中文摘要：

岩石在承载之初，由于微缺陷无序成核和有限生长，在材料内部形成大量分布性微裂纹。在该文中，这种演化机制被归结为：微缺陷随机、孤立成核生成最小微裂纹和微缺陷无重叠聚集成核、排列生长形成大尺度微裂纹，裂纹尺度生长是微缺陷成核数的函数。利用微裂纹尺度．频数分布分形以及微裂纹粗糙表面分形，建立基于微缺陷累计成核数序列的裂纹尺度生长模型和损伤演化模型。通过对二维岩石试件破坏过程的微裂纹尺度统计和损伤测试表明，模型的预测结果与观测值符合较好。由于微缺陷成核与声发射源机制具有相似性以及微缺陷成核数序列与声发射数序列具有相似性，所以该模型可用于通过声发射参数序列跟踪微裂纹生长和损伤演化。裂纹尺度生长对于完整认识材料宏观力学性质演化和预测材料灾变具有重要意义。

英文摘要：

At the initial stage of rock bearing load, a great amount of microcracks appeared in the material due to microdefects random nucleation and limited growth. In the paper, the mechanism of microcracks evolution at the initial stage rock damage was generalized that the isolated nucleation of microdefects formed the initial microcracks of the smallest size, and the clustering nucleation of microdefects close next to the initial microcracks formed the large-scale microcracks, in which the microcracks size growth was the function of the number of microdefects nucleation. By using the microcracks size and frequency distribution fractal and the microcrack rough surface fractal, two models were established. One was a relationship formula between accumulated number of microdefects nucleation and microcracks size, which was called the Crack Growth Model （CGM）. The other was an isotropic damage model based on microdefects nucleation number series, which was called the Damage Evolution Model （DEM）. The statistics analysis on the microcracks evolution in a gradually fractured rock plate shows that the predictive cracks growth and microcracks damage evolution are in good agreement with the measured values. Since a microdefect nucleation being accompanied by a acoustic emission （AE） and the number series of microdefects nucleations was similar to the AE series, the two models could be used to predict microcrack growth and microdamage evolution by the use of AE series. It is important to study microcracksgrowth and damage to the macro mechanical properties for the understanding of the whole course of evolution and prediction of catastrophe.