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A nonlinear ultrasonic test system is established to meet the needs of evaluating the interface bond quality of composite structure. Epoxy resin is chosen as adhesive to make three sets of specimens which are made up of synthetic glass/adhesive/steel so as to simulate the different bond strengths with three different rations of epoxy resin to curing agent. For the problem of the complexity to determine the mode of lamb using lamb wave approach and the situation of that bond states cant not be evaluated based on second harmonic exciting efficiency using pulse-echo ultrasonic techniques, a method is developed, in which the specimen is excited by a single-frequency ultrasound, and A2/A1², (the ratio of second harmonic A2 to fundamental wave A1²) is used to characterize the degree of nonlinear ultrasonic response. The experimental results indicate that the interface bond quality reduces with the increase in the degree of nonlinearity, and thus it can effectively evaluate the interface bond quality. [ABSTRACT FROM AUTHOR]

Dispersion equation of Lamb wave in underwater elastic plate coated with viscoelastic damping layers is derived, and the phase velocity and attenuation coefficient of Lamb wave propagating in the submerged composite plate at different frequency-thickness products are obtained under the condition of certain elastic modulus. The phase velocities and attenuation coefficients of the first two Lamb wave modes propagating in the composite plate at certain frequency-thickness product are measured by the echo measurement experiment of submerged elastic plate coated with viscoelastic damping layers, the elastic modulus of viscoelastic material is then inversed by substituting the experimental results into the dispersion e-quation. The results show that the phase velocity and attenuation coefficient of composite plate, and the inversed elastic modulus of viscoelastic material coincide with the theoretical values well, error in experiment less than four percent, it's proved to be feasible to inverse elastic modulus of viscoelastic material based on genetic algorithm and echo characteristic. [ABSTRACT FROM AUTHOR]