High-performance carbon fibers, especially polyacrylonitrile (PAN) carbon fibers are widely used as reinforcements in aircraft, automobiles, boats, high-grade sporting goods, wind turbine blades and others due to their unique properties of high specific strength and stiffness. Considerable efforts have been made to understand the microstructure of carbon fibers and to find ways of improving their mechanical properties [1-4]. Understanding the tensile deformation mechanism at nano-scale is important for the microstructure design. Direct observation of deformation process of a carbon fiber by in-situ tensile test in a transmission electron microscope (TEM) may shed some light on solving this problem. However, this research has never been carried out yet. It is probably due to the difficulties in sample preparation of in-situ TEM tensile test and in-situ experiment setup. Here we report the result of in-situ TEM tensile tests on a high strength T1000 carbon fiber sample fabricated by focused ion beam with thickness in the range of 50-100nm. A deformation mechanism was proposed based upon the experimental observations.
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