A new finite element approach to model microscale strain localization within olivine aggregates

Jean Furstoss,Carole Petit,Marc Bernacki,Daniel Pino-Muñoz,Clément Ganino

doi:10.5194/se-12-2369-2021

Abstract

Abstract. This paper presents a new mesoscopic full field approach for the modeling of microstructural evolutions and mechanical behavior of olivine aggregates. The mechanical framework is based on a reduced crystal plasticity (CP) formulation which is adapted to account for non-dislocation glide strain-accommodating mechanisms in olivine polycrystals. This mechanical description is coupled with a mixed velocity–pressure finite element (FE) formulation through a classical crystal plasticity finite element method (CPFEM) approach. The microstructural evolutions, such as grain boundary migration and dynamic recrystallization, are also computed within a FE framework using an implicit description of the polycrystal through the level-set approach. This numerical framework is used to study the strain localization, at the polycrystal scale, on different types of pre-existing shear zones for thermomechanical conditions relevant to laboratory experiments. We show that both fine-grained and crystallographic textured pre-existing bands favor strain localization at the sample scale. The combination of both processes has a large effect on strain localization, which emphasizes the importance of these two microstructural characteristics (texture and grain size) on the mechanical behavior of the aggregate. Table 1 summarizes the list of the acronyms used in the following.

Highlights

Strain localization is of first importance in the development and evolution of a tectonic plate regime (Tommasi et al, 2009)
In order to account for the continuous nature of the DRX in olivine, we propose to model the sub-grain rotation (SGR) process by considering each nucleus as a sub-grain surrounded by low-angle GB (LAGB)
The mechanical framework, based on a reduced-crystal plasticity (CP) formulation adapted for the specificities of olivine, is able to capture creep regimes controlled by both grain boundaries (e.g., grain boundary sliding (GBS)) and grain interiors

Summary

Introduction

Strain localization is of first importance in the development and evolution of a tectonic plate regime (Tommasi et al, 2009). The strain localizing mechanisms are often studied considering upper mantle rocks, which are mainly composed of olivine. The initiation of this localization takes place at different scales and is the result of different physical processes. Two main mechanisms are often invoked: the plastic anisotropy of olivine (Tommasi et al, 2009) and the relatively weaker behavior of fine grained olivine polycrystals compared to coarse grained aggregates when deformed under grain-sizesensitive (GSS) creep (Braun et al, 1999).

Results

Discussion

Conclusion