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THE EFFECT OF STRESS STATE ON HIGH-TEMPERATURE LOW-CYCLE FATIGUE

Description: A study of the behavior of Inconel at 1500 deg F under realistic dynamic stress states was performed to critically evaluate present criteria used to solve low-cycle fatigue problems and to demonstrate their applicability for the more complex situations. The relative agreement between the static complex stress- creep-rupture results and the low-cycle fatigue data is demonstrated. From the relationships developed for static complex stress-creep-rupture data, it is demonstrated that the magnitudes of the effects of stress state and frequency on low-cycle fatigue can be determined. (auth)
Date: March 21, 1963
Creator: Kennedy, C.R.
Partner: UNT Libraries Government Documents Department

TSX graphite for extended use in the N-Reactor

Description: This report reviews the limited amount of irradiation data available for grade TSX graphite with the purpose of obtaining reasonable estimates of material behavior. The results are enhanced by obtaining generalized behavior characteristics demonstrated by similar grades of graphite, such as CSF, AGOT, and PGA. Intent of this work is to furnish the necessary coefficients to describe the material behavior for inclusion in the constitutive equations for the anisotropic graphite grade TSX. Estimates of the free-dimensional changes of TSX graphite as a function of temperature and fluence have been made and shown to be in good agreement with the data. The effects of irradiation on other physical properties, such as elastic moduli, conductivity, and coefficient of thermal expansion, are also described. The irradiation creep characteristics of TSX graphite are also estimated on the basis of data for similar grades of graphite in the US and Europe. Crude approximations of stresses generated in the keyed structure were made to demonstrate the magnitude of the problem. The results clearly predict that the filler-block keys will fail and the tube-block keys will not. It is also indicated that the overall stack height growth will be increased by 25 to 38 mm (1 to 1.5 in.) because of creep.
Date: August 1, 1985
Creator: Kennedy, C.R.
Partner: UNT Libraries Government Documents Department

Evaluation of fracture strength by sonic testing

Description: The Griffith-Irwin equation is used to describe the fracture characteristics of graphite. The material constants, Young's modulus and mean flaw size, are measured sonically from velocity and attenuation measurements. The effects of steam oxidation and neutron irradiation on fracture strength are shown to be predictable assuming a constant strain-energy release rate.
Date: January 1, 1981
Creator: Kennedy, C.R.
Partner: UNT Libraries Government Documents Department

(Irradiation creep of graphite)

Description: The traveler attended the Conference, International Symposium on Carbon, to present an invited paper, Irradiation Creep of Graphite,'' and chair one of the technical sessions. There were many papers of particular interest to ORNL and HTGR technology presented by the Japanese since they do not have a particular technology embargo and are quite open in describing their work and results. In particular, a paper describing the failure of Minor's law to predict the fatigue life of graphite was presented. Although the conference had an international flavor, it was dominated by the Japanese. This was primarily a result of geography; however, the work presented by the Japanese illustrated an internal program that is very comprehensive. This conference, a result of this program, was better than all other carbon conferences attended by the traveler. This conference emphasizes the need for US participation in international conferences in order to stay abreast of the rapidly expanding HTGR and graphite technology throughout the world. The United States is no longer a leader in some emerging technologies. The traveler was surprised by the Japanese position in their HTGR development. Their reactor is licensed and the major problem in their graphite program is how to eliminate it with the least perturbation now that most of the work has been done.
Date: December 21, 1990
Creator: Kennedy, C.R.
Partner: UNT Libraries Government Documents Department

Irradiation creep of graphite

Description: Displacement damage of graphite by neutron irradiation causes graphite to change dimensions. This dimensional instability requires careful attention when graphite is used as as moderator and reflector material in nuclear devices. Natural gradients in flux and temperature result in time-varying differential growth generating stresses similar to thermal stresses with an ever increasing temperature gradient. Graphite, however, does have the ability to creep under irradiation, allowing the stress intensity to relax below the fracture strength of the material. Creep strain also serves to average the radiation-induced strains, thus contributing to the stability of the core. As the dimensional instability is a function of temperature, so are the creep characteristics of graphite, and it is of interest to generalize the available data for extension to more extreme conditions of fluence and temperature. Irradiation creep of graphite is characterized by two stages of creep; a primary stage that saturates with time and a secondary stage that is generally assumed to be linear and constant with time. Virtually all past studies have not considered primary creep in detail primarily because there is limited available data at the very low fluences required to saturate primary creep. It is the purpose of this study to carefully examine primary creep in detail over the irradiation temperature range of 150 to 1000{degree}C. These studies also include the combined effects of creep, differential growth, and structural changes in graphite by irradiation. 3 refs., 5 figs.
Date: January 1, 1990
Creator: Kennedy, C.R.
Partner: UNT Libraries Government Documents Department

Progress to Develop an Advanced Solar-Selective Coating

Description: The progress to develop a durable advanced solar-selective coating will be described. Experimental work has focused on modeling high-temperature, solar-selective coatings; depositing the individual layers and modeled coatings; measuring the optical, thermal, morphology, and compositional properties and using the data to validate the modeled and deposited properties; re-optimizing the coating; and testing the coating performance and durability.
Date: March 1, 2008
Creator: Kennedy, C. E.
Partner: UNT Libraries Government Documents Department

COLLAPSE OF TUBES BY EXTERNAL PRESSURE

Description: The problem of tube collapse by external pressure has been investigated experimentally. A graphical solution developed to simplify inelastic collapse design problems was shown to agree with the test results. The von Karman reduced modulus was used in the graphical solution to correct for the stress redistribution caused by yielding. The effects of the geometric imperfections of ovality and wall thickness variations on collapse pressure were shown to be related to the stress-strain behavior of the material. The concept of a critical time'' was discussed in regard to creep-buckling phenomenon. (auth)
Date: April 17, 1962
Creator: Kennedy, C.R. & Venard, J.T.
Partner: UNT Libraries Government Documents Department

Fracture toughness of anisotropic graphites

Description: Fracture toughness measurements have been made at 0, 30, 45, 60, and 90/sup 0/ from the extrusion axis on a reasonably anisotropic graphite, grade AGOT. It was found that the fracture toughness did not vary appreciably with orientation. An observed variation in strength was found to be the result of defect orientation.
Date: January 1, 1985
Creator: Kennedy, C.R. & Kehne, M.T.
Partner: UNT Libraries Government Documents Department

Statistical characterization of tensile strengths for a nuclear-type core graphite

Description: A data set of tensile strengths comprising over 1200 experimental points has been analyzed statistically in conformance with the observed phenomenon of background and disparate flaws. The data are consistent with a bimodal normal distribution. If corrections are made for strength dependence on density, the background mode is Weibull. It is proposed the disparate mode can be represented by a combination of binomial and order statistics. The resultant bimodal model would show a strong dependence on stress volume.
Date: September 1, 1986
Creator: Kennedy, C.R. & Eatherly, W.P.
Partner: UNT Libraries Government Documents Department

Dependence of strength on particle size in graphite

Description: The strength to particle size relationship for specially fabricated graphites has been demonstrated and rationalized using fracture mechanics. In the past, similar studies have yielded empirical data using only commercially available material. Thus, experimental verification of these relationships has been difficult. However, the graphites of this study were fabricated by controlling the particle size ranges for a series of isotropic graphites. All graphites that were evaluated had a constant 1.85 g/cm/sup 3/ density. Thus, particle size was the only variable. This study also considered the particle size effect on other physical properties; coefficient of thermal expansion (CTE), electrical resistivity, fracture strain, and Young's modulus.
Date: June 8, 1980
Creator: Kennedy, E.P. & Kennedy, C.R.
Partner: UNT Libraries Government Documents Department

Acoustic emission from thermal-gradient cracks in UO$sub 2$

Description: A feasibility study has been conducted to evaluate the potential use of acoustic emission to monitor thermal-shock damage in direct electrical heating of UO$sub 2$ pellets. In the apparatus used for the present tests, two acoustic- emission sensors were placed on extensions of the upper and lower electrical feedthroughs. Commercially available equipment was used to accumulate acoustic- emission data. The accumulation of events displayed on a cathode-ray-tube screen indicates the total number of acoustic-emission events at a particular location within the pellet stack. These tests have indicated that acoustic emission can be used to monitor thermal-shock damage in UO$sub 2$ pellets subjected to direct- electrical heating. 8 references. (auth)
Date: January 1, 1975
Creator: Kennedy, C.R.; Kupperman, D.S. & Wrona, B.J.
Partner: UNT Libraries Government Documents Department

Progress Toward Developing a Durable High-Temperature Solar Selective Coating (Poster)

Description: Increasing the operating temperature of parabolic trough solar fields from 400 C to >450 C will increase their efficiency and reduce the cost of electricity. Current coatings do not have the stability and performance necessary to move to higher operating temperatures. The objective is to develop new, more efficient selective coatings with both high solar absoprtance ({alpha} > 0.96) and low thermal emittance ({var_epsilon} < 0.07) that are thermally stable above 450 C, ideally in air, with improved durability and manufacturability, and reduced cost.
Date: March 1, 2007
Creator: Kennedy, C. & Price, H. W.
Partner: UNT Libraries Government Documents Department

Comparison of the characteristics of graphites irradiated at 600 and 900/sup 0/C

Description: Graphite for the reflector in the pebble-bed High-Temperature Reactor in the Federal Republic of Germany (FRG) requires exceptional irradiation resistance for economic viability. The candidate graphites are being irradiated in the High Flux Isotope Reactor (HFIR) at Oak Ridge to assess their irradiation life expectancy. This assessment is based upon dimensional stability, elastic constants from sonic testing, electrical resistivity from eddy-current testing, coefficient of thermal expansion, and brittle-ring fracture testing. To date 13 FRG grades have been irradiated and compared with four graphites made in the United States and one from the United Kingdom. The irradiation temperatures were 620, 715, and 900/sup 0/C.
Date: January 1, 1983
Creator: Kennedy, C.R.; Eatherly, W.P. & Minderman, D.
Partner: UNT Libraries Government Documents Department

State-of-the-art low-cost solar reflector materials

Description: Solar thermal technologies generate power by concentrating sunlight with large mirrors. The National Renewable Energy Laboratory (NREL) is working with industrial partners to develop the optical reflector materials needed for the successful deployment of this technology. The reflector materials must be low in cost and maintain high specular reflectance for extended lifetimes in severe outdoor environments. Currently, the best candidate materials for solar mirrors are silver-coated low-iron glass and silvered polymer films. Polymer reflectors are lighter in weight, offer greater flexibility in system design, and have the potential for lower cost than glass mirrors. In parallel with collaborative activities, several innovative candidate reflector-material constructions were investigated at NREL. The low-cost material requirement necessitates manufacturing compatible with mass-production techniques. Future cooperative efforts with the web-coating industry offers the promise of exciting new alternative materials and the potential for dramatic cost savings in developing advanced solar reflector materials.
Date: November 1, 1994
Creator: Kennedy, C & Jorgensen, G
Partner: UNT Libraries Government Documents Department

Development and Testing of Solar Reflectors

Description: To make concentrating solar power technologies more cost competitive, it is necessary to develop advanced reflector materials that are low in cost and maintain high reflectance for extended lifetimes under severe outdoor environments. The Advanced Materials Team performs durability testing of candidate solar reflectors at outdoor test sites and in accelerated weathering chambers. Several materials being developed by industry have been submitted for evaluation. These include silvered glass mirrors, aluminized reflectors, and front-surface mirrors. In addition to industry-supplied materials, NREL is funding the development of new, innovative reflectors, including a new commercial laminate reflector and an advanced solar reflective mirror (ASRM). To help commercialize the ASRM, a cost analysis was performed; it shows the total production cost could meet the goal. The development, performance, and durability of these candidate solar reflectors and cost analysis results will be described.
Date: January 1, 2005
Creator: Kennedy, C.; Terwilliger, K. & Milbourne, M.
Partner: UNT Libraries Government Documents Department

Development and Testing of High-Temperature Solar Selective Coatings

Description: The Solar Energy Technologies Program is working to reduce the cost of parabolic trough solar power technology. System studies show that increasing the operating temperature of the solar field from 390 to >450 C will result in improved performance and cost reductions. This requires the development of new more-efficient selective coatings that have both high solar absorptance (>0.96) and low thermal emittance (<0.07) and are thermally stable above 450 C, ideally in air. Potential selective coatings were modeled, identified for laboratory prototyping, and manufactured at NREL. Optimization of the samples and high-temperature durability testing will be performed. Development of spectrally selective materials depends on reliable characterization of their optical properties. Protocols for testing the thermal/optical properties of selective coatings were developed and a round-robin experiment was conducted to verify and document the reflectance and high-temperature emittance measurements. The development, performance, and durability of these materials and future work will be described.
Date: January 1, 2005
Creator: Kennedy, C. & Price, H.
Partner: UNT Libraries Government Documents Department