• Title/Summary/Keyword: 압입 균열시험

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Analysis of Cracking Characteristics with Indenter Geometry Using Cohesive Zone Model (Cohesive Zone Model을 이용한 압입자 형상에 따른 균열특성분석)

  • Hyun, Hong Chul;Lee, Jin Haeng;Lee, Hyungyil;Kim, Dae Hyun;Hahn, Jun Hee
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.12
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    • pp.1453-1463
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    • 2013
  • In this study, we investigated the effect of the indenter geometry on the crack characteristics by indentation cracking test and FEA. We conducted various cohesive finite element simulations based on the findings of Lee et al. (2012), who examined the effect of cohesive model parameters on crack size and formulated conditions for crack initiation and propagation. First, we verified the FE model through comparisons with experimental results that were obtained from Berkovich and Vickers indentations. We observed whether nonsymmetrical cracks formed beneath the surface during Berkovich indentation via FEA. Finally, we examined the relation between the crack size and the number of cracks. Based on this relation and the effect of the indenter angle on the crack size, we can predict from the crack size obtained with an indenter of one shape (such as Berkovich or Vickers) the crack size for an indenter of different shape.

Evaluation of Indentation Fracture Toughens in Brittle Materials Based on FEA Solutions (유한요소해에 기초한 취성재료의 압입파괴인성평가)

  • Hyun, Hong Chul;Lee, Jin Heang;Felix, Rickhey;Lee, Hyungyil
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.12
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    • pp.1503-1512
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    • 2013
  • In this study, we proposed an indentation evaluation method for fracture toughness using cohesive finite element simulations. First, we examined the effect of material properties (yield strain, Poisson's ratio, and elastic modulus) on crack size during Vickers indentation and then generated a regression formula that explains the relations among fracture toughness, indentation load, and crack size. We also proposed another indentation formula for fracture toughness evaluation using the contact size a and E/H (H: hardness). Finally, we examined the relation between the crack size and the indenter shapes. Based on this, we can generate from the formula obtained using the Vickers indenter a formula for an indenter of different shapes. Using the proposed method, fracture toughness is directly estimated from indentation data.

A Study on the Application of Pre-Indentation Technique for Fastener Hole Model (FASTENER HOLE 모델의 대한 예비압입 적용 연구)

  • Hwang,Jeong-Seon;Jo,Hwan-Gi
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.9
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    • pp.26-31
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    • 2003
  • Aging aircraft accumulates widespread fatigue damage commonly referred to as multiple site damage(MSO). For ductile material such as 2024-T3 aluminum, MSO may lower the service life below that which is predicted by conventional fracture mechanics. The present paper is concerned with the fatigue life extension by pre-indentation technique for thin 2024-T3 aluminum plate to decelerate the crack propagation rate in the panels with MSO. The panel with fastener holes can be simply modelled by Hole/Slot type Middle-Tension specimen. Results of fatigue testing show significantly improving failure cycles from 10 to 40 times. This retardation effect is decreased by increasing the loading level in the constant amplitude loading. In the sense of retardation mechanism, the crack propagation rate is gradually attenuated by entering the indentation mark and maintains at the lowest value for a long period after the edge of crack passes the center of indentation area.

Presumption on Wear life of TiN Film (TiN 경질박막의 마모 수명 예측에 관한 연구)

  • 정기훈;이영제
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1997.04a
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    • pp.41-46
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    • 1997
  • TiN 코팅은 마모에 대한 저항성 및 고체 윤활 효과가 매우 우수하여 내마모성 및 저마찰이 요구되는 절삭공구나 피스톤 베어링 및 각종 축계의 코팅막으로 사용이 증가되고 있다. 일반적으로 재료의 경도와 인성은 서로 상반 관계를 갖고 있어 공학적으로 경도와 인성을 모두 요구하는 표면을 얻기 위해 연질 모재 위의 세라믹 코팅은 그 요구를 만족시킬 수 있는 가장 각광받는 표면처리 방법중의 하나이다. 그러나, TiN과 같은 경질 박막의 공학적 적용시 가장 요구되는 마모수명은 모재의 조도나 경도, 증착 방법, 접촉 상태, 코팅막의 두께 및 마모의 발생 기구 등에 따라 마찰 및 마모 메커니즘의 현저한 차이를 나타내기 때문에 예측이 거의 불가능한 실정이고, 아직까지 이러한 마모수명 비교 평가방법에 대한 기준 설정 및 정량적 정립이 이루어지지 않고 있다. 본 연구에서는 모재의 경도, 조도, 코팅 두께가 다른 TiN 경질 박막에 압입시험과 스크래치시험시 발생되는 균열 발생 메커니즘과 미끄럼 시험시 발생되는 마모 메커니즘의 연계성을 밝히고 압입 및 스크래치 시험시 코팅막이 손상되는 임계하중과 미끄럼 시험시 접촉하중 변화에 따른 마모수명의 정량적 연관성을 찾아보고자 한다.

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Damage Analysis of Singly Oriented Ply Fiber Metal Laminate under Concentrated Loading Conditions by Using Acoustic Emission (음향 방출법을 이용한 집중하중을 받는 일방향 섬유 금속 적층판의 손상 해석)

  • 남현욱;김용환;한경섭
    • Composites Research
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    • v.14 no.5
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    • pp.46-53
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    • 2001
  • In this research, damage behavior of singly oriented ply (SOP) fiber metal laminate (FML) subjected to concentrated load was studied. The static indentation tests were conducted to study fiber orientation effect on damage behavior of FML. During the static indentation tests, acoustic emission technique (AE) was adopted to study damage characteristics of FML. AE signals were obtained by using AE sensor with 150kHz resonance frequency and the signals were compared with indentation curves of FML. The damage process of SOP FML was divided by three parts, i.e., crack initiation, crack propagation, and penetration. The AE characteristics during crack initiation show that the micro crack is initiated at lower ply of the plate, then propagate along the thickness of the plate with creating tiber debonding. The crack grow along the fiber direction with occurring 60∼80dB AE signal. During the penetration, the fiber breakage was observed. As fiber orientation increases, talc fiber breakage occurs more frequently. The AE signal behaviors support these results. Cumulative AE counts could well predict crack initiation and crack propagation and AE amplitude were useful for the prediction of damage failure mode.

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Microstructure and annealing effect on fracture behavior in the dental glass-infiltrated alumina (치아용 유리침윤 알루미나에서 파괴거동에 미치는 미세구조 및 어닐링 효과)

  • 정종원;최성철
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.10 no.4
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    • pp.330-336
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    • 2000
  • Effects of microstructure and indentation stress on fracture behavior of glass-infiltrated alumina composite for dental restorative application were investigated by the Hertzian and Vickers indentation method. Indentation stress-strain curve of glass-infiltrated alumina has showed the quasi-plastic behavior - deviation from linearity at high stress and the classical Hertzian cone crack, which could be confirmed the subsurface damage micrographs using bonded-interface specimen technique. The indentation stress-strain curves for the starting preforms are strongly dependent on porosity and microstructure of the preforms. On the other hand, the curves for the infiltrated composites are relatively insensitive to these factors. The failure of composite is originated at quasi-plastic deformation region. Damage and fracture behavior due to Hertzian stress field is theoretically examined, so that the indentation stress field plays a great role in material degradation. After Hertzian indentation annealing processing changes fracture behavior of alumina composite, so that stress field in material is healed through annealing.

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The Evaluation of Mechanical Properties for Alumina Ceramics (알루미나 세라믹스의 기계적 특성 평가)

  • 임헌진;조덕호;김무경;한상미;이와사미키오
    • Journal of the Korean Ceramic Society
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    • v.33 no.3
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    • pp.339-347
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    • 1996
  • Mechanical properties(flexural strength hardness fracture toughness) of alumina ceramics were evaluated. Alumina products of four companies were selected and three of those were made in Korea and one of those was made in Japan. The large differences according to manufacturing companies had resulted from flexural strength and weibull modulus which had a wide ranges of 300 to 400 MPa and 5 to 15 respectively. Critical indenstation load which could be neglected the effect of elastic recovery was about 9.8N and Vickers' hardness were about 15 GPa. Fracture toughnesses were evaluated by IF and ISB method. It was more preferable to the average at one indentation load that fracture toughness were obtained from the slope of the relationship between indentation load and crack length in IF method and between indentation load and fracture load in ISB method and fracture toughness was about 4 MPa·m1/2.

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The Signal Characteristics from Crack of Brittle Materials by Vickers Load (비커스 압입 하중에 의한 취성재료의 균열 신호특성)

  • Nam, Ki-Woo;Kim, Hyun-Soo
    • Journal of the Korean Society for Nondestructive Testing
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    • v.22 no.2
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    • pp.125-131
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    • 2002
  • we analyzed acoustic emission signals obtained from three kinds of brittle materials under compression load by Vickers hardness tester. The results obtained can be summarized as follows; The signal in each material could be divided into three signal based on the properties of load. All specimens were not detected acoustic emission signals in stage II which was load constant region., and were detected in stage I and stage III. Glass was detected high amplitude signals in stage III. $Al_2O_3\;and\;Al_2O_3/Sic$ were detected high amplitude signals in stage I.

Phase Transition of Single Crystal Silicon by Scratching Test (Scratching 시험에 의한 단결정 실리콘의 상전이)

  • 오한석;정성민;김현호;박성은;이홍림
    • Korean Journal of Crystallography
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    • v.12 no.2
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    • pp.102-112
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    • 2001
  • The mechanical properties of silicon crystals are important from the viewpoint of wafer and device fabrication processes. It is now widely recognized that silicon undergoes a series of phase transformations when subjected to high pressures, using conventional high pressure devices, such as diamond anvils or indenters. Diamond tip scratching on a silicon surface in the various conditions introduces various kinds of mechanical damage and stressed states. Micro Raman spectroscopy was used to observe the phase transition of single crystal silicon. As results, different morphologies were observed as functions of scratching speed and loading condition and various phases were observed as functions of scratching speed and loading condition.

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