친환경 부품 소재의 신뢰성평가를 위한 비접촉 공중 초음파 탐상방법의 적용

Abstract

NAUT(Non contact Air coupled Ultrasonic Testing) is an inspection technique to remedy the existing contact inspection by supplementing energy loss created by differences of acoustic impedance between the solid and the air with high power ultrasonic Pulser Receiver, PRE-AMP, and high sensitivity probe, and enabling the ultrasonic inspection which uses the air as a medium. In order to overcome weaknesses of the existing contact ultrasonic inspection that is not possible to apply couplant to a specimen with a rough surface or a narrow spot containing materials of the low and high temperature, NAUT that enables the non contact ultrasonic inspection in the air is applied. Applying NAUT, it is possible to inspect ultrasonic waves in the air without couplant and even in materials of the low and high temperature, or in a specimen with a rough surface, compared to the existing contact ultrasonic inspection, because it can transmit and receive them in a stable condition. Application of NAUT may save the time and expenses, because it can detect faults in real time. As explained above, this thesis observe how well NAUT is applied, by inspecting ultrasonic waves in spot welding part, to CFRP using its advantages. As the non destructive inspection is not yet employed in the manufacturing stage of environment-friendly cars, the establishment of this technique will enable us to produce environment-friendly vehicles with the excellent safety and quality. In this thesis, NAUT's manual, automatical, and image inspection are carried out targeting spot welding part and CFRP for verifying its utility. First of all, using a spot welding specimen, an experiment to select inspection conditions(transmission and reception angle, interval and output, etc.) considering transmission characteristics of ultrasonic waves depending on each location[(thick part(0.4mm), overlap part(0.3mm), spot welding part(0.3mm), thin part(0.1mm)], and mode conversion is carried out. For automatic inspection, after setting up the inspection distances(-10mm~10mm, -30mm~-15mm and 15mm~30mm), we perform scanning ultrasonic waves at an interval of 0.5mm pitch to observe penetration ratio of ultrasonic waves and difference of amplitude changes in a broader scope. Secondly, another experiment is implemented to examine the existence of delamination with inner defects using CFRP test pieces. After classifying each test piece into A, B and C, measuring conditions[A(X and Y axis scanning: -20mm~20mm, 2mm pitch), B(X and Y axis scanning: -40mm~40mm, 2mm pitch) and C(X and Y axis scanning: -30mm~30mm, 5mm pitch)] are set and then, the existence of delamination is observed through. After setting up image inspection conditions(Averaging count, Gain, Scanning pitch, Scanning speed and Probe) to find an accurate location of delamination, we verify the performance of proposed techniques using results and images. From above results, we observe that the NAUT is not only applicable to all the cases, but it also may be commercialized.