Characterization of material ductility of PP/EPR/talc blend under wide range of stress triaxiality at intermediate and high strain rates

Abstract

A ductile fracture locus formulated, in the space of the effective plastic strain to fracture and the stress triaxiality for the polypropylene (PP) blended with ethylene-propylene rubber (EPR) and talc fillers is obtained at the intermediate and high strain rates by using a combined experimental-numerical approach. Biaxial loading tests on the flat butterfly specimens are carried out to characterize fracture behaviors under pure shear, combined shear and tension, pure tensile loading conditions at various loading velocities. Corresponding finite element analysis is performed to determine the evolution of stress, strain, and strain rate states. It is found that the material ductility strongly depends on the stress triaxiality for the present PP/EPR/talc blend. Meanwhile, the fracture surfaces are observed by scanning electron microscopy, revealing that there exist two competing failure mechanisms: the multiple crazing at high positive stress triaxialities and void-sheeting like fracture mode at the low stress triaxiality. The transition of the failure modes occurs in the intermediate range of stress triaxialities. The obtained fracture locus covers a wide range of the stress triaxiality. It would be applicable to the fracture analysis of real automotive components such as interior or exterior polymeric components under various impact loading conditions. © 2008 Wiley Periodicals, Inc.