Nonlinearity Study of Damaged Spring Materials Using Guided Wave

Nonlinear ultrasonic techniques that can detect micro crack or defects before use of ultrasonic nonlinearity are emerging as a way to predict the life of materials. Guided wave propagates according to the shape of the material, thus providing great potential for non-destructive evaluation applications. However, in the non-destructive evaluation method using nonlinear guided waves, it is difficult to get necessary information due to the dispersion and multi-mode characteristics of guided wave. In this study, the nonlinearity of spring materials and the degree of fatigue was investigated using nonlinear guided wave. The specimens were prepared with different degree of fatigue through Nakamura fatigue test. The guided wave has generated a signal at the point that 460 mm far from the left end of the spring specimen and was received at a distance of 50 mm from the transmitted point. In addition, the experiment carried out for six sections at intervals of 10 mm. The signal was generated using a tone buster (RPR-4000), and the vicinity of the point, where the fatigue load was largest (the middle point of the specimen), was investigated. This study presents a quantitative evaluation method for the health of spring materials using nonlinear guided wave. Histological examinations, such as SEM imaging, can provide more accurate and meaningful results, and further, studies such as these must identify the cause.