The compression yield behaviour of polymethyl methacrylate over a wide range of temperatures and strain-rates
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The compression yield behaviour of PMMA has been investigated, here, over a wide range of experimental conditions which cannot be reached in tensile tests owing to the brittle nature of the material. The plot of the ratio of the compression yield stress to absolute temperature, as a function of the logarithm of the strain-rate, gives a set of parallel curves which can be accurately superimposed by shifting along a slanting straight line. A master curve is built from which the yield behaviour may be predicted for any state of stress, or value of temperature and strain-rate in the glassy range, using Bauwens' yield criterion.
The validity of the procedure is checked for compression tests at low temperatures, for tensile tests in the range of experimental conditions where PMMA yields and for torsional tests under hydrostatic pressure (data of Wardet al). In every case, the fit is found to be quite accurate.
A region of experimental conditions is determined where the compression yield behaviour may not be described by the Ree-Eyring treatment involving a hyperbolic sine function. In this region, the Bauwens approach, which consists of a modification of the Ree-Eyring theory, taking into account a distribution of relaxation times and linking the yield behaviour with theβ mechanical loss peak, is found to give an acceptable fit to the data.
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