• Tribology and Lubricants
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• 제18권3호
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• pp.219-227
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• 2002

A linear elastic fracture mechanics analysis of double subsurface cracks propagation in a half-space subjected to moving thermomechanical surface traction was performed using the finite element method. The effect of frictional heat at the sliding surface on the crack growth behavior is analyzed in terms of the thermal load and peclet number. The crack propagation direction is predicted in light of the magnitudes of the maximum shear and tensile stress intensity factor ranges. When moving thermomechanical surface traction exists, subsurface horizontal cracks are propagation in-plane crack growth rate at the beginning but they are propagation out-of-plane crack growth rate by the frictional heat which is occurrence by the repeated sliding contact.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.1151-1156
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• 2000

Temperature rise and restraint condition in mass concrete structures may induce the cracks at early ages. The method to prevent the cracks induced by heat of hydration has become the major concern in mass concrete structure. Therefore, the purpose of this study is to propose a method to control heat of hydration in mass concrete structures by using cryogenic liquefied nitrogen. The method in this study was applied to actual mass concrete structure to prevent the occurrence of thermal cracks at early ages. The surface observation of structure during more than one month shows that there are seldom cracks. This represent that the method in the study is effective in the control of heat of hydration.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.50-58
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• 2000

A linear elastic fracture mechanics analysis of multiful subsurface cracks propagation in a half-space subjected to moving thermomechanical surface traction was peformed using the finite element method. The effect of frictional heat at the sliding surface on the crack growth behavior is analyzed in terms of the thermal load and peclet number. The crack propagation direction is predicted in light of the magnitudes of the maximum shear and tensile stress intensity factor ranges. When moving thermomechanical surface traction exists, subsurface horizontal cracks are propagation in-plane crack growth rate at the beginning but they are propagation out-of-plane crack growth rate by the frictional heat which is occurrence by the repeated sliding contact.

• 대한기계학회논문집A
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• 제25권7호
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• pp.1139-1146
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• 2001

The reactor pressure vessel(RPV) is usually cladded with stainless steel to prevent corrosion and radiation embrittlement, and a number of subclad cracks have been found during an in-service-inspection. These subclad cracks should be assured for a safe operation under normal conditions and faulted conditions such as pressurized thermal shock(PTS). Currently available integrity assessment procedure for an RPV, ASME Code Sec. XI, are built on the basis of linear fracture mechanics (LEFM). In PTS condition, however, thermal stress and mechanical stress give rise to high tensile stress at the cladding and elastic-plastic behavior is expected in this area. Therfore, ASME Code Sec. XI is overly conservative in assessing the structural integrity under PTS condition. In this paper, the fracture parameter (stress intensity factor, K, and RT(sub)NDT) from elastic analysis using ASME Sec. XI and finite element method were validated against 3-D elastic-plastic finite element analyses. The difference between elastic and elastic-plastic analysis became significant with increasing crack depth. Therfore, it is recommended to perform elastic-plastic analysis for the accurate assessment of subclad cracks under TPS which causes plastic deformation at the cladding.

• 한국구조물진단유지관리공학회 논문집
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• 제12권6호
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• pp.164-172
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• 2008

초기 재령의 매스콘크리트는 양생과정에서 높은 온도를 유발한다. 수화열 저감 기법 중 내부구속이 지배적인 구조물에서 단면의 내외부 온도차를 관리하는 방식은 그 활용도가 매우 높다. 그러나 수화 균열을 예방하기위해 열경사를 조절하는 현재의 제한적인 방법은 콘크리트 중심과 표면 사이에 미세하거나 거대한 균열을 유발할 수 있다. 특히 냉각파이프를 이용하는 방법은 온도의 상승시에는 적용될 수 있지만, 내외부 온도차이가 심한 온도하강시의 대책으로는 적합하지 않다. 따라서 이 문제에 대한 해결방안으로 가열파이프를 동시에 사용하는 모델을 제안하여 유한요소법으로 해석하였다. 해석 결과, 제안된 냉각파이프와 가열파이프를 동시에 사용하는 방법이 열경사조절에 가장 효과적이며 이를 통해 온도균열을 효과적으로 제어할 수 있을 것으로 판단된다.

• Computers and Concrete
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• 제2권3호
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• pp.189-202
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• 2005

This paper presents an analysis of some experimental results concerning micro-structural tests, permeability measurements and strain-stress tests of four types of High-Performance Concrete, exposed to elevated temperatures (up to $700^{\circ}C$). These experimental results, obtained within the "HITECO" research programme are discussed and interpreted in the context of a recently developed mathematical model of hygro-thermal behaviour and degradation of concrete at high temperature, which is briefly presented in the Part 2 paper (Gawin, et al. 2005). Correlations between concrete permeability and porosity micro-structure, as well as between damage and cracks' volume, are found. An approximate decomposition of the thermally induced material damage into two parts, a chemical one related to cement dehydration process, and a thermal one due to micro-cracks' development caused by thermal strains at micro- and meso-scale, is performed. Constitutive relationships describing influence of temperature and material damage upon its intrinsic permeability at high temperature for 4 types of HPC are deduced. In the Part II of this paper (Gawin, et al. 2005) effect of two different damage-permeability coupling formulations on the results of computer simulations concerning hygro-thermo-mechanical performance of concrete wall during standard fire, is numerically analysed.

• 한국해양공학회지
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• 제13권3호통권33호
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• pp.57-67
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• 1999

Welding is widely applicable and reliable process and is mainly adopted for fabricating heavy structures. Recently, weld metal transverse cracks in butt and fillet weld joint is a serious problem, and they must be eliminated for improving weld joint reliability. The weld metal transverse crack susceptibility of butt and fillet joint was carried out by cantilever type tensile crack testing jig and CTS test. In this view of point, this study investigated the potential factors for weld metal transverse crack. The main results obtained were as follows: 1. The content o fdiffusible hydrogen in weld metal played an important role for weld metal transverse cracks. 2. From cantilever type tensile crack tests, it was pointed out that the higher the diffusible hydrogen content and tensile restraint, the more susceptible to weld metal transverse craking. 3. The TSN(thermal severity number) and diffusible hydrogen were important factors for determining weld metal transverse cracks in fillet weld joints.

• 대한기계학회논문집A
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• 제31권7호
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• pp.756-763
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• 2007

The majority of catastrophic wheel failures are caused by surface opening fatigue cracks either in the wheel tread or wheel flange areas. The inclined cracks at railway wheel tread are initiated and the cracks are caused by wheel damage-spatting after 60,000 km running. Because the failured railway wheel is reprofiled before regular wheel reprofiling, the maintenance cost for the railway wheel is increased. Therefore, it is necessary to analyze the mechanism for initiation of crack. In the present paper, the combined effect on railway wheels of a periodically varying contact pressure and an intermittent thermal braking loading is investigated. To analyze damage cause for railway wheels, the measurements for replication of wheel surface and the effect of braking application in field test are carried out. The result shows that the damages in railway wheel tread are due to combination of thermal loading and ratcheting.

• 터널과지하공간
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• 제7권3호
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• pp.238-245
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• 1997

A transient pulse methos has been used to measure the permeability of Pocheon granite pre-heated from $25^{\circ}C$ to $600^{\circ}C$ at effective pressure up to 32MPa. The permeability of whole rock ranged from 0.72 $\mu$d at 10MPa to 0.20 $\mu$d at 32MPa. The permeability of rock heated to $600^{\circ}C$ ranged from 18.07$\mu$d at 10MPa to 6.39$\mu$d at 32MPa. Confining pressure has greater effects on the rocks thermally treated to lower thermal-cycle temperatures than on the higher thermally treated rocks. The increase of permeability is most pronounced between 40$0^{\circ}C$ and $600^{\circ}C$. Below 40$0^{\circ}C$, permeability increase is expected to be associated with the formation of new cracks and widening of preexisting cracks, whereas above 40$0^{\circ}C$, permeability increase is expected to reflect widening of cracks. Using the equivalent channel model, author shows that the exponent n in the relationship relating the permebility(k) to porosity($\phi$) by k∝$$\phi$^n$ falls in the range 2.7$\leq$n$\leq$3.0.

• 한국철도학회논문집
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• 제9권6호
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• pp.657-663
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• 2006

By measuring concrete temperature and strains of concrete and reinforcing bars throughout gages embedded and also by observing the crack occurrence, this study aims at the characteristics of structural behavior of subway wall structure in associate with concrete ages. The length of 23.5m, thickness of 2.0m of real subway custody line was selected as a representative structure and 7 thermocouples and 6 strain gages were installed to measure the behavior of wall structure. The results were compared and verified with analytical results using MIDAS in order to show their usefulness. It was found that only attachment of strain gages on the surface of reinforcing bars can figure out the timing of crack occurrence and hydration heat program is useful to estimate comparatively exact magnitudes of temperature. Since estimated time of crack occurrence throughout thermal stress analysis depends on the period of transferred thermal stress from concrete to reinforcing bars, however, cracks from naked eyes were identified later than analytical results. Cracks were observed first at the center of wall line and then to the end of line symmetrically.