Session C06: Dynamic Compression of Polymers: Part I

High-pressure constitutive response of filled and unfilled silicones

Shear strength under dynamic compression loading has been measured for a range of silicone materials. Pressure-shear plate impact (PSPI) tests revealed that microfiller content had a modest effect on strength. Like prior particle tracking data, strain-rate sensitivity was found to be negligible. Unlike filler content and strain rate, pressure exerted a large effect on flow strength, as has been previously observed for other polymers. Finite element simulations and Bayesian regression permitted a strength model to be calibrated directly against the measured PSPI target velocities. This approach bypasses the usual PSPI analysis assumptions, which loosens the requirements for test validity, along with providing uncertainty measures. The result is a simple model which can be applied to a range of silicones with relatively well characterized uncertainty.   

Dynamic Strength in Polymethylmethacrylate

Polymethylmethacrylate (PMMA) is used in shock loading and dynamic applications as windows and as a standard material. A study by Bat’kov, et al. revealed a dramatic decrease in PMMA shear strength above 6 GPa. In this study, we use planar shock loading using gas gun drive to understand this phenomenon, in contrast to Bat’kov, et al. who used explosive loading.  Two experiments above 6 GPa are combined with previous experiments on PMMA to validate the

decrease in shear strength.   

Shock dissipation through epoxy materials with engineered internal domains, glass transitions, and isomers

Using a new synthesis, the structure of a phase-separating epoxy material can be tuned to consist of periodic internal soft and hard domains, ranging in length scales from nano- to micro-scale dimensions. Tuning these structures also results in materials with a broad distribution of glass transitions. In this work we showed an increase in interfaces between hard and soft domains, on the scale of 100's of nanometers, and a broad glass transition dissipates the shock energy more than domains on the micron scale with a narrow glass transition. The dominating mechanism is discussed. We also showed there is no shock dissipation mechanism through an epoxy with a negative coefficient for thermal expansion due to isomeric rearrangement at high temperature.