Numerical Simulation And Analysis Of Transient Wave Propagation In Layered Structures

The layered structure is generally a kind of continuous media,which is composed of elastic medium with multiple parallel interfaces.The advantage of layered structure is that various mechanical properties can be designed to meet the different requirements of engineering applications without changing the properties of a single layer material.The layered structure is widely used in civil engineering,transportation,aerospace and other industries.Therefore,more and more attentions have been paid to the research on the characteristics of layered structures.Transient wave is a kind of elastic wave,which has the characteristics of fast propagation,energy concentration and long propagation distance.Transient wave propagation in multi-layer media has attracted widespread attentions,such as in seismic response of complex geological areas in seismic engineering,damage detection using pulse in the field of nondestructive testing,etc.Therefore,it is of great significance to study the propagation of transient waves in layered structures.As for the propagation of transient waves in layered structures,the analytical solutions are only limited to some typical modeled structures currently.But the actual layered structures are more complicated,it is difficult to obtain the analytical solutions of transient waves in such layered structures.This paper will employ the finite element method to study and analyze the transient wave propagation in layered structures.Firstly,the basic equation of transient response in layered half-space,the idea of obtaining analytical solution and the transient solution in time domain are introduced in this paper.Then,the transient response of a particle in layered half-space excited by displacement load in plane is simulated by using finite element method.On this basis,the numerical simulation and analysis of transient wave propagating in multi-layered structure,shell of Solid Rocket Motor(SRM)and the China Railway Track System(CRTS)? slab track,are further carried out;and the propagation law of transient waves are studied in these two typical multi-layered structures.The study shows that:(1)For the layered half-space medium,the transient response obtained by the finite element simulation method is basically consistent with that obtained by the Cagniard method in the time domain.Therefore,the finite element simulation method employed in this paper can be used to obtain the transient response in layered structure accurately and quickly.(2)For the multi-layer SRM shell,the transient response amplitude increases linearly with the increase of excitation amplitude under the same structural parameters.When degradation damage occurs to the adhesive layer,the amplitude of the transient response increases gradually with the degradation of adhesive layer.In the frequency domain,the frequency of the transient response remains unchanged,but the amplitude will change,and the damage change rate increases with the increase of the degradation degree of the adhesive layer.(3)For the multi-layer structure of CRTS ? slab track,the amplitude of its transient response increases linearly in with the increase of excitation amplitude,regardless of whether there is crack damage or not.When there is crack damage,the frequency drift of the transient response signal appears with the increase of the crack length,and there is an approximate linear relationship between the drift and the damage length.Therefore,the transient wave can be used to effectively evaluate the damage of slab track.