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

Adsorption of monoethanolamine on clean, oxidized and hydroxylated aluminium surfaces: a model for amine-cured epoxy/aluminium interfaces

International audienc

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

Corrosion of Copper and Lead by Formaldehyde, Formic and Acetic Acid Vapours

The formation of corrosion products and the corrosion sensitivity of copper and lead were studied under experimental conditions in which formaldehyde (methanal), formic (methanoic) and acetic (ethanoic) acid concentration, relative humidity (RH) and duration of exposure were varied. Levels of formic acid above 0.4 parts per million based on volume (ppmv) affect the appearance of copper at 75% RH, and at levels above 4 ppmv the copper gains weight at both 54 and 75% RH. The main compound found on copper was cuprite, copper(I) oxide. Lead has a higher sensitivity to formic acid: at levels as low as 0.04 ppmv lead becomes darker, and at above 0.1 ppmv weight gains were measurable at both 54 and 75% RH, In the presence of different levels of mixed carbonyl vapours at 75% RH, copper reacted mainly with formic acid. On the other hand, the reaction of lead was more complex. Acetic acid tends to form a thick white layer (composed mainly of plumbonacrite and possibly lead acetate compounds) on the lead surface, while formic acid tends to form a rather thin and darker layer of lead formate hydroxide. In the presence of formic acid, the action of acetic acid on lead was inhibited. At levels of formaldehyde up to 3 ppmv, no significant contribution of formaldehyde to the corrosion process on lead and copper was observed.Peer Reviewe

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