Micromechanical analysis of composite laminates at cryogenic temperatures

A finite element analysis-based micromechanics method is developed to investigate development of microcracks in a graphite/epoxy composite liquid hydrogen tank at cryogenic temperatures. The unit cell of the composite is modeled using finite elements. Periodic boundary conditions are applied to the boundaries of the unit cell. The temperature-dependent properties including the coefficient of thermal expansion of the matrix material are taken into account in the analysis. The thermoelastic constants of the composite are calculated as a function of temperature. The stresses in the fiber and matrix phases and along the fiber-matrix interface are calculated. When the laminated composite structure is subjected to combined thermal and mechanical loads, the macrostrains are computed from the global analysis. Then, the macrostrains and temperatures are applied to the unit cell model to evaluate microstresses, which are used to predict the formation of microcracks in the matrix. The method is applied to a composite liquid hydrogen storage system. It is found that the stresses in the matrix phase could be large enough to cause microcracks in the composite.