MICROMECHANICS OF CRENULATED FIBERS

The stresses at the interface of fully bonded and fully disbonded cren ulated carbon fibers in a carbon matrix are presented. Interface stres ses for two loading cases, transverse tensile loading and a negative t emperature change, are discussed. A crenulated fiber is one which has a wavy or scalloped outer radius, the amplitude and frequency of the w aviness resulting from the manufacturing process. A square-packed arra y of fibers is assumed and the results are obtained using the finite-e lement method. For comparison to the crenulated fiber, the stresses fo r similarly loaded bonded and disbonded circular fibers are also prese nted. The level of disbond in each case is measured by the size of the radial gap between the fiber and the matrix. When fully disbonded, th e fiber and matrix are assumed to interact only through frictionless e lastic contact. Results from the fully disbonded case show that mechan ical 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 concentrations arise in the matrix tange ntial stress component at high crenulation amplitudes and high crenula tion frequencies. Overall, the work described provides new insight int o the complex interactions between fiber and matrix, specifically inte ractions that reflect on the reality of disbond, and innovations regar ding fiber architecture.