A common way of including damage in constitutive models is by utilising the Kachanov formalism [1] in which a damage parameter D is introduced to account for a loss of the load bearing capacity of a deforming material. Evolution equations describing the growth of damage in the process of deformation are part of such constitutive formulations [2,3]. As the physical nature of the damage variable D is rarely identified, the form of these evolution equations is usually chosen in a heuristic way. A more sound approach to damage was proposed by Ashby and Dyson [4]. In their excellent review they provide a catalogue of possible damage mechanisms, identify cases describable by the Kachanov formalism [1] and discuss the physical significance of the damage variable D.
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