Abstract
In this paper, it is studied how much of the piston blow energy will be transformed to the bending energy of drill rod in a percussive rock drilling process. The mathematical model is based on one-dimensional wave theory and Euler-Bernoulli beam theory. The axial and the transverse motions of drill rod are assumed to be coupled at the boundary only. The rod is considered as semi-infinite in length, and the rod/rock contact condition is modelled with an eccentric linear spring element.
Two kind of problems will be considered. First, the one in which the piston eccentrically impacts on the rod end, thus causing bending vibration; and second, the one in which the purely axial incident pulse arrives at the eccentrically spring-supported rod end, reflects back and generates bending vibration. Using Laplace-transformation techniques, the closed form solution for these problems is discovered. The results show that the disturbances at the rod/rock boundary cause stronger bending effect than those at the piston/rod boundary.
