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154. Fluage thermique et comportement non elastique du graphite artificiel
370
CARBON
elastic modulus. This general validity for polymers is put to the test for carbon mixes. Parallel plate apparatus designed in this laboratory is used for determining the viscoelastic properties of the carbon mixes with core mixture used in projector carbons as filler and pitch tar as binder. The initial block has to be standardized for getting reliable and repeatable results. A load of 2000 pounds kept for one minute before release results in a cylinder of 3 in. dia. and the same height and apparent density. The rubberlike modulus and the viscosity are calculated from the plot of generalized strain versus time for constant load assuming a rheological model consisting of three elements, a spring and a dashpot forming a parallel network added to another dashpot. The viscosity of the mixes generally shows a yield stress, then exhibits almost newtonean behaviour for a narrow range of stresses, and then goes through a highly nonnewtonean range. However after a temperature of 125”C, the behaviour of the mix tends to be nonnewtonean from the beginning. The rubberlike modulus is constant independent of stress during the newtonean range of viscosities but decreases with temperature. This rubberlike elastic modulus agrees in order of magnitude with the critical stress in actual extrusion of this core mix, thus confirming the behaviour in polymers. The dependence of viscoelastic properties on the nature and particle size of the filler as well as the nature of binder is reported. 153. The rheological properties of a carbon mix using a capillary rheometer R. L. Finicle (Union Carbide Corporation, Carbon Products Division, Fostoria, Ohio). The Westover High Pressure Capillary Rheometer was used to measure the rheological properties of a simple carbon mix consisting of a fine coke flour, coal tar pitch and an extrusion oil. This rheometer adapts very well to the carbon mix system and allows the separation and study of die entrance effects as well as viscous flow properties. Data are presented showing the effects of several important raw materials and mixing parameters on the die entrance losses and rheological properties of the resultant mixes. The study was conducted over a wide range of temperatures and shear rates. The data show an apparent shift in the levels of importance for some of the original parameters with temperature and shear rate indicating a complex flow mechanism. 154. Fluage thermique et comportement non elastique du graphite artikiel J. Rappeneau, G. Jouquet et M. Guimard (Commissariat h 1’Energie Atomique, Centre d’Ett&es Nuclkaires de Saclay, France). L’etude des proprietes mecaniques du graphite artificiel necessite au moms la connaissance de ses modules d’elasticite, de son comportement sous charge a la temperature ambiante et en fonction de la temperature. Les modules Clastiques du graphite nucleaire francais ant ete determines en pratiquant des essais dynamiques et statiques; un accord satisfaisant entre Ies difierentes methodes de mesure a CtC obtenu. L’analyse des courbes effort-deformation, en compression simple, a la temperature ambiante, a permis de verifier la validite des equations proposees par G. M. Jenkins. Un effet probable de la vitesse de charge sur la grandeur de la deformation a CtC observe. Des experiences de fluage thermique, en compression simple, dans l’air a des temperatures inferieures g 350°C et pendant des temps de l’ordre de 200 heures ont permis d’etablir l’equation empirique suivante, reliant la deformation de fluage sc au temps t: EF=Y log t-t-$ t 2’3. Cette relation est analogue a celle trouvee par d’autres auteurs mais pour des temperatures plus ClevCes et des temps plus courts. Le coefficient y diminue lorsque la densid apparente du graphite croit; il augmente avec la charge et la temperature. Le coefficient p du fluage secondaire semble &tre une fonction croissante de ces trois variables.
155. The variations in elastic modulus of carbons and graphites over the temperature range -196°C to 1000°C I. B. Mason and R. H. Knibbs (Atomic Energy Research Establishment, Harwell, England). Measurements of Young’s modulus have been made on a range of different carbon and graphite artefacts, using a flexural vibration technique. These results have been discussed in terms of a model, according to
CARBON
elastic modulus. This general validity for polymers is put to the test for carbon mixes. Parallel plate apparatus designed in this laboratory is used for determining the viscoelastic properties of the carbon mixes with core mixture used in projector carbons as filler and pitch tar as binder. The initial block has to be standardized for getting reliable and repeatable results. A load of 2000 pounds kept for one minute before release results in a cylinder of 3 in. dia. and the same height and apparent density. The rubberlike modulus and the viscosity are calculated from the plot of generalized strain versus time for constant load assuming a rheological model consisting of three elements, a spring and a dashpot forming a parallel network added to another dashpot. The viscosity of the mixes generally shows a yield stress, then exhibits almost newtonean behaviour for a narrow range of stresses, and then goes through a highly nonnewtonean range. However after a temperature of 125”C, the behaviour of the mix tends to be nonnewtonean from the beginning. The rubberlike modulus is constant independent of stress during the newtonean range of viscosities but decreases with temperature. This rubberlike elastic modulus agrees in order of magnitude with the critical stress in actual extrusion of this core mix, thus confirming the behaviour in polymers. The dependence of viscoelastic properties on the nature and particle size of the filler as well as the nature of binder is reported. 153. The rheological properties of a carbon mix using a capillary rheometer R. L. Finicle (Union Carbide Corporation, Carbon Products Division, Fostoria, Ohio). The Westover High Pressure Capillary Rheometer was used to measure the rheological properties of a simple carbon mix consisting of a fine coke flour, coal tar pitch and an extrusion oil. This rheometer adapts very well to the carbon mix system and allows the separation and study of die entrance effects as well as viscous flow properties. Data are presented showing the effects of several important raw materials and mixing parameters on the die entrance losses and rheological properties of the resultant mixes. The study was conducted over a wide range of temperatures and shear rates. The data show an apparent shift in the levels of importance for some of the original parameters with temperature and shear rate indicating a complex flow mechanism. 154. Fluage thermique et comportement non elastique du graphite artikiel J. Rappeneau, G. Jouquet et M. Guimard (Commissariat h 1’Energie Atomique, Centre d’Ett&es Nuclkaires de Saclay, France). L’etude des proprietes mecaniques du graphite artificiel necessite au moms la connaissance de ses modules d’elasticite, de son comportement sous charge a la temperature ambiante et en fonction de la temperature. Les modules Clastiques du graphite nucleaire francais ant ete determines en pratiquant des essais dynamiques et statiques; un accord satisfaisant entre Ies difierentes methodes de mesure a CtC obtenu. L’analyse des courbes effort-deformation, en compression simple, a la temperature ambiante, a permis de verifier la validite des equations proposees par G. M. Jenkins. Un effet probable de la vitesse de charge sur la grandeur de la deformation a CtC observe. Des experiences de fluage thermique, en compression simple, dans l’air a des temperatures inferieures g 350°C et pendant des temps de l’ordre de 200 heures ont permis d’etablir l’equation empirique suivante, reliant la deformation de fluage sc au temps t: EF=Y log t-t-$ t 2’3. Cette relation est analogue a celle trouvee par d’autres auteurs mais pour des temperatures plus ClevCes et des temps plus courts. Le coefficient y diminue lorsque la densid apparente du graphite croit; il augmente avec la charge et la temperature. Le coefficient p du fluage secondaire semble &tre une fonction croissante de ces trois variables.
155. The variations in elastic modulus of carbons and graphites over the temperature range -196°C to 1000°C I. B. Mason and R. H. Knibbs (Atomic Energy Research Establishment, Harwell, England). Measurements of Young’s modulus have been made on a range of different carbon and graphite artefacts, using a flexural vibration technique. These results have been discussed in terms of a model, according to