Franck Toussaint

Compartmentalized Model for the Mechanical Behavior of Titanium

As close as you watch them, the materials (especially metals) present discontinuities that can easily be qualified as strong. Dislocations, structures formed by these dislocations, phases and grains are all discontinuities, also sources of heterogeneity, with effects on material behavior that are not really well reproduced by a model based on a continuity assessment. Consequently, the materials should be considered as a set of compartments with different behaviors. This promotes an alternative way to define models. A coherent modeling process is probably the integration of the different behaviors of the material compartments within the global model. The objective is here to build an efficient elasto(visco)plastic model of the mechanical behavior of titanium combining compartmentalized behaviors. After setting the frame of the study, which is of primary importance, the proposed modeling process is running as follows (i) choose a local behavior, (ii) identify the parameters of crystalline texture that must be integrated into the simulation and (iii) finally formulate a way of combining local compartments behaviors. The intrinsic properties of Finite Element codes are used to achieve the integration of the whole system.

Characterization and Modeling of the Elastic Behavior of a XC68 Grade Steel Used at High Strain Rates and High Temperatures

This article discusses the characterization and modeling of the elastic behavior of a semi-hard steel used in incremental forming operations which implies great loading speeds at high temperatures and large springback after each passage of the roller. The knowledge of the elastic behavior is essential to correctly predict these springbacks during forming. The objective is therefore on the one hand the characterization of the elastic response of the material under different conditions and on the other hand the definition of a model that describes the material behavior with as much precision as possible. To this end, two models, one phenomenological and the other built on more physical basis, are considered.

FE simulation of a steel thin‐wall short‐tube forming process

This article concerns the forming of a steel thin‐wall short‐tube by an innovative small surface contact deformation process. A Finite Element model was built to predict the forming of the workpiece. The model controls the complex kinematics of the process. The problems associated with contact control and computation time are also investigated. Compared with measurements taken by the industrial partner, the first results obtained are highly promising, with regard to predicting both the workpiece geometry and the forces acting on the tools.

Experimental estimation of the Inelastic Heat Fraction from thermomechanical observations and inverse analysis

A new method to estimate the inelastic heat fraction (Taylor and Quinney Beta coefficient) during the deformation of a titanium material is proposed. It is based on (1) thermomechanical full field measurements during the loading and on (2) an inverse analysis. First, two cameras (a visible and an infrared) are used to measure the kinematic and the thermal fields on each face of a notched flat sample loaded in tension. Second, two coupled finite element simulations (a mechanical, then a thermal one) of the same tests are conducted. Associated with a Levenberg-Marquardt optimization algorithm, they are able to give, in a first step, optimized values of the anisotropic elastoplastic model parameters. Then, in a second step, parameters of four strain dependent Beta models are identified. Finally, the thermal responses of these models are compared to the experimental values.

Mixed Experimental and Numerical Study of Steel Ferrule Forming by Low-Contact Deformation Process

The present work aims to develop a steel ferrule forming by a low-contact deformation process using numerical analysis. Two Finite Elements (FE) models have been developed within ABAQUS. The first one is a 3D model that can both calculate the forming geometry of the part and the forces applied on the roller. The second one is a 2D axisymmetric model allowing reducing the CPU time without important loss of accuracy on the final part geometry. We present in this paper a mixed experimental/numerical comparison performed with each model and discuss the results with measurements coming from a part manufacturing by the industrial partner.Copyright