Commercial FEM Program Research Articles

A Fast Approach for Optimization of Hot Stamping Based on Machine Learning of Phase Transformation Kinetics

Hot stamping is one of the key technologies to produce lightweight components for the automotive industry. Numerical simulations are an important tool to design hot stamping tools. However, the hot stamping simulations are highly complex due to the deformation as well as heat transfer and phase transformation mechanisms taking place simultaneously. An accurate prediction of these mechanisms leads to high computational cost. Conventionally, an elastoplastic material model with temperature and strain rate dependence is used to describe the forming behavior, while austenite decomposition models are used to predict the kinetics of the phase transformation. The time spent on calculating the phase transformations can reach up to 40% of the total calculation time. To overcome these computational time issues, the current study introduces an alternative fast approach, to reduce the total calculation time of the hot stamping simulation during the die design stage. The simulation is sped up by replacing austenite decomposition models with surrogate models. A machine-learning (ML) model is used as a candidate for calculating the final phase fraction of hot-stamped parts. To train the model, various simulations models with varying degrees of deformation and cooling rates are set-up in the commercial FEM program LS-DYNA®. The ML model learns from the deformation histories and the final phase fractions to achieve the desired accuracy. For validation, the proposed approach is tested and compared with fully integrated phase transformations models. The final phase fraction and the total amount of floating operations are used as indicators to evaluate the performance of the fast approach. The results indicate that the ML model performs well in predicting the final phase fraction after hot-stamping and a significant reduction of the calculation time evaluated from the counting of floating operation FLOPS is reduced from 5713 to 12.

Finite element implementation of efficient absorbing layers for time harmonic elastodynamics of unbounded domains

An alternative approach to local transmitting boundaries for wave propagation problems in unbounded media is the application of the Perfectly Matched Layers (PML) around the finite region of interest. The PML model consists of absorbing layers that absorb almost perfectly propagating waves of all non-tangential angels-of-incident and all non-zero frequencies. This paper presents and verifies the concept of FE/PML methodology on the basis of two different formulations for the PML model in the context of time harmonic wave propagation analysis. A finite element numerical scheme is developed in which both PML formulations are successfully implemented as a macro-finite element in a commercial FEM program. Moreover, the parameters that influence the performance of the FE/PML method are extensively discussed and recommendations are given for the proper selection. Classical soil-structure interaction problems of surface or embedded rigid footing on homogeneous or heterogeneous half-plane containing layers and tunnels are investigated and the high accuracy and the easy implementation of FE/PML computational tool is demonstrated.

FE/PML numerical schemes for dynamic soil-structure interaction and seismic wave propagation analysis

The numerical solution of wave propagation in unbounded media is of great importance in many engineering applications. An alternative approach to the application of artificial boundaries in the FEM is the Perfectly Matched Layer (PML) technique. The main idea of this technique is that an absorbing layer is applied around the finite region of interest absorbing almost perfectly waves of all incident angles and frequencies propagating from the bounded region. A perfectly matched layer can be obtained by performing a complex-valued coordinate transformation inside the layer which can be expressed either as a change in the material properties or as a stretching of the coordinates. Both approaches are applied to the PML formulation and implemented in a commercial FEM program. All simulation results demonstrate the accuracy of the FE/PML models and the ability of the developed models to deal with complex dynamic soil-structure interaction systems.

Structural Stability Study Using Thermal and Structural Analysis of a Bimetal Cylinder in an Injection Molding Machine

사출성형기는 사출장치와 형체장치로 구분된다. 사출장치에서 고체의 플라스틱 수지는 밴드히터에 의한 열과수지간, 스크류 면, 그리고 실런더 내부 면과의 마찰로 인해 발생하는 열로 인해 용융된다. 용융된 수지가 특정한 형상을 가진 몰드 내로 사출될 때 실린더 선단부에는 높은 압력이 형성된다. 높은 압력으로 인해 실린더의 내부 면에 크랙이 발생한다. 실린더 내부의 압력을 지지하고 마모를 방지하기 위해 2개의 층으로 구성된 바이메탈 실린더가 제작되고 있다. 본 연구에서는 2개의 층으로 구성된 바이메탈 실린더의 구조적 안정성에 관하여 연구하였다. FEM 프로그램을 사용하여 열해석과 구조해석을 연계하여 분석하였다. 열해석을 통해서 바이메탈 실린더의 온도분포를 얻었다. 이 온도분포를 구조해석으로 연계하여 열과 사출압력에 따라 나타나는 실린더 선단에 발생하는 응력과 변형을 관찰하였다. 해석결과 실린더의 응력은 사출압력에 지배적이며 변형은 고온의 열에 지배적인 것으로 나타났다.

Precision Glass Molding: Validation of an FE Model for Thermo‐Mechanical Simulation

In precision glass molding process, the required accuracy for the final size and shape of the molded lenses as well as the complexity of this technology calls for a numerical simulation. The current paper addresses the development of an FE model for thermo‐mechanical simulation of the precision glass molding process including heating, pressing, and cooling stages. Temperature‐dependent viscoelastic and structural relaxation behavior of the glass material are implemented through a FORTRAN material subroutine (UMAT) into the commercial FEM program ABAQUS, and the FE model is validated with a sandwich seal test. Subsequently, precision molding of several glass rings is performed at three different pressing temperatures, and the experimental deformation of the glass rings at the end of the molding is compared with the predicted ones from FE simulation. Furthermore, the transient and residual stress distribution inside the glass rings are calculated by the developed FE model, and the effects of some important process parameters such as interface friction and mold temperature on the FE results are assessed. The developed FE model can be employed to predict the deformation behavior, final size/shape, and the residual stress state inside the glass lenses in a precision glass molding process.

T-shape upsetting–extruding test for evaluating friction conditions during rib–web part forming

Since the deformation features of existing friction testing methods are not as similar as those of the closed die forging process of rib–web parts, the friction conditions evaluated by these methods are not consistent with the actual situation. In this paper, a new friction testing method, the T-shape upsetting–extruding process employing a rectangular blank, is proposed for evaluating the friction conditions during rib–web part forming process. It was found that rib height and the web width are both sensitive to friction conditions. Therefore, the ratio of rib height to web width was chosen as a criterion for friction evaluation. With the utilization of a commercial FEM program, DEFORM, the effects of the geometrical parameters and testing variables on the friction sensitivity were investigated, and the friction conditions between different interfaces were analyzed. In order to verify the proposed method, friction factors of a water-based graphite lubricant measured by three different methods (the proposed one, the ring compression test and the double-cup extrusion test) at 723K were used to simulate the isothermal deformation process of a cross-rib part. The experimental results suggest that the proposed method is more accurate than the other two methods for rib–web part forming process.

Modal Analysis of S809 Wind Turbine Blade Considering Different Geometrical and Material Parameters

In recent years wind energy has been the world’s fastest growing source of energy. The wind turbine industry is booming and is spending a lot on research for improving the performance of its present machines and increasing their capacity. The purpose of this paper is to investigate the dynamic behavior characteristic of 1.5 MW wind turbine system (WTS) and carries out the analysis considering different geometrical and material parameters. Vibration of the blade of the WTS on the flap and edge section of the blade that is one of the most important elements of dynamic characteristic of WTS is evaluated. Natural frequency and mode shape are calculated by the finite element analysis, with commercial program (ANSYS). The results are compared which are performed by the finite element analysis with commercial FEM program (ANSYS) on the basis of the natural frequency and mode shape.

설계기준 개선에 따른 기존 고속철도 교량 내진보강 필요성 고찰

본 논문은 등가정적하중법에 의해 설계된 경부고속철도 구간 중 PSC Box Girder 대표 교량들을 대상으로 등가정적법과 응답스팩트럼법을 이용하여 지진력이 산정되었고, 지진력의 차이가 확인된다. 해석법 비교를 위하여 상용유한요소 프로그램을 이용하여 5개 교량에 대한 3차원 유한유소 모델이 구성되었고, 각 해석법의 의한 지진력이 비교되었다. 고유주기가 저차에서 지배되는 경우, 지반조건과 고유주기의 따라 지진가속도가 산정되는 응답스팩트럼법과 등가정적하중법과의 차이가 커지는 것이 확인되었다. 이렇게 산정된 지진력에 차이에 따른 내진성능 평가 결과 설계 지진력 보다 큰 지진력의 적용으로 인한 것으로 내진 보강의 필요성을 의미한다. This paper was calculated the earthquake load using ELFP(Equivalent Lateral Force Procedure) and RSA(Response Spectrum Analysis) for PSC Box Girder representative bridges by the Phase of KTX designed by ELFP and verified the difference of these analyses. It have been modeled 3 dimensional FE model of 5 bridges using a commercial FEM program for the comparison of these analyses using a commercial FEM program and were compared the earthquake load. It has been to confirm the increase of the difference ELFP of RSA calculated to seismic ground acceleration according to the ground condition and natural period. It is mean that the necessity of seismic reinforcement due to the application of a larger of earthquake load than designed earthquake load form the seismic performance evaluation result according to the difference of calculated earthquake loads.

Influence of Widened Embankment on the Slope of Existing Pavement on Soft Soils

Adding a new embankment adjacent to the existing highway embankment is a cost effective choice compared with building another new one and can mitigate the heavy traffic pressure. However, it may also cause some engineering problems including the change of slope of existing pavement or even local or global instability of embankments especially those on soft soils. How to prevent excessive change of the slope of the existing pavement induced by widening the existing embankments is of great importance in engineering practice. A numerical analysis by using a commercial FEM program was performed to explore the influence of the thickness of soft foundation soils, the widening width and the embankment height as well as the starting time of widening construction on the slope of the existing pavement. The results indicate that the bigger the thickness of the foundation soils as well as the bigger the widening width will result in bigger values of the slope of the existing pavement, especially at the early period of reconsolidation. Adverse slope will be induced by widening of the existing embankment.

Stresses of Existing Pavement Induced by Widened Embankment over Soft Soils

Widening of existing highway embankments can improve their capacities and ease the high traffic pressures, but it may cause a series of engineering problems including longitudinal pavement cracks, drop off or even local or global instability of embankments especially those on soft soils. How to prevent severe cracks occurring on pavement induced by widening of the existing embankments has been a great concern of geotechnical engineers. A numerical analysis by using a commercial FEM program was conducted to investigate the influence of the thickness of foundation soils on the development of transverse stress in the pavement of the existing and widened embankments. The effect of widening time on the stress was also discussed. The results indicate that compressive stress will be caused in the existing pavement prior to the widening, while considerately lager tensile stress will be induced in the existing pavement after widening. In the view of reducing pavement tensile stress, a most suitable time to begin widening was proposed for engineering practice.

A Numerical Analysis of Soil Arching in Piled Embankments

Soil arching has important influence on the behavior of piled embankments. How to calculate stress concentration ratio is of great concern when designing embankment over soft soils reinforced by rigid concrete piles. A numerical analysis by using a commercial FEM program was conducted to reveal the mechanism of soil arching in piled embankments. And also, the influence of embankment height, pile-soil relative displacement, cohesion and internal friction angle on the equal settlement plane was evaluated. The results indicate that the stress concentration ratio varies with the pile-subsoil relative displacement and has upper and lower bound value. The effect of pile-soil displacement and the strength parameters of embankment material on the equal settlement plane can be neglected. It was also found that the equal settlement plane height is equal to 1.6 times the pile-cap clear spacing. When the ratio of embankment height to the pile-cap clear spacing is greater than 1.6, no apparent differential settlement will occur on the embankment surface.

Extended Magnetization of Superconducting Pellets in Highly Inhomogeneous Magnetic Field

Abstract The magnetization of superconducting pellets is a worth point in the development of trapped flux superconducting motors. Experimental and simulated data have been reported extensively according to the framework of one or several pulses of a homogeneous magnetizing field applied to a pellet or a set of pellets. In case of cylindrical rotors of low power motors with radial excitation, however, the use of the copper coils to produce the starting magnetization of the pellets produces a highly inhomogeneous magnetic field which cannot be reduced to a 2D standard model. In this work we present an analysis of the magnetization of the superconducting cylindrical rotor of a small motor by using a commercial FEM program, being the rotor magnetized by the working copper coils of the motor. The aim of the study is a report of the magnetization obtained and theheat generated in the HTSC pellets.

Magnetization of Superconducting Pellets in Highly Inhomogeneous Magnetic Field

The magnetization of superconducting pellets is a worth point in the development of trapped flux superconducting motors. Experimental and simulated data have been reported extensively according to the framework of one or several pulses of a homogeneous magnetizing field applied to a pellet or a set of pellets. In case of radial rotors of low power motors, however, the use of the copper coils to produce the starting magnetization of the pellets produces a highly inhomogeneous magnetic field. In this work we present an analysis of the magnetization of the superconducting cylindrical rotor of a small motor by using a commercial FEM program, being the rotor magnetized by the working copper coils of the motor. We report on the magnetization obtained and heat generated in the HTSC pellets, in several possible configurations.

The effect of composite damage on fatigue life of the high pressure vessel for natural gas vehicles

In order to examine how the damages such as scratches, cuts and gouges on the composite materials have effects on the fatigue life of NGV vessels, several experiments on real vessels were conducted and finite element analyses were applied. The flaw depths of COPV used in the experiments were 1.5 mm, 2.0 mm, 3.0 mm, and 4.0 mm, while the flaw lengths were 50 mm, 100 mm, and 200 mm. A flaw tolerance test defined by ANSI/IAS NGV2-2000 was performed on 12 vessels using a combination of these flaw depths and lengths. In the finite element analyses, stress analyses were performed using a commercial FEM program after the 3-D modelling of liner, hoop and helical layers by using MSC.PATRAN™. The result of the tests and analyses demonstrated that the effect of the flaw damages on the fatigue life of high pressure vessel for natural gas vehicles increases when the flaw depth is more than 3.0 mm and the flaw length is more than 100 mm.

Nonlinear Behavior of Masonry Arch Bridge Under Ground Deformation

This paper discusses simple modeling and examples of masonry arch bridge analysis considering ground deformation. Preserving historicalmasonry arch bridges is important to continuing our industrial heritage for the next generations. A single-span masonry arch bridge was analyzed using the finite element method with two meshing schemes considering material nonlinearity to define reasonable modeling for such arch bridges. Results show that analytical model meshed automatically with a commercial FEM program preprocessor considering material plasticity reasonably simulates the behavior of the detailed masonry model. The effects of deformation on bridge behavior and stress distribution in arch bridges are also discussed.

Prediction of deformations of steel plate by artificial neural network in forming process with induction heating

To control a heat source easily in the forming process of steel plate with heating, the electro-magnetic induction process has been used as a substitute of the flame heating process. However, only few studies have analyzed the deformation of a workpiece in the induction heating process by using a mathematical model. This is mainly due to the difficulty of modeling the heat flux from the inductor traveling on the conductive plate during the induction process. In this study, the heat flux distribution over a steel plate during the induction process is first analyzed by a numerical method with the assumption that the process is in a quasi-stationary state around the inductor and also that the heat flux itself greatly depends on the temperature of the workpiece. With the heat flux, heat flow and thermo-mechanical analyses on the plate to obtain deformations during the heating process are then performed with a commercial FEM program for 34 combinations of heating parameters. An artificial neural network is proposed to build a simplified relationship between deformations and heating parameters that can be easily utilized to predict deformations of steel plate with a wide range of heating parameters in the heating process. After its architecture is optimized, the artificial neural network is trained with the deformations obtained from the FEM analyses as outputs and the related heating parameters as inputs. The predicted outputs from the neural network are compared with those of the experiments and the numerical results. They are in good agreement.

A study on thermal behaviour of curved steel box girder bridges considering solar radiation

Solar radiation induces non-uniform temperature distribution in the bridge structure depending on the shape of the structure and shadows cast on it. Especially in the case of curved steel box girder bridges, non-uniform temperature distribution caused by solar radiation may lead to unusual load effects enough to damage the support or even topple the whole curved bridge structure if not designed properly. At present, it is very difficult to design bridges in relation to solar radiation because it is not known exactly how varying temperature distribution affects bridges; at least not specific enough for adoption in design. Standard regulations related to this matter are likewise not complete. In this study, the thermal behavior of curved steel box girder bridges is analyzed while taking the solar radiation effect into consideration. For the analysis, a method of predicting the 3-dimensional temperature distribution of curved bridges is used. It uses a theoretical solar radiation energy equation together with a commercial FEM program. The behavior of the curved steel box girder bridges is examined using the developed method, while taking into consideration the diverse range of bridge azimuth angles and radii. This study also provides reference data for the thermal design of curved steel box girder bridges under solar radiation, which can be used to develop design guidelines.

Derivation of simplified formulas to predict deformations of plate in steel forming process with induction heating

To control the deformation of plate in the steel forming process with heating, the electro-magnetic induction process has been used as the substitute of the flame heating process. However, only few studies have been carried out to analyze the deformation of a workpiece in the induction heating process by using a mathematical model. This is mainly due to the difficulty of modeling the heat flux from the inductor traveling on the conductive plate during the induction process. In this study, the heat flux distribution over a steel plate during the induction process is firstly analyzed by a numerical method under the assumption that the process is in a quasi-stationary state around the inductor and also with the consideration that the heat flux itself greatly depends on the temperature of the workpiece. With the heat flux analyzed, heat flow and thermo-mechanical analyses on the plate are then performed with a commercial FEM program for 34 combinations of heating parameters. The deformations from the analyses and the input heating parameters are then synthesized with a statistical method to produce simplified formulas, which can easily provide the relation between the heating parameters and the deformations. The results obtained from the formulas are in good agreement with results of experiments.

대면적 OLED 증착용 새도우 마스크 설계

Deformation of the shadow mask is one of the problems encountered during the deposition of organic materials for manufacturing large size organic light emitting diode (OLED). The larger the glass substrate, the larger the shadow mask becomes. As the size of the shadow mask increases, its deformation becomes more severe, thereby making it difficult to deposit organic materials in a precise pattern on a substrate. In this paper, a new method for reducing drooping of the shadow mask for large size OLED vapor depositions is proposed. The proposed shadow mask with cross stripe wires has higher stiffness than the pure shadow mask, which results in reducing drooping of the shadow mask. A commercial FEM program, ANSYS, is used for the evaluation of the proposed shadow mask. The analysis showed that the shadow mask with cross stripe wires have an effect on reducing drooping about 18.6% or more.

3D Thermal Mechanical Coupled Elasto-Plastic Finite Element Analysis in the Whole Rolling Process of H-Beam

In the H-beam rolling process, the deformations and temperature field of workpiece significantly influence the mechanical properties due to the change of product microstructure. Prediction of them is important for the groove design and passes sequences. To get the deformation behavior and the temperature field of workpiece, commercial FEM program LS-DYNA has been used to analyze the whole process of H-beam rolling. The approach is based on 3D thermal mechanical coupled finite element method. The rolling process is divided into several units for calculation. The mesh of workpiece is rebuilt in the simulation for reducing the influence of element distortion. The result shows that, the temperature at the wed to flange position maintains the highest during the whole rolling process, while area of the web the lowest. After the rolling, temperature difference is above 150K between the web’s surface and flange’s inside surface, approximate 130K on the flange’s outside surface and 200K in the cross section. The simulation results show good agreement with the measured temperature data.