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RISS 인기검색어
- 검색키워드
- 저자 : Korkolis, Y.P. (검색결과 4 건)
- 무료
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- 유료
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3-D and Anisotropic Effects on the Prediction of Burst in Aluminum Tube Hydroforming
Y.P. Korkolis,S. Kyriakides 한국소성가공학회 2010 기타자료 Vol.2010 No.6
Thin-walled Al-6260-T4 aluminum tubes were hydroformed in a custom testing facility [1,8]. The major mode of failure observed in the experiments was bursting, despite the simultaneous application of axial compression while inflating the tubes. At the same time, a series of FE models were developed in the nonlinear code ABAQUS to simulate the experiments; however, initial computations failed to yield accurate predictions of burst. This was attributed to the adoption of the classical J2 plasticity, which is unsuitable for an anisotropic aluminum alloy, and led to an extensive study of the constitutive behavior of Al-6260-T4 and of its forming limits (see [2-4]). With the benefit of this improved understanding of the material behavior, the hydroforming simulations were revisited and models of different degrees of sophistication were developed. Starting with shell element models, the anisotropic yield functions calibrated earlier in [2-4] were shown to improve predictions over the J2 plasticity, but were found to still be deficient in predicting the failures observed in the experiments. This was in turn attributed to the fact that shell elements cannot capture the stress triaxiality associated with the gradual evolution of necking encountered in hydroforming. In addition, despite the relatively thinwalled geometries involved, significant through-thickness stresses develop in the regions of the tube in contact with the die. These stresses are again missed by a shell element discretization. Both of these observations point to the use of solid element models, to capture the stress triaxiality. We will show that when these models are run in conjunction with nonquadratic anisotropic constitutive models, accurate predictions of failure in tube hydroforming are obtained. The conclusion that solid elements are required for failure calculations in tube hydroforming and that shell element models are deficient in that respect, contrasts sharply the current industrial practice in hydroforming simulations.
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Recent developments in hydroforming technology
Lee, Myoung-Gyu,Korkolis, Yannis P,Kim, Ji Hoon SAGE Publications 2015 PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGIN Vol.229 No.4
<P>This article is the review of hydroforming technologies that have been used increasingly in various industries including automotive applications. General concepts and technological developments in tube hydroforming and sheet hydroforming are presented with recent research and development activities. Then, the theoretical background associated with the plasticity and constitutive laws and their implementation to the computational modeling of the hydroforming process are discussed.</P>
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Thermal Effects on the Enhanced Ductility in Non-Monotonic Uniaxial Tension of DP780 Steel Sheet
Omid Majidi,Frederic Barlat,Yannis P. Korkolis,Jiawei Fu,Myoung-Gyu Lee 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.6
To understand the material behavior during non-monotonic loading, uniaxial tension tests were conducted inthree modes, namely, the monotonic loading, loading with periodic relaxation and periodic loading-unloadingreloading,at different strain rates (0.001/s to 0.01/s). In this study, the temperature gradient developing duringeach test and its contribution to increasing the apparent ductility of DP780 steel sheets were considered. In order toassess the influence of temperature, isothermal uniaxial tension tests were also performed at three temperatures(298 K, 313 K and 328 K (25 °C, 40 °C and 55 °C)). A digital image correlation system coupled with an infraredthermography was used in the experiments. The results show that the non-monotonic loading modes increasedthe apparent ductility of the specimens. It was observed that compared with the monotonic loading, the temperaturegradient became more uniform when a non-monotonic loading was applied.
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Thermomechanical response of a TWIP steel during monotonic and non-monotonic uniaxial loading
Majidi, O.,De Cooman, B.C.,Barlat, F.,Lee, M.G.,Korkolis, Y.P. Elsevier Sequoia 2016 Materials science & engineering. properties, micro Vol.674 No.-
<P>The tensile properties of a Fe-18%Mn-0.6%C-1.5%Al Twinning-Induced Plasticity (TWIP) steel were investigated at different strain rates in three loading modes, i.e. uniaxial monotonic loading, stress relaxation and loading-unloading-reloading. Infrared thermography was used to investigate the effect of the dynamic strain aging, the strain rate and the temperature on the flow stress. In addition to the standard, i.e., non-isothermal tensile tests, isothermal uniaxial tensile tests were performed at 25 degrees C, 45 degrees C and 65 degrees C. While the non-monotonic loading modes resulted in an increase of the total elongation at a low strain rate of 10(-3) s(-1), no increase was observed for strain rates higher than 6 x 10(-3) s(-1). The temperature gradients observed during non-isothermal tests were reduced when non-monotonic loading conditions were used. Temperature changes were found to influence the hardening behavior, and consequently the ductility, of the TWIP steel. Deformation twinning also had a significant influence on the results as its kinetics in TWIP steel are determined by the temperature dependence of the stacking fault energy. (C) 2016 Elsevier B.V. All rights reserved.</P>
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