• Title/Summary/Keyword: Vickers Hardness

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A Study on new Photoinitiator of Visible Light Dental Composite Resin (치과용 가시광선 중합형 복합수지의 새로운 광개시제에 관한 연구)

  • Choi, Yong-Seok;Sun, Gum-Ju
    • Journal of Technologic Dentistry
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    • v.23 no.2
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    • pp.49-59
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    • 2002
  • The photopolymerization efficiency and surface hardness of composite resin containing 1,2-phenylpropanedione (PD) and diacetyl (DA) as photoinitiators were studied by IR and Vickers hardness and the results were compared with that of camphorquinone (CQ). Relative photopolymerization efficiency of the photoinitiators increased in the order of DA < CQ < PD. Vickers hardness of composite resin containing the photoinitiators increased in the order of CQ < PD < DA. Thus, PD is a new visible light photoinitiator for dental composite resin with higher photopolymerization efficiency and surface hardness than that of CQ. Mechanical properties such as Vickers hardness, diametral tensile strength, and flexural strength of the experimental resin composite prepared by addition of the photosensitizer into a resin of bis-GMA improved with increasing the photosensitizer content and irradiation time. The resin composite of bis-GMA containing DA or PD shows better mechanical properties than that of CQ.

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Surface Reaction between Phosphate bonded Investment and Ti-Zr-Cr based Alloy for Dental castings (인산염계 주형재와 치과주조용 Ti-Zr-Cr계 합금의 계면반응)

  • Jung, Jong-Hyun;Joo, Kyu-Ji
    • Journal of Technologic Dentistry
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    • v.27 no.1
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    • pp.73-78
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    • 2005
  • The surface-reacted layer of titanium castings greatly affects their mechanical properties. This study analyzed the interfacial zone of Ti-20%Zr-5%Cr alloy castings obtained from phosphate bonded investment and examined the relationship between the surface-reacted layer and hardness. The Vickers hardness of cast disks were tested at 20$\mu m$ intervals from the surface to 120$\mu m$ in depth. The cross-section was observed metallurgically, and line profile of the reacted layer was conducted under the EDX. The surface-reacted layer of Ti-20%Zr-5%Cr alloy is showed a similar tendency to Ti-6%Al-4%V alloy in thickness, and also Si diffusion in multiple reacted layer of Ti-20%Zr-5%Cr alloy is less than cp Ti and similar to Ti-6%Al-4%V alloy. The Vickers hardness in the surface layer was greater than in the inner part, and the Vickers hardness of Ti-20%Zr-5%Cr alloy ranged 650 to 390 and cp Ti ranged 810 to 160, Ti-6%Al-4%V alloy ranged 710 to 530 respectively.

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A study on wear damage of SKD11 steel material for a cutting mold jig (SKD11 절단금형치구용 소재의 마모손상에 관한 연구)

  • Nam, Ki-Woo;Kim, Cheol-Su;Ahn, Seok-Hwan
    • Journal of Power System Engineering
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    • v.20 no.5
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    • pp.5-13
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    • 2016
  • This study is on wear damage of the material for a molding machine that be used at finally cutting of metal beam made in roll forming process of vehicle bump beam process line. SKD11 steel was used with the material for cutting mold jig. In the cutting mold jig, Ti diffusion heat treatment after vacuum heat treatment was carried out for upgrade of surface hardness and anti-wear. Also, the heat treatments by various methods were performed to compare the wear damage degree against above the existing heat treatment. Wear loss and friction coefficient were obtained from wear test. And, micro Vickers hardness values were compared with damaged parts or not of cutting mold jig. Micro Vickers hardness value appeared higher at the undamaged part by Ti diffusion heat treatment. The micro Vickers hardness well followed a two-parameter Weibull probability distribution.

Evaluation on Degradation of Cr-Mo-V Steel by Micro-Vickers Hardness Measurement (미소 비커스경도에 의한 Cr-Mo-V강의 경년열화 평가)

  • Kim, Jung-Ki;Nahm, Seung Hoon;Kim, Amkee
    • Journal of the Korean Society for Heat Treatment
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    • v.11 no.1
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    • pp.54-61
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    • 1998
  • Since Cr-Mo-V steel has excellent fracture and creep properties at elevated temperature, they are extensively used as steam turbine components such as the turbine rotor. However, the turbine rotor steel used to suffer material degradation during long term service. Therefore, the assessment of the safety and residual life of the turbine rotor is periodically required during service. One of the most convenient techniques for that is the hardness method mainly due to its simplicity and nondestructive characteristics. In this research, six specimens with different aging times of turbine rotor steel were artificially prepared by an isothermal heat treatment at $630^{\circ}C$. The micro Vickers hardnesses of specimens were measured at room temperature. The relationships between the fracture properties and the hardness ratio were investigated. And also an indirect method to evaluate the residual life of degraded turbine rotor was proposed based on the micro Vickers hardness measurement.

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Failure Analysis and Weibull Statistical Analysis according to Impact Test of the Angular Pin for Injection Molding Machines (사출금형기계용 앵귤러핀의 충격시험에 따른 파손분석과 와이블 통계 해석)

  • Kim, Cheol-Su;Nam, Ki-Woo;Ahn, Seok-Hwan
    • Journal of Power System Engineering
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    • v.21 no.3
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    • pp.37-44
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    • 2017
  • In this study, failure analysis of the angular pin for molding machines to aluminum component molding was carried out. SM45C steel was used for the angular pin, it was surface hardened by the induction surface hardening heat treatment. The cross section of damaged angular pin was observed, and micro Vickers hardness value from the fractured part was measured. Brittle fracture was occurred from the fracture surface of angular pin, therefore, impact toughness value was evaluated by V-notch Charpy impact test. It was confirmed that the impact absorption energy was high when was tempered at a high temperature for a long time, and the toughness was slightly increased. Also, 2-parameter Weibull statistical analysis was investigated in order to evaluate the reliability of the measured micro Vickers hardness values and absorbed energy. The micro Vickers hardness and absorbed energy well followed a two-parameter Weibull probability distribution, respectively. The reverse design against angular pin was proposed as possible by using test results.

Sintering Behavior of Zircon with SiO2 (Silica가 첨가된 지르콘 소결거동)

  • Lee, Keun-Bong;Kang, Jong-Bong
    • Korean Journal of Materials Research
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    • v.18 no.11
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    • pp.604-609
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    • 2008
  • The sintering behavior of zircon with silica was investigated. Zircon with 5 vol% of sedimentation $SiO_2$ resulted in the apparent density of $4.45\;g/cm^3$, the diametral tensile strength of $12.125\;kgf/cm^2$, and the micro Vickers hardness of 1283 HV. The dissociation temperature and mechanical characteristics of the $ZrSiO_4$ were changed with different kinds of $SiO_2$. $SiO_2$ addition prevented dissociation of $ZrSiO_4$. Zircon with 5 vol% of sedimentation $SiO_2$ and with 5 vol% of fused $SiO_2$ resulted in increased diametral tensile strength and increased micro Vickers hardness by suppression of $ZrSiO_4$ dissociation and low temperature liquid $SiO_2$ formation. Zircon with fumed $SiO_2$ and quartz $SiO_2$ resulted in decreased diametral tensile strength and decreased micro Vickers hardness because of cristobalite and quartz phase formation and high temperature liquid $SiO_2$ formation. Zircon with 10 vol% of $SiO_2$ resulted in decreased diametral tensile strength and decreased micro Vickers hardness because of weak particle coupling due to excess formation of liquid $SiO_2$.

Effect of Experimental Fluoride Varnish upon the Vickers Hardness of Bovine Teeth (실험용 불소바니쉬가 우치의 비커스 경도에 미치는 영향)

  • Kim, Ah-Jin;Son, Ju-Lee;Oh, Seunghan;Bae, Ji-Myung
    • Korean Journal of Dental Materials
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    • v.43 no.1
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    • pp.81-89
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    • 2016
  • The purpose of this study was to evaluate the effect of the experimental and commercial fluoride varnishes on the Vickers hardness of bovine teeth. The experimental fluoride varnishes with 5 wt.% NaF were fabricated using Bis-GMA or rosin as the resin base. The components were mixed with over-head stirrer under warming up in a double boiler for 30 minutes. Four commercial fluoride varnishes (V-varnish, Flor-opal, Cavity shield, Fluor protector) were compared with the experimental fluoride varnishes. Vickers hardness was measured on the labial surface of bovine anterior teeth after applying fluoride varnish on 5th and 30th day. The surface of bovine teeth was observed with a scanning electron microscope before and after applying fluoride varnish and the change of the components on the bovine teeth surface was measured with EDX. In terms of hardness, the experimental rosin-based fluoride varnish showed significantly higher hardness on the 5th and 30th day than the control (bovine teeth without fluoride treatment)(p<0.05). EDX results showed that the fluoride content on the surface of bovine teeth treated with the experimental rosin-based fluoride varnish was highest on the 1st and 10th day. The higher hardness and fluoride content of experimental rosin-based fluoride varnish can be considered to be used as an effective fluoride varnish to prevent dental caries.

Presintering Temperature for Improving the Tool Life in Machining of $Si_3N_4$ Ceramics ($Si_3N_4$ 세라믹의 가공성을 고려한 예비소결온도 선정)

  • Lee Jae-Woo
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2005.06a
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    • pp.456-459
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    • 2005
  • The setting of a presintering temperature is carried out on the basis of the Vickers hardness of the presintered compact in the method for producing a ceramic sintered compact comprising presintering a formed compact composed of a ceramic powder and a sintering assistant, then machining the presintering compact and subsequently sintering the machined compact. The Presintering temperature is preferably set at a temperature so as to provide 213-230 Hv Vickers hardness of the compact for presintering. Furthermore, the presintering temperature is preferably within the range of 1,300-1,450$^{\circ}C$.

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Nondestructive Evaluation of Residual Life of 1Cr-1Mo-0.25V Steel from Reversible Magnetic Permeability

  • K.S. Ryu;S.H. Nahm;Kim, Y.I.;K.M. Yu;Kim, Y.B.;Cho, Y.;D. Son
    • Journal of Magnetics
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    • v.6 no.1
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    • pp.27-30
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    • 2001
  • We present a new procedure to evaluate the residual life of 1Cr-1Mo-0.25V steel from reversible magnetic permeability. The method is based on the existence of first harmonics in the differential magnetization around the coercive force. The apparatus is based on the detection of the voltage induced in a coil using a lock-in amplifier tuned to the frequency of the exciting coil. Results obtained for the first harmonics and Vickers hardness on aged samples show that the peak interval of reversible permeability and Vickers hardness decrease as aging time increases. The correlation between Vickers hardness and the peak interval of the reversible permeability may be used to evaluate the residual life of 1Cr-lMo-0.25V steel, nondestructively.

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저합금강판의 열간프레스성형에 따른 상변태 전산 해석

  • Bok, Hyeon-Ho;Kim, Hun-Dong
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2010.05a
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    • pp.39.2-39.2
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    • 2010
  • Recently, hot stamping process has been paid attention greatly by automobile makers in accordance with the fuel efficiency and environmental issues as well as crash safety issue. The hot-stamped parts, however, demand extreme mechanical properties such as tensile strength of over 1470 MPa or equivalently Vickers hardness of around 450. In this work, to meet the demand efficiently, a method to predict mechanical property of hot-stamped parts based on numerical phase transformation scheme has been proposed associated with the thermo-mechanical coupled finite element analysis. This work deals with various phase transformation equations and validates them to select appropriate model for 0.2C-0.1Si-1.4Mn-0.5Cr-0.01Mo-0.002B steel sheet. The authors show that an efficient method saving time and cost to develop hot-stamped automobile parts ensuring suitable mechanical properties such as Vickers hardness and strength.

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