The Finite Element Analysis and Resin Rich Area Characterization of Spread Tow Carbon Fibre Fabrics from Synchrotron X-ray Tomographic Microscopy

Abstract

The fact that most of the finite element method (FEM) on micromechanics of carbon fibre-reinforced polymers are generally constructed based on the two-dimensional image correlation obtained from optical or field emission scanning electron (FE-SEM) microscopes, interpretations of stress or strain distributions and resin-rich area characterizations are limited due to the lack of the dimensional views. To alleviate this issue, we obtained the three-dimensional structures of the spread tow carbon fibre/epoxy composites by using the synchrotron X-ray tomographic microscopy located at synchrotron light research institute, Thailand.  For FEM analysis based on a region of interest, the materials properties of the constituents in the composites were assigned according to the X-ray spectrum contrast differences.  Specifically, matrix and carbon fibre have a different material basis. Thus, the synchrotron X-ray imaging result showed different grey values, which can segregate the matrix and reinforcement region for the FEM process. The load is applied onto a side of 3D models to obtain the results in the form of maximum stress values, displacement etc. The imaging results indicated that the resin-rich areas of spread tow fabrics which are plain weaves were less than twill weaves due to the tighter weaving style and the larger crimp angle under the conditions of all spread tow fabrics which have the same fibre diameter measured by FE-SEM.  It was found that stress or strain distributions are consistent with the loading experiment. Resin-rich areas were detected in volumetric values, indicating that 3D modelling from synchrotron XTM imaging results can represent the characteristics of CFRP samples. FEM results showed the effect of fabric pattern in the stress distribution and implied that mechanical properties by weight of spread tow carbon fibre reinforced polymer, STCFRP fabrics are more than commonly used CFRP fabrics. Statistical analyses of phase-contrast X-ray computed micro-tomography reveal distinctive gradients as well as localized correlations between carbon fibre and matrix phases.  Based on these differences, a highly efficient algorithm for fibre tracking using statistical distributions of phase contrast has been proposed in this study.