Analysis of Micromechanical and Microstructural Effects on Compression Behavior of Unidirectional Composites

Abstract

It is well known that a variety of factors have an influence on the compres sion strength of unidirectional organic matrix composites. For example, for failure as a result of microfilament buckling, the strength can be shown [1] to be directly related to both the matrix shear stiffness as well as the fiber volume fraction. Other factors can also have a significant effect on the compression strength. These include the presence of a fiber/matrix interface [2], the degree of fiber misalignment [3], compression strain-to- failure of the fibers [4], and the nonlinear stiffness of the matrix material [5]. Recent ex perimental results [2,6-8] have led to the definition of parameters which can be used in performing analyses capable of determining the most significant microstructural and micromechanical aspects of the compression strength of carbon fiber composites. Mathe matical models which utilize both closed form analytical techmques as well as approx imate finite element methods have been constructed to assess the effects of interphases, nonlinear matrix stiffness, a distribution of fiber misalignments representative of actual composites, and the compression strain-to-failure of carbon fibers. Comparisons of calculated strengths and failure modes with available data have been made to verify the an alytical approach.