- Email: [email protected]
148. Dependence of physical properties of graphite specimens on machining
368
CARBON
the graphite single crystal. The compliance constants ~11 and sb4 were determined by resonant bar and compound torsional-oscillator techniques, The stiffness constants cl 1, cia, css, and c44 were determined by an ultrasonic pulse method. All five compliance constants and their associated stressstrain curves have been measured by static tensile, compressive and torsion tests; fracture strength values were also obtained. In addition, a simple shear test gave the shear strength associated with c44 as a function of normal stress. Complications in testing procedures caused by the extreme anisotropy of the material will be discussed. *Supported
in part by the U.S. Atomic Energy Commission.
146. Tensile properties of glassy carbon to 2900’C* W. V. Kotlensky and H. E. Martens (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CuZ+rniu). Tensile properties were measured on two different grades of glassy carbon over the range of room temperature to 2900°C. At room temperature strengths of approximately 6000 psi and elongations of less than 1% were measured for both grades. With an increase in test temperature the strength and elongation increased for both grades. The tensile strength reached a peak of 20,000 to 25,000 psi at 25Oo”C, and then decreased as the test temperature increased. The grade which had been heated to 2000°C during manufacture has a maximum elongation of 33% at 2700°C; the grade which had been heated to 3000°C had a maximum elongation of 5% at the same temperature. Changes in density, unit cell dimensions, hardness, diamagnetic susceptibility and other structural properties were also determined. *This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract NAS7-100, sponsored by the National Aeronautics and Space Administration.
147. The effect of specimen geometry on the tensile strength of graphite J. L. Jackson and M. E. Freed (Pacific Northwest Laboratories, Buttelle Memorial Institute, Richlund, Washington). An investigation of the effect of specimen geometry on the tensile strengths of two nuclear graphites using seven different tensile specimen shapes has been conducted. The design of some samples gave rise to stress concentrations where the fillet met the gage section. Evidence has been obtained that geometry effects can reduce the apparent tensile strength of graphite by as much as 34%. The most satisfactory designs, determined by reference to the strength, were the streamline fillet and the straight, cylindrical sample. A simple method of fastening the straight, cylindrical samples to a steel grip using an epoxy resin has been tested and proven satisfactory. 148. Dependence of physical properties of graphite specimens on machining M. Beutell and 0. Vohler (Siemens-Pluniuwerke AG, Meitingen, Germany). Machining of small graphite specimens, as used for irradiation tests in reactors, causes permanent deformation (strain). It has been proved that the stresses set up thereby can be cured by thermal treatment at high temperatures. The occurring dimensional changes are in the order of 0.1 percent. The extent of the dimensional changes depends on the mode of machining and shape of specimen; the magnitude is the higher the smaller the cross section of the specimen. A well defined dependence on Young’s Modulus could not be found. However, for one type of graphite, or graphites having the same solid component and processed under the same conditions, a relationship exists that the dimensional change is inversely proportional to the Young’s Modulus. These stresses induced by machining can (analogous to thermal curing) be also reduced by neutron irradiation. For irradiation tests it is therefore necessary to subject a finished graphite specimen to thermal curing prior to its use in the reactor. The growth in length of the specimens as obtained by heat treatment is compared to the irradiation induced dimensional change for a neutron dose up to lOi (>O.l meV).
CARBON
the graphite single crystal. The compliance constants ~11 and sb4 were determined by resonant bar and compound torsional-oscillator techniques, The stiffness constants cl 1, cia, css, and c44 were determined by an ultrasonic pulse method. All five compliance constants and their associated stressstrain curves have been measured by static tensile, compressive and torsion tests; fracture strength values were also obtained. In addition, a simple shear test gave the shear strength associated with c44 as a function of normal stress. Complications in testing procedures caused by the extreme anisotropy of the material will be discussed. *Supported
in part by the U.S. Atomic Energy Commission.
146. Tensile properties of glassy carbon to 2900’C* W. V. Kotlensky and H. E. Martens (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CuZ+rniu). Tensile properties were measured on two different grades of glassy carbon over the range of room temperature to 2900°C. At room temperature strengths of approximately 6000 psi and elongations of less than 1% were measured for both grades. With an increase in test temperature the strength and elongation increased for both grades. The tensile strength reached a peak of 20,000 to 25,000 psi at 25Oo”C, and then decreased as the test temperature increased. The grade which had been heated to 2000°C during manufacture has a maximum elongation of 33% at 2700°C; the grade which had been heated to 3000°C had a maximum elongation of 5% at the same temperature. Changes in density, unit cell dimensions, hardness, diamagnetic susceptibility and other structural properties were also determined. *This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract NAS7-100, sponsored by the National Aeronautics and Space Administration.
147. The effect of specimen geometry on the tensile strength of graphite J. L. Jackson and M. E. Freed (Pacific Northwest Laboratories, Buttelle Memorial Institute, Richlund, Washington). An investigation of the effect of specimen geometry on the tensile strengths of two nuclear graphites using seven different tensile specimen shapes has been conducted. The design of some samples gave rise to stress concentrations where the fillet met the gage section. Evidence has been obtained that geometry effects can reduce the apparent tensile strength of graphite by as much as 34%. The most satisfactory designs, determined by reference to the strength, were the streamline fillet and the straight, cylindrical sample. A simple method of fastening the straight, cylindrical samples to a steel grip using an epoxy resin has been tested and proven satisfactory. 148. Dependence of physical properties of graphite specimens on machining M. Beutell and 0. Vohler (Siemens-Pluniuwerke AG, Meitingen, Germany). Machining of small graphite specimens, as used for irradiation tests in reactors, causes permanent deformation (strain). It has been proved that the stresses set up thereby can be cured by thermal treatment at high temperatures. The occurring dimensional changes are in the order of 0.1 percent. The extent of the dimensional changes depends on the mode of machining and shape of specimen; the magnitude is the higher the smaller the cross section of the specimen. A well defined dependence on Young’s Modulus could not be found. However, for one type of graphite, or graphites having the same solid component and processed under the same conditions, a relationship exists that the dimensional change is inversely proportional to the Young’s Modulus. These stresses induced by machining can (analogous to thermal curing) be also reduced by neutron irradiation. For irradiation tests it is therefore necessary to subject a finished graphite specimen to thermal curing prior to its use in the reactor. The growth in length of the specimens as obtained by heat treatment is compared to the irradiation induced dimensional change for a neutron dose up to lOi (>O.l meV).