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在金属材料中,可以用多种物理监测方法确定临界开裂点.但是,其中一些很有效的方法如电位法等,在混凝土材料中不能应用,而声发射法则是可以应用的.本文用30根直三点弯曲混凝土试样进行断裂试验,对其声发射率(dN/dt)曲线及声发射累计(N)曲线进行了分析,並从而得出试样加载断裂过程可以分为两个阶段:失稳前阶段和失稳扩展阶段.但是,声发射信号的起始点並不是主裂纹起裂点,失稳前阶段也不能与亚临界扩展阶段等同.然而,可以明确地确定试样的失稳扩展点,其位置大约在最大荷载的90%～95%之间.因此,应按相应于该点的荷载计算混凝土的K_(1c)值.
In metallic materials, a variety of physical monitoring methods can be used to determine the critical cracking point. However, some of the most effective methods such as potentiometric methods cannot be applied in concrete materials, and the acoustic emission method can be applied. The three-point bending concrete specimens were subjected to a fracture test. The acoustic emission (dN/dt) curves and Acoustic Emission (N) curves were analyzed, and it was concluded that the specimen loading fracture process can be divided into two stages: The pre-stabilization stage and the instability expansion stage. However, the starting point of the acoustic emission signal is not the main crack initiation point, and the pre-destabilization stage cannot be equivalent to the subcritical expansion stage. However, the instability of the sample can be clearly determined. The extension point is located approximately between 90% and 95% of the maximum load. Therefore, the K_(1c) value of the concrete should be calculated according to the load corresponding to this point.