The Effects Of Carbon Fiber’s Defect On Tensile Strength And Modulus

Carbon fiber is widely used in aerospace, industry, sports with its excellentperformance, in high strength and high modulus characteristics. Nowadays, mainlyscientific researches of carbon fiber focus on the material properties, which onlyprovide the Griffith’s micro-crack theory and the weakest link theory.According to the actual observation of the microstructure of carbon fiber, anew theoretical model is given. The bonds between carbon atoms make up themolecular surface layer, and the molecular surface layers make up a complexlmicrostructure model with defects. The influence of bonds decides whether the loadcan be passed or not, the defects in the molecular surface layer can tell how theloads should be distributed, and the defects in the carbon fiber can contribute tocarbon chains which decide the effective stress area for the actual load. Themathematical expression formula of this model by mathematical statistics can givethe single tensile strength, and the statistics on massive carbon fibers describe thedistribution.Comparing the complex model with the micro-crack theory and the weakestlink theory, the correctness of the complex model can be confirmed. Given that theinfluence of carbon fiber strength and influence factors are similar, the massivefiber statistics by carbon fiber strength distribution is same comparing to thecomplex microstructure model with defects. The model used in this paper is morecomplex than the other two theories, and even closer to the fiber’s real structure.According to the model assumptions and mathematical derivation, variousparameters and the way how they effect the carbon fibers can be derived, even moremathematical formula can be given. Carbon content, lattice quantity, micro fiberorientation, length, diameter, impurity, void and crack of carbon fiber strength andmodulus effects make unique influences on carbon fibers, which effect the disparitybetween theory valve and real valve.With the help of the theory for the strength of carbon fiber, the solution for thevalue of theoretical180GPa gradually reduce to the actual process of2~5GPaintensity values can be explained.