International Journal of Engineering
Volume:15 Issue: 4, Nov 2002

A framework for development of constitutive models based on semi-micromechanical aspects of plasticity is proposed. The resulting of this model for material employed friction type failure criterion, sub-loading surface, and associated flow rule. This model is capable of predicting effects of the rotation of principal stress/strain axes and consequent plastic flow, induced anisotropy of strength, particularly, in cyclic loading. Also, this model has the potential of predicting the behavior of fully inherent anisotropic material, and strain history distributions at a point up to failure. The predicted model results and their conformity with experimental results of cyclic loading including the pre-failure specifications show the capability of the mode.

One of the approaches used to partition inputs consists in modifying and limiting the input set using an external transcoder. This method is strictly related to output coding. This paper presents an optimal output coding in PAL-based programmable transcoders. The algorithm can be used to implement circuits in PAL-based CPLDs.

In conventional direct torque control (DTC) of induction machines, undesirable flux and torque ripples are produced. These occur since non of the selected inverter''s voltage vectors are able to generate the exact voltage required to produce the desired changes in the electromagnetic torque and stator flux linkage in most of the switching instances. In addition, when direct torque control is implemented in a digital form these ripples will increase due to sampling and computation delays. In this paper, the influences of the amplitudes of flux and torque hysteresis bands and the sampling time of control program on the torque and flux ripples are investigated. A new method is then proposed for the determination and application of optimal hysteresis band amplitudes in DTC to reduce flux and torque ripples, and prevent the inverter switching frequency to exceed a desired limit. Extensive simulation results confirm the superiority of the DTC under the proposed method over the conventional DTC.

This paper presents the development of an Intelligent Cavity Layout Design System (ICLDS) for multiple cavity injection moulds. The system is intended to assist mould designers in cavity layout design at concept design stage. The complexities and principles of cavity layout design as well as various dependencies in injection mould design are introduced. The knowledge in cavity layout design is summarized and classified. The functionality, the overall structure and general process of ICLDS are explained. The paper also discusses such issues as knowledge representation and case-based reasoning used in the development of the system. The functionality of the system is illustrated with an example of cavity layout design problem.

Waiting in long queue is undesirable due to which in some practical situations customers become impatient and leave the system. In such cases providing additional servers can reduce long queue. This investigation deals with multi-server queueing system with additional servers and discouragement. The customers arrive in poisson fashion and are served exponentially by a pool of permanent and additional servers on the basis of FCFS queue discipline. The explicit formula to determine the number of customers in the queue has been obtained. Numerical illustration has been provided to validate the analytical results established. Graphs are drawn for expected number of customers in the system and probability of all additional servers being busy in order to visualize the effect of various parameters.

The present investigation presents a stochastic model for a flexible manufacturing system consisting of flexible machine, loading/unloading robot and an automated pallethandling device. We consider unreliable flexible manufacturing cell (FMC) wherein machine and robot operate under individual as well as common cause random failures. The pallethandling system is completely reliable. The pallet operation times, loading/unloading times and material handling times are considered to be random and exponentially distributed. By constructing governing equations for various system states at equilibrium, the steady-state probabilities are obtained. Some system characteristics namely utilization rate of the handling system, utilization rate of the production machine and utilization rate of the robot etc. are obtained. Some special cases are also discussed for reliable and unreliable cells. Sensitivity analysis is facilitated to examine the effect of parameters on system performance by taking numerical illustration.

In any metal forming process, both the strain rate and deformation rate depend on the die profile. The die profile also, is responsible for the non-uniformity of the deformation along the cross-section. These affect the quality and mechanical properties of the product. Therefore, if a die is designed, in which the affecting variables can be controlled spontaneously it is hoped to obtain a product with a desired quality. In this paper, the effect of the die profile on the mechanical and metallurgical properties of the product is investigated.

In this paper the steady state performance of a variable conductance heat pipe, which its working fluid consists of two components (R11+ R113) is modeled. The role of the liquid film momentum and axial normal stresses are considered by use of the mean property of mixture and the governing equations are solved by conventional numerical methods. The results of the present model have been compared with other numerical models and experimental works done by other investigators. The model presented could be used for optimization studies and design of variable conductance thermosyphons.

In this paper, a model for closed loop solar system is presented and an attempt is made to generalize the model to be utilized for primary design of any solar active thermal system. This model may be used for systems in which gas or a liquid are fluids that flow. Two new parameters, namely, the system heat delivery factor and the system heat absorption factor are introduced in the model. These two factors are fully discussed and some equations are developed for their determination

The Sungun porphyry copper deposit is located in northwestern Iran and is associated with diorite/granodiorite to quartz-monzonite of Miocene age, which intruded Eocene volcanosedimentary and Cretaceous carbonate rocks. Copper mineralization was accompanied by both potassic and phyllic alteration. Three main mineralization related alteration episodes (potassic, transition, and phyllic alterations) have been studied in terms of mass transfer and element mobility during the hydrothermal evolution of the Sungun deposit. In order to illustrate these changes quantitatively, isocon plots [1] have been applied. Isocon plots illustrate that Al, Ti and Ga were relatively immobile during alteration, and that mass was essentially conserved alteration. At all stages in the evolution of the hydrothermal system, the volume change is close to zero. In the potassic alteration zone, there is an obvious enrichment of K, and depletions of Na, Ca, Mn and Fe. These changes were due to replacement of plagioclase and amphibole by K-feldspar and biotite, respectively. Potassic alteration was associated with large addition of Cu as might be expected from the occurrence of disseminated chalcopyrite and bornite in this zone. In the transition alteration zone, Ca was added, Na, Fe and Mg were relatively unchanged, and K, Ba and Cu were depleted. The loss of K and Ba relatively to Na reflects replacement of K-feldspar by albite. Phyllic alteration wasaccompanied by the depletion of Na, K, Fe and Ba and enrichment of Si and Cu. The losses of Na, K and Fe reflect the sericitization of alkali feldspar and destruction of ferromagnesian minerals. The addition of Si is consistent with the widespread silicification, which is a major feature of phyllic alteration and the addition of Cu with mobilization from the transition zone which is depleted in this element