Speaker: Prof. Charles Mareau

Abstract

The development of fatigue damage in metallic materials is a complex process influenced by both intrinsic (e.g. crystallographic texture, defects) and extrinsic (e.g. loading mode, frequency) factors. To better understand this process, some efforts have been made to develop microstructure-sensitive models that consider the impact of microstructural heterogeneities on the formation of fatigue cracks. Such models often use some indicators inspired by fatigue criteria (e.g. Dang Van, Fatemi-Socie) to determine whether the conditions for initiation are met are not. In this work, an alternative strategy is explored. It consists in combining the concepts of continuum damage mechanics with the framework of crystal plasticity to describe the nucleation and the early growth of fatigue cracks in metallic materials. Some possible strategies for the construction of constitutive relations, in either a local or a non-local form, will be exposed in this talk. Some numerical examples will also be presented. These examples allow discussing the ability of the proposed model to describe the impact of loading conditions and pre-existing defects on the fatigue behavior of metallic polycrystals.

Biography

• 2004-2007 - PhD - Ecole Nationale Supérieure d’Arts et Métiers - LPMM (now LEM3) - Metz
• 2008-2010 - Postdoctoral Fellow - Queen’s university - Dpt of Mechanical and Materials Engineering - Ontario
• Since 2010 - Assistant professor - Ecole Nationale Supérieure d’Arts et Métiers - LAMPA - Angers

Notes

• It is well known that crack initiation and propagation is impacted by material microstructure. The goal is to understand how microstructures influence crack initiation and propagation (short cracks) in early stage of fatigue damage.


• Experimental techniques (DIC, DCT, XRD…）provide very valuable information but there are limitations on spatial and temporal resolutions. Numerical modeling is used here as a way to obtain complementary information.


• Several numerical approaches have been proposed, from dicrete approaches (molecular dynamics), to crystal plasticity-based laws, covering different spatial scales.


• Here, an alternative approach consisting in combining a crystal plasticity-based law and damage mechanics by introducing damage variables in the constitutive law.


• Mean-field model and Full-field model can be used to model the fatigue damage in metallic polycrystals. In Mean-field model, each grain is treated as an inclusion and is considered as a composite material which is consisted of hard and soft phase. Results show that damage is driven by normal and tangential stresses. In addition, no direct damage-plasticity coupling exists, which allows reproducing the impact of loading conditions. As for Full-field model, more accurate description of the strain and stress fields are introduced. With non-local formulation, it allows the evaluation of surface energy.

Suggested readings

• C. Mareau
  A non-local damage model for the fatigue behaviour of metallic polycrystals.
  Philosophical Magazine. 100(8), 955-981, 2020.


• C. Mareau
  A thermodynamically consistent formulation of the Johnson–Cook model.
  Mechanics of Materials. 143, 103340, 2020.


• C. Mareau, M. R. Daymond
  Micromechanical modelling of twinning in polycrystalline materials: Application to magnesium.
  International Journal of Plasticity. 85, 156-171, 2016.


• H. Abdolvand, M. R. Daymond and C. Mareau
  Incorporation of twinning into a crystal plasticity finite element model: Evolution of lattice strains and texture in Zircaloy-2.
  International Journal of Plasticity. 27(11), 1721-1738, 2011.


• M. Boeff, H. Hassan and A. Hartmaier
  Micromechanical modeling of fatigue crack initiation in polycrystals.
  Journal of Materials Research. 32(23), 4375-4386, 2017.


• T. Bonniot, V. Doquet V. and S. H. Mai
  Fatigue crack growth under non-proportional mixed-mode I + II. Role of compression while shearing.
  International Journal of Fatigue. Volume 134, 2020