Microstructure and Mechanical Properties of a Dissimilar Friction Stir Weld between Austenitic Stainless Steel and Low Carbon Steel

Dissimilar fusion welding of austenitic stainless steels to carbon steels has some metallurgical and technical problems.It was suggested that the solid-state nature of friction stir welding(FSW) can overcome these problems and produce a sound weld with reliable mechanical properties.In this study,plates of 304 stainless steel and st37 steel were welded together by FSW at tool rotational speed of 600 r/min and welding speed of 50 mm/min.In the stir zone(SZ) of 304 stainless steel,the results showed a refined grain structure with some features of metadynamic recrystallization.In the SZ of st37 steel,the hot deformation of material in the austenite region produced small austenite grains.These grains transformed to fine ferrite and pearlite by cooling the material after FSW.The production of fine grains increased the hardness and tensile strength in the SZ of both sides with respect to their base metals(BMs).     

Psychological separation, attachment security, vocational self-concept crystallization, and career indecision: A structural equation analysis.

Structural equation modeling was used to test theoretically based models in which psychological separation and attachment security variables were related to career indecision and those relations were mediated through vocational self-concept crystallization. In contrast to previous studies, which have found either weak or no support for a relation between separation or attachment security variables and career indecision, results based on a sample of 350 college students indicated that some components of separation and attachment security did relate to career indecision in a theoretically supportable direction. Results also revealed that regardless of whether global or component career indecision measures were used, separation and attachment security effects on indecision were at least partially mediated through vocational self-concept crystallization. The strongest mediated relations were observed for the effects of attachment anxiety and maternal separation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Design of sliding mode and model reference adaptive control strategies for multivariable tape transport mechanism: a performance comparison

This paper presents sliding mode control and model reference adaptive control strategies for the tape transport mechanism. A nonlinear multivariable MIMO model of the process, consisting of take-up and supply reel servos for tape tension control and capstan servo for speed control is considered. The sliding mode control is applied for the nonlinear dynamic model of the process, while the model reference adaptive control deals with the linearized one. Moreover, in order to associate with the realistic model of system, design of controllers is accomplished with respect to parametric uncertainties. It is shown that both control strategies can guarantee asymptotic stability of the closed-loop system and tracking of desired outputs with the appropriate pace in the presence of uncertainties. Finally, simulation results demonstrate the effectiveness of the proposed controllers.     

Application of discrete event simulation for robust system design of a melt facility

This paper presents a methodology to identify robust operating regions through the selection of controllable factory variables, using discrete event simulation. A casting plant melt facility was used as an industrial test bed to develop these techniques. A robust system design was determined by response surface analysis of key production parameters. Furthermore, robust operating policies that maximise throughput, while minimizing work-in-progress and thus energy consumption were identified.     

A comparison of critical distance methods for fracture prediction

This paper is concerned with four methods which are used to predict the failure of bodies containing notches and other stress concentration features. Two of these methods, which we call the line method (LM) and point method (PM), use parameters taken from the elastic stress field ahead of the notch. The other two methods make use of linear elastic fracture mechanics (LEFM): we call these the imaginary crack method (ICM) and finite fracture mechanics (FFM). A common feature of all the methods is the use of a material constant with the units of length, which we call the critical distance.In this work we test the hypothesis that these four methods all give similar predictions. Firstly, we show analytically that, for the simple case of a straight, through-thickness crack in an infinite body, predictions using the LM are identical to those of the ICM and FFM and, in addition, there is a very simple relationship between the critical distances for the three methods. For notches no precise relationship exists; we used both closed-form solutions and finite element analyses (FEA) to compare predictions of failure from common types of notches, such as circular holes, edge notches and slots, in large (essentially infinite) bodies. We modelled both isotropic and anisotropic materials. In all cases, we found that predictions from the four different methods were of similar magnitude, always falling within an error band of ±10%. However, large differences emerge in the case of finite bodies when the remaining width is similar in size to the critical distance; then predictions become asymptotic in different ways. These findings have practical consequences for the use of these methods in engineering design. The results also promote some discussion about the theoretical basis of critical distance approaches.     

A nondominated ranked genetic algorithm for bi-objective single machine preemptive scheduling in just-in-time environment

Motivated by just-in-time (JIT) manufacturing, we study the bi-objective scheduling problem of minimizing the total weighted earliness and the number of tardy jobs on a single machine, in which machine idle time and preemption are allowed. The problem is known to be NP-hard. In this paper, we propose a new mathematical model, with nonlinear terms and integer variables which cannot be solved efficiently for medium- and large-sized problems. A method combining the new ranked-based roulette wheel selection algorithm with Pareto-based population ranking algorithm, named nondominated ranking genetic algorithm (NRGA), has been presented to find nondominated solutions in a reasonable time. Various operators and parameters of the proposed algorithm are reviewed to calibrate the algorithm by means of the Taguchi method. A number of numerical examples are solved to demonstrate the effectiveness of the proposed approach. The solutions obtained via NRGA are compared against solutions obtained via ε-constraint method in small-sized problems. Experimental results show that the proposed NRGA is competitive in terms of the quality and diversity of solutions in medium- and large-sized problems.     

Mixed sulphide-oxide lead and zinc ores: Problems and solutions

Mixed sulphide-oxide lead and zinc ores are most often found in the transition, and occasionally in the oxidised, zones of lead-zinc ore-bodies. They are of great importance because there are numerous unexploited or abandoned reserves of these ores in the world.However they present difficulties for conventional mineral processing due to complex mineralogy. In this paper, the specific problems associated with these types of ores are described and methods for solving these problems, combining economic and technical considerations, are discussed.The results of experiments carried out at laboratory scale are presented, in which the dissolution of mixed ore in sulphuric acid without oxidising agents was investigated. The results show the feasibility of zinc recovery from mixed sulphide-oxide lead and zinc ores, which underlines the potential of this approach. We also propose a conceptual flow diagram for the hydrometallurgical processing of these ores.     

Estimation of Thermal Stresses in Hot-Rolled Steel Coils During Natural Air Cooling

Hot-rolled steel coils are stored upon manufacturing to cool to about 50°C. High temperatures of coiling cause thermal stresses during the cooling stage that result in spot welding between strip layers of coil. Under these conditions, surface defects or strip ruptures may occur during uncoiling. This paper will initially introduce the heat transfer model in the coil based on stress-dependent thermal conductivity in the radial direction of the coil. The two approaches of “solid body” and “thin-walled, concentric cylinders” for thermal stress analysis will then be used to compute the thermal compressive stresses in the coil. Comparison of the results obtained from these two approaches in the mathematical model reveals that the solid body approach overestimates the thermal stresses when compared to the thin-walled concentric cylinders approach, the inequality rising with reduced strip thickness. This difference, however, is found to have no considerable impact on predicting coil temperature.     

Role of nanoparticles on nanofluid boiling phenomenon: Nanoparticle deposition

Suspended nanoparticles inside the nanofluids can modify the characteristics of heated surfaces and the physical properties of the base liquids, offering a great opportunity to optimize boiling heat transfer. This paper reviews the mechanisms of nanoparticle deposition and the effects induced by deposited nanoparticles on surface roughness, force balance at the triple line, surface wettability, active nucleation site density, receding and advancing contact angles, boiling heat transfer coefficient and critical heat flux. Both enhancement and deterioration effects on boiling heat transfer coefficient and critical heat flux have been discussed. Most of the existing experimental data confirms the enhancement of critical heat flux using alumina nanofluid, however there is no consistency about its boiling heat transfer coefficient.