The relation of complex modulus of elasticity to the deflection or the strain of a viscoelastic cantilever under forced vibration was explained mathematically.
The deflection of the beam was expressed as a complex number, and we could understand the amplitude and the phase difference from the applied force. With this deflection diagram, the loss factor of the tested material was defined.
To find the viscoelastic properties of glass fiber reinforced plastics, the real part and the imaginary part of the complex modulus of elasticity were measured at various temperatures, using polyester resin reinforced with glass fiber roving cloth and polyvinyl chloride resin reinforced with glass fiber mat.
The values of the loss factor of these materials were about 0.01∼0.2, under various conditions of this study.
Generally, the viscoelastic behaviour of the materials became more viscous in accordance with the rise of temperature.
The rich content of glass fiber made the materials more elastic and resistible against heat, and the value of loss factor decreased. These effects mainly depended upon the fibers lying parallel to the direction of the stress.
