• Title/Summary/Keyword: 기계적 응력 저감

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Experiments and Finite Element Analysis for the Estimation of Stress Relief in Welded Structures (반복 하중을 받는 용접 구조물의 잔류 응력 저감 파악을 위한 유한요소 해석 및 실험적 연구)

  • Yang, Yong-Sic;Kang, Joong-Kyoo;Lee, Jang-Hyun;Kim, Sung-Chan;Hwang, Se-Yum
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.3
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    • pp.238-245
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    • 2011
  • Welding inevitably introduces the residual stresses which affect the fatigue strength of the joint structure. The mitigation of fatigue strength depends on the residual stress magnitude and distribution. Stress relief analyses are of practical interest for all cyclic loaded welded structures, such as ships and offshore structures. In order to estimate the effects of relaxation of residual stresses in the welded structure, this paper presents a finite element analysis procedure and experimental results for the welded structure. Cruciform specimens joint by MAG welding have been tested to measure the released stress. Relieved welding residual stresses obtained by finite element analysis are compared with those measured by experiment.

Thermal Stress Estimation due to Temperature Difference in the Wall Thickness for Thinned Feedwater Heater Tube (감육된 급수가열기 튜브의 두께 방향 온도차이에 의해 발생하는 열응력 평가)

  • Dinh, Hong Bo;Yu, Jong Min;Yoon, Kee Bong
    • Journal of Energy Engineering
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    • v.28 no.3
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    • pp.1-9
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    • 2019
  • A major stress determining the remaining life of the tube in feedwater heater of fossil fuel power plant is hoop stress by the internal pressure. However, thermal stress due to temperature difference across the wall thickness also contributed to reduce the remaining life of the tube. Therefore, thermal loading must be considered even though the contribution of internal pressure loading to the stresses of the tube was known to be much higher than that of the thermal loading. In this study, thermal stress of the tubes in the de-superheating zone was estimated, which was generated due to the temperature difference across the tube thickness. Analytic equations were shown for determining the hoop stress and the radial stress of the tube with uniform thinning and for the temperature across the tube thickness. Accuracy and effectiveness of the analytic equations for the stresses were verified by comparing the results obtained by the analytic equations with those obtained from finite element analysis. Using finite element analysis, the stresses for eccentric thinning were also determined. The effect of heat transfer coefficient on thermal stress was investigated using series of finite element analyses with various values of heat transfer coefficient for both inner and outer surface of the tube. It was shown that the effect of heat transfer coefficient at outer surface was larger than that of heat transfer coefficient at inner surface on the thermal stress of the tube. Also, the hoop stress was larger than the radial stress for both cases of uniformly and eccentrically thinned tubes when the thermal loading was only considered without internal pressure loading.

Seismic behaviors of twin tunnel with flexible segment (Flexible Segment가 설치된 병렬터널의 지진시 동적거동)

  • Kwak, Chang-Won;Park, Inn-Joon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.17 no.6
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    • pp.695-702
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    • 2015
  • Recently, the improvement of mechanical and theoretical issues in geo-centrifuge test enhances the applicability and accuracy of the test. Geo-centrifuge test is appropriate to simulate the behaviors of underground structures like tunnel, since tunnel interacts with the soil and/or rock around it and the test can embody the in-situ stress conditions effectively. In this study, the seismic behaviors of twin tunnel were analyzed based on geo-centrifuge test. Flexible segment to mitigate seismic acceleration were implemented in the model with thin and thick thickness. Based on the test results, it was found that flexible segment can decrease the peak acceleration generally, however, thin flexible segment was not able to reduce peak acceleration in short-period seismic wave. Thick flexible segment was more effective in case of high bedrock acceleration condition. Additionally, 3-dimensional numerical analysis was performed to verify the characteristics of seismic behavior and the effect of flexible segment. Consequently, the numerical analysis result showed good agreement with the test result.

Numerical Analysis on Stress Distribution of Vertebra and Stability of Intervertebral Fusion Cage with Change of Spike Shape (척추체간 유합케이지의 스파이크형상 변화에 따른 척추체의 응력분포 및 케이지의 안정성에 대한 수치적 해석)

  • 심해영;김철생;오재윤
    • Journal of Biomedical Engineering Research
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    • v.25 no.5
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    • pp.361-367
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    • 2004
  • The axial compressive strength, relative 3-D stability and osteoconductive shape design of an intervertebral fusion cage are important biomechanical factors for successful intervertebral fusion. Changes in the stress distribution of the vertebral end plate and in cage stability due to changes in the spike shape of a newly contrived box-shaped fusion cage are investigated. In this investigation, the initial contact of the cage's spikes with the end plate and the penetration of the cage's spikes into the end plate are considered. The finite element analysis is conducted to study the effects of the cage's spike height, tip width and angle on the stress distribution of the vertebral end plate, and the micromigration of the cage in the A-P direction. The stress distribution in the end plate is examined when a normal load of 1700N is applied to the vertebra after inserting 2 cages. The micromigration of the cage is examined when a pull out load of l00N is applied in the A-P direction. The analysis results reveal that the spike tip width significantly influences the stress concentration in the end plate, but the spike height and angle do not significantly influence the stress distribution in the end plate touching the cage's spikes. In addition, the analysis results show that the micromigration of the cage can be reduced by adjusting the spike angle and spike arrangement in the A-P direction. This study proposes the optimal shape of an intervertebral fusion cage, which promotes bone fusion, reduces the stress concentration in a vertebral end plate, and increases mechanical stability.

A Study on the Design and Experiment for the Profile of Lower-Noise Gear Tooth (저소음 치형의 설계 및 실험에 관한 연구)

  • 김호룡;안승준
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.1
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    • pp.1-10
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    • 1993
  • A design method of gear tooth profile which can reduce the noise of gear is studied. The tooth profile is generated by combining involute and cycloid tooth curves in which the involute tooth profile is near the pitch point and cycloid tooth profile at the addendum and the dedendum. Considering parameters which have an influence on the reduction of gear noise and building up a design conditions for the noise reduction of gear, the lower-noise combined gear tooth profile is designed. For the check of noise reduction of the combined gear profile, two pairs of combined profile gear, two pairs of involute gear, and a pair of cycloid gear were manufactured by the NC Wire Cutting Machine, and the experiment for measuring of gear noise was carried out on each pair. The noise reduction of the combined profile gear was obtained.

A Numerical Study on the Rock Fragmentation by TBM Cutter Penetration (TBM 커터 관입에 의한 암석 파쇄의 수치해석적 연구)

  • 백승한;문현구
    • Tunnel and Underground Space
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    • v.13 no.6
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    • pp.444-454
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    • 2003
  • Rock fragmentation technique by cutter penetration has widely been used in the mechanical tunnel excavation. Microcracks propagate and interact because of locally concentrated high stress induced by cutter penetration. which is caused by heterogeneity of rocks. In this study Weibull distribution function and degradation index are used to consider the strength heterogeneity of a rock and the degradation of rock properties after failure. Through the numerical analyses, it is shown that the lateral pressure has an important influence on the rock fragmentation. In the single cutter penetration, large chips are formed as lateral pressure increase. The cutter spacing is also an important factor that affects the rock fragmentation in the double cutter penetration. The fragmentation efficiency of the double cutter penetration is better when cutter spacing is 70 mm than 40 mm and 100 mm. From the results, it is expected that this study can be applied to a TBM tunnel design by understanding of chipping process and mechanism of rock due to cutter penetration.

Evaluation of Fatigue Life of Electro-Mechanical Actuator for Front Wheel Steering (전륜 조향용 전기식 작동기 피로수명 평가)

  • Young-Cheol Kim;Hyun-gi Kim;Dong-Hyeop Kim;Sang-Woo Kim
    • Journal of Aerospace System Engineering
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    • v.17 no.4
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    • pp.126-132
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    • 2023
  • Recently, the consideration of eco-friendly technology to reduce greenhouse gas is being emphasized in the aviation field. Various studies for applying electro-mechanical actuators that control mechanical linear and rotational movements using electricity as the primary power source are in progress. In this study, the fatigue analysis of the electro-mechanical actuator for the front wheel steering of a single aisle aircraft was carried out. A unit load stress table was constructed for the vulnerable part selected through structural analysis, and the representative stress for each load profile was calculated using the unit load stress table constructed for the vulnerable part. Then, individual profiles of representative stress group were extracted from continuous load profiles by applying the rainflow counting method. The damage of each profile was calculated by applying the S-N diagram. Finally, the total damage in the vulnerable parts was calculated by the linear cumulative damage law, and the fatigue life of the electro-mechanical actuator for the front wheel steering of a single aisle aircraft was evaluated.

Structural Stability, Weathering and Conservation Method of Granite Standing Sculptured Buddha at Hwangsang-dong, Kumi (구미 황상동 마애여래입상의 구조적 안정성, 풍화 및 보존방안)

  • Lee, Chan Hee;Choi, Suck Won;Suh, Mancheol;Chae, Sang Jeong
    • Journal of Conservation Science
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    • v.9 no.1
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    • pp.21-32
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    • 2000
  • Rock composition of the Hwangsang-dong Granite Standing Sculptured Buddha (Treasure No. 1122) in the Kumi City is biotite-hornblende granodiorite which consists of about 30 pieces of individual rock blocks of same compositions. However, the cap rocks is pebble-bearing coarse sandstone. Rock blocks of the Standing Buddha and surrounding out crops occur well developed several joint systems of $N25^{\circ}$ to $45^{\circ}W$ strike and nearly vertical (70 to $85^{\circ}SE$) dipping. Rock blocks of the Standing Buddha showed vertical, horizontal and oblique joints, and those blocks are well supported by individual blocks. However, the junction part of the blocks are under dangerous situation due 10 seriously mechanical and chemical weathering. Host rock of the Standing Buddha belongs to the HW grade, therefore mostly rock-forming minerals of the granodiorite Standing Buddha altered with clay and iron hydroxide minerals by mineralogical and chemical weathering. Near surface of the Standing Buddha show spore and mycelium of green algaes, and a joint plane alive with weeds. We suggest that if structural stability for the Standing Buddha remove essentially a unstable rock blocks from the main body, and the main body necessitate supporting by rock bolting method because of repeated unstability and minimizing stress to the rock blocks. For the opened joint planes, fractured surface and alive weeds will attempt to fill in a petro-epoxy, petro-filler and biochemical treatments for the algaes, and ground water curtain and wall seems to be necessary for water flow and diminishing humidity of the Standing Buddha.

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Behavior of Rapidly Expansion Materials for Maintenance Railroad Bed Subjected to Cyclic Loading (반복하중을 받는 철도노반 보수용 급속 팽창재료의 거동)

  • Lee, Jundae;Shin, Eunchul
    • Journal of the Korean GEO-environmental Society
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    • v.10 no.2
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    • pp.45-50
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    • 2009
  • The differential settlement may be generated by the variation of stresses caused by the soft ground or ground water. The cracks are usually created when the structures are leaned or deformed due to the differential settlement. A grouting method has been mainly used till now to improve the bearing capacity of the ground when the foundation of the structure is deformed by differential settlements. However, when this method is used, it takes too long time to obtain the required strength and the period of the reinforcement effect is not long enough. The advantage of GPCON injection method is to have good mechanical properties and durability, and easy construction. In addition, the GPCON method rapidly fills up the void in soils by injecting some materials into underground and also obtain the increase of bearing and shearing forces due to the expansion. In this paper the restoration capability of the foundation settlement of railway and subway subjected to cyclic loading is analytically and experimentally evaluated using the high density rapidly expansion GPCON in order to investigate the types of deformations and vibrational characteristics.

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Die Stress Reduction Design and Mechanical Properties Analysis of Warm Forging Process for the Application of Warm-Closed Forging of Automative Steering Unit Yoke (자동차 조향장치 부품 요크의 온간 밀폐 단조 적용을 위한 금형 응력 저감 설계 및 온간 단조품의 기계적 특성 분석)

  • Seong, S.G.;Kim, K.H.;Lee, Y.S.;Lee, S.Y.;Yoon, E.Y.
    • Transactions of Materials Processing
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    • v.31 no.2
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    • pp.51-56
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    • 2022
  • In this study, finite element analyses were performed by applying a stress ring and split die design to relieve the tensile stress acting on the die due to high surface pressure during warm-closed forging. The applied material was a yield-ratio-control-steel (YRCS). It was used without quenching or tempering after forging. In the case of stress rings design, the number of stress rings and the tolerance for shrink fit were different. Vertical and horizontal splits were applied for insert die split design. Case 5 die with three stress rings, 0.2 % shrink fit tolerance, and vertical split was selected as an effective die design for tensile stress reduction. Based on die stress reduction analyses, Case 5 die for warm-closed forging was produced and smooth forgeability was secured, making it possible to manufacture forging product of yoke with the required geometry. In addition, controlled cooling using warm forging heat was applied to secure mechanical properties of yokes. When oil cooling was used for direct controlled cooling after warm-closed forging, a relatively uniform Rockwell hardness distribution and high mechanical properties could be obtained.