Passive vibration reduction of advanced composite pretwisted plates using integral damping materials

An analytical procedure to incorporate viscoelastic damping into advanced composite bladed structures is described. A constrain layer damping technique is used to damp out specific modes in a cantilevered pre-twisted plate. A viscoelastic material, 3M Scotchdamp ISD 113 (ISD113), is placed in a small pocket at a specified location within the plate to isolate the damping of a particular vibration frequency. Analytical and experimental results are presented for a flat and pretwisted plate with the [O2/+0/-02/+0/O2/ISD113-border material]s lay-up. The results show that for a given patch size of the ISD113 the location can have a significant effect on the damping level and only a negligible effect on the structural stiffness. The results also show that the border material can be varied in such a way as to increase the damping level with only a slight decrease in the structure's natural frequency.