Wave Propagation And Regulation In Periodic Structure Based On 4D-Printing

In recent years,more and more people have been paying attention to the propagation of elastic waves in periodic composite materials.This crystal composed of a series of artificial periodic structures is called a phononic crystal.One of the most important physical properties of phononic crystals is the prohibition of wave propagation in certain frequency ranges,as bandgap.However,most of the phonon and acoustic metamaterial configurations proposed so far are characterized by passive response and operation at a fixed frequency range,limiting potential applications.In order to design a tunable system,it has been demonstrated that the Bragg-type bandgap can be controlled by mode switching caused by instability.4D printing is a technology for manufacturing smart material systems based on additive manufacturing(3D printing)that has the ability to change microstructures over time in a controlled shape under external stimuli(eg,light,temperature,etc.).This paper is based on stereolithography(SLA)printing of the shape memory polymer(SMP)periodic structure of tBA-co-PEGDA network,the thermal instability of the internal microstructure of SMP can be triggered by thermal induced shape memory behavior,thus causing a unidirectional reversible change from square voids to circular voids.The research content of this paper mainly has the following aspects.(1)The shape memory polymer(SMP)suitable for SLA printing was selected and the solution with different proportions was prepared to study the appropriate printing process.After the preparation,the mechanical properties of different proportions of cross-linking materials were studied by DMA 8000 and static mechanical tensile tester,and tested the shape memory effect of the material.Through the parameters of glass transition temperature,storage modulus,shape recovery rate and other parameters to explore the performance characteristics of SMP.(2)Firstly,we used finite element software COMSOL to simulate the influence of the wave propagation on the two-dimensional periodic structure of different pores,and then the band gap experimental data obtained by the LMS is compared with the simulation results.The results show that the unidirectional reversible transformation of the periodic structure from a square void to a circular void lead to a significant change in the phononic band structure,specifically in opening of three new narrow band gaps.(3)Based on the comparison of the previous experiment and the simulated data,we used the finite element software COMSOL to simulate the effects of different porosity and different ratio of shape memory polymer materials before and after deformation on the band gap under circular pores.The results show that the porosity and pore structure have a great influence on the band gap and the width of the band gap,while the material parameters do not affect the generation and width of the band gap,but affect the frequency of the band gap.