Micromechanics of Crenulated Fibers

Abstract

The stresses at the interface of fully bonded and fully disbonded crenulated carbon fibers in a carbon matrix are presented. Interface stresses for two loading cases, transverse tensile loading and a negative temperature change, are discussed. A crenulated fiber is one which has a wavy or scalloped outer radius, the amplitude and frequency of the waviness resulting from the manufacturing process. A square-packed array of fibers is assumed and the results are obtained using the finite-element method. For comparison to the crenulated fiber, the stresses for similarly loaded bonded and disbanded circular fibers are also presented. The level of disbond in each case is measured by the size of the radial gap between the fiber and the matrix. When fully disbanded, the fiber and matrix are assumed to interact only through frictionless elastic contact. Results from the fully disbonded case show that mechanical interference occurs between the fiber and the matrix. In general, the results of the study show that the stress levels present with the crenulated fiber are significantly higher than for the circular fiber. In particular, large stress concentations arise in the matrix tangential stress component at high crenulation amplitudes and high crenulation frequencies. Overall, the work described provides new insight into the complex interactions between fiber and matrix, specifically interactions that reflect on the reality of disbond, and innovations regarding fiber architecture.