Effect of the specimen dimensions and the test speed on the fracture toughness of iPP by the essential work of fracture (EWF) method

The fracture parameters of an isotactic polypropylene are studied by the es sential work of fracture method. The influence of the specimen height, widt h and thickness and the effect of the test speed are investigated. Results show that this method is very useful for studying the plane-stress fracture of this kind of materials in form of films and sheets. Varying the width ( 30 to 60 mm) and the test speed (2 to 100 mm/min) has no relevant influence , whereas the results are only length independent in a range from 40 to 100 mm. The influence of the thickness is very high, obtaining an important de crease of the specific essential work as the thickness is increased in a ra nge from 38 to 2500 mu m. This result is justified with the fracture surfac es obtained, observed by SEM, in which an evolution of the fracture behavio r is seen as a function of thickness (38, 100, 500, 1000, 2500 mu m). (C) 1 999 John Wiley & Sons, Inc.