Vibration Characteristics of Aluminum Plates Reinforced with Boron-Epoxy Composite Material

Vibration characteristics of aluminum plates reinforced with boron epoxy composite material were investigated experimentally and analyt ically. Variations in the natural frequencies, mode shapes, and damping with filament angle were studied. Vibration characteristics of the re inforced plates were also compared with all-aluminum plates.

Results of this study demonstrate the merit of using directional com posite materials in design for controlling vibration characteristics of plates. For example, experimental results show that the frequency of the first mode can be changed 77 percent by adjusting the fiber orientation with no change in the plate mass. Results also showed that the damping coefficients could be controlled with filament orientation and that the maximum damping occurred for modes having maximum straining of the matrix and minimum straining of the filaments. Regardless of the filament orientation, all the reinforced plates had more damping than the all-aluminum plates. However, these damping values tend to be less than those normally associated with conventional built-up aerospace structures.

Analytical results used in this report were in qualitative agreement with experimental trends for nodal pattern and frequency variations with filament orientation. However, in some cases, quantitative frequency corre lation was poor. To obtain better correlation, a more sophisticated finite element, including effects such as interlaminar shear, matrix viscoelasticity, and metal-epoxy interface properties, might be necessary.