スムースブラスティングにおけるガイドホールの効果について

抄録

In this study, at first, the behaviour of the rarefaction wave by which the tensile stress in the material is considered to be relaxed has been studied. The main results obtained are as follows:
1) Measured value of the propagation velocity of the rarefaction wave mentioned above agrees with that of the longitudinal wave in the material.
2) The tensile stress at a point in the material has been relaxed linearly by the rarefaction wave within about 10-20μsec after the wave has arrived at the point.
Through the discussion of the effect of the guide hole on the stress distribution in the material, it is clarified that the tangential tensile stress produced in the direction of the guide hole attains to greater value earlier than those produced in the other directions.It means that the crack towards the guide hole can be produced ahead of all other radial ones and its length might be the longest. As the rarefaction waves are projected from the surface of the crack in the direction of the guide hole into the material, the hoop stress in the material has been relaxed from the position of the crack. Therefore, no other radial cracks extend near the direction of the guide hole.And also, it is clarified that the effect to check the extension of radial cracks by the guide hole appears more effectively with decrease of the distance between the charge hole and the guide hole.
Lastly, a field experiment was carried out to confirm the results of the small scale experiments which were performed in the laboratory by using a polymethyl methacrylate, and it was shown that the results obtained in the field agreed fairly well with those obtained in the laboratory.