Vibration analysis and measurement of beams having multiple cracks

Vibration based methods are widespread through the non-destructive methods for detection and identification of cracks in mechanical and structural systems including beam type elements. The methods are effective since any damage leads to changes in vibration characteristics that are easily measured. However, identification of cracks can be more difficult for general beam elements having several complexities.This thesis presents continuous methods for flexural vibration analyses of multiple cracked beams and detection methods for single and double cracked beams. Vibration of beams are analysed with different geometric, boundary, and crack properties. Vibration analyses of the beams having multiple transverse cracks, multiple height-edge cracks, and asymmetric double edge cracks are all presented. Both open and breathing crack models are considered. Energy based numerical solution method is used in the analyses by describing the energies consumed caused by each crack. Interactions between the crack effects are also described.Contour lines representing natural frequency ratios are employed for detecting single crack. As a contribution to current literature addressing the inverse problems, a frequency based algorithm is developed for detection of double cracks. An automated single and double crack detection system is established by using theoretical and measured natural frequencies. In measurement, stable natural frequencies are obtained by means of a statistical approach (RSZF) using an interpolation technique (DASI). Direct and inverse methods presented in this thesis simplify the crack detection, are convenient for different structures, ideal for automation, and require low process time, memory and disc capacity.