Influence of matrix plastic properties on compressive strength of carbon fiber composites: A combined FEA and experimental study

Composite structures in aerospace vehicles (e.g. wings, fuselages) are subjected to complex compressive loads during flight, and insufficient compressive strength may lead to localized buckling or delamination failure, causing catastrophic accidents. The matrix is an important limiting factor for composite compressive strength improvement. This study examines how the plastic properties of epoxy resin matrices affect the compressive strength of unidirectional continuous carbon fiber reinforced polymer composites (UD-CFRPs) via combined finite element analysis (FEA) and experiments. The FEA proved that the friction angle (β) of the matrix and the lower yield strength (${\sigma }_{Y,L}$) point in its compressive constitutive curve were highly correlated with the compressive strength of UD-CFRPs. This is due to the influence of the two parameters on the plastic deformation of the matrix during compression of UD-CFRPs. In addition, the initial misalignment of the fibers will amplify the shear effect of the matrix during compression. Five sets of experiments were designed to verify the conclusions of FEA, in which epoxy monomers with different functionalities and amine curing agents with different stoichiometric ratios were used. The experimental results demonstrated that matrices with higher β and ${\sigma }_{Y,L}$ were more favorable for the preparation of UD-CFRPs with high compressive strength. Eventually, the conclusion of this work provides a strategy to optimize the compressive performance of UD-CFRPs through molecular design and formulation control.