Prevention Characteristics Of Elastoplastic Metamaterial Against Stress Wave

The protection of high amplitude and high energy stress waves resulting from intense dynamic loading such as earthquake,blast,impact,has always been a problem of widely concern.In recent years,elastic metamaterial possessing unusual mechanical properties beyond those found in nature,which is bestowed by the special manmade microstructures,provide unprecedented technology for artificial control of low amplitude and low energy stress waves.At the same time,it also opens new opportunity to prevent higher energy stress waves.However,under intense dynamic loading,material inevitably presents a nonlinear constitutive relation,which makes it very important to consider the effect of the nonlinear response of the material on metamaterial.The purpose of this study is to explore the influence of plastic response of component materials on the protective performance of metamaterial against high amplitude and high energy stress waves,and to reveal the law of the performance change with plastic parameters.Firstly,a finite element model of periodic Al/Cu laminate metamaterial is established,and the propagation law of stress wave in periodic layered metamaterial is investigated by introducing the Johnson-Cook constitutive model of Al and Cu.The results show that interface between the materials with different acoustic impedances is the main reason for the shock wave to evolve into a new pulse.Meanwhile,the reflection of stress wave at the Al/Cu interface promotes the dissipation of energy,which shortens the time of forming stress pulses and greatly improves the attenuation effect of periodic Al/Cu laminate on stress waves.Secondly,based on the understanding of the propagation of stress wave in periodic layered materials,a model of one-dimensional locally resonant metamaterial consisting of matrix-shell-core microstructure unit has been established.The modal analysis of the microstructure unit shows that the resonant frequency of it is positively correlated with the modulus of the shell,but the filling rate of the core structure has little influence on the resonance frequency.By introducing the two constitutive models of linear isotropic hardening and kinematic hardening,the response of the metamaterial to stress waves with different frequency is analyzed.It is found that shell plastic response greatly improves the attenuation performance of metamaterial to stress waves.However,when the frequency of stress wave is far away from the resonant frequency,the yield strength of shell material with isotropic hardening model increases with loading and unloading times,resulting in the attenuation effect of stress wave decreases.On the other hand,Bauschinger effect is considered for the shell material with kinematic hardening model when subjected to multiple loading and unloading,leading to the attenuation of stress wave more obvious.In addition,the attenuation of low frequency stress waves by metamaterial with kinematic hardening model is more obvious,indicating that the band gap is closer to the low frequency.Finally,the frequency band characteristics of the locally resonant metamaterial in which the shell is kinematic hardening are analyzed.Results show that the plastic response of shell plays an important role in the movement of the start frequency of band toward low frequency region,promoted to low frequency stress wave shielding.In addition,the smaller the hardening modulus of the shell is,the more the start frequency moves toward the lower frequency side.On the other hand,under the condition of the same hardening modulus,with the decrease of the yield strength,transmission in low frequency region becomes more and more small.What is interesting to note is that a stop band is formed at the low frequency region when the yield strength drop to a small value.Selecting the shell material with appropriate hardening modulus and yield strength may enable the metamaterial to shield the seismic wave or blast wave more effectively.