Scaling of specimen boundary effect on quasi-brittle fracture

The size effect on quasi-brittle fracture is modelled by considering tile distance of crack-tip to specimen boundary. It is shown that the tensile strength criterion applies if specimen boundary is very closeto the crack-tip, and the fracture toughness criterion applies if specimen boundary is far away from the cracktip. The specimen boundary influence captures the mechanism of size effect, i.e. the interaction of the cracktip fracture process zone with specimen boundary. The boundary effect model proposed in the study is thencompared with the common size effect model, which emphasizes the specimen size influence, by analysing the same experimental results.