No abstract

No abstract

Abstract-We report on work that is part of the development of an agent-based structural health monitoring system. The data used are acoustic emission signals, and we classify these signals according to source mechanisms, those associated with crack growth being particularly significant. The agents are proxies for communication-and computation-intensive techniques and respond to the situation at hand by determining an appropriate constellation of techniques. It is critical that the system have a repertoire of classifiers with different characteristics so that a combination appropriate for the situation at hand can generally be found. We use unsupervised learning for identifying the existence and location of damage but supervised learning for identifying the type and severity of damage. The supervised learning techniques investigated are support vector machines (SVM), naive Bayes classifiers, and feed-forward neural networks (FNN). The unsupervised learning techniques investigated are k-means (with k equal to 3, 4, 5, and 6) and self-organizing maps (SOM, with 3, 4, 5, and 6 output neurons). For each technique except SOM, we tested versions with and without principal component analysis (PCA) to reduce the dimensionality of the data. We found significant differences in the characteristics of these machine learning techniques, with trade-offs between accuracy and fast classification runtime that can be exploited by the agents in finding appropriate combinations of classification techniques. The approach followed here can be generalized for exploring the characteristics of machine-learning techniques for monitoring various kinds of structures.

No abstract

Relative motion between surfaces of mechanical parts causes surface wear and damage. The degradation to the surfaces has been monitored using vibration characteristics as well as acoustic emissions generated during the relative surface movements. In particular, acoustic emission signals were found to be sensitive to some of the microscopic processes occurring at the frictional interface. In this study, friction between two surfaces was monitored experimentally under controlled conditions. Relative velocity, contact pressure, and surface roughness values were varied in the experiments. Friction related acoustic emission signals were recorded and analyzed to understand the relationship between the signals generated and the physical processes giving rise to these signals. Information related to the stick-slip movements during cyclic motion, in the experiments, was observed from the signals. Features of the waveforms were found to reveal the conditions existing at the friction interface. In particular, the changes in the surface roughness and contact pressure were readily observed from the acoustic emission signals.

No abstract

No abstract

No abstract