Development of an object-oriented finite element program: application to metal-forming and impact simulations

During the last 50 years, the development of better numerical methods and more powerful computers has been a major enterprise for the scientific community. In the same time, the finite element method has become a widely used tool for researchers and engineers. Recent advances in computational software have made possible to solve more physical and complex problems such as coupled problems, nonlinearities, high strain and high-strain rate problems. In this field, an accurate analysis of large deformation inelastic problems occurring in metal-forming or impact simulations is extremely important as a consequence of high amount of plastic flow. In this presentation, the object-oriented implementation, using the C++ language, of an explicit finite element code called DynELA is presented. The object-oriented programming (OOP) leads to better-structured codes for the finite element method and facilitates the development, the maintainability and the expandability of such codes. The most significant advantage of OOP is in the modeling of complex physical systems such as deformation processing where the overall complex problem is partitioned in individual sub-problems based on physical, mathematical or geometric reasoning. We first focus on the advantages of OOP for the development of scientific programs. Specific aspects of OOP, such as the inheritance mechanism, the operators overload procedure or the use of template classes are detailed. Then we present the approach used for the development of our finite element code through the presentation of the kinematics, conservative and constitutive laws and their respective implementation in C++. Finally, the efficiency and accuracy of our finite element program are investigated using a number of benchmark tests relative to metal forming and impact simulations

Nanoindentation and tribological tests – Suitable tools for modelling the nanostructure of sheet nacre

1. Introduction Nacre (the pearly internal layer of seashells) is a natural nanocomposite currently studied for the design of new organic/inorganic hybrid materials by mimicking biomineralization processes. It is a bioceramic formed at ambient temperature and pressure [1] which displays an exceptional high strength, stiffness and toughness [2] to weight ratio, as well as a natural biocompatibility with human bones [3]

A generalized non-linear flow law based on Modified Zerilli–Armstrong model and its implementation into Abaqus/Explicit FEM code

Non-linear numerical modeling is increasingly used for the simulation of complex processes such as forming or machining. The constitutive laws necessary for these simulations are therefore becoming more and more complex regarding the increasingly precise consideration of physical phenomena (plasticity, thermal dependence, damage ...) and their implementation in numerical codes requires the identification of many parameters. The use of these constitutive laws for dynamic or quasi-static applications requires the identification of these parameters under conditions close to those encountered during the real process, mainly in terms of deformation, strain rates, and temperatures. The availability of a constitutive law in the finite element codes does not guarantee the success of a study to be carried out if it does not comply with the model development criteria. This is because the models integrated in the numerical codes are not developed based on forms that are adjustable to any type of study. In this study, a new form of non-linear constitutive flow law based on the Modified Zerilli-Armstrong model, which can answer the above problem, has been developed to apply it to the numerical simulation of two different tests (a quasi-static compression test, the necking of a circular bar). This flow law is based on the modified Zerilli-Armstrong model, which, together with the new modified Johnson-Cook model, has been compared to appreciate the relevance of the proposal. For that, an implementation of this new law via the VUHARD subroutine into the Abaqus/Explicit finite element code was made to model the two tests. The comparison of the results obtained (from identification) by our proposed law with those obtained using the NMJC shows that this new law better approaches the experiments than the other one. This is also showed through the numerical results using the Abaqus software. It can be said that this way of formulating a flow law allows to highlight the great performance of the proposed approach. Although this law has been only used for quasi-static tests, we can say that it can also be used in dynamic tests

A new impact test for the identification of a dynamic crack propagation criterion using a gas-gun device

The modelling of damage and fracture behaviour under high rates of loadings for metallic structures presents the more and more interests for engineering design, especially for crash phenomena. In order to perform a numerical simulation of such phenomena a crack propagation criterion must be identified using adapted laboratory tests. The objective of this paper is to present a new impact test intended for the identification of a cohesive crack criterion implemented into a home-made FEM code based on Extended Finite Element Method. Therefore, a double-notched specimen is impacted using a gas-gun device in order to obtain different crack paths depending on projectile speed. A post-impact macro-photographic observation allows to measure the crack path, the angles and the advancing length. These experimental results are used as input responses in the identification procedure for determining the crack cohesive criterion parameters. Some experimental results, for an aluminium alloy crack criterion identification, are presented to illustrate the proposed approach

A-ACTI-5. Methodology to predict the influence of process and material parameters on impact response in composite structures

International audienceno abstrac

Numerical propagation of dynamic cracks using X-FEM

This paper presents an application of the eXtended Finite Element Method for numerical modeling of the dynamic cracks propagation. The numerical cracks representation is adapted to the time-dependent mechanical formulation, using the Heaviside step function for completely cutted elements and the cohesive model for crack tips. In order to find the propagation parameters, a crack evolution model is proposed. The numerical implementation is achieved in new explicit FE module. A numerical example is proposed for proving the computational efficiency of this new module

A-ACTI-5. Methodology to predict the influence of process and material parameters on impact response in composite structures

International audienceno abstrac

A methodology for large scale finite element models, including multi-physic, multi-domain and multi-timestep aspects

This works concerns the development of a virtual prototyping tool dedicated to electro-thermo-mechanical simulation of power converters. The FEM code, written using an object-oriented language, includes a dual Schur Domain Decomposition Method. The solving of problems including floating subdomains can be performed in steady-state cases, whereas one can couple multi-timestep implicit and explicit integration schemes in transient analysis. The last part of this work is about the study of an industrial benchmark concerning the power converters used in railway transport: the electro-thermal simulation of a switch in transient analysis. This example allows to compare different strategies of tearing into subdomains and the use of different timesteps on the same structure