• Journal of the Korean Institute of Gas
• /
• v.11 no.1 s.34
• /
• pp.34-39
• /
• 2007

In this paper, the FEM result has been presented for a sealing safety between a valve packing and a valve seat during a open and close operation in a LPG cylinder. The sealing operation of a LPG valve is completed when the valve packing in which is made by a nylon-66 polymer is to stop a LP gas flow, which flows out from the outlet of a brass pipe in a LPG cylinder. The contact sealing mechanism of the valve may be classified by a flat contact of an unused valve packing and a circular groove contact of an used valve packing in a current LPG valve. Based on the FEM and experimental investigations the sealing force, 4.9 MPa for a flat contact mode of the unused valve packing is a little high compared to that of the used valve packing, which shows a circular groove contact geometry against a valve seat. But these sealing pressures for two contact modes are very low compared to the ultimate strenath 83 MPa of the nylon-66 and this may be designed with a excess strength of the valve.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.29 no.2 s.233
• /
• pp.169-175
• /
• 2005

In this paper, the contact stress and strain distributions in elastomer O-ring seals have been analyzed using a non-linear finite element method. The stress behavior of PTFE materials is assumed as Odgen model because the sealing clearance between the flange and the surface of the O-ring is not small and the sealing pressure of working fluids covers from the atmospheric pressure to high pressure of 15MPa. The contact normal force and stress in wavy O-rings in which is developed for this analysis are uniformly distributed along the flange and the wall of the rectangular groove. And the normal sealing forces are also kept high compared to other contact sealing models such as the conventional O-ring and X-ring, Thus, the FEM computed results indicate that the sealing characteristic of wavy O-rings is food compared with other contact seals.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.10a
• /
• pp.81-81
• /
• 2003

최근 유한요소법을 이용하여 절삭가공을 해석하는 연구가 많이 발표되고 있다. 이 때 가장 문제되는 점이 피삭재에서 칩으로 분리하는 조건이다. 일반적으로 칩 분리 조건이라 일컬어지는 이 조건을 어떻게 설정할 것인가에 대해 현재까지도 많은 연구가 이루어지고 있다. 현재까지 제시된 칩 분리 판별 조건은 두 가지 유형 - 기하학적, 물리적으로 나눌 수 있다. 기하학적 칩 분리 조건은 공구 끝단과 바로 앞 요소의 거리를 기준으로 정해진 특정한 값에 도달하면 요소가 분리되는 혹은 없어지는 방법을 이용하는 것이며(Fig. 1 참조), 물리적 칩 분리 조건은 요소 내의 소성변형률 혹은 변형률 에너지 밀도함수 등의 값을 기준으로 분리시키는 방법이다. 본 연구에서는 상용 유한요소 해석 프로그램인 ANSYS를 이용하였으며 이 프로그램에서 제공하는 element birth/kill 기법을 이용하여 기하학적 판별조건에 도달하면 공구 끝단 앞의 요소가 사라지는 방법을 취하였다. Fig. 2는 절삭가공을 위한 유한요소 모델링을 나타낸다. 칩-공구 접촉 부위에 접촉요소를 사용하였으며, 피삭재의 왼쪽과 아래쪽 부위는 각각 변위구속을 하였다. 공구의 이동은 변위경계조건의 값을 변화시킴으로써 구현하였다. 절삭력을 비교함으로써 해석결과의 타당성을 검토하였으며, 피삭재 내의 응력, 변형률 분포 등을 살펴보았다.

• Tribology and Lubricants
• /
• v.16 no.4
• /
• pp.289-294
• /
• 2000

This paper present the contact stresses, which considers the shear stress at the cam and follower interface in the direct acting type valve train system of a high speed engine. To determine the contact condition, the normal contact forces are calculated by using the lumped mass dynamic modeling. The line contact is considered between the cam and follower interface. The variations of dynamic stresses are presented as a function of camshaft rotational angle. Also the effects of various design parameters are investigated.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.2
• /
• pp.161-166
• /
• 2010

Elastomeric seals are widely used in dynamic seal applications, and it is well known that the sealing surfaces can be gradually worn out. Abrasive wear is known to be the most dominant factor; however, little research has been carried out on this problem until now. In this study, a new contact problem related to elastomeric seals-a small spherical particle and steel surface-was modeled and analyzed using MARC. Variations of von-Mises and residual stress distributions as well as deformed seal and steel surface shapes with seal materials and interferences are presented. The stress distribution and surface deformation are highly affected by the elastic properties of seal. For PTFE, the maximum von-Mises stress exceeds the yield strength, and plastic deformation occurs on the steel surface. Therefore, the sealing surface can also be worn down by sub-surface fatigue due to intervening hard particles in the sealing surfaces together with the well-known abrasion.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.7
• /
• pp.2097-2107
• /
• 1996

The dynamic photoelastic technique had been utilized to investigate the possibillity of relieving the large local singular stresses induced at the corner of a right- angle- indenter. The indenter compressed a semi-infinite body dynamically with an impact load applied on the top of the indenter. The effects of the geometric changes of the indenter in terms of the diameter (d) and the location (1) of the stress relieving notch on the behavior of the dynamic contact stresses were investigated. The influence of stress relieving notches positioned along the edge of the semi-infinite body on the dynamic contact stresses were also studied by changing the diameter (D) and the location (L) of the notch. A multi-speak-high speed camera with twelve sparks were used to take photographs of full field dynamic isochromatic fringe patterns. The contact singular stresses were found to be released significantly by the stress relief notches both along the indenter and the edge of the semi-infinite body. The optimal position and geometry of the stress relieving notches were obtained with the aid of limited experimental results.

• The Journal of Engineering Geology
• /
• v.4 no.2
• /
• pp.231-243
• /
• 1994

To better understand the fundamental problems of the true micro-damage in medium-grained granite under uniaxial compressive stress, micro-damage localization, initiation and propagation have been observed in a great detail in contact portion of two grains such as quartz and feldspar. For this purpose, new experimental system allowing us to observe the micro-damaging process continuously was developed. Earlier studies used the specimens of unloaded state and it is difficult to visualize stress-induced microcracks under unloading state. Thus, direct observation under loading state is very important for understanding the true micro-damage process. The results explain well the mechanism of micro-damage at two grains, and mechanics of the micro-damage is clarified well by Hertzian fracture mechanics.

• Journal of the Korean Society for Railway
• /
• v.12 no.3
• /
• pp.396-404
• /
• 2009

With developing the next generation high speed railway, there need to be plans to make sure of running safety though researchs on the crack and break of rail by rolling contact fatigue. Therefore, this study performed the parametric analysis effecting on the fatigue life of rail using simplified equations. It analyzed the internal stress of rail according to the track quality, train velocity, wheel radius, track stiffness, sleeper space, wheel load. For the more, via the finite element method, it analyzed shear force on the rail head which could be changed by the early length of crack, angle of crack and temperature. As a result, this study continued the main parameter effecting on the fatigue life of rail.

• Magazine of the Korea Concrete Institute
• /
• v.10 no.4
• /
• pp.145-151
• /
• 1998

The vertical tensile stress, ${\sigma}_y$, in the contact zone between the overlay (mortar layer) and substratum (base concrete) can be the main cause of the failure phenomenon of overlaid concrete structures. The development of tensile stress, ${\sigma}_y$, due to external rainy condition was analytically investigated using finite element method. Rainfall intensity $(n_R\;=\;1/a,\;t_R\;=\;10min,\;60min)$, thickness of overlay (do=1,2,4,10 cm) and overlay material (CM,ECM,EM) were the main variables in the analyses. An equation was suggested with which the development of vertical tensile stress, ${\sigma}_y$, in the rainy condition could be determined. Using this equation, it is possible to select proper material properties and overlay thicknesses to prevent failure in the contact zone due to thermally transient condition caused by rainfall.

• Proceedings of the KSR Conference
• /
• 2007.05a
• /
• pp.767-774
• /
• 2007

Even though a constant repeated load is applied, plastic deformation may cumulate. This kind of behavior is called ratcheting. Ratcheting may lead to cracks and finally to failure of the rail. Usually ratcheting occurs on high rails in curves. Ratcheting is influenced by residual stresses, wheel-rail contact stresses, thermal stresses due to wheel/rail rolling contact, shear strength of the rail, strain hardening behavior, etc. In this study, contact stresses and thermal stresses are examined. It is found their value is considerable compared to the maximum contact pressure.