Abstract:
Second-harmonic generation was measured in several man-made materials for possible application of nonlinear properties to nondestructive testing. Samples included several thicknesses of two types of polymer matrix composites, three types of concretes, and plywood. Steel and aluminum specimens were used as references and one of the composite samples was evaluated before and after fatigue cycles. A monochromatic ultrasonic signal was sent into each sample via a contact transducer placed on its top surface. The growth of the second harmonic was recorded, with a second transducer placed on the bottom face, as the amplitude of the input signal was gradually increased and for several values of the input frequency. Nonlinearity parameters could not be measured, due to the limitations of our equipment. Nonetheless, some interesting observations were made: (1) the two composites were much more nonlinear than the metals; (2) the concretes and the wood were extremely absorptive and an output signal was observed only at the lowest input frequency; and (3) fatigue cycles significantly increased the second harmonic, even though no damage was observed by C-scanning. [Work supported by NSF, TTU Manufacturing Center, and the FRG Program.]