Essential work of fracture: application for polymers showing ductile-to-brittle transition during fracture

The essential work of fracture (EWF) fails for the toughness determination of polymers showing a decrease of the specific work of fracture, as a funct ion of the specimen ligament. This type of behaviour was observed for poly( butylene terephthalate) (PBT) and its core/shell rubber modified blend (PBT /CS). It was found that this peculiar behaviour is due to a ductile-to-brit tle transition (DBT) in the crack propagation phase. Experimental data were corrected by considering only the ductile-fractured specimen area. When a non linear function of the type y=a+bx(-1) was applied for the corrected sp ecific work of fracture and ligament data, the specific essential work of f racture (w(e)) could be deduced. The latter being an inherent material toug hness parameter was compared with the critical J-integral (J(c)) values and a good correlation was found between them.