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Determination of the properties of plastics at high strain rates.

Dean, G; Mera, R D; Arranz, E (2002) Determination of the properties of plastics at high strain rates. NPL Report. MATC(A)116

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Computerised design methods are available for predicting the performance of tough plastics under impact loading. These methods require stress/strain data over a wide range of strain rates. These data are most conveniently measured in tension, but ISO standards for tensile property measurements are currently only applicable for strain rates up to around 0.1 s-1. To simulate behaviour under impact, data are required at rates 3 or 4 orders of magnitude higher than this. For accurate data acquisition at these higher rates, attention needs to be paid to apparatus design in order to minimise contributions from transient forces arising from resonances and the propagation of a shock wave pulse in the specimen. In addition, procedures and extensometers are not routinely available for determining strains at higher rates of deformation.
Furthermore, even at low strain rates, there are no standard procedures for measuring the strain in specimens that undergo non-uniform deformation (necking is an extreme example) in the specimen gauge length at strains above that corresponding to the stress maximum. ISO standards specify the determination of a nominal or average strain.
The attached paper illustrates the acquisition of data over a wide range of strain rate through a combination of measurements at low and moderate strain rates with extrapolation of these data to higher rate. Extrapolation is achieved by the use of mathematical functions to model the stress/strain curves and the rate dependence of parameters. A new tensile test specimen is proposed for the measurement of behaviour at moderate and large strains.

Item Type: Report/Guide (NPL Report)
NPL Report No.: MATC(A)116
Subjects: Advanced Materials
Advanced Materials > Polymers
Last Modified: 02 Feb 2018 13:17
URI: http://eprintspublications.npl.co.uk/id/eprint/2462

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