1 A New Algorithm for Crack Localization In Rotating Timoshenko Beam Samer Masoud Al-Said Associate Professor Visiting associate professor, at King Saud University, Kingdom of Saudi Arabia. (Associate Professor, Mechanical Engineering Department, Jordan University of Science and Technology, P. O. Box 3030, Irbid 22110, Jordan . ) A New crack localization algorithm based on mathematical model describing the lateral vibration of a rotating cracked Timoshenko beam is proposed. The Lagrange's equation and the assumed mode method are used to derive the model. The localization algorithm utilizes the variation in a single natural frequency of the beam versus few rotor speed values to identify crack location. This algorithm has different alternatives to check/reconfirm its output; as a result the identification accuracy can be improved. The effects of rotational speed and crack location on the system dynamic characteristics are investigated using the derived mathematical model. The results are compared with that obtained from the three dimensional finite element analyses, and good agreements between the two methods are found. Finally the identification algorithm is tested using the obtained finite element results; as outcome the crack is predicted with sound accuracy. Key Words: Crack localization, non destructive test, cracked beam, rotating beam 1. INTRODUCTION During the preceding two decades, many researchers have been focused on improving damage revealing techniques for vibrating structures such as aircraft structures, large space structures and structures used in ocean environment. The cracks can be occurring in structures due to their limited fatigue strengths or due to the manufacturing processes. During structural vibration these cracks breathe, making it grow over time, and may reach a point where they pose a threat to the integrity of the structure. Therefore, these cracks should be located and repaired before it propagate and impair the safety of the structure. In literature, it has been reported that a crack will not only change the dynamic characteristics of a system, but, in a blade it is