Calculating crack extension resistance of concrete based on a new crack propagation criterion

A crack propagation criterion was proposed for model I crack in concrete by using the initial fracture toughness K IC ini as an inherent material property. Based on this criterion, crack begins to propagate when the difference, between the stress intensity factors caused by the applied load K I P and that by the cohesive stress K I σ , exceeds K IC ini . Finite element analyses was then carried out to calculate the complete load vs. crack mouth opening displacement (P-CMOD) curve, the critical crack propagation length ΔaC and the unstable fracture toughness K IC un for notched beams under three-point bending. It was found that numerical results showed a good agreement with the experimental ones. Based on this crack propagation criterion, crack extension resistance, in terms of stress intensity factor, KR being able to consider the variation of fracture process zone (FPZ) was employed for describing crack propagation in concrete. KR is composed of K IC ini and K I σ , which is actually equal to the driving action of crack extension. It was concluded that given the elastic modulus E, the uniaxial tensile strength ft, the fracture energy GF and K IC ini , the complete fracture process in concrete and the KR-curve of concrete can be calculated based on the numerical method. Finally, discussion was made on the effects of fracture process zone, GF and specimens geometries on KR-curve.