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An air-coupled ultrasonic method, focusing on the problem that weak bonding interface is difficult to accurately measure using conventional nondestructive testing technique, is proposed to evaluate the bond integrity. Based on the spring model and the potential function theory, a theoretical model is established to predict the through-transmission spectrum in double-layer adhesive structure. The result of a theoretical algorithm shows that all the resonant transmission peaks move towards higher frequency with the increase of the interfacial stiffness. The reason for these movements is related to either the normal stiffness (KN) or the transverse stiffness (KT). A method to optimize the measurement parameters (i.e. the incident angle and testing frequency) is put forward through analyzing the relationship between the resonant transmission peaks and the interfacial spring stiffness at the frequency below 1MHz. The air-coupled ultrasonic testing experiments at the normal and oblique incident angle respectively are carried out to verify the theoretical analysis and to accurately measure the interfacial stiffness of double-layer adhesive composite plate. The experimental results are good agreement with the results from the theoretical algorithm, and the relationship between bonding time and interfacial stiffness is presented at the end of this paper.

The ultrasonic transmission spectrum in a double-layered bonded structure is related closely to its interfacial stiffness. Consequently, researching the regularity of the transmission spectrum is of significant interest in evaluating the integrity of the bonded structure. Based on the spring model and the potential function theory, a theoretical model is developed by the transfer matrix method to predict the transmission spectrum in a double-layered bonded structure. Some shift rules of the transmission peaks are obtained by numerical calculation of this model with different substrates. The results show that the resonant transmission peaks move towards a higher frequency with the increase of the normal interfacial stiffness, and each of them has different movement distances with the increasing interfacial stiffness. Indeed, it is also observed that the movement starting points of these peaks are at the specific frequency at which the thickness of either substrate plate equals an integral multiple of half a wavelength. The results from measuring the bonding specimens, which have different interfacial properties and different substrates in this experiment, are utilized to verify the theoretical analysis. Though the theory of “starting points” is not demonstrated effectively, the shift direction and distance exactly match with the result from the theoretical algorithm.

The optimal soaking time and nanosilica concentration were chosen by the physical properties of the nanosilica-modified recycled aggregate. Recycled aggregate concrete (RAC) and nanosilica recycled aggregate concrete (SRAC) were fabricated by using ordinary recycled aggregate and nanosilica-modified recycled aggregate. Based on the comparative experimental study of basic mechanical properties, the effects of nanosilica recycled aggregate(SRA) modification and recycled aggregate(RA) replacement percentage on the basic mechanical properties of recycled concrete were analyzed. Finally, the split-Hopkinson pressure bar (SHPB) was used to conduct comparative experimental research on the impact resistance of recycled aggregate concrete and nanosilica-modified recycled aggregate concrete. The effects of nanosilica recycled aggregate modification and aggregate replacement percentage on failure morphology, dynamic peak stress, dynamic increase factor (DIF), dynamic peak strain were analyzed.

In this work, a finite element model was developed for vibration analysis of sandwich beam with a viscoelastic material core sandwiched between two elastic layers. The frequency-dependent viscoelastic dynamics of the sandwich beam were investigated by using finite element analysis and experimental validation. The stiffness and damping of the viscoelastic material core is frequency-dependent, which results in complex vibration modes of the sandwich beam system. A third order seven parameter Biot model was used to describe the frequency-dependent viscoelastic behavior, which was then incorporated with the finite elements of the sandwich beam. Considering the parameters identification, a strategy to determine the parameters of the Biot model has been outlined, and the curve fitting results closely follow the experiment. With identified model parameters, numerical simulations were carried out to predict the vibration and damping behavior in the first three vibration modes, and the results showed that the finite model presented here had good accuracy and efficiency in the specific frequency range of interest. The experimental testing on the viscoelastic sandwich beam validated the numerical predication. The experimental results also showed that the finite element modeling method of sandwich beams that was proposed was correct, simple and effective.

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Two alternating homogeneous materials are periodically introduced along the radial direction, forming a circular plate of radial phononic crystal (CPRPC). To illustrate the characteristics of the out-of-plane transverse wave and the in-plane longitudinal wave propagating along the radial direction, the transfer matrices are derived based on the basic wave equations of a thin circular plate in cylindrical coordinates. Localization factors are introduced to evaluate the average attenuation of the transverse and longitudinal waves in the structure, and corresponding bandgaps are obtained. Moreover, finite element method simulations, numerical analyses and the insertion loss method are combined to investigate the effects of the main parameters on these wave bandgaps. The results show that significant transverse and longitudinal wave bandgaps caused by the radial periodicity of the CPRPC exist, and the structural and material parameters have essential influences on them.