金属塑性成形三维有限元模拟软件3D - PFS的开发

金属塑性成形过程的三维有限元模拟仿真是否有效的关键在于快速适用的算法和有效的模拟系统.介绍了自主开发的三维刚塑性/刚粘塑性有限元模拟分析软件3D-PFs的组成及关键技术问题的处理,并给出了计算实例.结果表明:利用该系统可实现对体积和板料成形过程的模拟分析,获得成形过程中材料在模腔中的流动情况及成形规律,该系统是研究金属塑性成形的有效工具.     

Automatic remeshing in 3‐D analysis of forming processes

Finite element modelling, employing updated Lagrangian techniques, is used extensively in the design and analysis of bulk forming processes. However, the full 3‐D capability has not seen widespread use in the automotive, aerospace, and, related industries due to, among other reasons, the need for remeshing, or, representation of the workpiece with a new finite element mesh as the analysis progresses. Automating the remeshing procedure of the deformed workpiece geometry would reduce the time required for a 3‐D analysis by several orders of magnitude. This paper discusses an algorithm for generating a new mesh to represent the deformed workpiece geometry during the analysis. The procedure is used to perform a 3‐D analysis of a valve forging problem. Copyright © 1999 John Wiley & Sons, Ltd.     

An overlapping domain decomposition method for the simulation of elastoplastic incremental forming processes

The implicit finite element (FE) simulation of incremental metal cold forming processes is still a challenging task. We introduce a dynamic, overlapping domain decomposition method to reduce the computational cost and to circumvent the need for sophisticated remeshing procedures. The two FE domains interchange information using the elastoplastic operator split and the mortar method. Copyright © 2008 John Wiley & Sons, Ltd.     

Process optimal design in non‐isothermal,steady‐state metal forming by the finite element method

A new approach to process optimal design in non‐isothermal, steady‐state metal forming is presented. In this approach, the optimal design problem is formulated on the basis of the integrated thermo‐mechanical finite element process model so as to cover a wide class of the objective functions and to accept diverse process parameters as design variables, and a derivative‐based approach is adopted as a solution technique. The process model, the formulation for process optimal design, and the schemes for the evaluation of the design sensitivity, and an iterative procedure for design optimization are described in detail. The validity of the schemes for the evaluation of the design sensitivity is examined by performing a series of numerical tests. The capability of the proposed approach is demonstrated through applications to some selected process design problems. Copyright © 1999 John Wiley & Sons, Ltd.     

Finite element simulation of the steel plates hot rolling process

In this paper we discuss our finite element procedure for simulating the hot rolling of flat steel products. We couple an Eulerian rigid‐viscoplastic model of the steel plates deformation to a Lagrangian elastic model of the rolls deformation. This latter model incorporates the bending deformation of the work rolls supported by the back‐up rolls and the flattening of the contact areas (Hertz problem) via an enhanced beam model. The finite element model is validated comparing its predictions with actual industrial measurements and then it is used to analyse different rolling set‐ups. Copyright © 2001 John Wiley & Sons, Ltd.     

Mismatching refinement with domain decomposition for the analysis of steady‐state metal forming process

The finite element analysis of three‐dimensional metal forming processes is generally subject to large computational burden due to its non‐linearity. For economic computation, the mismatching refinement, an efficient domain decomposition method with different mesh density for each subdomain, is developed in the present study. A modified velocity alternating scheme for the interface treatment is proposed in order to obtain good convergence and accuracy in the mismatching refinement. As a numerical example, the analysis of the axisymmetric extrusion processes is carried out. The results are discussed for the various velocity update schemes and for the variation of the length of overlapped region. The three‐dimensional extrusion processes for a rectangular section and an E‐section are analysed in order to verify the effectiveness of the proposed method. Comparing the results with those of the conventional method of full region analysis, the accuracy and the computational efficiency of the proposed method are then discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

金属激光3D打印过程数值模拟应用及研究现状

数值模拟可以高效、有针对性地对金属激光选区熔化成型过程中的温度场、熔池形状、残余应力和变形、凝固过程微观组织演变等过程建立相应的模型并对成形件的相关性能做出准确预测,为工艺优化提供科学的依据,显著降低工艺开发成本和缩短工艺开发周期,有力推动金属增材制造向工业级应用的转变。本文综述了金属激光增材制造过程中温度场、熔池动力学、成形件内部残余应力和变形、显微组织变化4个方面数值模拟的最新研究进展,概述了金属SLM过程数值模拟所取得的最新进展,分析了金属SLM数值模拟领域的研究热点和所存在的计算时间长、成本高等问题,最后提出金属SLM过程数值模拟应将3D打印过程中快速凝固、微熔池等特征与大数据、人工智能、深度学习等技术相结合,进一步提高数值模拟精度,拓宽金属激光增材制造加工窗口,为个性化产品开发提供指导。     

An object‐oriented programming approach to the Lagrangian FEM analysis of large inelastic deformations and metal‐forming processes

The general deformation problem with material and geometric non‐linearities is typically divided into a number of subproblems including the kinematic, the constitutive, and the contact/friction subproblems. These problems are introduced for algorithmic purposes; however, each of them represents distinct physical aspects of the deformation process. For each of these subproblems, several well‐established mathematical and numerical models based on the finite element method have been proposed for their solution. Recent developments in software engineering and in the field of object‐oriented C++ programming have made it possible to model physical processes and mechanisms more expressively than ever before. In particular, the various subproblems and computational models in a large inelastic deformation analysis can be implemented using appropriate hierarchies of classes that accurately represent their underlying physical, mathematical and/or geometric structures. This paper addresses such issues and demonstrates that an approach to deformation processing using classes, inheritance and virtual functions allows a very fast and robust implementation and testing of various physical processes and computational algorithms. Here, specific ideas are provided for the development of an object‐oriented C++ programming approach to the FEM analysis of large inelastic deformations. It is shown that the maintainability, generality, expandability, and code re‐usability of such FEM codes are highly improved. Finally, the efficiency and accuracy of an object‐oriented programming approach to the analysis of large inelastic deformations are investigated using a number of benchmark metal‐forming examples. Copyright © 1999 John Wiley & Sons, Ltd.     

Using genetic algorithm-back propagation neural network prediction and finite-element model simulation to optimize the process of multiple-step incremental air-bending forming of sheet metal

Using neural network to predict punch radius based on the results of air-bending experiments of sheet metal is a high efficiency work in spite of little error. A three-layer back propagation neural network (BPNN) is developed to best fit this discrete engineering problem involving many parameters of air-bending forming. A genetic algorithm (GA) is used to optimize the weights of neural network for minimizing the error between the predictive punch radius and the experimental one. Then, with the predicted punch radius and other geometrical parameters of a tool, 2D and 3D ABAQUS finite-element models (FEM) are established, respectively. The original forming process of multiple-step incremental air-bending of sheet metal, obtained from geometric planning for semiellipse-shaped workpiece, is simulated using the FEM. This process is further adjusted with simulation-optimization results, because of existing large errors in the workpiece simulated with the original forming process. Finally, a semiellipse-shaped workpiece, with average errors of +0.61/−0.62 mm, is manufactured with the optimized adjustment process. The experimental results show that the punch design method is feasible with the prediction model of GA-BPNN, and the means of optimizing process with FEM simulation is effective. It can be taken as a new approach for punch and process design of multiple-step incremental air-bending forming of sheet metal.     

Contamination test of metal and non‐metal elements from copper gas pipe to food gases

In the last decade, EC regulations have been issued to minimize any interaction between packaging materials intended to come in contact with foodstuffs and potential contaminants. In this paper, the concentrations of 26 metals and metalloids in a food gas (CO₂), possibly related to the migration of elements from copper pipes, which are commonly used during gas storage and distribution, were determined by ICP‐AES and ICP‐MS. A simple, though efficient, procedure to chemically trap these elements has shown that the copper pipes do not release significant concentrations of metals and metalloids, most of them being below or clustering below or around the instrumental detection limit. According to this study, only Al, Cu, Fe, Ni, and Zn can be related to the copper line. However, when considering the consumption of 3 L of water, at which 12 g/L of CO₂ is added, the computed concentrations of metals and metalloids are 3 to 6 orders of magnitude lower than the limit concentrations in mineral waters intended for human consumption (European Directive 98/83/EC). This implies that the amount of contaminants in CO₂ introduced in the human body is negligible.     

Non‐isothermal ‘2‐D flow/3‐D thermal’ developments encompassing process modelling of composites: flow/thermal/cure formulations and validations

In the manufacturing process of large geometrically complex components comprising of fibre‐reinforced composite materials by resin transfer molding (RTM), the process involves injection of resin into a mold cavity filled with porous fibre preforms. The overall success of the RTM manufacturing process depends on the complete impregnation of the fibre mat by the polymer resin, prevention of polymer gelation during filling, and subsequent avoidance of dry spots. Since a cold resin is injected into a hot mold, the associated physics encompasses a moving boundary value problem in conjunction with the multi‐disciplinary study of flow/thermal and cure kinetics inside the mold cavity. Although experimental validations are indispensable, routine manufacture of large complex structural geometries can only be enhanced via computational simulations, thus eliminating costly trial runs and helping the designer in the set‐up of the manufacturing process. This study describes the computational developments towards formulating an effective simulation‐based design methodology using the finite element method. The specific application is for thin shell‐like geometries with the thickness being much smaller than the other dimensions of the part. Due to the highly advective nature of the non‐isothermal conditions involving thermal and polymerization reactions, special computational considerations and stabilization techniques are also proposed. Validations and comparisons with experimental results are presented whenever available. Copyright © 2001 John Wiley & Sons, Ltd.     

3D‐based hp‐adaptive first‐order shell finite element for modelling and analysis of complex structures—Part 1: The model and the approximation

The paper presents a 3D‐based adaptive first‐order shell finite element to be applied to hierarchical modelling and adaptive analysis of complex structures. The main feature of the element is that it is equipped with 3D degrees of freedom, while its mechanical model corresponds to classical first‐order shell theory. Other useful features of the element are its modelling and adaptive capabilities. The element is assigned to hierarchical modelling and hpq‐adaptive analysis of shell parts of complex structures consisting of solid, thick‐ and thin‐shell parts, as well as of transition zones, where h, p and q denote the mesh density parameter and the longitudinal and transverse orders of approximation, respectively. The proposed hp‐adaptive first‐order shell element can be joined with 3D‐based hpq‐adaptive hierarchical shell elements or 3D hpp‐adaptive solid elements by means of the family of 3D‐based hpq/hp‐ or hpp/hp‐adaptive transition elements. The main objective of the first part of our research, presented in this paper, is to provide non‐standard information on the original parts of the element algorithm. In order to do that, we present the definition of shape functions necessary for p‐adaptivity, as well as the procedure for imposing constraints corresponding to the lack of elongation of the straight lines perpendicular to the shell mid‐surface, which is the procedure necessary for q‐adaptivity. The 3D version of constrained approximation presented next is the basis for h‐adaptivity of the element. The second part of our research, devoted to methodology and results of the numerical research on application of the element to various plate and shell problems, are described in the second part of this paper. Copyright © 2006 John Wiley & Sons, Ltd.     

A continuum sensitivity method for finite thermo‐inelastic deformations with applications to the design of hot forming processes

A computational framework is presented to evaluate the shape as well as non‐shape (parameter) sensitivity of finite thermo‐inelastic deformations using the continuum sensitivity method (CSM). Weak sensitivity equations are developed for the large thermo‐mechanical deformation of hyperelastic thermo‐viscoplastic materials that are consistent with the kinematic, constitutive, contact and thermal analyses used in the solution of the direct deformation problem. The sensitivities are defined in a rigorous sense and the sensitivity analysis is performed in an infinite‐dimensional continuum framework. The effects of perturbation in the preform, die surface, or other process parameters are carefully considered in the CSM development for the computation of the die temperature sensitivity fields. The direct deformation and sensitivity deformation problems are solved using the finite element method. The results of the continuum sensitivity analysis are validated extensively by a comparison with those obtained by finite difference approximations (i.e. using the solution of a deformation problem with perturbed design variables). The effectiveness of the method is demonstrated with a number of applications in the design optimization of metal forming processes. Copyright © 2002 John Wiley & Sons, Ltd.     

Application of the X‐FEM to the fracture of piezoelectric materials

This paper presents an application of the extended finite element method (X‐FEM) to the analysis of fracture in piezoelectric materials. These materials are increasingly used in actuators and sensors. New applications can be found as constituents of smart composites for adaptive electromechanical structures. Under in service loading, phenomena of crack initiation and propagation may occur due to high electromechanical field concentrations. In the past few years, the X‐FEM has been applied mostly to model cracks in structural materials. The present paper focuses at first on the definition of new enrichment functions suitable for cracks in piezoelectric structures. At second, generalized domain integrals are used for the determination of crack tip parameters. The approach is based on specific asymptotic crack tip solutions, derived for piezoelectric materials. We present convergence results in the energy norm and for the stress intensity factors, in various settings. Copyright © 2008 John Wiley & Sons, Ltd.     

An adaptive multi‐scale approach to the modelling of masonry structures

We present an adaptive multi‐scale approach for predicting the mechanical behaviour of masonry structures modelled as dynamic frictional multi‐body contact problems. In this approach, the iterative splitting of the contact problem into normal contact and frictional contact is combined with a semismooth Newton/primal‐dual active‐set procedure to calculate deformations and openings in the model structures. This algorithm is then coupled with a novel adaptive multi‐scale technique involving a macroscopic scale, which is the size of the masonry structure, and a mesoscopic scale, which is the size of the constituents (bricks, stone‐blocks), to predict appearance of dislocations and stress distribution in large‐scale masonry structures. Comparisons of the numerical results with data from experimental tests and from practical observations illustrate the predictive capability of the multi‐scale algorithm. Copyright © 2008 John Wiley & Sons, Ltd.     

A three‐invariant hardening plasticity for numerical simulation of powder forming processes via the arbitrary Lagrangian–Eulerian FE model

In this paper, a three‐invariant cap plasticity model with an isotropic hardening rule is presented for numerical simulation of powder compaction processes. A general form is developed for single‐cap plasticity which can be compared with some common double‐surface plasticity models proposed for powders in literature. The constitutive elasto‐plastic matrix and its components are derived based on the definition of yield surface, hardening parameter and non‐linear elastic behaviour, as function of relative density of powder. Different aspects of the new single plasticity are illustrated by generating the classical plasticity models as special cases of the proposed model. The procedure for determination of powder parameters is described by fitting the model to reproduce data from triaxial compression and confining pressure experiments. The three‐invariant cap plasticity is performed within the framework of an arbitrary Lagrangian–Eulerian formulation, in order to predict the non‐uniform relative density distribution during large deformation of powder die pressing. In ALE formulation, the reference configuration is used for describing the motion, instead of material configuration in Lagrangian, and spatial configuration in Eulerian formulation. This formulation introduces some convective terms in the finite element equations and consists of two phases. Each time step is analysed according to Lagrangian phase until required convergence is attained. Then, the Eulerian phase is applied to keep mesh configuration regular. Because of relative displacement between mesh and material, all dependent variables such as stress and strain are converted through the Eulerian phase. Finally, the numerical schemes are examined for efficiency and accuracy in the modelling of a rotational flanged component, an automotive component, a conical shaped‐charge liner and a connecting‐rod. Copyright © 2005 John Wiley & Sons, Ltd.     

A new three-dimensional finite element model for the simulation of powder forging processes: application to hot forming of P/M connecting rod

In powder metallurgy (P/M) the forming of industrial artifacts requires consolidation of loose powder into dense material leading to near-to-net shape components. In order to realize the economic advantages of the near-to-net shape formation, it is essential to understand the mechanical behaviour of powder deforming domain. The conventional P/M forming process consists of different stages such as closed cold die compaction, sintering and hot/cold forging. In the present study a finite element based computational model has been formulated to study the hot forging stage with particular reference to forging of P/M connecting rods. In order to achieve this purpose, a new finite element formulation has been developed to model the powder deformation under a given thermo-mechanical loading. Essentially, the computational model is formulated based on a visco-plastic Green type material model considering an independent idealization of strain rates into a total deformation part and a dilatational part, and the yield criterion takes into account the pressure sensitivity. The model is set in a perturbed Lagrangian functional, leading to a three field mixed formulation with velocity, Lagrangian multiplier/pressure and volumetric strain rates as three basic unknowns in the finite element domain. The developed finite element model can be used right from the compressible domain to the incompressible domain with the Lagrangian multiplier becoming then the pressure. A relative density-dependent visco-plastic type of friction law is used for characterizing the friction behaviour between the powder preform and the die. The required various material parameters are determined from experiments on aluminium powder preforms. In order to facilitate the non-isothermal deformation study, a powder-based transient thermal analysis has been developed. A computational scheme has been used to couple the mechanical and thermal calculations. Using the developed three-dimensional code, hot forging of automotive components can be simulated and which in the present study is exemplified by simulation of hot forging of a P/M connecting rod. © 1997 John Wiley & Sons, Ltd.