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

断裂能、脆性等断裂参数与断裂过程区微裂纹的累积过程密切相关。本研究的目的是利用三维声发射声源定位方法，获得恒定载荷作用下缺口混凝土梁断裂过程区内微裂纹的时变行为，裂纹张开位移的速度在一定临界点以上由稳定状态变为加速状态。稳态时声发射源位置分布较广，临界点后在破裂过程区前部呈直线分布。这意味着加速微裂纹的过程与拉伸软化的初始状态有关。为了研究该临界点，采用多元线性逆分析方法对拉伸软化图进行了评估。在对比声发射源位置和断裂断面上裂纹类型分布的基础上，探讨了拉伸软化过程中的细观断裂机理。结果表明，累积声发射能随裂纹形成能的增加而增加。这一结果表明，提出的声发射能量定量地代表了断裂过程区的微裂纹，今后有必要确定临界点对应的声发射能量，并研究其与脆性之间的关系。

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.