Silvio Valente

Is Mode II fracture energy a real material property

Abstract An experimental and numerical investigation is carried out for a particular testing geometry: a single-edge notched specimen subjected to four-point shear, where a mixed-mode crack propagation is activated in concrete, if the specimen is not too small and the aggregates are not too large. When both conditions are verified each crack growth step is governed locally by a mode I strain field and the energy dissipation is tendentially provided by the fracture energy G F , whereas permanent deformation in the bulk material and interlocking on the crack surface are negligible.

Cohesive crack model description of ductile to brittle size-scale transition: dimensional analysis vs. renormalization group theory

The present paper is a review of the research works carried out on the cohesive crack model and its applications at the Politecnico di Torino during the last decade. The topic encompasses experimental, numerical and theoretical aspects of the cohesive crack model. The research work followed two main directions. The earlywork concerns the development and the implementation of the cohesive crack model, which has been shown to be able to simulate experiments on concrete specimens and structures. It is referred to as the dimensional analysis approach, since it succeeds in capturing the ductile-to-brittle transition by increasing the structural size owing to the different physical dimensions of two material parameters: the tensile strength and the fracture energy. On the other hand, the later research direction aims at extending the classical cohesive model to quasi-brittle materials showing (as they often do) fractal patterns in the failure process. This approach is referred to as the renormalization group (or fractal) approach and leads to a scale-invariant cohesive crack model. This model is able to predict the size effects even in tests where the classical approach fails, e.g. the direct tension test. The two research paths, therefore, complete each other, allowing a deeper insight into the ductile-to-brittle transition usually detected when testing quasi-brittle material specimens or structures at different size-scales. � 2003 Elsevier Science Ltd. All rights reserved.