Prediction of Notched Strength of 3D Carbon-Carbon Material Under Simple Tension

Abstract

First of all, the development of inherent damage near notch tip in 3D carbon-carbon was examined with polariscopic microscope while loading. To track the notch tip during loading, a specially designed adjustable stand and loading apparatus were designed and fabricated. Based on the observation, a very simple analytical model was es tablished. In order to use micromechanics to predict the notched strength, the in-situ strength of fiber bundle was measured with a specially designed fixture. The notched strength of 3D carbon-carbon material was predicted from the longitudinal strength of the portion of the fiber bundle, where the stress concentration takes place. Hedgepeth's stress concentration factor for infinite plate is corrected for finite plate. Calculation of stress fac tors show that failure of a single fiber bundle nearest to the notch tip will cause total failure of the specimen. With Zweben's statistical strength criterion, the strength of the notched 3D carbon-carbon material was predicted and the prediction agrees with experimental results fairly well.