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Fabrication of prototype structures Figure 1 illustrates two of the fabricated prototype structures. The structures are composed of an aluminum box beam, whose low-frequency vibrations are to be controlled by viscoelastic insertions implementing (a) IAIR, or (b) chiral geometries. These inclusions are fabricated by waterjet carving of a thick rubber sheet. Internal resonating masses are implemented by steel cylinders. Overall structure size is 776mm x 166mm x19mm, and 754mm x 98mm x 19mm, for assemblies (a) and (b), respectively.
Figure 1: (a) IAIR and (b) chiral assembly. The backbone structure is an aluminum box beam. Internal resonators are made of rubber ligaments and steel cylinders.
Experimental setup Testing of fabricated prototypes is performed by clamping each structure on the vibrating base of a shaker as shown in Figure 2(a). A Siglab control system with Matlab graphical user interface (Figure 2(b)) provides white-spectrum excitation in the [0, 500] Hz frequency range. The structure response is recorded at various locations along the beam profile by accelerometers, and the controller computes the frequency response function (FRF) defined as the ratio of output displacement to input force.
Figure 2: Experimental setup including (a) structure placement on a shaker and vibration recording through accelerometers on the beam profile, as well as (b) graphical user interface of the Siglab controller.
Measurements Waterfall plots in Figure 3(a) and (b) have been obtained by measuring the frequency response at different locations along the profile of the box beam, respectively before and after insertion of the chiral lattice, as shown in Figure 3(c) and (d). Inclusions provide substantial damping over the whole frequency range considered. Moreover, shifts in low-frequency resonances are observed, which provide vibration control at specific frequencies. Similar results have been obtained for the IAIR assembly in Figure 1(a).
Figure 3: Waterfall plots of structural response for (a) a box beam shown in (c), and (b) beam + chiral inclusions shown in (d). Five measurement locations along the beam profile are considered, as shown in the pictures.
Damping potential of rubber material used to fabricate viscoelastic inclusions has been investigated by comparing the time transient response of box beams without and with inclusions in the presence of an impulsive excitation provided by an instrumented impact hammer. Figure 4(a) shows time traces recorded by an accelerometer at the upper corner of the box beam for the IAIR design. Drastic reduction of the transient duration is observed when the IAIR lattice (c) with, or (d) without resonating masses is inserted into the backbone structure (b). Design optimization including geometry and material selection is in progress to enhance effectiveness and minimize weight of viscoelastic resonating inclusions.
Figure 4: (a) Time transient response of the backbone structure in (b) (blue line), and of IAIR assemblies with resonating masses (c) (red line), or without mass insertions (d) (black line).
Georgia Institute of Technology – School of Aerospace Engineering Atlanta, Georgia 30332-0150 Contact Us:
Massimo Ruzzane Emanuele Baravelli	ruzzene@gatech.edu ebaravelli@gatech.edu