Cartridge tools provide a rapid method of making fastenings in the civil engineering construction and mining industries. In this paper the authors describe how a proprietary cartridge tool was used to fire steel fastener studs into rocks both in-situ and in a series of laboratory tests on cylindrical cores encased in concrete and reinforcement steel.
The depth of penetration of the studs into the rocks as a function of stud exit velocity from the tool, together with the nature of any superficial damage in the rock, were measured. The fasteners were then extracted from the rock, allowing the 'pull-out' strengths and modes of failure to be determined. After completion of some of the penetration tests, microscope slides of the rock section were prepared and examined under transmitted light to determine the extent and nature of internal damage caused by the shock penetration process.
A finite element, large deformation computer program was used to model the penetration dynamics of the laboratory tests in which non-linear behaviour of the rock was assumed. From the computational and experimental results, parameters were evaluated to fit simple empirical penetration laws.
The phenomenon of impact on and penetration of rock by metal projectiles has both military and civil engineering interest. In the latter context, for example, a common method of effecting rapid fixings in the construction industry utilizes a low-cost cartridge tool, of which several proprietary types exist in the UK. The method of operation of such tools relies on the detonation of an explosive cartridge to fire a metal projectile into target materials,. typically steel columns and beams or concrete lintels. Recent interest has been directed towards the adoption of such techniques for geotechnical and mining purposes, examples in the former case being the use of dynamic soil nailing for the improvement of cut slope stability and the dynamic pinning of access support to rock faces.
The response of the host material to the Penetration process is not well understood. It was the purpose of the investigation described in this paper to assess compatibilities or otherwise between experimental outcomes and numerical modelling of the impact and penetration phenomenon. An ultimate objective is to use the combined results of theory, experimentation and numerical modelling to appraise the design of the cartridge tool and its accessories.
The mechanical processes involved in this method of fixing are within the subject field of penetration dynamics (see Backman and Goldsmith (1978)). Penetration, as distinct from simple impact, ricochet or complete perforation, of a target by a projectile requires that the projectile, following impact, becomes embedded within the target. The penetration process has been studied extensively from comparatively early times. Since the Second World War, significant progress has been made both theoretically and experimentally. In particular the evolution of the modern generation of large capacity, high-speed computers and efficient software has enabled the realistic simulation of penetration processes using computational models (see Zukas et al. (1982) and Chandra and Flaherty (1983)).
