Prediction of Compressive Strength of Fibrous Composites Using Two Different Approaches

This paper presents two different approaches to predict the compressive strength of fibrous composites using three-dimensional analysis. These approaches are based on the optimization of compressive stress resulting from the relationship between the compressive stress of the fibrous composite and the shear strength of the matrix material. The first approach is an estimation of compressive strength based on the actual initial misalignment of fibers in the rotated plane. The second approach is an approximation of compressive strength in accordance with the components of the initial fiber misalignment relative to the global axes of the fibrous composite material. The initial fiber misalignment is defined as a curve in the form of a cosine function that has components on the two planes containing the longitudinal axis and defined by initial misalignment angles. Equilibrium equations are then derived for an infinitesimal element along the axis of the fibers using the total potential energy principle. Maximum compressive strength is calculated using the corresponding shear stresses and shear deformations in the matrix, since shear is the dominant mode of failure. The compressive strength corresponding to the shear mode is found to be related to the tangent shear modulus of a fibrous composite material. The two different approaches are used to study the following composites: Carbon/epoxy XAS/914C saturated and dry, Carbon/Peek AS4/PEEK (APC-2), AS4/E7K8, Glass-Vinyl Ester, Glass-Polyester and unidirectional HTS40/977-2. The results obtained in this paper are found to agree well with experimental results and theoretical results available in literature.