Damping characteristics of 0 degrees and 90 degrees AS4/3501-6 unidirectional laminates including the transverse shear effect

Material damping of laminates is determined analytically by the strain ener gy weighted dissipation method and experimentally by the half-power bandwid th method for cantilever beam specimens elicited with an impulse excitation . Data reduction and acquisition are conducted using both an IBM PC-AT and a GenRad 2500 series Fast Fourier Transform (FFT) analyser. Unidirectional continuous fiber 0 degrees and 90 degrees laminates were fabricated from gr aphite/epoxy (Hercules AS4/3501-6) to examine the effect of transverse shea r as a function of aspect ratio (length/thickness) on the damping of compos ites. The loss factor for 0 degrees AS4/3501-6 composites exhibits a linear increase with decreasing aspect ratio according to both theory and experim ent. Moreover, the loss factor for 90 degrees AS4/3501-6 laminates is not f ound to vary consistently with aspect ratio in the experiments, whereas the predicted values increase gradually with decreasing aspect ratio. In gener al, the 90 degrees laminates exhibited much higher damping than the 0 degre es laminates. It is also shown the transverse shear stress (sigma(xz)) has a considerable effect on the damping mechanisms in 0 degrees unidirectional polymer composites. However, the transverse shear stress (sigma(yz)) was s hown to be relatively insensitive to damping in 90 degrees unidirectional c omposites. (C) 2000 Published by Elsevier Science Ltd.