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°C to 300°C) 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, 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.
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Cady et al. (2003) studied this question.