The influence of intrinsic strain softening on the macroscopic deformation behaviour of amorphous polymers

In the present study the intrinsic strain softening behaviour of amorphous polymers is investigated. Intrinsic strain softening induces localisation phenomena in tensile deformation which are a key factor in the brittle fracture process of for instance PS and PMMA. Our hypothesis is, that by reducing the strain softening localisation of strain can be reduced or eliminated and tough macroscopic deformation behaviour can be obtained. From literature it is known that a thermal or mechanical pre-treatment of thematerial can reduce the amount of strain softening or the so-called ’yield-drop’. Therefore, tensile bars of PS and PMMA are tested in compression at different temperatures and strain rates to investigate the intrinsic properties. Next tensile tests are performed to examine the effects of the altered intrinsic properties on the macroscopic deformation behaviour. PS and PMMA prove to deform ductile at elevated temperatures and low strain rates. Examining the yield-drop as function of temperature and strain rate points out that under a certain level of yield-drop, macroscopic tough deformation behaviour is observed. Tensile bars of PS and PC are also subjected to mechanical rejuvenation. A subsequent tensile and compression tests shows that due to the reduction of strain softening tough deformation behaviour is obtained for PS, and homogeneous deformation without necking is observed in PC.