Strain gradient plasticity theories and their application to sheet metal forming

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There has been 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 in the vehicle structure and body panels. However, aluminum has a number of perceived and real technological limitations, such as its 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. In the last few years several techniques have been developed to fabricate laminated metal sheets of different alloy combinations. Traditional products are a compromise monolithic material to meet requirements of physical, mechanical, chemical and surface properties as well as ability to fabricate and cost. Laminating decouples these requirements to enable new materials to be developed using alloys optimized for their function in the composite. This enables the cost-effective production of alloy combinations that cannot be made conventionally. Another quick and economical route to new products is to design novel surface textures of varying scales for improved product enhancement in better optical appearance and formability. The critical deformation mechanism in the surface texturing and near interface in laminated sheet is at a length scale of only a few microns. The classical plasticity theories cannot describe material behaviour at the micron scale because their constitutive models possess no internal length scale. Improved continuum plasticity models for micron level applications have been thus developed. In this project the improved continuum plasticity models for micron level applications will be implemented into finite element models to simulate the surface texturing and plastic deformation near the interface in laminated sheet. The results of this project could be of great benefit to key industries involved in metal fabrication processes in that it will lead to cost-effective fabrication processes having optimum formability and performance characteristics as well as better optical appearance.