• 제목/요약/키워드: Conducting Crack

검색결과 58건 처리시간 0.027초

Al7050 합금의 인장-압축거동과 성형성 간 상관관계 (Correlation Between Tensile-compressive Behavior and Formability of Al7050 Alloy)

  • 배동화;오주희;정찬욱;김정기
    • 소성∙가공
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    • 제31권2호
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    • pp.64-72
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    • 2022
  • Since aluminum alloys experience both tensile and compression deformation modes during forming process, it is important to understand the role of deformation mode on the hot formability of metallic alloys. In the present work, the hot formability of Al7050 alloy was investigated by conducting both tensile and Gleeble tests at various temperatures and strain rates. Processing maps representing low efficiency regions were observed at low temperature and high strain rate in both tensile and compressive deformation modes while the maximum efficiency regions depended on different deformation modes. Moreover, samples tested at stable processing conditions presented a smaller pore fraction than those at instable conditions that resulted in crack initiation during plastic deformation. This result shows that different deformation modes during plastic forming can affect formability changes of metallic alloys. Understanding of tension-compression behaviors will help us solve this problem.

Interfacial shear resistance of angle shear connectors welded to concrete filled U-shaped CFS beam

  • Oh, Hyoung Seok;Shin, Hyeongyeop;Ju, Youngkyu;Kang, Thomas H.K.
    • Steel and Composite Structures
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    • 제43권3호
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    • pp.311-325
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    • 2022
  • For multi-story structural systems, Korean steel industry has fostered development of a steel-concrete composite beam. Configuration of the composite beam is characterized by steel angle shear connectors welded to a U-shaped cold formed-steel beam. Effects of shear connector orientation and spacing were studied to evaluate current application of the angle shear connector design equation in AC495. For the study, interfacial shear resistance behavior was investigated by conducting 24 push-out tests and attuned using unreinforced push-out specimens. Interfacial shear to horizontal slip response was reported along with corresponding failure patterns. Pure shear connector strength was also evaluated by excluding concrete shear contribution, which was estimated in relation to steel beam-slab interface separation or interfacial crack width.

컴포넌트에서의 비정상적인 금속간화합물 성장이 보드 레벨 기계적 신뢰성에 미치는 영향 (The Effect of Abnormal Intermetallic Compounds Growth at Component on Board Level Mechanical Reliability)

  • 최재훈;함현정;황재선;김용현;이동춘;문점주
    • 마이크로전자및패키징학회지
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    • 제15권2호
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    • pp.47-54
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    • 2008
  • 컴포넌트에서의 비정상적인 금속간화합물 성장이 보드 레벨 기계적 신뢰성에 미치는 영향을 연구하기 위하여, 전기 도금된 Ni/Au UBM과 Sn2.5Ag0.5Cu 솔더의 리플로우 횟수 및 고온 시효 시간에 따른 금속간 화합물 성장거동을 관찰하였다. 각 조건별로 처리된 컴포넌트에서 솔더 접합부의 기계적 특성을 비교하기 위하여, 전단 속도 변화에 따른 볼 전단 시험을 실시하여 전단에너지 값을 측정하였다. 마지막으로, 보드 레벨에서의 기계적 신뢰성 시험을 위하여 조건별로 처리된 컴포넌트를 PCB 보드에 실장하여, 3점 굽힘 시험 및 충격 시험을 실시한 후 파괴모드를 분석하였다.

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Local compression에 의한 CTOD 시편내의 용접잔류응력 재분포 (Redistributions of Welding Residual Stress for CTOD Specimen by Local Compression)

  • 주성민;윤병현;장웅성;방한서;방희선;노찬승
    • Journal of Welding and Joining
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    • 제27권6호
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    • pp.31-35
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    • 2009
  • When conducting CTOD test, especially in thick welded steel plate, fatigue pre-cracking occasionally failed to satisfy the requirements of standards thus making the test result invalid. Internally accumulated residual stress of test piece has been thought as one of the main reasons. The propagation of fatigue crack, started from the tip of machined notch, which might have propagated irregularly due to residual stress field. To overcome this kind of difficulty three methods to modify the residual stress are suggested in standard i.e. local compression, reverse bending and stepwise high-R ratio method. In this paper not only multi pass welding but also local pre-compressing process of thick steel plate has been simulated using finite element method for clarifying variation of internal welding residual stress. The simulated results show that welding residual stress is compressive in the middle section of the model and it is predominantly increased after machining the specimen. Comparing as-welded state all component of the welding residual stress changing to compressive in the tip of machine notch whereas residual stress of the outer area remain as tensile condition relatively. Analysis results also show that this irregular residual stress distribution is improved to be more uniformly by applying local compression.

슬리브덮개를 이용한 배관 보수용접시 필릿용접부의 기계적특성에 관한 연구 (A Study on Mechanical Properties of Fillet Weldment in Pipeline Repair Welding Using Sleeve)

  • 김영표;김형식;김우식;홍성호
    • Journal of Welding and Joining
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    • 제14권5호
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    • pp.49-58
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    • 1996
  • In Korea Gas Corporation, as one of the pipeline repairing methods, damaged pipelines are sometimes treated with a temporally employment of split sleeve. On conducting the repair process, circumferential fillet and longitudinal groove welding usually must be included. For the case of groove welding, a considerable amount of R&D have been carried out related to property changes, while few study on the property change in fillet welding has been conducted. In this paper, so as to confirm the specification of fillet welding in terms of safety and reliability, properties changed by fillet welding were investigated for two welding processes. Qualifying tests such as reviewing macrostructure and nick-break tests were performed according to API 1104 and ASME section IX. In addition, tensile properties and hardness were evaluated according to KS B0841 and BS 4515. The fillet weld prepared by the qualified procedure showed melting depth of 0.8∼1.3mm and heat affected zone of 2.8∼3.4mm length. No crack and lack of penetration were observed. And the results of hardness and nick-break tests satisfied code requirements. The area crossed by fillet and groove welding line was found to have minimal tensile strength.

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국제공동연구 PARTRIDGE를 통한 확률론적 건전성 평가 기술 개발 현황 (Current Status of an International Co-Operative Research Program, PARTRIDGE (Probabilistic Analysis as a Regulatory Tool for Risk-Informed Decision GuidancE))

  • 김선혜;박정순;김진수;이진호;윤은섭;양준석;이재곤;박홍선;오영진;강선예;윤기석;박재학
    • 한국압력기기공학회 논문집
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    • 제9권1호
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    • pp.62-69
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    • 2013
  • A probabilistic assessment code, PRO-LOCA ver. 3.7 which was developed in an international co-operative research program, PARTRIDGE was evaluated by conducting sensitivity analysis. The effect of some variables such as simulation methods (adaptive sampling, iteration numbers, weld residual stress model), crack features(Poisson's arrival rate, maximum numbers of cracks, initial flaw size, fabrication flaws), operating and loading conditions(temperature, primary bending stress, earthquake strength and frequency), and inspection model(inspection intervals, detectable leak rate) on the failure probabilities of a surge line nozzle was investigated. The results of sensitivity analysis shows the remaining problems of the PRO-LOCA code such as the instability of adaptive sampling and unexpected trend of failure probabilities at an early stage.

솔-젤 법을 이용한 Pb(Zr, Ti)$O_3$ 박막의 성장 및 전기적 특성에 관한 연구 (Growth and electrical properties of Pb(Zr, Ti)$O_3$ thin films by sol-gel method)

  • 김봉주;전성진;이재찬;유지범
    • 한국진공학회지
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    • 제8권4A호
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    • pp.425-431
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    • 1999
  • $Pb(Zr_{0.52}, Ti_{0.48})O_3$ (PZT) thick films as an actuating material with conducting oxides, $(La_{0.5}Sr_{0.5}) CoO_3$ (LSCO), have been fabricated by sol-gel method for Optical Micro-Electro-Mechanical System (MEMS) devices, in which PZT/LSCO/SiO2 structures were used. In order to improve the adhesion to LSCO solution in order to enhance the wetting behavior of a water-based LSCO precursor solution and further to improve the adhesion between LSCO and $SiO_2$ layers. PZT films were made using 1-3 propanediol based precursor solution which has a high viscosity and a boiling point appropriate for thick film fabrication. In the precursor solution, Ti-propoxied and Zr-propoxied are partially substituted with acetylacetone to achieve the solution stability while maintaining reactivity. Crack free PZT films (0.8~1$\mu\textrm{m}$) have been successfully fabricated at crystallization temperatures above $700^{\circ}C$. Dielectric constants and dielectric losses of the PZT films were 900~1200and 2~5%, respectively. Piezoelectric constant $d_{33}$ of the PZT films constrained by a substrate were 200pm/V at 100kV/cm.

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철도차량 차륜의 기계적 특성 및 잔류응력평가 (Evaluation of Mechanical Characteristic and Residual Stress for Railway Wheel)

  • 서정원;권석진;이동형;전홍규;박찬경
    • 한국정밀공학회지
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    • 제31권9호
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    • pp.783-790
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    • 2014
  • Railway wheels and axles are the most critical parts of the railway rolling stock. The wheel carry axle loads and guide the vehicles on the track. Therefore, the contact surface of wheel are subjected to wear and fatigue process. The wheel damage can be divided into three types; wear, contact fatigue failure and thermal crack due to braking. Therefore, in the contact surface between the wheel and the rail, the materials are heat treated to have a specific hardness. The manufacturing quality of the wheel have a considerable influence on the formation of tread wear and damage. Also, the residual stress on wheel is formed during the manufacturing process is one of the main sources of the damage. In this paper, the mechanical characteristic and the residual stress according to wheel material have been evaluated by applying finite element analysis and conducting mechanical tests.

MLS 가스겔용 NBR 피복 SUS301 박판의 피로파손 (Fatigue Fracture of NBR-coated SUS301 Thin Plate for MLS Gasket)

  • 한병기;조성산;장훈;김범근
    • 한국자동차공학회논문집
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    • 제12권4호
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    • pp.207-212
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    • 2004
  • Full-beads of multi-layer steel engine head gaskets that are used to seal the combustion gas between the head and the block are subject to cyclic bending stresses due to the variation of the head/block gap during engine operation. The S-N curve for the fatigue durability assessment of the full-bead formed on NBR-coated SUS301 thin plate is deduced from the axial fatigue test results because of the difficulty in conducting the bending fatigue test of thin plate. The experimental verification of the deduced S-N curve is presented. It is shown that the NBR coating increases the endurance limit of the plate significantly. Mechanism of crack nucleation and propagation in the full-bead is discussed with photographs of the fatigue cracks.

무전해 니켈/금도금에서의 내부 금속층의 결함에 대한 연구 (A Study of the fracture of intermetallic layer in electroless Ni/Au plating)

  • 박수길;정승준;김재용;엄명헌;엄재석;전세호
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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    • pp.708-711
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    • 1999
  • The Cu/Ni/Au lamellar structure is extensively used as an under bump metallization on silicon file, and on printed circuit board(PCB) pads. Ni is plated Cu by either electroless Ni plating, or electrolytic Ni plating. Unlike the electrolytic Ni plating, the electroless Ni plating does not deposit pure Ni, but a mixture of Ni and phosphorous, because hypophosphite Is used in the chemical reaction for reducing Ni ions. The fracture crack extended at the interface between solder balls of plastic ball grid (PBGA) package and conducting pads of PCB. The fracture is duets to segregation at the interface between Ni$_3$Sn$_4$intermetallic and Ni-P layer. The XPS diffraction results of Cu/Ni/Au results of CU/Ni/AU finishs showed that the Ni was amorphous with supersaturated P. The XPS and EDXA results of the fracture surface indicated that both of the fracture occurred on the transition lesion where Sn, P and Ni concentrations changed.

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