An Investigation of the Evolution of Mechanical Properties of Materials During Metalworking

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9617227 Rajagopol Metalworking processes such as rolling, forming, forging, extrusion, stamping etc. are a multibillion dollar industry in the USA. In the recent years, metalworked products are being increasingly used to make a variety of products ranging from food containers to automobile body panels. The metalworking processes have a big impact on the performance and reliability of these products because, microstructural effects (such as evolution of crystallographic texture, dislocation structures and precipitates) and residual stresses which are induced during the metalworking process play a vital role in determining their mechanical properties. The goal of this proposal is to examine the evolution of the mechanical properties of metals with a special emphasis on the prediction of evolving anisotropy during sheet rolling and forming processes. This will be accomplished by first developing a constitutive theory to model the effect of rolling and sheet forming on the salient mechanical properties (such as the yield surface) the material. The principal idea of the theory is that the response of the material depends upon the evolution of multiple structures (such as the lattice structure, dislocation networks etc.) These are modeled by assuming that the material possesses more than one evolving natural configuration. As far as the elastic response and the yield function are concerned, the evolving natural configurations are the stress-free configurations of the material. This notion allows for a detailed discussion of the evolution of the anisotropy of the elastic response and the yield surface. The yield behavior is the most significant aspect mf the mechanical behavior of the material -.3ince it determines the formability, necking behavior etc., of the material. Even a slight error in the modeling of the yield behavior significantly degrades the prediction of these vital parameters. For the past three years, there has been a collaboration between Scientists at the Alcoa Technical Center and the University of Pittsburgh to develop comprehensive constitutive assumptions to accurately model the changing anisotropy. The current proposal builds upon this effort and takes it to the next stage, namely detailed experimentation and validation of the constitutive theory. The predictive capabilities of the theory are expected to provide researchers with some of the tools necessary to make reliable estimates of mechanical properties of the sheet metal product from information regarding the manufacturing processes that it has undergone. In the process, it will help graduate students to gain both industrial and academic training.