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3 차원 열전달/열응력 해석을 통한 STD61 열간 금형강의 하드페이싱 재료 및 두께 예측
박나라(Na-Ra Park),안동규(Dong-Gyu Ahn) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.4
이 연구에서는 STD61 열간금형강 상부에 생성되는 하드페이싱층에 적합한 하드페이싱 재료와 두께를 3 차원 비정상 열전달 및 열응력 해석을 통하여 예측하고자 한다. Stellite6, Stellite21 과 19-9DL 초합금을 하드페이싱 재료로 적용하였다. 하드페이싱 재료와 두께가 하드페이싱된 시편 내부 온도, 열응력 및 변형률 분포 변화에 미치는 영향에 대하여 분석하였다. 이 결과로부터 큰 열전도도를 가지는 재료로 얇은 하드페이싱 층을 생성하는 것이 열전달 특성 측면에서는 효과적인 것을 알 수 있었다. 또한, Stellite21 초합금으로 2 mm 두께의 하드페이싱부를 STD61 열간 금형강 상부에 생성할 경우, 하드페이싱부와 기저부의 경계부에서 유효응력 및 주변형률 편차가 최소화됨을 알 수 있었다. 이 결과들로부터 STD61 열간금형강에 적합한 하드페이싱 재료와 두께를 예측할 수 있었다. The goal of this paper is to estimate proper hardfacing material and thickness of STD61 hot-working tool steel through three-dimensional heat transfer and thermal stress analyses. Stellite6, Stellite21 and 19-9DL superalloys are chosen as alternative hardfacing materials. The influence of hardfacing materials and thicknesses on temperature, thermal stress and thermal strain distributions of the hardfaced part are investigated using the results of the analyses. From the results of the investigation, it has been noted that a hardfacing material with a high conductivity and a thinner hardfaced layer are desired to create an effective hardfacing layer in terms of heat transfer characteristics. In addition, it has been revealed that the deviation of effective stress and principal strain in the vicinity of the joined region are minimized when the Stellite21 harfaced layer with the thickness of 2 mm is created on the STD61. Based on the above results, a proper hardfacing material and thickness for STD61 tool steel have been estimated.
박상하,이민구,한나라,성굉모,Park, Sang-Ha,Lee, Min-Gu,Hahn, Na-Ra,Sung, Koeng-Mo 한국음향학회 2011 韓國音響學會誌 Vol.30 No.5
The sounds of the Korean temple bells, that are located in the various places, were recorded and classified into two groups according to the size of bells. The sound preference was investigated with the subjective listening test on the bells of each group. And the acoustic characteristics of the bells such as the frequency, amplitude, beat period, and 20 dB decay rate of the partials was analyzed. The correlation between the acoustic parameters and timbre preference were analyzed and the acoustic characteristics of highly preferred bell sound were presented. 본 논문에서는 전국 각지의 범종 소리를 녹음하고 이를 크기에 따라 두 개의 그룹으로 분류한 후, 두 그룹에 대하여 주관청취 평가를 시행하여 사람들이 어떤 범종 소리를 선호하는지 조사하였다. 또한, 범종 음향 분석을 통해 부분음의 위치, 크기, 맥놀이 주기, 20 dB 감쇠 시간을 분석하였다. 이후, 분석된 음향학적 파라미터와 선호도의 상관관계를 파악함으로써 선호도가 높은 범종과 선호도가 낮은 범종을 구분짓는 음향학적 특징을 알아보았다.
펄스전류 활성 소결법에 의한 나노구조의 3Ti-2Al2O3 복합재료 제조 및 특성
박나라 ( Na Ra Park ),손인진 ( In Jin Shon ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.11
Nanopowders of TiO2 and Al were prepared from a high energy ball milling method to fabricate sintered 3Ti-Al2O3 composites with nanostructures. A dense nanocrystalline 3Ti-2Al2O3 composite was consolidated by a pulsed current activated sintering method from the mechanically activated powder. Consolidation of dense 3Ti-Al2O3 composites with a relative density of up to 99% was accomplished under the combined contribution of a pulsed current and a mechanical pressure of 60 MPa. The hardness and fracture toughness of the fabricated composites were 1207 kg/mm2 and 7 MPa¥m1/2, respectively.
NiAl3 첨가가 (W,Ti)C 초경재료 소결 및 기계적 성질에 미치는 영향
박나라 ( Na Ra Park ),나권일 ( Kwon Il Na ),권한중 ( Han Jung Kwon ),임재원 ( Jae Won Lim ),손인진 ( In Jin Shon ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.10
Co or Ni was added to cemented (W,Ti)C as a binder for forming composite structures. The high cost of Co or Ni and the low corrosion resistance of (W,Ti)C-Co or (W,Ti)C-Ni cermet have generated interest in recent years in the search to find alternative binder phases. It has been reported that aluminides have a higher oxidation resistance, a higher hardness and are cheaper materials than Co and Ni. Using a pulsed current activated sintering (PCAS) method, the densification of (W,Ti)C and (W,Ti)C-NiAl3 hard materials were accomplished within 3 minutes. The advantage of this process is not only rapid densification to near theoretical density but also the prohibition of grain growth in nano-structured materials. Highly dense (W,Ti)C and (W,Ti)C-NiAl3 with a relative density of up to 99% were obtained within 3 minutes by PCAS under a pressure of 80 MPa. The average grain sizes of the (W,Ti)C was lower than 100 nm. The hardness and fracture toughness of the dense (W,Ti)C and (W,Ti)C-NiAl3 produced by PCAS were also investigated. (Received March 22, 2013)
고주파유도가열 연소합성에 의한 4.25 Co<sub>0.53</sub>Fe<sub>0.47</sub>-Al<sub>2</sub>O<sub>3</sub> 복합재료 제조
박나라,남궁훈,고인용,손인진,Park, Na-Ra,NamKung, Hoon,Ko, In-Yong,Shon, In-Jin 한국분말야금학회 2009 한국분말재료학회지 (KPMI) Vol.16 No.2
Nanopowders of $Co_3O_4$ and FeAl were fabricated by high energy ball milling. Dense 4.25 $Co_{0.53}Fe_{0.47}-Al_2O_3$ composite was simultaneously synthesized and consolidated by high frequency induction heated combustion method within 2 min from mechanically activated powders. Consolidation was accomplished under the combined effects of a induced current and mechanical pressure of 80 MPa.