A STUDY ON MECHANICAL BEHAVIOR OF FRACTURE PROCESS ZONE IN CONCRETE USING ENERGY APPROACH

It is generally accepted that the development of fracture process zone (FPZ) in front of the stress-free crack in quasi-brittle materials like concrete is responsible for the non-linear fracture behavior of concrete and size effect phenomena. Therefore, since the beginning of concrete fracture mechanics, it has been believed that the quantitative analysis of both physical and mechanical behaviors of fracture process zone is of significant importance to better understand the potential fracture mechanisms in concrete fracture as well as to more accurately develop nonlinear fracture models for crack stability analysis and safety assessment in concrete. Considering this point, referring to the definition of fracture energy proposed by Hillerborg, a general equation for calculating average energy dissipation per unit length of FPZ propagation is presented in this paper. Taking three-point bending beam as an example, step-by-step procedures for computing this average energy dissipation are further given in details, in which Reinhardt’s non-linear softening relationship is used. After obtaining the characteristic crack opening displacement w0 by mathematic fitting according to nonlinear softening equation, in which fracture energy is approximately equal to the measured fracture energy of each specimen, during the entire fracture process the average value of energy dissipation in FPZ at any loading moment is calculated. The calculated results indicate that the change of energy dissipation in fracture process zone with crack propagation is independent of specimen size, and is a good description of mechanical behavior occurred in FPZ in concrete.