Evaluation of Interface in Composites with Short-Fiber Based on Viscoelastic Properties

Abstract

Measurement of interfacial shear stress has been difficult on a composite with short-fiber, since the fiber length is shorter than the critical length. In this study, a mechanical model is proposed for the composites and the interfacial shear stress is evaluated with viscoelastic propeties of the model. Injection molded composite specimens are used in short-term creep tests. The coefficients in a viscoelastic model are evaluated by the optimization analyses of experimental results. The strain shared by fiber for a given macroscopic strain is analysed from the change of the coefficients for elements in the mechanical model. The stress in fiber is obtained by substituting the mean stress into Cox's relation. The interfacial shear stress, from the shear-lag analysis, is compared with the prediction after Cox. As a result, the maximum shear stress was found to be bigger than that of Cox's prediction and also least affected by fiber volume fraction.