A study on ion‐exchanged, soda‐lime glass’s residual stress relationship with K+/Na+ concentration

In the past, studies have shown that the chemical composition within the exchanged layer could influence both the stress build‐up magnitude and the stress relaxation rate. In this work, a novel approach was proposed to estimate the relationship between the stress relaxation parameters, the dilation coefficient, and the relative K+/Na+ concentration. The proposed method required knowledge of the residual stress profiles, the molten salt bath’s temperature and soaking time, and the bath’s composition. Based on the analyses performed on various residual stress profiles in ion‐exchanged soda‐lime glass, both the dilation coefficient and the magnitudes of the relaxation time constants were found to consistently decrease with K2O concentration.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152723/1/ijag14077.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152723/2/ijag14077_am.pd

Rheological Controls on Asperity Weakening During Earthquake Slip

International audienceEvolution of fault strength during the initial stages of seismic slip plays an important role in the onset of velocity-induced weakening, which in turn, leads to larger earthquake events. A key dynamic weakening mechanism during the early stages of slip is flash heating, where stress concentrations at contacts on the interface lead to the rapid generation of heat. Although potential weakening from flash heating has been extensively modeled, there is little recorded microstructural evidence of its physical manifestations. We present results of a series of triaxial experiments on synthetic faults in quartz sandstone. Samples were subjected to a variety of normal stresses and ambient temperatures, to induce a range of slip event sizes and sliding velocities. We show the microstructural evolution of asperity interactions from the onset of flash heating through to the formation of grain-scale areas of sheared melt. Using microstructural observations and mechanical data from the experiments, we model temperature and the viscoelastic behavior of the glass. Results suggest that, in the earliest stages of slip asperity contacts melt, but temperatures remain too low for viscous shear to occur within the melt layer. Instead melted asperities behave as glassy solids, facilitating continued frictional heating. With further slip, increased asperity temperatures allow the transition to viscous shear within the melt layer, facilitating weakening. These results highlight the dynamic evolution of the viscoelastic properties of the melt and resulting effects on asperity strength. Such complexity has, to-date, not been fully addressed in modeling of flash heating