Essential work of fracture on PET films:: influence of the thickness and the orientation

This paper presents the fracture behaviour of films of a bioriented poly(ethylene terephthalate) (BOPET), that was studied by the Essential Work of Fracture (EWF) method. The influence of specimen thickness and molecular orientation was investigated. The results show that this method is a useful alternative for studying the plane-stress fracture of this material, finding that the specific essential work of fracture is strongly affected by the orientation [w(e) was smaller in the direction of extrusion (MD) than in the perpendicular one (TD)], but independent of the specimen thickness in a range from 50 to 250 mu m. On the other hand, the plastic work item is sensitive to variations of thickness but does not depend on orientation. (C) 2000 Elsevier Science Ltd. All rights reserved.