Effect of loading history and material’s structural state on the yield onset of a polymethylmethacrylate

Constant strain rate tests at different rates and stress-relaxation tests at different intensities of the applied strain were performed on a polymethylmethacrylate under uniaxial loading conditions. Shear yielding onset was properly determined for each of the applied loading histories. Following previous works, different quantities were evaluated at the onset of yielding to identify a parameter, which could be fit for the definition of a yield criterion that takes into account the effect of the mechanical history. The influence of the material structural state on the parameters’ values at the onset of yielding was examined too.