Variations In Material Composition Research Articles

Design of heterogeneous turbine blade

Constantly rising operating pressure and temperature in turbine drivers push the material capabilities of turbine blades to the limit. The recent development of heterogeneous objects by layered manufacturing offers new potentials for the turbine blades. In heterogeneous turbine blades, multiple materials can be synthesized to provide better properties than any single material. A critical task of such synthesis in turbine blade design is an effective design method that allows a designer to design geometry and material composition simultaneously. This paper presents a new approach for turbine blade design, which ties B-spline representation of a turbine blade to a physics (diffusion) process. In this approach, designers can control both geometry and material composition. Meanwhile, material properties are directly conceivable to the designers during the design process. The designer's role is enhanced from merely interpreting the optimization result to explicitly controlling both material composition and geometry according to the acquired experience (material property constraints). The mathematical formulation of the approach includes three steps: using B-spline to represent the turbine blade, using diffusion equation to generate material composition variation, using finite element method to solve the constrained diffusion equation. The implementation and examples are presented to validate the effectiveness of this approach for heterogeneous turbine blade design.

Birefringence in gradient-index rod lenses: a direct measurement method and interferometric polarization effects

Gradient-index (GRIN) media can contain stress birefringence resulting from the variation in material composition. Anisotropy in a GRIN rod lens affects ray propagation and can degrade image quality. A technique, believed to be new, for measuring birefringence in GRIN rod lenses has been developed. The change in optical path difference (OPD) for orthogonal polarizations is measured directly. With this method, effects on OPD from standard imaging aberrations are excluded. Birefringence measurements for various GRIN rod samples are presented. The data are compared with results obtained previously by use of a Twyman-Green measurement method. Also, the polarization effects on tilt fringes observed with the direct measurement method and the Twyman-Green method are presented and modeled theoretically. Tilt fringes for large birefringence test cases are also modeled.

Tensile properties of some zinc-based alloys comprising 27.5% Al: effects of alloy microstructure, composition and test conditions

This paper deals with tensile properties of a few zinc–27.5% Al based alloys under varying material composition (wherein copper has partially been replaced through nickel/silicon/nickel plus silicon) and microstructural features. The effects of: (i) strain rate at room temperature; and (ii) test temperature at a typical strain rate on the tensile (strength and elongation) properties of the alloys have also been studied. Tensile properties improved with strain rate irrespective of the alloy composition/microstructure. On the contrary, the tensile strength deteriorated with temperature while elongation followed a reverse trend. In general, the nickel/silicon-free alloy attained highest strength and elongation under all the test conditions except at the maximum test temperature. This was followed by those of the nickel containing alloy while the presence of silicon/silicon plus nickel also deteriorated the property at lower temperatures. However, alloying with nickel/silicon/nickel plus silicon caused the strength of the alloy system to become less temperature sensitive. The study suggests that it is quite possible to develop a variety of zinc-based alloys with different combinations of mechanical properties through compositional/microstructural modifications. The (partial) replacement of copper through nickel and/or silicon imparts thermal stability to the alloy system. The behaviour of the alloys has been discussed in terms of the specific nature of their constituent phases whose contribution towards governing the overall performance of the alloys greatly depends on the test conditions. The view has also been substantiated through the features of the fractured surfaces and subsurface regions of typical samples.

Plasma treatment of polyolefins: Influence of material composition: 1. Bulk and surface characterization

Injection-moulded plates of ten polypropylene (PP) and thermoplastic polyolefin (TPO) materials with varying material composition (different type of rubber, varying degree of ethylene etc.) were characterized before and after oxygen plasma treatments. Untreated materials were studied by means of differential scanning calorimetry (d.s.c.), size exclusion chromatography (s.e.c.), Fourier-transform infrared spectroscopy (FTi.r.), attenuated total reflectance (ATR) and transmission measurements, and the effect of plasma treatment conditions was followed by X-ray photoelectron spectroscopy (X.p.s.) and contact angle measurements. S.e.c. analysis revealed only minor variations among the materials, while the d.s.c. and FTi.r. experiments confirmed that the differences were to be expected as a result of the variation in material composition. The FTi.r.-ATR results showed that all samples had a gradient in material composition. The materials were generally more rich in PP in the topmost ∼ 200 nm than in the first ∼800 nm, and a lesser extent of ethylene modification and/or rubber was observed in the topmost ∼ 200 nm. It was also shown that the degree of surface crystallinity was normally greater at ∼ 800 nm than at ∼ 200 nm, and that a higher mould temperature led to a higher degree of surface crystallinity. The water contact angles and the atomic composition showed that the materials were more oxidized after plasma treatment at high power-to-gas pressure (P/G) ratios than at low ratios. Moreover, the dependence on material composition was weak for samples that were plasma-treated at low P/G ratios whereas the materials that were least ethylene-modified were less oxidized than the others at high P/G ratios. © 1997 Elsevier Science Ltd.

Design of multilayer polymeric coatings for indentation resistance

Indentation is often a mode of in-service loading for a thin coating deposited on a substrate. Under such a loading, the strong adherence of the coating to the substrate is a basic necessity for successful performance of the coating. In this study, we investigate the indentation behavior of thin single and multilayered polymeric coatings using the finite element method. The deformation patterns and the stress fields that are generated during indentation are obtained by employing constitutive models which accurately represent the elastic-viscoplastic and hyperelastic behavior of the glassy and rubbery states of the polymeric layers under investigation. Three types of loading conditions are considered: indentation to (1) a fixed depth; (2) a fixed work; and (3) a fixed force. For these loading conditions, we then investigate the mechanical performance of various composite coatings subjected to an overall thickness design constraint. The composite structure is altered via variation in individual layer material composition, layer thickness and layer arrangement. It is shown how the placement of different material layers in a multilayer coating can alter the flow pattern and hence the distribution of stress state and resulting failure. It is also shown that a soft rubber elastic layer acts to greatly minimize the interfacial shear stress at the substrate, thereby reducing the risk of delamination of the coating, but the presence of the rubber can also produce detrimental tensile stresses on the surface. We then demonstrate that the tensile stress state can be eliminated through manipulation of the rubber layer thickness, without increasing the interface shear stress. Through these examples, a framework for evaluation and design of multilayer coatings for indentation resistance is provided.

Time-Dependent Conjugate Heat Transfer Characteristics of Self-Sustained Oscillatory Flows in a Grooved Channel

Convective heat transport in a grooved channel is numerically investigated using a time-dependent formulation. Conjugate conduction/convection and uniform heat-flux representations for the solid domain are considered. For the conjugate representation, the solid domain is composed of multiple materials and concentrated heat generation. The associated cooling flows include laminar and transitional regimes. Steady and time-dependent contours of the streamfunction and local skin-friction coefficients are presented. Additionally, local distributions of Nusselt number and surface temperature are displayed for both the conjugate and convection-only representations. These results are contrasted over the range of Reynolds numbers explored to demonstrate the significance of including time-dependency and conjugation in the study of convective heat transport. Such considerations are found to be important in the design and analysis of heat exchanger configurations with spatially varying material composition and concentrated heat generation.

Vision-Based Weld Pool Width Control

Methods for controlling weld penetration for arc welding processes from top-side measurements have long been sought. One indirect variable that has been reported to correlate with penetration is weld pool geometry. A system which uses weld pool geometry sensing for controlling weld penetration is described in this paper. The system uses a miniature camera mounted in a modified coaxial viewing torch to view the weld pool. A robust machine vision algorithm has been developed for this system to measure weld pool width. The algorithm was designed to locate the edges of the weld pool despite the presence of other edges caused by the heat affected zone, scratches, marks, and weld pool impurities. The algorithm uses a matched edge filter and a majority voting scheme to measure the width of the pool. A control system was developed to regulate weld pool width in the presence of disturbances caused by such items as incorrect parameter settings, small variations in material composition, and material thickness changes. Experiments were conducted to test the control system by simulating some of these disturbances. The experiments demonstrated that for certain classes of materials, this technique works quite well. However, for other materials such as stainless steel 304, surface impurities in the weld pool visually obscure the weld pool and its edges to such a degree that the system fails to lock onto the edges of the pool.

The fatigue properties of pressure diecast zinc-aluminum based alloys: Sawalha, K. Diss. Abstr. Int. (Oct. 1992) 53 (4) 281 pp

This paper deals with tensile properties of a few zinc–27.5% Al based alloys under varying material composition (wherein copper has partially been replaced through nickel/silicon/nickel plus silicon) and microstructural features. The effects of: (i) strain rate at room temperature; and (ii) test temperature at a typical strain rate on the tensile (strength and elongation) properties of the alloys have also been studied. Tensile properties improved with strain rate irrespective of the alloy composition/microstructure. On the contrary, the tensile strength deteriorated with temperature while elongation followed a reverse trend. In general, the nickel/silicon-free alloy attained highest strength and elongation under all the test conditions except at the maximum test temperature. This was followed by those of the nickel containing alloy while the presence of silicon/silicon plus nickel also deteriorated the property at lower temperatures. However, alloying with nickel/silicon/nickel plus silicon caused the strength of the alloy system to become less temperature sensitive. The study suggests that it is quite possible to develop a variety of zinc-based alloys with different combinations of mechanical properties through compositional/microstructural modifications. The (partial) replacement of copper through nickel and/or silicon imparts thermal stability to the alloy system. The behaviour of the alloys has been discussed in terms of the specific nature of their constituent phases whose contribution towards governing the overall performance of the alloys greatly depends on the test conditions. The view has also been substantiated through the features of the fractured surfaces and subsurface regions of typical samples.

Materials And Image Formation In X-ray Lithography

AbstractIn proximity X-ray lithography there is no imaging system in the traditional sense of the word. There are no mirrors, lenses or other means of manipulating the radiation to form an image from that of a pattern (mask). Rather, in proximity X-ray lithography, mask and imaging systems are one and the same. The radiation that illuminates the mask carries the pattern information in the region of the wavefronts that have been attenuated. The detector (photoresist) is placed so close to the mask itself that the image is formed in the region where diffraction has not yet been able to deteriorate the pattern itself. The quality of the image formation then is controlled directly by the interaction between the mask and the radiation field. In turn, this means that both the illumination field and the mask are critical. The properties of the materials used in making the mask thus play a central role in determining the quality of the image. For instance, edge roughness and slope can strongly influence the image by providing the equivalent of a blur in the diffraction process. This blur is beneficial in reducing the high frequency components in the aerial image but it needs to be controlled and be repeatable. The plating (or other physical deposition) process may create variation in density (and thickness) in the deposited film, that will show up as linewidth variation in the image because of local changes in the contrast; the same applies to variations in the carrier membrane. In the case of subtractive process, variations in edge profile across the mask must be minimized.The variations in material composition, thickness and density may all affect the finale image quality; in the case of the resist, local variations in acid concentration may have strong effect in linewidth control (this effect is of course common to all lithographies).Another place where materials will affect the final image quality is in the condensing system. Mirrors will exhibit some degree of surface roughness, leading to a scattered radiation away from the central (coherent) beam. For scanning systems, this is not harmful since no power is lost in the scattering process and a blur is actually created that reduces the degree of spatial coherence. Filters may also exhibit the same roughness; typically it will not affect the image formation. The presence of surface (changes of reflectivity) or bulk (impurities) defects may however strongly alter the uniformity of the transmitted beam. This is particularly true of rolled Be filters and windows, which may include contaminants of high-Z materials. Hence, the grain structure of the window plays a very important role in determining image uniformity.Finally, a seemingly minor but important area is that of the gas used in the exposure area, typically helium. The gas fulfills several needs: heat exchange medium, to thermally clamp the mask to the wafer; low-loss X-ray transmission medium; protection from reactive oxygen radicals and ozone formation. Small amounts of impurities (air) may have a very strong effect on the transmission, and non-uniform distributions are particularly deleterious.All these factors need to be controlled so that the final image is within the required tolerances. Unfortunately, some of these are difficult to characterize in the visible (e.g., reflectivity variations) and testing at X-ray wavelengths is necessary. Although these obstacles are by no means unsurmountable, foresight is necessary in order to deliver a functional X-ray lithography process.This work was supported by various agencies, including ARPA/ONR/NRL and the National Science Foundation.

Measurement of elastic resisting forces of intraocular haptic loops of varying geometrical designs and material composition

The relationship between experimentally induced intraocular lens (IOL) haptic deformation and resulting elastic haptic counter-resisting forces measured by electronic dynamometry was examined for 34 different IOL haptics of varying material composition and geometrical designs. Poly(methyl methacrylate) (PMMA) and polypropylene loops of similar geometry did not fundamentally differ from one another, although lenses of differing geometry behaved differently. Unlike PMMA and polypropylene loops, soft haptics of poly-HEMA and silicone rubber demonstrated a larger elastic resistance force to the same degree of deformation. This was based upon design characteristics of the lenses and not upon intrinsic properties of the materials, which would have produced the opposite result. By comparative analysis of these dynamometer measurements and considerations of the lens design and elastic properties (including memory) of the component materials, we can calculate the stresses upon the zonular and capsular bag structures during and after IOL implantation.

Microprobe Analysis of Nanophase Metal-Oxides using Inelastic Light Scattering

ABSTRACTNanophase TiO2 and ZnO were investigated with a Raman microprobe in order to determine the spatial variations in material composition, oxygen stoichiometry, and phase. Calibration of the oxygen stoichiometry of nanophase TiO2 was determined through a combination of Raman scattering and thermogravimetric analysis.

Performance characteristics of electrochemically impregnated nickel oxide electrodes for alkaline batteries

Nickel oxide electrodes are widely used as cathodes in alkaline batteries. The introduction of electroactive material can take place by chemical and electrochemical methods. The effects of various additives to nickel nitrate solutions, used to impregnate sintered nickel electrodes electrochemically, have been studied at different current densities. The variation in active material composition was determined using atomic absorption and infrared spectroscopy. Ideal conditions for the preparation of nickel oxide electrodes have been identified.

Thermoelectric magnetohydrodynamics

Thermoelectric currents in the presence of magnetic fields can cause pumping or stirring of liquid-metal coolants in nuclear reactors or stirring of molten metal in industrial metallurgy. The interaction between the thermal and magnetohydrodynamic fields is a mutual one owing to alterations in the thermal convection and to the Peltier and Thomson effects (although these are usually small). This paper sets up the equations of magnetohydrodynamics and thermal convection when coupled by thermoelectricity and solves some illustrative problems in which the thermal field is known ab initio. Examples where the effects are due to either continuous or discontinuous variation of material composition are included. Practical magnitudes are discussed for the case of a fusion-reactor blanket, where the effects are potentially important owing to the unusual thermoelectric power of lithium.

Welding of Electronic Modules for the Polaris Missile

Some time ago the potential value of welding electronic modules was recognized. An investigation was authorized to locate and solve the problems which would be encountered Jf this technique were to be applied to the electronic modules. This paper summarizes the status of findings to date, the number of problems still under investigation, and other subjects requiring study. Preparations have been made for the first production application of welding electronic modules. A welding specification OS 11889 has been released. This specification states the requirements of suitable welding machines and the criteria for certifying weld schedules and in-process and final inspection. Preliminary weld schedules have been developed which meet the broad requirements of the specification. The thousands of welds made and tested during the development of these schedules have served to field test the requirements and related conditions to current experience in industry. The investigations offer evidence that nickel, Dumet, and Kovar are weldable lead materials to nickel interconnecting media. To meet standards, separate weld schedules are required for each material size; moreover, variations in material composition and temper must be limited. Continuing study of other essential aspects of the problems are being pursued.