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Ramadas Chennamsetti,Irfan Khan,Avinash Hood,Makarand Joshi 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.
Misalignments are a major concern, when air-coupled ultrasonic probes are deployed for transmission and reception of Lamb waves. Misalignments between the air-coupled probes result in reduction in amplitude and change in arrival time of the Lamb waves. This reduction in amplitude can give a false alarm in Non-destructive Testing (NDT) applications, if amplitude is the criterion for flaw or damage detection. In the present work, one of the probe’s (transmitter or receiver) position was kept fixed, and the other probe was rotated to introduce a misalignment termed ‘rotational misalignment’. This rotation had violated the co-planarity condition,resulting in reduction in amplitude of the received fundamental anti-symmetric mode (Ao) in an isotropic material plate. Interestingly,variation in amplitude of the Ao mode with the rotational misalignment angle revealed that, at certain angular locations, there exists a local maximum and local minimum resembling sync function. Subsequently, the angular location of occurrence of these is attributed to dispersion characteristics of the Ao mode.
Ramadas Chennamsetti,Avinash Hood,Siddlingappa Guruprasad,Sajal Roy,Makarand Joshi 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.
Constrained layer damping is one of the passive techniques to control amplitude of vibration of structural components. In the present work an attempt has been made to quantify and compare damping ratios of composite-rubber-composite sandwich beam with that of pristine composite beam having nearly the same flexural stiffness and range of frequency of vibration from 20 Hz to 100 Hz. Length and thickness of sandwich and pristine beams in order to have the same flexural stiffness and desired frequency range of vibration were specifically designed. The damping ratio of each sandwich and pristine composite beams were measured experimentally using logarithmic decay and half-power bandwidth techniques.