rd, C

c gr terms which modify the response of the standard elastic macroscopic continuum: one internal length the tips of sharp cracks. This is commonly ascribed to the lack of microstructural information in classical elasticity. In order to describe the mechanical behaviour of complex struc-tures such as human bones and take into account the information from the different levels of observation, multiscale modelling tech-niques should be used. Several multiscale modelling strategies exist. A straightforward, but computationally intensive approach to represent the underlying microstructure. In its simpler form gra-dient elasticity involves one additional term, the Laplacian of a Hookean-like stress in the standard stress–strain law of classical elasticity (Aifantis, 1992). Of particular significance for the model-ling of fracture is the capability of gradient elasticity to simulate stresses and strains around the tips of sharp cracks without the singularities that appear in classical elasticity (see, for example, Ru and Aifantis, 1993; Altan and Aifantis, 1997 for the first preli-minary considerations on this topic). In this connection it is also re-marked that gradient elasticity has also been used (Aifantis, 1999) * Corresponding author