An experimental study on second harmonic generation of guided wave in fatigued spring rod

Conventional ultrasonic inspection techniques especially ultrasonic guided wave and wave testing methods show excellent capability for evaluating the material integrity of the structures. The dominate characteristics of nonlinear guided wave testing are long-range testing and higher sensitivity through various modes selection, which are favorable for diagnosing micro-defects or micro-structural changes at early stage. In this study, nonlinear studies on the valve spring coil using nonlinear induced ultrasound conducted. The nonlinear guided ultrasonic test performed on four specimens subjected to the Nakamura fatigue test. Experimental results show that nonlinear parameters increase with increasing distance. In addition, the nonlinear parameters increased with increasing fatigue degree. This study suggests a method to diagnose early damage of machine structure in an appropriate way and it expected to prevent accidents of structures.