Strain rate dependence of the anisotropic fracture toughness of rubber modified polypropylene films

A rubber modified cast polypropylene film has been tested by the essential work of fracture method to assess the effect of material orientation on the fracture toughness. The tests have been performed under different quasi-static rates, in order to analyze the strain rate effects on the material toughness: impact rates were also considered, but results are still at a preliminary stage. Results indicate a marked anisotropy with higher essential work of fracture values for cracks propagating transversally to the extrusion direction. Fracture toughness in both direction is substantially independent of testing speed up to 500 mm/min and markedly decreases under impact conditions. Furthermore, the specific essential work of fracture was partitioned into two terms, one representing the specific work for yielding up to the onset of fracture, and another term related to the specific work for subsequent necking and tearing. Scanning electron microscopy observations have been conducted to reveal fracture surfaces morphology.