GEOMETRY-DEPENDENT R-CURVE FOR QUASI-BRITTLE MATERIALS

Fracture of quasi-brittle materials such as ceramics and cement-based materials can be described by an R-curve, defined as fracture resistance. The R-curve can be constructed as the envelope of the strain energy release rates (G). In this study, R-curve is defined as an envelope of G-curves obtained by varying the dimensions of identical specimens, while keeping the geometry and the initial flaw size constant. By approximating the G-curve with a second-order function of the crack length, a simple formulation of the R-curve is derived by solving a differential equation. Three parameters are needed for the proposed R-curve. These parameters can be obtained by testing a notched-beam specimen and using linear elastic fracture mechanics. The proposed R-curve simulates well the geometry dependency as well as other characteristics of the fracture response of quasi-brittle materials.