Determining the constitutive response of polymeric materials as a function of temperature and strain rate

摘要

Compression stress-strain measurements have been conducted on two commercial high temperature thermoplastic polymers (polyamideimide (PAI) and partially crystalline polyetheretherketone (PEEK)) as a function of temperature (-55 ℃ to 300 ℃) and strain rate (0.001 s~(-1) to 2500 s~(-1)). A split-Hopkinson pressure bar (SHPB) was used to achieve strain rates of about 2500 s~(-1) and conventional testing machines were used for strain rates from 0.001 s~(-1) to 1 s~(-1). A large variation in the mechanical response was observed over the range of temperatures tested for both polymers showing "yield" and "plastic" deformation below the glass transition temperature (T_g). Above T_g both thermoplastic polymers exhibited increasing loading moduli with increasing strain rate or decreasing temperature. T_g appears to shift to higher temperatures as the strain rate increases. Below T_g both thermoplastic polymers exhibited a yield-type behavior followed by anelastic deformation. PEEK was seen to be more sensitive to strain rate and temperature than PAI. A range of different flow stress versus strain behaviors was observed at different temperatures and strain rates.