Dynamic Mechanical Behavior of Fiber-Reinforced Composites: Measurement and Analysis

This paper describes analytical and experimental efforts to find the internal damping and elastic stiffness of E-glass fiber-reinforced epoxy beams under flexural vibration. Stiffness and damping are expressed in terms of effective complex moduli. The parameters considered in the study are geometric configuration, vibration frequency, and vibration amplitude. Comparison. of measured values of the complex moduli with predicted moduli and with predicted bounds on the moduli shows that, for small amplitudes, the predicted values are reasonably accurate. Damping and stiffness are independent of amplitude as long as the maximum strain amplitude does not exceed the threshold strain for material damage. Once this threshold strain is exceeded, however, permanent changes occur in damping and stiffness. The resulting increase in damping is much more significant than the corresponding reduction in stiffness.