REBCO) coated conductor (CC) tapes have good potential as high-field and high-energy superconductors. In superconducting applications, several joints are required for conjugating comparatively short REBCO CC tapes. Soldering lap joints are the simplest and most commonly applied REBCO CC joints. In addition to joint resistance, the mechanical behavior and electromechanical properties are also crucial for superconducting applications. In this paper, the electromechanical properties and mechanical behaviors of soldering lap joints at 77 K under a self-field were studied. The mechanical behavior was addressed by using a full three-dimensional multilayer elastic-plastic finite element model (FEM) with REBCO CC tape main layers and solder connecting layers. Then, the electromechanical properties were analyzed by using Gao's strain-Ic degradation general model on the basis of the FEM results. Both the mechanical behavior and electromechanical properties were verified by experimental results. The effects of soldering lap conditions including lap length, soldering thickness and lap style on the electromechanical properties and mechanical behaviors were discussed. The results indicate that shorter overlap lengths and a thinner solder can reduce the premature degradation of Ic due to stress concentrations nearby the joint edges; moreover, the irreversible critical strain is significantly higher in the back-to-back joint approach compared to the widely used face-to-face joint approach.

Deformation caused by T-shape expansion of existing metro station: complex challenges and strategies

This case study presents an investigation on existing metro station deformation characteristics during T-type expansion in Nanjing, China. A three-dimensional elastic-plastic finite element model is adopted to consider the interaction of soil, retaining structure, horizontal support system and existing station structure. The results indicate that coupling deformation of asymmetric uplift deflection and existing structure rotation occurs on existing structure. Moreover, the sensitivity of influencing factors is analyzed, including the dimension of retaining structure, the support spacing, the excavation method, the soil reinforcement depth in passive area, the width of retaining soil during excavation, the relative position between foundation pit and existing structure, the excavation depth, the existing structure rigidity. Furthermore, based on the analysis of difficulties in the T-shape expansion projects, the controlling measures for the deformation of existing metro station are proposed. The achievements of this case study can be used as a reference for similar underground expansion projects.

Prediction and control of profile for silicon steel strip in the whole tandem cold rolling based on PSO-BP algorithm

In the rolling process of silicon steel strip of the five-stand UCMW tandem cold rolling line, the quality of finished profile is the result of cooperative control of five stands, the exit profiles of the first four stands jointly decide the exit profile of the fifth stand, so it is necessary to accurately control the strip profile in the rolling process. However, the shapemeter is only typically equipped at the exit of fifth stand, making it impossible to obtain the strip profile of the first four stands. A profile prediction model for the whole tandem cold rolling based on PSO-BP algorithm is established, compared with the finite element method, this model can satisfy the demand for fast prediction of strip profile and quickly analyzing the profile change characteristics for five stands according to the adjustment of profile control parameters in the industrial field. Firstly, a 3D elastic-plastic finite element model of rolls and strip for five stands is built, and a large number of profile calculation data are as the training sample sets to build the PSO-BP model. Through the transfer calculation of strip profile between adjacent stands, the PSO-BP model of five stands is established, and the validity is verified by comparing with the actual measured data. Secondly, to improve the quality of product profile, focusing on the unreasonable setting of production parameters, many improvement schemes of WRB and WRS for five stands are designed, and the PSO-BP model is used to quickly calculate the strip profile, then comparing the result of each scheme, the optimum improvement scheme is selected, which is furtherly carried out rolling experiments in the industrial field, and the quality of strip profile is well improved. At present, the new scheme has been successfully applied to industrial production.

Three-dimensional mechanical characteristics analysis of bolted joints and loosening mechanism

Bolted joints are widely used in various industries. However, in challenging conditions such as shock, vibration, and temperature fluctuations, threads can loosen, leading to equipment damage and accidents. Scholars have introduced self-locking thread designs like wedge-shaped self-locking threads and stepped threads to improve anti-loosening performances. While experiments support their effectiveness, previous research primarily focused on optimizing thread structure parameters, and the studies of loosening mechanism are not in-depth enough, which restricts the development of anti-loosening bolted joints. This paper proposes a parametric modeling approach to create 3D elastic–plastic finite element models of bolted joints with different thread profiles. This approach allows for a comprehensive analysis of structural behavior, stress distribution, and load conditions, enabling the in-depth examination of the mechanical properties for thread loosening. A novel arc-lock anti-loosening threads design is proposed. Arc-lock threads are found to provide superior load distribution uniformity, increased normal force, and enhanced frictional resistance. Furthermore, the correctness of the finite element results is validated through photoelastic experiments and transverse vibration experiments. Results show that under a preload force of 225.5kN, the assembly of M24 Grade 10.9 bolts with Grade 10 nuts exhibit RMSE (Root Mean Square Error) values of 11.25, 9.02, and 8.76 for regular threads, wedge-shaped threads and arc-lock threads, respectively. Arc-lock threads demonstrate a more uniform stress distribution. In transverse vibration experiments under fully tightened conditions, regular threads loosened at the 2326th vibration cycle, while wedge-shaped self-locking threads and arc-lock threads maintained the preload percentages of 91.24% and 93.51%, respectively. These findings offer a scientific basis for understanding anti-loosening mechanisms in bolted joints and inform anti-loosening thread design.

Grain-Scale Study of SAC305 Oligocrystalline Solder Joints: Anisotropic Elasto-Plastic Constitutive Properties of Single Crystals

Abstract This paper focuses on anisotropic elastic-plastic constitutive modeling of SAC (SnAgCu) solder grains because of their importance in modeling the behavior of oligocrystalline (few-grained) micron-scale solder joints that are increasingly common in heterogeneous integration. Such grain-scale anisotropic modeling approach provides more accurate assessment of the mechanical response of solder interconnects in terms of predicting different failure modes, failure sites, and variability in time-to-failure. Anisotropic plasticity is represented using Hill–Ramberg–Osgood (RO) continuum plasticity model, which utilizes Hill's anisotropic plastic potential along with a RO power-law plastic hardening flow rule. Mechanistically motivated empirical scaling factors are proposed to extrapolate the stress–strain response for different grain sizes/shapes and for different coarseness of microstructures within each grain (generated with different cooling rates). This scaling factor can therefore also capture the effects of microstructural coarsening due to isothermal aging. This goal is achieved by first conducting monotonic tensile and shear tests on monocrystalline and oligocrystalline SAC305 solder joints containing grains of various geometries and also intragranular microscale (dendritic and eutectic) structures of various coarseness. The grain structures are characterized for each tested specimen using electron backscattered diffraction (EBSD). The Hill–RO model constants and the empirical scaling factors are then estimated by matching grain-scale anisotropic elastic-plastic finite element models of each tested specimen to the measured stress–strain behavior, using an inverse-iteration process. Grain shape is seen to influence the sensitivity of the effective stress–strain curves to the applied stress state (i.e., to the orientation of the principal stress directions) relative to (i) the material principal directions and (ii) the geometric principal directions of grains with high aspect ratio. Limitations of the current results and opportunities for future improvements are discussed.

Influences of thermal crown and wear crown of work roll on strip shape in tandem cold rolling using a novel 3D multi-pass FE model

Thermal crown and wear crown of work roll (TWW) are the main interfering factors of loaded roll gap profile in tandem cold rolling (TCR). However, the effect of TWW on the strip shape is not well understood. This paper presents a quantitative study about the effect of TWW on the strip crown and strip flatness based on a novel 3D multi-pass elastic-plastic finite element (EPFE) model that has been validated by industrial trials in the TCR. The results show that the thermal crown introduces the centre wave and quarter wave, while the wear crown brings in the edge wave and edge-centre coupled wave; the thermal crown has a larger influence efficiency on the quadratic strip shape than the wear crown does, while the wear crown exerts a larger influence efficiency on the quartic strip shape than the thermal crown does. In addition, the influence efficiency of TWW on the strip crown decreases nonlinearly with an increase in strip plastic rigidity from Pass 1 (P1) to Pass 5 (P5). This is the first scientific report on the link between the strip plastic rigidity and the effect of TWW on the strip crown, affording the mathematical models for predicting the influence efficiency of TWW based on the strip plastic rigidity at each pass.

Numerical and experimental investigation of the residual stress distribution of internal thread cold extrusion and tap wear

AbstractIn order to improve the thread‐forming quality of diesel engine piston connecting rod, the internal thread cold extrusion process was adopted for the through‐hole structure of 42CrMo4 high‐strength steel. The influence of different structural parameters of the tap on the residual stress distribution of the cold extrusion internal threads and self‐wear were discussed with the help of three‐dimensional elastic–plastic finite element model. The wear of tap was observed by an electron microscope, coordinated with the residual stress distribution of thread was measured by X‐ray diffraction to explore the relationship between residual stress distribution of the cold extrusion internal thread, tool wear and tap structure. The optimal combination of tap structure parameters of residual stress and tool wear was obtained through grey relation method. The residual compressive stress and the depth of stress layer near the thread surface increased and the wear condition of the extrusion tap was improved when the tap with optimised structural parameters was used for processing, while maintaining the original thread connection strength. The results show that the internal thread with better‐forming quality can be obtained by using the optimised extrusion tap, while the service life of the tap was prolonged.

Finite element analysis of reinforcement for gas insulated switchgear

Considering the burgeoning requirement for reinforcing gas-insulated metal-enclosed switchgear, a three-dimensional elastic-plastic finite element model was established to examine the stress distribution before and after reinforcement. The results showed that, under an internal pressure of 3.8 MPa, the maximum stress of the defective sample surpassed the yield strength of the material, leading to its destruction. On the other hand, the maximum stress value of the reinforced sample, with a gel and a reinforcing plate, decreased to 145 MPa and was lower than the yield strength of the material. Moreover, the results of the hydrostatic test further demonstrated that the gel was effective in reducing the stress concentration at the defect within a certain range. In particular, the results indicated that the gel was capable of decreasing the maximum stress value by 33 MPa, thereby safeguarding the structural integrity of the switchgear.

Numerical Investigation on Reduction Characteristics of Welding Deformation According to Standoff Distance in Heat Sink Welding Process

Welding with a trailing heat sink process is proposed as a useful technique to reduce welding deformation without a significant loss of manufacturing efficiency. In particular, this method is effective than the existing mechanical or thermal correction method in thin plate steel structures with low stiffness. In this study, a three-dimensional thermal elastic-plastic finite element model using a 3-mm thick 304L stainless steel sheet was developed to simulate heat sink welding. The reduction characteristics of welding deformation according to the standoff distance between the welding heat source and the heat sink zone was investigated in the numerical simulation. The results confirmed that the longitudinal and angular deformations were significantly reduced compared with those by conventional welding. The longitudinal deformation was reduced by approximately 60%, from 5.50 mm to 2.22 mm, and the angular deformation was reduced by approximately 70%, from 1.68 mm to 0.51 mm. The overall results obtained in the numerical analysis indicated that welding deformation significantly decreased as the standoff distance was shorter owing to the temperature cooling effect of the welds.

Data-driven artificial neural network for elastic plastic stress and strain computation for notched bodies

An integration of artificial neural network (ANN) and finite element (FE) analysis was developed to predict elastic–plastic stress and strains at notch locations based on a linear elastic FE analysis solution. Two FE models were created for different materials and multiaxial load cases to produce hypothetical elastic and elastic–plastic stress and strain datasets. One model was based on an elastic state, and the other was based on an elastic–plastic state. The ANN was trained with the elastic stress data from the linear elastic FE model as input and the elastic–plastic stress–strain data from the nonlinear elastic–plastic FE model as output. The dataset was divided into three groups: training, verification, and testing data. The ANN was trained using the training data, evaluated using the verification data, and tested for generalizability using the testing data. The results showed that the proposed methodology can predict elastic–plastic stress and strain fields for notched bodies under multiaxial loadings accurately and efficiently using only the elastic FE analysis solution.

Factors influencing fault-propagation folding in the Kuqa Depression: Insights from geomechanical models

Understanding the rock mass deformation and strain state is critical to a range of endeavors. Geomechanical modeling is an excellent approach simulating the formation processes of faulting and folding, which can reproduce the geometry of fold structures and track strain and stress through the whole deformation process. In this study, five series of two-dimensional (2D) elastic-plastic finite element models were built to investigate the influences of shortening distance, ramp cutoff angle, interlayer slip, fault friction, fault number and fault slice width on structural styles and strain distribution patterns during fault-propagation folding in the Kuqa Depression of Tarim Basin. The results indicate that, i) All above mentioned factors can influence the structural style and strain distribution of fault-propagation fold (FPF) to varying degrees. Fault friction, interlayer slip and fault slice width are the most important parameters influencing the deformation geometry and strain patterns of FPF; ii) There are critical values for fault friction coefficient and shortening distance to create a secondary fold besides the FPF; iii) A “step pattern” occurs both in the forelimb and backlimb of the FPF when fault slice width reaches a certain high value; iv) Structural position in the FPF controls volumetric changes. The evolution of FPF can be divided into two stages: layer parallel shortening and volume loss, and folding; v) The steep forelimb region of FPF develops more natural fractures, which may serve as a favorable location for potential reservoirs in the Kuqa Depression. The results are also expected to provide clues for the exploration and development of oil and gas in regions with similar geological conditions.

Finite Element Analysis of Large Plastic Deformation Process of Pure Molybdenum Plate during Hot Rolling

The rare molybdenum resources are being increasingly used in heavy industries. In this study, the common unidirectional and cross hot rolling operations, for pure molybdenum plates, were numerically simulated by using MSC. Marc software. An elastic–plastic finite element model was employed, together with the updated Lagrange method, to predict stress and strain fields in the workpiece. The results showed that there was a typical three-dimensional additional compressive stress (σy> σz > σx) in the deformation zone, while strain could be divided into uniaxial compressive strain and biaxial tensile strain (εy > εx > εz). Tensile stress σx increased with the accumulation of reduction and the decrease in friction coefficient at the edge of the width spread. More importantly, the interlaced deformation caused by cross-commutations, which were helpful in repairing the severe anisotropy created by unidirectional hot rolling. The evolution of the temperature field of pure molybdenum plate was investigated. The surface quenching depth of the pure molybdenum plate was about 1/6 H under different initial temperatures and reductions. In addition, the fundamental reason for the nonuniform distribution of stress and strain fields was the joint influence of rolling stress, contact friction, and external resistance. By comparing the theoretical simulation value of the model with the experimental verification data, we found that the model was aligning well with the actual engineering.

DYNAMIC FINITE ELEMENT SIMULATION OF WHEEL–RAIL CONTACT RESPONSE FOR THE CURVED TRACK CASE

The wheel–rail interaction will be intensified on account of the complexity of the wheel–rail contact geometry on a curved track. It also may become more complicated and/or have significant difference as the train speed increases, since the dynamic effects cannot be ignored then. In this study, based on explicit Finite Element (FE) software LS-DYNA 971, a Three-Dimensional (3D) elastic-plastic FE model was built to simulate the dynamic wheel–rail contact behaviour of curve negotiating, where the superelevation and roll angle as well as the strain rate effect were considered. The evolution of contact patch and pressure, wheel–rail contact force, the stress/strain state and the acceleration of the axle were employed to examine the wheel–rail transient dynamic response. Furthermore, the influences of axle load, curve radius and strain rate effect were also discussed. It is found that the maximum vertical contact force, contact pressure, stress and strain on the curved track increase with the decreasing curve radius, and they increase with the increasing axle load except for lateral contact force. The wheel–rail dynamic responses on the curved track are significantly enhanced compared to the straight track. Moreover, the strain rate effect can enhance von-Mises stress and contact pressure, suppress the plastic deformation of the rail and wheel, but it has little effect on the vertical and lateral contact forces and stable acceleration of axle. The Rate-Sensitive Factors (RSF) of the wheel and rail on the curved track are weaker than those on the straight track. These findings will be very helpful to study the competitive relationship between the rolling contact fatigue and wear, as well as the crack initiation and propagation problem.

A plastic design method based on multi-objective performance for high-strength steel composite K-shaped eccentrically braced frame

A plastic design method based on multi-objective performance (PDMP) for high-strength steel composite K-shaped eccentrically braced frame (HSS-KEBF) is developed in this study, which explicitly considers the different seismic fortification objectives of the structure and the shear distribution relationships of the brace-frame system. The performance objectives of the structure under three seismic hazard levels were obtained by combining different roof drift ratios and displacement ductility demands, and a trilinear capacity curve of HSS-KEBF considering the change of post-yield stiffness was proposed. The energy balance principle was used to calculate the elastic and elastic–plastic shear distributions of the brace-frame system under different performance objectives, to facilitate the elastic–plastic design of HSS-KEBF. A ten-story HSS-KEBF structure was designed using the proposed design method, and an elastic-plastic finite element model of the structure was established using OpenSees for analysis. The results show that the structural model achieves the expected performance objectives in terms of capacity curves, roof drift ratios, base shears, and failure modes. From the SLE level to MCE level, the base shear distribution ratio borne by the frame component increased from 36% to 46%, which satisfies the design idea of multi-aspect fortification.

Numerical Simulation on Hydraulic Fracture Height Growth across Layered Elastic–Plastic Shale Oil Reservoirs

Shale oil reservoirs are characterized by having various types of vertical sublayers, a large contrast in rock mechanical properties, well-developed bedding, and high clay content, which are likely to cause rock elastic–plastic deformation. In numerical simulations of hydraulic fracture (HF) propagation in the shale oil reservoirs, the effects of rock elastic–plastic deformation and complex bedding structure on the layer-crossing behavior of HF are not considered. To understand the mechanism of HF height growth in shale oil reservoirs, we used the cohesive zone method to establish an elastic–plastic finite element model of HF propagation by considering the effects of shell limestone interlayers, the Mohr–Coulomb yield criterion for shear–plastic failure, the cross-mechanical interaction between bedding and shale oil reservoir, and the complex situations such as the HF height across high-electrical resistivity bedding and high-conductivity fractures. The effects of internal friction angle, cohesion, layer stress contrast, fracture toughness, bedding bond strength, injection rate, elastic modulus, and bedding shear strength on HF height growth in shale oil reservoirs are studied, and the characteristics of HF width profile, injection pressure, failure mode, and maximum HF width are compared. Compared with the layer stress contrast, cohesion, internal friction angle, and fracture toughness, the injection rate, elastic modulus, and bedding shear strength and bond strength have a larger effect on the vertical HF width. Increment of the injection rate, decrease of the elastic modulus, and increment of the bedding shear strength and bond strength are favorable for HF height growth in the shale oil reservoir. As rock cohesion and internal friction angle increase, the HF width decreases. At the initial stage of fracturing fluid injection, the maximum HF height and injection pressure fluctuate. Lower cohesion and internal friction angle promote rock shear failure in HF height growth. Our study provides guidance for the stimulation of fracture crossing layers in the shale oil reservoirs.

Mechanical behavior of all-lignocellulose composites—Comparing micro- and nanoscale fibers using strain field data and FEM updating

Hot-pressed, binder-free wood fiber (WF) composites can serve as load-bearing and eco-friendly materials, and the comparison of nanoscale fibril reinforcement with microscale wood fibers is of interest. We investigated property differences and interpreted deformation mechanisms with strain field measurements using digital image correlation combined with orthotropic, elastic–plastic finite element model updating predictions. Random-in-plane microfibrillated lignocellulose (MFLC) composites showed better mechanical properties than WF composites due to stronger strain-hardening from lower porosity and better interfibrillar adhesion, provided by the intrinsic lignin-hemicellulose binder. Axially oriented wood fiber composites (O-WF) achieved comparable mechanical properties to random MFLC, with lower values for eco-indicators. The FEM updating method could successfully determine all 4 independent elastic constants from one 45° off-axis experiment, although the plasticity model required two more experiments.

Influence of contact behavior on welding distortion and residual stress in a thin-plate butt-welded joint performed by partial-length welding

Partial-length butt-welded joint is a typical weldment which is often used in vehicle parts such as car door and body. In order to clarify the influence of contact behavior on the final distortion and residual stress distribution in thin-plate butt-welded joints, a computational approach considering multiple nonlinearities was proposed based on ABAQUS code, and a series of three-dimensional thermal–elastic–plastic finite element models were developed to simulate welding distortion and residual stress in mild steel thin-plate butt-welded joints performed by partial-length welding. Meanwhile, the corresponding experiments were carried out to verify the calculation accuracy of the proposed computational approach. Moreover, the influence of initial gap size on welding distortion and residual stress was numerically and experimentally examined. Based on the simulated results, the formation mechanism of welding deformation in the thin-plate partial-length butt-welded joint was also discussed.

Prediction of welding residual stress and distortion in multi-layer butt-welded 22SiMn2TiB steel with LTT filling metal

The objective of this study is to investigate the influence of low transformation temperature (LTT) filling metal on residual stress and distortion in multi-layer butt-welded 22SiMn2TiB steel. A three-dimensional thermal elastic–plastic finite element model is developed for LTT filling metals, and metallurgical phase transformation is taken into account to predict the martensite fraction of the weld metal. A thermodynamic-based method is employed to calculate martensite start temperature (Ms) and the influence of dilution on Ms is also considered. Volume change due to austenite transformation during heating and martensite transformation during cooling are coupled with the numerical simulation of welding process. The evolution of welding residual stress and welding distortion are both predicted. The simulation results revealed that the distortion of welding plate using LTT filling metal is much smaller than that using austenitic metal. In the weld zone, transverse residual stress is lower using austenitic filling metal, but longitudinal stress is much smaller using LTT filling metal. Longitudinal stress distribution for both LTT and austenitic filling metals is very high in the heat-affected zone, which is close to the yield stress of base metal. The LTT filling metal can not only guarantee the strength of welded joint for armor steel, but also reduce the welding distortion obviously, and the residual stress is also very low at the same time. The predicted temperature profiles and welding distortion are generally in good agreement with the experimental ones.

Residual Stress Around the Fatigue Crack Front in a Rectangular Sample Cut from CT Specimen

In this paper, an elastic–plastic finite element model was built to simulate the stress field around a fatigue crack in a standard CT specimen before and after splitting to obtain a rectangular specimen for further investigation. Plane stress and plane strain, as well as 3D simulations, were performed and compared. The simulations consist of two steps: (i) The standard CT-specimen undergoes cyclic loading until the fatigue crack tip achieves the middle of the specimen, and (ii) A rectangular sample with the crack to one half of its width was cut from the CT-specimen. A parametric plane strain study was carried out to determine the location of the cutting plane relative to the edge of the plastic zone, where the impact on the residual stress due to stress relief after cutting is negligible. It was also found that in the peripheral parts of the front close to the free surface, the stress is strongly influenced by the curvature of the crack front.

Numerical Simulation and Parametric Analysis of Fatigue Crack in UIC60 Rail Thermite Welded Joint

The mechanism of rail-wheel contact is the most essential field of study in railway engineering since it requires extensive application expertise, diagnostic skills, and a trustworthy analysis technique. In this research the fatigue life of a UIC60 rail AT weld under vertical load and its parametric effect has been studied, and for that a three-dimensional elastic-plastic finite element model is created using ANSYS space-claim software, and then finite element method is employed to analyse the full-scale model of wheel-track and weld system with realistic three-dimensional solution. Model assembly components include axle, wheel, and thermite-welded rail. Simulation of contact between wheel and UIC60 rail weld with crack on weld at angles of 30 and 60 degrees with different coefficients of friction between the weld wheel contact and between crack surfaces was carried out under vertical loadings. In general, the Hertz contact theory assumptions are taken into consideration throughout the analysis, and the impacts on fatigue life are given by using damage mechanics method. The results of the wheel/weld fatigue crack analysis have been displayed to demonstrate the influence of different parameters on the fatigue life of cracks. The purpose of this study is to identify and safeguard the rail against failure, as well as to ensure the safety of passengers and to reduce the cost of maintaining the rail system.