The influence of temperature and strain rate on the tensile and compressive constitutive response of four fluoropolymers

Fluoropolymers posses several advantageous properties for load-bearing structural components including higher strength at elevated temperatures and higher toughness at lowered temperatures. Stress-strain studies have been conducted on two homopolymers (Teflon (PTFE) and KEL-F 81 (PCTFE)) and two copolymers (KEL-F 800 and THV 500G) as a function of temperature and strain rate. A split-Hopkinson pressure bar (SHPB) was used to achieve a strain rate of $\sim $3200/s in compression, while screw-driven testing machines afforded a strain rate of 0.001/s. A tensile split-Hopkinson pressure bar (T-SHPB) was used for testing at strain rates of 800/s in tension. To address the large strains to failure (up to 700% extension) an optical extensometer was employed for a strain rate of 0.005/s in tension. The effects of temperature and strain rate for this family of polymers is presented in detail, including an observed shift in glass transition ($T_{\rm g})$ to higher temperatures with increased strain rate and rate insensitivity of thermally-induced phase transitions