• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1648-1651
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• 2005

Fretting contact and fretting fatigue are known to occur in mechanical devices which have fasteners subjected to oscillatory tangential load. Theoretical studies on fretting contact have been focussed on simple geometries, such as cylindrical contact problem. Recently, the contact problem of a flat rounded punch has been solved theoretically. The purpose of this paper is to show that the results of finite element analysis for the fretting contact problem are nearly consistent with the theoretical solutions.

• 대한기계학회논문집A
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• 제26권7호
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• pp.1270-1279
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• 2002

Residual stress is a dominant obstacle to efficient production and safe usage of device by deteriorating the mechanical strength and failure properties. Therefore, we proposed a new thin film stress-analyzing technique using a nanoindentation method. For this aim, the shape change in the indentation load-depth curve during the stress-relief in film was theoretically modeled. The change in indentation depth by load-controlled stress relaxation process was related to the increase or decrease in the applied load using the elastic flat punch theory. Finally, the residual stress in thin film was calculated from the changed applied load based on the equivalent stress interaction model. The evaluated stresses for diamond-like carbon films from this nanoindentation analysis were consistent with the results from the conventional curvature method.

• 대한기계학회논문집A
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• 제28권7호
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• pp.992-998
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• 2004

During the tube hydropiercing, the region adjacent to the pierced hole will be deformed and will be drawn away from the die block as the punch advances through the wall of the tube. The deformation in the region may range from a substantially flat form to a countersunk form, so called rollover. In this study, the effects of material properties, shape of piercing punches, roundness of tube surface and internal pressure within the tube during piercing on the rollover have been investigated experimentally. The results provide the quantitative variation of rollover at given hydropiercing parameters, and a relationship between the deformed radius and the rollover caused by the deformation has been established.

• 한국정밀공학회지
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• 제22권11호
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• pp.125-134
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• 2005

Recently, there have been reported on the results that the material life is reduced by fretting conditions and the initial crack made by low stress under fretting. The purpose of this paper is to show that the results of finite element analysis for the fretting contact problems of a flat rounded punch are nearly consistent with the theoretical solutions and to research that the results about effects of the contact zone according to geometries and mechanical properties of pad.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 추계학술대회논문집
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• pp.37-47
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• 1995

Forging of trapezoidal spline, serration and square spline with solid cylindrical billets and hollow one has been investigated by means of upper bound method. Kinematically admissible velocity fields for forging of splines have been proposed in this study. The half pitch of splines has been divided into deformation regons. The neutral surface is introduced into forging of splines with flat punch and, for each step, it is assumed as a circle with its radius rn upper bound solutions obtained obtained by proposed kinematically admissible velocity fields are useful to predict the loads for forging of splines.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 춘계학술대회논문집
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• pp.41-53
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• 1995

Forging of spur gears has been investigated by means of upper-bound method. The term forging means forging of spur gears with solid cylindrical billets, hollow billets with flat punch. Kinematically admissbile velocity field for forging of spur gears has been proposed in this study. The 1/2 pitch of spur gear has been divided into seven dieformation regions, wherein, an involute curve has been introduced to represent the shape of die profile. Especially neutral surface has been introduced intor forging of hollow gears from hollow billets. By using the kinematically admissible velocity field, the powder requirements and suitable conditions for forging fo spur gears were successfully calculated with numerical method. According to the analysis , the acceptable number of teeth for forging of spur gears is from 15 to 20.

• 소성∙가공
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• 제13권2호
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• pp.154-159
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• 2004

Deformation surrounding the hole in the tube during the hydropiercing process has been investigated in this study. The tube is expanded and internally pressurized between upper and lower dies, and a piercing punch is driven forcefully through a cross passage in the die and through the wall of the tube. The pressurized fluid within the tube provides support to the wall of the tube during a piercing step to form a hole in the tube having less deformation surrounding the hole in the tube. The deformation area may be fully retracted to a substantially flat form or partially retracted to a countersunk form. In this study, a mathematical model that can predict deformation surrounding the hole has been proposed and experimentally verified by actual hydropiercing test.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.183-186
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• 1995

A simulation method basee on upper bound method is developed in order to characterize forging characters in forging of spur gears. In this paer, utlizing a kinematically admissible velocity field and applying it to study the effect of inner diameter of holow billet. To predict the variation of inner diameter of hollow billet, neutal surface has been introduced into forging of hollow gears from hollow billes with flat punch. The neutral surface of each step is assumed as a circle and determined in order to have minimum forging energy by golden section method. According to the analysis, the magnitude of inner diameter of initial billet is vary important to reduce the relative pressure and forging load. And the variation of inner diameter of billet during spur gear forging is successfully predicted.

• 한국정밀공학회지
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• 제13권1호
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• pp.108-115
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• 1996

Forging of trapezoidal spline, serration and square spline with solid cylindrical billets and hollow one has been investigated by means of upper bound method. Kinematically admissible velocity fields for forging of splines have been proposed in this study. The half pitch of spline has been divided into several deformation regions. The neutral surface is introduced into forging of splines with flat punch and, for each step, it is assumed as a circle with its radius $r_n$. Upper bound solutions obtained by proposed kinematically admissible velocity fields are useful to predict the loads for forging of splines.

• 한국정밀공학회지
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• 제13권9호
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• pp.77-83
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• 1996

This paper describes forging of trochoidal gears, which are being widely used in timing belt pulley, pump pulley etc., as a series of development of the simulator for non-axisymmetric elements. Kinematically admissible velocity fields for forging of trochoidal gear were proposed and the loads were calculated by numerical method. When the simulation was carried out, half pith of gear was divided into 6 deformation regions which have different velicity fields by assumptions and boundary conditions. The neutral surface was introduced into forging of trochoidal gears with flat punch and, for each step, it is assumed as a circle with its radius r$_{n}$. The experimental set-up was installed in 200 ton hydraulic press for forging. The billets, of A1 2218 aluminum alloy, were slightly phosphate-coated. It was shown that thd theoretical solutions, as upper bound, are useful to predict the forging load for forging of trochoidal gears, because thdt give estimates that are substantially higher than experimental loads.s.