CHARACTERIZATION OF THE VIBRATION DAMPING LOSS FACTOR OF GLASS AND GRAPHITE FIBER COMPOSITES

Material damping of laminated composites is experimentally determined by the half-power bandwidth method for cantilever beam specimens excited with an impulse excitation. Data acquisition and manipulation are carried out using both an IBM PC-AT and a GenRad 2500 Series FFT Analyzer. Unidirectional continuous fiber 0-degrees and 90-degrees laminates were fabricated from glass/epoxy (Hercules S2-Glass/3501-6), graphite/epoxy (Hercules AS4/3501-6) and graphite/poly(ether ether ketone) (ICI AS4/PEEK [APC-2]) to investigate the effect of fiber and matrix properties as a function of frequency, up to 1000 Hz, on the damping of composites. The S2-glass/3501-6 composite has a higher loss factor than the AS4/3501-6 in the 0-degrees orientation with the loss factor for the AS4/3501-6 exhibiting a linear increase with increasing frequency and the loss factor for the S2-glass varying nonlinearly with frequency. The 90-degrees material exhibited a higher damping loss factor than the 0-degrees, varying nonlinearly with increasing frequency. In the 90-degrees orientation, the glass fiber composite had loss factors that were approximately fourfold greater than the 0-degrees orientation at frequencies greater than 200 Hz. The 0-degrees AS4/PEEK had a loss factor that was approximately equal to that of the 0-degrees AS4/3501-6. The 90-degrees AS4/PEEK had a loss factor that was approximately 50% less than the AS4/3501-6 and 25% greater than the S2-glass/3501-6 composite.