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In the past decades, an increasing trend towards the structural combination of lightweight materials and traditional metals has been observed. For these multi-material interfaces, traditional joining technologies such as bolting and welding have to be re-thought and adhesive bonds can be a valid alternative. The substitution of the joints has an impact on the stiffness, damping, and mass distribution of the entire assembly and should be taken into account while designing for NVH, durability, and performance. The aim of this work is to experimentally compare the effect of bolts and adhesive bonding on the vibrational response of the assembly, in terms of modal frequency, shape, and damping. Plate-to-plate single lap joints are tested under transverse vibration. In particular, we compare one M4 bolted connection and three adhesive connections, respectively, realized with stiff epoxy, flexible foam tape, and toughened acrylic. Results show that, in a low-mid frequency region between 0 and 250 Hz, the substitution of bolts with adhesives has a limited influence on mode shapes but can lead up to a 6-fold increase of the modal damping values and 10% increase of the modal frequencies. [ABSTRACT FROM AUTHOR]

The bending wave stop band behavior of locally resonant metamaterial and phononic crystal plates can strongly improve the vibration performance of flexible plates in targeted frequency ranges. Their acoustic insulation performance, however, is found to strongly depend on the stop band mechanism, also influencing the frequency range of improvement. While sound transmission loss improvements are predicted for both infinite periodic plates, the finite phononic crystal plate performance can differ significantly.