This paper explains, using fracture mechanics principles, that common size effects observed in the fracture toughness of concrete and similar materials can be clarified by failures of test samples with crack tips close to either front or back surfaces. From…
This paper explains, using fracture mechanics principles, that common size effects observed in the fracture toughness of concrete and similar materials can be clarified by failures of test samples with crack tips close to either front or back surfaces. From the strength and toughness criteria a simple asymptotic function, akin to the original Bazant's size effect law, is acquired for edge cracks at the front surfaces. The key parameter used in the asymptotic function, the reference crack length a*, is similar to the original Hillerborg's characteristic length Ith introduced for concrete. The size effect due to crack tips close to the back surfaces is further considered by a local energy distribution function gf. It shows that the size effects in toughness are inevitable when the distance from a crack tip to either front or back surface is comparable to the crack-tip fracture process zone.