Dynamic Plasticity and Failure of Microscale Glass: Rate-Dependent Ductile-Brittle-Ductile Transition.

Glass has been recently envisioned as a stronger and more robust alternative to silicon in microelectromechanical system applications, including high-frequency resonators and switches. Identifying the dynamic mechanical properties of microscale glass is thus vital for understanding their ability to withstand shocks and vibrations in such demanding applications. However, despite nearly half a century of research, the micromechanical properties of glass and amorphous materials in general are primarily limited to quasi-static strain rates below ∼0.1/s. Here, we report the in situ high-strain-rate experiments of fused silica micropillars inside a scanning electron microscope at strain rates up to 1335/s. A remarkable ductile-brittle-ductile failure mode transition was observed at increasing strain rates from 0.0008 to 1335/s as the deformation flow transitions between homogeneous-serrated-homogeneous regimes. Detailed surface topography investigation of the tested micropillars revealed that at the intermediate strain rate (<∼6/s) serrated flow regime, the load drops are caused by the sequential propagation of individual shear bands. Further, analytical calculations and finite element simulations suggest that the atomistic mechanism responsible for the homogeneous stress-strain curves at very high strain rates (>∼64/s) can be attributed to the simultaneous nucleation of multiple shear bands along with dissipative deformation heating. This unique rate-dependent deformation behavior of the glass micropillars highlights the importance and need of extending such microscale high-strain-rate studies to other amorphous materials such as metallic glasses and amorphous metals and alloys. Such investigations can provide critical insights about the damage tolerance and crashworthiness of these materials for real-life applications.