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Effect of Fiber-Orientation on the Long-Term Thermo-Oxidative Degradation in Composite Laminates



Polymer composites have a limited service-life in high temperature environments due to oxidation-induced material degradation. The degradation processes are controlled by oxygen diffusion and reaction kinetics during the initial hours of exposure and over a longer-term by the oxidation-induced chemical and dimensional changes as well as damage evolution. Longer-term aging after damage initiation causes formation of discrete crack surfaces that adsorb oxygen and lead to acceleration in oxidative degradation and the permeation of oxidation deeper into the composite. This work focuses on model-based calculation of oxidation growth rates over thousands of hours of aging in both axial and transverse directions of a polymer matrix composite lamina. In a G30 Carbon/PMR-15 Polyimide lamina that is exposed along its edges and on the transverse surfaces, the axial (along the fiber-axis) oxidation growth rate before the crack initiation starts at ~4.12 ô€Ÿ¤ô€Â‰/â„Ž and reduces to ~ 2.18 ô€Ÿ¤ô€Â‰/â„Ž, if a surface oxidation layer grows without crack initiation. Similarly, the transverse oxidation growth rate before crack initiation starts from a relatively high value (~ 1.12 ô€Ÿ¤ô€Â‰/â„Ž) and decreases to its lowest value (~ 0.09 ô€Ÿ¤ô€Â‰/â„Ž) as the active reaction zone moves deeper into the material. These rates estimation of the use-life or conversely a durability-substantiated design of surface ply thickness.

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