Micromechanics of Superplasticity

本项目旨在从微观力学的角度阐明控制超塑性变形的微观组织变化过程，为精确描述各种材料的超塑性行为建立新的理论框架，并探讨开发新的超塑性材料和新的超塑性成形和制造工艺的可能性。项目期间取得的研究成果总结如下：1)村上组长进行了一系列在多种复合应力状态下的超塑性变形和断裂试验，从细观力学和连续介质力学的角度对试验结果进行了讨论，从而建立了描述超塑性材料变形和断裂过程的新的力学模型。该模型为模拟Al5083合金超塑性材料的变形过程提供了可能。2)研究者Aizawa开发了更广泛的用于超塑性成形过程分析的计算材料模型，并建立了新的超塑性成形方法。他成功地利用改进的颗粒模型和微观宏观应力分析开发了一种超塑性锻造的模拟方法。提出了超塑性注射成形和超塑性旋压的方法。这两种方法将作为下一代超塑性成形的原型而发展。3)研究者Maruyama观察了Ti-Al-Fe合金的超塑性行为和相关变形机制，并建立了两相结构材料的超塑性本构方程。拉伸试验结果表明，在1050K ~ 1200K温度范围内，材料的超塑性伸长率达到800%。根据显微组织观察，发现集中应力的松弛机制是应力诱发的相变，这与以往观察到的机制不同。基于这一机理，提出了一种新的本构方程。4)研究者Tokuda通过对Al5083合金管状试样进行复合载荷试验，阐明了该超塑性材料的宏观和微观性能。他基于粘塑性和细观力学的本构理论讨论了超塑性变形，提出了一种用于三阶段有限元分析的细晶超塑性本构模型。少

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