Health monitoring of bolted joints using modal-based vibrothermography

This article presents a novel modal-based vibrothermographic approach for health monitoring of loosening bolted joints in coupled structures. In this article, the theoretical background supporting this proposed approach is firstly presented. Through finite element analyses on a simple bolted structure with varying joint conditions achieved by adjustment of bolt loads, the relationship between the bolt load and the temperature increase in the vibrating bolted joint during vibrothermographic tests was revealed. Experimental vibrothermographic tests on a more complex structure were completed to verify the observations from the finite element analyses while demonstrating the viability of the vibrothermographic approach in a laboratory environment. It has been shown that this vibrothermographic approach was able to determine the stage of a bolted joint in its progression of failure by tracing the changes in the temperature increase in relevant regions during vibrothermographic tests. Moreover, additional tests have been performed to illustrate that this approach was effective even by using only the residual responses of the structure’s vibration that were away from the resonances, which indicates it is more applicable to structures with higher damping as such structures have stronger residual responses during vibration that can be utilized. In the concluding observations of the article, the procedure for practical application of this approach is summarized, and its potential for further development is discussed

Low-Frequency Vibrothermography Using Lightweight Piezoelectric Actuators:The Location of Excitation and Application to Composite Materials

This article presents a novel infrared thermographic approach for damage detection by utilizing the heat generated around damage sites during vibrations below 1000 Hz induced by lightweight piezoelectric actuators. In this research, the optimal location of excitation was first investigated through finite element analyses, where two generalized equations were obtained to describe the relationship between the excitation and the resulting displacement response. These observations were then verified experimentally on an aerospace-grade composite plate, followed by vibrothermographic tests conducted on the same structure to demonstrate the effectiveness of the proposed damage detection process employing only a single lightweight piezoelectric disk as the actuator

Modal-based vibrothermography using feature extraction with application to composite materials

This research focuses on the development of a damage detection algorithm based on modal testing, vibrothermography, and feature extraction. The theoretical development of mathematical models is presented to illustrate the principles supporting the associated algorithms, through which the importance of the three components contributing to this approach is demonstrated. Experimental tests and analytical simulations have been performed in laboratory conditions to show that the proposed damage detection algorithm is able to detect, locate, and extract the features generated due to the presence of sub-surface damage in aerospace grade composite materials captured by an infrared camera. Through tests and analyses, the reliability and repeatability of this damage detection algorithm are verified. In the concluding observations of this article, suggestions are proposed for this algorithm’s practical applications in an operational environment