Mode Shape Based Approach to Identify the Location of Crack and the Influence of Crack on Critical Speed of Gas Turbine Disc

In an aeroengine, the rotating gas turbine disc is susceptible to cracks in its service tenure due to its complex loadings and operating conditions. The appearance of crack in disc alters the stiffness near crack location which further affects vibration characteristics of the rotating disc and it is a serious reliability concern for aeroengine applications. Critical speed is one of the important design parameters which is also affected by the presence of crack on the disc. The early detection of crack is a challenging task and the variation in the vibrational behaviour under the influence of crack must be known. In the present work an attempt has been made to introduce an efficient procedure to locate the crack position on the disc and also to compare the vibrational characteristics of healthy and cracked disc under the factual operating condition specific to aeroengine. Critical speed of cracked discs is compared with that of the healthy disc to identify the influence of crack on the safe zone of operation within the permissible speed limit. In the present findings, it is appealing to note that the vibrational mode shape can be employed as an effective tool in detection of the location of the crack. The present work is expected to serve as guidelines during the design phase of gas turbine discs of aeroengine applications.