• 소성∙가공
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• 제16권8호
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• pp.582-589
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• 2007

This paper is related to an analysis on the surface expansion in backward can extrusion process using spherical punches. It is generally known that the backward can extrusion process usually experiences severe normal pressure and heavy surface expansion. This is a reason why the backward can extrusion process is one of most difficult operations among many forging processes. Different punch nose radii have been applied to the simulation to investigate the effect of punch nose radius on the surface expansion, which is a major effort in this study. AA 2024 aluminum alloy is selected as a model material for investigation. Different frictional conditions have also been selected as a process parameter. The pressure applied on the punch has been also investigated since heavy surface expansion as well as high normal pressure on the tool usually leads to severe tribological conditions along the interface between material and tool. The simulation results are summarized in terms of surface expansion at different reduction in height, deformation patterns including strain distributions and maximum pressure exerted on the workpiece and punch, the effect of punch nose radius and the frictional condition on the surface expansion and the location and magnitude of maximum pressure exerted, respectively.

• 소성∙가공
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• 제11권8호
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• pp.668-675
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• 2002

The circles deform into various shape during deformation, the major and minor axes of which indicate the direction of the major and minor principal strains. Likewise, the measured dimensions are used to determine the major and minor principal strain magnitudes. This circular grid technique of measuring strains can be used to diagnose the causes of necking and fracture in industrial practice and to investigate whether these defects were caused by material property variation, changes in lubrication, of incorrect press settings. In non-axisymmetric deep drawing, three modes of forming regimes are found: draw, stretch, plane strain. The stretch mode for non-axisymmetric deep drawing could be defined when the major and minor strains are positive. The draw mode could be defined when the major strain is positive and minor strain is negative, and plane strain mode could be defined when the major strain is positive and minor strain is zero. Through experiments the draw mode was shown on the wall and flange are one of a drawn cup, while the plane strain and the stretch mode were on the punch head and the punch corner area respectively, We observed that the punch load of elliptical deep drawing was decreased according to increase of die corner radius and the thickness deformation of minor side was more large than major side.

• Steel and Composite Structures
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• 제29권5호
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• pp.579-590
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• 2018

Size-dependent free vibration responses and magneto-electro-elastic bending results of a three layers piezomagnetic curved beam rest on Pasternak's foundation are presented in this paper. The governing equations of motion are derived based on first-order shear deformation theory and nonlocal piezo-elasticity theory. The curved beam is containing a nanocore and two piezomagnetic face-sheets. The piezomagnetic layers are imposed to applied electric and magnetic potentials and transverse uniform loadings. The analytical results are presented for simply-supported curved beam to study influence of some parameters on vibration and bending results. The important parameters are spring and shear parameters of foundation, applied electric and magnetic potentials, nonlocal parameter and radius of curvature of curved beam. It is concluded that the increase in radius of curvature tends to an increase in the stiffness of curved beam and consequently natural frequencies increase and bending results decrease. In addition, it is concluded that with increase of nonlocal parameter of curved beam, the stiffness of structure is decreased that leads to decrease of natural frequency and increase of bending results.

• 소성∙가공
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• 제8권4호
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• pp.331-339
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• 1999

In this study, to analyze the shaped drawing process from round bar, the practical conical die with considering die radius and bearing was defined by a mathematical expression, and also a simple technique for initial mesh generation to the shaped drawing process was proposed. The drawing of rectangular section from round bar, one of the shaped drawing process, has been simulated by using non-steady state 3D rigid plastic finite element method in order to evaluate the influence of semi-die angle and reduction in area to corner filling. Other process variables such as friction constant, rectangular ratio, die radius and bearing length were fixed during the simulation. An artificial neural network has been introduced to obtain the optimal process conditions which gave rise to a fast simulation.

• 한국생산제조학회지
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• 제9권5호
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• pp.150-156
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• 2000

The objective of this study is to investigate effects of prebuckling on the buckling of laminated composite cylindrical shells. Axial compression and lateral pressure are considered for laminated composite cylindrical shells with the ratios of length to radius. The shell walls are made of a laminate with several symmetric ply orientations. The study was made using finite difference energy method, utilizing the nonlinear bifurcation branch with nonlinear prebuckling displacements. The results are compared to the buckling loads determined when membrane prebuckling displacements are considered. Review the influence of nonlinear prebuckling for the buckling loads, the difference between the actual and classical buckling loads are increased as the increments with the ratios of length to radius, for which is applied the axial compression, but almost same for the lateral pressure.

• 한국안광학회지
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• 제3권1호
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• pp.33-37
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• 1998

렌즈 중심잡기는 베이스 커브에 의존함을 알 수 있는데, flat한 렌는는 중심에서 더 이탈되었고, 주변부로 움직임이 크게 나타났다. 대부분의 경우 중심이탈은 위쪽 또는 귀쪽이었다. 또 더 flat한 렌즈를 장용한 환자가 장용감에 대한 불편함을 느꼈다. 세 개의 K값 영역에서 최적상태로 피팅된 상태는 베이스 커브가 8.4mm일때였으며 베이스 커브가 커짐에 따라 최적조건은 줄어들었다.

• 한국항공운항학회지
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• 제15권4호
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• pp.38-44
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• 2007

This paper describes the structural safety of solid fuel in the Hybrid Rocket Motor (HRM). Hybrid rocket combustion has the distinct regression characteristics which include the process of thermal pyrolysis and fuel vaporization. Most of all, this regression characteristics would structurally affect the strength of the fuel having a multi-port configuration, and even may cause the breaking from the fuel grain. This problem would probably influence the performance and operating safety of HRM. Therefore, for the safe operation of HRM, the critical port radius which determines the structurally safe region was discussed from the heat analysis of the solid fuel.

• 대한기계학회논문집
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• 제18권6호
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• pp.1474-1482
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• 1994

In order to study the influence of a circular inclusion on a stress field neat a crack tip, mutual interference of a crack and the circular inclusion is analyzed by using the two dimensional boundary element method program made for the analysis of a bimaterial inclusion. The stress intensity factor of an inclusion which has small stiffness is a little greater than that of large stiffness in the near-by crack tip, and similar values tends to appear for distant crack tips. A line crack shows the repetition phenomena which caused by stress mutual interference depending on the radius and stiffness of an inclusion, and the repetition phenomena becoms weak in the inclusion which has large stiffness. Stress mutual interference shows repetition phenomena after extension of a line crack by the length of the radius of the inclusion which has small stiffness.

• 한국철도학회논문집
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• 제9권5호
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• pp.618-623
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• 2006

Understanding the contact between wheel and rail is a starting point in railway vehicle dynamic research area and especially analysis for the contact geometry between wheel and rail is important. On the one hand, the critical speed as the natural characteristics of rolling-stock is generally tested on the roller rig. The geometrical characteristics of the wheel/roller contact on the roller rig are different from these of the general wheel/rail contact because the longitudinal radius of roller is not infinite compared with rail. Thus, in this paper we developed the algorithm to analyze the wheel/roller contact geometry of our roller rig which is constructed now and analyzed the difference between whee/roller contact and wheel/rail contact. In conclusion, we found that the yaw motion of wheelset and the roller radius influence the geometrical contact parameters in wheel flange contact area.

• 대한기계학회논문집
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• 제19권7호
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• pp.1749-1757
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• 1995

The structure of turbulence of fully developed flow through three concentric annuli with both rough inner and outer walls was investigated experimentally for Reynolds number range Re=15000-93000. Turbulence intensities were measured in three (u, v, w) directions, and turbulence shear stresses in annuli of radius ratios .alpha.= 0.26, 0.4 and 0.56, respectively. The result showed that the structure of turbulence for these asymmetric flows was not the same as that for the annulus with smooth walls. The velocity fluctuations of all three components (u, v, and w-directions) showed little discernible variation with Reynolds numbers, but became apparent with the influence of radius ratio (.alpha.) The experimental results for an annulus with the roughened outer wall and a smooth annulus were shown in the figures as a reference. The eddy diffusivities and friction factors were also presented and discussed.