Mechanism of the early stages of α1 plate formation in a Cu-39 Pct Zn alloy

The early stages in the formation of α₁ plates in the ordered β′ matrix of a Cu-39 pct Zn alloy have been studied with transmission electron microscopy (TEM). The early stage plates were found to be free of stacking faults. Their contrast features are indeed those normally expected from small coherent plates. Electron microdiffraction confirms that these plates have the 9R structure characteristic of α₁ with the same lattice parameters and orientation relationships reported by previous investigators at much later stages of growth. Similarly, the 9R structure was disordered, even though it was formed in an ordered matrix, again repeating previous results obtained at a later stage of growth. These results further support the view that the α₁ Cu-Zn plates form by a diffusion-controlled mechanism. This article is based on a presentation made at the Pacific Rim Conference on the “Roles of Shear and Diffusion in the Formation of Plate-Shaped Transformation Products,” held December 18-22, 1992, in Kona, Hawaii, under the auspices of ASM INTERNATIONAL’S Phase Transformations Committee.     

Size effect on creep energy dissipation during stable crack growth

Creep energy dissipation (CED) due to crack tip creep zone is determined under steady state conditions for centre cracked thin specimen of 1.25CrO.5Mo steel, with different widths and crack length to width ratios. The creep energy rate increases when the increment in crack length Δa increases and the slope increases with increase in aspect ratio a/W and decreases with increase in width W.     

Analysis of electromagnetic forces in a levitated short rotor LIM.II. Lateral stabilization

For pt.I see ibid., vol.17, no.1, p.95-101 (2002). This paper proposes a method for lateral stabilization of the levitated linear induction motor and also gives the analysis for calculating the stabilizing force in detail. The calculated force has been experimentally verified using the laboratory prototype described previously     

Simplified steady-state model of an SCR-inverter-basedload-commutated commutatorless series motor

This paper presents a simplified analytical model of a silicon-controlled-rectifier based, load-commutated inverter driven, commutatorless series motor to predict its speed-current, torque-current and torque-speed characteristics. The model has been formulated, keeping in view the steady state equivalent circuit of a conventional DC series motor. The proposed analytical expressions relating torque and current with speed are found to follow an inverse law and that relating torque and current is found to be parabolic, as is expected in a "series" machine. The drive has been implemented, loaded with a DC generator and experimentally similar characteristics have been obtained, as predicted by the analytical model. The characteristics obtained experimentally are seen to follow the ones, predicted by the analytical model closely     

Microstructural development in microsecond pulsed laser melted polycrystalline nickel

The microsecond Nd glass pulsed laser interaction with polycrystalline nickel was studied with particular emphasis on melting and the nature of the microstructural development following irradiation. The change in the melt pool shape and the melting efficiency as a function of the total laser power has been determined. Evidence is presented to show that for low energy pulse, the microstructural development accompanies fresh nucleation of grains and leads to a finer grain size than that of the substrate. At a higher energy level, growth competition leads to a coarser grain size. We also report a banded feature roughly parallel to the melt substrate interface that develops in the resolidified region during high energy interaction. These results are discussed in the light of our present understanding of rapid solidification processes.     

Application of optimization methods to helicopter rotor blade design

The minimum weight design of helicopter rotor blades with constraints on multiple coupled flap-lag natural frequencies is studied in this paper. A constraint is also imposed on the minimum value of the autorotational inertia of the blade to ensure sufficient autorotational inertia to autorotate in case of an engine failure. A stress constraint is used to guard against structural failure due to blade centrifugal forces. Design variables include blade taper ratio, dimensions of the box beam located inside the airfoil and magnitudes of the nonstructural weights. The program CAMRAD is used for the blade modal analysis and the program CONMIN for the optimization. In addition, a linear approximation involving Taylor series expansion is used to reduce the analysis effort. The procedure contains a sensitivity analysis which consists of analytical derivatives of the objective function, the autorotational inertia constraint and the stress constraints. A central finite difference scheme is used for the derivatives of the frequency constraints. Optimum designs are obtained for both rectangular and tapered blades. The paper also discusses the effect of adding constraints on higher frequencies and stresses on the optimum designs. b box beam width - c chord - f ₁,f ₃,f ₄ first three lead-lag dominated frequencies (elastic modes) - f ₂,f ₅ first two flapping dominated frequencies (elastic modes) - g constraint function - h box beam height - h(z) box beam height variation along blade span - n number of blades - r _j distance from the root to the center of thej-th segment - t ₁,t ₂,t ₃ box beam wall thicknesses - x, y, z reference axes - A box beam cross-sectional area - AI autorotational inertia - E Young's modulus - F objective function - FS factor of safety - GJ torsional stiffness - I _x ,I _y total principal area moments of inertia about reference axes - L _j length ofj-th segment - M _j total mass ofj-th segment - N total number of blade segments - NDV number of design variables - R blade radius - W total blade weight - W() blade weight as a function of design variable - W _b box beam weight - W _o nonstructural blade weight (weight of skin, honeycomb, etc. along with tuning/lumped weights) - prescribed autorotational inertia - design variable increment - _h taper ratio inz direction - _i i-th design variable - _j mass density of thej-th segment - _j stress inj-th segment - _max maximum allowable stress - blade RPM - r root value - t tip value - L lower bound - U upper bound - ^ approximate value This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States     

Evaluation of wear of turning carbide inserts using neural networks

Recent trends, being towards mostly unmanned automated machining systems and consistent system operations, need reliable on-line monitoring processes. A proper on-line cutting tool condition monitoring system is essential for deciding when to change the tool. Many methods have been attempted in this connection.Recently, artificial neural networks have been tried for this purpose because of its inherent simplicity and reasonably quick data-processing capability. The present work uses the back propagation algorithm for training the neural network of 5-3-1 structure. The technique shows close matching of estimation of average flank wear and directly measured wear value. Thus the system developed demonstrates the possibility of successful tool wear monitoring on-line.     

Activation analysis of environmental pollutants

Activation analysis is a highly sensitive and specific technique for the detection of trace heavy metal pollutants in environmental materials. Comparison of natural “baseline” levels with elevated levels provides direct evidence of contamination. Neutron activation analysis (NAA) is used in this study to determine arsenic, zinc, cadmium, and mercury. Photo-nuclear activation analysis (PNAA) is used to determine lead in soils. Holland Marsh, a market-gardening area north of Toronto, has been studied as various herbicides and fungicides have been used there. The analyses of soil and vegetation samples, and of human head hair collected from residents are reported.     

Pixel rearrangement based statistical restoration scheme reducing embedding noise

In this paper, a block based steganographic algorithm has been proposed where a sequence of secret bits are embedded into a set of pixels by rearranging the pixel locations. This algorithm has been devised as an improvement over existing statistical restoration based algorithms in order to reduce the additive noise which occurs due to embedding. It is shown that the proposed scheme substantially reduces the additive noise compared to existing statistical restoration based schemes.     

Combustion of single char particles in a turbulent fluidized bed

The combustion of single bituminous char particles (4-12 mm diameter) was studied in a turbulent fluidized bed operated at 1098 K using air as the fluidising medium. Results indicated that particles burn with constant density following a shrinking sphere model. Burning rates are much higher than those observed in a bubbling fluidized bed. The rate of transfer of oxygen to the particle surface is also higher than that observed in bubbling beds. A model is proposed to calculate the Sherwood numbers of the burning carbon particles. Experimental values of the Sherwood numbers agree well with those predicted from the model.