Time-temperature equivalence and adiabatic heating at large strains in high density polyethylene and ultrahigh molecular weight polyethylene

Time-temperature equivalence is a phenomenon common to many time-dependent material systems. This is typically used to generate loci of material properties as a function of temperature and strain-rate. Past work in polyethylene has shown the yield strength to obey a simple empirical temperature/strain-rate equivalence law, with one-decade increase in strain-rate approximately equivalent to a 10 K drop in temperature. This work extends this equivalence relation to continuous stress-strain curves in polyethylene for isothermal deformation states. Large strains are accommodated by invoking adiabatic heating at elevated strain-rates, and equivalence of the isothermal response under adiabatic conditions is checked by constructing a locus of isothermal flow stresses from a series of strain-rate jump tests. Good agreement between isothermal deformation response curves was found. Finally, the system of temperature/strain-rate equivalent curves was validated for large compressive deformations at ∼104 s−1 Taylor impact, with good agreement. Thus, temperature/strain-rate equivalence methods can be used to populate a high strain-rate constitutive description directly from continuous stress-strain curves from the laboratory without extrapolating to those states using an advanced constitutive model.

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