Inspection of compositionally graded mullite coatings using laser based ultrasonics

Functionally graded materials (FGMs) have spatial variations in composition and structure resulting in corresponding changes in material properties. These materials can be developed for applications in which the functional requirements of a component are position dependent. In this paper, we evaluate the feasibility of using a laser based ultrasonic technique to determine the distribution of elastic properties in FGMs. A model for the laser generation of ultrasound in a compositionally graded coating on a semi-infinite substrate is used to explore the relationship between the acoustic wave propagation and depth dependent elastic property profile. Surface acoustic waves (SAW) generated in such a system are dispersive, and the dispersion characteristics are highly dependent on the mechanical property profile. A high-resolution laser ultrasonic system has been developed, and experimental measurements of the mechanical properties of single layer mullite coatings are presented. Using compositionally graded mullite coatings as a model system, numerical results are reported showing the sensitivity of SAW dispersion behavior to various composition profiles.     

A new algorithm for implementation of design functions by availabledevices

In CAD systems, it is often required to implement desired behaviors by some available device. The selection of the device that can implement the behavior, and the required interfacing, is usually done by human experts. The interface consists of transformations that may have to be performed on the inputs and outputs of the device. This paper describes an approach to automatically derive the specifications of the device's interface. For sequential circuits, the behaviors are often represented as FSMs, and hence the task is to determine whether the FSM of the desired function can be contained in the FSM of the device, subject to the transformations of the interface. A related objective, addressed in this paper, is to model the behaviors of complex devices in a way that facilitates the analysis     

Non-destructive characterization of zirconia-toughened alumina ceramics using ultrasonics

Ultrasonics has been used for the characterization of sintered zirconia-toughened alumina (ZTA) ceramics. The variation of ultrasonic velocity with volume fraction of zirconia in an alumina matrix was studied. Variation of ultrasonic velocity with volume fraction of ZrO₂ content was analysed in terms of a second-degree polynomial in the volume fraction of ZrO₂. The elastic moduli and Poisson's ratio evaluated from the longitudinal and shear velocities have also been described in terms of a similar equation. The observed variation in velocity and moduli with porosity has been compared with the predicted values based on elasticity theory.     

Degradation of solar cells made of upgraded metallurgical grade silicon

The aging effect of solar cells made of upgraded metallurgical grade silicon under continued exposure to ultraviolet light has been studied. It has been observed that in 3 years the cell degrades from 6.6% to 4.7% in efficiency mainly because of an increase in reflectivity and a decrease in the shunt resistance. Measurements of diode ideality factors and reverse saturation current densities revealed that the overall junction and the material quality suffered significantly large damages.     

Preparation of silica monolith via sol-gel route

The present investigation deals with the synthesis of monolithic NiCl₂-silica gels obtained by hydrolysis and polycondensation of tetraethoxy silanes. This sol to gel formation can mainly be controlled by adjusting some variables e.g. acid content of the solution, ageing and leaching times. A minimum acid content was found necessary to prepare uncracked gel while ageing and leaching times were found to be not that sensitive for the formation of uncracked gels.     

Studies in Urban Crises: Problems of Response and Prevention

Power, Poverty and Poison: Disaster and Response in an Indian City, James Manor, Sage Publications, New Delhi (1993), 197 pp. Bhopal: Anatomy of a Crisis (second edition), Paul Shrivastava, Paul Chapman, London (1992), 169 pp.     

Finite element discretization of open-type axisymmetric elements

A series of open-type elements which are compatible with axisymmetric thin shell elements have been dervied. These elements allow the effects of intermediate openings and discrete support systems for rotational shells to be realistically modelled in the dynamic regime. Also, consistent load vectors for several common cases are derived. The availablility of these elements in a public domain computer program enhances the possibility for modelling systems which are basically axisymmetric but which include intermediate or end supports using a rotational shell code.