10. Micromechanics of Fracture

The phenomenon of fracture of solids may be approached from different viewpoints depending on the scale of observation. At one extreme is the atomic approach where the phenomena take place in the material within distances of the order of 10⁻⁷ cm; at the other extreme is the continuum approach which models material behavior at distances greater than 10⁻² cm. In the atomic approach, the problem is studied using the concepts of quantum mechanics; the continuum approach uses the theories of continuum mechanics and classical thermodynamics. A different approach should be used to explain the phenomena that take place in the material between these two extreme scales: movement of dislocations; formation of subgrain boundary precipitates, slip bands, grain inclusions and voids. The complex nature of the phenomenon of fracture prohibits a unified treatment of the problem, and the existing theories deal with the subject either from the microscopic or the macroscopic point of view. Attempts have been made to bridge the gap between these two approaches.