• Title/Summary/Keyword: Crack Examination

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A Study on the Effect of Fatigue and Crack Propagation Behavior in Spot Weld of High Strength Steel( I ) - Experimental Examination - (고장력 강판의 점용접부에서 면내 굽힘 모멘트가 피로특성 및 균열 성장 거동에 미치는 영향에 관한 연구(I) - 실험적 검토 -)

  • 성기찬;장경복;정진우;김기순;강성수
    • Journal of Welding and Joining
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    • v.19 no.1
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    • pp.112-117
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    • 2001
  • The factor affecting on the fatigue strength of spot welded specimen have been studied. To analyze and predict crack initiation position and propagation directions on the spot welded area are very important for strength design of the automobile body structure. In fact, there are a various of loads in running automobile but, it is impossible to replay like an actual conditions in the laboratory. So, in this study tensile-shear type and in-plane bending type specimens were used in fatigue test and includes an analysis of fatigue crack initiation position and propagation directions about earth specimens. The results obtained in the present study are summarized as follows: 1. In tensile-shear type fatigue test, the region of fatigue crack initiation position was affected by out-of-plane bending deformation due to bending angle. 2 In in-plane bending type fatigue test, the behavior of fatigue crack initiation position and propagation derections due to angle between upper plate and lower plate was dominated by magnitude of in-plane bending moment.

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Analysis of a Composite Panel with Transverse Matrix Cracks under Bending and Twisting Moments (굽힘 및 비틀림 하중작용시 횡방향 모재균열을 갖는 복합재료 판넬 해석)

  • Park, Jung-Sun;Hur, Hae-Kyu;Lee, Soo-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.6
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    • pp.971-980
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    • 1997
  • This study is to investigate the stiffness degradation of a composite laminated panel including transverse matrix cracks subjected to bending and twisting moments. Micromechanics theory on the composite material is derived by introducing crack density. Iterative numerical scheme is developed to calculate the degraded composite stiffness which has nonlinear relation due to the crack density. The finite element method is used for structural analysis of the composite panel. Structural responses of the composite panel are examined for various laminated angles and crack density under the bending and twisting moments. Also, the effect of crack opening and closing is considered in the examination. It is realized that the matrix cracks may cause severe stiffness reduction and should be considered in the composite laminated panel.

Treatment of Quarter Crack Using Polymethyl Methacrylate Composites with a Reshaped Gluing Shoe in a Warmblood Foal

  • Ryu, Seung-Ho;Kim, Byung-Sun;Jeong, Soon-Wuk
    • Journal of Veterinary Clinics
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    • v.39 no.2
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    • pp.65-69
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    • 2022
  • A 5 day-old Warmblood foal was presented with a quarter crack due to the dam accidentally stepping on his left hind foot. Physical examination revealed the vertical crack included the coronary band of the medial side of the left hind hoof (quarter crack) with the lower pastern avulsion wound. Different from adult horses, the foot of the 5 day-old foal lacked adequate hoof wall thickness for stainless steel wire insertion and hoof size for a reinforcing fabric to be applied. Therefore, the authors decided to stabilize the edges of the cracked wall only by the polymethyl methacrylate (PMMA) composites without wiring and a reinforcing fabric application; and gluing a plastic shoe that was reshaped to protect the lower pastern and to spread pressure to other parts of the hoof when bearing weight. Disinfection and a supportive bandage were applied daily for 2 weeks. A month after the hoof crack accident, lameness had diminished. The quarter crack in this foal was treated successfully by the application of the composites three times with a reshaped gluing shoe, with approximately a month interval over the 4 months. After 4 months, it presented a successful functional recovery and needed no further treatment. When followed up 8 months after the accident, it revealed successful outcomes without hoof shape distortion and unbalanced hoof/limb growth.

A Study on the Fatigue Behaviors of Cr-Mo-V Alloy for Steam Turbine at High Temperature Difference (터빈용 Cr-Mo-V강의 고온 환경변화에 따른 피로거동에 관한 연구)

  • Song, Sam-Hong;Kang, Myung-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.1
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    • pp.173-179
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    • 1997
  • The high temperature fatigue tests were performed using the specimens taken from Cr-Mo-V steel, widely used as thermal power plant turbine materials for examination fatigue behavior of materials in power plants which have been operated for long periods. The fatigue tests at high temperature were performed at the various temperature and applied stress. The results obtained are summarized as follows : The fatigue crack length increases and the fatigue life decreases with temperature and applied stress according to the same number of stress cycle. The fatigue crack propagation and the fatigue life were much influenced by temperature and applied stress.

Effect of Compressive Residual Stress on the High Temperature fatigue Crack Propagation Behavior of Shot-peened Spring Steel (압축잔류응력이 스프링강의 고온환경 피로균열 진전거동에 미치는 영향)

  • 정찬기;박경동
    • Journal of Ocean Engineering and Technology
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    • v.16 no.5
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    • pp.73-79
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    • 2002
  • In this paper, the effect of the compressive residual stresses was obtained at the test conditions of the higher temperature than the ambient temperature. The examination was performed with the CT specimen result of the material(JISG SUP9) which is being commonly used for the marine engine parts and the ocean structures. As a result, the test conditions at the higher temperature were acquired considering the peak values of the compressive residual stresses of the specimens and the effect on the fatigue crack propagation speed da/dN in stage II and the threshold stress intensity factor range Δth in stage I. Also the material constant C and the fatigue crack propagation index m in the formula of Paris Law da/dN=C (ΔK)$^{m}$ were suggested to estimate the dependence on the test temperature.

A Study on Fatigue Life of Weld Method for Excavator Bucket (굴삭기 버킷 용접부의 피로수명에 관한 연구)

  • Park, K.D.;Jung, J.W.
    • Journal of Power System Engineering
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    • v.9 no.4
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    • pp.102-109
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    • 2005
  • An attachment part of the construction equipment frequently claimed from the crack occurrence that takes especially at the bucket. therefore we execute the fatigue examination and changes the welding method at the same materials. we executed a fatigue crack propagation experiment and got the conclusions at the normal temperature and Frequency 10Hz. We carried out butt welding for structure steel of SM490A and make three kinds of specimen of different weld method each. The fatigue limit of CASE 1 was determined to the low than CASE 2, CASE 3. the CASE 2 putting the interval of the 2mm creates back plate and make fatigue limit to high. Bead shapes and weld surfaces shape influence on fatigue life of materials. Specially, the crack growth becomes starting point that gap of back-plate and boundary surface of bead. It is confirmed by fracture showing on this study.

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Resistance Spot Weldability of Coated Steels for Automobile Applications (자동차용 도금강재의 저항 점용접부 특성)

  • Kim Ki Choi;Cha Joon Ho;Park Hwa Soon
    • Korean Journal of Materials Research
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    • v.14 no.4
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    • pp.239-245
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    • 2004
  • Resistance spot weldability of coated steels for automobile applications was investigated. Test samples were prepared from commercial products of 0.8 mm in thickness. Based on the tensile-shear test, surface quality examination and cracking behavior, it was clear that aluminized steels showed good weldability. Microstructural inspection revealed that the coated materials was piled up at the split zone in the welding of aluminized steels. It was also demonstrated that no weld crack was found in the aluminized steel weld metal even the welding was carried out with higher current. However, through thickness cracks were detected at the weld metal of zinc coated steel. Small particles were found on the crack surface of zinc coated steel weld metal. It was thought that zinc vapor played key role to form the weld crack.

A Program Development of Life Prediction Simulation for Multi-Surface Cracks on the Finite Plate (무한 평면체에 존재하는 복수 표면균열의 성장에 대한 수명예측용 시뮬레이션 개발에 관한 연구)

  • 황남성;서창민;남승훈
    • Journal of Ocean Engineering and Technology
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    • v.11 no.4
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    • pp.61-75
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    • 1997
  • The social demand urges us to use some equipments and structures in high temperature environment. By this occasion, the necessity of studying the fatigue crack growth is an important aspect of new materials. However, the present situation is rarely to accumulate the fatigue data. Especially, 1Cr-1Mo-0.25V steel and 304 stainless steel have been increased to be used under the severe condition of high temperature. And so, the fatigue estimation of those materials is important and appropriate. Fatigue tests have been carried out to examine the crack initiation, growth behaviour for the small fatigue crack of 1Cr-1Mo-0.25V steel and 304 stainless steel at room temperature and 538^{\circ}C$. The remote measurement system which has many merits of checking and saving the image for detailed examination was applied to closely detect the crack length. Generally, the fatigue crack initiated in the form of multiple cracks and grew each other. And then it coalesced to become a major crack. The major crack governed the rest of the fatigue life. In the growing process, each peripheral cracks interact and grow for a certain period. After then, it coalesced and fractured. On the basis of the above experimental data for the small crack, a simulation program was developed to predict the residual life time and to estimate the integrity of machine elements and structures. At the same time, the simulation was extended to 1Cr-1Mo-0.25V steel. The simulation results have shown a good agreement to those of the experimental ones for both materials of 1Cr-1Mo-0.25V steel and 304 stainless steel with small cracks. The NASCRAC has applied to compare the fatigue life with the experimental results. And so, it can be said that the simulation program is valuable tools to the industrial fields.

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Effects of loading conditions on the fatigue failure characteristics in a polycarbonate

  • Okayasu, Mitsuhiro;Yano, Kei;Shiraishi, Tetsuro
    • Advances in materials Research
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    • v.3 no.3
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    • pp.163-174
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    • 2014
  • In this study, fatigue properties and crack growth characteristics of a polycarbonate (PC) were examined during cyclic loading at various mean stress (${\sigma}_{amp}$) and stress amplitude (${\sigma}_{mean}$) conditions. Different S vs. N and da/dN vs. ${\Delta}K$ relations were obtained depending on the loading condition. The higher fatigue strength and the higher resistance of crack growth are seen for the PC samples cyclically loaded at the higher mean stress and lower stress amplitude due to the low crack driving force. Non-linear S - N relationship was detected in the examination of the fatigue properties with changing the mean stress. This is attributed to the different crack growth rate (longer fatigue life): the sample loaded at the high mean stress with lower stress amplitude. Even if the higher stress amplitude, the low fatigue properties are obtained for the sample loaded at the higher mean stress. This was due to the accumulated strain energy to the sample, where severe plastic deformation occurs instead of crack growth (plasticity-induced crack closure). Shear bands and discontinuous crack growth band (DGB) are observed clearly on the fracture surfaces of the sample cyclically loaded at the high stress amplitude, where the lower the ${\sigma}_{mean}$, the narrower the shear band and DGB. On the other hand, final fracture occurred instantly immediately after the short crack growth occurs in the PC sample loaded at the high mean with the low ${\sigma}_{amp}$, i.e., tear fracture, in which the shear bands and DGB are not seen clearly.

Fracture Analysis of Implant Components using Scanning Electron Microscope : Part II - Implant Retaining Screw (임플란트 구성요소의 파절면에 관한 주사전자현미경적 연구 : Part II - 임플란트 유지나사)

  • Lim, Kwang-Gil;Kim, Dae-Gon;Cho, Lee-Ra;Park, Chan-Jin
    • Journal of Dental Rehabilitation and Applied Science
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    • v.26 no.4
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    • pp.373-388
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    • 2010
  • Fracture causes serious problems in many instance of prosthetic failures. But it is hard to find the definite causes when fractures occur. Fractography encompasses the examination of fracture surfaces that contain features resulting from the interaction of the advancing crack with the microstructure of the material and the stress fields. All fractured specimens(implant retaining screw) retrieved from Gangneung-Wonju national university dental hospital for 3 years(from 2007 to 2009). After pretreatment of samples, the scanning electon microscope were used for surface examination and fracture analysis. In case of most of the fractured specimens, fracture took place by fatigue fracture and fractured surface represents fatigue striation. Fatigue striation indicate the progression of the crack front under cyclic loading, are characteristic of stage 2 crack growth. The site of crack initiation and stage 1 crack growth were not easily identified in any of the failure, presumably because of the complex microstructural features of the polycrystalline sample. In case of fractured by overload, dimpled or cleavage surface were observed. Using the interpretation of characteristic markings(ratchet mark, fatigue striation, dimple, cleavage et al) in fracture surfaces, failure events containing the crack origin, crack propagation, material deficiency could be understand. Using the interpretation of characteristic markings in fracture surfaces, cause and mechanism of fractures could be analyzed.