• Title/Summary/Keyword: C-shaped specimen

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Low Cycle Fatigue Life Evaluation of External Grooved C-shaped Specimen (외경홈을 지닌 C형 시험편의 저주기 피로수명평가)

  • Lee, Song-In
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.2
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    • pp.199-208
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    • 1997
  • A local strain approach was applied to an external single and double grooved C-shaped specimen in order to evaluate and predict the fatigue crack initiation life by using low cycle fatigue properties. The low cycle fatigue properties were determined from the strain-controlled fatigue tests using smooth cylindrical axial specimens. Fatigue crack initiation life was evaluated by a life prediction software, FALIPS, based on the local strain approach. The fatigue life was significantly influenced by the mean stress, and SWT parameter represented the fatigue life effectively. The predicted fatigue crack initiation life was then compared to the experimental fatigue life evaluated from the C-shaped fatigue test specimens. A good correlation was found between the experimental and predicted fatigue lives within factors of 2 and 4 for the single and double grooved C-shaped specimens respectively. Also, experimental fatigue life of the double grooved specimen was 10-12 times longer than that of the single grooved specimen.

Effects of Specimen Depth on Flexural Compressive Strength of Concrete (부재의 깊이가 콘크리트의 휨압축강도에 미치는 영향)

  • 이성태;김진근;김장호
    • Journal of the Korea Concrete Institute
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    • v.12 no.5
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    • pp.121-130
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    • 2000
  • Currently, in evaluating a flexural strength of a concrete member, the effect of specimen depth has not been systematically studied, even though its effect on ultimate strength of a section is very important. For all types of loading conditions, the trend is that the strength of a member tends to decrease when the member depth increases. In this study, the influence of specimen depth on flexural compressive strength of concrete member was examined experimentally. A series of C-shaped specimens subjected to axial compressive force and bending moment were tested using three geometrically similar specimens with different length-to depth ratios (h/c = 1, 2 and 4) which have compressive strength of 55 MPa. The results indicate that the flexural compressive strength decreased as the specimen depth increased. A model equation was derived based on regression analyses of the experimental data. Also, the results show that ultimate strain decreases as the specimen depth increases. Finally, a general model equation for the depth effect is proposed.

Effects of Specimen Length on Flexural Compressive Strength of Concrete (부재의 길이가 콘크리트의 휨압축강도에 미치는 영향)

  • 김진근;이성태;이태규
    • Journal of the Korea Concrete Institute
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    • v.11 no.4
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    • pp.63-71
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    • 1999
  • In evaluating the ultimate strength of a section for a reinforced concrete flexural member, the effect of member length is not usually considered, even though the strength tends to decrease with increase of member length. In this paper the influence of specimen length on flexural compressive strength of concrete was evaluated. For this purpose, a series of C-shaped specimens subjected to axial compression and bending moment were tested using four different length-to-depth ratios (from 1,2,3 and 4) of specimens with compressive strength of 590 kgf/$\textrm{cm}^2$. Results indicate that for the region of h/c <3.0 the reduction in flexural compressive strength with increase of length-to-depth ratios was apparent. A model equation was depth of an equivalent rectangular stress block was larger than that by ACI. It was also founded that the effect of specimen length on ultimate strain was negligible. Finally more general model equation is also suggested.

The Investigation of Stress Block of C-Shaped Specimen for High-Strength Polymer Concrete (고강도 폴리머 콘크리트 C 형보의 응력블럭 고찰)

  • 김관호;연규석;김남길;박광수;신수균;이준구
    • Proceedings of the Korea Concrete Institute Conference
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    • 2001.05a
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    • pp.1023-1028
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    • 2001
  • This study was conducted to develop a procedural method to produce a high strength polymer concrete using polyester resin to experimentally examine the stress block properties of the high strength polymer concrete. C-shaped specimens were Produced and test to compute parameter of the stress block. They were $k_{1}$ : 0.73 and $\gamma$ : 0.845, respectively. $k_{1}$ is the ratio of the depth of the maximum compressive strength of the beam

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The Effects of Homogenization, Hot-Forging, and Annealing Condition on Microstructure and Hardness of a Modified STD61 Hot-Work Tool Steel (균질화, 열간단조, 어닐링 조건이 개량된 STD61 열간 금형강의 미세조직과 경도에 미치는 영향)

  • Park, Gyujin;Kang, Min-Woo;Jung, Jae-Gil;Lee, Young-Kook;Kim, Byung-Hoon
    • Journal of the Korean Society for Heat Treatment
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    • v.26 no.2
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    • pp.72-79
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    • 2013
  • The effects of homogenization, hot-forging, and annealing condition on microstructure and hardness of a modified STD61 hot-work tool steel were investigated. The ingot specimen had a dendritic structure consisting of bainite and martensite. Spherical VC particles of approximately 50 nm and cuboidal (V,Ti)C particles of about 100 nm were observed in the ingot specimen. After homogenization, the dendritic structure was blurred, and the difference in hardness between martensite and bainite became narrow, resulting in the more homogeneous microstructure. Needle-shaped non-equilibrium $(Fe,Cr)_3C$ particles were additionally observed in the homogenized specimen. The hot-forged specimen had bainite single phase with spherical VC, cuboidal (V,Ti)C, and needle-shaped $(Fe,Cr)_3C$ particles. After annealing at $860^{\circ}C$, the microstructures of specimens were ferrite single phase with various carbides such as VC, $(Fe,Cr)_7C_3$, and $(Fe,Cr)_{23}C_6$ because of relatively slow cooling rates. The size of carbides in annealed specimens decreased with increasing cooling rate, resulting in the increase of hardness.

The Aging Characteristics of an RS-P/M Al-Zn-Mg- Zr-Mn-Cu Alloy (급속응고 분말법으로 제조한 Al-Zn-Mg-Zr-Mn-Cu합금의 시효특성)

  • 이갑호
    • Journal of Powder Materials
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    • v.4 no.2
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    • pp.100-105
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    • 1997
  • In this study the changes of the hardness and microstructures during aging at 120$^{\cire}C$ of an RS-P/M Al-5.6wt%Zn-2.0wt%Mg-1.3wt%Zr-1.0wt%Mn-0.25wt%Cu alloy were studied using a transmission electron microscopy. The hardness increased rapidly at early stage of aging and reached the maximun when the specimen was aged for 24 hr. The many irregular-shaped $Al_4Mn$ and rod-shaped $Al_6Mn$ dispersoids with 0.1-0.4 $\mu$m in length were observed in the as-extruded alloy. The dark particles with 2-3 nm in size were observed in aged specimen for 5hr and those are thought to be G.P.zones or precursor of $\eta'$ precipitates. In aged specimen for 24 hr, the $\eta'$ phases were distributed homogeneously within the matrix and the PFZ with 30-40 nm in width was observed along the grain boundary. With further aging, the width of PFZ increased and $\eta$ phases were also detected within the matrix.

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Effects of Specimen Depth on Flexural Compressive Strength of Concrete (콘크리트의 휨압축강도에 미치는 부재깊이의 영향)

  • Yi, Seong-Tae;Kim, Jin-Keun;Lee, Yun;Kim, Jang-Ho;Yang, Eun-Ik
    • Proceedings of the Korea Concrete Institute Conference
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    • 2000.10a
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    • pp.115-120
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    • 2000
  • Currently, in evaluating a flexural strength of a concrete member, the effect of specimen depth has not been systematically studied, even though its effect on ultimate strength of a section is very important. For all types of loading conditions, the trend is that the strength of a member tends to decrease when the member depth increases. In this study, the influence of specimen depth on flexural compressive strength of concrete member was examined experimentally. A series of C-shaped specimens subjected to axial compressive force and bending moment were tested using three geometrically similar specimens with different length-to-depth ratios(h/c=1, 2 and 4) which have compressive strength of 55MPa. The results indicate that the flexural compressive strength decreased as the specimen depth increased. A model equation was derived based on regression analyses of the experimental data. Also the results show that ultimate strain decreases as the specimen depth increases. Finally, a general model equation for the depth effect is proposed.

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Effects of Specimen Length on Flexural Compressive Strength of Polymer Concrete (부재의 길이가 폴리머 콘크리트의 휨압축 강도에 미치는 영향)

  • 연규석;김남길;주명기;유근우;권윤환
    • Proceedings of the Korea Concrete Institute Conference
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    • 2002.05a
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    • pp.99-104
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    • 2002
  • In this paper the influence or specimen length on flexural compressive strength and parameter or equivalent rectangular stress block of polymer concrete was evaluated. For this purpose, a series of C-shaped specimens subjected to eccentric compression were tested using four different length-to-depth ratios(from 1.0, 2.0, 3.0 and 4.0) of specimens with compressive strength of 1,020kgf/cm$^2$. Results indicate that for the region of h/c$\leq$3.0 the reduction in equivalent rectangular stress block depth and flexural compressive strength with increase of length-to-depth ratios was apparent but for the region of h/c$\geq$3.0 they were nearly constant. It means that for the region of h/c$\geq$3.0 effect of specimen length on equivalent rectangular stress block depth and flexural compressive strength was negligible. It was also founded that the effect of specimen length on v, a coefficient of strength, that was from 0.84 to 0.86 regardless of h/c was petty. Finally, predictive equation is, suggested by using modified law of effect of specimen length and results.

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Stress Block of High Strength Polymer Concrete Flexural Members (고강도 폴리머 콘크리트 휨부재의 응력블럭)

  • 김관호;김남길;연규석
    • Journal of the Korea Concrete Institute
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    • v.14 no.5
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    • pp.638-644
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    • 2002
  • The stress-strain relationship of polymer concrete flexural member was evaluated using C-shaped polyester concrete specimen, the compressive strength of which is 1400 kgf/$\textrm{cm}^2$. Eccentric compression test was performed to estimate the parameters, ${\alpha}$, ${\beta}$1, ${\gamma}$ for equivalent rectangular stress block. The ultimate moment strength ware obtained from the bending test on reinforced polymer concrete beams which were prepared with S different tensile steel ratios with a shear span ratio of 4.0. These values were compared with theoretical ultimate moment strengths, which were obtained using the parameters ${\alpha}$=0.61 and ${\beta}$1=0.73 from stress-stain curves of C-shaped specimens. The results showed that, when tensile steel ratio was over 0.50 $\rho$b, the experimentally obtained moment strengths were well matched with theoretically calculated values. In order to develop accurate criteria for polymer concrete flexural members, however, many other expermental studies for parameter determination are necessary using C-shaped specimens which have various compressive strengths and different sizes.

Fabrication and Characterization of BSCCO System High-Temperature Superconductor Using Centrifugal Forming Process (원심성형법을 이용한 BSCCO계 고온초전도체 제조 및 특성 분석)

  • 박용민;장건익
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2000.07a
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    • pp.189-192
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    • 2000
  • High-temperature superconductor of Bi-2212 system was fabricated by CFP(centrifugal forming process). To make a uniform specimen slurry was prepared in the ratio of 7:3(powder:binder) and ball milled for 24 hours. Milled slurry was charged into a rotating mold with 450 rpm and dried at room temperature. Then the specimen was performed binder burn-out at 35$0^{\circ}C$ and heated for partial melting to 86$0^{\circ}C$. XRD analysis of most specimens were shown 2212 phase and observed a local plate shaped microstructure with a well aligned c-axis direction from SEM images. T$_{c}$(Critical temperature) of Bi-2212 was 64K.K.

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