• Title/Summary/Keyword: surface stresses

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Improvement of Chloride Induced Stress Corrosion Cracking Resistance of Welded 304L Stainless Steel by Ultrasonic Shot Peening

  • Hyunhak Cho;Young Ran Yoo;Young Sik Kim
    • Corrosion Science and Technology
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    • v.23 no.4
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    • pp.266-277
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    • 2024
  • Due to its good corrosion and heat resistance with excellent mechanical properties, 304L stainless steel is commonly used in the fabrication of spent nuclear fuel dry storage canisters. However, welds are sensitive to stress corrosion cracking (SCC) due to residual stress generation. Although SCC resistance can be improved by stress relieving the weld and changing the chloride environment, it is difficult to change corrosion environment for certain applications. Stress control in the weld can improve SCC resistance. Ultrasonic shot peening (USP) needs further research as compressive residual stresses and microstructure changes due to plastic deformation may play a role in improving SCC resistance. In this study, 304L stainless steel was welded to generate residual stresses and exposed to a chloride environment after USP treatment to improve SCC properties. Effects of USP on SCC resistance and crack growth of specimens with compressive residual stresses generated more than 1 mm from the surface were studied. In addition, correlations of compressive residual stress, grain size, intergranular corrosion properties, and pitting potential with crack propagation rate were determined and the improvement of SCC properties by USP was analyzed.

An Accurate and Efficient Analysis of Composite Plates Based on Enhanced First-order Shear Deformation Theory (개선된 일차전단변형이론을 이용한 복합재료 적층평판의 고정밀 해석)

  • Kim, Jun-Sik;Cho, Maeng-Hyo
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.19 no.4 s.74
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    • pp.407-418
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    • 2006
  • In this paper, an efficient yet accurate stress analysis based on the first-order shear deformation theory (FSDT) is presented. The transverse shear strain energy is modified via the mixed variational theorem, so that the shear correction factors are automatically involved in the formulation. In the mixed variational formulation, the transverse stresses are taken to be functions subject to variations. The transverse shear stresses based on an efficient higher order plate theory (EHOPT, Cho and Parmerter, 1993) are utilized and modified, while the transverse normal stress is assumed to be the third-order polynomial of thickness coordinates, which satisfies both zero transverse shear stresses and prescribed surface fractions in top and bottom surfaces. On the other hand, the displacements are assumed to be those of the FSDT Resulting strain energy expressions are referred to as an EFSDTM3D that stands for an enhanced first-order shear deformation theory based on the mixed formulation for three dimensional elasticity, The developed EFSDTM3D preserves the computational advantage of the classical FSDT while allowing for important local through-the-thickness variations of displacements and stresses through the recovery procedure that is based on the least square minimization of in-plane stresses. Comparisons of displacements and stresses of both laminated and sandwich plates using the present theory are made with the classical FSDT, three-dimensional exact solutions, and available data in the literature.

A Study on the Stress Distribution in Soil According to the Composition of the Soil Layer in Case of Surface Loading (지표면 재하시 토층구성에 따른 지중응력분포에 관한 연구)

  • Lim, Jong-Seok;Jung, Sang-Kyun;Ha, Hyuk
    • Proceedings of the Korean Geotechical Society Conference
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    • 2005.10a
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    • pp.510-516
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    • 2005
  • This research aims to verify the stress distribution in soil according to the composition of the soil layer in case of surface loading. For this purpose, loading tests with measurement of stresses in the soil on four kinds of layered model ground in laboratory were performed. Those are (1)homogeneous sand, (2)gravel underlain by sand, (3)sand underlain by clay and (4)gravel underlain by clay. Test results are compared and analysed for the compositions of the soil layers. based on the results obtained, it is found that the larger the difference of the strengths of upper and lower layer is, the smaller the stress in the soil in case of surface loading is.

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The Contact Fatigue Life Analysis of Transmission Gear considering Running-in (길들이기 과정을 고려한 변속기용 기어의 접촉피로 수명 해석)

  • Moon, Kil-Hwan;Lee, Sang-Don;Cho, Yong-Joo
    • Transactions of the Korean Society of Automotive Engineers
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    • v.15 no.5
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    • pp.133-138
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    • 2007
  • Surface pitting is a major failure mode for gears. The contact fatigue life analysis of transmission gear considering running-in process is presented in this paper. Surface roughness change of rolling test is used in a life analysis. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. The life analysis considering running-in is in good agreement with the experimental results.

Shape Finding and Stress Finding for Pneumatic Membrane Structures by Dynamic Relaxation Method (동적이완법에 의한 공기막구조물의 형태탐색과 응력해석)

  • 문창훈;이경수;배종효;최옥훈;한상을
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 1999.04a
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    • pp.268-275
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    • 1999
  • The purpose of this study is to propose the method of determining the initial pneumatic membrane structures surface and stresses and displacements. Tension structure such as pneumatic membrane structures is stabilized by their initial prestress and air pressure. The process to find initial structural overall shape of tension structures produced by initial prestress called shape finding. One of the most important factor for the design of membrane structures is to search initial smooth surface, because unlike steel or concrete building elements which resist loads in bending, all tension structure forces are carried within the surface by membrane stress. The result for initial surface of pneumatic membrane element and maximum displacement in large deformation in analysis is compared with well-known nonlinear numerical method such as Newton-raphson method and dynamic relaxation method

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A Study of Abrasive Flow Machining on EDMed Surfacs of Tool Steel (방전가공된 공구강표면의 연마재 유동가공에 관한 연구)

  • 최재찬;김창호;허관도
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1996.04a
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    • pp.8-13
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    • 1996
  • A relatively new non-traditional finishing process called Abrasive Flow Machining(AFM) is being used to deburr, polish and radius workpiece or produce compressive residual stresses by flowing an abrasive-laden viscoelastic compound across the surface to be machined. This paper presents the effects of AFM on surfaces of tool steel produced by EDM and W-EDM. Using AFM, white layer produced by EDM is erased almost equally and the amount of metal removal is significantly affected the initally machined surface condition of workpiece. The dimension of workiece is enlarged and its surface roughness is improved as AFM time is increased. The optimal AFM time can be established from the experimental results. It is considered that the grinding method lide AFM is useful to grind complex or slim geometry of workpiece even. Scanning Electron Microscopy(SEM) was used to study the surface characteristics of the workpiece before and after AFM.

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The Mechanics of Crack Formation Induced by Sliding on a Brittle Material (슬라이딩에 의해 취성재료에 발생하는 균열 성장에 관한 연구)

  • Kim, J.H.
    • Journal of the Korean Society for Precision Engineering
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    • v.12 no.11
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    • pp.36-44
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    • 1995
  • When sliding a hard cylinder along the surface of glass, periodic surface cracks appear on the flat surface due to tensile stresses induced by the slider. These cracks propagate into the substrate and will affect the fracture properties of a body. Crack spacings and the directions of crack propagation into glass were calculated numerically by applying the finite element method and linear elastic fracture mechanics. The calculated crack spacings were in the range of the experimental results. Stress intensity factors and crack extension angles depended on the radius of slider and the load, and from these two factors the possible directions of crack propagation were calculated. The calculated propagation directions were in good agreement with real crack propagation.

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Aircraft Wing Spar Cross-section Area Optimization with Response Surface Method (반응면 기법을 이용한 항공기 날개 스파 단면적의 최적화 연구)

  • Park, Chan-Woo
    • Journal of the Korean Society for Precision Engineering
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    • v.19 no.4
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    • pp.109-116
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    • 2002
  • The solution of the aircraft wing spar cross-section area optimization problem is obtained by the response surface method. The object function of the problem is wing total weight, design variables are spar cross-section areas, constraints are the conditions that the stresses at the each spar is less than the allowable stress. D-Optimal condition is utilized to obtain the experimental points to construct the response surfaces. D-Optimal experimental points are obtained by the commercial software "Deign-Expert". Response values for the object function and constraints for each experimental point are calculated by the NASTRAN. Response surfaces for object function and constraints are approximated from the response values by the least square method. The optimization solution is obtained by the DOT for the response surfaces of object function and constraints. The optimization results obtained from the response surface are compared with the results obtained by the NASTRAN SOL200.

Contact Fatigue Life Prediction of Automotive Wheel Bearing (차량용 휠베어링의 접촉 피로수명 예측에 관한 연구)

  • Lee, Sang-Don;Moon, Kil-Hwan;Cho, Yong-Joo
    • Transactions of the Korean Society of Automotive Engineers
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    • v.16 no.3
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    • pp.137-143
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    • 2008
  • For most bearings, it is a common requirement to have long durability. Especially wheel bearing fatigue life is the most important in automotive quality. The contact fatigue life analysis of automotive wheel bearing considering real raceway rough surface is presented in this paper. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. The life analysis considering real rough surface of wheel bearing raceway is in good agreement with the experimental results.

Effect of the Peening Intensity by Shot Peening (쇼트피닝 가공조건이 피닝강도에 미치는 영향)

  • Jeong, Seong-Gyun;Lee, Seung-Ho;Jeong, Seok-Ju
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.10
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    • pp.1590-1596
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    • 2001
  • The shot peening process is most often used to improve fatigue properties of metal parts. The single most critical parameter of the shot peening process is the shot ball itself. Without the correct quality media, all other shut peening parameters are extraneous and the desired fatigue improvement and consistency of improvement will not be achieved. Shot peening involves modifications of the surface and subsurface condition of a material that can be described by the change of the residual stresses, the hardness, and the surface roughness. This Paper Presents the shot peening to optimize the shot ball parameters. The effect of shot peening parameter on the surface roughness, surface hardness and residual stress are investigated.