This book contains the lectures of the 5th Advanced Seminar on Fracture Mechanics (ASFM 5) held at the Joint Research Centre, Ispra, on 14-18 October 1985. The series of the ASFMs is one of the two main regularly scheduled international events sponsored by the European Group on Fracture (EGF) , alternating with the European Conferences of Fracture (ECFS). Whereas ECFs are held in a different place on even years (the last. ECF6,was in Amsterdam in June 1986), ASFMs are hosted at the JRC­ Ispra on odd years. This establishment belonging to the Commission of the European Communities performs research work of common interest to the EC Member countries. One of the activities of the JRC-Ispra is the organization of Ispra-Courses aiming at the transfer of knowledge and the strengthening of exchanges and ties between European scientific workers. ASFMs are designed to give an advanced level treatment in selected areas of fracture mechanics. Previous ASFMs had been devoted to elastic-plastic fracture mechanics and to subcritical crack growth due to fatigue, stress corrosion and creep. In the early stages of preparation of ASFM5 it was decided to concentrate on a new theme, the fracture phenomena and fracture mechanics of non-metallic materials. Whereas fracture mechanics started with the study of glass by Griffith, its later developments centered predominantly on metallic alloys. However, in recent years non-metallic materials have found increasing uses and correspondingly efforts have been made to develop testing and prediction methods for these materials.