Microstructural evolution of Carrara marble during semi-brittle deformation

TL;DR

This study investigates how Carrara marble's microstructure evolves during semi-brittle deformation under various temperatures and strains, revealing mechanisms like twinning and dislocation activity, and proposing a microphysical deformation model.

Contribution

It provides detailed microstructural analysis and a phenomenological model for semi-brittle deformation of marble, highlighting temperature effects and deformation mechanisms.

Findings

Twins accommodate most shortening in early deformation.

Lattice curvature develops mainly in later stages.

Microfracture intensity correlates with strain.

Abstract

Fifteen marble samples were subjected to semi-brittle deformation through triaxial compression experiments, reaching axial strains of 0.5%, 1.0%, 2.0%, 4.0%, or 7.5% at temperatures of 20C, 200C, or 350C, under a confining pressure of 400 MPa. Deformation twins, lattice curvature, and intragranular microfractures in the samples were quantitatively characterised using forescattered electron images and electron backscatter diffraction. Microstructural analyses revealed that twins accommodate most of the shortening during the first 2% strain, whereas lattice curvature associated with geometrically necessary dislocations predominantly develops in the later stages. Intragranular fracture intensity exhibits an almost linear correlation with strain during the first 2% strain but increases more slowly thereafter. The mechanical data indicate a strong temperature dependence of yield stress, consistent with the temperature dependence of the critical resolved shear stress for dislocation glide. The subsequent strain hardening is likely caused by progressively increasing intensity of interactions among dislocations and between dislocations and twin boundaries. Based on the microstructural data and interpreted hardening mechanisms, we propose a phenomenological model, with microstructural state variables, for semi-brittle deformation at our experimental conditions as a step towards development of a microphysical constitutive model of semi-brittle deformation.