• Title, Summary, Keyword: hardening

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Springback FE modeling of titanium alloy tubes bending using various hardening models

  • Shahabi, Mehdi;Nayebi, Ali
    • Structural Engineering and Mechanics
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    • v.56 no.3
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    • pp.369-383
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    • 2015
  • In this study, effect of various material hardening models based on Holloman's isotropic, Ziegler's linear kinematic, non-linear kinematic and mixture of the isotropic and nonlinear kinematic hardening laws on springback prediction of titanium alloy (Ti-3Al-2.5V) in a tube rotary draw bending (RDB) process was investigated with presenting the keynotes for a comprehensive step by step ABAQUS simulation. Influence of mandrel on quality of the final product including springback, wall-thinning and cross-section deformation of the tube was investigated, too. Material parameters of the hardening models were obtained based on information of a uniaxial test. In particular, in the case of combined iso-nonlinear kinematic hardening the material constants were calibrated by a simple approach based on half-cycle data instead of several stabilized cycles ones. Moreover, effect of some material and geometrical parameters on springback was carried out. The results showed that using the various hardening laws separately cannot describe the material hardening behavior correctly. Therefore, it is concluded that combining the hardening laws is a good idea to have accurate springback prediction. Totally the results are useful for predicting and controlling springback and cross-section deformation in metal forming processes.

Microscopic Investigation of the Strain Rate Hardening for Metals (금속재료 변형률속도 경화의 미시적 관찰)

  • Yoon, J.H.;Huh, H.;Huh, M.Y.;Kang, H.G.;Park, C.G.;Suh, J.H.;Kang, J.S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.352-355
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    • 2007
  • Polycrystalline materials such as steels(BCC) and aluminum alloys(FCC) show the strain hardening and the strain rate hardening during the plastic deformation. The strain hardening is induced by deformation resistance of dislocation glide on some crystallographic systems and increase of the dislocation density on grain boundaries or inner grain. However, the phenomenon of the strain rate hardening is not demonstrated distinctly. In this paper, tensile tests for various strain rates are performed in the rage of $10^{-2}$ to $10^2s^{-1}$ then, specimens are extracted on the same strain position to investigate the microscopic behavior of deformed materials. The extracted specimen is investigated by using the electron backscattered diffraction(EBSD) and transmission electron microscopy(TEM) results which contain grain size, grain shape, aspect ratio and dislocation substructure.

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A Study on the strain hardening behavior of hydroformed Engine Cradle (액압성형공정을 적용한 엔진크레들의 가공 경화 특성 연구)

  • Park, H.K.;Yim, H.S.;Yi, H.K.;Kim, K.S.;Moon, Y.H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.154-157
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    • 2008
  • It is important to know the variations of the mechanical properties in the hydroforming process for the safe and durable design purposes. In this study, strain hardening behavior during hydroforming has been investigated by hydroforming of engine cradle as a model process. The variation of mechanical properties such as local hardness and flow stress were used as an index of strain hardening during respective processes. By using the inter-relationships between hardness-flow stress-effective strain at variable pre-strains, the strain hardening behavior during hydroforming has been successfully analyzed. The comparison of predicted hardness with measured hardness confirmed that the methodology used in this study was feasible and the strain hardening behavior can be quantitatively estimated.

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Hardening Temperature Dependence of Epoxy Resin (Epoxy 수지의 경화 온도 의존성)

  • Kim, Tae-Seoung;Yeo, In-Seon;Chung, Hwa-Kyun;Lee, Jin
    • Proceedings of the KIEE Conference
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    • pp.499-503
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    • 1987
  • The electrical characteristics of Epoxy Robin vary with temperature. In this study, the variation of the electric characteristics of Epoxy Resin with various hardening temperature was studied. Epoxy Resin used as samples are Epotohto YD-128 of Diglycidyl Ether of Bisphenol A (DGEBA) series and hardener, Goodmide G-240. It's mixing rate is 3 to 1. Hardening temperature was varied from 25[$^{\circ}C$] to 50[$^{\circ}C$] by 5[$^{\circ}C$]. During the hardening progress, illumination, resistivity and the internal temperature of material which were dependet on the variety of hardening temperature were measured. The electrical properties of hardened samples were examined by means of X-ray diffraction, tan $\delta$ test, TG-DTA analysis and treeing test. On this basis, optimal hardening temperature in insulation characteristics was examined.

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Design of Robot Direct-Teaching Tool and its Application to Path Generation for Die Induction Hardening

  • Ahn, Jae-Hyung;Sungchul Kang;Changhyun Cho;Jisun Hwang;Mansuk Suh
    • 제어로봇시스템학회:학술대회논문집
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    • pp.118.5-118
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    • 2002
  • To apply induction hardening method to a press die having 3-D free surface, the induction hardening tool moves on a press die above 1~2mm gap with constant velocity. Since the induction hardening process requires its own hardening path for each die, a direct teaching method which generates working path directly guided by operators is more suitable than an offline method using CAD/CAM data. The direct teaching apparatus in this work includes a teaching tool with a force/torque sensor and data processing computer to finally generate robot's Induction hardening program , in direct teaching operation, an operator teaches working path maintaining contact with surface of press die by holding...

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A Study on 40Cr Alloy steel of Laser Surface Hardening (40Cr 강의 Laser Surface Hardening 에 관한 연구)

  • Ryu, Nung-Hee;Kang, Sung-Goon
    • Korean Journal of Materials Research
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    • v.11 no.11
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    • pp.1001-1005
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    • 2001
  • In this study, the surface of 40Cr steel was hardened by $CO_2$Laser, and then the microstructural transformations and the hardness distributions of the laser surface hardened layer were observed. The experimental results showed the surface hardening layer was consisted of three parts, which is outmost surface layer of needle martensite, middle layer of martensite and remained pearlite, and transitory boundary layer. In hardness distributions, the surface hardeness of the surface hardening layer had Hv 800~1000, that was 2 to 4 times of matrix's hardness. The hardeness distribution of laser hardening layer that of surface layer hardened by general heat treatment.

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Transformation Hardening of High Power Laser (고출력 레이저에 의한 표면 경화)

  • Kim, J.D.
    • Journal of the Korean Society for Heat Treatment
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    • v.8 no.1
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    • pp.24-31
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    • 1995
  • Heat flow equation and FEM have been used to calculate the hardening section of material in laser transformation hardening. SCM440 used as the diesel engine piston of vessel has been hardened by a $CO_2$ laser with the wavelength of $10.6{\mu}m$. The specimens were inclined from 0 to 70 degree to investigate the characteristics of laser hardening. The geometrical factor of heat flow equation affects the size of hardening area. The case width decreased with increasing travel speed and the case width increased with increasing inclined angle. Maximum case depth was achieved about 1.0mm and maximum hardness of laser hardened area was of 2.8 times than that of base metal. Experimental data show good agreement with the theoretical calculations for given laser hardening conditions.

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Nondestructive Measurement of Case Hardening Depth with Eddy Current Method (와전류법을 이용한 강의 표면경화층 깊이의 비파괴적 측정)

  • Lee, K.W.;Han, S.Y.;Park, U.S.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.11 no.1
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    • pp.38-43
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    • 1991
  • The relationship between eddy current response and case hardening depth has been studied on SM40C(KS D-3752) and SCM440(KS D-3711) steels which were surface hardened by high frequency induction hardening. The results obtained in this study were as follows ; 1) Case hardening depth was successfully measured by observing the eddy current impedance changes of each steel. The impedance decreased linearly with increasing case hardening depth. 2) For large impedance gradient between the hardened surface and core metal, the eddy current response was more sensitive to case hardening depth than for low impedance gradient.

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Prediction of Temperature and Moisture Distributions in Hardening Concrete By Using a Hydration Model

  • Park, Ki-Bong
    • Architectural research
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    • v.14 no.4
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    • pp.153-161
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    • 2012
  • This paper presents an integrated procedure to predict the temperature and moisture distributions in hardening concrete considering the effects of temperature and aging. The degree of hydration is employed as a fundamental parameter to evaluate hydro-thermal-mechanical properties of hardening concrete. The temperature history and temperature distribution in hardening concrete is evaluated by combining cement hydration model with three-dimensional finite element thermal analysis. On the other hand, the influences of both self-desiccation and moisture diffusion on variation of relative humidity are considered. The self-desiccation is evaluated by using a semi-empirical expression with desorption isotherm and degree of hydration. The moisture diffusivity is expressed as a function of degree of hydration and current relative humidity. The proposed procedure is verified with experimental results and can be used to evaluate the early-age crack of hardening concrete.

Strain Hardening Behavior in the Tube Hydroforming (튜브 액압성형품의 가공 경화 특성 연구)

  • Park, H.K.;Yim, H.S.;Yi, H.K.;Kim, K.S.;Moon, Y.H.
    • Transactions of Materials Processing
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    • v.17 no.8
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    • pp.564-569
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    • 2008
  • Strain hardening behavior during hydroforming has been experimentally investigated. The variation of flow stress was used as an index of strain hardening during respective processes and the flow stress was estimated from the correlationship between flow stress and effective strain. The local hardness after hydroformig was also predicted by effective strain. By using the inter-relationships between hardness-flow stress-effective strain at variable pre-strains, the strain hardening behavior during hydroforming has been successfully analyzed. The comparison of predicted hardness with measured hardness confirmed that the methodology used in this study was feasible and the strain hardening behavior can be quantitatively estimated.