Man-Yong Choi

Quantitative Defects Detection in Wind Turbine Blade Using Optical Infrared Thermography

Abstract A wind turbine blade is an important component in wind-power generation, and is generally exposed toharsh environmental conditions. Ultrasonic inspection is mainly used to inspect such blades, but it has beendifficult to quantify defect sizes in complicated composite structures. Recently, active infrared thermography hasbeen widely studied for inspecting composite structures, in which thermal energy is applied to an object, and aninfrared camera detects the energy emitted from it. In this paper, a calibration method for active optical lock-inthermography is proposed to quantify the size. Inclusion, debonding and wrinkle defects, created in a wind bladefor 100 kW wind power generation, were all successfully detected using this method. In particular, a 50.0φ mmdebonding defect was sized with 98.0% accuracy. Keywords: Wind Turbine Blade, Optical Infrared Thermography, Lock-in Method, Quantitative Defects Detection[Received: December 18, 2014, Revised: February 3, 2015, Accepted: February 17, 2015] *과 학기술연합 대원교(UST) ** ,항공기시스템공학 한국표준과학연구원 안전측정센터 Corresponding Author: Safety MeasurementCenter, Korea Research Institute of Standards and Science, Daejeon 305-340, Korea (E-mail: mychoi@kriss.re.kr)

The Study of Micro Crack Detection in Dissimilar Metal Weld Using a Variable Ultrasound Infrared Thermography

Abstract As a nondestructive inspection technology currently in use, infrared thermography has gradually expandedits application range to industry. The method detects only defect areas by grafting ultrasound on a technique ofdetecting infrared energy emitted from all objects with absolute temperature of 0 K and converting this energy intothermography for inspection. Ultrasound infrared thermography has merits including the ability to inspect a widearea in a short time without contacting the target object. This study investigated the applicability of the techniquefor defect detection using variable ultrasound excitation inspection methods on samples of Terfenol-D, amagnetostrictive material with a tunable natural resonant frequency. Keywords: Infrared Thermography, Absolute Temperature, Variable Ultrasound, Magnetostrictive Material, Terfenol-D[Received: June 2, 2015, Revised: June 22, 2015, Accepted: June 22, 2015] * ,한국표준과학연구원안전측정센터** ,한국스마트구조시스템연구원 Corresponding Author: Department of Research & Development, Korea ResearchInstitute of Smart Material and Structures System Association, Daejeon 302-852, Korea (E-mail: m55nring@naver.com)

Study on the Micro Crack Detection in Joints by Using Ultrasound Infrared Thermography

This study detected SCC defects of dissimilar metal welded(STS304 and SA106 Gr. b) pipes using the ultrasonic infrared thermography method and the lock-in image treatment method among infrared thermography method. The infrared excitement equipment has 250 Watt of output and 20 kHz of frequency. By using the ultrasound infrared thermography method, the internal defects of dissimilar metal weld joints of pipes used at nuclear power plants could get detected. By an actual PT test, it was observed that the cracks inside the pipe existed not as a single crack but rather as a multiple cracks within a certain area and generated a hot spot image of a broad area on the thermography image. In addition, UT technology could not easily defects detected by the width of fine hair cracks. but, ultrasound infrared thermography technique was defect detected.

Infrared Thermography Characterization of Defects in Seamless Pipes Using an Infrared Reflector

Infrared thermography uses infrared energy radiated from any objects above absolute zero temperature, and the range of its application has been constantly broadened. As one of the active test techniques detecting radiant energy generated when energy is applied to an object, ultrasound infrared thermography is a method of detecting defects through hot spots occurring at a defect area when 15~100 kHz of ultrasound is excited to an object. This technique is effective in detecting a wide range affected by ultrasound and vibration in real time. Especially, it is really effective when a defect area is minute. Therefore, this study conducted thermography through lock-in signal processing when an actual defect exists inside the austenite STS304 seamless pipe, which simulates thermal fatigue cracks in a nuclear power plant pipe. With ultrasound excited, this study could detect defects on the rear of a pipe by using an aluminium reflector. Besides, by regulating the angle of the aluminium reflector, this study could detect both front and rear defects as a single infrared thermography image.

Detection of defects in CFRP impact damage specimens by using Infrared Thermography

Recently, composite materials have been usually used in the main wings, ailerons and fuselages of aircrafts and the rotor blades of helicopters.[1] In the case of an aircraft using composite material for rapid-moving structures, their physical reactions to external shock also become different from those of the existing metal structures. In this connection, this study applied impact load to CFRP composite specimens by using the infrared thermography technology and different light sources, and then investigated the method for detecting damage to composite materials more quickly and more accurately. http://dx.doi.org/10.21611/qirt.2017.021

Study on the Performance of Infrared Thermal Imaging Light Source for Detection of Impact Defects in CFRP Composite Sandwich Panels

Recently, composite materials have been mainly used in the main wings, ailerons, and fuselages of aircraft and rotor blades of helicopters. Composite materials used in rapid moving structures are subject to impact by hail, lightning, and bird strike. Such an impact can destroy fiber tissues in the composite materials as well as deform the composite materials, resulting in various problems such as weakened rigidity of the composite structure and penetration of water into tiny cracks. In this study, experiments were conducted using a 2 kW halogen lamp which is most frequently used as a light source, a 2 kW near-infrared lamp, which is used for heating to a high temperature, and a 6 kW xenon flash lamp which emits a large amount of energy for a moment. CFRP composite sandwich panels using Nomex honeycomb core were used as the specimens. Experiments were carried out under impact damages of 1, 4 and 8 J. It was found that the detection of defects was fast when the xenon flash lamp was used. The detection of damaged regions was excellent when the halogen lamp was used. Furthermore, the near-infrared lamp is an effective technology for showing the surface of a test object.

Detecting the Honeycomb Sandwich Composite Material’s Moisture Impregnating Defects by Using Infrared Thermography Technique

Many composite materials are used in the aerospace industry because of their excellent mechanical properties. However, the nature of aviation exposes these materials to high temperature and high moisture conditions depending on climate, location, and altitude. Therefore, the molecular arrangement chemical properties, and mechanical properties of composite materials can be changed under these conditions. As a result, surface disruptions and cracks can be created. Consequently, moisture-impregnating defects can be induced due to the crack and delamination of composite materials as they are repeatedly exposed to moisture absorption moisture release, fatigue environment, temperature changes, and fluid pressure changes. This study evaluates the possibility of detecting the moisture-impregnating defects of CFRP and GFRP honeycomb structure sandwich composite materials, which are the composite materials in the aircraft structure, by using an active infrared thermography technology among non-destructive testing methods. In all experiments, it was possible to distinguish the area and a number of CFRP composite materials more clearly than those of GFRP composite material. The highest detection rate was observed in the heating duration of 50 mHz and the low detection rate was at the heating duration of over 500 mHz. The reflection method showed a higher detection rate than the transmission method.

Study on the Defects Detection in Composites by Using Optical Position and Infrared Thermography

Non-destructive testing methods for composite materials (e.g., carbon fiber-reinforced and glass fiberreinforced plastic) have been widely used to detect damage in the overall industry. This study detects defects using optical infrared thermography. The transient heat transport in a solid body is characterized by two dynamic quantities, namely, thermal diffusivity and thermal effusivity. The first quantity describes the speed with thermal energy diffuses through a material, whereas the second one represents a type of thermal inertia. The defect detection rate is increased by utilizing a lock-in method and performing a comparison of the defect detection rates. The comparison is conducted by dividing the irradiation method into reflection and transmission methods and the irradiation time into 50 mHz and 100 mHz. The experimental results show that detecting defects at 50 mHz is easy using the transmission method. This result implies that low-frequency thermal waves penetrate a material deeper than the high-frequency waves.

A Method to Simulate Frictional Heating at Defects in Ultrasonic Infrared Thermography

Ultrasonic infrared thermography is an active thermography methods. In this method, mechanical energy is introduced to a structure, it is converted into heat energy at the defects, and an infrared camera detects the heat for inspection. The heat generation mechanisms are dependent on many factors such as structure characteristics, defect type, excitation method and contact condition, which make it difficult to predict heat distribution in ultrasonic infrared thermography. In this paper, a method to simulate frictional heating, known to be one of the main heat generation mechanisms at the closed defects in metal structures, is proposed for ultrasonic infrared thermography. This method uses linear vibration analysis results without considering the contact boundary condition at the defect so that it is intuitive and simple to implement. Its advantages and disadvantages are also discussed. The simulation results show good agreement with the modal analysis and experiment result.