Sandwich designs for high levels of noise and vibrations

Abstract

Lightweight materials with high structural damping and reasonably well flexural performance are demanded in some components of aerial vehicles such as interior part of helicopters where high levels of noise and vibrations exist. One of the best choices for this is through the use of a polymer matrix composite with suitable fiber orientations and a structural foam core. In this study, face sheets from a woven carbon fiber reinforced polymer plies and a foam core with three different thicknesses (10.7 mm, 25.4 mm, and 49.8 mm) have been used to manufacture sandwich structures to yield high dynamic values (damping and flexural rigidity). To measure these values, the sandwich beams with free-free boundary conditions were subjected to free vibration tests using a non-contact response measuring system. The measurements were made for the first, second and third natural frequencies, and compared to numerical modal analysis via the ANSYS package program. The results from experimental and numerical methods are found to be reasonably good in agreement and show that the sandwich structures are able to give high damping values, in general. It seems the specimens with relatively low thickness give relatively high damping values compared to the others, whereas the thicker ones are useful for high frequency domains and flexural rigidity. The behaviors of the beams have been found frequency dependent, due to the viscoelastic behavior of the foam cores at high frequency levels.