• 대한기계학회논문집A
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• 제28권5호
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• pp.524-531
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• 2004

To investigate relevance of the definition of the reference stress to estimate J and $C^{*}$ for surface crack problems, this paper compares FE J and $C^{*}$ results for surface cracked pipes with those estimated according to the reference stress approach using various definitions of the reference stress. Pipes with part circumferential inner surface crack and finite internal axial crack are considered, subject to internal pressure and global bending. The crack depth and aspect ratio are systematically varied. The reference stress is defined in four different ways using (i) the local limit load, (ii) the global limit load, (iii) the global limit load determined from the FE limit analysis, and (iv) the optimized reference load. It is found that the reference stress based on the local limit load gives overall excessively conservative estimates of J and $^{*}$. Use of the global limit load clearly reduces the conservatism, compared to that of the local limit load, although it can provide sometimes non-conservative estimates of J and $^{*}$. The use of the FE global limit load gives overall non-conservative estimates of J and $^{*}$. The reference stress based on the optimised reference load gives overall accurate estimates of J and $^{*}$, compared to other definitions of the reference stress. Based on the present finding, general guidance on the choice of the reference stress for surface crack problems is given.

• 한국철도학회논문집
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• 제10권5호
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• pp.546-553
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• 2007

본 연구는 압입축에 프레팅이 발생할 경우 프레팅 마모에 의한 접촉형상의 변화가 접촉응력의 분포, 균열발생 위치에 미치는 영향을 분석하고자 하였다. 압입축의 프레팅 피로실험시 측정한 접촉면의 프로파일을 이용하여 유한요소 해석을 수행하고 피로 사이클별 마모형상 변화에 따른 접촉면의 응력 변화를 분석하였다. 접촉면의 응력 해석결과를 이용하여 프레팅 피로손상 파라미터와 다축 피로이론를 적용하여 마모에 따른 균열발생위치의 변화를 해석하고 실험과 비교, 분석하였다. 프레팅 마모에 의해 접촉 끝단의 응력집중은 초기에 급격하게 감소하며, 마모가 진행될수록 응력집중의 위치는 접촉끝단에서 안쪽으로 이동한다. 따라서 프레팅 마모에 의한 접촉응력의 변화가 균열발생 위치의 변차와 다중균열발생의 주요원인임을 명확히 하였다.

• 문화기술의 융합
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• 제10권3호
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• pp.845-849
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• 2024

현재 도시철도 레일의 노후화로 인한 레일표면결함이 증가하고 있으나 국가에서 제정된 궤도성능평가에 관한 세부지침에서 레일표면손상을 기술자의 육안, 간단한 측정 도구로 점검을 수행하는 실정이다. 주기적인 선로순회작업 및 육안점검을 통해 레일표면의 결함을 발견하는 것은 매우 중요하다. 그러나 점검자의 주관적 판단에 의해 레일표면의 결함의 경중을 평가하는 것은 레일 내부의 손상을 예측하기에 상당한 제약이 따른다. 본 연구에서는 레일표면손상에 따른 레일내부 균열특성에 관한 연구로서 현장측정에서는 레일표면 손상개소를 선정하여 가속구간 및 제동구간의 노후레일 시료를 채취하여 레일표면손상 상태를 평가하고자 전자주사현미경(SEM)을 이용하여 균열특성을 분석하였다. 분석결과, 주행 중인 열차로 인해 발생하는 균열 메커니즘과 레일표면방향으로 올라오는 각도로 균열이 발생하는 가속구간의 균열특성을 실험적으로 입증하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 봄 학술발표회 논문집
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• pp.309-316
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• 2004

A probabilistic structural integrity assessment is performed for a reactor pressure vessel under PTS(Pressurized Thermal Shock). A semi-elliptical finite axial crack is assumed to he in the beltline region(either base metal or weld meta)1 of the reactor vessel inside surface. The selected random variables are initial crack depth, neutron fluence on the vessel inside surface, copper, nickel, and phosphorus content of the vessel material, and RT/sub NDT/. The probabilities of crack initiation or vessel failure where the crack is propagated through vessel wall are calculated. The probabilities obtained with random crack size are compared to these obtained with deterministic us. Since the failure function cannot to explicitly by selected by selected random variables, Monte Carlo Simulation is applied to perform probabilistic analysis The influence of the amount of neutron fluence is also examined to assess the structural reliability for vessel life time.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.659-662
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• 1999

Ultrasonic pulse velocity method is employed for evaluation of crack depth in concrete structures. Due to the heterogeneous nature of concrete and the indirect transmission arrangement for the transit time measurement through the surface-opening cracks in concrete structures, ultrasonic pulse velocity has so many variations as crack depths and transmission lengths vary. In this study, ultrasonic pulse velocity method is investigated to evaluate the surface-opening crack depth of concrete slabs, reinforced concrete slabs, reinforced concrete flexural members. the resent study gives a modified method for deminishing errors in transit time measurements and show limitations to the evaluation of crack depth in reinforced concrete structures.

• Journal of Advanced Marine Engineering and Technology
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• 제30권6호
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• pp.731-739
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• 2006

Corrosion and lassitude are very important in the metal construction Currently, the shot peening is used much for removing the defect on the surface, improving the fatigue strength on surface. In this study. the influence of shot peening to the corrosion property were investigated in 3.5% NaCl, 10% HNO3 + 3% HF. 6% FeC13. The immersion test was performed on two kind of specimen(Removed corrosion product. RCP and Continuous immersed specimen: CIS). The immersion periods was 3600hours. Corrosion potential. weight loss, and fatigue crack growth characteristics were investigated. The result, shot peening in corrosion potential showed stable potential. Also, shot peening displayed small Weight loss than un peening. And Fatigue crack resistivity of shot peening in corrosion solution's fatigue crack appeared greatly than un peening.

• 비파괴검사학회지
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• 제31권1호
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• pp.1-10
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• 2011

Nonlinear harmonic waves generated at cracked interfaces are investigated both experimentally and theoretically. A compact tension specimen is fabricated and the amplitude of transmitted wave is analyzed as a function of position along the fatigued crack surface. In order to measure as many nonlinear harmonic components as possible a broadband Lithium Niobate ($LiNbO_3$) transducers are employed together with a calibration technique for making absolute amplitude measurements with fluid-coupled receiving transducers. Cracked interfaces are shown to generate high acoustic nonlinearities which are manifested as harmonies in the power spectrum of the received signal. The first subharmonic (f/2) and the second harmonic (2f) waves are found to be dominant nonlinear components for an incident toneburst signal of frequency f. To explain the observed nonlinear behavior a partially closed crack is modeled by planar half interfaces that can account for crack parameters such as crack opening displacement and crack surface conditions. The simulation results show reasonable agreements with the experimental results.

• 한국정밀공학회지
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• 제18권11호
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• pp.174-178
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• 2001

Chrome-molybden steel or chrome steel for machine structures has been shown to excellent hardenability adding boron of a small amount at low carbon steel. These days, boron steel has been used high strength bolt and wear resistant components of construction equipment. SEM results showed classical fatigue fractures, consist with surface crack initiation. The specimens were tested repeatedly(9 times) under controlled load rotary bending fatigue tests. In the study, the fatigue crack initiation as well as fatigue crack growth behavior and the fracture mechanism were investigated through observations of fracture of boron steel surface(AISI 51B20).

• 대한기계학회논문집A
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• 제25권8호
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• pp.1163-1172
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• 2001

The two dimensional problem of a layered tribological system(TiN/Steel) containing a vertical surface breaking crack and subject to rolling contact is considered in this study. Using finite elements and stress extrapolation method, a series of preliminary models are developed. Preliminary results indicate that the extrapolation technique is valid to determine Modes I and II stress intensity factors for cracks. In the case of TiN/Steel medium, KI and KII were determined for variations in crack length, layer thickness, and load location. The results show that KII reaches maximum values when the contact is adjacent to the crack where Mode I stresses are compressive. KII values decrease with decreased crack length and significantly decrease for reduced layer thickness.

• 한국환경과학회지
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• 제19권6호
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• pp.737-746
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• 2010

Restraint to drying shrinkage is the most common cause of concrete cracking. In many applications, drying shrinkage cracks are inevitable. In this paper, the surface cracks of soil concrete caused by drying shrinkage were considered to become an one of concrete textures. So, laboratory shrinkage tests were conducted and the results were applied to the field applications. The study results were summarized as follows; First, the use of vinyl sheets and concrete polymers helped to control the concrete cracking. Second, crack propagation usually started at the interfaces of soil concrete slabs and the cracks grew to the inner slabs. Third, surface cracks of soil concrete slabs could be an one of good concrete textures