The Interaction of Crack and Creep in Cross-Ply Composites

For cross-ply laminates micro-matrix cracks in the 90° plies and creep deformation of the 0° and 90° plies are two forms of damages which affects the long-term durability of the materials. In this paper, a general framework for the analysis of cross-ply laminates with matrix cracks and creep deformation is proposed. For this purpose admissible stress fields are constructed which satisfy equilibrium and all boundary and interface conditions. The principle of minimum complementary energy is utilized to derive a differential equation for the stress function from which the stress field of the composite can be derived. The inhomogeneous term of the differential equation involves the creep strains which are loading history dependent. The Green’s function of the differential equation is then obtained. Using the Green’s function and a constitutive equation, two-dimensional stress and strain states in the composites at any time are represented through an integral of the Green’s function and the accumulated creep strains. This new analysis takes into consideration the microcrack-microcrack interaction, as well as the interaction between the microcracks and the creep deformation, and provides a point-wise stress field instead of average stress field as most of the analytical approaches yield. The interactions of matrix cracks and creep deformation of an eight-harness satin weave (8H SW) Nextel 610/Aluminosilicate ceramic matrix composite is studied using the proposed model. The predicted creep strain of the composite shows good correlation with experimental data at different levels of temperature and stress conditions.