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

本研究旨在阐明裂纹扩展行为的规律，以实现对断裂在工程材料切割或切割应用中裂纹扩展的完美控制。作为这项研究的一部分，本研究项目处理了众所周知的现象，(I)在均匀加热后下降到冷水中的玻璃板(管)中的正弦(螺旋)裂纹扩展和(Ii)正弦裂纹在高压气体管中的扩展。对裂纹扩展行为及其机理进行了实验和理论研究。结果表明，在(I)中观察到，下降速度越大或加热温度越高，正弦裂纹的波长越小。此外，热应力分析表明，当裂纹尖端位于水面以下时，裂纹很可能垂直于水面扩展，而当尖端上升到水面上时，裂纹倾向于转向平行于水面的方向扩展。其次，关于(Ii)，使用玻璃管通过水内部加压进行了断裂试验。作为结果，澄清了以下几点。1.正弦裂纹扩展机制不是受压管的塑性变形所致。2.正弦裂纹扩展的机理不是由于裂纹快速扩展产生的惯性效应所致。3.无论试件的直径或厚度如何，正弦裂纹的形状都是相似的。4.在反平面剪应力的作用下，裂纹路径向管轴方向倾斜。采用连续分布位错模型的弹性分析表明，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.