Evaluation of fatigue degradation using nonlinear ultrasonics

Abstract

A study on the evaluation of fatigue degradation in SUS316L material using nonlinear ultrasonics was reported. The nonlinearity of ultrasonic wave was estimated by relative nonlinear parameter defined by the ratio of fundamental and second-harmonic wave amplitude. A measurement system with contact transducers was constructed, which has a capability of reliable measurement by keeping measurement condition in consistent and reducing extra harmonics generated in the measurement system. Two types of SUS316L specimen were tested: one was a rotating bar fatigue specimen and another was a tensile fatigue specimen. Fatigue condition was high cycle fatigue. The former has cylindrical shape and was used to observe the change of nonlinear parameter while the fatigue accumulation in a specimen. The latter is a plate-shaped specimen and was used to confirm the change of nonlinear parameter in the spot where the stress concentration was occurred. Measured nonlinear parameter showed strong correlation with damage level of both fatigue tests.