Finite element analysis of the impact process of concrete drilling
Percussive drilling, that uses rotary torque and axial impact simultaneously, is an established method of making holes in concrete. This paper deals with the development of a finite element model, based on three-dimensional wave propagation, which represents the impact process of percussive drilling in concrete. The solid model of the percussive drilling system consists of five separate components, viz. shank, fluted body, socket tip, carbide blade and concrete target. After integration and meshing, the finite element model is analysed using three-dimensional wave propagation techniques. The bias weight and the impact impulse were set up as inputs to the drilling system. A "surface to surface eroding" interface was selected for the drill tip-concrete contact surface while a "rigid wall" interface was chosen for the concrete-ground support contact surface. Simulation results showed the usefulness of the model in understanding how the three-dimensional wave, due to impact, propagates through the drilling system resulting in penetration of the drill bit into concrete. The accuracy of the model was successfully verified with prior-known one-dimensional analytical model and experimental penetration results. Finally, to illustrate the potential use of this model to design and analyse percussive drilling system, the effect of variation of rake angle, helix angle, point angle, and bias weight on the extent of penetration is presented. The results clearly showed the importance of simulating the impact process for designing new percussive drill bits.
A theory of percussive drill bit penetration
Abstract The author has developed a theory of percussive bit penetration. The theory is in substantial agreement with his experimental results. In developing the theory the author has assumed a mathematical model which is based on some of his experimental observations. The mathematical force-penetration relationships deduced by the author have been compared with experimental results of the author himself and also with the results obtained by Reichmuth, and Gnirk and Cheatham. It is concluded that (a) the force-penetration curve for each bit-rock combination reflects the characteristics of both the rock type and the bit. (b) During the crushing phase, rock in contact with the bit becomes pulverized to a certain depth and subsequently becomes compact under increasing force. The size of this zone is a function of bit geometry, penetration and angle of internal friction of the rock. (c) The friction between the pulverized wedge and the confining solid rock has a great influence on the chipping force. (d) The angle of fracture, profile and shape of the crater are in substantial conformity with the theoretical prediction and from the theory it is also possible to predict the forces for given depths of penetration.
Comparative Industrial Sociology and the Convergence Hypothesis
Industrial sociology grew spectacularly after World War II, concentrating on three areas: workers' relations with each other, their managers, and their unions; the social organization of the factory; and the impact of technology on social systems extending from the factory to the society. Unable to sus­ tain leadership in all of these areas, industrial sociology shrivelled as other fields invaded its domains. Human relations became the ideological property of the business schools; labor economics maintained its grip on industrial relations; industry-community relations waned as interest in community power soared; industrial organizations were absorbed into the study of com­ plex organizations; occupational sociology maintained research impetus in labor force analysis; and the sociology of the economy dominated the study of industry's institutional relationships. Industrial sociology survived on remnants: worker-machine relationships (job satisfaction, alienation, un­ employment), organizational responses to technological changes. and a bit of working-class ethnology. Enduring interest in technology, however, en­ abled industrial sociology to take part in sociology's expanding interest in comparative studies.