Investigation on the Law Governing Crack Propagation Behaviors (with Sinusoidal or Spiral Cracks as Examples)

本研究的目的在于阐明裂纹扩展行为的规律，以实现对裂纹扩展的完美控制，为断裂在工程材料切割或劈砍中的应用提供理论依据。作为本研究的一部分，本研究项目处理了众所周知的现象，（I）正弦（螺旋）裂纹扩展在玻璃板（管）下降到冷水后均匀加热和（II）正弦裂纹扩展在高压气体管。从实验和理论上研究了裂纹扩展行为及其机理。根据（I）的结果，观察到向水中的下降速度或加热温度越大，正弦裂纹的波长变得越小。此外，热应力分析表明，裂纹很可能是垂直于水面时，其尖端在水面下，但它往往转向平行于水面的方向时，其尖端出现在水面上。接着，关于（II），使用玻璃管通过内部水加压进行断裂实验。作为结果，澄清了以下内容。1.正弦裂纹扩展的机制不是由于受压管的塑性变形。2.正弦裂纹扩展的机理不是由于裂纹快速扩展所产生的惯性效应。3.尽管试件的直径或厚度不同，但正弦裂纹的形状彼此相似。4.由于反平面剪应力的作用，裂纹路径从管的轴向方向倾斜。用连续分布位错模型方法进行的弹性分析表明，裂纹间的干涉或多轴应力效应是正弦裂纹扩展机制中的一个重要因素。

This study aims at clarifying the law governing crack propagation behaviors in order to realize perfect control of crack propagation for applications of fracture to cutting or chopping of engineering materials. As a part of this study, this research project has treated the well known phenomena, (I) sinusoidal (spiral) cracks propagating in a glass plate (tube) lowered into cold water after heated uniformly and (II) sinusoidal crack propagating in high pressure gas tube. The crack propagation behavior and its mechanism were investigated experimentally and theoretically. As a result on (I), it has been observed that the larger the descent speed into water or the heating temperature is, the smaller the wavelength of sinusoidal cracks becomes. Furthermore, thermal stress analysis revealed that a crack is likely to propagate perpendicularly to the water surface when its tip is under the water surface but that it tends to turn to the direction parallel to the water surface when its tip comes up over the water surface. Next, regarding (II), fracture experiments were conducted using glass tubes by pressurizing internally by water. As the results, the followings were clarified. 1.The mechanism of sinusoidal crack propagation is not due to plastic deformation of the pressurized tube. 2.The mechanism of sinusoidal crack propagation is not due to the effect of inertia resulting from the rapid crack propagation. 3.The shapes of sinusoidal cracks are similar to one another in spite of the difference of the diameter or the thickness of specimens. 4.The crack path becomes inclined from the axial direction of the tube due to the effect of anti-plane shear stress. The elastic analysis using the method of continuously distributed dislocations model suggests that the interference between cracks or multi-axial stress effect is an important factor in the mechanism of sinusoidal crack propagation.