CREEP FRACTURE IN BONES WITH DIFFERENT STIFFNESSES

Creep fracture experiments were used to examine the differences in time to fracture of bones with very different Young's moduli (bovine bone and red deer antler) and the implications of these differences for the 'cumulative-damage' model of Caler and Carter [J. Biomechanics 22, 625-635 (1989)] for bone fracture. Using normalised stress as the explanatory variable, the slopes of the distributions agreed quite well with that of Caler and Carter for human bone. However, antler took far longer to fracture at any given normalised stress than did bovine bone. Using stress alone as the explanatory variable, the relationships within each bone type almost disappeared. Within any bone type strain is the important determinant of time to fracture, but less mineralised bone takes much longer to fracture at any given strain, or normalised stress, which seems not to be in accord with the cumulative-damage model. The rate of damage accumulation in lightly mineralised bone at high strains (> 1%) is much less than that occurring in more heavily mineralised bone.