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Dynamic Plasticity and Failure of Microscale Glass: Rate-Dependent Ductile–Brittle–Ductile Transition
journal contribution
posted on 2019-02-27, 00:00 authored by Rajaprakash Ramachandramoorthy, Jakob Schwiedrzik, Laszlo Petho, Carlos Guerra-Nuñez, Damian Frey, Jean-Marc Breguet, Johann MichlerGlass
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.