Seung-Chan Hong

Development of pulse-echo ultrasonic propagation imaging system and its delivery to Korea Air Force

This paper proposes a full-field pulse-echo ultrasonic propagation imaging (FF-PE-UPI) system for non-destructive evaluation of structural defects. The system works by detection of bulk waves that travel through the thickness of a specimen. This is achieved by joining the laser beams for the ultrasonic wave generation and sensing. This enables accurate and clear damage assessment and defect localization in the thickness with minimum signal processing since bulk waves are less susceptible to dispersion during short propagation through the thickness. The system consists of a Qswitched laser for generating the aforementioned waves, a laser Doppler vibrometer (LDV) for sensing, optical elements to combine the generating and sensing laser beams, a dual-axis automated translation stage for raster scanning of the specimen and a digitizer to record the signals. A graphical user interface (GUI) is developed to control all the individual blocks of the system. Additionally, the software also manages signal acquisition, processing, and display. The GUI is created in C++ using the QT framework. In view of the requirements posed by the Korean Air Force(KAF), the system is designed to be compact and portable to allow for in situ inspection of a selected area of a larger structure such as radome or rudder of an aircraft. The GUI is designed with a minimalistic approach to promote usability and adaptability while masking the intricacies of actual system operation. Through the use of multithreading the software is able to show the results while a specimen is still being scanned. This is achieved by real-time and concurrent acquisition, processing, and display of ultrasonic signal of the latest scan point in the scan area.

An arm wearable haptic interface for impact sensing on unmanned aerial vehicles

In this paper, an impact monitoring system using fiber Bragg grating (FBG) sensors and vibro-haptic actuators have been introduced. The system is suggested for structural health monitoring (SHM) for unmmaned aerial vehicles (UAVs), by making a decision with human-robot interaction. The system is composed with two major subsystems; an on-board system equipped on UAV and an arm-wearable interface for ground pilot. The on-board system acquires impact-induced wavelength changes and performs localization process, which was developed based on arrival time calculation. The arm-wearable interface helps ground pilots to make decision about impact location themselves by stimulating their tactile-sense with motor vibration.

In-situ NDE of Composite Repair Patch and Thick Panel with Substructures using Mobile Pulse-Echo Ultrasonic Propagation Imager

Composites are widely used as structural materials due to its advantage for weight to strength ratio compared to metallic structures in aircrafts. Thus, their usage is increasing in aircraft industry and the technique of composite manufacturing has been rapidly developing. However, detection of defects in composite structure is challenging compared to that in metallic structure. Based on this, various structural health monitoring and nondestructive inspection techniques have been researched to detect the defect in composite structure. Among the techniques, in-situ nondestructive evaluation (NDE) is increasingly used to avoid time-consuming work such as aircraft disassembly for inspection. Recently, laser ultrasonic generator is widely used because it generates broadband ultrasound of diverse modes by thermoelastic mechanism and it works as non-contact excitation. In addition, non-contact sensing laser for measuring ultrasound is drawing attention because it has a benefit of non-contact sensing in inaccessible area. In this study, fully non-contact mobile pulse-echo ultrasonic propagation imager (PE UPI) based on laser ultrasound is introduced as an in-situ NDE tool. The mobile PE UPI is configured with scanning laser head, two-axis translation scanner and UPI controller. The scanning laser head including generation and sensing lasers scans with two-axis translation stage to generate and sense pulse-echo through-the-thickness ultrasounds as bulk wave. After completing the scan, the defects are visualized by fullfield pulse-echo ultrasonic wave propagation imaging (FF PE UWPI) technique and variable time window amplitude map (VTWAM). For nondestructive evaluation, the mobile PE UPI inspected composite repair patch and composite thick panel with substructures. As a result, the defects in the composite repair patch and composite panel with substructures were visualized by FF PE UWPI video and VTWAM

Remote defect visualization of standard composite coupons using a mobile pulse-echo ultrasonic propagation imager

A new laser-ultrasonic-based defect monitoring system, a mobile pulse-echo ultrasonic propagation imager, has been developed to evaluate damage to composite and metallic structures. The system integrates a Q-switched Nd:YAG laser for the generation of thermoelastic waves, a laser Doppler vibrometry sensor for sensing ultrasound and a two-axis translation stage for raster scanning of the combined generation and sensing laser beams. The system allows scanning of both ultrasound generation and sensing laser beams simultaneously. Thus, a full-field pulse-echo ultrasound, as large as the scan area, can be generated that visualizes the longitudinal wave propagation through the thickness. The full-field pulse-echo ultrasonic wave propagation imaging algorithm is used for real-time structural damage evaluation. Four F-16 Lockheed Martin aircraft reference standard composite specimens with different shapes, sizes, thicknesses, compositions, and aspect ratio of damages were tested: the stepped graphite-to-aluminum, the graphite-to-graphite, and the steel-to-graphite composite panel with flat bottom holes and the graphite-to-aluminum core sandwich structure with core missing. Moreover, the effects of laser pulse energy on damage visualization using the system has been presented and tested on the 4-mm-thick aluminum plate with 2-mm-thick wall-thinning. The proposed system successfully detected and visualized all the artificially introduced defects in the standard coupons.

Composite NDE using full-field pulse-echo ultrasonic propagation imaging system

In this paper, a novel ultrasonic propagation imaging system, called a full-field pulse-echo ultrasonic propagation imaging (FF PE UPI) system is presented. The coincided laser beams for ultrasonic sensing and generation are scanned and pulse-echo mode laser ultrasounds are captured. This procedure makes it possible to generate full-field ultrasound in through-the-thickness direction as large as the scan area. The system nondestructively inspected targets with two-axis translation stages. Various structural inspection results in the form of full-field ultrasonic wave propagation videos are introduced, which are an aluminum honeycomb sandwich, ailerons and carbon fiber reinforced plastic (CFRP) honeycomb sandwich structures including various defects.

Korea Air force standard NDE coupon test of full-field pulse-echo laser ultrasonic propagation imaging system

Korea Air force standard NDE coupons which are practical structures used in real aircraft construction were inspected using full-field pulse-echo ultrasonic propagation imaging (FF PE UPI) system. The Korea Air force standard NDE coupons consist of a laminated carbon fiber reinforced plastic (CFRP) step and a CFRP skin/honeycomb sandwich, an aluminum honeycomb sandwich, a bonded aluminum-aluminum coupon, an aircraft magnesium fin including various defects. The FF PE UPI system inspects based on combined generation and sensing laser beams for generating and sensing pulse-echo ultrasound and two-axis transition stage for raster scan. In order to visualize various defects of the coupons, pulse-echo ultrasonic wave propagation imaging algorithm is used after scanning the coupons.

Advances in Smart Hangar and Its Real-world Applications

Composites are widely used as structural materials in aircrafts made recently and its usage is increasing rapidly. However, it is easy to occur structural damages and defects such as disbond, delamination, impact damage and so on in composite structures unlike those of common aircraft made of metallic materials. In this research, to detect this kinds of damage or defect of composite structures in aircraft, we suggest concept of the Smart Hangar which is a full-scale structural inspection technique for aircraft based on the built-in ultrasonic propagation imaging (UPI) system, mobile UPI systems for built-in PZT sensors and for external noncontact/contact sensors and fullfield pulse-echo UPI system. The high-performance mobile ultrasonic propagation imaging is a non-destructive inspection technique to visualize damage or defect in structures by combination of high-accuracy rapid laser scanning excitation and highspeed DAQ and signal processing based on the field programmable gate arrays. The UPI technique is able to scan rapidly at a pulse repetition rate of 20 kHz. After acquiring the generated ultrasonic wave signal induced by laser excitation, ultrasonic wave propagation imaging movies for the in-plate guide wave or through-transmission wave are displayed. The built-in UPI system is based on long-range scanning and is integrated in the Smart Hangar. The built-in UPI system is also extended to multi-area simultaneous inspection by adding a beam expander, a laser mirror scanner and a beam splitter. In case of the full-field pulse-echo UPI system, the two laser beams scan real structures along raster scanning pattern based on two-axis linear translation stage. The sensing laser can capture pulse-echo through-the-thickness ultrasound by impinging the sensing laser beam at the same point as the generation laser beam. In this work, we present a few real world applications, a large military UAV with 10 m long composite wing, a military transport airplane with composite fairing. In the application results using the mobile UPI system, the developed mobile UPI system and built-in UPI system provided the damage visualization results showing disbond area between the skin and spar and disbond damage in the fairing. In the application results using the full-field pulse-echo UPI system, barely visible impact damages in a carbon fiber reinforced plastic (CFRP) wing skin panel and artificial defects which are two drilled holes in a glass fiber reinforced plastic (GFRP) aircraft encoder case. doi: 10.12783/SHM2015/311