Indamping treatment design, thereare different ways to apply viscoelastic materials as shown in Figure 1; (i) the full treatment of unconstrainedviscoelastic material layer, (ii) the full treatment of constrainedviscoelastic material layer, and (iii) the partial treatment of viscoelasticlayers. The free layer damping (FLD) treatment is unconstrained layerconstruction with the viscoelastic layer bonded using an adhesive to one orboth sides of the base structure as shown in Figure1(a). When the base structure is deflected in bending, the viscoelasticlayer undergoes extension and compression in planes parallel to base structure.
The hysteresis loop of the cyclic stress and strain dissipates the energy inthe form of heat. The degree of damping is constrained by the thickness andweight limits. The vibration analysis of the beam with the viscoelastic layerwas firstly conducted in 12.Theviscoelastic material’s characteristic was modelled using complex modulusapproach. It has been found that the system loss factor in a free layertreatment increases as the thickness, storage modulus and loss factor of theviscoelastic material layer increase. The constrained layer damping (CLD)consists of an additional top layer on the free layer damping treatment asshown in Figure 1(b).
When the base structureundergoes bending vibration, the viscoelastic material is forced to deform inshear because of the upper stiff layer. The constrained layer damping is moreefficient than free layer damping because the core layer can store more strainenergy and therefore dissipates more energy. The symmetric design, in whichbase structure and top constraining layer has same thickness, exhibits the mosteffective configuration as it maximizes the shear strain in the core layer. TheCLD can be extended to multiple constrained layers, which are very effectivefor obtaining damping over wide temperature and frequency ranges. In addition,in order to reduce the weight of structure, the constrained layers areimplemented in patches as partial treatment as shown in Figure 1(c).The locations of the partial treatment can be optimizedto achieve maximum loss factor or damping property of the sandwich structures.