Abstract: It is common to determine dynamic moduli of materials through vibration measurements. There usually exist adding masses in vibration tests. However, the effects of adding masses in the vibration tests for the determination of dynamic moduli of composite materials can not be ignored since the specimens are generally small in dimension due to the high expenses of composite materials. Based on Timoshenko beam theory, two characteristic equations considering adding masses, one for a cantilever and another for a free-free beam, are derived in this paper, which can eliminate the effects of adding masses in vibration tests theoretically. The correction of dynamic moduli by using Be-rnoulli-Euler beam theory and without considering adding masses is further disscussed. In addition, a general technique for the determination of shear dynamic modulus G12 through a flexural vibration measurement is developed. A specific example is given at the end of this paper.

Key words: fiber-reinforced composites, dynamic moduli, chwracte- ristic equntion