A New LEFM based description of concrete fracture and size effects

Concrete is a so called quasi-brittle material which, despite predominantly elastic material response, exhibits in tension loading a stable non-linear fracture response, when tested under displacement control. The reason for the non-linearity is the development of a fracture process zone, in front of the crack, due to micro-cracking and crack bridging. It has become increasingly popular to model the fracture process zone with different cohesive zone models. However, their use requires sophisticated finite element modeling and their success is directly related to the correctness of the assumed stress relaxation in the fracture process zone. An alternative is to use LEFM combined with an effective crack length. The effect of the fracture process zone is to make the specimen sense the crack as being longer than a0+?a. The fracture process zone causes thus an effective increase in the crack driving force but also the apparent fracture resistance increases since the fracture process zone effectively "blunts" the crack tip. This simple method, that does not require any finite element modeling, can be used as an aid to select the proper cohesive zone model for more sophisticated modeling