Instrumentation and techniques for the measurement of low frequency internal friction

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Abstract
An instrumentation system for measuring the amplitude and period of oscillation of low frequency internal friction pendula is described. It can be constructed from commercially available operational amplifiers and functional modules and includes a small computer to record data. It can be used to provide an amplitude feedback signal for a pendulum amplitude control system. Measurement techniques and estimation of errors are discussed, with particular emphasis on the measurement of strain amplitude dependent damping. A method of correcting low frequency strain amplitude dependent damping for the strain distribution in the specimen is outlined.