Inelastic Deformation Behaviour of Polypropylene in Large Strain Region and after Cyclic Preloadings

Inelastic deformation behaviour of polypropylene in tensile large strain region and after axial pre-cyclings is investigated experimentally and analysed using the three-element model based on the overstress theory. In this experiment, cylindrical tubular specimen as well as solid bar specimen are used for torsional loading and volume change is measured to get the true stress-true strain curves. It is found that flow stress is almost constant in strain range of more than 0.1, Poisson’s ratio varies depending on strains and the viscosity does not change even after cyclic preloadings in tension, torsion, and compression. The quasi-static stress-strain curve g is represented as a function of temperature. Good agreement can be obtained between predicted results based on obtained constitutive equations having the first invariant of stress (static pressure) effect and the experimental results on both the flow stress and relaxation