AN INTEGRATED APPROACH TO DETECTION OF CRACKS USING VIBRATION CHARACTERISTICS

An integrated technique based on the vibration theory to nondestructiv ely identify multiple discrete cracks in a structure is presented. Two damage modeling techniques, one involving the use of massless, infini tesimal springs to represent discrete cracks and the other one employi ng the continuum damage concept, are integrated to provide a crack-det ection technique that utilizes the global vibration characteristics of a structure but offers local information on each individual crack, in cluding location and extent of the cracks. In the spring model, the Ca stigliano's theorem and the perturbation technique are used to derive a theoretical relationship between the eigenfrequency changes and the location and extent of the discrete cracks. In the continuum damage mo del, the effective stress concept coupled with the Hamilton's principl e are used to derive the similar relationship that is cast in a contin uum form. A unified g(beta) function emerges from the two model approa ches. The g(beta) function can be determined through the mode shapes o f an intact structure by means of the modal strain energy density. In the proposed integrated approach, the continuum damage model can be us ed first to identify the discretizing elements of a structure that con tain cracks. Then, the spring damage model can be used to quantify the location and severity of the discrete crack in each damaged element. An example of a simply-supported beam containing two discrete cracks i s given to illustrate the application and accuracy of the proposed app roach.