Shear band formation and cracking of a metallic glass irradiated with high energy laser pulses

A concentric deformation pattern, shear bands and cracks are produced in Fe₈₀B_14.8Si_3.5C₂ glass, irradiated with 12 msec duration ruby laser pulses, ranging in power densities between 10⁵ and 10⁷ W cm^–2. This deformation front propagates through a steep temperature gradient and a partially crystallized heat-affected zone, giving rise to variations of the macroscopic deformation mode as a function of radial distance from the centre of the laser spot. For the first time, a direct experimental mapping of crack tip plasticity, in the form of an elliptical shear band zone, has been recorded. A theoretical model, which predicts such a shear band zone at the crack tip, is used to discuss the elastic-plastic response of the metallic glass.     

Digital measurements of the efficiency of inverter-inductionmachines

The authors describe a digital technique and the required instrumentation to measure the electric power output into inverter-induction machine drives, where the voltage and current signals are nonsinusoidal. The voltage and current signals representing the electrical power input into the motor are stored in a suitable storage oscilloscope with built-in computing capability. The power input is calculated by multiplying the appropriate voltage and current signals and integrating over one cycle. The mechanical power output is obtained from a standard strain-gage-type torque meter. The ratio of the output-to-input power yields the efficiency. The accuracy level attained is within ±1.0% and was verified by comparison with standard instruments using sinusoidal power and by checking the power flow into a resistive load for nonsinusoidal waveform. In both cases, the digital instrumentation gave results that were within ±0.5% of the standard instrumentation. Results of digital measurements obtained on a set of drives in the range of 2-50 hp that were operated over a speed range of 10-100% of rated speed and at rated load torque are presented     

Achieving product variety through optimal choice of module variations

The trade-off in designing products typically involves consideration of manufacturing and development costs, and the potential market share. Modular design of products has been identified as one way of providing firms with a competitive advantage. In the context of modular product design, some of the pertinent questions are: (i) how many product varieties in a product group should be introduced in the market; and (ii) what is the minimum number of module-options required to support this variety? In this paper we study the optimality of such decisions related to modularization in two separate scenarios: (i) the module supplier is an independent operator whose decisions are not coordinated with that of the firm; and (ii) the module supplier is a wholly owned subsidiary of the firm. For these scenarios, we show how the choice of module-options affects product variety, total sales, product development cost, and hence, the firm's profit. We establish that the module-options can be rank ordered, based on profit margin and customer rating, and that the optimal set of module-options to be acquired or developed would include only the top ranked options. We also show how to determine the number and type of module-options a firm should acquire to maximize its profit. Finally, we discuss how our algorithm can be extended to the case of firms that deal with products having multiple module-types.     

Validating for Liveness in Hidden Adversary Systems

Multi-stream interactive systems can be seen as “hidden adversary” systems (HAS), where the observable behaviour on any interaction channel is affected by interactions happening on other channels. One way of modelling HAS is in the form of a multi-process I/O automata, where each interacting process appears as a token in a shared state space. Constraints in the state space specify how the dynamics of one process affects other processes. We define the “liveness criterion” of each process as the end objective to be achieved by the process. The problem now for each process is to achieve this objective in the face of unforeseen interferences from other processes. In an earlier paper, it was proposed that this uncertainty can be mitigated by collaboration among the disparate processes. Two types of collaboration philosophies were also suggested: altruistic collaboration and pragmatic collaboration. This paper addresses the HAS validation problem where processes collaborate altruistically.     

General-Purpose Situational Simulation Environment for Construction Education

The traditional construction education model based on precise well-defined problems and formal definitions is not satisfactorily fulfilling its mission of educating the decision makers of tomorrow. This realization has moved several researchers to explore alternatives where problem solving is carried out in conjunction with the environment, and concepts are embedded in the context promoting learning within the nexus of the activity. Several efforts have been undertaken to develop these environments resulting in a variety of special-purpose situational simulations. However, special-purpose situational simulations exhibit inherent limitations related to their application breadth, flexibility, and promotion of collaborations. These limitations cannot be resolved within the framework of special-purpose learning environments. A general-purpose environment is required to overcome these shortcomings and take full advantage of the situational learning paradigm. This paper describes the conceptual framework and pilot implementation of such an environment called the Virtual Coach.     

Energy use efficiency in the Indian manufacturing sector: An interstate analysis

This paper approaches the measurement of energy efficiency from a production theoretic framework and uses Data Envelopment Analysis to measure energy efficiency in the Indian manufacturing sector. Using data from the Annual Survey of Industries for the years 1998–99 through 2003–04, the study compares the energy efficiency in manufacturing across states, based on several models. The results show considerable variation in energy efficiency across states. Comparing the results across our models, we find that the relative pricing of energy does not provide the appropriate incentives for energy conservation. A second-stage regression analysis reveals that states with a larger share of manufacturing output in energy-intensive industries have lower energy efficiency. Also, higher quality labor force associates with higher energy efficiency. Finally, the power sector reforms have not yet had any significant impact on achieving energy efficiency.     

BEM and FEM analysis of planar moving cracks in creeping solids

Applications of the boundary element method (BEM) and the finite element method (FEM), to the analysis of two-dimensional problems of moving cracks in creeping bodies, is the subject of this paper. In the absence of an acceptable crack growth law valid under small scale transient as well as extended steady state creep conditions, the computer simulations are carried out here for crack extension at prescribed constant speeds. It is shown here that the BEM is most effective for the analysis of transient crack growth under small scale creep conditions while the FEM appears to be best suited for the study of crack growth under conditions of extensive creep throughout most of the structure. These two methods, therefore, tend to complement each other for this class of problems. It is felt that the numerical methods presented here can, in conjunction with experiments, be very useful for the evaluation of existing crack growth laws as well as for the development of new ones.

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Résumé Le sujet du mémoire est l'application de la méthode par valeurs aux limites (BEM) et de la méthode par éléments finis (FEM) à l'analyse de problèmes bidimensionnels de fissures en extension dans des composants soumis à fluage.En l'absence d'une loi d'extension de fissure qui soit applicable tant sous des conditions de fluage transitoire à petite échelle que de fluage stable généralisé, on procède aux simulations per calcul on considérant le développement d'une fissure à des vitesses constantes fixées.On montre que la méthode BEM est plus efficace pour analyser la croissance d'une fissure de fluage en régime transitoire à une petite échelle, tandis que la méthode FEM convient le mieux pour étudier la croissance d'une fissure dans des conditions de fluage s'étendant à l'ensemble du composant.Dès lors, les deux méthodes tendent à se compléter pour cette classe de problèmes. On estime que les méthodes numériques qui sont présentées ici, peuvent être très utiles, en association avec des essais, pour évaluer les lois existantes en matière de propagation de fissures, ainsi que pour en développer de nouvelles.