• Title/Summary/Keyword: 균열전파속도

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동적 파괴역학 에 대하여(II)

  • 이억섭;김상철
    • Journal of the KSME
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    • v.25 no.1
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    • pp.39-46
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    • 1985
  • 동적 탄성 파괴역학 문제들을 실험적으로 연구하기 위해서는 우선 빠르게 전파하고 있는 균열 선단(전파속도 V=100m/sec∼1000m/sec for various polymers) 부근의 응력분포 상태나 변위분포 상태등을 기록하는 실험장치가 필수적으로 필요하다. 먼저 Wells와 Post(7)에 의하여 처음으로 사용되었고 Kobayashi(18,19,20)와 Dally(21)등에 의해서 발전, 개선된 동적 광탄성 실험범에 대 하여 설명하고 이 실험에 의하여 동적 응력확대계수를 추출하는 방법을 아울러 강의하고 그의 문제점 등을 논의 하고자 한다.

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L-System Based Procedural Synthesis Method to Efficiently Generate Dense, Radial, and Concentric Cracks of Glass (유리의 미세, 방사상, 동심원 균열을 효율적으로 생성하기 위한 L-System 기반의 절차적 합성 방법)

  • Kim, Jong-Hyun
    • Journal of the Korea Computer Graphics Society
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    • v.23 no.5
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    • pp.1-7
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    • 2017
  • We propose a complex crack generation technique which is represented when impact is applied to glass. The crack patterns expressed when external forces are applied to the glass are classified into dense, radial, and concentric cracks, and we use procedural methods to efficiently represent crack patterns. Based on the input external force, we synthesize the crack example and apply the L-system based on this example to model the propagation shape of the crack in real time. Although physics based crack generation can analyze and model accurate cracks, it has a disadvantage of slow computation because of its high computational cost, and procedural methods have a relatively fast rate of continuity, but are not sufficient to capture accurate crack characteristics. We modeled cracks in glass using L-system to achieve both of these advantages. As a result, it realistically represented the microscopic crack patterns of glass in real time.

A Study on Fatigue Crack Retardation Using NDT Test in a Hybrid Composite Material Reinforced with a CFRP (CFRP로 보강한 하이브리드 복합재료의 비파괴검사법을 이용한 피로균열 지연의 연구)

  • 윤한기;박원조;허정원
    • Composites Research
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    • v.12 no.3
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    • pp.1-7
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    • 1999
  • New hybrid composite material CPAL(Carbon Patched ALuminum alloy), an Al2024-T3 plate doubleside reinforced with carbon/epoxy laminates were made. Fatigue crack growth tests were carried out at R=0.2, 0.5 in the CPAL specimens. The retardation mechanism and behavior of fatigue crack growth were examined basing on investigation of the crack and the delamination using a X-Ray and a ultrasonic C-Scan. The fatigue crack growth rates of CPAL specimens were remarkedly retarded compared to that of the Al2024-T3 specimen. The retardations amounts of the fatigue crack growth rates get higher in $0^{\circ}$/$90^{\circ}$ CPAL specimen than in $\pm$$45^{\circ}$ CPAL specimen, and get higher at R=0.2 than at R=0.5. The retardation of fatigue crack growth rates in CPAL specimen was generated by the crack bridging mechanism, that is the behavior that the fibers in CFRP layers decrease the COD in the Al2024-T3 plate.

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The Fatigue Behavior of Laser Weldment in Heterogeneous Materials (이종재료 레이저 용접부의 피로거동)

  • 권응관;오택열;곽대순;이종재
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.10a
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    • pp.759-764
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    • 1997
  • In this study, Fatigue behavior of laser weldment in heterogeneous materials was investigated. Fatigue strength test and fatigue crack propagation test were performed for specimens with laser weldment in heterogeneous materials, and hardness test was performed. From the fatigue strength test. it was observed that the difference of strength between heterogeneous materials had eflect on crack initiation position and fatigue limit. From the fatigue crack propagation test. it was observed that fatigue behavior of laser weldment in heterogeneous materials is different from that in same materials. The difference of strength between heterogeneous materials and laser weldment had effect on fatigue crack propagation rate.

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The Effect of Overload Variation on the Fatigue Crack Behavior at the Axial Direction Hole Defects (과대하중변화가 축방향 원공결함의 피로균형거동에 미치는 영향)

  • 송삼홍;김민철
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.10a
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    • pp.829-832
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    • 1997
  • It is difficult to explain the effects of complex variable loading experienced by the machine and the structure only with the studies of the single-overload itself. Hence, it is thought that the variation of overload-holding time are required to explain the effects more clearly. The effects of the overload were analyzed by means of the crack retardation, and the fractography on retardation zone. A characteristic of the fractography on retardation zone was that striation distribution did not appear due to decreased crack driving force. Rotary bending fatigue tests were performed with the circular shaft which has two hole defects.

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Fatigue Crack Propagation Behavior in STS304 under Mixed Mode Loading (혼합모드 하중에서의 STS304의 피로균열 전과거동)

  • Song, Sam-Hong;Lee, Jeong-Moo
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.9
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    • pp.131-139
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    • 2001
  • The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failure occur from cracks subjected to mixed mode loadings. Hence, it is necessary to evaluate the fatigue behavior under mixed mode loading. Under mixed mode loading conditions, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. The mode I and II stress intensity factors of CTS specimen were calculated using elastic finite element method. The propagation behavior of the fatigue crack of the STS304 steeds under mixed mode loading condition was evacuated by using stress intensity factors $K_I$ and $K_II. The MTS criterion and effective stress intensity factor were applied to predict the crack propagation direction and the fatigue crack propagation rate.

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Fatigue behavior of Cr-Mo-V steel at high temperature for turbines -Propagation characteristics of high cycle fatigue crack- (터빈용 Cr-Mo-V강의 고온 환경변화에 따른 피로거동-고사이클 피로균열의 전파특성-)

  • Song, Sam-Hong;Kang, Myung-Soo
    • Journal of the Korean Society for Precision Engineering
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    • v.14 no.11
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    • pp.69-76
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    • 1997
  • The rotating bending fatigue tests were performed using the specimens taken from Cr-Mo-V steel, widely sued in thermal power plant turbines, at various temperatures such as room temperature, 300 .deg. C, 425 .deg. C and 550 .deg. C. The characteristics of fatigue crack propagation were examined and analyzed by using fracture mechanics parameter. The plastic replica method was also applied in order to measure the crack length on the basis of serial observation of fatigue crack propagation behavior on the defected specimen surface. The fatigue crack propagation behavior of Cr-Mo-V steel was investigated within the frame work of elastic-plastic fracture mechanics. The propagation law of fatigue crack is obtained uniquely by using the term .sigma. $^{n}$ sub a/where .sigma. $_{a}$ is the service stress, a is the crack length and n is a constant. The values of constant n are nearly equal to 2.48, 2.60 and 8.61 at room temperature, 300 .deg. C and 425 .deg. C.

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A Numerical Study on the Effect of a Guide Hole on Crack Propagation Control in Blasting (발파에서 가이드공의 균열제어 유효성에 관한 수치 해석적 연구)

  • Lee, Hee-Gwang;Kim, Hak-Man;Kim, Seung-Kon;Cho, Sang-Ho
    • Tunnel and Underground Space
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    • v.20 no.4
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    • pp.299-307
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    • 2010
  • The model experiments, which employ a charge hole and guide hole, are simulated to examine the effect of the guide hole on the crack propagation control in blasting. Crack patterns resulted from the analysis models, which consider the distance between the charge hole and guide hole, were compared. From the simulation analysis for the model experiments, it was revealed that all the guide holes used in this study were effective for controlling the crack propagation in blasting.

The Effect of Stress Ratio on the Surface Crack Growth Behavior in 7075-T651 Aluminum Alloy (7075-T651 Al合金의 表面균열進展에 미치는 應力比의 影響)

  • 박영조;김정규;신용승;김성민
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.10 no.1
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    • pp.62-69
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    • 1986
  • Fatigue surface crack growth was studied in 7075-T651 aluminum alloy plates subjected largely to bending loads. The surface crack length and its depth were measurement by the unloading elastic compliance method. The surface crack growth rate dc/dN, on the surface and da/dN, in the depth direction were obtained by the secant method. The stress intensity factor range .DELTA.K was computed by means of Newman and Raju equation. The aspect ratio a/c was presented in form of a/c=0.815-0.853(a/T). The effect of the stress ratio on the stable surface crack growth rates under increasing .DELTA.T is larger in lower .DELTA.K, while the relation between dc/dN, da/dN and the effective stress intensity factor range .DELTA.K$_{eff}$ is weakly dependent on the stress ratio.o.

The Behavior of Crack Growth Rate for APAL and CPAL Patched with FRP Laminate in Aluminum Alloy Plate (알루미늄 합금판재에 FRP 라미네이터를 보강한 APAL 및 CPAL 재의 균열전파속도 거동)

  • 윤한기;정해용;허정원
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.4
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    • pp.1013-1022
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    • 1995
  • A hybrid composite (APAL;Aramid Patched ALuminum alloy, CPAL;Carbon Patched ALluminum alloy), consisting of a Al 2024-T3 aluminum alloy plate sandwiched between two aramid/epoxy and carbon/epoxy laminate, was developed. Fatigue crack growth behavior was examined at stress ratios of R=0.2, 0.5. The APAL and CPAL showed superior fatigue crack growth resistance, which may be attributed to the crack bridging effect imposed by the intact fibers in the crack wake.