• Title/Summary/Keyword: yield strengths

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Effect of Martensite Fraction on the Tensile Properties of Dual-phase Steels Containing Micro-alloying Elements (미량합금 원소가 첨가된 2상 조직강의 인장 특성에 미치는 마르텐사이트 분율의 영향)

  • Lim, Hyeon-Seok;Kim, Ji-Yeon;Hwang, Byoungchul
    • Journal of the Korean Society for Heat Treatment
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    • v.30 no.3
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    • pp.106-112
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    • 2017
  • In this study dual-phase steels with different ferrite grain size and martensite fraction were fabricated by varying micro-alloying elements and intercritical anneling temperatures, and then the tensile properties were investigated in terms of yield and tensile strengths, elongation, and yield ratio. The addition of micro-alloying elements reduced ferrite grain size, and the increased intercritial transformation tempeature increased the martensite fracton. The tensile test results showed that yield and tensile strengths of all the steel specimens increased with increasing the martensite fraction. However, the elongation and yield ratio were differently changed according to variations in the morphology and carbon content of martensite, ferrite grain size, and precipitates resulting from the addition of micro-alloying elements and intercritical annealing.

High-Temperature Tensile Strengths of Alloy 617 Diffusion Weldment (Alloy 617 확산용접재의 고온 인장강도)

  • Sah, Injin;Hwang, Jong-Bae;Kim, Eung-Seon
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.14 no.1
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    • pp.15-23
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    • 2018
  • A compact heat exchanger is one of critical components in a very high temperature gas-cooled reactor (VHTR). Alloy 617 (Ni-Cr-Co-Mo) is considered as one of leading candidates for this application due to its excellent thermal stability and strengths in anticipated operating conditions. On the basis of current ASME code requirements, sixty sheets of this alloy are prepared for diffusion welding, which is the key technology to have a reliable compact heat exchanger. Optical microscopic analysis show that there are no cracks, incomplete bond, and porosity at/near the interface of diffusion weldment, but Cr-rich carbides and Al-rich oxides are identified through high resolution electron microscopic analysis. In high-temperature tensile testing, superior yield strengths of the diffusion weldment compared to the code requirement are obtained up to 1223 K ($950^{\circ}C$). However, both tensile strength and ductility drop rapidly at higher temperature due to the insufficient grain boundary migration across the interface of diffusion weldment. Best fit curves for minimum yield strength and average tensile strength are drawn from the experimental tensile results of this study.

Effects of Tempering on Tensile Properties of Medium-Carbon Low-Alloy Steels (중탄소 저합금강의 인장성질에 미치는 템퍼링의 영향)

  • Lee, Young-Kook;Krauss, George
    • Journal of the Korean Society for Heat Treatment
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    • v.12 no.4
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    • pp.327-337
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    • 1999
  • A series of Ni-Cr-Mo alloy steels were austenitized, quenched to martensite, and tempered at various temperature and time conditions. Tensile testing was conducted at room temperature with cylindrical specimens, and hardness was measured using Rockwell hardness tester. In the tempering stage I, high strain hardening and yield strength accounted for the high ultimate strength and hardness. In the tempering stage II, strengths and hardness linearly decreased with increasing tempering temperature. Specimens tempered in the temperin stage III showed incipient discontinuous yielding and tensile strengths only slightly higher than yield strengths. Ductilities decreased slightly in specimens tempered in the tempered martensite embrittlement range, and severely decreased in specimens tempered for 10 hours at $500^{\circ}C$ in the temper embrittlement range. Specimens tempered at $600^{\circ}C$ for 10 hours showed recrystallized microstructures, a number of fine dimples, and increased strain hardening, probably due to the precipitation of alloy carbides. The simple formulae for the mechanical properties of these steels were suggested as a function of carbon content and Hollomon-Jaffe tempering parameter.

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Evaluation of Forming Performance of Cold Rolled Steel Pipes & Tubes for Building Structure (건축구조용 냉간성형 강관의 가공성능 평가)

  • Im, Sung Woo;Choi, Kwang;Chang, In Hwa
    • Journal of Korean Society of Steel Construction
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    • v.16 no.1 s.68
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    • pp.33-42
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    • 2004
  • Making use of SN steel in the building structure should be a prerequisite to adopt the design strength of said steel. As a preceding study, the material properties of STKN400B/490B tubes and SPAP235/325 and SPAR295 square pipes manufactured using SN400B/490B plates were evaluated. Compared with the yield and ultimate strengths of SN400B/490B plates, those of STKN400B/490B tubes increase. Nonetheless, the yield and ultimate strengths of STKN400B/490B tubes satisfied the design codes of STKN400B/490B tubes even though the tubes were fabricated via roll bending or press forming. On the other hand, the yield and ultimate strengths at the edges of SPAP235/325 square pipes did not satisfy the design codes based on the values at the sides. The maximum tensile and compressive residual stresses at the SN490B tube were equal to and 40% of the yield strength of the SN490B plate, respectively, In the case of the SPAP325 square pipe, both the maximum tensile and compressive residual stresses were 80% of the yield strength of the SN490B plate. The axial compressive loaded column test results snowed that the buckling strengths were not very different regardless of the mode of fabrication of STKN490B tunes. i.e., through roll bending or press forming. On the other hand, the buckling strength of the SPAP325 square pipe was higher than that of the built-up square pipe.

Performance evaluation of high-performance lattice girder using numerical analysis (수치해석을 통한 고성능 격자지보재의 성능 평가)

  • Kim, Dong-Gyou;Ahn, Sungyoull
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.21 no.6
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    • pp.897-908
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    • 2019
  • The objective of this study is to evaluate the field support performance of highperformance lattice girder (BK-Lattice Girder) by using numerical analysis. Three types (50, 70, 95-type) of existing and high performance lattice girders were applied to the cross section of highway 2, 3, and 4 lane tunnels to compare the supporting performance. The numerical analysis was the finite element method and the lattice girder was modeled in three dimensions with an elasto-plastic frame. The ground was modeled as a spring receiving only compression. The load was applied as a concentrated load on the central ceiling of the tunnel section. The yield strengths of the lattice girders were determined from the numerical results to compare the supporting performance of lattice girder. In case of 50-type, the yield strengths of high-performance lattice girders were increased by 6.7~10.0% compared with those of the existing lattice girders. In the case of 70-type, the high-performance lattice girders increased yield strengths by 12.1~14.9% than the existing lattice girder. In the case of 95-type, the high-performance lattice girders increased yield strengths by 13.3~20.0% than the existing lattice girder. As a result of numerical analysis, it was considered that the high-performance lattice girder supported better than the existing lattice girder when only the lattice girders were constructed.

Pullout Test of Headed Reinforcement 2: Deep Embedment

  • Choi, Dong Uk;Shin, InYong
    • Proceedings of the Korea Concrete Institute Conference
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    • 2003.05a
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    • pp.1091-1096
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    • 2003
  • Pullout tests of single headed bars using plain concrete blocks indicate that the embedment depth of $10d_b$ is in general required for the headed bars to develop pullout strength equivalent to 125% of bar yield strength. In this experimental study, test results of multiple headed bars installed in reinforced concrete column sections are presented. Test variables included embedment depth, column main reinforcement ratio, and spacing of column ties. 2D29 bars were pulled out at one time from normal strength concrete. Test results indicated that the embedment depths, column tie spacings, and column main reinforcement ratios all influenced the pullout strengths of the headed bars. When the embedment depth was not sufficient, narrow tie spacings especially resulted in increased pullout strengths of the headed bars. Test results also indicated that the embedment depth of 15㏈ was sufficient for the closely spaced two headed bars (head-to-head spacing =$6d_b$) to develop pullout strength equivalent to 125% of the bar yield strength.

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Effect of the Reflectivity of Both Facets and the Phase of a Phase Tuning Section on the Yield Characteristics of a Multisection Index-Coupled DFB Laser (양 단면 반사율과 위상 조정 영역의 위상이 다중 영역 Index-Coupled DFB 레이저의 수율 특성에 미치는 영향)

  • Kim, Tae-Young;Ryu, Jong-In;Kim, Boo-Gyoun
    • Korean Journal of Optics and Photonics
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    • v.17 no.6
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    • pp.548-555
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    • 2006
  • We investigate the effect of the reflectivity of both facets and the phase of a phase tuning section on the self-pulsation (SP) characteristics of multisection index-coupled (IC) DFB lasers composed of two index-coupled DFB sections and a phase tuning section between them in terms of yield. In the case of weak coupling strength, as the reflectivity of both facets increases, the effect of reflected fields from both facets and the other DFB section on the mode characteristics of one DFB section increases. Thus the number of mode hoping increases and yield decreases for the variation of phases of both facets. In the case of strong coupling strength, as the reflectivity of both facets increases, the spatial hole burning effect increases, so that the yield decreases. The maximum yield and the range of the phase of a phase tuning section with yield more than 40% decrease as the facet reflectivity increases irrespective of coupling strength. As the coupling strength increases, the variation of yield for the variation of the phase of a phase tuning section increases and the variation of the phase of a phase tuning section with the maximum yield for the variation of the reflectivity of both facets decreases. The yield characteristics of the cases with the coupling strengths of 2 and 3 are better than those with the coupling strengths of 1.2 and 4.

Electrorheology and universal yield stress function of semiconducting polymer suspensions

  • Choi, Hyoung-J.;Cho, Min-S.;Kim, Ji-W.
    • Korea-Australia Rheology Journal
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    • v.13 no.4
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    • pp.197-203
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    • 2001
  • We reported on the eletrorheological (ER) properties of several semiconducting polymers including poly (p-phenylene) (PPP), poly (acene quinone) radicals (PAQRs), microencapsulated polyaniline (MPANI) and polyaniline (PANI) those we synthesized. The yield stress dependence on electric field strength for the ER fluids using these semiconducting polymers was mainly examined. The yield stress, which is an important design parameter for ER fluids, was observed to satisfy a universal scaling function, allowing that yield stress data for all the ER fluids examined in this study collapse onto a single curve for a broad range of electric field strengths. The proposed scaling function incorporates both the polarization and conductivity models.

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Seismic performance of RC bridge piers reinforced with varying yield strength steel

  • Su, Junsheng;Dhakal, Rajesh Prasad;Wang, Junjie;Wang, Wenbiao
    • Earthquakes and Structures
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    • v.12 no.2
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    • pp.201-211
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    • 2017
  • This paper experimentally investigates the effect of yield strength of reinforcing bars and stirrups on the seismic performance of reinforced concrete (RC) circular piers. Reversed cyclic loading tests of nine-large scale specimens with longitudinal and transverse reinforcement of different yield strengths (varying between HRB335, HRB500E and HRB600 rebars) were conducted. The test parameters include the yield strength and amount of longitudinal and transverse reinforcement. The results indicate that the adoption of high-strength steel (HSS) reinforcement HRB500E and HRB600 (to replace HRB335) as longitudinal bars without reducing the steel area (i.e., equal volume replacement) is found to increase the moment resistance (as expected) and the total deformation capacity while reducing the residual displacement, ductility and energy dissipation capacity to some extent. Higher strength stirrups enhance the ductility and energy dissipation capacity of RC bridge piers. While the product of steel yield strength and reinforcement ratio ($f_y{\rho}_s$) is kept constant (i.e., equal strength replacement), the piers with higher yield strength longitudinal bars are found to achieve as good seismic performance as when lower strength bars are used. When higher yield strength transverse reinforcement is to be used to maintain equal strength, reducing bar diameter is found to be a better approach than increasing the tie spacing.

Effect of Grain Size on the Tensile Properties of an Austenitic High-Manganese Steel (오스테나이트계 고망간강의 인장 특성에 미치는 결정립 크기의 영향)

  • Lee, Sang-In;Cho, Yun;Hwang, Byoungchul
    • Korean Journal of Materials Research
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    • v.26 no.6
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    • pp.325-331
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    • 2016
  • This paper presents a study of the tensile properties of austenitic high-manganese steel specimens with different grain sizes. Although the stacking fault energy, calculated using a modified thermodynamic model, slightly decreased with increasing grain size, it was found to vary in a range of $23.4mJ/m^2$ to $27.1mJ/m^2$. Room-temperature tensile test results indicated that the yield and tensile strengths increased; the ductility also improved as the grain size decreased. The increase in the yield and tensile strengths was primarily attributed to the occurrence of mechanical twinning, as well as to the grain refinement effect. On the other hand, the improvement of the ductility is because the formation of deformation-induced martensite is suppressed in the high-manganese steel specimen with small grain size during tensile testing. The deformation-induced martensite transformation resulting from the increased grain size can be explained by the decrease in stacking fault energy or in shear stress required to generate deformation-induced martensite transformation.