Inelastic Deformation and Fracture of Graphite/Epoxy by Damage Mechanics

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Inelastic deformation and damage process of Graphite 1 Epoxy**45ﾟ*_4 laminate tubes under axial and combined axial and tersional loadings are discussed. The elastic deformation and ruptuse properties under combined loading are discussed first. Significant viscoplastic deformation is induced by axial loading due to fiber rotation and matrix dominant deformation. The comprissire strength of the laminate tubes is about 15% smaller than the tensile strength. In the case of cyclie axial loadings, significant hysteresis loups and salient viscoplastic deformation are induced due to matrix dominant dyormation. The negative stress ratios have masked effects on hysteresis curnes, stifyness reduction and on fatigue life. These phenomena are attributable to the matrix dominant deformation of laminas and the accelerated viscoplastic deformation of polymer matrix under reversed loading. However, the fatigue stlength is govesned mainly by the maximum (or minimum) stress, and is influenced by the stress ratios. The fatigue strength under cyclic compression is 10-20% smaller than that of chclic tention. The stress loci for fotigue the are also discussed. A personal computer program by using the intelligent finite-element methods has been depeloped in order to analyze the construction and staching sequence of laminate by which some design objection can be satisfied. In this paper, the strength, weight and cost of laminate were seleeted as the design objectives.