Characterization of elastic modulus at glass/fiber interphase using single fiber composite tensile tests and utilizing DIC and FEM

The bonding performance and formation of the interphase region between fiber and matrix have significant effects on the strength and durability of composites. A new approach, involving combined experimental and numerical analyses, has been developed to avoid the shortcomings and scattering associated with local experimental methods. For this purpose, tensile tests are performed on specimens fabricated from a single glass fiber and epoxy resin. The elongations for specified lengths are measured using the digital image correlation (DIC) technic. The size of the fiber diameter and specimen section are also measured from SEM images. The obtained experimental displacements for micro tensile tests are used in an inverse elastic finite element solution to obtain the interphase elastic modulus. It is shown that, considering the interphase thickness of 1.0 & mu;m that is more realistic, the interphase elastic modulus is in the range of 12 & SIM; 19 GPa. However, the performed sensitivity analysis shown that considering interphase thickness ranging from zero to 2.0 & mu;m the interphase elastic modulus varies between 9 and 46 GPa. It is shown that the proposed procedure can be used to obtain the overall mechanical properties of the matrix/fiber interphase in long fiber composites.