A. Saito, M. Castanier, B. Epureanu, University of Michigan - Ann Arbor, Ann Arbor, MI; R. Morris, United Technologies / Pratt & Whitney, East Hartford, CT
Cracking of metallic components in complex structural systems is an important structural health consideration for a wide variety of aerospace systems. In particular, predicting crack growth is of paramount importance. The growth is dependent on amplitude and frequency of the local stresses in the structure, which are determined by the dynamics of the structure. In turn, this dynamics is affected in a complex and nonlinear way by the crack. Although the crack propagation occurs at time scales considerably slower than the time scales of the dynamics of the structure, the crack size affects the amplitude of vibration, the level of stresses in the vicinity of the crack, and the frequency of vibration. Hence, the feedback mechanism between the crack propagation and the dynamics of the structure is essential for ensuring accurate predictions of the next-generation of crack propagation algorithms. Thus, an efficient and accurate analysis framework for such structures with a crack is highly desirable.
The focus of this presentation is a novel high-fidelity approach for modeling the nonlinear effects of a crack on the dynamics of complex structures. Special attention is paid to turbomachinery rotors with a cracked blade. A key challenge addressed is that a vibrating cracked structure features a non-smooth nonlinearity caused by repetitive opening and closing, or intermittent contacts of crack faces during vibration cycles. This nonlinearity dramatically reduces the accuracy of current linear-based techniques for predicting the structural dynamics. Also, this nonlinearity affects the dynamics of the overall structure and, more importantly, significantly influences the amplitude and frequency of the stresses in the vicinity of the crack.
This presentation discusses fundamental aspects of the nonlinear dynamics of cracked structures. Also, a novel methodology for accurately predicting with very high computational efficiency the dynamics of a cracked structure and the stresses in the vicinity of a crack is presented. This methodology is based on a novel combination of finite-elements, component-mode-synthesis, and harmonic-balance-based nonlinear forced-response predictions. The analysis is demonstrated for a turbomachinery rotor with a cracked blade, and the crack effects on the system-level response are discussed. Finally, a new resonant-frequency-approximation method for turbomachinery is presented.
Summary: Cracking of metallic components in complex structural systems is an important structural health consideration for a wide variety of aerospace systems. In particular, predicting crack growth is of paramount importance. The growth is dependent on amplitude and frequency of the local stresses in the structure, which are determined by the dynamics of the structure. In turn, this dynamics is affected in a complex and nonlinear way by the crack. Although the crack propagation occurs at time scales considerably slower than the time scales of the dynamics of the structure, the crack size affects the amplitude of vibration, the level of stresses in the vicinity of the crack, and the frequency of vibration. Hence, the feedback mechanism between the crack propagation and the dynamics of the structure is essential for ensuring accurate predictions of the next-generation of crack propagation algorithms. Thus, from both practical and theoretical standpoints, an efficient and accurate analysis framework for such structures with a crack is highly desirable. The focus of this presentation is a novel high-fidelity approach for modeling the nonlinear effects of a crack on the dynamics of complex structures. Special attention is paid to turbomachinery rotors with a cracked blade. A key challenge addressed in this work is that a vibrating cracked structure features a non-smooth nonlinearity caused by repetitive opening and closing, or intermittent contacts of crack faces during vibration cycles. This nonlinearity dramatically reduces the accuracy of current linear-based techniques for predicting the structural dynamics. Also, this nonlinearity affects the dynamics of the overall structure and, more importantly, significantly influences the amplitude and frequency of the stresses in the vicinity of the crack. This presentation discusses some of the fundamental aspects of the nonlinear dynamics of cracked structures. Also, a novel methodology for accurately predicting with very high computational efficiency the dynamics of a cracked structure and the stresses in the vicinity of a crack is presented. This methodology is based on a novel combination of finite elements, component mode synthesis, and harmonic-balance-based nonlinear forced response predictions. The analysis is demonstrated for a turbomachinery rotor with a cracked blade, and the effects of a cracked blade on the system-level response are discussed. Finally, a new resonant-frequency-approximation method is presented, and its applicability to turbomachinery is discussed.
