Analysis Of Concrete Damage Mechanism And Critical Damage Characteristics

Concrete is a kind of engineering material with inherent defects. The failure caused by occurrence, propagation and coalescence of cracks is to start as loading. In this thesis, the failure processes of concrete were studied, including the critical damage characteristics, the mechanism of damage-nucleation, and the damage modeling. The research work involves several aspects as follows:1. Distribution of the initial damage of concrete before loading, evolution of the micro-cracks while loading, and features of the fracture surface can be characterized with fractal philosophy. Based on the fractal theory, considering the features of concrete damage failure, a model describing a critical state of concrete damage development was set up. According to the theory of the renormalization group, the critical probability, the fractal dimension, and the critical damage value were presented when concrete is in a critical damage state.2. Krajcinovic 4-parameter damage model is originated from the strain equivalent principle. Therefore, the four material parameters in Krajcinovic 4-parameter damage model can be replaced with two material parameters to be easily determined. As a result, a new damage model with two parameters was suggested. Comparisons of the stress-strain curves indicate that 2-parameters damage model suggested is a good agreement with Krajcinovic 4-parameter damage model.3. On the basis of self-resemble character in multi-scales, damage-nucleation of concrete is described as a fractal round. Renormalization group theory was used to analyze the evolving process of the micro-crack group. The energy caused by the damage evolvement can be divided into two parts. One is the damage strain energy in the form of Helmholtz free energy; the other is the releasing energy due to formation of the micro-cracks at the damaged area. A damage-nucleation model considering two energy processes was established.