Journal
STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL
Volume 18, Issue 3, Pages 869-881Publisher
SAGE PUBLICATIONS LTD
DOI: 10.1177/1475921718784451
Keywords
Nonlinear ultrasonic detection; fatigue crack; contact acoustic nonlinearity; Lamb wave; structural health monitoring
Funding
- National Natural Science Foundation of China [51605224]
- Grant of State Key Laboratory of Mechanics and Control of Mechanical Structures [0516G02]
- JSPS KAKENHI [JP15K06457]
- Nanjing University of Aeronautics and Astronautics
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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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