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From microstructure towards plastic behaviour of single- and multiphase materials

Research project P5/08 (Research action P5)


Persons :


Description :

OBJECTIVE

To develop a set of constitutive models for the influence of various generic aspects of the microstructure on the plastic deformation of single- or multiphase metallic materials. The long term objective is to improve our understanding of materials behaviour in order to be able to design better advanced materials, and to design better products to be made from them. This implies (on medium to long term) that this knowledge must be implemented in finite element models for the deformation of engineering materials. The following generic aspects of the microstructure will be considered:

- number of phases (one, two, several);
- shape of second phase particles: spherical, lamellar;
- phase stability (for materials which feature stress-induced martensitic transformations or mechanical twinning);
- influence of grain size;
- influence of texture.

It has been decided that any modelling work that will be done, must be inspired by/validated by experimental work. In other words, the entire approach will start from experiments and will end with validation through experiments.
The models to be developed must be able to predict properties such as flow stress, work hardening, anisotropy of plastic properties, evolution of microstructural features and other state variables (dislocation density, texture, etc.) as deformation proceeds, and stability of plastic flow.
Recrystallisation will not be considered. Temperature effects will not be systematically studied.

MOTIVATION

Several satisfactory models which can predict the properties listed above have already been developed and have even been successfully implemented in elasto-plastic finite element codes. However, most of these models are restricted to comparatively conventional materials, or can only predict a restricted set of the properties listed above. There is a need for a systematic assessment of the influence of generic microstructural parameters, as advanced metallic materials for structural applications more and more tend to feature unconventional microstructures (nano- or submicron grain size, duplex structures, TRIP or TWIP effect, etc.)

WORK PLAN

Six model materials have been chosen which allow for a range of variations of the generic aspects of the microstructure listed above. They will be deformed in order to observe their mechanical response as well as the resulting development of microstructure and texture. This will increase our understanding of the mechanical behaviour of these materials both at macroscopic and microscopic level. This knowledge will then be used to develop two types of constitutive models:

- micro-macro models based on the knowledge of the physical deformation mechanisms at the nanometer or micrometer scale;
- models of a phenomenological type, containing parameters to be identified. The"inverse method" to determine the values of these parameters will also be used.

These models will then be implemented in elasto-plastic finite element models for the simulation of forming operations. All models developed will be validated by comparing their results to experimental observations.


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