• Title/Summary/Keyword: micro fracture

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Evaluation of Fracture Detection Function for the Concrete by Self-Diagnosis CPGFRP (자기진단 CPGFRP의 파괴예측기능 평가를 위한 콘크리트 적용실험)

  • Choi, Hyun-Soo;Park, Jin-Sub;Jnng, Min-Soo;Kang, Byeung-Hee
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2003.11a
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    • pp.27-31
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    • 2003
  • To maintain serviceability of concrete structure more than proper it is necessary not only predict service life through periodical monitor but also need monitoring system to recognize optimal time and method for repair. Recently, CPGFRP, replacing some GFRP with CF, is developed and used for monitoring concrete fraction. But dramatic resistance change of CPGFRP is showed below 0.5% strain and it is not small strain in terms of monitoring micro crack in concrete. In other word, monitoring with CF is not suitable in low stress hut hight stress. In this study, we accessed applicable possibility and reliability of CPGFRP composite as monitoring sense that is proved very sensitive to stress through domestic and oversea previous study. CPGFRP composite plays a role in specimen like steel and increases flexural strength. CPGFRP composite shows resistance increasement in micro crack. In particular, CPUFRP is more sensitive than strangage in low stress. Resistance change ratio curve is very similar to strain curve so sensitivity and reliability is very excellent to monitor concrete fracture.

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Evaluation of Fracture Detection Function for the Concrete by Self-Diagnosis CPGFRP (자기진단 CPGFRP의 파괴예측기능 평가를 위한 콘크리트 적용실험)

  • 최현수;박진섭;정민수;강병희
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2003.05a
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    • pp.27-31
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    • 2003
  • To maintain serviceability of concrete structure more than proper it is necessary not only predict service life through periodical monitor but also need monitoring system to recognize optimal time and method for repair. Recently, CPGFRP, replacing some GFRP with CF, is developed and used for monitoring concrete fraction. But dramatic resistance change of CPGFRP is showed below 0.5% strain and it is not small strain in terms of monitoring micro crack in concrete. In other word, monitoring with CF is not suitable in low stress but hight stress. In this study, we accessed applicable possibility and reliability of CPGFRP composite as monitoring sense that is proved very sensitive to stress through domestic and oversea previous study. CPGFRP composite plays a role in specimen like steel and increases flexural strength. CPGFRP composite shows resistance increasement in micro crack. In particular, CPGFRP is more sensitive than strangage in low stress. Resistance change ratio curve is very similar to strain curve so sensitivity and reliability is very excellent to monitor concrete fracture.

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Evaluation of Failure Mode and Strength on Baking Time of Adhesive for Hybrid Joining (접착제 경화시점에 따른 하이브리드 접합 파단모드 및 접합강도 평가)

  • Choi, Chul-Young;Saha, Dulal Chandra;Choi, Won-Ho;Kim, Jun-Ki;Kim, Jong-Hoon;Park, Yeong-Do
    • Journal of Welding and Joining
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    • v.29 no.6
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    • pp.49-55
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    • 2011
  • With the development of pre-painted steel sheets for automotive body application, a new joining method is required such as hybrid joining with combination of adhesive bonding and mechanical joining. The objective of this study is to investigate the effect of pre- and post-baking of adhesive bonding on failure mode and strength of hybrid joining of automotive steel sheets. Experiments show that the hybrid joining exhibits better bonding strength and displacement than conventional adhesive joining and mechanical fastening each. Comparison of pre- and post-baked hybrid joining results suggested that baking at $160^{\circ}C$ after mechanical joining was found to have higher joining properties than pre-baking condition. The prebaking condition changed its fracture mode from interfacial to button fracture. The changes in fracture mode with post-baking of hybrid joining was attributed to variation in neck thickness and undercut of joint.

Fabrication and High-temerature Mechanical Property of Liquid-Phase-Sintered SiC (액상소결 탄화규소 세라믹스의 제조 및 고온기계적 특성)

  • Lee, Moonhee;Kim, Sungwon;Lee, Jongho;Hwang, SeungKuk;Gwak, Jaehwan;Lee, Jinkyung;Lee, Sangpill
    • Journal of the Korean Society of Industry Convergence
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    • v.23 no.4_2
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    • pp.669-674
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    • 2020
  • Liquid-phase-sintered (LPS) SiC materials were briefly examined with their microstructure and mechanical property. Especially, effect of high-temperature exposure on the tendency of fracture toughness of LPS-SiC were introduced. The LPS-SiC was fabricated in hot-press by sintering powder mixture of sub-micron SiC and sintering additives of Al2O3-Y2O3. LPS-SiC represented dense morphology and SiC grain-growth with some amount of micro-pores and clustered additives as pore-filling. The strength of LPS-SiC might affected by distribution of micro-pores. LPS-SiC tended to decrease fracture toughness depending on increasing exposure temperature and time.

The change in mechanical properties of bond materials for micro-blades with the amount of lubricants (충진 윤활제의 첨가량에 따른 블레이드용 결합제의 기계적 특성)

  • Kim, Song-Hee
    • Journal of Industrial Technology
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    • v.28 no.A
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    • pp.195-198
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    • 2008
  • Graphite and $MoS_2$ were added respectively to the Cu/Sn bond materials of the same composition as a lubricant in order to find out the effect of lubricants on the mechanical properties and the increase in density of the sintered products for microblades. The addition of $MoS_2$ as a lubricant was more beneficial to strength, fracture toughness, and hardness as well as densification than graphite. $MoS_2$ seemed to be more effective in reducing the friction between the metallic powders and die wall during hot pressing process. Due to the better wettability of MoS2 with bond metal alloy, less amount of interfacial defects which is detrimental to mechanical properties use observed.

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A Study on Slot Grinding for Lead Pin Punching Die (리드 핀 제조용 펀치 금형의 홈 가공에 관한 연구)

  • 이용찬;정상철;정해도
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.4
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    • pp.106-113
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    • 2000
  • 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 optics, electronics and semiconductor parts. Slot grinding is very efficient for the generation of micro ordered groove with hard and brittle materials. In the process of slot grinding, chipping at the sharp edges and microcracks of the ground grooves are inevitable defects. Chipping should be reduced for the improvement of surface integrity. Mechanical contact with diamond grits causes microcracks at the grooves. This damage resides subsurface, and can be the cause of failure of the punch die. This paper deals with chipping generation at the sharp edges, surface integrity of side groove and fracture strength is related to the microcracks in the slot grinding.

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Machining and Crack Characteristics of the Glass Cap for OELD by Powder Blasting (파우더 블라스팅에 의한 OELD용 유리캡의 가공 및 크랙 특성)

  • Park, Dong-Sam;Kang, Dae-Kyu;Kim, Jeong-Keun;Seong, Enu-Je;Han, Jin-Yong
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.15 no.5
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    • pp.51-58
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    • 2006
  • The old technique of sandblasting which has been used for paint of scale removing, deburring and glass decorating has recently been developed into a powder blasting technique for brittle materials, capable of producing micro structures larger than $100{\mu}m$. Recently, this technique is applied to fabrication of the glass cap for OELD packaging. But, micro crack is generated on the blasted glass, which cause to decrease fracture strength. In this paper, we investigated the effect of blasting parameters on surface characteristics, surface shape and fracture strength of the powder blasted glass surface.

Deformation Properties of Gold Bonding Wire for VLSI Packaging Applications (반도체 패키징용 Gold Bonding Wire의 변형특성 및 해석)

  • Kim K.;Hong S. H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2001.05a
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    • pp.250-253
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    • 2001
  • Mechanical properties of gold bonding wire for VLSI packaging have been studied. The diameters of gold wires are about 20-30 micrometer and fracture loads are 8-20 gram force. The elastic modulus, yield strength, fracture strength and elongation properties have been evaluated by micro-tensile test method. This work discusses for an appropriate selection of micro-force testing system and grip design in mim testing. The best method to determine gauge length of wire and to measure tensile properties has been proposed. The mechanical properties such as strength and elastic modulus of current gold bonding wire are higher than pure those of gold wire.

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Mechanical Properties and Fracture Behavior of Cylindrical Shell Type for Unidirectional CFRP Composite Material under Tension Load (원통형 셀 구조를 갖는 한방향 CFRP 적층 복합재료의 정적인장파괴거동)

  • 오환섭
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 1998.10a
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    • pp.273-278
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    • 1998
  • In this paper, basic micro-mechanical properties of unidirectional CFRP composite shell such as bonding strength, fiber volume fraction and void fraction are measured and tensile strength test is performed with a fixture. And then fracture surfaces are observed by SEM. In case of basic micro-mechanical properties, bonding strength is reduce with decreasing of radius of each ply in a shell for the effect of residual stress, fiber volume fraction is smaller than plate, and void fraction is vise versa. For these reason, tensile strength of shell is smaller than plate fabricated with same prepreg. For failure mode shell has many splitted part along its length, and it is assumed that this phenomenon is caused by the difference of bonding strength for residual stress.

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Evaluation of Crack Length and Thickness Effects of Fracture Specimen using Damage Mechanics (손상역학에 근거한 파괴시편의 균열길이와 두께 영향 평가)

  • Chang Yoon-Suk;Lee Tae-Rin;Choi Jae-Boong;Seok Chang-Sung;Kim Young-Jin
    • Journal of the Korean Society for Precision Engineering
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    • v.23 no.4 s.181
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    • pp.116-123
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    • 2006
  • During the last two decades, many researchers investigated influences of stress triaxiality on ductile fracture for various specimens and structures. With respect to a transferability issue, the local approach reflecting micro-mechanical specifics is one of effective methods to predict constraint effects. In this paper, the applicability of the local approach was examined through a series of finite element analyses incorporating modified GTN (Gurson-Tvergaard-Needleman) and Rousselier models as well as fracture toughness tests. To achieve this goal, fracture resistance (J-R) curves of several types of compact tension (CT) specimens with various crack length, with various thickness and with/without 20% side- grooves were estimated. Then. the constraint effects were examined by comparing the numerically estimated J-R curves with experimentally determined ones. The assessment results showed that the damage models might be used as useful tool for fracture toughness estimation and both the crack length and thickness effects should be considered for realistic structural integrity evaluation.