Microstructural modelling of sheet metal formability

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There is considerable societal and government legislative pressure on the North American automotive producers to reduce the fuel consumption and exhaust gas emissions from vehicles. One of the most effective ways to achieve this is by the weight reduction that can be obtained by replacing steel with aluminum, magnesium or advanced high strength steel in the vehicle structure and body panels. However, these materials have a number of perceived and real technological limitations, the most significant of which is their reduced formability as compared with conventional steel. It is believed that this could be eliminated by the development of improved materials, or must be circumvented by the development of new application methods, so that they can be used effectively in the volume manufacturing of reduced weight automobiles. The major uncertainty, therefore, is whether it is possible or not to develop sheet materials which have better combinations of strength and formability than the materials available today, and which can also be manufactured through processes that reduce the costs associated with the final gauge sheet. This means that a comprehensive scientific program to understand the metallurgy of the potential materials systems must be pursued together with vigorous process and product development programs. The main purpose of this proposed research program is to relate localized necking under stretching, shear band development under bending, and failure in tubes under hydroforming to sheet surface instability. Such a surface instability is expected to be very sensitive not only to work hardening, texture, and strain rate but also to the local spatial distribution of grain orientations. Detailed experimental and numerical studies on surface instabilities, at the local scale of the grain boundary and at the global scale of the sheet thickness, will clarify the failure mechanisms in hydroforming and bending.