Papers by Keyword: Internal Variable Theory

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Authors: H.S. Lee, Won Kyu Bang, D.W. Kim, S. Lee Semiatin, Young Won Chang
Authors: Jeoung Han Kim, S. Lee Semiatin, Chong Soo Lee
Abstract: The high temperature deformation mechanisms of two phase a+b alloy and a near-a alloy were investigated, and compared within the framework of inelastic-deformation theory. For this purpose, load-relaxation tests were conducted on the two alloys at temperatures of 750~900°C. The flow stress-vs.-strain rate curves for both alloys were well fit with inelastic deformation equations describing dislocation glide and grain boundary sliding. The amount of grain boundary sliding resistance was higher in the near-a alloy rather than the two phase a+b alloy due to difficulty in stress relaxation at triple junction region.
Authors: J.E. Park, J.B. Jeon, S. Lee Semiatin, Chong Soo Lee, Young Won Chang
Abstract: Textures developed during hot rolling process may affect the high temperature deformation behaviors of Ti alloys, but their relation has not been well understood or quantitatively analyzed yet. A series of load relaxation and creep tests for hot rolled Ti-6Al-4V alloy has been conducted in this work to clarify the effect of textures on the deformation behaviors of the alloy under 700 °C and the result was analyzed by using an internal variables approach. The internal strength σ* was found to vary significantly by the textures, but not by the temperature change, while the texture effect was found to decrease at higher temperatures.
Authors: Tae Kwon Ha, Yong Nam Kwon, Young Won Chang
Authors: Won Kyu Bang, Tae Kwon Ha, Young Won Chang
Authors: Won Kyu Bang, J.E. Park, Yong Nam Kwon, Chong Soo Lee, Young Won Chang
Abstract: The superplastic deformation behavior of a fine-grained 7075 Al has been investigated to clarify the issue of threshold stress. A series of mechanical tests has been conducted at various temperatures for the specimens with various grain sizes. The quantitative constitutive parameters have been determined from load relaxation test by applying the internal variable theory of structural superplaticity (SSP) proposed by Chang et al. The GBS flow could be formulated as a viscosity-type equation, characterized by the Newtonian exponent of 1.0. The unresolved issue of threshold stress is clarified and identified as a critical stress required for the GBS. The micro-mechanical roll of grain size refinement has also been manifested in terms of proposed constitutive parameters.
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