Effect of temperature and strain rate on the constitutive behaviour of oriented polypropylene tubes

The lighter weight of thermoplastics compared with metals make these materials an attractive alternative for automotive structural components. In particular, oriented thermoplastic tubes, typically uniaxially or biaxially oriented by an extrusion process, possess increased strength along the orientation directions. In addition to their good strength, the ductility of these materials, when formed at elevated temperatures, is also improved. For development of analytical and/or finite element models of the elevated-temperature forming of uniaxially oriented thermoplastic tubes, suitable constitutive models describing the temperature- and strain-rate-dependent stress—strain behaviour of the material along the axial (or orientation) and hoop (perpendicular to orientation) direction are required. The behaviours along both directions of the tube are required since its properties are anisotropic as a result of the extrusion process. The G'Sell et al. constitutive model, modified in this study to account for the effect of temperature, was shown to capture the uniaxial behaviour of oriented polypropylene tubes accurately along the axial and hoop direction at a range of elevated temperatures and strain rates.