[Show abstract][Hide abstract] ABSTRACT: The conventional acoustic nonlinear technique to evaluate the contact acoustic nonlinearity (CAN) at solid-solid contact interfaces (e.g., closed cracks), which uses the through-transmission of normally incident bulk waves, is limited in that access to both the inner and outer surfaces of structures for attaching pulsing and receiving transducers is difficult. The angle beam incidence and reflection technique, where both the pulsing and receiving transducers are located on the same side of the target, may allow the above problem to be overcome. However, in the angle incidence technique, mode-conversion at the contact interfaces as well as the normal and tangential interface stiffness should be taken into account. Based on the linear and nonlinear contact stiffness, we propose a theoretical model for the reflection of an ultrasonic wave angularly incident on contact interfaces. In addition, the magnitude of the CAN-induced second harmonic wave in the reflected ultrasonic wave is predicted. Experimental results obtained for the contact interfaces of A16061-T6 alloy specimens at various loading pressures showed good agreement with theoretical predictions. Such agreement proves the validity of the suggested oblique incidence model.
[Show abstract][Hide abstract] ABSTRACT: A nonlinear model for contact acoustic nonlinearity (CAN) of closed crack was proposed and analyzed to investigate the nonlinear characteristics of transmitted wave for normal incident wave. Closed crack was modeled as an imperfectly jointed interface that has nonlinear discontinuity in displacement across its boundary. Based on the interfacial stiffness of contact interface, a nonlinear parameter was defined as the ratio of second harmonic component to first harmonic, and derived in terms of discontinuous displacements across the interface. It is found that the amplitude of second order harmonic wave is highly dependent on interfacial stiffness. This was verified by experiments for a real crack. For this, a CT fatigue specimen of Al6061 with V-notch was prepared to initiate the crack, and the amplitude of second order harmonic was measured by scanning along the crack direction. From the results of pre-test to evaluate the contact condition of crack interfaces by monitoring the amplitudes of echo and through transmission, the crack was regarded as gradually closed. It could be observed that the harmonic amplitude had a good correlation with the crack closure and agreed well with the theoretical expectation. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Keywords (in text query field) Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints