• Title/Summary/Keyword: Grain sizes

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Evaluation of Fracture Strength of WA-Vitrified and Resinoid Bond Grinding Wheels by Acoustic Emission (AE에 의한 WA계 비트리파이드 및 레지노이드 結合劑硏削숫돌의 破壞强度評價)

  • 강명순;한응교;권동호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.2
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    • pp.241-251
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    • 1988
  • The purpose of this paper is to evaluate fracture strength of WA-vitrified and resinoid bond grinding wheels by means of acoustic emission. The paper conducts tension test, compression test, splitting tensile test and bending test with AE measuring system. These tests have been carried out in accordance with the grain sizes and grades of grinding wheels. The fracture strength of grinding wheels is evaluated by the clarification of biaxal fracture criterion of Babel and Sines. It clarifies the influence of factors of grinding wheel upon AE characteristics and evaluates the predictability of life of grinding wheels and the perception of fracture.

Electron Beam Weld ability of Alloy 718 Nozzle for Jet Propulsion Component (고속 추진체용 Alloy 718 노즐 단조품의 전자빔 용접성 평가)

  • Lee, C.H.;Kim, J.H.;Hong, J.K.;Yeom, J.T.;Yoon, J.W.;Park, N.K.
    • Transactions of Materials Processing
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    • v.17 no.7
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    • pp.523-527
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    • 2008
  • In this study, mechanical properties of Alloy 718 welded after forgings for jet propulsion component was investigated. Hot-forged and machined work-pieces($230mm\times70mm\times15mm$) which have different grain sizes are welded by electron beam welding technique. After welding, the components were solution heat-treated and aged. Samples were sectioned to analyze the microstructural evolution and formation of micro-crack. It was found that HAZ grain boundary liquation crack generally initiates in the coarse grains rather than the fine grains. Needle-like phases with high Nb contents were found at the outer part near the base metal. Vickers hardness and tensile tests were carried out at room temperature and at $649^{\circ}C$. The tensile properties of electron beam welding specimens exhibited around 100MPa and 10% decrease in strength and elongation, respectively.

The Response Characteristics of the Hydrogen Peroxide Monopropellant Thruster as Injector and Catalyst Grain Size (인젝터 방식 및 촉매 알갱이 크기에 따른 과산화수소 단일추진제 추력기의 응답 특성)

  • An, Sung-Yong;Park, Dae-Jong;Chung, Seung-Mi;Kwon, Se-Jin
    • Journal of the Korean Society of Propulsion Engineers
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    • v.13 no.1
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    • pp.19-26
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    • 2009
  • The response characteristics of $H_2O_2$ monopropellant thrusters at a pulse mode were presented in this paper. A catalyst bed was fixed to $MnO_2$/$Al_2O_3$ to investigate the thruster design effect to response time. Three different thrusters (50 N class) having different injectors, ullage volumes, catalyst grain sizes, and reactor volumes were prepared to investigate the response characteristics. As a result, the ignition delay, pressure rising and tail-off time of case 2-2 thruster with 16-20 mesh catalyst size were 14, 108, 94 ms respectively, which were comparable to requirement of response time at commercial hydrazine thrusters.

The Effect of Zirconia Particle Size on Mechanical Properties of Zirconia Toughened Alumina (ZrO2의 분말크기가 ZTA의 기계적 물성에 미치는 영향)

  • Sohn, Jeongho;Shin, Hyung-Sup
    • Korean Journal of Materials Research
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    • v.24 no.12
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    • pp.652-657
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    • 2014
  • The purpose of this study was to investigate the microstructures and mechanical properties of zirconia toughened alumina (ZTA) ceramics prepared from two kinds of 3Y-TZP powders. ZTA composites were prepared by adding two kinds of 3Y-TZP powders, 3YEH (BET = $7m^2/g$) and 3YEM (BET = $16m^2/g$), to ${\alpha}$-alumina in the range of 5-25 wt%. It was found that the microstructure photographs of the ZTA composites showed that the average grain size of alumina decreased as the content of zirconia increased. In our present study, specimens containing 3YEM zirconia exhibited smaller grain sizes compared to those of 3YEH zirconia. The Vickers hardness of the ZTA composites that were sintered at $1600^{\circ}C$ for 2 hrs was found to smoothly decrease with increasing zirconia content because of the low Young modulus in zirconia. The Vickers hardness of the ZTA containing 3YEH zirconia was greater than that of the 3YEM zirconia. In substance, the fracture toughness ($K_{1c}$) of the ZTA composites increased as the content of zirconia increased. The fracture toughness ($K_{1c}$) of ZTA containing 3YEM zirconia was greater than that of 3YEH zirconia.

Late Pleistocene Variation in Intensity of Deep Western Boundary Current from Vertical Change in Size of Terrigenous Silt in the Rekohu Sediment Drift, SW Pacific (남서태평양 리코후 드리프트 퇴적층의 쇄설성 실트입자 크기의 수직적 변화를 이용한 플라이스토세 후기 심해서안경계해류의 세기 변화)

  • Kim, B.K.;Lee, Y.J.;Park, Y.H.;Bahk, J.J.
    • Ocean and Polar Research
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    • v.28 no.4
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    • pp.451-457
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    • 2006
  • Hole 1124 of ODP Leg 181 was located in the Rekohu sediment drift off eastern New Zealand in the southwest Pacific Ocean. Mean gain sizes of sortable silt were measured in two drilled cores (1124A and l124B). Chronostratigraphy of core 1124 was correlated with the well-dated nearby core S931, resulting that the age of core 1124 covers the late Pleistocene spanning about MIS (Marine Isotope Stage) 5. Mean grain size of sortable silt seemed to be relatively large during the glacial period, whereas that of the interglacial period was smaller, although several tephra layers contain some coarse-grained pyroclatic particles. The variation in mean grain size of sortable silt in Rekohu sediment drift during the late Pleistocene indicates that the intensity of Deep Western Boundary Current (DWBC) might have been enhanced during the glacial period as a result of increased production of Antarctic Bottom Water (AABW).

Fabrication of Injection Molded Fe-50%Ni Sintered Bodies (사출성형된 Fe-50%Ni 소결체의 제조)

  • Kim Ki-Hyun;Yoon Hyeong-Chul;Choi Chul-Jin;Lee Byong-Taek
    • Journal of Powder Materials
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    • v.11 no.6 s.47
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    • pp.472-476
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    • 2004
  • The Fe-Ni compact bodies were fabricated using Fe-Ni mixed powders with 50 nm in diameter by injection molding process. The relationship between microstructure and material properties was characterized with respect to the volume ratio of powder/binder and sintering temperature with SEM and TEM. In the compact body having the volume percent ratio of 45(Fe-Ni) : 55(binder), which was sintered at $900^{\circ}C$ the values of relative density and hardness were low about 97.7% and 277.1 Hv, respectively. Using the composition of 50(Fe Ni) : 50(binder) and sintered at $900^{\circ}C$, the values of relative density and hardness were 98.5%, 294.4 Hv, respec-tively. The grain size of sintered bodies strongly depended on the sintering temperature. In both samples sintered at $600^{\circ}C$ and $900^{\circ}C$, the average grain sizes were about 150 nm and 500 nm in diameter, respectively.

The Effect of Low Melting Point Phase on Mechanical Properties of Al-Cu-Li-X(In, Be) Alloys (Al-Cu-Li-X(In, Be) 합금의 기계적 성질에 미치는 저융점상의 영향)

  • Lee, J.S.;Lee, S.H.;Kim, S.W.;Woo, K.D.
    • Journal of the Korean Society for Heat Treatment
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    • v.8 no.4
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    • pp.245-254
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    • 1995
  • The purpose of this study was to examine the effects of low melting point phase(LMPP) on mechanical properties in the Al-Cu-Li-X(In, Be) alloys. This study was performed by the differential scanning calorimetry(DSC), the transmission electron microscope(TEM), hardness test, tensile test and notch tensile test. The shape of LMPP in the specimens homogenized at $570^{\circ}C$ was film type due to remelting at grain boundary during homogenization. Low melting point phases had no effects on mechanical properties in the aging treated materials, because the density of LMPPs was low. Mechanical properties of the aging treated materials were affected by the density of matrix precipitation phases and grain sizes. For the In or In, Be added Al-Cu-Li alloys, the optimum solution treatment temperature was $550^{\circ}C$. The strength of Al-Cu-Li-In-Be $T_6$ treated alloy was higher than that of 2090-$T_8$ alloy.

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Microstructures and Mechanical Properties of HIPed Submicron WC-(5~20) mass% Co Cemented Carbides (HIP처리한 초미립 WC-(5~20) mass% Co 초경 합금의 미세조직과 기계적 성질)

  • 이승원;이완재
    • Journal of Powder Materials
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    • v.5 no.4
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    • pp.279-285
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    • 1998
  • The microstructures and mechanical properties of submicron WC-Co cemented carbides were investigated in relation to cobalt content. To inhibit the WC grain growth during sintering, VC was added as a inhibitor in each alloy with 3 mass% to the cobalt content. The WC-(5, 8, 10, 15, 20) mass% Co compacts were sintered at $1400^{\circ}C$ for 30 min in vacuum. Some of WC-(5, 8, 10) mass% Co sintered compacts were HIPed with 120 atm at 130$0^{\circ}C$ for 1 hr. The shrinkages of all HIPed alloys were increased without depending on the cobalt contents and the sintered densities of them. The relative densities of the alloys were increased with the cobalt content and HIPing. The less the cobalt content, the larger the WC grain. Many contiguities of WC grains were found in WC-5 mass% Co alloy. The sizes and numbers of pores in the alloys were decreased by HIPing. And also the strength and the hardness of each alloy were increased. The maximum hardness was about 18.95 GPa in the WC-5 mass% Co alloy HIPed and the maximum transverse-rupture strength (T.R.S.) 3.2 GPa in the WC-20 mass% Co alloy sintered.

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A Study on the Mechanical Properties Based on Frit Addition in 3Y-TZP Zirconia Composition (3Y-TZP Zirconia 조성에서 Frit의 첨가에 의한 기계적 특성 연구)

  • Kwon, Eun-Ja;Lee, Gyu-Sun;Lee, Chae-Hyun
    • Journal of Technologic Dentistry
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    • v.29 no.1
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    • pp.49-57
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    • 2007
  • This study was to add crushed frit with different grain sizes to 3Y-TZP so that it could determine the mechanical properties depending on sintering temperature. In this study, 3 types specimens were prepared in powder with respective additions of 20wt.% frit, which was sized through 24-, 48- and 72-hour ball milling with zirconia. Then, sintered pellets were tested in experiments under the temperature variations for different compositions. As a result, this study came to the following findings: 1. It was found that the higher sintering temperature and the longer ball milling time of frit led to the higher sintered density. 2. Bending strength tended to increase with higher sintering temperature and longer ball milling time of frit. 3. Hardness tended to increase with higher sintering temperature and longer ball milling time of frit. 4. However, it was found that fracture toughness didn't vary significantly depending on sintering temperature. From these findings, it was concluded that the smaller frit grain size and the narrower particle size distribution of frit lead to the better mechanical properties.

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Evaluation of Compressibility of Rock Fill Materials by Large-Scale Oedometer Tests (대형 오이도미터 시험을 통한 Rockfill 재료의 압축성 평가)

  • Kim, Bum-Joo;Shin, Dong-Hoon;Jeon, Je-Sung;Lim, Jeong-Yeul
    • Proceedings of the Korean Geotechical Society Conference
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    • 2005.03a
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    • pp.627-632
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    • 2005
  • In this study, a series of large-scale oedometer tests was performed to investigate the compressibility of rock fill materials. The testing samples were prepared to have three different grain size distributions and for each distribution, exist in two different states(dried and saturated). The test results indicated that particle breakages occurred mainly for the particles larger than 4.75mm in size and increased with increasing grain sizes. Also, it was found that, for a dry sample as it became well-graged, its compressibility decreased and accordingly, its tangent constrained modulus increased. A comparion between the samples in dry and saturated states revealed that compressibility of the materials increases with increasing water content. The values of tangent constrained modulus calculated for the tested dry samples were larger by about 10 to 20%, on average, than those for the saturated samples.

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