Simulation of Manufacturing Processes : Scipedia

On the constitutive modeling of coupled thermomechanical phase-change problems
C. Agelet de Saracibar, M. Cervera, M. Chiumenti

International Journal of Plasticity (2001). 17 (12), pp. 1565-1622.

Abstract
This paper deals with a thermodynamically consistent numerical formulation for coupled thermoplastic problems including phase-change phenomena and frictional contact. The final goal is to get an accurate, efficient and robust numerical model, able for the numerical simulation of industrial solidification processes. Some of the current issues addressed in the paper are the following. A fractional step method arising from an operator split of the governing differential equations has been used to solve the nonlinear coupled system of equations, leading to a staggered product formula solution algorithm. Nonlinear stability issues are discussed and isentropic and isothermal operator splits are formulated. Within the isentropic split, a strong operator split design constraint is introduced, by requiring that the elastic and plastic entropy, as well as the phase-change induced elastic entropy due to the latent heat, remain fixed in the mechanical problem. The formulation of the model has been consistently derived within a thermodynamic framework. All the material properties have been considered to be temperature dependent. The constitutive behavior has been defined by a thermoviscous/elastoplastic free energy function, including a thermal multiphase change contribution. Plastic response has been modeled by a J2 temperature dependent model, including plastic hardening and thermal softening. The constitutive model proposed accounts for a continuous transition between the initial liquid state, the intermediate mushy state and the final solid state taking place in a solidification process. In particular, a pure viscous deviatoric model has been used at the initial fluid-like state. A thermomecanical contact model, including a frictional hardening and temperature dependent coupled potential, is derived within a fully consistent thermodinamical theory. The numerical model has been implemented into the computational finite element code COMET developed by the authors. Numerical simulations of solidification processes show the good performance of the computational model developed.
Abstract
This paper deals with a thermodynamically consistent numerical formulation for coupled thermoplastic problems including phase-change phenomena and frictional contact. The [...]
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Advances in FE explicit formulation for simulation of metalforming processes
J. Rojek, O. Zienkiewicz, E. Oñate, E. Postek

Journal of Materials Processing Technology (2001). Vol. 119, pp. 41-47

Abstract
This paper presents some advances of finite element explicit formulation for simulation of metal forming processes. Because of their computational efficiency, finite element programs based on the explicit dynamic formulation proved to be a very attractive tool for the simulation of metal forming processes. The use of explicit programs in the sheet forming simulation is quite common, the possibilities of these codes in bulk forming simulation in our opinion are still not exploited sufficiently. In our paper, we will consider aspects of bulk forming simulation. We will present new formulations and algorithms developed for bulk metal forming within the explicit formulation. An extension of a finite element code for the thermomechanical coupled analysis is discussed. A new thermomechanical constitutive model developed by the authors and implemented in the program is presented. A new formulation based on the so-called split algorithm allows us to use linear triangular and tetrahedral elements in the analysis of large plastic deformations characteristic to forming processes. Linear triangles and tetrahedra have many advantages over quadrilateral and hexahedral elements. Linear triangles and tetrahedra based on the standard formulations exhibit volumetric locking and are not suitable for large plastic strain simulation. The new formulation allows to overcome this difficulty. New formulations and algorithms have been implemented in the finite element code Stampack developed at the International Centre for Numerical Methods in Engineering in Barcelona. Numerical examples illustrate some of the possibilities of the finite element code developed and validate new algorithms.
Abstract
This paper presents some advances of finite element explicit formulation for simulation of metal forming processes. Because of their computational efficiency, finite element [...]
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Finite element simulation of the filling of thin moulds
R. Codina, O. Soto

Int. J. Numer. Meth. Engng. (1999). Vol. 46 (9), pp. 1559-1573

Abstract
In this work we present a finite element formulation to simulate the filling of thin moulds. The model has as starting point a 3‐D approach using either div‐stable elements, such as the Q2/P1 element (tri‐quadratic velocities and piecewise linear, discontinuous pressures) or stabilized finite element formulations. The tracking of the free surface is based on the Volume‐Of‐Fluid (VOF) method. The velocity profile is assumed to be parabolic in the direction normal to the mid‐plane, so that one element along the width of the mould is enough to reproduce this profile if this element is quadratic. The velocity is prescribed to zero on the upper and lower surfaces and the normal to the mid‐plane is also prescribed to zero. In the case of div‐stable elements, the pressure profile is prescribed to be constant along the width of the mould. This can be achieved by using as interpolation degrees of freedom the pressure values at the element centroid and its derivatives in the directions tangent and normal to the mid‐plane, and prescribing the latter to zero. No modifications are needed when stabilized formulations are employed. To advance in time the function used in the VOF technique, we use a constant velocity across the width of the mould, which is taken as the projection on the tangent plane of each element of the nodal velocities. This is needed in order to have mass conservation.
Abstract
In this work we present a finite element formulation to simulate the filling of thin moulds. The model has as starting point a 3‐D approach using either div‐stable elements, [...]
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On the numerical modeling of frictional wear phenomena
C. Agelet de Saracibar, M. Chiumenti

Comput. Methods Appl. Mech. Engrg., (1999). Vol. 177 (3-4), pp. 401-426

Abstract
The evolution of the contact surfaces wear may become particularly important in the definition of the frictional behavior, in particular for frictional contact problems involving large slips, typically in sheet metal forming and bulk forming operations. Despite this fact, most of the current applications reported in the literature are restricted to a standard Coulomb law, using a constant friction coefficient. Such simple models may represent only a limited range of tribological situations and it appears to be necessary to develop a class of models which incorporate the state conditions and their evolution at the contact surfaces, taking into account the influence of complex phenomena such as wear, lubrication and chemical reactions, among others, see Oden and Martins [1]. In this paper a simple numerical model for the simulation of frictional wear behavior, within a fully nonlinear setting, including large slip and finite deformation, is presented. The model relies on the introduction of an internal variable related to the state conditions at the contact surface. Here, two possible definitions of this internal variable have been considered. The fully nonlinear frictional contact formulation, entirely derived first on a continuum setting by Laursen and Simo [2–6], has been extended here to accomodate the characterization of the wear frictional behavior. Within the computational aspects, two families of robust time stepping algorithms, arising from an operator split of the constrained frictional evolution equations, are discussed. Finally, following current approaches, see Lassen [9], Lassen and Bay [10], Owen et al. [11], de Souza et al. [12], Stromberg et al. [13] and Stromberg [14], a long-term tools wear prediction is given by introducing an a priori wear estimate derived from Archard's law, Archard [15]. The numerical model has been implemented into a enhanced version of the computational finite element program FEAP. Numerical examples show the suitability of the proposed model to capture the essential features of the frictional behavior at the contact interfaces and to provide a prediction of tool wear in forming operations.
Abstract
The evolution of the contact surfaces wear may become particularly important in the definition of the frictional behavior, in particular for frictional contact problems involving [...]
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On the formulation of coupled thermoplastic problems with phase-change
C. Agelet de Saracibar, M. Cervera, M. Chiumenti

International Journal of Plasticity (1999). Vol. 15 (1), pp. 1-34

Abstract
This paper deals with a numerical formulation for coupled thermoplastic problems including phase-change phenomena. The final goal is to get an accurate, efficient and robust numerical model, allowing the numerical simulation of solidification processes in the metal casting industry. Some of the current issues addressed in the paper are the following. A fractional step method arising from an operator split of the governing differential equations has been used to solve the nonlinear coupled system of equations, leading to a staggered product formula solution algorithm. Nonlinear stability issues are discussed and isentropic and isothermal operator splits are formulated. Within the isentropic split, a strong operator split design constraint is introduced, by requiring that the elastic and plastic entropy, as well as the phase-change induced elastic entropy due to the latent heat, remain fixed in the mechanical problem. The formulation of the model has been consistently derived within a thermodynamic framework. The constitutive behavior has been defined by a thermoelastoplastic free energy function, including a thermal multiphase change contribution. Plastic response has been modeled by a J2 temperature dependent model, including plastic hardening and thermal softening. A brief summary of the thermomechanical frictional contact model is included. The numerical model has been implemented into the computational Finite Element code COMET developed by the authors. A numerical assessment of the isentropic and isothermal operator splits, regarding the nonlinear stability behavior, has been performed for weakly and strongly coupled thermomechanical problems. Numerical simulations of solidification processes show the performance of the computational model developed.
Abstract
This paper deals with a numerical formulation for coupled thermoplastic problems including phase-change phenomena. The final goal is to get an accurate, efficient and robust [...]
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Numerical prediction of temperature and density distributions in selective laser sintering processes
G. Bugeda, M. Cervera, G. Lombera

Rapid Prototyping Journal (1999). Vol. 5 (1), pp. 21-26

Abstract
A finite element model has been developed for the 3D simulation of the sintering of a single track during a selective laser sintering process (SLS). The model takes into account both the thermal and the sintering phenomena involved in the process. Owing to the continuous movement of the laser beam the model takes also into account the transient nature of the problem. This is transformed into a pseudo‐static one through a transformation of the coordinates system of the equations. Nevertheless, this transformation introduces a convective term into the heat equations that produces instabilities in the solution. These instabilities have been solved by using a stream upwind Petrov Galerkin (SUPG) strategy together with a shock capturing scheme. Finally, a fixed point strategy is used for the solution of the analysis. The model has been tested through the solution of some examples.
Abstract
A finite element model has been developed for the 3D simulation of the sintering of a single track during a selective laser sintering process (SLS). The model takes into account [...]
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Thermo‐mechanical analysis of industrial solidification processes
M. Cervera, C. Agelet de Saracibar, M. Chiumenti

Int. J. Numer. Meth. Engng. (1999). Vol. 46 (9), pp. 1575-1591

Abstract
The paper presents an up‐to‐date finite element numerical model for fully coupled thermo‐mechanical problems, focussing in the simulation of solidification processes of industrial metal parts. The proposed constitutive model is defined by a thermo‐visco‐elasto‐(visco)plastic free energy function which includes a contribution for thermal multiphase changes. Mechanical and thermal properties are assumed to be temperature‐dependent, and viscous‐like strains are introduced to account for the variation of the elastic moduli during the cooling process. The continuous transition between the initial fluid‐like and the final solid‐like behaviour of the part is modelled by considering separate viscous and elasto‐plastic responses as a function of the solid fraction. Thermo‐mechanical contact conditions between the mould and the part are specifically considered, assuming that the heat flux is a function of the normal pressure and the thermal and mechanical gaps. A fractional step method arising from an operator split of the governing equations is used to solve the non‐linear coupled system of equations, leading to a staggered product formula solution algorithm suitable for large‐scale computations. Representative simulations of industrial solidification processes are shown, and comparison of computed results using the proposed model with available experimental data is given.
Abstract
The paper presents an up‐to‐date finite element numerical model for fully coupled thermo‐mechanical problems, focussing in the simulation of solidification processes [...]
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Application of explicit FE codes to simulation of sheet and bulk metal forming processes
J. Rojek, E. Oñate, E. Postek

Journal of Materials Processing Technology (1998). Vols. 80-81, pp. 620-627

Abstract
This paper presents the application of an explicit dynamic finite element code for simulation of metal forming processes, of both sheet and bulk forming. The experiences reported here have been gained during the development and use of our own explicit program Stampack. An original formulation of a triangular shell element without rotational degrees of freedom is reviewed combining the explicit sheet forming simulation with the implicit springback analysis as well as the parallelization of the explicit program described. An extension of a finite element code for coupled thermomechanical analysis is discussed. A new thermomechanical constitutive model developed by the authors and implemented in the program is presented. Numerical examples illustrate some of the possibilities of the finite element code developed.
Abstract
This paper presents the application of an explicit dynamic finite element code for simulation of metal forming processes, of both sheet and bulk forming. The experiences [...]
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A new frictional time integration algorithm for large slip multi-body frictional contact problems
C. Agelet de Saracibar

Comput. Methods Appl. Mech. Engrg., (1997). Vol. 142 (3-4), pp. 303-334

Abstract
In this paper a new frictional time integration algorithm suitable for large slip multibody frictional contact problems is presented. The algorithm is introduced within the simple context of a model problem: the sliding motion of a particle onto a rough surface. Time integration of frictional traction is performed introducing a new slip path parametrization, which is defined independently traction is performed introducing element parametrization used in the spatial triangularization. The key point of the algorithm is that now, in presence of large slips, problems associated with slip motions such that a full incremental slip path is not within a single surface element, are completed bypassed. Remarkably, the algorithm is defined on the solely basis of the unit outward normal field to the surface without any appeal to the underlying local surface finite element triangularization. Geometrically, the assumed slip path can be viewed as an approximation to the geodesic passing throughout the initial and final points of each incremental slip path. The algorithm is amenable to exact linearization and asymptotic quadratic rate of convergence can be achieved within a Newton-Raphson iterative solution scheme. The algorithm can easily be extended to large slip multi-body frictional contact problems, involving finite strains.
Abstract
In this paper a new frictional time integration algorithm suitable for large slip multibody frictional contact problems is presented. The algorithm is introduced within the [...]
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Industrial applications of sheet stamping simulation using new finite element models
J. Rojek, J. Jovicevic, E. Oñate

Journal of Materials Processing Technology (1996). Vol. 60 (1-4), pp. 243-247

Abstract
The paper is aimed to present industrial applications of sheet stamping simulation using new finite element formulations developed in the International Center for Numerical Methods in Engineering in Barcelona. Theoretical formulation is briefly reviewed. Both continuum and shell elements have been considered. The new shell elements developed are based on a geometrically exact shell model treating the shell as one-director Cosserat surface. The formulation of the continuum elements employs the multiplicative decomposition of the deformation gradient tensor into its elastic and plastic parts. The new finite element models have been implemented in the in-house explicit dynamic code STAMPACK. A number of practical problems of sheet metalforming have been solved with the program. Some of the problems, namely stamping of a kitchen sink, hydraulic forming of an aeronautical part and stamping of a food can, have been presented in the paper. The examples give an idea of practical information that can be obtained from the computer simulation of a forming process. The results confirm a good behaviour of the formulation and program used in the industrial applications.
Abstract
The paper is aimed to present industrial applications of sheet stamping simulation using new finite element formulations developed in the International Center for Numerical [...]
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Numerical analysis of stereolithography processes using the finite element method
G. Bugeda, M. Cervera, G. Lombera, E. Oñate

Rapid Prototyping Journal (1995). Vol. 1 (2), pp. 13-23

Abstract
Stereolithography (SLA) is one of the most important techniques used in rapid prototyping processes. It has a great industrial interest because it allows for dramatic time savings with respect to traditional manufacturing processes. One of the main sources of error in the final dimensions of the prototype is the curl distortion effect owing to the shrinkage of the resin during the SLA process. Presents a study of the influence of different constructive and numerical parameters in the curl distortion, an analysis which was made using the computer code stereolithography analysis program, developed to model SLA processes using the finite element method. Also briefly presents this code.
Abstract
Stereolithography (SLA) is one of the most important techniques used in rapid prototyping processes. It has a great industrial interest because it allows for dramatic time [...]
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NUMISTAMP: a research project for assessment of finite-element models for stamping processes
E. Oñate, J. Rojek, C. Garino

Journal of Materials Processing Technology (1995). Vol. 50 (1-4), pp. 17-38

Abstract
This paper describes the objectives and current status of the research project NUMISTAMP currently under development at the International Center for Numerical Methods in Engineering of (CIMNE) located in Barcelona, Spain. The aim of this project is the assesment of different finite element models for simulation of sheet stamping processes. The models currently analyzed include: quasistatic viscoplastic flow and elastoplastic solid models and explicit dynamic models. Both shell and continuum elements are considered in most of these cases. The paper presents an overview of the basic features of the different models. Examples of application including some benchmark test cases proposed at NUMISHEET are also presented.
Abstract
This paper describes the objectives and current status of the research project NUMISTAMP currently under development at the International Center for Numerical Methods in Engineering [...]
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On the pseudomaterial approach for the analysis of transient forming processes
M. Cruchaga, E. Oñate, S. Idelsohn

Commun. Numer. Meth. Engng (1995). Vol. 11 (2), pp. 137-148

Abstract
A fixed‐mesh method for the analysis of transient forming processes is presented. The mesh covers material regions and zones through which the material may flow. These last zones are identified by a pseudomaterial with relatively small physical parameters. During time processing, the interface between both materials is followed by an arbitrary Lagrangian mesh. This technique appears to be suitable for the treatment of moving surfaces with sharp corners. A particular boundary condition for the Navier‐Stokes equations is also introduced in order to model a porous wall.
Abstract
A fixed‐mesh method for the analysis of transient forming processes is presented. The mesh covers material regions and zones through which the material may flow. These last [...]
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A temperature‐based formulation for finite element analysis of generalized phase‐change problems
D. Celentano, E. Oñate, S. Oller

Int. J. Numer. Meth. Engng. (1994). Vol. 37 (20), pp. 3441-3465

Abstract
A finite element formulation for solving multidimensional phase‐change problems is presented. The formulation considers the temperature as the unique state variable, it is conservative in the weak form sense and it preserves the moving interface condition. In this work, an approximate jacobian matrix that preserves numerical convergence and stability is also derived. Furthermore, a comparative analysis with other different phase‐change finite element techniques is performed. Finally, several numerical examples are analysed in order to show the performance of the proposed methodology.
Abstract
A finite element formulation for solving multidimensional phase‐change problems is presented. The formulation considers the temperature as the unique state variable, it [...]
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Mould filling simulation using finite elements
R. Codina, U. Schäfer, E. Oñate

Int. J. of Num. Meths. for Heat and Fluid Flow (1994). Vol. 4 (1), pp. 291-310

Abstract
In this paper we consider several aspects related to the application of the pseudo‐concentration techniques to the simulation of mould filling processes. We discuss, in particular, the smoothing of the front when finite elements with interior nodes are employed and the evacuation of air through the introduction of temporary free wall nodes. The basic numerical techniques to solve the incompressible Navier—Stokes equations are also briefly described. The main features of the numerical model are the use of div‐stable velocity—pressure interpolations with discontinuous pressures, the elimination of the pressure via an iterative penalty formulation, the use of the SUPG approach to deal with convection‐dominated problems and the temporal integration using the generalized trapezoidal rule. At the end of the paper we present some numerical results obtained for a two‐dimensional test problem showing the ability of the method to capture complicated flow patterns.
Abstract
In this paper we consider several aspects related to the application of the pseudo‐concentration techniques to the simulation of mould filling processes. We discuss, in [...]
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A finite element model for thermomechanical analysis in casting processes
D. Celentano, S. Oller, E. Oñate

Journal of Physique IV (1993). Vol. 3 (C7), pp. 1171-1180

Abstract
This paper summarizes the recent work of the authors in the numerical simulation of casting processes. In particular, a coupled thermomechanical model to simulate the solidification problem in casting has been developed [7,8,9]. The model, based on a general isotropic thermoelasto-plasticity theory and formulated in a macroscopical point of view, includes generalized phase-change effects and considers the different thermomechanical behaviour of the solidifying material during its evolution from liquid to solid. For this purpose, a phase-change variable, plastic evolution equations and a temperature-dependent material constitutive law have been defined. Some relevant aspects of this model are presented here. Full thermomechanical coupling terms have been considered as well as variable thermal and mechanical boundary conditions : the first are due to air gap formation, while the second involve a contact formulation. Particular details concerning the numerical implementation of this model are also mentioned. An enhanced staggered scheme, used to solve the highly non-linear fully coupled finite element equations, is proposed. Furthermore, a proper convergence criterion to stop the iteration process is adopted and, although the quadratic convergence of Newton-Rapshon's method is not achieved, several numerical experiments demonstrate reasonable convergence rates [9]. Finally, an experimental cylindrical casting test problem, including phase-change phenomena, temperature-dependent constitutive properties and contact effects, is analyzed. Numerical results are compared with some laboratory measurements.
Abstract
This paper summarizes the recent work of the authors in the numerical simulation of casting processes. In particular, a coupled thermomechanical model to simulate the solidification [...]
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Comparative study on sheet metal forming processes by numerical modelling and experiment
W. Sosnowski, E. Oñate, C. Agelet de Saracibar

Journal of Materials Processing Technology (1992). Vol. 34 (1-4), pp. 109-116

Abstract
In this paper some results of a wide experimental program are presented and compared with some finite element solution of sheet metal forming problems using a viscous shell formulation.
Abstract
In this paper some results of a wide experimental program are presented and compared with some finite element solution of sheet metal forming problems using a viscous shell [...]
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Finite element analysis of sheet metal forming problems using a selective viscous bending/membrane formulation
E. Oñate, C. Agelet de Saracibar

Int. J. Numer. Meth. Engng. (1990). Vol. 30 (8), pp. 1577-1593

Abstract
In this paper the possibilities of the viscous voided shell approach for deriving bending/membrane finite elements for sheet metal forming problems are presented. These elements can be selectively used for membrane or full bending analysis of some parts of the sheet according to the nature of the deformation. Numerical aspects of this approach are discussed and some examples of application are also given.
Abstract
In this paper the possibilities of the viscous voided shell approach for deriving bending/membrane finite elements for sheet metal forming problems are presented. These elements [...]
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Plastic and viscoplastic flow of void‐containing metals. Applications to axisymmetric sheet forming problems
E. Oñate, M. Kleiber, C. Agelet de Saracibar

Int. J. Numer. Meth. Engng. (1988). Vol. 25 (1), pp. 227-251

Abstract
A formal analogy between the equations of pure plastic and viscoplastic flow theory for void‐containing metals and those of standard non‐linear elasticity is presented. The formulation is particularized for the analysis of axisymmetric sheet metal forming problems using simple two node linear finite elements. Details of the treatment of friction and strain hardening phenomena, time increment computation and elastic effects are also given. Examples of the effect of void porosity on the hemispherical stretching of a circular sheet are presented.
Abstract
A formal analogy between the equations of pure plastic and viscoplastic flow theory for void‐containing metals and those of standard non‐linear elasticity is presented. [...]
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A viscous shell formulation for the analysis of thin sheet metal forming
E. Oñate, O. Zienkiewicz

Int. J. Mechanical Sciences (1983). Vol. 25 (5), pp. 305-335

Abstract
A finite element method to analyse large plastic deformations of thin sheets of metal is presented. The formulation is based on an extension of the general viscoplastic flow theory for continuum problems to deal with thin shells. Axisymmetric situations are considered first and here the simple two noded reduced integration element is used. Numerical results for the stretch forming and deep drawing of circular sheets are presented and comparison with experimental results is made. The second part of the paper deals with the deformation of sheets of arbitrary shape. The general viscous shell element is derived from the standard reduced integration, “thick shell element. Numerical results for simple 3-D sheet forming problems are given.
Abstract
A finite element method to analyse large plastic deformations of thin sheets of metal is presented. The formulation is based on an extension of the general viscoplastic flow [...]
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On the constitutive modeling of coupled thermomechanical phase-change problems

Advances in FE explicit formulation for simulation of metalforming processes

Finite element simulation of the filling of thin moulds

On the numerical modeling of frictional wear phenomena

On the formulation of coupled thermoplastic problems with phase-change

Numerical prediction of temperature and density distributions in selective laser sintering processes

Thermo‐mechanical analysis of industrial solidification processes

Application of explicit FE codes to simulation of sheet and bulk metal forming processes

A new frictional time integration algorithm for large slip multi-body frictional contact problems

Industrial applications of sheet stamping simulation using new finite element models

Numerical analysis of stereolithography processes using the finite element method

NUMISTAMP: a research project for assessment of finite-element models for stamping processes

On the pseudomaterial approach for the analysis of transient forming processes

A temperature‐based formulation for finite element analysis of generalized phase‐change problems

Mould filling simulation using finite elements

A finite element model for thermomechanical analysis in casting processes

Comparative study on sheet metal forming processes by numerical modelling and experiment

Finite element analysis of sheet metal forming problems using a selective viscous bending/membrane formulation

Plastic and viscoplastic flow of void‐containing metals. Applications to axisymmetric sheet forming problems

A viscous shell formulation for the analysis of thin sheet metal forming

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