Current Issue : October - December Volume : 2014 Issue Number : 4 Articles : 6 Articles
Traveling wire electrochemical machining is a promising approach for the fabrication of various metal parts. However, the straycurrent\nattack deteriorates the surface quality while it is employed to cut thick workpiece as a normal pulse or DC is used. In this\npaper, the characteristics of the stray-current attack in reciprocated traveling wire electrochemical machining are firstly identified,\nand special insulating methods are proposed to reduce the effect of the stray-current.The model of electric field is built. Both the\nsimulation and the experimental results illustrate that the stray-current attack can be reduced significantly by the proposed insulatingmethods.\nFinally, structures with fine surface quality on stainless steel 304 with thickness of 20mmwere successfully produced....
This paper presents a method of assessing fatigue strength for a body in conditions of cyclical tension and torsion. The theoretical\ncalculations have been conducted using the criterion of averaged structural microdamage resulting fromlocal slips.Thedescription\nof microdamages of such a body, in the view of the slip concept, was done by using a half-sphere with a unit radius, on the surface\nof which the location of all local physical planes and slip systems was determined employing three angles. A computer method was\nused to determine the slip boundaries in a complex stress state, analyzing the slip condition for all combinations of angles. Based on\nthe calculated values of the microdamages� intensity function, the number of loading cycles until the moment of fracture initiation\nwas estimated. Experimental verification of the suggested criterion was conducted using cylindrical smooth specimens, made of\nC45 steel.The tests of fatigue strength were made under conditions of a constant amplitude of zero-start pulsating loads....
An important parameter in the design of leaf spring is the width to thickness ratio (W/T). Decrease in W/T ratio decreases the material required and consequently the weight of the leaf spring for the same vertical load caring capacity. But at the same time this increases the stiffness and required deflection in the vertical direction may not be obtained. Deflection/stiffness is also equally important in spring design since a certain minimum required amount of deflection at a particular load is always necessary in springs, although in design of other mechanical components, deflection is undesirable within the working load range. The increase in vertical stiffness due to decrease in W/T ratio is beyond the acceptable limit due to the high value of modulus of elasticity for steel i.e. 210000 MPa. But W/T ratio can be decreased without increase in vertical stiffness if some material having low value of modulus of elasticity i.e. 32500 MPa is used. Reduction in vertical stiffness i.e. increase in vertical deflection range is also possible if W/T ratio is decreased within a certain limit. Hence in the present work the width to thickness ratio is decreased followed by change in material and stress analysis of a mono leaf spring is done by F.E.M. before and after changing the material. After this the values of stress at different points along the length (average values at various cross sections) after applying a point load of 2943 N for both materials are compared by overlapping of graphs....
Integrated casting and forging process (ICFP) is a new manufacturing method combining the advantages of both casting and\nforging. Aluminum structure parts, such as aluminum alloy automobile wheel, with complex shape and excellent mechanical\nproperties can be produced by this process. The effects of different process parameters on the ICFP of the automobile wheel were\nsimulated by Forge software. Microstructure of forging region and the nonforging region were studied by experiment. The results\nshow that die temperature, static pressure of the injection piston, forging speed, and material flow have significant influences on\nthe process. Compared with nonforging region, the microstructure of forging region becomes finer, more uniform, and denser.\nMeanwhile, the casting defects can be removed and mechanical properties improved....
Amajor problem associatedwith themembrane separation processes is the permeate flux drop, limiting the widespread of industrial\napplication of this process. This occurs due to the accumulation of solute concentration near the membrane surface. An exact\nquantification of the concentration polarization as a function of process conditions is essential to estimate the system performance\nsatisfactorily. In this sense, this work aims to predict the behavior of the concentration polarization boundary layer along the\nlength of a permeable tubularmembrane, over various operation conditions. Thenumerical solution of the Navier-Stokes equation,\ncoupled to Darcy�s and mass transfer equations, is obtained by the commercial software ANSYS CFX 12, considering a twodimensional\ncomputational domain. The study evaluates the effects of axial Reynolds and Schmidt numbers on the concentration\npolarization boundary layer thickness during the cross-flow filtration process. Numerical results have shown that themathematical\nmodel is able to predict the formation and growth of the concentration polarization boundary layer along the length of the tubular\nmembrane....
Global sensitivity is used to quantify the influence of uncertain model inputs on the output variability of static models in general.\nHowever, very few approaches can be applied for the sensitivity analysis of long-term degeneracy models, as far as time-dependent\nreliability is concerned. The reason is that the static sensitivity may not reflect the completed sensitivity during the entire life\ncircle. This paper presents time-dependent global sensitivity analysis for long-term degeneracy models based on polynomial chaos\nexpansion (PCE). Sobol� indices are employed as the time-dependent global sensitivity since they provide accurate information on\nthe selected uncertain inputs. In order to compute Sobol� indices more efficiently, this paper proposes a moving least squares (MLS)\nmethod to obtain the time-dependent PCE coefficients with acceptable simulation effort. Then Sobol� indices can be calculated\nanalytically as a postprocessing of the time-dependent PCE coefficients with almost no additional cost. A test case is used to\nshow how to conduct the proposed method, then this approach is applied to an engineering case, and the time-dependent global\nsensitivity is obtained for the long-term degeneracy mechanism model....
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