차천앙 교수

Abstract This article presents a comprehensive review of the laser-based guided ultrasonic waves propagation imaging (G-UPI) system and respective signal/data processing methods related to the nondestructive testing and evaluation of thin-walled structures. The primary goal of this study is to review and recognize various processing methods, explain the working principles of the most influential methods, and highlight outstanding capabilities. In addition, the suitability of the methods for mult

Two aircraft wings made of carbon fiber-reinforced plastic material were inspected using the laser-based ultrasonic propagation imaging system for the visualization of manufacturing defect and damages of debonding mode. Hypotheses of the detection mechanism of composite debonding were presented and validated through the inspection results for the bonding lines of the composite wing structures. The inspection showed that the location, shape, and size of the poor bonding defect, artificial stringe

The direct attachment of piezoelectric transducers onto hot targets raises formidable challenges as piezoelectric transducers lose their piezoelectric characteristics at elevated temperatures or debond due to thermal expansion coefficient mismatches. We developed a welded fibre acoustic-wave PZT (FAWPZT) sensor to alleviate these temperature limitations. One end of the FAWPZT sensor, made from a stainless steel fibre, was welded onto a stainless steel target plate and the other end was bonded to

An ultrasonic propagation imaging (UPI) system consisted of a Q-switched Nd-YAG pulsed laser and a galvanometer laser mirror scanner was developed. The system which requires neither reference data nor fixed focal length could be used for health monitoring of curved structures. If combined with a fiber acoustic wave PZT (FAWPZT) sensor, it could be used to inspect hot target structures that present formidable challenges to the usage of contact piezoelectric transducers mainly due to the operating

Abstract Incipient thermal damage (ITD) in polymer-matrix composites could cause substantial loss of material properties and it is notoriously difficult to be detected using nondestructive evaluation (NDE) techniques. The emerging ultrasonic propagation imaging (UPI) could be the solution for the detection problem and its detection probability for ITD was studied in this work. Glass fiber reinforced epoxy plate specimens insulted at temperatures ranging between 1.1 and 1.7 times of the glass tra

The inability to statistically evaluate the damage size based on amplitude mapping has long plagued the ultrasound propagation imaging (UPI) system and related non-destructive evaluation (NDE) community. This paper proposes a damage visualization method called the Statistically Thresholded Anomaly Mapping (STAM) method to solve this problem. It could isolate the damage-induced anomalous waves from an ultrasonic full wavefield data, map their amplitudes into an image and statistically differentia

Arcing effects, such as that due to lightning, on glass fiber reinforced epoxy composite laminate used in aerospace applications, have been studied. Lightning voltage impulses (1.2/50 micro seconds) were applied at breakdown voltage on the specimens and the arc points were inspected nondestructively using an Ultrasonic Propagation Imaging (UPI) system. The data acquired were processed using the Statistically Thresholded Anomaly Mapping (STAM) method. The outcomes depict that the size of lightnin

Joints in aero-mechanical structures are critical elements that ensure the structural integrity but they are prone to damages. Inspection of such joints that have no prior baseline data is really challenging but it can be possibly done using the Ultrasonic Propagation Imager (UPI). The feasibility of applying UPI for detection of loosened fastener is investigated in this study. A simple lap joint specimen made by connecting two pieces of 2.5mm thick SAE304 stainless steel plates using five M6 sc

Guided ultrasonic wavefield propagation imaging (GUPI) is useful for visualizing hidden flaws in aerospace thin-walled structures, but the need for subjective signal processing involving three-dimensional Fourier transformation to increase the visibility of subtle flaws hinders its wider acceptance. A high-resolution wavenumber bandpass filter capable of consolidating subtle flaw-relevant information from a wide frequency band using only two-dimensional Fourier transformation was proposed. The f

A focusing-free ultrasonic imaging system for in-situ ground structural health monitoring (SHM) was developed using a Q-switched laser and a 2D laser mirror scanner. Two imaging methods, i.e. a frequency-selectable Ultrasonic Energy Propagation Imaging (UEPI) and Ultrasonic Frequency Tomography (UFT) methods were included. The UEPI result movie could be seen as ultrasonic energy wavefront emerging from the sensing location with concentrated energy at structural damages. The UFT generates tomogra

Visualization of wavefield propagation has been evolving as one of the most significant nondestructive imaging methods for structural damage evaluation and shock analysis. Corresponding visualization systems that are commonly used are potentially affected by aliasing due to the nature of discrete sampling in spatial and temporal domains. This study was conducted to define the problem and produce a spatial sampling guideline for aliasing-free visualization. Experimental demonstration was given at