Carl Labergère

2D Adaptive FE Simulations in Finite Thermo-Elasto-Viscoplasticity with Ductile Damage: Application to Orthogonal Metal Cutting by Chip Formation and Breaking

Fully coupled thermo-elasto-visco-plastic-damage constitutive equations based on the state variables under large plastic deformation are developed for metal forming simulation. Relevant numerical aspects concerning both the global resolution strategy as well as the local integration scheme are discussed. The model is implemented into ABAQUS/Explicit using the Vumat user subroutine and used in connection with a 2D adaptive mesh facility. Application is made to the orthogonal metal cutting resulting in chip formation and segmentation or breaking. This example is studied in order to examine the ability of this adaptive fully coupled approach to predict qualitatively the formation and the segmentation of the chip compared to the classical procedure, which neglects the damage effect.

Prediction of serrated chip formation in orthogonal metal cutting by advanced adaptive 2D numerical methodology

In this work a complete numerical methodology combining ‘advanced’ thermo-elasto-viscoplastic constitutive equations accounting for mixed (isotropic and kinematic) non-linear hardening, thermal effects, isotropic ductile damage and contact with friction is proposed to simulate the 2D orthogonal cutting process of AISI4340 steel. First, the fully coupled constitutive equations are presented and their specificities highlighted. The relevant numerical aspects concerning both the local integration scheme as well as the global resolution strategy together with the 2D adaptive remeshing facility are discussed. This model is implemented into ABAQUS/EXPLICIT using the Vumat user subroutine and connected with an adaptive 2D meshing program. Application is made to the 2D orthogonal metal cutting by chip formation. A special care is put in the prediction of the primary shear band where the temperature, the strain and the damage are highly localised giving the serrated shape and possible segmentation of the ship.

Numerical Design of Extrusion Process Using Finite Thermo-Elastoviscoplasticity with Damage. Prediction of Chevron Shaped Cracks

The influence of the initial temperature and its evolution with large plastic deformation on the formation of the fully coupled chevron shaped cracks in extrusion is numerically investigated. Fully coupled thermo-elasto-viscoplastic constitutive equations accounting for thermal effects, mixed and nonlinear isotropic and kinematic hardening, isotropic ductile damage with micro-cracks closure effects are used. These constitutive equations have been implemented in Abaqus/Explicit code thanks to the user subroutine vumat and used to perform various numerical simulations needed to investigate the problem. It has been shown that the proposed methodology is efficient to predict the chevron shaped cracks in extrusion function of the main process parameters including the temperature effect.

Multi-objective optimization based on meta-models of an aeronautical hub including the ductile damage constraint

In forging process, geometric design of initial billet and tools is very important. Traditionally, engineers use their knowledge and experience to design and optimize the geometric model of forging process by using trial-and-error methods. Such methods are time consuming and cost expensive. It is therefore interesting to design an automatic tools builder based on optimization methodology coupled with virtual finite element simulations, thus helping engineers to improve products and reduce cost. In this article we describe a meta-model based multi-objective optimization methodology for forging process designed to build the theoric Pareto optimal front of the mechanical problem. We go through a four-step process: building parametric computer-aided design geometry model, simulating the forging process according to the DOE, fitting meta-models, and optimizing the process by using an advanced algorithm. Two different meta-models, including polynomial and kriging methods, are constructed, based on the simulation values for different responses. Then optimization algorithms NBI-NLPQLP and NSGA-II are applied to find the optimum solutions based on each different meta-model. In order to drive this procedure automatically we use ModeFRONTIER® software. Using this environment, several macro commands are used to connect the geometry modelling (made with CATIA V5™) and numerical simulation process. As an industrial example, a two-step forging of an aeronautic component shows the efficiency of the proposed methodology. That shows contributions of research in dealing with optimization design of die geometry taking into account technological interactions related to the process and the ductile damage inside the deformed part. A set of solutions selected in particular points of the optimal Pareto front are also presented and analysed.

Prediction of Low Cycle Fatigue Life Using Cycles Jumping Integration Scheme

In this paper, cycles jumping scheme integration is used to numerically integrate fully coupled constitutive equations in order to predict the low cycle fatigue life under cyclic loading. This procedure avoids the calculation of the full loading cycles (some millions of loading cycles) while considering the transient stages due to the hardening (at the beginning) and the high damage-induced softening during the last tens of loading cycles. The model parameters have been identified using the results obtained from a 316L steel cylindrical specimen subject to symmetric tension-compression loading path. The effects of the specimen size as well as the mesh size on the fatigue life prediction are investigated.

Modelling and numerical simulation of thick sheet double slitting process using continuum damage mechanics

This work concerns the modelling and numerical simulation of specific thick sheet cutting process using advanced constitutive equations accounting for elasto-plasticity with mixed hardening fully coupled with isotropic ductile damage. First, the complex kinematics of the different tools is modelled with specific boundary conditions. Second, the fully and strongly coupled constitutive equations are summarized and the associated numerical aspects are shortly presented. An inverse material identification procedure is used to determine the convenient values of the material parameters. Finally, the double slitting process is numerically simulated and the influence of the main technological parameters studied focusing on the cutting forces.

Optimization of Forging Preforms by Using Pseudo Inverse Approach

A simplified method called “Pseudo Inverse Approach” (PIA) has been developed for axi-symmetrical cold forging modelling. The approach is based on the knowledge of the final part shape. Some intermediate configurations are introduced and corrected by using a free surface method to consider the deformation paths without classical contact treatment. A new direct algorithm of plasticity is developed using the notion of equivalent stress and the tensile curve, which leads to a very fast and robust plastic integration procedure. Numerical tests have shown that the Pseudo Inverse Approach is very fast compared to the incremental approach. In this paper, the PIA will be used in an optimization loop for the preliminary preform design in multi-stage forging processes. The optimization problem is to minimize the effective strain variation in the final part and the maximum forging force during the forging process. The numerical results of the optimization method using the PIA are compared to those using the classical incremental approaches to show the efficiency and limitations of the PIA.

Multi-objective optimization of gear forging process based on adaptive surrogate meta-models

In forging industry, net shape or near net shape forging of gears has been the subject of considerable research effort in the last few decades. So in this paper, a multi-objective optimization methodology of net shape gear forging process design has been discussed. The study is mainly done in four parts: building parametric CAD geometry model, simulating the forging process, fitting surrogate meta-models and optimizing the process by using an advanced algorithm. In order to maximally appropriate meta-models of the real response, an adaptive meta-model based design strategy has been applied. This is a continuous process: first, bui Id a preliminary version of the meta-models after the initial simulated calculations; second, improve the accuracy and update the meta-models by adding some new representative samplings. By using this iterative strategy, the number of the initial sample points for real numerical simulations is greatly decreased and the time for the forged gear design is significantly shortened. ...

An Adaptive Remeshing Procedure for Modeling the Clinch Forming Process

This work presents the case of a press clinching commonly met in the industry and denoted as TOX. The mechanical strength of the assembly is highly dependent on the final geometry of the clinched joint and among the numerous parameters which govern the process (applied load, lubrication, sheet thickness, friction, mechanical behavior of materials), the tool geometry plays a major role in the evolution of the final shape of the clinched joint. One of the objectives of this work is to provide an accurate numerical evolution of the final geometry of the clinched joint by the use of an adaptive remeshing procedure including error indicators and field variable transfer built by a meshless technique denoted as Diffuse Approximation. The resolution of the updated Lagrangian formulation is based on a static explicit approach (ABAQUS). Our numerical results are validated in comparison with experimental data.Copyright

2D Meshless Solution of Elastoplastic with Damage Problem

The Finite Element Method (FEM) is today the most widely used in numerical simulation of forming processes, due essentially to the continuous improvement of the FEM over the years and the simplicity of its implementation. However, this method has some limitations such as the distortion of elements under large inelastic deformation and the influence of the mesh on the results in several applications. The simulation of metal forming process with large plastic strain is a classical example where the successive remeshing is often the proposed solution in this case. But the remeshing raises the problems of precision and computing time. In this context and in order to avoid the remeshing process, a Meshless method is experimented in the solving of an elastoplastic problem coupled to the isotropic ductile damage. An Element Free Galerkin (EFG) method based on Moving Least Square (MLS) concept is considered in this proposal. A two-dimensional Mechanical problem was studied and solved by a Dynamic-Explicit resolution scheme where the material behaviour is based on an isotropic hardening fully coupled to ductile damage model. In a first step a parametric study is conducted in order to find the most influent parameters on the accuracy of the results. The effect of the number of nodes, of support nodes, of quadrature points, the effect of the time-step and the support domain size are analysed and optimal values are found. In a second step, the meshless results are compared with those of the finite element method and some concluding remarks relative to the accuracy and the computing time are given.