ABSTRACT
Abstract In this paper we emphasize the need for teaching the physical basis of fracture mechanics at both undergraduate and postgraduate level courses. It is recognised that much of fracture mechanics has developed a long way and is being applied without much reference to its basic physical principles. In a series of recent papers we have discussed with specific examples the dangers of this approach. False expectations can be easily be built upon arguments based on fallacious energy balance concepts and students should be made aware of these limitations. In particular the notion should be dispelled that plastic deformation (or other dissipative processes) increase the resistance to crack propagation (or toughness) by an amount which can be calculated from the rate of energy dissipation. The effect of plastic deformation or any other dissipative process is that of modifying (in general relaxing) the stress field at the crack tip thus reducing the magnitude of the crack driving force, whether expressed in terms of energy release rate or by means of the stress intensity factor.
