| Popis: |
Various important aspects of discontinuous fiber composites have been studied in detail both experimentally and theoretically through a model composite containing polydiacetylene (PDA) single crystal as the reinforcement fiber and epoxy resin as the matrix. The aspects encompass varying degrees of fiber behavior as well as fiber/matrix interaction, such as compressive behavior of the reinforcement fiber, geometry effects of the fiber on the stress distribution along the fiber, fiber orientation, residual thermal stress, and the role of fiber/matrix interfacial properties on the performance of composites. The compressive failure mode of the PDA fiber used in this study is the formation of readily observable kink bands. The critical compressive strain of the fiber was found to be 0.3%. By monitoring the behavior of the C$\equiv$C bond frequency in PDA in response to applied compressive loads, the stress along the fiber can be determined leading to the establishment of a calibration curve describing the relationship between the frequency change of the bond and the compressive strain due to residual thermal stress caused by differences in thermal expansion between fiber and matrix. This thermal stress will cause fiber compressive failure if the critical compressive strain is achieved. A quantitative analysis of the data reveals that no slippage occurs at the fiber/matrix interface during the build-up of thermal stress. The geometry of the fiber was found to play a significant role. Both experimental and finite element analysis demonstrate the advantage of tapered end fiber over the ordinary blunt end fiber, i.e. fiber with a uniform diameter. The experimental apparatus constructed in this study allows the measurement of tensile strain distribution of the fibers orientated at any angle with respect to the draw direction to be determined accurately. For a thin layer coating of the fiber, it was found that the tensile strain distribution along the fiber was unaffected, and so by extension neither would the modulus of a composite in fiber axial direction be affected. This observation indicates that for most composite systems perfect bonding is easily formed at the fiber/matrix interface as far as tensile stress transfer is concerned. (Abstract shortened with permission of author.) |
