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SUMMARYA new approach to modelling solids that are anisotropic and heterogeneous is presented with applications to structures of composite material. A parametric cubic modelling system is presented for lines, surfaces, volumes, and physical data that uses construction-in-context to generate numerical data. This system automates the construction of discrete element models and can reduce input data requirements by more than an order of magnitude. A tricubic isoparametric discrete element is presented that does not require displacement derivatives to define connectivity. This element is capable of exact displacement and strain continuity over a surface while permitting strain discontinuities at heterogeneous material interfaces. The shape of an element can be any hexahedron, pentahedron, or tetrahedron and the material properties are allowed to vary over the volume. Evaluation of modelling error with respect to closed-form solutions for curved geometries indicate a single element can model up to 90-degree segments with stresses accurate to 1 per cent. Applications of the system to composite structures are presented for interlaminar edge effects and attachment stresses in a sandwich panel.

The inelastic mechanics of isotropic materials are usually modeled by scalar functions of the material stress or strain state. Simple effective stress-strain models work well because of the material symmetry and homogeneity usually found in structural materials, and because a single deformation mechanism accounts for inelastic strain behavior. In contrast, laminated carbon-carbon composites are anisotropic with a weak matrix phase and exhibit at least two inelastic deformation mechanisms in coupon tests. The motivation for the present work was the bimodular nonlinear strain response found in testing involute cylinders of a low modulus carbon-carbon material typical of a composite used in nozzle components for several years and now used in several industrial products to replace asbestos. These experimental results raised basic questions about nonlinear material modeling and characterization for this class of composites. The present paper describes results from a program that developed and demonstrated a nonlinear model for two-dimensional carbon-carbon composites based directly on coupon stress-strain data. A low modulus bidirectional material, K-KARB, was used to validate the model in room temperature tests.