VIBRATION OF CRACKED STRUCTURES - A STATE-OF-THE-ART REVIEW

The presence of a crack in a structural member introduces a local flex ibility that affects its vibration response. Moreover, the crack will open and close in time depending on the rotation and vibration amplitu de. In this case the system is nonlinear. Furthermore, if general moti on is considered, the local stiffness matrix description of the cracke d section of the shaft leads to a coupled system, while for an uncrack ed shaft the system is decoupled. This means that the crack introduces new harmonics in the spectrum. In fact, in addition to the second har monic of rotation and the subharmonic of the critical speed, two more families of harmonics are observed: (1) higher harmonics of the rotati ng speed due to the nonlinearity of the closing crack, and (2) longitu dinal and torsional harmonics are present in the start-up lateral vibr ation spectrum due to the coupling. Over 500 papers on the subject wer e published in the past 10 yrs. A wealth of analytical, numerical and experimental investigations now exists. However, a consistent cracked bar vibration theory is yet to be developed. There are still many unan swered questions, especially in the area of closing cracks in rotating shafts. Copyright (C) 1996 Elsevier Science Ltd.