Viscoplastic Rheology of α‐Quartz Investigated by Nanoindentation

다국어 초록 (Multilingual Abstract)

Quartz is an abundant mineral in Earth's crust whose mechanical behavior plays a significant role in the deformation of the continental lithosphere. However, the viscoplastic rheology of quartz is difficult to measure experimentally at low temperatures without high confining pressures due to the tendency of quartz (and other geologic materials) to fracture under these conditions. Instrumented nanoindentation experiments inhibit cracking even at ambient conditions, by imposing locally high mean stress, allowing for the measurement of the viscoplastic rheology of hard materials over a wide range of temperatures. Here we measure the indentation hardness of four synthetic quartz specimens and one natural quartz specimen with varying water contents over a temperature range of 23°C to 500°C. Yield stress, which is calculated from hardness but is model dependent, is fit to a constitutive flow law for low‐temperature plasticity to estimate the athermal Peierls stress of quartz. Below 500°C, the yield stresses presented here are lower than those obtained by extrapolating a flow law constrained by experiments at higher temperatures irrespective of the applied model. Indentation hardness and yield stress depend weakly on crystallographic orientation but show no dependence on water content.
Quartz is an important mineral in the Earth's crust whose strength can be affected both by temperature and the amount of water contained in its crystal structure. At low temperatures, it is often difficult to measure the strength of quartz because many minerals tend to fracture without high confining pressure. Here we report measurements of the strength of quartz at temperatures between 23°C to 500°C using a nanometer scale diamond tip which prevents the sample from cracking during deformation. We explore several models for determining the yield stress of quartz at these temperatures and report flow laws, which can be used to describe the mechanical behavior of quartz at low‐temperature and high‐stress conditions. We find that quartz strength in these experiments does not depend on the amount of water in the crystal structure but does depend on crystallographic orientation. Increasing temperature results in weakening of quartz.



Indentation hardness of quartz is determined by more than 2,200 nanoindentation measurements between 23°C and 500°C

Indentation hardness and calculated yield stress decrease with temperature and show no dependence on water content

The athermal yield stress of quartz is constrained by a flow law for low‐temperature plasticity


Indentation hardness of quartz is determined by more than 2,200 nanoindentation measurements between 23°C and 500°C
Indentation hardness and calculated yield stress decrease with temperature and show no dependence on water content
The athermal yield stress of quartz is constrained by a flow law for low‐temperature plasticity