ABSTRACT
During the 1970’s, a new branch of vibration engineering was developed, encompassing the most powerful aspects of both experimental and analytical techniques. The resulting technology has become known as experimental modal analysis or modal testing. The purpose of this preliminary phase was to investigate the influence of defect (failure) development in geologic materials on modal behavior at the laboratory scale. The influence of material damage on modal characteristics of a rock structure has been successfully investigated. Originally, the transfer function obtained from impact tests on rock was expected to be much noisier, since such materials are generally anisotropic and inhomogeneous in comparison with other materials. Alternatively a finite element program could be used to give, at least, an approximate idea of how the modal behavior could change due to material failure. Such theoretical techniques should help to locate the weak points in the structure and assist in the design of an experimental modal testing program for the actual field structure.
