
Modelling fracture processes in orthopaedic implants 339
Especially in materials sintered at the interface between grains cracks may
appear, which under the in uence of loads will initiate the development of a
fracture. To describe fracture resistance, the stress intensity factor K is used,
expressed by the formula:
[11.5]
where:
σ is the stress in the element (MPa) and
a is the crack length (m).
When the value of K is large, then at a given level of tensile stress, σ , there
may be a longer crack, a , in the product. Small values of K mean that the
existence of a very short crack is possible. Ceramic has very small ...