Vibration-based identification of interphase properties in long fiber reinforced composites

The interphase properties of fiber-reinforced composite materials affect significantly the dynamic behavior of the material, and hence they have to be accounted for accurately. However, the small thickness of the interphase makes it hard to measure precisely its properties directly. In this paper, a new approach is proposed to determine the properties of the interphase by using the vibratory response of coupons made of the composite material. A model obtained from first principles combining Euler-Bernoulli beam theory and the strain energy method is used to identify interphase properties from experimental data. The model of a vibrating cantilevered beam is parameterized to obtain effective properties of the material, which include the interphase properties. The identified interphase properties are verified using composites with different fiber volume fractions. It is found that the predicted vibration response matches very well the experimental measurements; hence, the proposed approach is feasible to characterize the interphase properties.