Molecular Dynamics Study on the Effect of Single Grain Boundary on the Mechanical Behavior of α-Quartz

Uniaxial compression test was performed on twinned crystal (TC) models and monocrystal (MC) α-quartz to study the effect of the single grain boundary on the strength and fracture of α-quartz. Based on the stress and strain curves, for any given strain rate, MC has a higher stress than any other TC. Based on the bond length changes, bond breaks are found in the TC but no bond break is found in the MC. Thus, the grain boundary causes stress concentration and leads to bond breakage. Larger transformation of bonds absorbs more energy, which results in lower bonding strength. Moreover, the fracture does not necessarily start from the grain boundary but also depends on the initially large bond length. The averaged mean square displacement (AMSD) is also calculated. For the results of MC, only one set of peaks corresponding to the maximum stress appears on the AMSD and strain curves. For TC, two sets of peaks indicate the largest stretching of bond length and the start of fractures, separately. These characteristics illustrate that the vibration of atoms will intensify when the structure reaches the limit of compressive strength.