Analyses of Time Dependent Behavior of Fracture Process Zone in Concrete and Constitution of Its Numerical Model

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The fracture parameters such as fracture energy and brittleness are deeply concerned with the cumulative process of micro cracking in the fracture process zone. The purpose of this research is to obtain the time dependent behavior of micro cracking in the fracture process zone of notched concrete beam under constant loadings, using three dimensional AE source location method.The velocity of the crack mouth opening displacement changes from steady to accelerative state beyond a certain critical point. AE source locations distribute widely in the steady state, and in a line at the front of the fracture process zone after the critical point. This means that the process of accelerative micro craking is connected with the initial state of tension softening.To research on the critical point, the tension softening diagram is evaluated by means of poly-linear inverse analysis method. On the basis of comparison between AE source locations and the crack type distributions in the fractured cross section, meso-scopic fracture mechanism in tension softening process is considered. It makes clear that the cumulative AE energy is increasing with the same manner of the energy of crack formation. This result suggests that the proposed AE energy represents quantitatively micro cracking in fracture process zone.In the future, it is necessary to determine the amount of AE energy correspond to the critical point and to investigate the relation between brittleness.