Microstructural modelling of sheet metal formability

北美汽车生产商面临着相当大的社会和政府立法压力，要求它们减少汽车的燃油消耗和废气排放。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、镁或先进的高强度钢取代钢来实现重量减轻。然而，这些材料有一些明显的和实际的技术限制，其中最重要的是与传统钢相比，它们的成形性降低。人们认为，这可以通过改进材料的开发来消除，或者必须通过开发新的应用方法来避免，以便它们能够有效地用于减重汽车的批量制造。因此，主要的不确定性是，是否有可能开发出比目前可用的材料具有更好的强度和成形性组合的薄板材料，并且还可以通过降低与最终规格薄板相关的成本的工艺来制造。这意味着，必须进行全面的科学计划，以了解潜在材料系统的冶金性能，同时还必须实施强有力的工艺和产品开发计划。该研究计划的主要目的是将拉伸下的局部缩颈、弯曲下的剪切带发展和液压成形下的管材失效与板材表面不稳定性联系起来。这种表面不稳定性不仅对加工硬化、织构和应变率非常敏感，而且对颗粒取向的局部空间分布也非常敏感。在晶界局部尺度和板厚全局尺度上对表面不稳定性进行详细的实验和数值研究，将有助于阐明液压成形和弯曲的破坏机制。

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.