The damping plays a vital role in structural dynamic and acoustic performance of aluminium honeycomb sandwich structures. The viscoelastic damping treatment of skins is most common. An alternative, the use of sustainable cork inserts to improve the damping of cores and the whole assembly is investigated in this study. Structures with different filling degrees are analysed as well as the optimum location for inserts is determined. The structural dynamic as well as the vibro-acoustic performance is estimated numerically. Average squared displacement amplitude reduction efficiency is defined as the target parameter for structural dynamic performance, whereas average transmission loss effectiveness for vibro-acoustic performance. The structural dynamic models are validated by experimental vibration analysis, whereas the vibro-acoustic models are validated against published data. Different ways of bonding the inserts to the host structure are analysed in order to maximise damping. The highest improvement is obtained with a filling degree of 64% honeycomb voids and 9.76% increase in mass, for which an average squared displacement amplitude reduction of 35.25% and an average increase in transmission loss of 1.5dB is achieved. The transmission loss increase in relation to the added mass is much higher than that achieved by doubling of mass in the mass law region. The introduction of cork inserts spreads the energy in local modes to a larger space, effectively decreasing the resonance amplitudes. Interestingly, damping does not increase with the number of inserts in a monotonic way and the improvement depends on the spatial distribution of inserts.
Monninger, P.Thite, Anand N.
Faculty of Technology, Design and Environment\School of Engineering, Computing and Mathematics
Year of publication: 2018Date of RADAR deposit: 2018-08-01