Micromechanics of Superplasticity

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The present project aims to elucidate the process of microstructural change governing superplastic deformation from micromechanics point of view, to establish a new theoretical framework for the precise description of superplastic behavior of various materials, and to investigate the possibility of developing new superplastic materials and new superplastic forming and manufacturing processes. The research results obtained during the term of the project are summarized as follows :1) The Head Investigator Murakami performed a series of tests on superplastic deformation and fracture under wide variety of combined states of stress, discussed the results from the micromechanics and continuum mechanics points of view, and thereby formulated a new mechanical model of describing the process of deformation and fracture of superplastic materials. The model made possible the simulation of the deformation process of the commercial superplastic material of Al5083 alloy.2) Investigator Aizawa develo … More ped extensively computational material models for the analysis of superplastic forming rocess, and established new methods of superplastic forming. He succeded in developing a simulation method for the superplastic forging by the use of the modified granular model and micro-macro stress analysis. He proposed methods of the superplastic injection forming and superplastic spinning. These two methods will be developed as a prototype of superplastic forming in the next generation.3) Investigator Maruyama observed the superplastic behavior and the associated deformation mechanisms of Ti-Al-Fe alloys, and formulated a superplastic constitutive equation for materials of two-phase structure. The results of tensile tests of the material showed superplastic elongation of 800 % at the temperature range of 1050K through 1200K. According to the microstructural observations, the relaxation mechanism of the concentrated stress was found to be the stress-induced phase transformation which is different from the mechanisms observed so far. A new constitutive equation was proposed based on this mechanism.4) Investigator Tokuda elucidated the macroscopic and microscopic properties of the commercial superplastic material of Al5083 alloy by performing combined load tests on the tubular specimens of the material. He discussed the superplastic deformation based on the constitutive theory of viscoplasticity and micromechanics, and proposed a constitutive model of fine-grained superplasticity for three-stage Finite Element Analysis. Less