Research on transfer characteristics of vibration of shaft and beam sonic crystals under concentrated mass boundary condition

In order to obtain the transfer characteristics of vibration of sonic crystal structure under concentrated mass boundary condition, “epoxy + aluminum” shaft and beam sonic crystals were built and the transmissibility curves of torsional vibration and bending vibration of these structures were calculated under free boundary and concentrated mass boundary conditions respectively. The curves were analyzed together with the band gaps obtained by theoretical calculation and the results showed that: under free boundary condition single material shaft (or beam) hasn´t any ability of vibration reduction while shaft (or beam) sonic crystal possessed obvious band gaps in which corresponding vibration could be suppressed distinctly; under concentrated mass boundary condition torsional (or bending) vibration could be reduced within a wide frequency band in single material shaft (or beam) while many resonant peaks could be found in transmissibility curve which would be harmful to vibration reduction. As to shaft and beam sonic crystals, vibration could be suppressed distinctly by the effect of band gaps and the ability of vibration reduction was improved much more than that under free boundary condition. However, owing to the mutual action of “spring-vibrator” system and band gap effect, high resonant peaks may be brought in band gaps evidently which would impair the ability of vibration reduction. Additionally, with the increase of the concentrated mass the vibration reduction ability of the shaft and beam sonic crystals could be enhanced further.