A 3-D finite element method for non-isothermal sheet-forming processes

In sheet forming of ductile materials, the forming limit and strain distribution are governed by plastic instability and fracture following strain localization. A number of phenomena influence the localization process, including the best-known plastic properties of strain hardening, strain-rate sensitivity and yield-surface shape. The temperature gradient caused by deformation heating, heat transfer, and friction between sheet and tools also controls strain localization. In this paper, a numerical method for analyzing the non-isothermal, rigid-viscoplastic deformation of sheets is presented. The method consists of two parts: a rigid-viscoplastic finite element model (FEM) to solve the plastic deformation, and transient heat transfer FEM to evaluate the temperature change throughout the specimen during the deformation process. Bishop's step-wise decoupled method is adopted to handle coupling between mechanical deformation and the temperature change. Using this method, the effect of temperature distribution on strain patterns was investigated. As illustrative 3-D examples, hemispherical punch-stretching and square punch-stretching operations have been analyzed, including deformation heating, frictional heating, heat transfer to tooling and air, and internal heat conduction in the workpiece. The role of temperature gradients is revealed by examination of the simulation results.     

声表面波器件测量牙种植体微扭矩的三维有限元仿真

为了利用微扭矩准确、非破坏性地测量牙种植体的稳定性,采用三维有限元分析方法研究了声表面波器件(SAW)检测牙种植体稳定性的可行性.首先,在梯度剪切应力场下建立了SAW器件的谐振频率和扭矩之间的理论模型.然后,利用ANSYS有限元软件对梯度剪切应力场下SAW器件的谐振频率变化情况进行谐振响应分析.最后,对比分析了理论模型和仿真得到的数据.分析结果表明:SAW器件谐振频率的变化量与最大剪切应力呈线性关系,但两者之间存在3％的误差;种植体的微扭矩与SAW器件的谐振频率呈线性关系.因此,在理论上能够利用SAW器件测量种植体的微扭矩,从而实现对种植体稳定性的检测.     

Enriched finite element method for 2-D and 3-D blunt crack problems in a viscoelastic medium

The analysis of two-dimensional and three-dimensional blunt crack problems in a linear viscoelastic medium is numerically investigated using the enriched finite element method. The enriched crack-tip elements are established by enriching the asymptotic displacement fields at the blunt crack front to the regular elements. The corresponding transition elements are formulated to eliminate displacement field incompatibility. The viscoelastic incremental formulations for the enriched finite element method in time domain are derived according to the Boltzmann superposition principle. The time-dependent deformations of crack are presented and the stress intensity factors are directly obtained from the enriched degree of freedoms. The numerical examples indicate that the enriched finite element method is extremely suitable for dealing with complicated blunt crack problems.     

平板对接焊三维数值模拟分析

焊接是一个涉及多学科的复杂过程,随着计算机技术的发展焊接数值模拟受到越来越广泛的关注,且越来越多的应用于实际生产过程中,利用Marc对平板对接焊进行熔深方向的三维数值模拟,对比了打底焊和三层焊接的焊接温度场及横向变形,分析了模拟结果,得到与实际情况相符合的结论,验证数值模拟的准确性.     

Simulation of T-section profile ring rolling by the 3-D rigid-plastic finite element method

The three-dimensional rigid-plastic finite element method is used to simulate the open pass profile ring rolling of a T-shaped section from an initially rectangular cross-section. Because the ring rolling process is incremental and the deforming region is restricted to the vicinity of the roll gap, only a ring segment spanning the roll gap is analysed in order to save computation time. As the thickness of the ring is reduced, the mesh system is progressively modified to treat profile development more effectively. Roll separating force, strain distribution, strain rate distribution and cross-sectional configuration of the deformed ring are calculated. Comparisons between computation and experiment show good agreement in roll separating force and cross-sectional configuration of the deformed ring.     

基于反求工程技术的三维有限元建模方法

Pro/E软件在设计开发过程中为逆向工程提供了Pro/Scan.tools等接口模块,为产品开发设计中逆向反求工程技术的实施提供了软件条件.结合该软件的逆向反求工程设计模块,阐述如何在Pro/E环境下进行产品逆向反求开发的三维有限元建模方法.     

Combined finite volume and finite element method for convection-diffusion-reaction equation

A combined finite volume and finite element method is presented for solving the unsteady scalar convection-diffusion-reaction equation in two dimensions. The finite volume method is used to discretize the convection-diffusion-reaction equation. The higher-order reconstruction of unknown quantities at the cell faces is determined by Taylor’s series expansion. To arrive at an explicit scheme, the temporal derivative term is estimated by employing the idea of local expansion of unknown along the characteristics. The concept of the finite element technique is applied to determine the gradient quantities at the cell faces. Robustness and accuracy of the method are evaluated by using available analytical and numerical solutions of the two-dimensional pure-convection, convection-diffusion and convection-diffusion-reaction problems. Numerical test cases have shown that the method does not require any artificial diffusion to improve the solution stability. This paper was recommended for publication in revised form by Associate Editor Dongshin Shin Pramote Dechaumphai received his B.S. degree in Industrial Engineering from Khon-Kaen University, Thailand, in 1974, M.S. degree in Mechanical Engineering from Youngstown State University, USA in 1977, and Ph.D. in Mechanical Engineering from Old Dominion University, USA in 1982. He is currently a Professor of Mechanical Engineering at Chulalongkorn University, Bangkok, Thailand. His research interests are numerical methods, finite element method for thermal stress and computational fluid dynamics analysis. Sutthisak Phongthanapanich received his B.S. degree in Mechanical Engineering from Chiangmai University, Thailand in 1990. He then received his M.S., and Ph.D. degrees in Mechanical Engineering from Chulalongkorn University, Thailand in 2002, and 2006, respectively. He is a Lecturer of Mechanical Engineering Technology at King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand. His research interests are finite element method, finite volume method, mesh generation and adaptation, and shock wave dynamics.     

Improvement of cutting simulation using the octree method

This paper develops an octree-based algorithm for machining simulation. Most commercial machining simulators are based on the Z-map model, which has several limitations in terms of achieving a high level of precision in five-axis machining simulation. Octree representation being a three-dimensional (3D) decomposition method, an octree-based algorithm is expected to be able to overcome such limitations. With the octree model, the storage requirement is reduced. Moreover, recursive subdivision is processed in the boundaries, which reduces useless computations. The supersampling method is the most common form of antialiasing and is typically used with polygon mesh rendering in computer graphics. The supersampling technique is being used to advance the efficiency of the octree algorithm.     

高速切削温度场的三维有限元建模与动态仿真

根据温度场控制方程及其边界条件,建立高速切削的三维有限元分析模型,将切削过程的温度分布和变化情况以及切削速度、进给量和切屑厚度等对切削温度的影响进行仿真分析,与相同切削条件下的二维仿真结果和实际测试结果进行对比,可以得出结论:三维建模仿真得到的高速切削温度变化趋势与相关文献结果基本一致,但三维仿真获得的温度值比二维仿真要高些,并且三维仿真的温度值更接近于实际测量值。     

Stress recovery techniques for natural element method in 2-D solid mechanics

This paper is concerned with the stress recovery for the natural element method in which the problem domain is discretized with Delaunay triangles and the structural behavior is approximated with Laplace interpolation functions. Basically, the global and local patch recovery techniques based on the L ₂-projection method are adopted. For the local patch recovery, the local element patches are defined by the supports of each Laplace interpolation function. For the comparison purpose, the local stress recovery is also performed using Lagrange-type basis functions that are used for 3- and 6-node triangular elements. The stresses that are recovered by the present global and local recovery techniques are compared each other and compared with the available analytic solution, in terms of their spatial distributions and the convergence rates. As well, the dependence of the recovered stress field on the type of test basis functions that are used forbnov-Galerkin (BG) and Petrov-Galerkin (PG) natural element methods is also investigated.

     

高压管件斜三通结构的三维有限元分析

综合运用三维设计软件PRO／Engineer和有限元分析软件AN—SYS对高压管件的斜三通结构进行了强度和刚度分析，得到了一些重要的结论，为高压管件结构的合理设计奠定了一个良好的理论基础。     

A 3-D finite element method analysis of cold rolling of thin strip with friction variation

In this paper, a three-dimensional rigid-plastic finite element method (FEM) model to simulate the cold rolling of thin strip with different friction models is described. The effects of rolling parameters, such as work roll diameters and reductions, are analysed in this study. The simulation and experimental values of rolling pressure and spread (the difference of strip width before and after rolling) show a good agreement when friction variation in the roll bite is considered. The roll separating force, spread and forward slip for constant friction and friction variation models are also compared. The friction variation in the roll bite has a significant effect on the simulation results.     

Microscopy analysis of bone marrow-derived osteoprogenitor cells cultured on hydrogel 3-D scaffold

Bone marrow contains progenitor cells that are able to differentiate into several mesenchymal lineages, including bone. These cells may also provide a potential therapy for bone repair. The purpose of this study was to select the osteoprogenitor cell subpopulation from bone marrow-derived mesenchymal stem cells (MSCs) and to test the ability of a hydrogel scaffold to support growth and osteogenic differentiation. MSCs isolated from rat femur bone marrow were cultured in DMEM medium supplemented with antibiotics, FCS, and L-glutamine. Osteogenic supplements (dexamethasone, sodium beta-glycerophosphate, and ascorbic acid) were added for one, two or three weeks. A selective subpopulation of osteoprogenitor cells was identified by immunohistochemistry, general morphology, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Committed osteogenic cells were transferred to a 3-D hydrogel scaffold and cultured for an additional week. In standard culture, the osteoprogenitor cells formed cell clusters identified by Alizarin red S staining and by positive osteocalcin immunostaining. The number of osteoprogenitor cells, matrix synthesis, and mineralization increased gradually up to three weeks in culture. Mineral deposition in the matrix analyzed by EDS revealed the presence of calcium and phosphate ions at a Ca/P molar ratio of 1.73 in both the osteogenic cultures and the scaffold osteoprogenitor culture. Histological preparations revealed cell clusters within the hydrogel scaffold and SEM analysis revealed cell clusters attached to the scaffold surface. It is concluded that the hydrogel scaffold can support growth and differentiation of osteogenic cultures including mineralization and can potentially serve as a bone graft substitute containing committed osteoprogenitor cells.     

3-D finite element analysis for thermo-mechanical behavior of laminated carbon-phenolic composite ring

In this paper, the thermal insulator structure of a real rocket which is fabricated in a way that laminated composite rings are connected in series is analyzed using 3-dimensional axisymmetric finite element models. Simulation of cowl zone using real operating conditions provides that the stress distribution in the laminated composite ring is largely influenced by ply-angles, axial dimensions, and boundary conditions. It is hypothesized that notably the ply-lift that is the precursor to the wedge-out occurs in the ring-to-ring bonding region to a limited ply angle. Moreover, it is suggested that the wedge-out is dropped out due to the maximum shear stress in a fixed ply-angle direction and the axial compressive stress.     

Low-stiffness spring element constraint boundary condition method for machining deformation simulation

Journal of Mechanical Science and Technology - The 3-2-1 constraint principle has been widely applied as the boundary conditions for the finite element method (FEM) to simulate machining...     

鼓风机叶轮过盈配合的有限元数值仿真

借助有限元软件ALGOR,对大型PTA项目用RPF循环鼓风机叶轮与轴的过盈配合问题进行三维有限元计算分析,针对不同的过盈量和转速进行了计算,获得了叶轮与轴之间接触应力的相应分布规律.这对于确定合理过盈量和改进设计具有参考意义.     

Application of 3-D finite element method using Lagrangian formulation to dilution control in laser cladding process

In this study a three-dimensional finite element model is presented for precisely simulating laser cladding process with a focus on dilution control. Dilution is referred to as an important quality index in the laser cladding process, indicating the contamination level of the properties of clad layer by substrate metals. As regards a good quality of laser clad layer, low dilution as well as metallurgical bond of interface are prerequisite, so the dilution control is essential in the process. Unfortunately despite of its importance, to date, any practically usable computation techniques have not been reported, which is a motivation of this work. In the paper, proposing a simulation procedure, we develop and verify a code of finite element method with Lagrangian view-point. Following the procedure, the dilution control is precisely estimated. The effects of process parameters on the dilution of clad layer are quantitatively discussed by the numerical and experimental means.     

机器人工作空间求解的蒙特卡洛法改进和体积求取

针对传统的蒙特卡洛法求解机器人工作空间时精确度不够的问题,提出了一种改进的蒙特卡洛法。用传统的蒙特卡洛法生成一个种子工作空间,基于标准差动态可调的正态分布对种子工作空间进行扩展。在扩展过程中设定一个精度阈值,确保得到的工作空间中每个位置都能被准确的描述。基于得到的工作空间,提出了一种体元化算法求取工作空间的体积,寻找到工作空间的边界部分和非边界部分,通过对边界部分的不断细化,降低了体积求取误差。为了验证算法的有效性和实用性,以九自由度的超冗余串联机械臂为例,对本文改进的蒙特卡洛法和提出的体积求取算法进行仿真分析。结果表明:采样点数量相同时,改进的蒙特卡洛法生成的工作空间边界光滑,"噪声小";得到精确的工作空间时改进方法需要的采样点数仅是传统方法的4.67%;体积求取算法效率较高,相对误差小于1%;求得的工作空间体积可用于评估机械臂性能,为后续机械臂构型优化奠定了理论基础。     

A Granular motion simulation by discrete element method

A granular system is defined as a group of tiny particles; they interact with each other by collisions and elastic force. To analyze granular dynamics, conventional methods based on continuum mechanics are not applicable, so new simulation methods are needed. Recently, thanks to improvement in computing technology, the discrete element method (DEM) is being focused on, in which equations of motion are built on each particle and the behavior of all particles is analyzed by solving those equations. In this paper, a computer program has been developed to analyze particle dynamics by using the discrete element method. As examples, the particle packing process and mono-component non-contact development process in a laser printer are simulated. It is seen that the particle motions in the processes are well described by the program.