Cost-affordable titanium: The component fabrication perspective

Titanium is the material of choice for a wide variety of applications. However, because of its relatively high price—a result of extraction and processing costs—it is used only when it is the only choice. This paper will overview the potential areas that are amenable to cost reduction for titanium products, emphasizing all steps in component fabrication from extraction and processing to the fabrication of final parts.     

Development,theoretical analysis and performance evaluation of shelf type solar driers

A brief summary of solar driers is given. A simple shelf type drier is described and test results are outlined.The mathematical model of the multi-shelf type drier is developed and its solution using a digital computer is compared with test results to verify the mathematical formulation. Theoretical values of temperatures and drying rates are presented. Extension of the analysis for the refinement of the shelf type driers is discussed.     

An electron metallographic study of the commercial zinc-based pressure-die-cast alloy 3

The solidification structure of pressure-die-cast commercial alloy 3 was examined using scanning electron microscopy and thin foil transmission electron microscopy techniques. It was found that the rapidly cooled alloy commenced solidification by the formation of small rounded primary zinc (η) particles followed by pseudo-primary β particles and then a fine eutectic of β + η. The high temperature β phase subsequently decomposed into -aluminum and η, the phases stable at ambient temperature, but an intermediate transitional phase was found in alloys examined shortly after casting. Chemical analysis by energy-dispersive spectroscopy showed that this phase contained zinc with 11.8 wt.% Al, suggesting that it was a transitional phase since none of the stable phases in the Al---Zn system has that composition. This transitional phase had almost entirely disappeared after aging for a period of 5 years.

Precipitates had formed during or immediately after casting within the central regions of the zinc-rich primary dendrites. These were identified as the aluminium-rich solid solution with f.c.c. structure. The orientation relationship between the phases was determined as

[0001][111]

Each grain contained two families of precipitates with a common (0001)_η habit plane, each adopting one of the two non-equivalent variants of the orientation relationship.

Since this work had shown that aluminium precipitation from η was completed rapidly, the long-term dimensional changes found in zinc alloy castings on aging are considered to be due to the gradual replacement of the zinc-rich metastable phase by equilibrium and η.     

Numerical Parametric Study of Piezocone Penetration Test in Clays

This paper presents a numerical model for the simulation of the piezocone penetration test that is used to carry out a parametric study of the piezocone penetration test in cohesive soils. The piezocone penetration is numerically simulated using an axisymmetric elasto-plastic large deformation finite-element analysis code. The numerical simulation is accomplished in two stages. First, the piezocone is expanded radially from an initial small radius (0.1ro) to the piezocone radius, ro, at the specified depth. Second, the continuous penetration of the piezocone is simulated by applying incremental vertical displacements of the nodes representing the piezocone boundary. The constraint approach is used to model the soil-piezocone interface friction. The Mohr-Coulomb frictional criterion is used to define the sliding potential of the nodes. The main objective of this paper is to present the numerical model and to investigate the effect of the lateral and vertical stresses and the overconsolidation ratio on the cone tip resistance and the developed excess pore pressure around the piezocone. The variation of the horizontal and vertical hydraulic conductivity coefficients on the developed spatial excess pore pressure and its dissipation are also investigated. The results of the numerical study are also compared with the miniature piezocone penetration tests in cohesive soil specimens conducted at the Louisiana State University Calibration Chamber. Results of this study are in good agreement with the measured values.     

Abnormal Grain Growth in Alumina: Synergistic Effects of Yttria and Silica

Abnormal grain growth without strong anisotropy or faceting of the grains has been observed in high-purity yttria-doped alumina specimens, often starting at the surface and spreading right through the bulk at higher sintering temperatures. This appears to occur because of an interaction between Si contamination from sintering and the yttria doping; no such effect is seen for undoped samples. Similar microstructures were observed after deliberate Y/Si codoping. Analytical STEM showed that some grain boundaries bordering on large grains contained more Si than Y. HRTEM and diffuse dark-field imaging revealed thin (0.5–0.9 nm) disordered layers at some boundaries bordering large grains. It appears that Si impurities are accumulating at some boundaries and together with the Y inducing a grain boundary structural transformation that accounts for the dramatically increased mobility of these boundaries.     

Effect of elevated temperatures on the residual mechanical properties of high-performance mortar

The effect of high temperature on the mechanical properties of high-strength mortar was investigated. Specimens were heated up to elevated temperatures (300, 600, 900 °C ) without loading. After being exposed to these oven temperatures, the residual modulus of elasticity, flexural strength and compressive strength of the specimens were determined. The effect of the rate of heating, duration of exposure to maximum temperature and the role of graphite powder, which is known as a high-temperature refractory material on the behavior of the mortar specimens, were observed. Temperatures up to 600 °C resulted in considerable losses in mechanical properties, and at 900 °C, specimens lost almost all of their strength. Higher rate of heating and exposure to the maximum temperature for a shorter period of time resulted in higher residual properties. The useful effect of graphite addition on the residual compressive strength and modulus of elasticity of the mortar specimens as percentages of initial values for each of the heating cycles are clearly observed.     

On the existence of common quadratic Lyapunov functions for second‐order linear time‐invariant discrete‐time systems

Necessary and sufficient conditions for the existence of a common quadratic Lyapunov function (CQLF) are given for two second‐order linear time‐invariant discrete‐time systems. These conditions are later extended to an arbitrary number of systems. The conditions are readily verifiable both analytically and graphically. The paper also provides a constructive procedure for computing a CQLF when it exists. Copyright © 2002 John Wiley & Sons, Ltd.     

Comparison of four different mobile devices for measuring heart rate and ECG with respect to aspects of usability and acceptance by older people

In the area of product design and usability, most products are developed for the mass-market by technically oriented designers and developers for use by persons who themselves are also technically adept by today's standards. The demands of older people are commonly not given sufficient consideration within the early developmental process. In the present study, the usability and acceptability of four different devices meant to be worn for the measurement of heart rate or ECG were analyzed on the basis of qualitative subjective user ratings and structured interviews of twelve older participants. The data suggest that there was a relatively high acceptance concerning these belts by older adults but none of the four harnesses was completely usable. Especially problematic to the point of limiting satisfaction among older subjects were problems encountered while adjusting the length of the belt and/or closing the locking mechanism. The two devices intended for dedicated heart rate recording yielded the highest user ratings for design, and were clearly preferred for extended wearing time. Yet for all the devices participants identified several important deficiencies in their design, as well as suggestions for improvement. We conclude that the creation of an acceptable monitoring device for older persons requires designers and developers to consider the special demands and abilities of the target group.