The damping of carbon fiber reinforced plastics (CFRP) is generally low at fiber volume fractions used for practical structures, such as aircraft components. If resonant behavior is induced in service, there is obvious merit in increasing material damping. Experimental and theoretical studies have been carried out to examine methods for increasing the damping of CFRP by use of short aligned fibers and combinations of fiber types; some configurations yielding moderate damping increases have been found. Stiffness to weight ratio is also a significant parameter for high performance structures, therefore both the loss factor and dynamic modulus of elasticity of specimens must be measured if experimental studies are carried out. Techniques for measuring these dynamic characteristics of material specimens have been developed. Attention has been given to the development of simple, rapid methods for measuring the properties, such as structural loss factor, of beams through a frequency range for comparative purposes. A technique for the more fundamental determination of material loss factor is also described. Results from tests on various types of CFRP are given. [Work supported by the Ministry of Defence.]

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