応力波の伝播にともなうき裂の生成機構について

抄録

It is well known that when an explosive charge is detonated in a material, the radial cracks are produced and grow around the explosion by the hoop stress in the spherical stress wave. But, there are many unknown points which must be clarified in the growth mechanism and the properties of these radial cracks, therefore, in this paper, the behaviour of the crack propagation has been discussed through the observation of the surface of the crack produced in a polymethyl methacrylate plate by a detonator's attack. The main results obtained are as follows;
1. The radial crack caused by an explosion (See Fig.2) is not produced continuously from the surface of the explosion. The intense stress wave projected into the material by an explosion creates at first many nuclei of the crack, and then the cracks from the respective nucleus interlink with each other producing finally the continuous long radial cracks (See Fig.12, 14).
2. The relation between the number of the nucleus per unit area N and the distance from the inner surface of the borehole r in which an explosive is detonated is shown in Fig.15. In the case where the decoupling coefficient is 1.1, the maximum value of N which is about 2.5×10³ pieces/cm² appears at the distance of r≅1.0cm, in the case where the decoupling coefficient is 2. 0, the maximum value of N that is about 5×10³ pieces/cm², appears nearer to the inner surface of the borehole. Thus, the number of the nucleus produced near by the inner surface of the borehole is less in the case where the decoupling coefficient is 1.1 than in the case where the decoupling coefficient is 2.0. It may be considered that one of the reason why this phenomenon appeared is the increase in the ductility of the material caused by the temperature rise in the material due to the adiabatic compression accompanied with the propagation of an intense stress wave.