crack propagation. Third, the permeability of various composite materials is evaluated to
investigate the effect of cryogenic cycling on permeability.
Micromechanics Analysis of Laminated Composites at Cryogenic Conditions
From a macroscopic perspective, the composite material is considered to be
homogeneous and transversely isotropic or orthotropic in general. For example, the
laminated plate theory has been formulated based on this assumption. Even when three-
dimensional analyses are used for composite structures, each ply or layer of the
composite is modeled as a homogeneous orthotropic material. This macroscopic
approximation has been found to be satisfactory in most analyses including thermal stress
analyses. Thus most of the thermal stress problems in composites focus on the differences
in thermal expansion coefficients between the plies. However, in extreme situations a
micromechanics approach wherein the fiber and matrix phases are differentiated is
necessary for accurate prediction of stresses, and hence failure. The present problem falls
in this category. In order to predict the failure of a composite structure at the macroscopic
scale, investigation of micromechanical behavior and understanding the failure
mechanisms in the fibers and matrix at a micro-scale are necessary [2].
To make effective use of fiber-reinforced composites, we need a methodology to
predict the thermo-mechanical properties at various temperatures as a function of fiber,
matrix and interphase properties. These properties will be a strong function of
temperature. Micromechanics is the study of such macroscopic properties from that of the
constituent materials. In this study, micro-cracking behavior of the liquid hydrogen
composite tank at cryogenic temperature is investigated using the micromechanics
method. Failure of the composite tank under thermal and mechanical loads is evaluated
by utilizing the commercial finite element software ABAQUS. Also, the analysis is