• 제목/요약/키워드: edge crack

검색결과 340건 처리시간 0.019초

Multiple unequal cracks between an FGM orthotropic layer and an orthotropic substrate under mixed mode concentrated loads

  • M. Hassani;M.M. Monfared;A. Salarvand
    • Structural Engineering and Mechanics
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    • 제86권4호
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    • pp.535-546
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    • 2023
  • In the present paper, multiple interface cracks between a functionally graded orthotropic coating and an orthotropic half-plane substrate under concentrated loading are considered by means of the distribution dislocation technique (DDT). With the use of integration of Fourier transform the problem is reduced to a system of Cauchy-type singular integral equations which are solved numerically to compute the dislocation density on the surfaces of the cracks. The distribution dislocation is a powerful method to calculate accurate solutions to plane crack problems, especially this method is very good to find SIFs for multiple unequal cracks located at the interface. Hence this technique allows considering any number of interface cracks. The primary objective of this paper is to investigate the effects of the interaction of multiple interface cracks, load location, material orthotropy, nonhomogeneity parameters and geometry parameters on the modes I and II SIFs. Numerical results show that modes I/II SIFs decrease with increasing the nonhomogeneity parameter and the highest magnitude of SIF occurs where distances between the load location and crack tips are minimal.

연성파괴기준을 이용한 허브홀 확장과정에서의 파단 예측 (Prediction of fracture in Hub-hole Expansion Process Using Ductile fracture Criteria)

  • 고윤기;이종섭;허훈;김홍기;박성호
    • 소성∙가공
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    • 제14권7호
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    • pp.601-606
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    • 2005
  • A hole expansion process is an important process in producing a hub-hole in a wheel disc of a vehicle. In this process, the main parameter is the formability of a material that is expressed as the hole expansion ratio. In the process, a crack is occurred in the upper edge of a hole as the hole is expanded. Since prediction of the forming limit by hole expansion experiment needs tremendous time and effort, an appropriate fracture criterion has to be developed for finite element analysis to define forming limit of the material. In this paper, the hole expansion process of a hub-hole is studied by finite element analysis with ABAQUS/standard considering several ductile fracture criteria. The fracture mode and hole expansion ratio are compared with respect to the various fracture criteria. These criteria do not predict its fracture mode or hole expansion ratio adequately and show deviation from experimental results of hole expansion. A modified ductile fracture criterion is newly proposed to consider the deformation characteristics of a material accurately in a hole expansion process. A fracture propagation analysis at the hub-hole edge is also performed for high accuracy of prediction using the new fracture criterion proposed.

텅스텐 카바이드 공구를 사용한 앤드밀 가공에서 Si3n4-hBN 머시너블 세라믹스의 표면특성과 공구마멸 (Surface Properties and Tool Wear of Si3n4-hBN Machinable Ceramics in Endmill Machining using Tungsten Carbide Tool)

  • 장성민;조명우
    • 한국기계가공학회지
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    • 제3권1호
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    • pp.15-21
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    • 2004
  • The machining process of ceramics can be characterized by cracking and brittle fracture. In the machining of ceramics, edge chipping and crack propagation are the principal reasons to cause surface integrity deterioration. Such phenomenon can cause not only poor dimensional and geometric accuracy, but also possible failure of the ceramic parts. Thus, traditional ceramics are very difficult-to-cut materials. To overcome such problems, in this paper, h-BN powder, which gives good cutting property, is added for the fabrication of machinable ceramics by volume of 5, 10, 15, 20, 25 and 30%. The objectives of this paper is to evaluate the fracture phenomenon of the tungsten carbide tool and the variation of surface integrity of the manufactured machinable ceramics under various cutting conditions during end mill machining With CNC machining center.

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절삭 선단의 축 방향 경사각이 가공성 세라믹에 미치는 영향 (Effect on Axial Rake Angle of Cutting Edge for Machinable Ceramics)

  • 장성민;윤여권
    • 한국안전학회지
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    • 제24권2호
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    • pp.7-12
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    • 2009
  • The machining process of ceramics can be characterized by cracking and brittle fracture. In the machining of ceramics, edge chipping and crack propagation are the principal reasons to cause surface integrity deterioration. Such phenomenon can cause not only poor dimensional and geometric accuracy, but also possible failure of the ceramic parts. Thus, traditional ceramics are very difficult-to-cut materials. Generally, ceramics are machined using conventional method such as grinding and polishing. However these processes are generally costly and have low MRR(material removal rate). To overcome such problems, in this paper, h-BN powder, which gives good cutting property, is added for the fabrication of machinable ceramics by volume of 10 and 15%. The purpose of this study is an analysis of endmill's rake angle for appropriate tools design and manufacturing for the machinable ceramics. In this study, Experimental works are executed to measure cutting force, surface roughness, tool fracture, on different axial rake angle of endmills. Cutting parameters, namely, feed, cutting speed and depth of cut are used to accomplish purpose of this paper. Required experiments are performed, and the results are investigated.

모서리균열이 있는 알루미늄판의 복합재 패치보수시 수명예측 연구 (Fatigue Life Prediction of Composite Patch for Edge Cracked Aluminum Plate)

  • 김위대
    • 한국항공우주학회지
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    • 제35권1호
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    • pp.52-57
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    • 2007
  • 노후항공기의 균열보수 방법 중 복합재를 이용한 균열보수 방법을 이용하여 항공기 알루미늄 재료의 피로수명 예측을 위해 유한요소해석을 이용 하였다. 패치보수의 해석 시에는 접착제 층이 매우 얇기 때문에 모델링의 어려움이 있는데, 본 연구에서는 3층 기법을 이용하여 해석을 수행하였다. 피로수명의 예측 시에는 Paris의 법칙을 적용하였고, 효율적 수명예측을 위해 수정된 균열닫힘법을 적용하였다. 해석에 의한 수명예측 결과는 실험치를 잘 모사할 수 있었으며, 항공기의 피로수명 예측이나 수명연장기법으로 활용될 수 있을 것으로 생각된다.

플라즈마 화학증착된 TiN박막의 마모특성 (Wear Behavior of TiN Coatings Deposited by Plasma Assisted Chemical Vapor Deposition)

  • 인치범;천성순
    • 한국재료학회지
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    • 제3권5호
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    • pp.451-458
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    • 1993
  • 베아링강(AISI S2100) 위에 TiCi/sub 4/, N/sub 2/,H/sub 2/,그리고 Ar의 기체혼합계를 이용하여 플라즈마화학증착법으로 내마모 TiN증착층을 얻었다. 증착된 TiN층 내의 잔류 CI에 의한 결정성, 미소경도, 접착력, 그리고 마모특성에 대해 연구하였다. TiN 중착층은 좋은 내마모성을 가지고 있었으며, TiN의 기계적 특성은 잔류CI함량이 증가할때 나빠졌다. 마모측정결과 마모면의 trailing edge에 인장응력이 걸려 많은 crack이 관찰되엇다.

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치과용(齒科用) 아말감의 파괴인성(破壞靭性)에 관한 연구(硏究) (A STUDY ON THE FRACTURE TOUGHNESS OF DENTAL AMALGAMS)

  • 허현도;김영해
    • Restorative Dentistry and Endodontics
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    • 제15권1호
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    • pp.20-32
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    • 1990
  • The plane strain fracture toughness of a material characterize the resistance to fracture in the presence of a sharp crack under severe tensile condition. Fracture toughness can be determined by indentation method. The purpose of this study was to investigate the fracture toughness of dental amalgams by measuring the plane strain fracture toughness and the fracture toughness from indentation method. Two conventional and four high copper amalgam alloys were employed for this study. The amalgams were prepared according to the A.D.A. spec. No. 1 and inserted into the specially designed mould with the single edge notch specimen to use in 3-point bending method. The specimens (20mm long, 4mm wide, 2mm thick) were stored at $37^{\circ}C$ for 1 week, and tested in 3-point bending by means of Instron at a cross-head speed of 1mm/min. In indentation method, the specimens were made in same manner as single edge notch specimens. The test was conducted with Vickers hardness tester at 10kg load. The following results were obtained. 1. The plane strain fracture toughness and the fracture toughness from indentation method were higher in the low copper amalgams than the high copper amalgams. 2. In high copper amalgams, the fracture toughness of amalgams decreases according as the copper contents increase. 3. In similar copper contents, the single composition amalgams have a higher fracture toughness than the admixed amalgams.

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Dynamic reliability of structures: the example of multi-grid composite walls

  • Liu, Pei;Yaoa, Qian-Feng
    • Structural Engineering and Mechanics
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    • 제36권4호
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    • pp.463-479
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    • 2010
  • Based on damage accumulation of multi-grid composite walls, a method of dynamic reliability estimations is proposed. The multi-grid composite wall is composed of edge frame beam, edge frame columns, grid beams, grid columns and filling blocks. The equations including stiffness, shear forces at filling blocks cracking and multi-grid composite walls yielding, ultimate displacement, and damage index are obtained through tests of 13 multi-grid composite wall specimens. Employing these equations in reliability calculations, procedures of dynamic reliability estimations based on damage accumulation of multi-grid composite walls subjected to random earthquake excitations are proposed. Finally the proposed method is applied to the typical composite wall specimen subjected to random earthquake excitations which can be specified by a finite number of input random variables. The dynamic reliability estimates, when filling blocks crack under earthquakes corresponding to 63% exceedance in 50 years and when the composite wall reach limit state under earthquakes corresponding to 2-3% exceedance in 50 years, are obtained using the proposed method by taking damage indexes as thresholds. The results from the proposed method which show good agreement with those from Monte-Carlo simulations demonstrate the proposed method is effective.

An efficient adaptive finite element method based on EBE-PCG iterative solver for LEFM analysis

  • Hearunyakij, Manat;Phongthanapanich, Sutthisak
    • Structural Engineering and Mechanics
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    • 제83권3호
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    • pp.353-361
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    • 2022
  • Linear Elastic Fracture Mechanics (LEFM) has been developed by applying stress analysis to determine the stress intensity factor (SIF, K). The finite element method (FEM) is widely used as a standard tool for evaluating the SIF for various crack configurations. The prediction accuracy can be achieved by applying an adaptive Delaunay triangulation combined with a FEM. The solution can be solved using either direct or iterative solvers. This work adopts the element-by-element preconditioned conjugate gradient (EBE-PCG) iterative solver into an adaptive FEM to solve the solution to heal problem size constraints that exist when direct solution techniques are applied. It can avoid the formation of a global stiffness matrix of a finite element model. Several numerical experiments reveal that the present method is simple, fast, and efficient compared to conventional sparse direct solvers. The optimum convergence criterion for two-dimensional LEFM analysis is studied. In this paper, four sample problems of a two-edge cracked plate, a center cracked plate, a single-edge cracked plate, and a compact tension specimen is used to evaluate the accuracy of the prediction of the SIF values. Finally, the efficiency of the present iterative solver is summarized by comparing the computational time for all cases.

가속도 데이터 기반 교량 안전 판단을 위한 Edge AI 모델 (Bridge Safety Determination Edge AI Model Based on Acceleration Data)

  • 박진효;홍용근;윤주상
    • 한국산업정보학회논문지
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    • 제29권4호
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    • pp.1-11
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    • 2024
  • 교량은 노후화와 지진, 유지보수 미비, 기상환경 등의 외부 요인에 의해 균열과 손상이 발생한다. 노후화 교량이 늘어나고 있는 상황에서 유지보수 작업을 진행하지 않으면 안전성이 저하되어 구조적 결함과 붕괴 문제가 발생할 수 있다. 이러한 문제를 예방하고 유지보수 비용을 절감하기 위해 교량의 상태를 모니터링하고 신속하게 대응할 수 있는 시스템이 필요하다. 이를 위해 기존의 연구에서 센서 데이터를 이용해 균열 위치와 정도를 파악하는 인공지능 모델이 제안되었다. 하지만 기존 연구에서 모델의 성능을 파악할 때 실제 교량의 데이터를 사용하지 않고 시뮬레이션을 통해서 교량의 형상을 제작하여 데이터를 획득하여 학습에 사용하였기 때문에, 실제 교량의 환경을 반영하지 못하고 있다. 본 논문에서는 실제 현장에서 발생하는 교량의 가속도 데이터를 활용하여 인공지능 기반 교량의 이상을 감지하는 '교량 안전 판단 Edge AI 모델'을 제안한다. 이를 위해 가속도 데이터에서 유효 데이터를 추출하기 위한 필터링 규칙을 새롭게 정의하고 이를 적용하는 모델을 구성하였다. 또한 현장에서 수집된 데이터를 기반의 제안된 교량 안전 판단 Edge AI 모델의 성능을 평가하였다. 그 결과 F1-Score가 최대 0.9565로 실제 교량의 데이터를 이용해 안전성을 판단할 수 있음을 확인할 수 있었고, 실제 충격 데이터를 유사한 데이터 패턴을 생성하는 규칙일수록 좋은 성능의 결과가 나왔다는 것을 확인하였다.