Thermomechanical Design Criteria for Ceramic-Coated Surfaces

Some early history of ceramic applications is presented. Finite element modeling of components to determine service and fabrication loads found inelastic behavior and residual stresses to be significant to component life. Inelastic behavior mitigates peak strains but enhances residual strains. Results of furnace, Mach 0.3 burner, and engine tests are discussed and categorized into design criteria (loading, geometry, fabrication, materials, analysis, and testing). These design rules and finite element analyses are brought to bear on two test cases: turboshaft engine seals, and rocket thrust chambers

Constraints on Inflation in Einstein-Brans-Dicke Frame

The density perturbation during inflation seeds the large scale structure. We consider both new inflation-type and chaotic inflation-type potentials in the framework of Einstein-Brans-Dicke gravity. The density perturbation gives strong constraints on the parameters in these potentials. For both potentials, the constraints are not much different from those obtained in the original inflationary models by using of Einstein gravity.Comment: 6 pages, Revtex file, typos adde

Plastic Flow in Plasma Sprayed Ceramics

Ceramics plasma sprayed onto metal substrates have a considerable potential application in gas turbine engines and other high temperature devices as thermal/mechanical insulation since plasma spraying is convenient and widely available. However, there is disturbing evidence of expulsive shedding of the ceramic after cyclic heating to approximately 1000° C. Analyses were made and experiments were designed to measure the effect of tensile and compressive strain in the ceramic when at temperature in order to determine the cause of failure. Plastic flow was predicted and inelastic behavior measured for plasma sprayed binary oxide ceramics both on metal substrates and also when stripped from the substrate before exposure to temperature. Differential expansion between the metal substrate and plasma sprayed materials ZrO2-Y2O3, ZrO2-CaO or Al2O3-TiO2results in irreversible flow. Loading of the stripped binary oxide ceramic sheet materials at temperatures up to 1200° C also produced plastic flow, but annealing before loading eliminated the inelastic behavior. The conclusion is that plasma spraying of binary oxide ceramics results in a metastable state which is inelastic at temperature but can also be stabilized or devitrified through heat treating, so as to decrease plastic properties. Mechanical properties of the as-plasma sprayed and devitrified binary oxide ceramic sheet materials have been measured. Stresses associated with sheet formation and component applications have been calculated using the finite element codes MARC and ADINA/ ADINAT. These studies point to significant inelastic behavior at elevated temperatures

Thermomechanical Loading of Multilayered Cylindrical Geometries in Thermal Cycling from 300 to 1300 K

The principal of multiple material layering is well known as an effective method of reducing heat transfer; however, thermal gradients can impose significant loads and lead to delamination and subsequent component failure. An analysis is developed and experimental data are discussed for the thermomechanical effects of multilayered materials on a heat sink substrate of cylindrical geometry subject to thermal cycling. The geometry is heated in cross-flow by a high-velocity flame and cooled in crossflow by ambient-temperature air from a critical flow orifice. Each layer of material possesses a threshold beyond which small changes in temperature or mechanical loading greatly influence the life in thermal cycling of the layered materials. Comparisons are made between the thermomechanical loads predicted by various numerical codes for the linear case and by a simplified analytic model

Study of Graphite Targets Interacting with the GEV Proton Beam of the BNL Muon Target Experiment

A tightly focused beam on target is required in the muon collider/neutrino factory study. Specifically, up to 16 TP (1 TP = 10{sup 12} protons) per pulse of a 24 GeV proton beam are to be delivered on target, with a pulse length of a few microseconds and a beam spot of 1.5 mm rms sigma. Experiment E951 at BNL was set up to explore the potential of various target materials. Target integrity issues leads one to consider low-Z materials as potential targets. Thus, in the first phase of the E951 experiment, graphite and carbon-carbon composite targets were exposed to the AGS beam and their response to the induced thermal shock was studied. This paper presents theoretical prediction results as well as experimental results and makes an assessment of the abilities of prediction models to capture the dynamic response of the solid target