Direct Carbothermic Reduction of Weathered Ilmenite for Efficient Removal of Iron by Leaching

Metallurgical and Materials Transactions B - The commercial processes to extract iron from ilmenite (FeTiO3) essentially include energy-intensive methods, such as high-temperature reduction...     

An Integrated Assessment of Process-Microstructure-Property Relationships for Thermal-Sprayed NiCr Coatings

Process-microstructure-property relationships have been systematically investigated and quantified for a large process window of thermal-sprayed Ni-20 wt.%Cr coatings. Detailed monitoring of particle state, coating formation, and multifunctional characterization has been performed providing a framework to not only examine the product coating, but also concurrently their evolution dynamics. Several distinct microstructures resulted from this expanded process window and shed light into the effects of in-flight particle state, nature of the interfaces, impact-induced peening, strain hardening, oxide content, on coating properties notably hardness, residual stress, elastic modulus, electrical and thermal conductivity. Nine processing conditions from five different thermal spray torches provided a wide range of particle velocities from 150 to 800 m/s and temperatures from 1800 to 2400 °C. Correlation between particle states and evolving stress obtained via in situ monitoring of coating deposition indicated increment of compressive stress at high particle kinetic energies, as well as enhanced strain hardening via peening. Hardness, therefore, showed strong dependency on the residual stress evolution. Elastic modulus was found to be strongly dependent on densification and intersplat bonding, whereas electrical and thermal conductivities were found to be more sensitive to defects in the intersplat interfaces (oxides, interlamellar porosity). In comparison to bulk properties, elastic modulus, and thermal conductivity of the sprayed coatings were generally lower, while electrical conductivity can approach the bulk value. Coating hardness exceeds the bulk property in most cases owing to the strain hardening during impact. Hardness was the most sensitive property to the process condition.     

Deformation and strain distribution in plasma sprayed nickel–aluminum coating loaded by a spherical indenter

The deformation underneath a spherical indent was investigated on samples prepared by the bonded-interface technique from a plasma sprayed nickel–5%aluminum coating. Prior to the spherical indentation a set of Vickers micro-indents was produced as fiduciaries on one of the cross-sections. This allowed the calculation of plastic strain components from the relative displacements of micro-indents during subsequent surface indentation. Using a modified procedure based on a method proposed by Tabor [1], stress–strain curve was evaluated by measuring the contact radii of spherical indentations produced at several different loads. The derived stress–strain relationship was used in 2D and 3D finite element models to estimate the plastic deformation field under the indenter. The comparison between the measured and calculated strain profiles revealed notable differences. The normal plastic strain in the direction along the vertical axis of indentation displayed higher values directly under the indenter compared to the finite element analysis which predicted lower values under the indenter and less rapid decrease of the plastic strain with depth. The differences were attributed to the compaction of the lamellar structure in the plasma sprayed coatings. The compaction of the lamellae was directly observed on polished coating cross-sections.     

Optimal Orthogonal Tiling of 2-D Iterations

Iteration space tiling is a common strategy used by parallelizing compilers and in performance tuning of parallel codes. We address the problem of determining the tile size that minimizes the total execution time. We restrict our attention to uniform dependency computations with two-dimensional, parallelogram-shaped iteration domain which can be tiled with lines parallel to the domain boundaries. The target architecture is a linear array (or a ring). Our model is developed in two steps. We first abstract each tile by two simple parameters, namely tile periodP_tand intertile latencyL_t. We formulate and partially resolve the corresponding optimization problem independent of the machine and program. Next, we refine the model with realistic machine and program parameters, yielding a discrete nonlinear optimization problem. We solve this analytically, yielding a closed form solution, which can be used by a compiler before code generation.     

Bidding-based multi-agent system for integrated process planning and scheduling: a data-mining and hybrid tabu-SA algorithm-oriented approach

This paper conceptualizes a bidding-based multi-agent system for solving integrated process-planning and scheduling problem. The proposed architecture consists of various autonomous agents capable of communicating (bidding) with each other and making decisions based on their knowledge. Moreover, in contrast to the traditional model of integrated process-planning and scheduling problem, a new paradigm has been conceptualized by considering tool cost as a dynamic quantity rather than a constant. Tool cost is assumed to comprise tool-using cost and its repairing cost. The repairing cost is considered to depend on the tool-breaking probability, which is predicted by the data-mining agent equipped with the virtues of C-fuzzy decision tree. When a job arrives at the shop floor, the component agent announces a bid for one feature at a time to all the machine agents. Among the machine agents capable of producing the first feature, one comes forward to become a “leader”, and groups other machine agents for the processing of remaining features of the job. Once all features are assigned to the appropriate machines, the leader then sends this allocation information to the optimization agent. The optimization agent finds optimal/near-optimal process plans and schedules via the hybrid tabu-SA algorithm.     

A heuristic game theoretic approach to resource sharing in reconfigurable manufacturing

Agility is an essential requirement for manufacturers to increase market share and profitability in a highly competitive industry. Having reconfigurable production lines is considered an essential aspect of modern manufacturing operations. This article investigates the possibility of using a non-cooperative game theoretic technique for making reconfiguration decisions at the resource controller level in such an environment. Under the proposed approach, a resource controller evaluates a configuration game in order to determine appropriate actions when faced with a reconfiguration decision. The prescribed action is defined by pure or mixed strategy equilibriums inside the configuration game. By evaluating each game, the resource controller can account for the potential actions and reactions of other resource controllers in the system. The investigation shows the applicability of such an approach to optimally resolving resource-sharing issues in an example semiconductor manufacturing environment .     

Theoretical and Numerical Aspects in the Thermo-Viscoelastic Material Behaviour of Rubber-Like Polymers

Most current models for finite deformation thermo-viscoelasticity are restricted to linear evolution laws for the viscous behaviour and to thermorheologically simple materials. In this paper, we extend a model for finite deformation viscoelasticity that utilizes a nonlinear evolution law to include thermal effects. In particular, we present a thermodynamically consistent framework for the model and give a detailed form for then on-equilibrium Helmholtz free energy of the material in terms of the isothermal free energy function. The use of the model in a computational setting is addressed and it is shown that an efficient predictor-correct oralgorithm can be used to integrate the evolution equation of the proposed constitutive model. The integration algorithm makes crucial use of the exponential map as has been done previously in elastoplasticity. Numerical examples are presented to show some interesting features of the new model. This revised version was published online in July 2006 with corrections to the Cover Date.