Compression And Vibration Characteristics Of Multilayer Lattice Sandwich Structures

Aiming at the problem of mechanical vibration and noise control in the operation of power system,there is an urgent demand for lightweight structures with both bearing and vibration isolation performance in the field of ships.The lattice sandwich structure with excellent mechanical properties is favored in many fields because of its connected truss core,which provides space for multifunctional design.In view of the above background,how to design and prepare a lightweight lattice sandwich structure with excellent bearing and vibration isolation performance is the main research purpose of this paper.Based on bionic idea and acoustic metamaterial principle,single-layer and multi-layer metallic lattice sandwich structure,hybrid bionic gradient lattice structure and lightweight vibration isolation multifunctional metamaterial structure were designed and prepared.The compression behaviors,vibration characteristics and vibration isolation performances of the structures were studied by experiment and simulation which verificated by experiment to reveal mechanism.To explore the vibration characteristics of single layer lattice sandwich structures with excellent mechanical properties,the single layer Hourglass and pyramidal lattice sandwich structures were prepared by vacuum brazing method.Based on the modal superposition theory,the modal parameters and harmonic response characteristics were studied.The effects of boundary conditions and inclination angle of the trusses on the vibration and frequency response characteristics were analyzed and discussed.It is found that the natural frequencies of the Hourglass lattice sandwich structure are higher than that of pyramidal lattice sandwich structure with the same relative density of the core.Due to the high fundamental frequency,the resonance is avoided in the low frequency range within the first-order natural frequency,and the response amplitudes of Hourglass lattice sandwich structure are reduced.So the vibration reduction performance of the Hourglass lattice sandwich structure is better than that of the pyramidal lattice sandwich structure.When it is higher than the first-order natural frequency range,the Houeglass lattice sandwich structure shows good vibration isolation performance.Boundary conditions have a great influence on the natural frequencies of the structures.When the inclination angle of the trusses is 45°,increasing the core height has no obvious effect on improving the vibration isolation performance of the Hourglass lattice sandwich structure.With the increase of the inclination angle of the trusses,the acceleration frequency response amplitudes of the Hourglass lattice sandwich structure changes significantly compared with that of the pyramidal lattice sandwich structure.The acceleration frequency response amplitudes of the sandwich structures can be adjusted by optimizing the design of the inclination angle of the trusses.The vibration isolation performances of single layer lattice sandwich structures are limited.Inspired by pomelo peel,the multilayer bionic gradient lattice sandwich structures with variable interlayer density gradient were prepared by designing the width of the trusses based on bionic idea.The vibration characteristics and vibration isolation performance of the multilayer bionic gradient lattice sandwich structure were investigated by modal test,shaking table frequency sweep test and simulation calculation.The influences of gradient on vibration and vibration isolation performance were analyzed.The results show that the natural frequencies of the gradient structures are not significantly different under free boundary condition.In general,the natural frequencies of the gradient structures are lower than that of the control group structure B.The gradient change has obvious influence on the structural performance.Within the frequency band below the natural frequency of the structure,the greater the relative density gradient between layers,the better the vibration isolation performance of the structure.In the frequency band containing the first order natural frequency of the structure,the natural frequency of the positive gradient structure is higher while the amplitude of the vibration level difference is lower than that of the non-gradient structure B.Among the hybrid structures with higher stiffness of facesheet material and lower stiffness of core material,the positive gradient structure has smaller amplitude of vibration level difference and lager natural frequency compared with the non-gradient structure.Namely,the positive gradient structure can reduce the amplitude of structural response while improving the bearing capacity.Under the advantages of structural bionic gradient design,the material hybrid method was introduced to change the structural impedance and improve the hysteretic energy dissipation performances.Therefore,the multilayer hybrid bionic gradient lattice sandwich structure composed of carbon fiber composite facesheets and aluminum truss cores were prepared by assembly and hot pressing molding process.In addition,the control group specimens filled with polyurethane foam in the core were also fabricated.The compression and hysteresis characteristics of the multilayer hybrid bionic gradient lattice sandwich structure were tested through experiments.Then the failure mechanism of the structures under in-plane compression was revealed.It is found that the facesheet close to the truss core layer with large slenderness ratio is more prone to failure,and the failure caused by fiber compression fracture.The results also show that the design of structural gradient and the filling of polyurethane foam have significant effects on the compressive response and hysteretic damping characteristics of the structures.The filling of polyurethane foam improves the compression performance of the structure,and the high damping and compression rebound characteristics of polyurethane foam improve the hysteresis damping characteristics of the structures.The positive gradient structure D1 filled with polyurethane foam are comprehensively evaluated as the best structure with good mechanical and hysteresis energy dissipation characteristics.In order to solve the vibration problem in the low frequency band,the stiffness and fundamental frequency of the structure need to be further reduced.The resonant unit and curved beam spring were integrated into the multilayer lattice sandwich structures.The in-plane compression characteristics,hysteretic energy dissipation characteristics and vibration isolation performance of the structures were investigated.The results show that,although the strength of the curved beam spring lattice sandwich structure is reduced to a certain extent,the energy absorption characteristics is better than that of the pyramidal lattice sandwich structure in the elastic deformation section.The frequency corresponding to the directional bandgap in the curved beam spring lattice sandwich structure is lower than that in the pyramidal lattice sandwich structure.There are more directions that block the vibration propagation in the curved beam spring lattice sandwich structure.Increasing the mass of resonant unit can make the directional bandgaps of the structure move to the low frequency,and the number of bandgaps in the low frequency band increases.Increasing the number of resonant units is helpful to realize the transformation from directional bandgap to complete bandgap.The above rules provide a reference for the design of lightweight structures with both bearing and vibration isolation performance in engineering practice.