金属塑性成形中的韧性断裂微观机理及预测模型的研究进展

为实现汽车轻量化，同时保证其具有较好的碰撞安全性，高强度-质量比金属板材在汽车制造领域得到了广泛的应用.然而，在传统冲压成形过程中，上述板材（如先进高强钢、铝合金和镁合金等）会出现无明显缩颈的韧性断裂行为.特别是发生在纯剪切加载路径附近的剪切型韧性断裂行为超出了传统缩颈型成形极限图的预测范围.此外，在近些年来快速发展的单点渐进成形中，缩颈失稳被抑制，取而代之的则是无明显缩颈的韧性断裂.以上问题对基于缩颈失稳的传统成形极限分析方法提出了新的挑战，同时也限制了高强度-质量比金属板材的应用及其新型成形工艺的研发.为此，世界各国学者开始普遍关注金属材料韧性断裂预测模型的开发及其应用研究.本文首先从孔洞的演化行为方面出发，对金属韧性断裂的微观机理研究进行了介绍.随后重点评述了韧性断裂预测模型的研究进展和应用现状.最后，对韧性断裂研究的发展趋势进行了展望.本文可以为金属韧性断裂模型的选择、应用及其开发提供有益参考.

Research progress on the micro-mechanism and prediction models of ductile fracture in metal forming

Metals with a high strength-to-weight ratio are being increasingly used in the automobile industry to achieve a reasonable tradeoff between weight reduction, crashworthiness, fuel efficiency, and environmental friendliness. However, sheets of lightweight metals such as advanced high strength steel, aluminum alloy, magnesium alloy, and titanium alloy, tend to crack without obvious necking during widely-used stamping processes. In particular, so-called shear-induced ductile fracture, which occurs near the pure shear loading path, exceeds the prediction spectrum of traditional necking-based forming limit curves. In addition, the single point incremental forming (SPIF) process, which is currently under rapid development because of its high flexibility in rapid prototyping or customized production process, demonstrates a strong necking suppression. Consequently, ductile fracture without distinct necking has been considered as the forming limit for SPIF. Although the classical forming limit prediction approach, which is, in principle, based on necking instability, has been widely applied as a standard solution for predicting failures in the process of sheet-metal forming, it barely provides feasible solutions to the aforementioned issues. This limitation greatly restricts the application of lightweight materials and the development of novel forming processes. Therefore, researchers have devoted increasing attention to accurately predicting the ductile fracture of metallic materials. In the current paper, we first review studies related to the micro-mechanisms that trigger ductile fracture. We then systematically review ductile fracture prediction models in two categories:coupled models and uncoupled models. Model applications in metal forming processes are summarized as well. Toward the conclusion, prospective trends in ductile fracture research are surveyed. The objective of this paper is to provide engineers and researchers with a beneficial overview of the selection, utilization, and development of ductile fracture prediction models.