Nonlinear Acoustic Effect due to Evolution of a Crack and Detection of Micro-Scale Cracks in a Fatigue Process

摘要

Nonlinear acoustic effect is sensitive to a micro-scale crack or pre-cracking stage of the fatigue process. A resonant ultrasound spectroscopy technique was used for a diagnosis of micro-scale crack in a compact tension (CT) specimen. Information on the normalized amplitude and resonance frequency was analyzed to quantify the degree of nonlinearity and diagnose the micro-cracks. The damage produces a nonlinear stress-strain relationship and the nonlinearity can be measured by increasing excitation amplitudes. The more damage, the larger is the level of a nonlinearity, and it can be used for diagnosis of micro-cracks. The amount of nonlinearity is highly correlated to the damaged state of the material. A shift of resonance frequency as a function of driving voltage or strain is chosen as a nonlinear parameter to correlate the micro-cracks or damage. In addition amplitude of a normalized resonance pattern also reflects the nonlinearity. The normalized pattern of an intact CT specimen and cracked CT specimen were compared.