Correlations between polymer matrix and composite mechanical properties

During the past decade or more, the composite materials community has restricted itself primarily to the use of only a few structural epoxy matrix materials. Very recently, whole new families of polymer matrices have become of practical interest. In order to select from this wide range of new polymers for each specific structural application, the relation between the various polymer mechanical and physical properties, e.g., modulus, strength, strain to failure, thermal and moisture expansion coefficients, moisture absorption rate, etc., and resulting composite properties must be known. Correlations of finite element analysis predictions with actual experimental data will be presented, using measured mechanical and physical response properties of various toughened epoxy, bismaleimide, polyimide, and thermoplastic matrix systems as inputs to the analyses. Results will include fracture mechanics evaluations, the role of matrix nonlinear response, crack initiation and propagation, thermally induced damage, and the influence of the interface. Matrix properties to be modeled have been generated in the author's own laboratories, as part of several current and ongoing funded research studies for various government and industry groups. Several types of finite element analyses have been used, including 2-dimensional generalized plane strain with longitudinal shear loading, 2-dimensional axisymmetric, and fully 3-dimensional formulations. All of these analyses permit the input of actual matrix nonlinear stress-strain response, and how it varies as a function of temperature and moisture content. Fibers having anisotropic properties in a composite of arbitrary fiber volume are included. Time-dependent response, e.g., creep, recovery, and relaxation, and crack propagation are also possible response modes. Results will be presented in the form of composite stress-strain curves, plots of stress contours in the matrix, and at the fiber-matrix interface.