Stick-slip instabilities and shear strain localization in amorphous materials

Eric G. Daub, & Jean M. Carlson

Published 2009, SCEC Contribution #1319

We study the impact of strain localization on the stability of frictional slipping in dense amorphous materials. We model the material using Shear Transformation Zone (STZ) Theory, a continuum approximation for plastic deformation in amorphous solids. In the STZ model, the internal state is quantified by an elective disorder temperature, and the elective temperature dynamics capture the spontaneous localization of strain. We study the elect of strain localization on stick-slip instabilities by coupling the STZ model to a non-inertial spring slider system. We perform a linear stability analysis to generate a phase diagram that connects the small scale physics of strain localization to the macroscopic stability of sliding. Our calculations determine the values of spring stillness and driving velocity where steady sliding becomes unstable, and we confirm our results through numerical integration. We investigate both homogeneous deformation, where no shear band forms, and localized deformation, where a narrow shear band spontaneously forms and accommodates all of the deformation. Our results show that at a given velocity, strain localization leads to unstable frictional sliding at a much larger spring stillness compared to homogeneous deformation, and that localized deformation cannot be approximated by a homogeneous model with a narrower material. We also find that strain localization provides a physical mechanism for irregular stick-slip cycles in certain parameter ranges. Our results quantitatively connect the internal physics of deformation in amorphous materials to the larger scale frictional dynamics of stick-slip.

Citation
Daub, E. G., & Carlson, J. M. (2009). Stick-slip instabilities and shear strain localization in amorphous materials. Physical Review E, 80, 066113.