This paper investigates the application of highly nonlinear solitary waves as a nondestructive evaluation method to detect localized corrosion in metallic structures. An experiment was conducted by using chains of monoperiodic particles in contact with a steel plate subjected to localized accelerated corrosion. A few damage-sensitive features were extracted from the time waveforms and fed into a multivariate statistical analysis to enhance the sensitivity of the proposed non-invasive monitoring approach. The experiment was complemented by a finite element model to quantify the effects of localized corrosion on certain features of the solitary waves propagating along the chain. Both the numerical and the experimental results show that the solitary waves reflected at the chain-plate interface are affected by the presence and progression of corrosion. Furthermore, the multivariate statistical analysis improved the sensitivity of the proposed approach. In the future, the proposed method may be implemented in those applications in which high temperature or radioactive environments are detrimental for the use of piezoelectric based ultrasonic testing.
In recent years, there has been an increasing interest in the use of highly nonlinear solitary waves (HNSWs) for nondestructive evaluation and structural health monitoring applications. HNSWs are mechanical waves that can form and travel in highly nonlinear systems, such as granular particles in Hertzian contact. The easiest setup consists of a built-in transducer in drypoint contact with the structure or material to be inspected/monitored. The transducer is made of a monoperiodic array of spherical particles that enables the excitation and detection of the solitary waves. The transducer is wired to a data acquisition system that controls the functionality of the transducer and stores the time series for post-processing. In this paper, the design and testing of a wireless unit that enables the remote control of a transducer without the need to connect it to sophisticated test equipment are presented. Comparative tests and analyses between the measurements obtained with the newly designed wireless unit and the conventional wired configuration are provided. The results are corroborated by an analytical model that predicts the dynamic interaction between solitary waves and materials with different modulus. The advantages and limitations of the proposed wireless platform are given along with some suggestions for future developments.
A new corrosion monitoring technique based on the generation and propagation of highly nonlinear solitary waves in 1D granular crystals has been developed recently. In this method, a monoperiodic array of spherical particles, interacting via Hertzian contact forces, is in point contact with the structure or material to be inspected. The array is part of a wireless unit used to induce the wave in the chain and record the solitary waveform remotely. Compared to classical NDE techniques used for thickness monitoring, the developed method is low cost, portable, and simple. This study presents a numerical and an experimental investigation of the sensitivity of solitary waves to localized corrosion. In the experimental study, a corroding steel plate was monitored using solitary waves to examine the effect of corrosion in the plate on the solitary waves interacting with the plate. Furthermore, a discrete element model was coupled with a finite element model to numerically predict the effect of localized corrosion on the delay and the amplitude of the reflected solitary waves formed at the chain-plate interface. The plate was studied in both pristine and corroded conditions. Furthermore, the study investigated customizing the granular chain design to achieve solitary wave-based sensors that can be used in high-temperature environments with maximum sensitivity to corrosion. The numerical results were in good agreement with experimental results and showed that the reflected solitary waves are affected by the presence and the propagation of corrosion in the plate. It was also shown that the sensitivity of the method increases for thinner plates or when the depth of corrosion exceeds half of the plate thickness.
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