Boundary effect on specific fracture energy of concrete

The influence of specimen back-face boundary on the shape and size of the crack-tip fracture process zone during crack growth is related to the fracture energy distribution along the crack path. The governing mechanism responsible for the size effect on the specific fracture energy of concrete is the height variation of the crack-tip fracture process zone. Such a height variation exists in the boundary zone where the development of the crack-tip fracture process zone is limited due to the confined space and sharp stress gradient. The reduction in the fracture process zone height leads to a decreasing specific fracture energy distribution along the crack path in the back-face boundary region. The adhesive thickness effect on the critical energy release rate of the adhesive joint sandwiched between two non-yielding substrates and the un-cracked ligament effect on the large scale yielding of polymers and metals provide further proof to the relationship between the height variation of the crack-tip plastic zone and the specific fracture energy.