ABSTRACT
The fracture process was always considered to occur at the tip of a sharp crack, either real or equivalent. However, such models are strictly applicable only when the fracture process zone is small compared to the relevant dimensions of the specimen. Furthermore, they neglect a detailed description of what is happening in the fracture process zone because they lump it all into the crack tip. This chapter introduces the simplest models that describe the fracture process in full, albeit with many simplifications. Such full description is essential when the crack length or other dimensions of the specimen are small relative to a fully developed fracture process zone, which is a common situation for structures of concrete and tough ceramics. The main ingredient of the cohesive crack model is the softening curve of the material, which, in a sense, replaces the stress-strain curve in theories such as plasticity.
