Torsional nonlinear elasticity and damping of carbon fibers

Torsional nonlinear elasticity and damping of carbon fibers

Abstracts cance when one realizes that the modulus of elasticity of graphite may be easily determined with Ultrasonic test equipment thus enabling one...

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Abstracts cance when one realizes that the modulus of elasticity of graphite may be easily determined with Ultrasonic test equipment thus enabling one to nondestructively determine the strength of graphite.

70. Influences on the change in the Young’s modulus of graphitic materials for HTR under fast neutron exposure at irradiation temperaturesbetween 400 and 1400°C W. W. Delle, H. A. Schulze and R. E. Schulze (Kemforschungsanlage Julich GmbH, Fed. Rep. Germany). Influence parameters on the irradiation induced change in the Young’s modulus investigated for the graphitic matrix for spherical fuel elements are discussed. The irradiation behaviour is compared with that of gilsocarbon graphite.

71. Mechanistic model of graphite behavior J. D. Buch (Prototype Development Associates, Inc., Santa Ana, CA). A mechanistic and microstructural model of material behavior is presented which will accept a realistic description of material composition and predict response. The ability and associated logic for the model to treat grain and pore size distributions will be emphasized.

75. Subcritical crack propagationin glassy carbon? T. M. Hollenback, W. P. Minnear, R. C. Bradt and P. L. Walker, Jr. (Pennsylvania State University, University Park, PA 16802, U.S.A.). Subcritical crack growth was studied in six glassy carbons in water at room temperature. Stress corrosion is characterized by (K-V) diagrams generated using fracture mechanics techniques. Results follow the equation, V = AKIN, where the stress intensity exponent, N, is related to the elastic modulus of the glassy carbon. tSupportedby Airco Speer Carbon-GraphiteCompanyGrant. 76. Thermal shock and strength degradationof electrode graphitest T. M. Hollenbeck, R. C. Bradt, P. L. Walker, Jr. (Department of Material Sciences, Pennsylvania State University, UniversityPark, PA 14802, U.S.A.) and F. J. Rusinko, Jr. (Airco-Speer Carbon-Graphite, St. Marys, PA 158.57, U.S.A.). Regular and premium steelmelting electrode graphites were thermally shocked by single and multiple quenches from elevated temperatures into liquid nitrogen. Damage was monitored by transverse breaking strength changes. Results indicate that no kinetic crack growth occurs, but rather that strength degradation is the result of oxidation of the graphite. tsupported by Airco SpeerCarbon-GraphiteCompanyGrant.

72. A fracture criterion for anisotropic graphites in polyaxial stress states J. G. Crose, J. D. Buch and E. Y. Robinson (Prototype Development Associates, Inc., Santa Ana, CA). A statistical fracture criterion for graphite is proposed which accounts for arbitrary stress states, anisotropy and volume effects. It is based on rational flaw orientation and strength distributions, has been coded for computer application and via the finite element method of structural analysis can be used to estimate structural reliability.

73. Mechanics of curved strands as related to 3-D carbon-carbon composites J. D. Buch (Prototype Development Associates, Inc., Santa Ana, CA). The mechanics of fracture of curved free strands will be presented. It will be shown that curved filaments in a yarn can contribute to a lower yarn fracture stress than traditional statistical treatments of fiber stress. Relevance to brittle fiber composites will be illustrated.

74. Torsional nonlinear elasticity and damping of carbon fibers R. E. Henrichsen and D. R. Fischbach (University of Washington, Seattle, WA 98195, U.S.A.). For most types of carbon fiber, the material torsional rigidity increases with static tensile stress u and decreases with static torsional strain y. Damping is independent of u but increases with y. These effects are reversible, increase in size with graphitization and are consistent with a fibrillar substructure model.

77. Fatigue behavior of a near-isotropicgraphite R. E. Bullock (General Atomic Company, San Diego, CA 92138, U.S.A.). Near-isotropic H-451 graphite was tested in simple-tension fatigue at room temperature. The endurance limit at 10’ cycles for specimens orientated parallel and perpendicular to the extrusion direction was about 70% of the ultimate tensile strengths in question, where UTS (II)= 1755psi and UTS (1) = 1465psi. Weibull statistical analyses indicate wider variations in fatigue lifetimes for the perpendicular orientation than for the parallel one. 78. High temperature irradiation enhanced creep in graphites for HTR application H. J. Veringa and R. Blackstone (Reactor Centrum Nederland, Petten, The Netherlands). Restrained shrinkage experiments up to 5 x 10”* (DNE) in the range 400-1400°C on various reactor graphites were performed in the High Flux Reactor at Petten, The Netherlands. The data were evaluated to yield the steady state irradiation creep coefficient. It was found that for all the graphites investigated the irradiation creep coefficient is temperature dependent and inversely proportional to both Young’s modulus and neutron flux density. These results are explained in terms of pinning and unpinning of basal plane dislocations. 79. Statistical study of the strength of near-isotropic graphite R. J. Price (General Atomic Company, San Diego, CA, U.S.A.). Groups of tensile samples with three different volumes and 4-point bend samples from a log of H-451