damping treatment design, there
are different ways to apply viscoelastic materials as shown in Figure 1; (i) the full treatment of unconstrained
viscoelastic material layer, (ii) the full treatment of constrained
viscoelastic material layer, and (iii) the partial treatment of viscoelastic
layers. The free layer damping (FLD) treatment is unconstrained layer
construction with the viscoelastic layer bonded using an adhesive to one or
both sides of the base structure as shown in Figure
1(a). When the base structure is deflected in bending, the viscoelastic
layer undergoes extension and compression in planes parallel to base structure.
The hysteresis loop of the cyclic stress and strain dissipates the energy in
the form of heat. The degree of damping is constrained by the thickness and
weight limits. The vibration analysis of the beam with the viscoelastic layer
was firstly conducted in 12.The
viscoelastic material’s characteristic was modelled using complex modulus
approach. It has been found that the system loss factor in a free layer
treatment increases as the thickness, storage modulus and loss factor of the
viscoelastic material layer increase. The constrained layer damping (CLD)
consists of an additional top layer on the free layer damping treatment as
shown in Figure 1(b).When the base structure
undergoes bending vibration, the viscoelastic material is forced to deform in
shear because of the upper stiff layer. The constrained layer damping is more
efficient than free layer damping because the core layer can store more strain
energy and therefore dissipates more energy. The symmetric design, in which
base structure and top constraining layer has same thickness, exhibits the most
effective configuration as it maximizes the shear strain in the core layer. The
CLD can be extended to multiple constrained layers, which are very effective
for obtaining damping over wide temperature and frequency ranges. In addition,
in order to reduce the weight of structure, the constrained layers are
implemented in patches as partial treatment as shown in Figure 1(c).The locations of the partial treatment can be optimized
to achieve maximum loss factor or damping property of the sandwich structures.