Papers by jesus mediavilla
of state variables. Abstract. Finite element simulations of blanking require frequent remeshing i... more of state variables. Abstract. Finite element simulations of blanking require frequent remeshing in order to trace the evolving geometry of the problem. Remeshing must be accompanied by transfer of a set of state variables from the old mesh to the new. Inaccuracies which are inevitably introduced by this transfer may easily lead to loss of convergence in subsequent loading increments and therefore to breakdown of the simulation. In order to avoid such failures, a remeshing-transfer algorithm has been developed which is more forgiving with respect to inaccuracies and thus allows for efficient and robust simulations. 1 R.H.J. Peerlings, J. Mediavilla, M.G.D. Geers
Structural Engineering and Mechanics, 2009
ABSTRACT
AIP Conference Proceedings, 2007
ABSTRACT
Nytt: Stegvis kontroll i registreringsformulären ger hjälp att skriva in korrekt data. De långa n... more Nytt: Stegvis kontroll i registreringsformulären ger hjälp att skriva in korrekt data. De långa namnlistor man behövde navigera i för att skapa publikationslistor för personer har ersatts av en sökfunktion. Delvis finns också en dubblettkontroll för importerade poster på plats. ...
International Journal of Material Forming, 2008
Fracture of Nano and Engineering Materials and Structures
The proposed methodology is applied to several examples, including double notched specimen and te... more The proposed methodology is applied to several examples, including double notched specimen and tensile test on a rectangular specimen. These examples demonstrate the viability and the three dimensional features of the algorithm both for initiation and propagation of cracks.
International Journal for Numerical Methods in Engineering, 2010
Through-the-thickness crack propagation in thin-walled structures is dealt with in this paper. Th... more Through-the-thickness crack propagation in thin-walled structures is dealt with in this paper. The formulation is based on the cohesive zone concept applied to a kinematically consistent shell model enhanced with an XFEM-based discontinuous kinematical representation. The resulting formulation comprises the representation of continuous deformation, represented by midsurface placement, director and thickness inhomogeneous fields, and discontinuous deformation, represented by discontinuous placement and director fields. The shell model is implemented both for the implicit static analysis and in the context of explicit dynamic integration pertinent to impact loading, and the implementation results in a 7-parameter solidshell element based on a 6-noded triangular element. In order to properly formulate the dynamic fracture characteristics, a rate-dependent cohesive zone model is employed with respect to, e.g. limiting crack speeds as observed experimentally. In the final example, this model has been applied to a blast loaded pressure vessel that has been experimentally tested. The results indicate that the right crack speed as well as fracture characteristics are relatively well captured. Furthermore, it appears that the discontinuous model exhibits the expected properties with respect to critical time step size in the dynamic analysis and convergence behavior towards the analytical static solution.
International Journal for Numerical Methods in Engineering, 2006
A combined approach towards ductile damage and fracture is presented, in the sense that a continu... more A combined approach towards ductile damage and fracture is presented, in the sense that a continuous material degradation is coupled with a discrete crack description for large deformations. Material degradation is modelled by a gradient enhanced damage-hyperelastoplasticity model. It is assumed that failure occurs solely due to plastic straining, which is particularly relevant for shear dominated problems, where the effect of the hydrostatic stress in triggering failure is less important. The gradient enhancement eliminates pathological localization effects which would normally result from the damage influence. Discrete cracks appear in the final stage of local material failure, when the damage has become critical. The rate and the direction of crack propagation depend on the evolution of the damage field variable, which in turn depends on the type of loading. In a large strain finite element framework, remeshing allows to incorporate the changing crack geometry and prevents severe element distortion. Attention is focused on the robustness of the computations, where the transfer of variables, which is needed after each remeshing, plays a crucial role. Numerical examples are shown and comparisons are made with published experimental results.
Proceedings of IV …, 2010
... A cohesive zone formulation of fracturing shells based on XFEM. Författare: Martin Fagerström... more ... A cohesive zone formulation of fracturing shells based on XFEM. Författare: Martin Fagerström (Institutionen för tillämpad mekanik, Material-och beräkningsmekanik); Ragnar Larsson (Institutionen för tillämpad mekanik, Material-och beräkningsmekanik); Jesus Mediavilla (-). ...
Abstract. Finite element simulations of blanking require frequent remeshing in order to trace the... more Abstract. Finite element simulations of blanking require frequent remeshing in order to trace the evolving geometry of the problem. Remeshing must be accompanied by transfer of a set of state variables from the old mesh to the new. Inaccuracies which are inevitably ...
Engineering Fracture Mechanics, 2006
This paper addresses the simulation of ductile damage and fracture in metal forming processes. A ... more This paper addresses the simulation of ductile damage and fracture in metal forming processes. A combined continuous-discontinuous approach has been used, which accounts for the interaction between macroscopic cracks and the surrounding softening material. Softening originates from the degradation processes taking place at a microscopic level, and is modelled using continuum damage mechanics concepts. To avoid pathological localisation and mesh dependence and to incorporate length scale effects due to microstructure evolution, the damage growth is driven by a non-local variable via a second order partial differential equation. The two governing equations, i.e. equilibrium and non-local averaging, are solved in an operator-split manner. This allows one to use a commercial finite element software to solve the equilibrium problem, including contact between the tools and work piece. The non-local averaging equation is solved on a fixed configuration, through a special purpose code which interacts with the commercial code. A remeshing strategy has been devised that allows: (i) to capture the localisation zone, (ii) prevent large element distortions and (iii) accommodate the crack propagation. To illustrate the capabilities of the modelling tool obtained by combining these continuum mechanics concepts and computational techniques, process simulations of blanking, fine-blanking and score forming are presented.
Engineering Fracture Mechanics, 2008
Building on the local approach to fracture, a framework for finite element simulations of damage ... more Building on the local approach to fracture, a framework for finite element simulations of damage development during metal forming is presented. Its application to the fabrication of a food-can lid demonstrates the capabilities, but also the limitations of the framework. One such limitation, the phenomenological basis on which the damage evolution laws are formulated, is subsequently addressed by studying the micromechanics of the underlying damage mechanism -microvoid-growth. Finite element studies illustrate the relevant phenomena and are subsequently used to calibrate evolution laws which are based on understanding of these phenomena. The paper closes with directions for future developments.
Computers & Structures, 2006
This paper addresses the numerical simulation of quasi-static ductile fracture. The main focus is... more This paper addresses the numerical simulation of quasi-static ductile fracture. The main focus is on numerical and stability aspects related to discrete crack propagation. Crack initiation and propagation are taken into account, both driven by the evolution of a discretely coupled damage variable. Discrete ductile failure is embedded in a geometrically nonlinear hyperelasto-plastic model, triggered by an appropriate criterion that has been evaluated for tensile and shear failure. A crack direction criterion is proposed, which is validated for both failure cases and which is capable of capturing the experimentally observed abrupt tensile-shear transition. In a large strain finite element context, remeshing enables to trace the crack geometry as well as to preserve an adequate element shape. Stability of the computations is an important issue during crack propagation that can be compromised by two factors, i.e. large stress redistributions during the crack opening and the transfer of variables between meshes. A numerical procedure is developed that renders crack propagation considerably more robust, independently of the mesh fineness and crack discretisation. A consistent transfer algorithm and a crack relaxation method are proposed and implemented for this purpose. Finally, illustrative simulations are compared with published experimental results to highlight the features mentioned.
Computer Methods in Applied Mechanics and Engineering, 2006
In this contribution a nonlocal damage-plasticity framework is developed which allows to describe... more In this contribution a nonlocal damage-plasticity framework is developed which allows to describe the evolution of ductile damage in a continuum sense. Focus is on two main aspects of the ductile damage model, which constitute an improvement of recently developed theories. First, the degradation of both the elastic and plastic response is accounted for, using the concept of effective stress and strain equivalence between the homogenised and the hyperelastoplastic matrix material. Second, the role of the stress triaxiality in triggering ductile failure is taken into account by using a triaxiality-dependent local damage-driving variable, whose nonlocal counterpart acts as a localisation limiter. The resulting coupled problem, i.e., equilibrium and nonlocal averaging, is implemented in an implicit, fully coupled form, for which consistent tangent operators are derived. Details of the numerical implementation and remeshing issues are given. To illustrate the response of the model, simulations of tensile tests on notched and unnotched bars are compared with the results of previous models and with published experimental data.
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Papers by jesus mediavilla