• 대한기계학회논문집A
• /
• 제35권10호
• /
• pp.1257-1264
• /
• 2011

짧은 시간에 장거리를 전파하는 유도 초음파의 특성을 이용하면 빠르게 넓은 영역의 검사가 가능하다. 그러나 레일의 경우와 같이 단면이 단순하지 않고 임의의 형상을 갖는 구조물의 경우 초음파 전달시 발생하는 분산 특성이나 다수의 모드의 발생으로 초음파 신호의 분석에 어려움을 겪는다. 따라서 실용적인 유도 초음파 검사 시스템을 개발하기 위해서는 먼저 레일내를 전파하여 전달되는 초음파의 거동특성을 이해하여야 한다. 특히 레일내를 전파하는 초음파의 분산특성은 필수적으로 확인되어야 할 특성이다. 본논문에서는 SAFE법을 활용하여 KS60 레일내를 전파하는 초음파의 분산곡선을 구하는 방법을 소개하고 유도초음파를 활용한 레일 검사의 가능성에 대하여 살펴보았다.

• Structural Engineering and Mechanics
• /
• 제75권4호
• /
• pp.435-444
• /
• 2020

Ultrasonic guided wave testing is a very promising non-destructive testing method for rails, which is of great significance for ensuring the safe operation of railways. On the basis of the semi-analytical finite element (SAFE) method, a analytical model of 59R2 grooved rail was proposed, which is commonly used in the ballastless track of modern tram. The dispersion curves of ultrasonic guided waves in free rail and supported rail were obtained. Sensitivity analysis was then undertaken to evaluate the effect of rail elastic modulus on the phase velocity and group velocity dispersion curves of ultrasonic guided waves. The optimal guided wave mode, optimal excitation point and excitation direction suitable for detecting rail integrity were identified by analyzing the frequency, number of modes, and mode shapes. A sinusoidal signal modulated by a Hanning window with a center frequency of 25 kHz was used as the excitation source, and the propagation characteristics of high-frequency ultrasonic guided waves in the rail were obtained. The results show that the rail pad has a relatively little influence on the dispersion curves of ultrasonic guided waves in the high frequency band, and has a relatively large influence on the dispersion curves of ultrasonic guided waves in the low frequency band below 4 kHz. The rail elastic modulus has significant influence on the phase velocity in the high frequency band, while the group velocity is greatly affected by the rail elastic modulus in the low frequency band.

• Smart Structures and Systems
• /
• 제22권4호
• /
• pp.481-493
• /
• 2018

Ultrasonic guided waves have attracted increasing attention for non-destructive testing (NDT) and structural health monitoring (SHM) of bridge cables. They offer advantages like single measurement, wide coverage of acoustical field, and long-range propagation capability. To design defect detection systems, it is essential to understand how guided waves propagate in cables and how to select the optimal excitation frequency and mode. However, certain cable characteristics such as multiple wires, anchorage, and polyethylene (PE) sheath increase the complexity in analyzing the guided wave propagation. In this study, guided wave modes for multi-wire bridge cables are identified by using a semi-analytical finite element (SAFE) technique to obtain relevant dispersion curves. Numerical results indicated that the number of guided wave modes increases, the length of the flat region with a low frequency of L(0,1) mode becomes shorter, and the cutoff frequency for high order longitudinal wave modes becomes lower, as the number of steel wires in a cable increases. These findings were used in design of transducers for defect detection and selection of the optimal wave mode and frequency for subsequent experiments. A magnetostrictive transducer system was used to excite and detect the guided waves. The applicability of the proposed approach for detecting and locating wire breakages was demonstrated for a cable with 37 wires. The present ultrasonic guided wave method has been found to be very responsive to the number of brokenwires and is thus capable of detecting defects with varying sizes.