A Representation of Anisotropic Creep Damage in Fiber Reinforced Composites

A creep damage model is presented that allows for anisotropic distributions of damage in composite materials. An earlier model by the writers allowed for anisotropic damage growth rate but, based on a scalar state variable, failed to account for anisotropic distributions of damage. A vectorial state variable is introduced that allows a representation of anisotropic damage distribution. As in earlier work, a fundamental assumption is that the principally damaging stress components are tensile traction and longitudinal shear at the fiber/matrix interface. Application of the creep damage model is made to calculations involving homogenously stressed composite elements under transverse tensile and longitudinal shear stress and to cross plied thin-walled tubes under tension/torsion. Although the emphasis is phenomenological, with focus on a mathematical structure for representing anisotropic distributions of damage, a meaningful creep damage model must rest on fundamental material science and microstructural examination. Verification experiments involving tension/torsion testing of thin-walled composite tubes together with detailed microstructural examination are discussed and outlined.