Flow stress peaks at high strain rates in PMMA

Abstract

The results of an investigation into the stress-strain behaviour of PMMA in the strain rate region of 10 to 10 s over a range of temperatures from room temperature up to 90xC are reported. The investigation was carried out in an effort to detect the presence, or absence, of peaks in the flow stress – strain rate response. All tests were carried out in compression on a standard Hopkinson Bar system. Although not as clearly defined as the sharp peak in flow stress reported by previous workers in PEEK, there is good evidence of a peak in the flow stress in the strain rate range 10 to 10 which both narrows and moves to a higher strain rate as the temperature approaches the glass transition. Previously reported peaks in flow stress had only been observed in semi-crystalline polymers. The current observations in PMMA suggest that this may be a universal phenomenon. Preliminary work at similar strain rates and temperature ranges on PCTFE, show less conclusive indications of peaks in the flow stress at strain rates around 3r10 s.