Plastic banding in glassy polycarbonate under plane simple shear

Samples of amorphous polycarbonate were tested in plane simple shear at various temp. (--100 - +150 deg C) and shear rates (3 x 10 exp --5 -3 x 10 exp --2 s exp --1 ). In the glassy state, it was observed that the deformation concentrated at yield inside a single shear band whose elongation and widening phases correspond to well marked stages of the recorded stress--strain curve. Birefringence and X-ray diffraction in the growing band show that the molecular orientation follows a pseudoaffine evolution with the local plastic strain. Although the shear is inhomogeneous during the growth of the shear band, it is fairly uniform inside the band itself, down to the scale of 100 nm. After the band has completed its widening (for an overall shear of approx 0.9) the overall shear in the whole specimen is homogeneous and then one can deduce the constitutive equation for steady state plasticity of the glassy material, up to shear strains as large as 2.0. It is characterized by a linear strain hardening whose value, such as the extrapolated yield stress, decreases gradually with temp. 48 ref.--AA