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133. The relationship between preferred orientation and elasticity of carbon fibers
ABSTRACTS
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are considerably under-estimated. This difficulty must be understood before defect structure calculations can be carried out adequately for graphite. The Morse potential yields a much larger anharmonic coefficient than is deduced from thermal expansion measurements. 129. The effect of thermal oxidation by water vapour on the mechanical strength of nuclear graphites W. Karcher, R. Krefeld and P. Claude (Joint Nuclear Research Centre, European AEC, Petten Establishment, Netherlands). The influence of thermal oxidation by 1000 vpm Hz0 vapour at 1ooo”C on mechanical strength of two nuclear graphite grades has been investigated, by determining tensile strength and Young’s modulus as a function of thermal burn-off. It was found that a low burn-off grades which are of most interest for reaction conditions the decrease of strength follows quite distinct patterns which are explained on the base of a different macropore size distribution. 130. Tensile creep rate studies on pyrolytic carbon D. B. Fischbach (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, Calzfornia). In a continuation of work on the stress-dependence of the a-direction tensile creep of as-deposited pyrolytic carbon presented at the 8th Carbon Conference, some previously unreported features of the deformation behavior have been observed. After l-2 per cent elongation an increase in creep rate and a decrease in stress exponent (from 4 to 1.5) indicate a change in deformation mechanism. During the initial 8 per cent elongation, graphitization (with accompanying dens&cation) and a large preferred orientation increase occur, but AH _ 250 2 40 kcal/mole out to at least 30 per cent elongation. Initial breakdown of the as-deposited structure involving dislocation climb apparently gives way to a near-viscous mechanism such as lattice self-diffusion creep. 131. Creep behavior of hot isostatically pressed graphite E. G. Zukas and W. V. Green (Los Alamos ScientiJicLaboratory, University of California, Los Alamos, New Mexico). ZTA and ATJ graphites were not isostatically pressed by BMI to about 95 per cent theoretical density. High temperature creep properties, including overall strength level, the stress and temperature dependences of the creep rate, creep curve shape, recovery behavior, and microstructural changes were compared with those from identical samples which had not been hot pressed. 132. Microstructural changes produced in graphite by high temperature creep W. V. Green and E. G. Zukas (Los Alumos Scientific Laboratory, University of Calzfornia, Los Alamos, New Mexico). Identical areas of creep specimens were examined before and after creep strain with the optical and scanning electron microscopes using techniques previously described. We identify the deformation made in compression, the deformation features in pressure annealed pyrolytic graphite deformed in bending, and additional features in deformed ‘manufactured graphites’. 133. The relationship between preferred orientation and elasticity of carbon fibers W. Ruland (Union Carbide European Research Associates, S.A., 95, rue Gatti & Gamond, Brussels 18, Belgium). For carbon fibers of cellulosic origin a unique relationship exists between Young’s modulus (corrected for porosity) and preferred orientation over a wide range of HTT and stretching. This relationship can be given in a relatively simple form if one assumes that the elasticity is mainly due to a reversible ‘unwrinkling’ of the microstructure. It is shown that the unique relationship is not followed when partial graphitization occurs. 134. Characterization of high modulus and high strength graphite fiber M. Yamamoto and S. Yamada (Tokai Electrode Manufacturing Company, Ltd., 466 Nagoya, Tokyo, Japan). As a result of a systematic research on the carbonization and graphitization of polyacrylonitrile fiber, the maximum Young’s modulus, 110 X lo6 psi and tensile strength, 340 X lo3 psi were obtained as the average of 12 after graphitization. Relevant data and discussion will be presented. 135. Properties of CVD infiltrated composites W. V. Kotlensky and J. Pappis (Raytheon Company, Research Division, Waltham, Massachusetts). The mechanical properties measured for three different classes (cloth lay-up, felts, 3-D weave) of CVD infiltrated carbon-carbon composites will be discussed. Tensile and flexural strengths of approximately 20,000 psi were measured for CVD infiltrated 3-D weave composite; strength values for the multiple
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are considerably under-estimated. This difficulty must be understood before defect structure calculations can be carried out adequately for graphite. The Morse potential yields a much larger anharmonic coefficient than is deduced from thermal expansion measurements. 129. The effect of thermal oxidation by water vapour on the mechanical strength of nuclear graphites W. Karcher, R. Krefeld and P. Claude (Joint Nuclear Research Centre, European AEC, Petten Establishment, Netherlands). The influence of thermal oxidation by 1000 vpm Hz0 vapour at 1ooo”C on mechanical strength of two nuclear graphite grades has been investigated, by determining tensile strength and Young’s modulus as a function of thermal burn-off. It was found that a low burn-off grades which are of most interest for reaction conditions the decrease of strength follows quite distinct patterns which are explained on the base of a different macropore size distribution. 130. Tensile creep rate studies on pyrolytic carbon D. B. Fischbach (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, Calzfornia). In a continuation of work on the stress-dependence of the a-direction tensile creep of as-deposited pyrolytic carbon presented at the 8th Carbon Conference, some previously unreported features of the deformation behavior have been observed. After l-2 per cent elongation an increase in creep rate and a decrease in stress exponent (from 4 to 1.5) indicate a change in deformation mechanism. During the initial 8 per cent elongation, graphitization (with accompanying dens&cation) and a large preferred orientation increase occur, but AH _ 250 2 40 kcal/mole out to at least 30 per cent elongation. Initial breakdown of the as-deposited structure involving dislocation climb apparently gives way to a near-viscous mechanism such as lattice self-diffusion creep. 131. Creep behavior of hot isostatically pressed graphite E. G. Zukas and W. V. Green (Los Alamos ScientiJicLaboratory, University of California, Los Alamos, New Mexico). ZTA and ATJ graphites were not isostatically pressed by BMI to about 95 per cent theoretical density. High temperature creep properties, including overall strength level, the stress and temperature dependences of the creep rate, creep curve shape, recovery behavior, and microstructural changes were compared with those from identical samples which had not been hot pressed. 132. Microstructural changes produced in graphite by high temperature creep W. V. Green and E. G. Zukas (Los Alumos Scientific Laboratory, University of Calzfornia, Los Alamos, New Mexico). Identical areas of creep specimens were examined before and after creep strain with the optical and scanning electron microscopes using techniques previously described. We identify the deformation made in compression, the deformation features in pressure annealed pyrolytic graphite deformed in bending, and additional features in deformed ‘manufactured graphites’. 133. The relationship between preferred orientation and elasticity of carbon fibers W. Ruland (Union Carbide European Research Associates, S.A., 95, rue Gatti & Gamond, Brussels 18, Belgium). For carbon fibers of cellulosic origin a unique relationship exists between Young’s modulus (corrected for porosity) and preferred orientation over a wide range of HTT and stretching. This relationship can be given in a relatively simple form if one assumes that the elasticity is mainly due to a reversible ‘unwrinkling’ of the microstructure. It is shown that the unique relationship is not followed when partial graphitization occurs. 134. Characterization of high modulus and high strength graphite fiber M. Yamamoto and S. Yamada (Tokai Electrode Manufacturing Company, Ltd., 466 Nagoya, Tokyo, Japan). As a result of a systematic research on the carbonization and graphitization of polyacrylonitrile fiber, the maximum Young’s modulus, 110 X lo6 psi and tensile strength, 340 X lo3 psi were obtained as the average of 12 after graphitization. Relevant data and discussion will be presented. 135. Properties of CVD infiltrated composites W. V. Kotlensky and J. Pappis (Raytheon Company, Research Division, Waltham, Massachusetts). The mechanical properties measured for three different classes (cloth lay-up, felts, 3-D weave) of CVD infiltrated carbon-carbon composites will be discussed. Tensile and flexural strengths of approximately 20,000 psi were measured for CVD infiltrated 3-D weave composite; strength values for the multiple