• Title, Summary, Keyword: hardness

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Hardness and microstructural changes by cooling rate and holding time during porcelain firing of a multi-purpose dental gold alloy (다목적용 치과용 금합금의 소성 시 냉각속도와 계류시간에 따른 경도와 미세구조의 변화)

  • Cho, Mi-Hyang
    • Journal of Technologic Dentistry
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    • v.33 no.4
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    • pp.271-281
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    • 2011
  • Purpose: The aim of this study is to investigate the changes in hardness and microstructure of a dental multipurpose alloy after simulated complete firing with controlled cooling rate and holding time by characterizing the changes in hardness and microstructure after simulated firing with various cooling rates and holding times. Methods: Before hardness testing, the specimens were solution treated and then were rapidly quenched into ice brine. The specimens were completely fired in furnace. Hardness measurements were made using a Vickers microhardness tester. The specimens were examined at 15 kV using a field emission scanning electron microscope. Results: The maximum hardness value was obtained at stage 0 after simulated firing with various cooling rates (quick cooling, stage 0, stage 1, stage 2, stage 3). By the repetitive firing, the hardness of the tested alloy decreased gradually. By holding the specimen at $500^{\circ}C$ for 10-20min after simulated firing, the hardness increased apparently. However, to hold the alloy for long periods of time in the relatively high temperature after simulated firing resulted in the formation of thick oxidation layer. The oxide film formed on the surface of the alloy after simulated complete firing with controlled cooling rate, which was mainly composed of O and Zn. Conclusion: It is reasonable to hold the alloy at $500^{\circ}C$ for 10-20min after complete firing in other to improve the final hardness of the alloy.

Effects os Cold Drawing Ratio on the Hardness of Inconel 718 Wire (Inconel 718 선재의 경도에 미치는 냉간신선가공의영향)

  • Jeong, Yong-Kwon;Jo, Chang-Yong;Jung, Byong-Ho;Kim, In-Bae
    • Korean Journal of Materials Research
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    • v.8 no.4
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    • pp.354-358
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    • 1998
  • Effect of cold drawing ratio and aging time on the hardness of lnconel 718 wire aged at 11l6K were investi¬gated by hardness measurement and scanning & transmission electron microscopy. Hardness which was 245Hv in as¬solution treated condition increased very rapidly to 450Hv as cold drawing ratio increased to 50%. The hardness in the early stage of aging was increased by the precipitation of $\gamma^{'}$ and $\gamma^{'}$ phases and after the peak hardness, the hardness was decreased by the transformation of $\gamma^{'}$ phase to $\delta$ phase. The time to reach peak hardness during aging appeared to be reduced with the increase of cold drawing ratio, and those times were 30, 10, and 5 minutes for 0, 30 and 50% cold drawn materials, respectively. For the 50% cold drawn material. $\gamma^{'}$ and $\gamma^{'}$ were precipitated by aging for 5 minutes at 1116K. The hardness in the same material was largely decreased under the initial hardness by the recrystallization.

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Development of an Automatic Soil Hardness Measuring System Mountable on Agricultural Tractors (트랙터 부착형 자동 토양경도 측정 시스템 개발)

  • 이현동;김기대;김찬수;김성환
    • Journal of Biosystems Engineering
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    • v.27 no.6
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    • pp.537-546
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    • 2002
  • In this study an automatic soil hardness measuring system mountable on agricultural tractors was developed to improve the accuracy of manual soil hardness testers by a constant penetrating rate, right direction of the cone-penetrometer and the isolation of vibration from the operator. This was necessary to supply similar experimental condition for performance test of new model and comparative experiment. The results of the study are summaried as follows; 1. The system consisted of a sensing part of soil hardness, a driving part of the measuring system and an attaching part between the tractor and the measuring system. 2. The allowable limit value of the system developed was set to 392N to protect from breaking the serve motor and the coupling used in this system. 3. The driving shaft penetrated into soil by 0.3m to measure soil hardness. The soil hardness was measured at the depth of 0.3m from the soil surface but the penetrating work was stopped and the driving shaft was pulled out to protect the system when the value of the soil hardness was too big on foreign substances like stones or straws. 4. Two values measured by automatic measuring system developed in this research and manual penetrometer were compared by statistics hypothesis testing method. When two people measured the soil hardness at the depth of 0.1 and 0.15m by manual cone penetrometer, there was no relationship between two values by two people but the values at the same depths by automatic measuring system developed showed similarity. The automatic system, therefore, developed in this research was proper for measuring soil hardness.

Research on the Electric device for the Noncontacting Hardness Tester (비접촉식 경도 측정용 전기 설비에 관한 연구)

  • 이진락;백기남
    • Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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    • pp.45-47
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    • 1991
  • In this research, we verify the relations between the mechanical hardness of a strip and the output of Residual Magnetic Flux Detector, which is installed in the end side of #2 CAL. First, we install the strip speed detector and get a hardness signal and a speed signal 2 seconds, and then do signal processing and send an output to a printer every 30 seconds. The system that performs above functions is Magnetic Hardness Data Acquisition & Processing System. We got the relation between output current and hardness for the strip of T3 BP through on-line tests. Seconds, we made a hardness Measurement Simulator and observed the speed characteristics of residual magnetic flux, with using it.

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Effect of Heat Treatments on the Final Hardness of STS 420J2 Martensitic Stainless Steel (420J2마르텐사이트 스테인레스강의 최종경도에 미치는 열처리조건의 영향)

  • Kim, K.D.;Sung, J.H.
    • Journal of the Korean Society for Heat Treatment
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    • v.7 no.3
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    • pp.175-183
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    • 1994
  • The effect of batch annealing conditions and austenitizing temperatures on the hardness and microstructural factors were examined by using 420J2 martensitic stainless steel. In spite of the similler hardness after batch annealing, the difference in hardness at the same austenitizing temperature was caused by changes in dissolved carbon during batch annealing. The highest hardness of the specimen was obtained at the batch annealing temperature of $820^{\circ}C$ and austenitizing temperature of $1050^{\circ}C$. The main factor affecting the final hardness of the cold annealed 420J2 specimen was proved to the austenitizing temperature rather than batch annealing temperature.

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Studies on the cigarette hardness(II) The Influence of relative humidity, temperature and net weight on cigarette hardness (담배 경도에 관한 연구(II) 상대습도, 온도 및 진충량이 담배의 경도에 미치는 영향)

  • 정한주;민영근;김병구;김기환
    • Journal of the Korean Society of Tobacco Science
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    • v.13 no.1
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    • pp.13-18
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    • 1991
  • This experiment carried out to review influence of relative humidity, temperature and net weight on cigarette hardness for the uniformal control of cigarette quality. Obtained results are as follows: 1. The difference in the cigarette physical properties of constant hardness control is considerably lower than that of constant net weight control. 2. Contribution rate for cigarette hardness is relative humidity > net weight > temperature. 3. The multiple regression equation of cigarette hardness related with relative humidity, temperature and net weight is calculated as follows.

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Effects of Zn, Zr Addition on Microstructures and Hardness of Mg/SiCp Composites Fabricated by Rheo-Compocasting (Rheo-Compocasting법으로 제조한 Mg/SiCp 복합재료의 조직 및 경도 특성에 미치는 Zn, Zr 첨가의 영향)

  • Hong, Sung-Kil;Choe, Jung-Chul
    • Journal of Korea Foundry Society
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    • v.15 no.6
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    • pp.588-595
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    • 1995
  • SiC particles reinforced Mg-Zr, Mg-Zn and Mg-Zn-Zr composites were manufactured by Rheocompocasting method. Effects of Zn, Zr addition on microstructures and hardness were investigated by using the micro Vickers hardness tester, the optical and scanning electron microscopy. By the Zr addition to the pureMg/SiCp composites, SiC particles become more homogeneously dispersed and grain refined so that the micro hardness of the composite increased. In case of Zn addition, although grain refinement and homogeneous dispersion effects of SiC particles were not obtained, hardness was more increased than the only Zr added composite by the formation of many Mg-Zn intermetallic compounds at grain boundary. In the Mg-Zn-Zr/SiCp composite, the highest value of hardness was obtained by triple effects such as grain refining, dispersion hardening of SiC particles and Mg-Zn compounds.

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A Study on the Evaluation of Brinell Standard Hardness Tester and Automatic Indentation Measurement System (브리넬 경도 표준 시험기 및 압입 자국 자동 측정장치의 특성 평가에 대한 연구)

  • Bahng, G.W.;Tak, Nae-Hyung
    • Journal of the Korean Society for Heat Treatment
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    • v.12 no.4
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    • pp.294-302
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    • 1999
  • Evaluation of Brinell standard hardness tester was carried out to secure its application as a national standard for Brinell hardness. Accuracies and reliabilities in load application, indenter diameter and indentation measurement were tested through evaluation of these components. The accuracies of load application for various loading conditions were within the limit of ISO and KS specifications. Errors in the indentation measurement due to the difference in personnel characters were successfully removed by utilising automatic indentation measurement system. In overall, the tester and the indentation measuring system were found to be eligible as a national standard of Brinell hardness.

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Controlling the Hardness and Tribological Behaviour of Non-asbestos Brake Lining Materials for Automobiles

  • Mathur, R.B.;Thiyagarajan, P.;Dhami, T.L.
    • Carbon letters
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    • v.5 no.1
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    • pp.6-11
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    • 2004
  • In spite of unparalleled combination of essential material properties for brake linings and clutch facings, replacement for asbestos is seriously called for since it is a health hazard. Once asbestos is replaced with other material then composition and properties of brake pad changes. In certain cases hardness of the material may be high enough to affect the rotor material. In this study, hardness of the brake pad has been controlled using suitable reinforcement materials like glass, carbon and Kevlar pulp. Brake pad formulations were made using CNSL (cashew net shell liquid) modified phenolic resin as a binder, graphite or cashew dust as a friction modifier and barium sulphate, talc and wollastonite as fillers. Influence of each component on the hardness value has been studied and a proper formulation has been arrived at to obtain hardness values around 35 on Scleroscopic scale. Friction and wear properties of the respective brake pad materials have been measured on a dynamometer and their performance was evaluated.

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Effect of Bilayer Thickness on Hardness of Ag/Ni Nanoscale Multilayers (Ag/Ni 나노다층박막의 경도에 미치는 Bilayer 두께의 영향)

  • Kang Bong Cheol;Kim Hee Yeoun;Kwon Oh Yeol;Lim Byung Kyu;Hong Soon Hyung
    • Proceedings of the Korean Society For Composite Materials Conference
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    • pp.23-26
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    • 2004
  • Ag/Ni multilayers with different bilayer thickness between 3 and 100 nm produced by DC magnetron puttering have been studied by cross-sectional TEM and nanoindentation. The micrograph shows perfect layered structure with sharp interfaces between Ag and Ni layers. Absolute hardness is calculated as a reference value to compare hardness of specimens regardless of indent depth. A hardness enhancement of nearly $100\%$ over the rule-of-mixtures values, calculated from the measured hardness of single Ag and Ni thin films, is observed. The hardness increases with decreasing bilayer thickness until 8nm. This enhancement shows a good agreement with Hall-Petch relation using grain size (one half of the bilayer thickness) confined within a layer. The deformation behavior can be explained by dislocation pile-up in smaller grains.

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