MICROSTRUCTURAL FINITE ELEMENT MODELING OF HIGH-PERFORMANCE CARBON FIBER-REINFORCED COMPOSITES TO CHARACTERIZE MICROSCALE MATERIAL PROPERTIES AND FIBER-DIRECTION COMPRESSIVE STRENGTH

Abstract

Carbon fiber-reinforced composites are increasingly used in aerospace application thanks to their excellent specific stiffness and strength. However, incomplete understanding of their failure behaviors leads to composite components often being designed with a high Safety Factor, limiting their advantages. Using computational methods, this project studies carbon fiber-reinforced composite microstructures for the objective of understanding and improving material performances under compression load which is one of the main considerations in primary aerospace structure design. A Finite Element (FE) model for the evaluation of composite compression behaviors was developed, allowing the identification of several key material properties affecting composite performance. The numerical micromodels require information of the microscale components including the reinforcing fibers, the matrix and the fiber-matrix interface. An extensive literature review was done on the microscale component properties including their potential impact on composite strength. Combined with results from the FE modeling, a strategy was decided where the assessment of important material properties was given priority. Several authors, numerically and experimentally, demonstrated the significant impact of microscale residual stress on composite strengths. Yet, there was no established method for the characterization of residual stress in matrix at microscale. This project proposes a new method for the assessment of microscale residual stress in composite matrix. The new method is based on the fiber push-out experiment that creates local matrix deformation induced by the relaxed stress and evaluation by the Finite Element Method Updating technique for the inverse characterization of residual stress field in the corresponding specimen. Literature review and FE modeling results identified the Interfacial Shear Strength (IFSS) as a key material property affecting composite strength. Meanwhile, the IFSS measurement using the standard push-out method suffers from several unwanted effects, potentially lowering its accuracy. These effects were analyzed using FE modeling. Notably, the results suggest that the effect of microscale residual stress on the IFSS measurement is rather insignificant.