Characterization of Hybrid Material Interphases

A comprehensive non-linear finite element analysis study has been performed of the single fiber fragmentation test and the microindentation test to evaluate the mechanics of these techniques for measuring fiber-matrix adhesion in fiber reinforced polymeric composite materials. The determination of the fiber-matrix interphase modulus and its spatial variation has been shown to be important to relating microtesting methods to composites properties. As a result, a novel micro testing technique has been proposed for adherend-adhesive or fiber-matrix interphase properties characterization. A modified shear lag relationship was combined with the fiber strain energy equation to obtain an equation for meanaverage interfacial shear stress and pseudo mean interfacial shear modulus. Good agreement was found. An experimental study using dynamic mechanical analysis was performed using these methods. The influence of test parameters has been evaluated and have been found to give a clear, reproducible reading of the loss and storage modulus as well as the exact glass transition temperature. The sensitivity of the DMA has proven to be exceptionally high. The viscoelastic response of an interphase with a thickness of only 3 by volume of the fiber can be detected and the interphase influence on the storage modulus of the composite can be quantified.