A Full Spectrum Analysis of a Jeffcott Rotor with Switching Crack in the Presence of Internal and External Damping D. K. Roy and Rajiv Tiwari Abstract This paper presents the full spectrum analysis of a cracked Jeffcott rotor with the internal and external damping. In this study, a mathematical model is devel- oped for a Jeffcott rotor considering both external and internal damping, crack force, and unbalance force. The crack in the rotor model is considered as switching crack function in the form of a rectangular shape, which provide forces that generate the forward and backward whirls at varied harmonics. The assumption of weight domi- nance simplifies the switching crack model to a linear one; however, it gives rise to the internal damping due to rubbing on crack faces. The rotor model is numerically simulated to provide responses from two orthogonal directions to obtain the full spectrum analysis to show both forward and backward whirls. Keywords Internal damping · External damping · Full spectrum · Jeffcott rotor · Switching crack · Unbalance · Weight dominance 1 Introduction Condition monitoring is in increasing demand due to its importance in supervision of safe and quality functioning of high-speed rotating machinery. The probability of faults may arise in rotors due to the high speed. Crack is the most common fault that may give rise to change in dynamic behavior of the rotor system. Correspondingly, the occurrence of internal (rotating) damping is due to rubbing between disc and shaft. The internal damping effect also comes into existence in cracked rotor system because of the rubbing between crack face and the material hysteresis due to the intermolecular interaction within the shaft material during rotation of a cracked D. K. Roy Department of Mechanical Engineering, Research Scholar at Indian Institute of Technology, Guwahati 781039, India e-mail: r.dipendra@iitg.ac.in; dipuroyjul@gmail.com R. Tiwari (B ) Indian Institute of Technology, Guwahati 781039, India e-mail: rtiwari@iitg.ac.in; rtiwariv@yahoo.co.in © Springer Nature Singapore Pte Ltd. 2020 S. Dutta et al. (eds.), Advances in Rotor Dynamics, Control, and Structural Health Monitoring, Lecture Notes in Mechanical Engineering, https://doi.org/10.1007/978-981-15-5693-7_9 113