ABSTRACT
Linear elastic fracture mechanics (LEFM) is the basic theory of fracture, originated by Griffith and completed in its essential aspects by Irwin. Formation of a crack in an elastic solid initially subjected to uniform uniaxial tension disrupts the trajectories of the maximum principal stress. The central problems of elastic fracture mechanics are to measure the crack growth resistance, R, for particular materials and situations, on one hand, and to calculate the energy release rate G, on the other. It was a great achievement of Irwin to reformulate LEFM problem in terms of the stress states in the material close to the crack tip rather than energetically and prove that this, so-called local, approach was essentially equivalent to the Griffith energetic approach. With respect to quasibrittle materials, and particularly concrete, it is important to note that they contain plenty of microcracks, but failure does not happen as soon as one of these microcracks starts to grow.
