• Title, Summary, Keyword: Critical stress ratio

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Critical Stress for a Crack in Orthotropic Material under Biaxial Loading (2축하중을 받는 직교이방성재료 내 균열의 임계응력)

  • Lim, Won-Kyun;Cho, Hyoung-Seok
    • Proceedings of the KSME Conference
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    • pp.37-42
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    • 2003
  • The problem of an orthotropic material with a central crack is studied. The material is subjected to uniform biaxial loading along its boundary. The normal stress ratio theory is applied to predict fracture strength behavior in cracked orthotropic material. The dependence of the critical stress with respect to the biaxial loading and the crack orientation is discussed. Our analysis shows significant effects of biaxial loading on the critical stress. The additional tenn in the asymptotic expansion of the crack tip stress field appears to provide more accurate critical stress prediction.

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Fatigue Crack Growth Equation considered the Effect of Stress Ratio (응력비의 영향을 고려한 표면피로균열의 균열성장식)

  • 강용구;김대석
    • Journal of Ocean Engineering and Technology
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    • v.12 no.1
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    • pp.39-49
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    • 1998
  • In this work, fatigue tests by axial loading were carried out to investigate the effect of stress ratio on the growth behaviors of surface fatigue crack for SM45C steel and Al 2024-T4 alloy. The growth behaviors of surface crack have been monitored during fatigue process by measuring system attached CCTV and monitor. When the growth rates of surface crack were investigate by the concept of LEFM based on Newman-Raju's .DELTA.K, the dependence of stress ratio appears both SM45C steel and Al 2024-T4 alloy. Therefore, modified stress intensity factor range, .DELTA.K' [=(1+R)/sup n/.DELTA.K] are intorduced to eliminate the dependence of stress ratio. Using .DELTA.K', it is found that the dependence of stress ratio disappears both SM45C steel and Al 2024-T4 alloy.

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Study of reinforcement effect of sandwich plate structure according to core shape (샌드위치형 판 구조물의 코어형상에 따른 보강효과에 관한 연구)

  • 한근조;안성찬;심재준;김진영
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.740-743
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    • 2001
  • Sandwich structure is widely used in various fields of industry due to its excellent strength and stiffness compared with weight. We studied the sandwich structure which has honeycomb core type. We are concerned about its buckling and bending stress with respect to its side length, thickness and the height ratio of its unit core. After obtaining the buckling critical load of unit core, we applied it to the sandwich structure to observe the bending behavior. When we compared the buckling with bending stress under buckling critical load, we observed that models of which length ratio of unit honeycomb core, A, is lower than 0.04 and the thickness of core, t, is thicker than 0.09 mm, is subjected to the ultimate stress by bending before buckling.

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Effect of PWHT and stress ratio on fatigue behavior of welded joints in steel (강용접부의 피로거동에 미치는 용접후열처리 및 응력비의 영향)

  • 김경수;임재규;정세희
    • Journal of Welding and Joining
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    • v.5 no.3
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    • pp.53-61
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    • 1987
  • Post weld heat treatment(PWHT) is usually carried out to remove the residual stress and to improve the microstructure and mechanical properties of welded joints. By the way, welding structure transformed owing to PWHT and reheating for repair loads the random cycles fatigue as offshore welding structure of constant low cycle fatigue as pressure vessel, and then, pre-existing flaws or cracks exist in a structural component and those cracks grow under cyclic loading. Therefore, the effects of PWHT and stress ratio on fatigue crack growth behaviors were studied on the three regions such as HAZ, sub-critical HAZ and deposit metal of welded joints in SM53 steel. Fatigue crack growth behavior of as-weld depended on microstructure and fatigue crack growth rate of HAZ was the lowest at eac region, but after PWHT it was somewhat higher than that of as-wel. In case of applying the stress($10kg/mm^2$) during PWHT, fatigue crack growth resistance tended to increase in the overall range of .DELTA.K.

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Prediction of the Critical Stress for the Inclined Crack in Orthotropic Materials under Biaxial load (2축하중을 받는 직교이방성 경사균열에서 임계응력의 예측)

  • Lim, Won-Kyun;Cho, Hyung-Suk;Jeong, Woo-Kil;Lee, Ill-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.11
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    • pp.1384-1391
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    • 2006
  • The problem of an infinite anisotropic material with a crack inclined with respect to the principal material axes is analyzed. The material is subjected to uniform biaxial load along its boundary. It is assumed that the material is homogeneous, but anisotropic. By considering the effect of the horizontal load, the distribution of stresses at the crack tip is analyzed. The problem of predicting critical stress in anisotropic solids which is a subject of considerable practical importance is examined and the effect of load biaxiality is made explicitly. The present results based on the normal stress ratio theory show significant effects of biaxial load, crack inclination angle and fiber orientation on the critical stress. The analysis is performed for a wide range of the crack angles and biaxial loads.

The Effect of the Area Ratio and Change of Location on the Buckling Stress of Two Rectangular Plates Spot-welded (면적비와 위치변화가 점용접된 두 사각평판의 좌굴응력에 미치는 영향)

  • Han, Geun-Jo;An, Seong-Chan;Sim, Jae-Jun;Lee, Hyeon-Cheol;Jang, Hwal-Su
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.12
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    • pp.54-59
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    • 2001
  • The stability of a thin plate structure is very crucial problem which results buckling. Because the buckling strength of thin plates is lower than the yield strength of the material, reinforcement plate must be used to increase the buckling strength. And, in this case, spot welding is commonly used, however, the spot welded joints are practically designed by experimental decisions, so it is Inefficient and has the risks of buckling demolition. In this study, two parameters, such as the area ratio and the distance ratio of spot welding which have influence on the buckling strength, should be chosen. Under compressive and shearing load, the effect of two parameters on the critical stress is discussed.

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The study of bending and buckling behavior of sandwich structure according to design parameter variation (설계변수 변화에 따른 샌드위치 구조물의 굽힘 및 좌굴 거동에 관한 연구)

  • 한근조;안성찬;안성찬;김진영
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.841-844
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    • 1997
  • Sandwich structure is widely used in various fields of industry due to its excellent strength and stiffness compared with weight. We studied the buckling and bending behavior with respect to the variation of design parameters such as length, height, and thickness of honeycomb sandwich core. We found that as the density and the thickness of core become higher, the value of critical bucking load increased significantly. We found that the effect of bending stress due to critical buckling load resulted in high bending stress and the value of bending stress decreased in half according to the increase of length of core. The effect by bending stress is dominant above the portion of the intersection line between bending stress and the effect of buckling is dominant below the potion of it. We could get proper thickness ratio and density of core according to applied load conditions.

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Molecular dynamics study of Al solute-dislocation interactions in Mg alloys

  • Shen, Luming
    • Interaction and multiscale mechanics
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    • v.6 no.2
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    • pp.127-136
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    • 2013
  • In this study, atomistic simulations are performed to study the effect of Al solute on the behaviour of edge dislocation in Mg alloys. After the dissociation of an Mg basal edge dislocation into two Shockley partials using molecular mechanics, the interaction between the dislocation and Al solute at different temperatures is studied using molecular dynamics. It appears from the simulations that the critical shear stress increases with the Al solute concentration. Comparing with the solute effect at T = 0 K, however, the critical shear stress at a finite temperature is lower since the kinetic energy of the atoms can help the dislocation conquer the energy barriers created by the Al atoms. The velocity of the edge dislocation decreases as the Al concentration increases when the external shear stress is relatively small regardless of temperature. The Al concentration effect on the dislocation velocity is not significant at very high shear stress level when the solute concentration is below 4.0 at%. Drag coefficient B increases with the Al concentration when the stress to temperature ratio is below 0.3 MPa/K, although the effect is more significant at low temperatures.

Stress Distribution in Concrete Pavements under Multi-Axle Vehicle Loads Obtained Using Transformed Field Domain Analysis (변환영역 해석법을 통한 콘크리트 도로 포장의 다축 차량 하중에 대한 응력 분포 분석)

  • Kim, Seong-Min;Shim, Jae-Soo;Park, Hee-Beom
    • Journal of the Korea Concrete Institute
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    • v.18 no.5
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    • pp.695-702
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    • 2006
  • The stress distribution and the critical stresses in concrete pavements were analyzed using formulations in the transformed field domains when dual-wheel single-, tandem-, and tridem-axle loads were applied. First the accuracy of the transformed field domain analysis results was verified by comparing with the finite element analysis results. Then, the stress distribution along the longitudinal and transverse directions was investigated, and the effects of slab thickness, concrete elastic modulus, and foundation stiffness on the stress distribution were studied. The effect of the tire contact pressure related to the tire print area was also studied, and the location of the critical stress occurrence in concrete pavements was finally investigated. From this study, it was found that the critical concrete stress due to multi-axle loads became larger as the concrete elastic modulus increased, the slab thickness increased, and the foundation stiffness decreased. The number of axles did not tend to affect the critical stress ratio except for a small foundation stiffness value with which the critical stress ratio became significantly larger as the number of axles increased. The critical stress location in the transverse direction tended to move into the interior as the tire contact pressure increased, the concrete elastic modulus increased, the slab thickness increased, and the foundation stiffness decreased. The critical stress location in the longitudinal direction was under the axle for single- and tandem-axle loads, but for tridem-axle loads, it tended to move under the middle axle from the outer axles as the concrete elastic modulus and/or slab thickness increased and the foundation stiffness decreased.

Relationship between Concrete Pavement Stresses under Multi-Axle Interior and Edge Loads (중앙부와 모서리부 다축 차량 하중에 의한 콘크리트 도로포장의 응력 상관관계)

  • Kim Seong-Min;Cho Byoung-Hooi;Ryu Sung-Woo
    • International Journal of Highway Engineering
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    • v.8 no.3
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    • pp.143-153
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    • 2006
  • The differences in the stress distribution and the critical stresses in concrete pavement systems were analyzed when the dual-wheel single-, tandem-, and tridem-axle loads were applied at the interior and the edge of the pavement. The effects of the concrete elastic modulus, slab thickness, foundation stiffness, and tire contact pressure were investigated. The stresses under the interior loads were calculated using the transformed field domain analysis and stresses under the edge loads were obtained using the finite element method. The critical stresses under the interior and the edge loads were compared with respect to various parameters and the equations to predict the ratio between the stresses under the edge and the interior loads were developed and verified. From this study, it was found that the trends of the changes in the critical concrete stresses under the interior and the edge loads were very similar and the critical stress locations under those loads were identical. The critical stress ratio, which was obtained by dividing the critical stress under the edge loads into that under the interior loads, decreased with increasing the number of axles. That ratio became larger as the concrete elastic modulus increased, the slab thickness increased, the foundation stiffness decreased, and the tire contact pressure increased.

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