Static Implicit Research Articles

Optimization of Forming Parameters of Ti-3Al-2.5V Titanium Tubes by Differential Heating Push-Bending Based on a Modified Johnson−Cook Constitutive Model

This study addresses the challenges associated with the difficult formation and low quality of formed Ti-3Al-2.5V titanium alloy thin-walled tubes with small bending radii (r / D < 1.5, where r is the bending radius, D is the outer diameter of the tube) by proposing a differential heating push-bending (DHP-B) forming approach. Initially, the stress−strain curves of Ti-3Al-2.5V at various strain rates and temperatures were obtained through high-temperature uniaxial tensile tests. Subsequently, a modified Johnson−Cook (JC) model for Ti-3Al-2.5V within the temperature range of 25℃ to 800℃ was developed to enhance the accuracy of the finite element model. Based on the static implicit and dynamic explicit algorithms, a thermomechanically coupled finite element model for differential heating push-bending of titanium alloy thin-walled tubes has been established. Taking the heating temperature, friction coefficient, counterthrust force and rubber block thickness as the optimization parameters, the prediction model of the maximum wall thinning rate and thickening rate is obtained by using the response surface method, and the best parameter combination is obtained via the NSGA-II algorithm and the minimum distance selection method, which realizes the optimization of differential heating push-bending parameters, as verified by experiments in which the maximum wall-thinning rate is reduced to 9%, and the maximum wall thickness thickening rate is reduced to 14.2%, which improves the forming quality of the titanium tube.

Development of Calculation Technique for FEM Thermal Simulation Using Virtual Fluid Elements

In recent years, CAE (Computer-aided engineering) using FEM (Finite element method) simulations were generally used in the design field. FEM simulations were classified as static implicit and explicit dynamics methods. Particularly FEM simulations using the static implicit method were very generally and usefully used in the industrial world. The static implicit method FEM consists of static, buckling, thermal, vibration analyses, and so on. This FEM thermal analysis can't calculate the phenomena of heat transfer and internal forced cooling in some enclosures of a machine tool. On the other hand, when the temperature distributions in a structure such as that are calculated, FVM fluid simulation was used for that. However, this simulation can't exactly calculate a complex structure in a machine tool, needs very long calculation times and the calculation accuracy is very poor. Therefore, in this research, the calculation technique regarding FEM thermal simulation using 4 virtual fluid elements was developed and evaluated for the phenomena of heat build-up and internal forced cooling in some enclosures of a machine tool. The algorithms and the calculation models regarding 4 virtual fluid elements were developed, then the proposed method was evaluated in the experiment. It is concluded from the results that; (1) the 4 virtual fluid elements were developed for FEM thermal simulation instead of FVM fluid simulation, (2) FEM thermal simulation with the developed 4 virtual fluid elements has high calculation accuracy and a short calculation time, (3) the proposed method was very effective in the design.

The influence of material model on the neck development for aluminium alloy sheet

The neck development for bore expansion problem is analyzed. Static implicit calculations are carried out for the A2219 Aluminium alloy sheet using ABAQUS/Standard. The equations to give the conditions of the onset of the localized necking of sheet metal based on the general bifurcation theory are presented for plane stress. Since accurate calculation of stresses and strains are the basis for the necking prediction, both associated and non-associated flow rule are adopted in the material model in which Hill’s quadratic functions are used. User defined subroutine UMAT is developed using a fully implicit integration scheme. The results of necking prediction show that necking occurrence delays for the Hill solid using both AFR and NAFR based model compared with Mises solid and necking occurrence slightly delays for the Hill solid using AFR based model compared with Hill solid using NAFR based model. Initial necking occurs when equivalent plastic strain is respectively 0.33, 0.39 and 0.348 for the Mises solid and Hill solids using AFR and NAFR based models. Theses indicate that the material model has significant influence on the accuracy of necking prediction.

An implicit formulation of a two-grain cluster type homogenization approach for polycrystals

The crystal-plasticity-based finite element method has received considerable attention in the field of sheet-metal forming. When the size of stamped sheets is hundreds to thousands of millimeters, a homogenization approach with a lower computational cost is required. A previous study proposed a two-grain cluster (TGC)-type homogenization method, which allows relaxation from the fully-constrained Taylor model (Yoshida, 2022. An alternative formulation of a two-grain cluster model for homogenization of elastoviscoplastic behavior of polycrystal, International Journal of Plasticity, 156, 103368). In the present study, a fully implicit numerical procedure was developed for the TGC model, and it was applied to a cup drawing simulation. The present implicit TGC model used the fully implicit stress integration method. In addition, the relaxation vector that satisfies the equilibrium and compatibility conditions at the end of increment was determined. Moreover, the algorithmic tangent moduli that are consistent with the Newton–Raphson method were derived analytically. These features facilitate the implementation of the TGC model in the FEM. The developed model was implemented in static implicit FEM software (MSC Marc), and cylindrical cup drawing was simulated. Consequently, the FE simulation in conjunction with the TGC model was found to more accurately predict the cup height and thickness than that in conjunction with the Taylor model. The better prediction accuracy of R-values obtained by the TGC model contributed to the accurate prediction of the drawn cup profile.

Numerical Modeling of Damage Caused by Seawater Exposure on Mechanical Strength in Fiber-Reinforced Polymer Composites.

Fiber-reinforced polymer composites are frequently used in marine environments which may limit their durability. The development of accurate engineering tools capable of simulating the effect of seawater on material strength can improve design and reduce structural costs. This paper presents a numerical-based approach to predict the stress–strain response of fiber-reinforced polymer composites exposed to different seawater immersion times, ranging from 0 to 900 days. A three-dimensional numerical model has been implemented using a static implicit finite element analysis along with a user-defined material (UMAT) subroutine. Puck’s failure criterion was used for ultimate failure analysis of the laminates, while Fick’s first diffusion law was used to predict the seawater absorption rate. Overall, the simulated stress–strain curves were close to those obtained experimentally. Moreover, the model agreed well with the experimental data regarding the maximum stress and the strain at failure leading to maximum errors lower than 9% and 11%, respectively. Additionally, the simulated strain fields agreed well with the experimental results measured by digital image correlation. Finally, the proposed procedure was also used to identify the most critical surfaces to protect the mechanical components from marine environments.

Study on explosion-resistance performance of concrete-filled steel tubular columns considering the influence of elevated temperatures

Fire and explosion often occur together that seriously threatens the safety of engineering structures. In order to investigate the explosion resistance of concrete-filled steel tubular (CFST) columns at elevated temperatures, the finite element (FE) model of explosion resistance performance for circular CFST columns at elevated temperatures was established using the ABAQUS software. The fire and blast loads were simulated using ISO 834 standard fire and ConWep model, respectively. In the model, the static implicit and dynamic explicit analysis was coupled using “Restart” and “Import” commands and the strain-rate effect was considered. The experiment results of related literatures, including the temperature field, fire resistance duration and explosion resistance of CFST columns, were used to verify the feasibility of the method. Based on the validated FE models, the explosion mechanism of CFST columns subjected to standard fire was analyzed, including the failure modes, full-range analysis, development of stress and strain, interaction between steel tube and concrete and energy consumption. The influence of duration time, material strength, steel ratio and explosion equivalent on the explosion resistance were studied. The maximum mid-span deflection (Δpeak) was employed to quantitatively analyze the explosion-resistance performance of the CFST columns. The results show that shear failure firstly occurs at both fixed ends, and then the whole column presents flexural failure mode when subjected to explosion load under fire condition. With the increase of duration time, the proportion of energy consumption of steel tube decreases, and plastic deformation of concrete gradually becomes the main energy consumption mechanism. The concrete strength, explosion equivalent and axial load ratio have significant influence on the explosion resistance of CFST at high temperatures. After 0 min and 90 min fire duration, the explosion resistance is improved by approximately 21% and 42% respectively when the concrete cubic compressive strength increases from 30 MPa to 50 MPa.

Direct measurement of shot velocity and numerical analysis of residual stress from pneumatic shot peening

Shot peening is widely used in several fields to improve the fatigue strength of manufactured parts via the introduction of compressive residual stresses. The shot velocity is significant physical factor; however, it is difficult to measure this velocity directly in pneumatic shot peening. In this study, an experiment was performed to record shot movement with a high-speed camera. Particle image velocimetry (PIV) was used to measure the shot velocity distribution: the shot accelerated after being projected from the nozzle and reached a steady shot velocity at approximately 80 mm from the nozzle. The steady shot velocity was proportional to approximately the 0.51st power of the air pressure: 30 m/s at 0.14 MPa and 49 m/s at 0.35 MPa for steel shot ASR170. For an A7075 aluminum alloy, the depth of the compressive residual stress increased with the shot velocity and was greater than 0.5 mm at 0.35 MPa air pressure. Finite element analysis (FEA) was performed on the residual stress distribution with the shot velocity measured by PIV as the input value. Peening with multiple shots was evaluated through dynamic explicit FEA. The residual stress distribution after shot peening was obtained through subsequent static implicit FEA. The analytical results for the residual stress distribution complied with the experimental results. Thus, the shot velocity measurement technology and the FEA model that were used to calculate the residual stress from shot peening were both validated.

Quasi-Dynamic Implicit Finite Element Analysis of Steel-Clad, Wood-Framed Shear Walls

HighlightsA new finite element modeling method was developed to predict performance of steel-clad, wood-framed diaphragms.The new method overcomes limitations of previous models and accurately predicts yielding and buckling behaviors.The new method will save time and money in developing design values for steel-clad, wood-frame diaphragms.Abstract. Various finite element codes and solution techniques have been developed for steel-clad, wood-framed (SCWF) shear walls over the past few decades. Most previous finite element models for SCWF shear walls under monotonic loading were based on a static implicit solution technique. Previous researchers stated that the static implicit technique showed promise for modeling SCWF diaphragms; however, the solution technique failed to converge to equilibrium as local instabilities in the form of snap-through buckling of steel cladding occurred or geometric nonlinearities were included in the model. In this study, a nonlinear quasi-dynamic implicit finite element analysis (FEA) of SCWF shear walls subjected to monotonic loading was developed to overcome the deficiencies of the static implicit approach. Three types of elements were used, including beam elements to model wood framing, shell elements to model steel cladding, and nonlinear spring elements to model connectors. Screw connector tests were conducted to obtain the load-displacement constitutive relationships needed for finite element models. Nine types of SCWF shear walls with and without lap seam stitching were tested to validate the finite element model. The ratios of predicted to test values for ultimate shear strength averaged 0.97 with a coefficient of variation (COV) of 8.1%, and the ratios for effective shear modulus averaged 1.13 with a COV of 30%. The quasi-dynamic implicit FEA is a significant improvement over previous static implicit techniques and should be a useful tool to predict the ultimate shear strength and effective shear modulus of SCWF shear walls under monotonic loading. Keywords: Diaphragm design, Post-frame building, Steel-clad wood-frame diaphragm.

Determining factors affecting sheet metal plastic wrinkling in response to nonuniform tension using wrinkling limit diagrams

Abstract In thin plate plastic forming, the efficient, accurate prediction and control of wrinkling is a basic requirement. Because there is no clear means of determining the main strain space curve (similar to the fracture forming limit diagram) when establishing the critical wrinkling state, this work used diagonal tensile plate tests to verify a numerical simulation of plastic wrinkling in thin plates. This model included a buckling mode obtained by an eigenvalue buckling analysis as the initial shape defect in a dynamic explicit numerical simulation of the plastic deformation of the test pieces. This permitted calculation of the true instability morphology of the test piece and avoided the difficulty associated with simulating plastic deformation wrinkling morphologies using existing static implicit or dynamic explicit numerical simulation algorithms. The morphology and characteristics of the critical wrinkling limit diagram (WLD) associated with nonuniform tension were investigated. The effect of the specimen thickness and boundary conditions on the WLD in the main strain space were also examined and the effects of various processing parameters on crease resistance were established. Finally, the effectiveness of the WLD established in this work was verified based on using non-contact full-field strain measurements to examine the plastic wrinkling of thin plates. This research provides a means of establishing the critical wrinkling line for various conditions.

Study on the Forming Process and Deformation Behavior of Inner Ring in the Wheel Hub Bearing Based on Riveting Assembly.

The orbital riveting process has been successively adopted in the assembly of wheel hub bearing, due to its special merits of high efficiency, low cost, and so on. The forming process and deformation behavior of the inner ring have significant influence on the axial clamping force and bearing clearance, however, which haven’t been addressed yet. In this study, a numerical simulation platform for the assembly of the hub bearing is established by the joint use of the static implicit and dynamic explicit algorithms. Based on the platform, the deformation process and deformation behavior of the inner ring are investigated, along with the interference assembly and riveting assembly on the loading process of the inner ring. Finally, relevant experimental verifications are carried out to consolidate the simulation results. The research findings could be used to guide the design and optimization of the axial clamping force and bearing clearance.

Integration process of stamping and welding for DP600 advanced high strength steel sheets

The springback behavior of AHSS (Advanced High Strength Steels) is more serious than ordinary mild steels. Currently, deformations due to springback can be compensated by modifying the tool geometry in the industry, which often consumes for a long time. In addition, the stamping parts usually need welding and assembly, and the welded part also has deformation. Therefore, an integrated process combines stamping and welding is presented in this paper, including stamping, placing welding parts and spot welding a total of 3 processes. This paper takes Ω-shaped parts as the object of study. The dynamic explicit method is adopted in the stamping process, and the static implicit method is used for the analysis of the stress release process. The effect of welding location, thickness of welding plate and width of welding plate on geometrical dimension are considered. Finally, the results of finite element analysis is evaluated by the validation experiment. The result shows that the combination of stamping and welding process can effectively reduce the springback value, and the deformation of the stamping part is less than 1mm. After the stress of the welded part is released, the stress on the inner and outer surface of the Ω-shaped part can be greatly reduced along the thickness direction.

Predicting pressure distribution between transfemoral prosthetic socket and residual limb using finite element analysis

A static implicit nonlinear finite element model (FEM) was created and analysed to determine the pressure distribution between the residual limb and the prosthetic socket of a transfemoral amputee. This analysis was performed in an attempt to develop a process allowing healthcare providers and engineers to simulate the fit and comfort of transfemoral prosthetics to reduce the number of re-fittings. The FEM considered the effects of donning and body weight and included geometric nonlinearity due to large deflections, nonlinear contacts due to friction, and nonlinear hyper-elastic material properties for the residual limb's soft tissue. The results attained can provide prosthetic fitting clinicians customised information on where the prosthetic fits too tight, and how stress concentrations would change as a result of geometric modifications to the prosthetic. This knowledge can improve patients' comfort levels by providing well targeted and more accurate modifications to the prosthetic, minimising the need for numerous refittings.

Predicting pressure distribution between transfemoral prosthetic socket and residual limb using finite element analysis

A static implicit nonlinear finite element model (FEM) was created and analysed to determine the pressure distribution between the residual limb and the prosthetic socket of a transfemoral amputee. This analysis was performed in an attempt to develop a process allowing healthcare providers and engineers to simulate the fit and comfort of transfemoral prosthetics to reduce the number of re-fittings. The FEM considered the effects of donning and body weight and included geometric nonlinearity due to large deflections, nonlinear contacts due to friction, and nonlinear hyper-elastic material properties for the residual limb's soft tissue. The results attained can provide prosthetic fitting clinicians customised information on where the prosthetic fits too tight, and how stress concentrations would change as a result of geometric modifications to the prosthetic. This knowledge can improve patients' comfort levels by providing well targeted and more accurate modifications to the prosthetic, minimising the need for numerous refittings.

INFLUENCE OF TECHNOLOGICAL PARAMETERS ON THE SPRINGBACK ANGLE OF HIGH-STRENGTH STEELS

The most common problem in area of sheet metal forming technology is a problem of achieving accurate and repeatable shapes of drawn and bent parts. This phenomenon is caused by the elastic springback. Springback can be defined as an elastically-driven change of shape of the deformed part upon removal of external loads. Several technological parameters influence amount of springback, between these belong friction coefficient, blankholder force, different geometry of tools, etc. In this paper is presented this topic, and also numerical simulation of this process. For an experimental process were used two high-strength steels. Steel with TRIP effect and dual phase steel DP 600. Numerical simulation was performed in the static implicit code Autoform. Results were compared and discussed.

Comparisons of Explicit and Implicit Finite Element Methods for Sheet Metal Forming

Sheet metal forming is one of the most commonly practiced fabrication processes in industry. Numerical simulations of the complex parts are possible by finite element method in the past thirty years. The most important problem of the simulation is the reliability of the model. Static implicit method (SI) and dynamic explicit method (DE) were used to simulation sheet metal forming process. It was found that simulation speed in dynamic explicit software has large effect on the simulation results. The best simulation speed is 5~10 m/s. Compared with the simulation and experimental results of thickness, draw-in and CPU time, the DE method is preferred.

Thermo-mechanical coupled 3D-FE modeling of heat rotary draw bending for large-diameter thin-walled CP-Ti tube

The heat rotary draw bending of large-diameter thin-walled (LDTW) commercial pure titanium (CP-Ti) tube is a highly nonlinear thermo-mechanical coupled physical process. Developing a reliable finite element (FE) model for this process is an effective way to investigate the heat loading and the complex bending behaviors. In this study, considering the characteristics of multi-die constraints and local heating, a thermo-mechanical 3D-FE model was established for preheating and heat bending of LDTW CP-Ti tube in terms of both accuracy and efficiency. First, using the static implicit algorithm, a preheating model was developed to predict the temperature distribution of bending tools. In this model, the key issues such as the full-sized geometry modelling, thermal interaction definition, and automatic heating control were solved to increase the simulation accuracy and efficiency. Then, introducing the predictions of preheating model and using the dynamic explicit algorithm, a thermo-mechanical coupled 3D-FE model was established for the heat bending simulation via the geometry modelling simplification, temperature definition of bending tools, realization of non-uniform temperature distribution, etc. Considering the temperature history of bending tools and wall thickness changing of bent tube, the reliability of preheating model and heat bending model was verified by several experiments. The results showed that the maximum relative errors of both predicted temperature and wall thickness changing degree were less than 9 %. Based on the reliable models, the effects of preheating temperature on the temperature distribution of bending tools and wall thickness changing of tube were numerically evaluated. The established model provides the scientific basis for the prediction and control of bending qualities of the heat RDB process, and the modeling method is also of general significance to the other heat-aided forming process.

Experimental Investigation and Numerical Simulation of Pure Copper Foil Springback in Micro-Bending Process

Springback is an important factor influencing forming precision in bending process, which becomes more complex for micro metal foil due to the size effect existing. Bending springback is studied through the micro bending experiments designed with different grain sizes and foil thicknesses using T2 purple copper in this paper. The accurate stress-strain relationships are obtained based on the copper foil tensile experiments; the bending process of micro-component is simulated based on both dynamic explicit and static implicit codes. Comparison of simulation results with experimental results shows that: thickness can serve as an important parameter effecting on the springback; the trend of springback amount rising with a thickness diminishing enhances in small size; sheets with same thickness exhibit phenomenon of springback angle reducing with an increasing grain size. Bending springback of micro metal foil indicates obvious size effect on foil thickness and grain size.

静的陰解法を用いた大ひずみ弾塑性有限要素解析における弾性構成式の選択が解に及ぼす影響

静的陰解法を用いた大ひずみ弾塑性有限要素解析における弾性構成式の選択が解に及ぼす影響

ビル用マルチエアコン室外機の準静的変形解析への動的陽解法の適用

Generally speaking, it is difficult to obtain simulation results for a nonlinear quasi-static problem of a large-scale structure using the static implicit FEM. This is because not only the calculation cost such as necessary memory consumption becomes enormous but also iterative calculation does not often converge for a large-scale analysis model in consideration of the contact between the parts and material nonlinearity of the structure. Therefore, in this paper, we tried to perform a torsion deformation analysis of a multi-split type air-conditioning outdoor unit using the dynamic explicit FEM with the system damping method and mass scaling method. The torsion displacement based on the dynamic explicit method shows good agreement with the test result. It is found that the dynamic explicit method has an advantage in large-scale model analysis.

NUMERICAL AND EXPERIMENTAL DETERMINATION OF SPRINGBACK IN U-BENDING PROCESS

The most common problem in area of bending technology is problem of achieving accurate and repeatable bending angle. This problem is caused by elastic springback. Springback can be defined as an elastically-driven change of shape of the deformed part upon removal of external loads. This phenomenon is observed also in other sheet metal forming processes. Several technological parameters influence springback amount. In this paper were presented results for different bending curvature and its influence to the springback amount springback. Difference between springback amount caused by Bauschinger effect was also discussed. Process was also modelled in the static implicit finite element (FE) code – Autoform. In this paper were used two different materials – UHS and mild steel. Experimental and numerical results were compared and discussed. associated with economical aspect, it is necessary to predict it. This can be realized using analytical, empirical and also numerical methods. Nowadays is very frequently used numerical simulation