Strain gradient plasticity theories and their application to sheet metal forming

北美汽车生产商面临着相当大的社会和政府立法压力，要求他们减少汽车的燃料消耗和废气排放。实现这一目标的最有效方法之一是通过在车辆结构和车身面板中用铝代替钢来减轻重量。然而，铝具有许多可感知和实际的技术限制，例如与传统钢相比，其可成形性降低。人们相信，这可以通过改进材料的发展来消除，或者必须通过开发新的应用方法来规避。在过去的几年中，已经开发了几种技术来制造不同合金组合的层压金属板。传统产品是一种折衷的单片材料，以满足物理、机械、化学和表面性能以及制造能力和成本的要求。层压消除了这些要求，使新材料的开发能够使用优化合金在复合材料中的功能。这使得以低成本生产传统方法无法生产的合金组合成为可能。另一种快速而经济的新产品途径是设计不同尺度的新型表面纹理，以改善产品的光学外观和成型性。层合板表面织构和近界面的临界变形机制仅在几微米的长度尺度上。经典塑性理论由于其本构模型没有内部长度尺度，无法描述材料在微米尺度上的行为。因此，改进的连续介质塑性模型适用于微米级的应用。本项目将改进的微米级连续塑性模型应用于有限元模型中，模拟层合板界面附近的表面织构和塑性变形。该项目的研究结果将为涉及金属制造工艺的关键行业带来巨大的利益，因为它将导致具有最佳成形性和性能特征以及更好的光学外观的经济高效的制造工艺。

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.