Charakterisierung der Brucheigenschaften von Gestein

The fracture properties of rock play an important role in many fields of technical life. Rock has to be exploited first, crushed and shaped then into smaller pieces for different purposes. Therefore, knowledge of the fracture mechanisms of rock is necessary. An important means to characterize the fracturing features of rock is to use fracture mechanical principles, but many aspects of rock fracture have not been satisfactory characterized so far. It was the main aim of this project therefore to develop testing and evaluation procedures, which better characterize and quantify the fracture properties of rock by introducing special rock features into fracture mechanical considerations. Former investigations on other inhomogenous non-metallic materials, like wood, concrete, asphalt etc showed that the so called "specific fracture energy" is a parameter, which is appropriate to charactarize these materials effectively. It is, however, rather complicated and expensive to measure the fracture energy with converntional experimental techniques; long and heavy beams are used as specimens in notch bending experiments, for example. The wedge splitting technique, which has been developed and patented by Tschegg (1986) does not have these drawbacks. Relatively small cubic or cylindric specimens (edge lengths between some centimeters up to a few decimeters) are needed. The testing equipment is such that complete "load-displacement curves" can be detected, which render the basic data for calculation of the specific fracture energy. It was the aim of this project to adapt and establish the wedge splitting method according to Tschegg (1986) for rock. With this, the "specific facture energy" of various rocks, especially of granites, as well as of artificial and natural stone plates of different composition was derived. In addition, the "strain-softening behaviour", which quantifies crack growth in more detail, has been derived from the measured load-displacement curve. Applying partly new evaluation procedures and FEM modeling, the stages and mechanisms of crack propagation have been characterized and quantified . Other experimental techniques, like acoustic emission, optical and electron scanning microscopy in addition served to identify the micromechanisms of deformation, crack initiation and especially propagation. "Damage zone" ahead of the crack tip and "weak zone" around the fractured area, which determine the fracture properties of rock essentially, thus were investigated in more detail. As a result of the described experimental and theoretical investigations, a better characterization and modeling of the fracture properties of rock and rock compounds (like plate combinations, fiber reinforced artificial stone etc) is possible in an easier way now. This means that the desired parameters can be obtained by industrial laboratories with standard experimental equipment easily.