【摘要】 本文研究了水介质中玻璃表面单个小裂纹的生长与多个小裂纹的聚合规律,首次对共面三裂纹聚合及非共面双裂纹演变特征进行了探索。结果表明,小裂纹扩展规律明显不同于长裂纹的扩展;裂纹间的交互作用显著地影响其生长规律;非共面双裂纹的聚合取决于裂纹的几何形状及取向。更多还原

【Abstract】 The critical size of crack propagation of glass and ceramic materials is extremely small. The growth and coalescence of small crack on glass surface has gradually attracted researchers’ attention in recent years[1-4]. Up to now, experimental study has been preliminary and limited to the characteristics of one small crack or two coplanar small cracks[1,3,4]. It appears that characteristics of neither many small cracks nor noncoplanar small cracks have been explored experimentally. Such an exploration is the main contribution of this paper. Besides, this paper presents some results that go beyond Refs.[1,4]. The authors’ findings are: (1) For two noncoplanar cracks(Fig.9), when they have the same crack shape and size and the same geometrical shape and size, first the nearest crack tips of the two cracks propagate toward each other rapidly due to the effect of stress superposition. When they meet like two opp(?)sitely moving trains that arrive at the same railway station, they both, turning an angle of 45°, continue to propagate until they come to a stop (Fig. 10). Then only the farthest crack tips propagate until critical size is reached and fracture occurs. (2) For one, two, three coplanar or noncoplanar cracks, it is always true that crack propagation rate da/dt first drops to a low point and then increases with increasing K. This is the so-called minimum value phenomenon. The authors’ research proves that such a phenomenon is caused by residual stresses, but neither by material microstructure nor by environment medium. The residual stresses are shown by experiments to be carried by indention load. (3) It is found that there are important differences between coplanar cracks and noncoplanar cracks. For coplanar cracks, only superposition of stresses occurs, but for noncoplanar cracks, not only stress superposition but also stress relaxation can occur. Because coplanar cracks are more liable than noncoplanar ones to coalesce, the former ones are more dangerous to engineering structure.更多还原