Micropolar damage model for brittle matrix composites
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Metal and ceramic matrix composites reinforced with large fibers are usually not spatially homogeneous materials. That is, the characteristic microstructural dimension, the fiber diameter, is of the same order of magnitude as the characteristic overall structural dimension, the laminate thickness. In the present paper it is proposed to model the resulting nonlocal effects using a thermodynamically based, damage dependent constitutive model that includes ply-level moments and curvatures in addition to the classical ply-level stresses and strains. The laminate-level tangent stiffness matrix is given in terms of the ply-level tangent stiffness matrix, the ply thickness, and the ply location in the stacking sequence. The damage evolution is derived from the assumption of stable, or nondissipative fracture. It is shown that the stable fracture condition implies that during loading the damage is controllable by an external observer, and is therefore not an internal state variable in the classical sense.
