Professor Kyung-Young Jhang of the School of Mechanical Engineering is the vice-president of the Korean Society for Nondestructive Testing (KSNT). He once served as the director of the Reliability Analysis Research Center and Survivability Technology Defense Research Center. His research interests are experimental mechanics, ultrasonic nondestructive evaluation, optical measuring systems, visual image processing, random signal processing, and laser-material interaction. Recognized by many researchers around the world, Jhang received the Most Downloaded Articles Award from the International Journal of Precision Engineering and Manufacturing for his paper on ultrasonic nondestructive evaluation in 2010.

As the founder of the Intelligent Sensing & Nondestructive Evaluation (ISNDE) Lab, Jhang has been devoted to training expert human resources and developing the core technology, “The active safety” for 25 years. The active safety is technology that allows for the prediction of the possibilities of damage or breakdown in a variety of fields such as the automobile industry, where car accidents can be avoided. Other fields include the bio industry where diagnosis for organic tissues such as cancers can be rendered, and in the power plant industry for checking defects. Jhang’s lab has been a hub for developing and spreading nonlinear ultrasonic and laser-ultrasonic technologies, which has been novel in Korea.

In his recent work, Jhang conducted a series of experimental investigations to examine fatigue deformation of austenitic stainless steel 316, which is a common raw material used in constructing diverse mechanisms. In light of the fact that fatigue failure accounts for almost all service failures with mechanical problems that occur when structural materials are subjected to repetitive or fluctuating stress, Jhang decided to explore fatigue damage and deformation from fatigue crack initiation of metallic materials subjected to cyclic loading and vibrations.

To conduct his experiment, he used innovative nonlinear acoustics sensitive to microstructural evolutions to characterize fatigue-induced micro-damage of austenitic stainless steel 316. Since the internal structures of microstructures are complicated, the interpretation of nonlinear acoustics and microstructural evolution has been essential for micro-damage characterization in his experiment. In his experimental investigation, ultrasonic testing was conducted to examine acoustic wave propagation through nonlinear elastic materials. With precise measurements of the acoustic nonlinear parameter, micro-plasticity was characterized using microstructural observations to shed light on the effects of fatigue-induced micro-damage on the nonlinearity parameter.

As illustrated by the figure that shows the bell-shaped curve of acoustic nonlinearity as a function of position, the curve indicates that the fatigue damage was localized to the middle of the test specimen, corresponding to the area of stress concentration. On the whole, this demonstrates that the acoustic linearity is very sensitive to microstructural evolution induced by fatigue deformation.

Through his study, Jhang found that as the materials accumulate fatigue, noticeable changes in the microstructure and the micromechanical properties owing to dislocations, slip bands, and dislocation substructures are often observed. By proving a strong correlation between fatigue-induced micro-damage and acoustic nonlinearity, he was able to conclude that the use of nonlinear characteristics determined by the oblique incidence technique could possibly improve the evaluation of fatigue in industrial applications. “With this technique, one could test whether the internal structure of particular industrial mechanism is damaged. This will surely help prevent future catastrophes resulting from such damage,” Jhang said.

Currently, he is leading a very large scale project with his Failure Insight Nondestructive Evaluation Research (FINDER) team. The project is sponsored by the Ministry of Science, ICT and Future Planning and is expected to take seven years to complete. The research group is composed of four teams and each one is helping to develop the technology based on a different raw material. The team led by Jhang for instance, is using the Nonlinear Ultrasonic Technique to render a structure health diagnosis of Dissimilar Metal Welds (DMW) in nuclear facilities. The aim of the project is to develop an innovative nondestructive evaluation technique that can ensure that the safety and reliability of diverse industrial facilities and processes is achieved. Jhang hopes the technology he has been developing will contribute toward the improvement in the quality of industrial products and the safe performance of equipment and industrial plants, including the safety of metallic and concrete structures and constructions.

Meanwhile, he has been endeavoring to improve the Laser Ultrasonic Technique that could aid in nondestructive evaluation of industrial products and construction. By providing a theoretical analysis of laser-generated ultrasound, he has been in fact developing non-contact Nondestructive Evaluation techniques. Through his analysis of laser-generated surface waves, Jhang has successfully detected microcracks and degradation for safety assessments. Using the Laser Ultrasonic Technique, Jhang has been working in a project to develop defense technology that involves the use of laser weapons. By analyzing damage on a silicon wafer surface irradiated by a high power Near Infrared (NIR) laser, he has been able to make nondestructive evaluations for directed-energy weapons.

Having dedicated 25 years of his life to scientific research for nondestructive evaluation, Jhang has demonstrated the limitless potential of the powerful technology in this interdisciplinary field of study. With great faith in the potential of science and technology to solve the problems of the human race, he plans to invest another seven years of dedication in his grand scale project with FINDER.

”I will work as hard as I can to have our project ready for submission in the World Conference on Non-Destructive Testing (WCNDT) which will be hosted by Seoul in 2020. Hard work pays off in the end,” Jhang concluded.

yikyunghwa@hanyang.ac.kr

 

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Photo by Kyujin Jung