In-situ SEM micropillar compression and nanoindentation testing of SU-8 polymer up to 1000 s-1 strain rate

In situ micropillar compression and nanoindentation were performed on photolithographically fabricated SU -8 polymer inside a scanning electron microscope (SEM), covering seven orders of strain rates from 10-3 to 103 s-1. The extracted mechanical properties - modulus, hardness, yield strength, strain rate sensitivity (SRS) exponent - were systematically compared from both microscale tests and showed excellent agreement. No change in deformation mechanism was observed at high strain rates. We report a novel experimental protocol for high strain rate nanoindentation, comprising of input profile smoothing, that minimizes resonance amplitude during unloading and allows reliable extraction of modulus and hardness using standard Oliver-Pharr analysis. To the best of our knowledge, this is the first report of mechanical properties of SU -8 beyond 1 s-1 strain rate using nanoindentation based tests.