The effect of anisotropy on the ultrasound wave generation and propagation in the unidirectional fi- ber-reinforced composite plate has been investigated. A quantitative numerical model for the la- ser-generated ultra...The effect of anisotropy on the ultrasound wave generation and propagation in the unidirectional fi- ber-reinforced composite plate has been investigated. A quantitative numerical model for the la- ser-generated ultrasound in the thermoelastic regime was presented by using a finite element method. All factors, such as spatial and time distributions of the incident laser beam, optical penetration, ther- mal diffusivity, and source-receiver distance can be taken into account. Numerical results show that the effect on ultrasound waveform of the size of the laser volume source produces strong bipolar longitu- dinal waves and improves the amplitude and directivity of the longitudinal waves. A fiber-reinforced composite material exhibits isotropic or homogenous behavior for ultrasonic wave propagation per- pendicular to the fiber direction. For ultrasonic propagation along the fiber direction, ultrasonic dis- persion resulting from the inhomogeneous nature of the material affects the laser ultrasonic waveforms. As the dimensions of the laser pulse are increased in space and time, the displacement waveform be- comes broader and its magnitude decreases.展开更多
The propagation characteristics of laser-generated like-Rayleigh waves in viscoelastic adhesive coating/substrate structures were studied.Considering the viscoelasticity of the coating and substrate,we have establishe...The propagation characteristics of laser-generated like-Rayleigh waves in viscoelastic adhesive coating/substrate structures were studied.Considering the viscoelasticity of the coating and substrate,we have established the finite element models in frequency domain for the laser-generated like-Rayleigh waves in the epoxy coating/aluminum substrate,epoxy coating/brass substrate,and epoxy coating/foam substrate structures,respectively.In addition,we have investigated the waveform and propagation characteristics of the like-Rayleigh waves and studied the influences of the coating transparency,coating thickness,coating viscoelasticity,and substrate viscoelasticity on the propagation characteristics of the like-Rayleigh waves.Moreover,we have verified the results by the theoretical phase velocity and attenuation curves.The results show that the coating viscoelasticity induces the attenuation characteristics of the higher frequencies of the like-Rayleigh waves,but has little effect on the lower frequencies,and the substrate viscoelasticity has the influences on both the higher and lower frequencies of the like-Rayleigh waves,especially the lower frequencies.Furthermore,the mode and dispersive characteristics of the like-Rayleigh waves are closely related to the substrates.This study provides a useful theoretical basis for inverting mechanical parameters and evaluating the adhesive quality of the viscoelastic adhesive coating/substrate structures.展开更多
A valley topological acoustic waveguide based on two chiral sonic crystals is studied.Two sonic crystals composed of right-handed and left-handed chiral scatterers have different valley topology properties.When both t...A valley topological acoustic waveguide based on two chiral sonic crystals is studied.Two sonic crystals composed of right-handed and left-handed chiral scatterers have different valley topology properties.When both types of chiral windmill scatterers rotate from-60°to 60°,their corresponding sonic crystals exhibit two accidental degenerated Dirac points and valley Hall phase transition.Two chiral sonic crystals with opposite valley Hall phase are selected to design a valley topological waveguide.It is found that there exist a pair of valley edge states localized at the domain wall of the waveguide in the overlapping band gap.The experimental results show that the edge states can support valley topological acoustic transport well,and have a certain robustness to the defects of bends and disorder around the domain wall of the waveguide.展开更多
基金Supported by the Natural Science Foundation of Jiangsu University (Grant No. 05JDG007)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant Nos. 08KJB140003 and 07KJB140019)
文摘The effect of anisotropy on the ultrasound wave generation and propagation in the unidirectional fi- ber-reinforced composite plate has been investigated. A quantitative numerical model for the la- ser-generated ultrasound in the thermoelastic regime was presented by using a finite element method. All factors, such as spatial and time distributions of the incident laser beam, optical penetration, ther- mal diffusivity, and source-receiver distance can be taken into account. Numerical results show that the effect on ultrasound waveform of the size of the laser volume source produces strong bipolar longitu- dinal waves and improves the amplitude and directivity of the longitudinal waves. A fiber-reinforced composite material exhibits isotropic or homogenous behavior for ultrasonic wave propagation per- pendicular to the fiber direction. For ultrasonic propagation along the fiber direction, ultrasonic dis- persion resulting from the inhomogeneous nature of the material affects the laser ultrasonic waveforms. As the dimensions of the laser pulse are increased in space and time, the displacement waveform be- comes broader and its magnitude decreases.
基金supported by National Basic Research Program of China(2012CB921504)Major Program of National Natural Science Foundation of China(51239005)+4 种基金National Natural Science Foundation of China(11404147,11174142)Natural Science Foundation of Jiangsu Province(BK20140519)China Postdoctoral Science Foundation(2015M571672)Research Fund for Advanced Talents of Jiangsu University(11JDG118)Training Project of Young Backbone Teachers of Jiangsu University
文摘The propagation characteristics of laser-generated like-Rayleigh waves in viscoelastic adhesive coating/substrate structures were studied.Considering the viscoelasticity of the coating and substrate,we have established the finite element models in frequency domain for the laser-generated like-Rayleigh waves in the epoxy coating/aluminum substrate,epoxy coating/brass substrate,and epoxy coating/foam substrate structures,respectively.In addition,we have investigated the waveform and propagation characteristics of the like-Rayleigh waves and studied the influences of the coating transparency,coating thickness,coating viscoelasticity,and substrate viscoelasticity on the propagation characteristics of the like-Rayleigh waves.Moreover,we have verified the results by the theoretical phase velocity and attenuation curves.The results show that the coating viscoelasticity induces the attenuation characteristics of the higher frequencies of the like-Rayleigh waves,but has little effect on the lower frequencies,and the substrate viscoelasticity has the influences on both the higher and lower frequencies of the like-Rayleigh waves,especially the lower frequencies.Furthermore,the mode and dispersive characteristics of the like-Rayleigh waves are closely related to the substrates.This study provides a useful theoretical basis for inverting mechanical parameters and evaluating the adhesive quality of the viscoelastic adhesive coating/substrate structures.
基金supported by the National Natural Science Foundation of China(11774137,12274183)the China Postdoctoral Science Foundation(2020M671351)the Postdoctoral Research Funding Program of Jiangsu Province(2021K567C)。
文摘A valley topological acoustic waveguide based on two chiral sonic crystals is studied.Two sonic crystals composed of right-handed and left-handed chiral scatterers have different valley topology properties.When both types of chiral windmill scatterers rotate from-60°to 60°,their corresponding sonic crystals exhibit two accidental degenerated Dirac points and valley Hall phase transition.Two chiral sonic crystals with opposite valley Hall phase are selected to design a valley topological waveguide.It is found that there exist a pair of valley edge states localized at the domain wall of the waveguide in the overlapping band gap.The experimental results show that the edge states can support valley topological acoustic transport well,and have a certain robustness to the defects of bends and disorder around the domain wall of the waveguide.
