Fracture Mechanics of an Elastic Softening Material like Concrete

Concrete is modelled as a linear elastic softening material and introduced into fracture mechanics. A discrete crack is considered with softening zones at the crack tips. Following the approach of Dugdale/Barenblatt, closing stresses are applied to the crack faces in the softening zone. The stresses are described by a power function. Relations are worked out between the remote stress on a cracked plate, the tensile strength of the material and the size of the softening zone. The finite width of a plate is considered and so are various stress distributions of the softening zone. Experiments were performed to estabilish the stress-strain behaviour of concrete in deformation-controlled uniaxial tensile loading. Furthermore, it was investigated whether cyclic loading affects the static envelope curve. A qualitative model is presented which illustrates the effect of prepeak cyclic loading on deformation and stress distribution in a specimen. The results show that nonlinear fracture mechanics can be applied to concrete. The loadbearing capacity of a cracked plate can be predicted with reasonable accuracy. As appears from the experiments, the application of this approach to cyclic loading is very promising.