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

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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.