Highly Nonlinear Solitary Waves to Estimate Orientation and Degree of Anisotropy in Rocks

This paper delves into the use of highly nonlinear solitary waves for the nondestructive identification and characterization of anisotropy in rocks. The nondestructive testing approach proposed expands upon a technique developed recently by some of the authors for the nondestructive characterization of engineering materials and structures. The technique uses the characteristics of solitary waves propagating in a periodic array of spherical particles in contact with the rock to be characterized. The features of the waves that bounce off the chain rock interface are used to infer some properties of the geomaterial under consideration. Numerical models and experimental validation were conducted to explore the feasibility of the method and to standardize the methodology for future widespread applications.

Cure Monitoring of Adhesive for Composite/Metal Bonded Structure Based on Highly Nonlinear Solitary Waves

In this paper, a nondestructive evaluation technique based on highly nonlinear solitary waves (HNSWs) is proposed to monitor the curing process of adhesive for composite/metal bonded structure. HNSWs are mechanical waves with high energy intensity and non-distortive nature which can form and propagate in a nonlinear system, such as a one-dimensional granular chain. In the present study, a finite element model of the one-dimensional granular chain is established with the commercial software Abaqus, to study the reflection behavior of HNSWs at the interface between the particle at the end of chain and the sample. The simulation results show that the time of flight (TOF) of the primary reflected solitary wave decreases with the stiffness of the sample increases, and the amplitude ratio (AR) between the primary reflected solitary wave and the incident solitary wave increases. An HNSWs transducer based on the one-dimensional granular chain is designed and fabricated. The relationship between the characteristic parameters of the primary reflected solitary wave (TOF and AR) and the curing time of adhesive for a composite/metal bonded structure is experimentally investigated. The experiment results suggest that the TOF decreases and the AR increases as the epoxy cures. The experimental results are in good agreement with the simulation results. This study provides a new characterization method for monitoring the curing process of adhesive for composite/metal bonded structure.

Outlier analysis of nonlinear solitary waves for health monitoring applications

The structural health monitoring/nondestructive evaluation method based on the generation and detection of highly nonlinear solitary waves is emerging as a cost-effective technique to monitor or inspect a variety of structures and materials. These waves possess unique characteristics not seen in conventional ultrasounds. Outlier analysis is a statistic tool able to identify anomalies in data that diverge from a set of baseline data. Although outlier analysis has received considerable attention for defect detection using modal data, guided ultrasonic waves, or other nondestructive approaches, its application for the analysis of solitary waves has never been explored. In the study presented in this article, the use of outlier analysis in terms of discordancy test and Mahalanobis squared distance was investigated to enhance the damage detection capability of a monitoring system based on highly nonlinear solitary waves. Two experiments were performed to demonstrate the procedure. In the first experiment, a thick steel plate was probed with a solitary wave transducer placed above the plate, and damage was simulated in terms of a foreign object magnetically attached to the bottom of the plate, at different distances from the transducer. In the second experiment, two aluminum plates were placed above each other in dry contact with the top plate subjected to localized, mostly hidden, defects. The transducer used in the first experiment was in this second test encased in a small cart with wheels to scan the sample at discrete positions. For both experiments, a few features were extracted from the time waveforms and fed to a univariate and a multivariate analysis that compared the testing data to a set of baseline data. The results show that the outlier analysis significantly improves the ability to detect damage using solitary waves.

A Nondestructive Evaluation Approach to Characterize Tennis Balls

Sometimes, nondestructive evaluation (NDE) or structural health monitoring methods commonly used in engineering structures are used for the betterment of consumer goods. A classic example is the use of sensor systems to monitor the pressure and the quality of car tires. In this paper, we present a nondestructive method to characterize tennis balls. The International Tennis Federation (ITF) specifies which characteristics a tennis ball must have in order to be commercialized. One of these characteristics is bounciness and the standardized method to measure it is the rebound test, where a ball is released from 2.54 m onto a smooth rigid surface and, in order to be approved, the ball must bounce within a certain range. This test can be staged by manufacturers and testing authorities but the equipment necessary to perform it is not readily available to the average consumer. In the study presented in this paper, an empirical method based on the propagation of highly nonlinear solitary waves (HNSWs) is proposed to establish whether a given ball conforms the specifications set by the ITF in terms of bounciness and allowed deformation. The experiments conducted in this study aim to discover a correlation between some features of the waves and the values obtained with the rebound test and the compression test in which the deformation of the ball under a known load is measured. The presence of such correlations could represent a viable alternative to establish the conformity of tennis balls. Based on the empirical evidences collected in this study, a possible new standard is suggested.