Response of a structural health monitoring fastener to fatigue crack growth and loads in metallic joints

2009 ◽  
Author(s):  
Alexi S. Rakow ◽  
Fu-Kuo Chang
Keyword(s):  
Fatigue Crack ◽  
Structural Health Monitoring ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Health Monitoring ◽  
Structural Health

A Digital Mems-based Strain Gage for Structural Health Monitoring

1997 ◽  
Vol 503 ◽  
Author(s):  
B. J. Maclean ◽  
M. G. Mladejovsky ◽  
M. R. Whitaker ◽  
M. Olivier ◽  
S. C. Jacobsen
Keyword(s):  
Fatigue Crack ◽  
Structural Health Monitoring ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Health Monitoring ◽  
Dynamic Range ◽  
Axial Strain ◽  
Sampling Rate ◽  
Capacitive Coupling ◽  
Structural Health

ABSTRACTOne approach for structural health monitoring of aging aircraft is to take discrete airframe strain measurements and record the flight loads history. A complementary method consists of measuring changes in dynamic response due to fatigue crack growth. The challenge in implementing such methods is the need for inexpensive networks of distributed strain sensors which possess high resolution with no drift over time. The Uni-Axial Strain Transducer (UAST) has been developed as a digital, absolute encoding device to address these very issues. The UAST is a micro-electromechanical system (MEMS) which exploits the capacitive coupling between an array of electrostatic field emitters and an array of 64 field detectors on a CMOS IC chip. The slightly different array element spacings form a vernier scale and digital signal processing of the detector outputs is used to calculate the absolute translational displacement of the emitter array relative to the CMOS detector chip. The UAST provides a dynamic range of 11,500 μ-strain and displacements of 2.5 nm are easily resolved. The sensor sampling rate is dynamically configurable for 150, 290, 540, 1000, 1600 or 2500 Hz, providing 15, 14, 13, 12, 11, or 10 bits of resolution (equal to 0.35, 0.7, 1.4, 2.8, 5.6, or 11.4 μ-strain), respectively. The sensor network can communicate with up to 128 UASTs on a common 5-wire digital bus, eliminating the need for shielding and considerably reducing the number of wires which will have to be routed through the airframe. A network technology demonstration is being conducted on a 1/2 scale F-I 8 vertical tail where dynamic loads are applied to evaluate network performance related to monitoring of fatigue crack growth or rivet-line failures. Application of the UAST in a helicopter rotor health usage and monitoring system, and the design of a bi-axial transducer under development, are also mentioned.

scholarly journals Toward identifying crack-length-related resonances in acoustic emission waveforms for structural health monitoring applications

2017 ◽  
Vol 17 (3) ◽  
pp. 577-585 ◽  
Author(s):  
Md Yeasin Bhuiyan ◽  
Jingjing Bao ◽  
Banibrata Poddar ◽  
Victor Giurgiutiu
Keyword(s):  
Finite Element ◽  
Acoustic Emission ◽  
Fatigue Crack ◽  
Structural Health Monitoring ◽  
Crack Growth ◽  
Health Monitoring ◽  
Resonance Phenomenon ◽  
Vibration Modes ◽  
Local Vibration ◽  
Structural Health

In this study, we focus on analyzing the acoustic emission waveforms of the fatigue crack growth despite the conventional statistics-based analysis of acoustic emission. The acoustic emission monitoring technique is a well-known approach in the non-destructive evaluation/structural health monitoring research field. The growth of the fatigue crack causes the acoustic emission in the material that propagates in the structure. The acoustic emission happens not only from the crack growth but also from the interaction of the crack tips during the fatigue loading in the structure. The acoustic emission waveforms are generated from the acoustic emission events; they propagate and create local vibration modes along the crack faces (crack resonance). In-situ fatigue and acoustic emission experiments were conducted to monitor the acoustic emission waveforms from the fatigue cracks. Several test specimens were used in the fatigue experiments, and corresponding acoustic emission waveforms were captured. The acoustic emission waveforms were analyzed and distinguished into three types based on the similar nature in both time and frequency domains. Three-dimensional harmonic finite element analyses were performed to identify the local vibration modes. The local crack resonance phenomenon has been observed from the finite element simulation that could potentially give the geometric information of the crack. The laser Doppler vibrometry experiment was performed to identify the crack resonance phenomenon, and the experimental results were used to verify the simulated results.

scholarly journals Crack-Length Estimation for Structural Health Monitoring Using the High-Frequency Resonances Excited by the Energy Release during Fatigue-Crack Growth

Sensors ◽  
2021 ◽  
Vol 21 (12) ◽  
pp. 4221
Author(s):  
Roshan Joseph ◽  
Hanfei Mei ◽  
Asaad Migot ◽  
Victor Giurgiutiu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Length ◽  
Crack Growth ◽  
Health Monitoring ◽  
Acoustic Waves ◽  
High Frequency ◽  
Fem Analysis ◽  
Signal Frequency ◽  
Propagation Pattern

Acoustic waves are widely used in structural health monitoring (SHM) for detecting fatigue cracking. The strain energy released when a fatigue crack advances has the effect of exciting acoustic waves, which travel through the structures and are picked up by the sensors. Piezoelectric wafer active sensors (PWAS) can effectively sense acoustic waves due to fatigue-crack growth. Conventional acoustic-wave passive SHM, which relies on counting the number of acoustic events, cannot precisely estimate the crack length. In the present research, a novel method for estimating the crack length was proposed based on the high-frequency resonances excited in the crack by the energy released when a crack advances. In this method, a PWAS sensor was used to sense the acoustic wave signal and predict the length of the crack that generated the acoustic event. First, FEM analysis was undertaken of acoustic waves generated due to a fatigue-crack growth event on an aluminum-2024 plate. The FEM analysis was used to predict the wave propagation pattern and the acoustic signal received by the PWAS mounted at a distance of 25 mm from the crack. The analysis was carried out for crack lengths of 4 and 8 mm. The presence of the crack produced scattering of the waves generated at the crack tip; this phenomenon was observable in the wave propagation pattern and in the acoustic signals recorded at the PWAS. A study of the signal frequency spectrum revealed peaks and valleys in the spectrum that changed in frequency and amplitude as the crack length was changed from 4 to 8 mm. The number of peaks and valleys was observed to increase as the crack length increased. We suggest this peak–valley pattern in the signal frequency spectrum can be used to determine the crack length from the acoustic signal alone. An experimental investigation was performed to record the acoustic signals in crack lengths of 4 and 8 mm, and the results were found to match well with the FEM predictions.

Nonlinear ultrasonic detection for evaluating fatigue crack in metal plate

2018 ◽  
Vol 18 (3) ◽  
pp. 869-881 ◽  
Author(s):  
Rong Wang ◽  
Qi Wu ◽  
Fengming Yu ◽  
Yoji Okabe ◽  
Ke Xiong
Keyword(s):  
Fatigue Crack ◽  
Structural Health Monitoring ◽  
Health Monitoring ◽  
Lamb Wave ◽  
Fatigue Cracks ◽  
Crack Model ◽  
Monitoring Method ◽  
Cycle Number ◽  
Structural Health ◽  
Nonlinear Ultrasonic

In engineering structures, metal materials always endure fatigue cracks under long-term service. There has been a demand for developing a structural health monitoring method to evaluate micro-sized fatigue cracks, as cracking is considered as a precursor to structural failure. However, conventional linear-ultrasound-based technology is not sensitive to crack when it is barely visible in a metal medium. In this article, we present a nonlinear ultrasonic technology based on crack–wave interaction to investigate the growth of a fatigue crack. A breathing-crack model with a plastic zone around it was precisely established to reveal the change in the Lamb wave. The relative nonlinear parameter calculated from the fundamental and harmonic components of the Lamb wave showed linearly increasing with the growth of the fatigue crack. The relative nonlinearity was related to ultrasonic parameters, such as the cycle number and the excited frequency of the tone-burst signal. In addition, it was also related to the angle between the sensor and the crack rather than their distance. A set of experiments were conducted, demonstrating that the increasing trend of ultrasonic nonlinearity fits very well to the finite element analysis results. In conclusion, the nonlinear ultrasonic method that can be applied to the detection of micro fatigue cracks in metal plates is an effective structural health monitoring technique.

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