Papers by Author: S.S. Hong

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Authors: Nho Kwang Park, Jong Taek Yeom, Young Sang Na, J.S. Lee, In Ok Shim, S.S. Hong
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Authors: J.Y. Kim, In Ok Shim, H.K. Kim, S.S. Hong, Soon Hyung Hong
Abstract: Deformation behaviors under quasi-static and dynamic compression and high velocity impact condition of Ti-6Al-4V ELI (extra low interstitial) alloys in two different conditions were investigated. Mill annealed (MA) alloy, consisted of equiaxed α, and thermomechanically treated (TMT) alloy, consisted of mixed structure of equiaxed α and transformed β, were prepared. Compression tests were performed in low strain rate regime using hydraulic testing machine and were performed in high strain rate regime using split Hopkinson pressure bar. High velocity impact tests were also performed by impacting the test projectiles made of these alloys against a steel target at a velocity of ~400m/s. The compression test results showed that deformation behaviors were influenced by the strain hardening exponent at low strain rate regime, and by both the strain hardening exponent and the strain-rate hardening rate at high strain rate regime. TMT alloy showed higher strength but almost similar fracture strain as MA alloy at a high strain rate of ~6000/s, due to the effect of strain-rate hardening. The high velocity impact test results showed that the projectile of TMT alloy withstood without fracture at higher impact velocity, but the maximum amounts of deformation prior to crack were nearly the same for both alloys. These results were in accord with the results of compression tests at high strain rate regime, that is, higher strength but same fracture strain of TMT alloy compared to MA alloy.
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Authors: You Hwan Lee, T.J. Shin, Jong Taek Yeom, Nho Kwang Park, S.S. Hong, In Ok Shim, Sang Moo Hwang, Chong Soo Lee
Abstract: Prediction of final microstructures after high temperature forming of Ti-6Al-4V alloy was´attempted in this study. Using two typical microstructures, i.e., equiaxed and Widmanstätten microstructures, compression test was carried out up to the strain level of 0.6 at various temperatures (700 ~ 1100°C) and strain rates (10-4 ~ 102/s). From the flow stress-strain data, parameters such as strain rate sensitivity (m) and activation energy (Q) were calculated and used to establish constitutive equations for both microstructures. Then, finite element analysis was performed to predict the final microstructure of the deformed body, which was well accorded with the experimental results.
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