Polycarbonate was subjected to static tests under several loading conditions (simple tension and compression, bi-axial tension, and torsion under hydrostatic pressure) at room temperature at a constant low strain rate. Simultaneous readings of longitudinal and circumferential strains of a specimen were obtained continuously during the loading period until the onset of instability or necking appeared.
Particular attention was given to the importance of the anelastic component of strains for ductility of polycarbonate. Careful observations were made on the anelastic deformation of solid bars during uniform tensile or compressive deformation, and of thin-walled tubes subjected to various combinations of axial tension and internal pressure. The stress-strain relations of all the tests were compared each other in terms of maximum shear stress and maximum shear strain.
There was no consistency in the stress-strain curves for all the tests, owing to the effect of mean normal stress (hydrostatic pressure) on the stress-strain relation for polymeric solids. From these stress-strain curves, plots of the maximum shear stress versus the mean normal stress at corresponding strain in each test were produced, and it was observed that the maximum shear stress increased linearly with hydrostatic compression up to the yield point but decreased rapidly under hydrostatic tension.
