Microstructure-based modelling of spot weld failure in third generation advanced high strength steels

为了提高乘客的安全性和燃油经济性，汽车公司一直在将强度越来越高的钢材整合到车辆结构中。最新的材料是第三代先进高强度钢(3G AHSS)，它们具有优异的成形和碰撞性能，但含有高碳和合金化添加剂，导致焊接区的机械性能变化很大。3G AHSS组件的结构完整性和碰撞性能最终由这些控制故障路径和能量释放的局部异质属性决定。由于3G AHSS最近才开始商业化，因此对焊接关键子区域的本构和断裂特性缺乏足够的知识，无法在整车碰撞模拟中准确预测它们的行为。围绕3G AHSS焊接断裂行为的相当大的不确定性导致汽车公司过度设计3G AHSS部件或避免采用它们。 建议的研究将优化两个等级的3G AHSS的电阻点焊缝的力学性能，极限拉伸强度(UTS)分别为980 Mpa和1180 Mpa，然后开发一个详细的理解和预测碰撞过程中的失效行为的模型。这项研究将导致：(I)工业上可行的点焊工艺；(Ii)焊接组织和性能的详细表征；(Iii)了解3G AHSS点焊失效的机制；以及(Iv)开发适合工业模拟的焊接断裂模型，这将为下一代轻型汽车结构提供设计工具。 该项目的成果将直接有助于加拿大钢铁、零部件、工具、焊接设备和汽车制造商在该项目上合作的竞争力。优化的焊接参数将被应用于加拿大的零部件和组装厂，新的模拟工具将被纳入汽车设计和碰撞安全模拟，这将创造对这些新钢材的市场需求。

To improve passenger safety and fuel economy, automotive companies have been integrating steels of increasing strength into the vehicle architecture. The newest materials of interest are third generation advanced high strength steels (3G AHSS) that have excellent forming and crash properties, but contain high carbon and alloying additions that create large variations in the mechanical properties within the weld zone. The structural integrity and crash performance of a 3G AHSS component is ultimately governed by these local heterogeneous properties that control the failure path and energy release. Since 3G AHSS have only recently become commercially available, there is insufficient knowledge of the constitutive and fracture properties of the critical sub-regions of the weld to accurately predict their behavior in full vehicle crash simulations. The considerable uncertainty surrounding the fracture behavior of 3G AHSS welds has led automotive companies to over-design 3G AHSS parts or to avoid their adoption. The proposed research will optimize the mechanical performance of resistance spot welds in two grades of 3G AHSS with ultimate tensile strengths (UTS) of 980 MPa and 1180 MPa, then develop a detailed understanding and predictive model of the failure behaviour during crash. This research will result in: (i) industrially-viable spot welding processes; (ii) a detailed characterization of weld microstructure and properties; (iii) an understanding of the mechanisms responsible for 3G AHSS spot weld failure; and (iv) the development of weld fracture models appropriate for industrial simulation, which will provide design tools for future generation lightweight automotive structures. The project outcomes will directly contribute to the competitiveness of the Canadian steel, parts, tooling, welding equipment and automotive manufacturers partnering on this project. Optimized welding parameters will be adopted into Canadian parts and assembly plants and the new simulation tools will be incorporated in automotive vehicle design and crash safety simulation, which will create market demand for these new steels.