In this work, we investigated a Hyperspectral NDE (HySpecNDE) technique for detection of early damage and material degradation in metallic structures and components. A hyperspectral imaging camera in middle wavelength infrared (MWIR) was used to examine metallic specimens with damage and material degradation created from tensile testing. Hyperspectral data in the MWIR range at ambient and elevated temperatures was acquired and analyzed with a set of data analysis and image processing algorithms. By comparing the digital image correlation results during tensile testing and the hyperspectral analysis results, we demonstrated that HySpecNDE technique unveils the variations in emission intensity, which correspond to early damage and material degradation in materials.
A traceable micro-force sensor capable of measuring forces in the range of micronewtons to millinewtons was developed. This sensor consists of a pair of parallel electrodes to provide precise capacitance measurements. In conjunction with a traceable ultrahigh accuracy capacitance bridge, this sensor can be used as a secondary transfer micro-force standard after being calibrated against the primary forces realized with deadweights. This micro-force senor was used to verify commercial nanoindentation instruments. By comparing the measurement readings from the calibrated micro-force sensor and those recordings from a nanoindentation system, the errors of loading from that instrument can been determined. The calibration results show that significant errors present in the commercial nanoindentation instruments when their loading forces are extended to the micronewton range, which is not, and unable to be calibrated directly with available standards and current practices.
Thermosonic imaging is a new nondestructive testing (NDT) technique capable of provide full-field, rapid inspection of crack-type of defects in materials or structures. Conventional thermosonic imaging system employs an ultrasonic welder, which is designed of a single frequency to generate high-power ultrasonic excitation in a work piece, and an infrared (IR) camera to capture thermal images of surface and subsurface defects under ultrasonic excitation. Most thermosonic imaging NDT is applied for metallic materials to detect crack-like defect, since the heat is generated from the rubbing surfaces of a defect. The inspection of composite structures using thermosonic NDT remains challenging due to their high acoustic attenuation and low surface hardness. In this paper, we present the development of a thermosonic imaging system, which is capable of exciting the ultrasonic transducer at different frequencies for Thermosonic NDT to overcome the limitations associated with single frequency power source as well as the spring loaded transducer design. One particular application of this new thermosonic imaging system is for rapid inspection of composite structures. Various composite structures have been tested to verify and valid the new thermosonic imaging system performance.
Autonomous structural health monitoring (SHM) of aerostructures strengthens the reliability, increases the lifetime, and reduces the maintenance cost of aerovehicles such as airplanes and unmanned aerial vehicles (UAV). The continuous monitoring of aerostructures for early damage detection and identification is made possible through a wireless network of sensors deployed on the structure. Usually, the data collected by these sensors is communicated to a central unit for real-time data processing using electromagnetic waves at radio frequencies (RF). However, the emission of RF signals for autonomous SHM creates additional sources of interference to on-board RF communication systems used for aircraft control and safety-related services. To overcome this issue, we propose in this paper an acoustic data communication system for autonomous health monitoring of aerostructures which are modeled as thin plate-like structures. In the proposed system, both damage detection and wireless communication are performed using guided elastic waves. Data communication across an elastic channel is challenging because of the severe frequency-dispersive and multimodal propagation in solid media which distorts, delays, and greatly attenuates the transmitted data signals. To cope with this problem, we introduce a sensor network based on time-reversal pulse position modulation that compensates for channel dispersion and improves the signal-to-noise ratio of the communication link without relying on sophisticated channel estimation algorithms. We demonstrate the viability of the presented system by conducting experiments on an homogeneous and isotropic aluminum plate specimen using Lead Zirconate Titanate (PZT) sensor discs at a resonant frequency of 300 kHz.
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