Dynamic behavior of sandwich beams with internal resonators

Bhisham Sharma, Purdue University

Abstract

Dynamic behavior of sandwich beams with internal resonators was investigated. The effect of inserting spring-mass resonators into the sandwich core was theoretically analyzed and it was shown that a wave attenuation bandgap exists due to local resonance. Steady state experiments were used to demonstrate such an attenuation bandgap. Frequency response functions were obtained for a beam with resonators and without resonators. It was shown that insertion of resonators into the core causes a wave attenuation bandgap to open up. The experimental results were verified using finite element simulations. Further experiments were carried out by tuning the resonators at 12 Hz and it was demonstrated that a wave attenuation bandgap can be created at low frequencies which would help attenuate low frequency periodic loads such as those associated with hull slamming. The antiresonance phenomenon was experimentally demonstrated. By inserting local resonators tuned at the first flexural resonance frequency of the beam, it was shown that the excessive vibrations associated with resonance modes can be attenuated by inserting local resonators tuned at the global beam resonance frequency. The behavior of such sandwich beams under impact loads was also considered. Using finite element simulations, the effect of a chosen local resonance frequency on attenuating impact loads was analyzed. The behavior of a chosen internal resonator under different impact loads was also considered. By performing transverse impact experiments, the finite element models were verified and the advantage of using internal resonators in impact loading conditions was demonstrated. The effect of resonator periodicity was analyzed using a phased array method. The propagation constant for a sandwich beam with internal resonators was obtained by treating the resonators as an array of phase shifted forces. It was shown that the resonator periodicity causes Bragg gaps in addition to the local resonance gaps. The effect of resonator parameters on these bandgaps was analyzed and the relationship between the bounding frequencies and the unit cell mode shapes was obtained. The interaction between the local resonance bandgap and the periodicity induced bandgaps was studied. It was shown that a wider combined gap, with a very narrow passband in between, can be obtained by tuning the local resonators at the Bragg gap cut-on frequency.

Degree

Ph.D.

Advisors

Sun, Purdue University.

Subject Area

Engineering|Materials science

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