抄録
As in the previous report1), it has been considered that the direction of stress wave propagation during “impact load” has to be taken into account in order to clarify the intrinsic nature of the impact strength of bolts. Consequently, the impact load was applied on bolts from both the bolt-head side and the nut side, and the intrinsic nature of the high-speed impact tensile characteristic of bolts was investigated.
It has been found that the impact tensile characteristic of bolts not only depends on the inherent strength of the material used, but also it varies greatly with such factors as the screw thread, shank, screwed-in position of a nut and acting direction of impact load. For example, in the case that the shank diameter is equal to the outside diameter of thread, the shank is elongated and acted as the so-called“damper”when impact load is applied on the bolt-head side. This fact reveals the intrinsic nature of the impact tensile characteristic of bolts. Accordingly, in such case, the direction of stress wave propagation is important and it is deemed advisable to apply impact load on the bolt-head side.
Further, as for the bolt itself, if the shank is made slender, the screw part does not break but the shank elongates, resulting in a remarkable increase of energy absorption. In addition, the longer the length of shank between a bolt head and a nut becomes, the greater the energry absorption becomes. On the other hand, it was found effective from the viewpoint of energy absorption to leave a part of screw idle when a nut is screwed in.
