A Maxwell rotating beam apparatus was used to measure the dynamic mechanical properties as well as the fatigue life of nylon 6 filled with glass beads or fine silica powder, a nylon 66 filled with calcined clay, an epoxy filled with glass beads, and high-impact polystyrene. Attempts to monitor damage by changes in the dynamic mechanical properties failed; the properties remained essentially constant until only a relatively few cycles before failure occurred. The decrease in modulus and increase in damping with increasing maximum cyclic stress were due mostly to heat build-up rather than to any permanent damage. The fatigue life can be drastically decreased by small surface scratches.
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