Semicrystalline polymers deformation and fracture behaviour under quasistatic strain rates and triaxial states of stress

In this work both experimental and numerical results are presented for plain and notched Ultra-High Molecular Weight Polyethylene UHMWPE and Polyoxymethylene (POM) specimens. The experimental results include the true stress-strain curves, load-time curves and the fracture strains for different notch profile radii. Numerical simulations of the experiments have been carried out using the finite element code NIKE2D. The numerical results include load-time curves, variation of stress-triaxiality factor (defined as the ratio of mean stress σ_m to the von Mises effective stress σ_e) with radial strain for the center-most element for different notch radii, variation of local element strain rates with radial strain for different notch radii, radial distribution of local element strain at the minimum cross-section of notched specimen versus the non-dimensional radius and local element strain versus stress triaxiality factor at fracture. The experimental results for plain specimens show that the materials under investigation are sensitive to strain rate changes. The experimental results of the notched specimens indicate that the fracture strain decreases with reducing specimen notch profile radii. The combined experimental and numerical results indicated that Johnson-Cooke style fracture model may be used to predict the fracture of these polymers as a function of stress triaxiality.