Breathing crack detection using Lamb wave and DORT method

2012 ◽  
Author(s):  
Wenzhong Qu ◽  
Li Xiao
Keyword(s):  
Lamb Wave ◽  
Crack Detection ◽  
Breathing Crack

Time-Domain Spectral Element Simulation of Lamb Wave Time Reversal Method for Detecting a Breathing Crack in a Plate

2019 ◽  
Author(s):  
Zexing Yu ◽  
Fei Du ◽  
Chao Xu
Keyword(s):  
Finite Element ◽  
Time Domain ◽  
Time Reversal ◽  
Lamb Wave ◽  
Crack Detection ◽  
Spectral Element ◽  
Penalty Function Method ◽  
Relative Depth ◽  
Breathing Crack ◽  
Spectral Finite Element

Abstract Lamb wave is considered as an appropriate approach to detect the cracks in structures. This paper combines an efficient time-domain spectral finite element with time reversal method to develop an efficient breathing crack detection method. In this regard, Gauss-Lobatto-Legendre quadrature rules and penalty function method are carried out to construct an effective and accurate approach. Comparing the computation scales and results of this method and traditional finite element method, the validity and superiority of the proposed model is stressed. The reconstructed signals of two scenarios, intact and impaired structures, are captured. It is concluded that, this approach is capable of detecting breathing cracks. In addition, the influences of the relative depth of the notch and incident region are studied. This research may provide the guidance for experiment configuration and the further study.

Reference-Free Breathing Crack Identification of Beam-Like Structures Using an Enhanced Spatial Fourier Power Spectrum with Exponential Weighting Functions

2019 ◽  
Vol 19 (02) ◽  
pp. 1950017 ◽  
Author(s):  
J. Prawin ◽  
A. Rama Mohan Rao
Keyword(s):  
Fatigue Crack ◽  
Power Spectrum ◽  
Crack Detection ◽  
Crack Problem ◽  
Experimental Studies ◽  
Crack Identification ◽  
Successful Implementation ◽  
Breathing Crack ◽  
Fourier Power Spectrum ◽  
Exponential Weighting

Detection of incipient damage of structures at the earliest possible stage is desirable for successful implementation of any health monitoring system. In this paper, we focus on breathing crack problem and present a new reference-free algorithm for fatigue crack detection, localization, and characterization for beam-like structures. We use the spatial curvature of the Fourier power spectrum as a damage sensitive feature for fatigue crack identification. An exponential weighting function that takes into account nonlinear dynamic signatures, such as sub- and superharmonics, is proposed in the Fourier power spectrum in order to enrich the damage-sensitive features of the structure. Both numerical and experimental studies have been carried out to test and verify the proposed algorithm.

Numerical Investigation of Nonlinear Lamb Wave Time Reversing for Fatigue Crack Detection

2019 ◽  
Author(s):  
Junzhen Wang ◽  
Yanfeng Shen
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Time Reversal ◽  
Lamb Wave ◽  
Crack Detection ◽  
Guided Waves ◽  
Fatigue Cracks ◽  
Contact Dynamics ◽  
Virtual Time ◽  
Fatigue Crack Detection

Abstract This paper presents a numerical study on nonlinear Lamb wave time reversing for fatigue crack detection. An analytical framework is initially presented, modeling Lamb wave generation, propagation, wave crack linear and nonlinear interaction, and reception. Subsequently, a 3D transient dynamic coupled-field finite element model is constructed to simulate the pitch-catch procedure in an aluminum plate using the commercial finite element software (ANSYS). The excitation frequency is carefully selected, where only single Lamb wave mode will be generated by the Piezoelectric Wafer Active Sensor (PWAS). The fatigue cracks are modelled nucleating from both sides of a rivet hole. In addition, contact dynamics are considered to capture the nonlinear interactions between guided waves and the fatigue cracks, which would induce Contact Acoustic Nonlinearity (CAN) into the guided waves. Then the conventional and virtual time reversal methods are realized by finite element simulation. Advanced signal processing techniques are used to extract the distinctive nonlinear features. Via the Fast Fourier Transform (FFT) and time-frequency spectral analysis, nonlinear superharmonic components are observed. The reconstructed signals attained from the conventional and virtual time reversal methods are compared and analyzed. Finally, various Damage Indices (DIs), based on the difference between the reconstructed signal and the excitation waveform as well as the amplitude ratio between the superharmonic and the fundamental frequency components are adopted to evaluate the fatigue crack severity. The DIs could provide quantitative diagnostic information for fatigue crack detection. This paper finishes with summary, concluding remarks, and suggestions for future work.

scholarly journals Effects of Crack on Vibration Characteristics of Mistuned Rotated Blades

2017 ◽  
Vol 2017 ◽  
pp. 1-18 ◽  
Author(s):  
Hailong Xu ◽  
Zhongsheng Chen ◽  
Yongmin Yang ◽  
Limin Tao ◽  
Xuefeng Chen
Keyword(s):  
Natural Frequency ◽  
Vibration Amplitude ◽  
Crack Detection ◽  
Vibration Characteristics ◽  
Lumped Parameter Model ◽  
Crack Model ◽  
Breathing Crack ◽  
Vibration Localization ◽  
Lumped Parameter ◽  
Amplitude Increase

Rotated blades are key mechanical components in turbine and high cycle fatigues often induce blade cracks. Meanwhile, mistuning is inevitable in rotated blades, which often makes it much difficult to detect cracks. In order to solve this problem, it is important and necessary to study effects of crack on vibration characteristics of mistuned rotated blades (MRBs). Firstly, a lumped-parameter model is established based on coupled multiple blades, where mistuned stiffness with normal distribution is introduced. Next, a breathing crack model is adopted and eigenvalue analysis is used in coupled lumped-parameter model. Then, numerical analysis is done and effects of depths and positions of a crack on natural frequency, vibration amplitude, and vibration localization parameters are studied. The results show that a crack causes natural frequency decease and vibration amplitude increase of cracked blade. Bifurcations will occur due to a breathing crack. Furthermore, based on natural frequencies and vibration amplitudes, variational factors are defined to detect a crack in MRBs, which are validated by numerical simulations. Thus, the proposed method provides theoretical guidance for crack detection in MRBs.

Smart Rotating Machines for Condition Monitoring

2009 ◽  
Vol 413-414 ◽  
pp. 423-430
Author(s):  
Michael I. Friswell ◽  
Yong Yong He
Keyword(s):  
Crack Detection ◽  
Dynamic Behaviour ◽  
Normal Operation ◽  
Active Magnetic Bearings ◽  
Static Deflection ◽  
Breathing Crack ◽  
The Past ◽  
Rotating Machine ◽  
Run Up

The concept that changes in the dynamic behaviour of a rotor could be used for general fault detection and monitoring is well established. Current methods rely on the response of the machine to unbalance excitation during run-up, run-down or normal operation, and are mainly based on pattern recognition approaches. Of all machine faults, probably cracks in the rotor pose the greatest danger and research in crack detection has been ongoing for the past 30 years. For large unbalance forces the crack will remain permanently open and the rotor is then asymmetric, which can lead to stability problems. If the static deflection of the rotor due to gravity is large then the crack opens and closes due to the rotation of the shaft (a breathing crack), producing a parametrically excited dynamical system. Although monitoring the unbalance response of rotors is able to detect the presence of a crack, often the method is relatively insensitive, and the crack must be large before it can be robustly detected. Recently methods to enhance the quality of the information obtained from a machine have been attempted, by using additional excitation, for example from active magnetic bearings. This research is directed towards the concept of a smart rotating machine, where the machine is able to detect and diagnose faults and take action automatically, without any human intervention. This paper will consider progress to date in this area, with examples, and consider the prospects for future development.

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