• 대한기계학회논문집A
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• 제39권7호
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• pp.729-736
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• 2015

본 논문에서는 파단전누설 평가를 위한 J-R 파괴인성시험에 미치는 시편 크기와 측면 홈의 영향을 분석하였다. 이를 위해서 SA508 Gr.1a 배관재에서 채취된 측면 홈이 가공되거나 가공되지 않은 크기가 다른 3종류의 CT 시편(12.7mm 두께의 1T-CT, 25.4mm 두께의 1T-CT, 25.4mm 두께의 2T-CT)을 이용하여 상온과 $316^{\circ}C$에서 J-R 시험을 수행하였다. 시험 결과, 시편 두께에 관계없이 측면 홈이 가공된 시편은 측면 홈이 없는 시편에 비해 낮은 J-R 곡선을 보였으며, 상온에 비해 $316^{\circ}C$에서 측면 홈의 영향이 더욱 뚜렷하였다. 상온에서는 시편의 두께가 감소하고 폭이 증가함에 따라 J-R 곡선이 약간씩 감소하는 경향을 보였으나, $316^{\circ}C$에서는 시편의 두께가 감소하고 폭이 증가됨에 따라 J-R 곡선이 증가하였다. 그러나 SA508 Gr.1a 배관재에서 전체적으로 시편의 폭과 두께에 따른 J-R 곡선의 변화는 크지 않았다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.285-291
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• 2003

An experimental method to measure Q-parameter in-situ is described. The basic idea comes from the fact that the side necking near a crack tip indicates the loss of stress triaxiality, which can be scaled by Q. From the out-of-plane displacement and the in-plane strain near the surface of side necking, stress field averaged through the thickness is calculated and then Q is determined from the difference between the stress field and the HRR field corresponding to the identical J-integral. To prove the validity, three-dimensional finite element analysis has been performed for a CT configuration with side-groove. Q-value which was calculated directly from the near-tip stress field is compared with that determined by simulating the experimental procedure according to the proposed method, that is, the Q-value determined from the lateral displacement and the inplane strain. Also, the effect of location where the displacement and strain are measured is explored.

• Journal of Advanced Marine Engineering and Technology
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• 제37권6호
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• pp.589-595
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• 2013

본 논문은 플라즈마 절단 면 특성이 I Groove 서브머지드 아크 용접 용락 현상에 미치는 영향과 용락 현상을 감소시키는 방법에 대하여 연구하였다. 조선해양 구조물의 주판은 대부분 후판으로 설계되고 깊은 용입을 얻기 위하여 고 전류를 사용하게 된다. 용접부의 절단 품질에 따라서 서브머지드 아크용접 진행 시 용락 현상이 자주 발생되고 이는 용접부의 품질 저하와 수정 작업을 유발시킨다. 본 연구의 플라즈마 절단 실험에서 나타난 특성으로 I형상 그루브 직각 절단 시 상,하면에 플라즈마 열원에 의한 녹음 현상과 함께 하면 한 방향에 약 2~4도 정도의 각 변형 베벨이 형성됨을 확인하였다. 이는 맞대기 이음에서 용락 현상의 주된 원인이며 모재 절단 시 상면 방향에 I 그루브 형상에 가깝도록 한 방향 기준으로 V형상 그루브 4도 베벨을 시공하여 서브머지드 아크 용접을 실시한 결과 용락 현상을 현저히 저감시키는 결과를 얻을 수 있었다.

• 한국안전학회지
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• 제13권4호
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• pp.79-86
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• 1998

The effect of specimen thickness on fatigue crack growth behavior has been carried out by compact tension specimens of thickness of 3mm, 10mm and 25mm for maraging steel and Al 7075-T6. The closure points were determined during the test by means of a clip-gage situated at the notch mouth. Specimen thickness have no apparent influence on the fatigue crack growth rate of maraging steel, but the crack growth rate of 25mm thickness specimen for Al 7075-T6 is faster than that of 3 and 10mm specimens. The difference of crack growth rates can be successfully explained by considering the different stress state of plane strain and plain stress due to the variation of specimen thickness. Also the crack opening ratio of 25mm specimen is greater than those of 3 and 10mm specimens. When a side groove is introduced in a 10mm specimen, the crack growth rate is approximately similar to that of 25mm specimen. The effective thickness expression of $B_e=B_o-(B_o-B_N)^2B_o$ is the most appropriate to evaluate the crack growth rate of side-grooved specimen. Fatigue crack growth rates can be well described by $\Delta K_{eff}$ of the crack closure points in regardless of all thickness and side-grooved specimens.

• 대한기계학회논문집A
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• 제27권9호
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• pp.1607-1613
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• 2003

An experimental method to measure Q-parameter in-situ is described. The basic idea comes from the fact that the side necking near a crack tip indicates the loss of stress triaxiality, which can be scaled by Q. From the out-of-plane displacement and the in-plane strain near the surface of side necking, stress field averaged through the thickness is calculated and then Q is determined from the difference between the stress field and the HRR field corresponding to the identical J-integral. To prove the validity, three-dimensional finite element analysis has been performed for a CT configuration with side-groove. Q-value which was calculated directly from the near-tip stress field is compared with that determined by simulating the experimental procedure according to the proposed method, that is, the Q-value determined from the lateral displacement and the in-plane strain. In addition, the effect of location where the displacement and strain are measured is explored.

• 대한기계학회논문집A
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• 제26권2호
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• pp.300-307
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• 2002

Partial penetration welding joint is defined as groove welds welded from one side, without steel backing or groove welds welded from both sides but without back gouging. So it has an unwelded portion at the root of the weld. Study of partial penetration weldment fracture behavior includes residual stress analysis and fracture analysis. The J-integral loses its path independency in residual stress field. Therefore, it is necessary to introduce a new J-integral, J, which is defined including the effect of plastic deformation and thermal strain. In this study, theoretical formulation and program were developed for the evaluation of J-integral for the crack tip located in the weldment. Evaluations of fracture behavior were performed for partial penetration multi-pass weldment of 25.4mm thick plate by J-integral. From a point of fracture in partial penetration multi-pass welding, it seemed to be better to control root face smaller than 6.35mm.

• 한국정밀공학회지
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• 제16권1호통권94호
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• pp.68-74
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• 1999

One of the recent changes in machining technology is rapid application of micro- and high precision grinding processes. A fine groove generation is necessary for the fabrication of optic, electronic and semiconductor parts, and achieved by chemical or mechanical processes. Slot grinding is very efficient for the generation of micro ordered groove with hard and brittle materials. As slot grinding is continuous, the ground depth become gradually shallow because of wheel wear. The form accuracy become worse from the increase of ground slot width by the loading phenomena at wheel side, results on chipping damage of the workpiece. The experiments achieve to the enhancement of the form accuracy and chipping free of the brittle materials using V shaped cast iron bonded diamond wheels. In this study we focused on the investigation of the effect of the high pressure air jet on the grinding characteristics. As a results, we found that the high pressure air jet is very effective on the reductions of the wheel wear, enhancement of the form accuracy.

• 대한기계학회논문집A
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• 제25권11호
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• pp.1813-1819
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• 2001

Partial penetration welding Joint defines that groove welds without steel backing, welded from on side, and groove weeds welded from both sides but without back gouging, that is. it has an unwelded portion at the root of the weld. In this study we analysed fur residual stress and displacement distribution on partial penetration welding condition of thick plate metal. For 25.4mm thick plate, theoretical residual stress and displacement analysis by finite element method using ABAQUS was carried out and compared with the experimental result using hole-drilling method. In results of the condition of partial penetration, it appeared that longitudinal stress at welding area was a little difference and transverse stress did not have any effect by partial penetration multi-pass welding. From a point of welding distortion in partial penetration multi-pass welding, it seemed to be better to control root face smaller than 6.35mm.

• Journal of Welding and Joining
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• 제5권2호
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• pp.44-52
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• 1987

The fracture toughness, $J_{IC}$ of high frequency electric resistance welded steel pipe for smooth and side-grooved CT specimen was evaluated by unloading compliance method. The crack growth, .${\delta}a$ was obtained from the equation of Donald and Saxena & Hudak, and $J_{IC}$ was determined from the curve of J-${\delta}a$ relations. The crack growth on the experiment using unloading compliance method is underestimated as compared with ${\delta}a$ measured directly by the SEM, so the reliability of $J_{IC}$ from saxena & Hudak equation is large than that from Donald. The $J_{IC}$ value of side-grooved CT Specimen is estimated less than that of smooth, and this is the effect of the side-groove, the shear-lip of crack tip and the reduction of crack tunnelling phenomena.

• 한국안전학회지
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• 제8권4호
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• pp.41-46
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• 1993

This Paper aims to examine the effect of shear lip formation from cross-sections on fatigue crack propagation rate in order to study the fatigue fracture behavior of the high strength aluminum material (Al 2024-T3). The following tests were achieved from this research. 1. As a result of depressing shear lip artificially by adding a side groove to a specimen, it is shown that the propagation rate of fatigue crack is faster than that of general specimen. 2. Through the two-step load test, the phenomenon that the shear lip decreases In the part of changed load gets observed. Consequently It Is shown that the crack propagation rate gets faster.