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(et hylene terephthalate) (BOPET), that was studied by the Essential Work of Fr acture (EWF) method. The influence of specimen thickness and molecular orie ntation was investigated. The results show that this method is a useful alt ernative for studying the plane-stress fracture of this material, finding t hat the specific essential work of fracture is strongly affected by the ori entation [w(e) was smaller in the direction of extrusion (MD) than in the p erpendicular one (TD)], but independent of the specimen thickness in a rang e from 50 to 250 mu m. On the other hand, the plastic work item is sensitiv e to variations of thickness but does not depend on orientation. (C) 2000 E lsevier Science Ltd. All rights reserved.