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金屬塑性成形中的韌性斷裂微觀機理及預測模型的研究進展

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

  • 摘要: 為實現汽車輕量化,同時保證其具有較好的碰撞安全性,高強度-質量比金屬板材在汽車制造領域得到了廣泛的應用.然而,在傳統沖壓成形過程中,上述板材(如先進高強鋼、鋁合金和鎂合金等)會出現無明顯縮頸的韌性斷裂行為.特別是發生在純剪切加載路徑附近的剪切型韌性斷裂行為超出了傳統縮頸型成形極限圖的預測范圍.此外,在近些年來快速發展的單點漸進成形中,縮頸失穩被抑制,取而代之的則是無明顯縮頸的韌性斷裂.以上問題對基于縮頸失穩的傳統成形極限分析方法提出了新的挑戰,同時也限制了高強度-質量比金屬板材的應用及其新型成形工藝的研發.為此,世界各國學者開始普遍關注金屬材料韌性斷裂預測模型的開發及其應用研究.本文首先從孔洞的演化行為方面出發,對金屬韌性斷裂的微觀機理研究進行了介紹.隨后重點評述了韌性斷裂預測模型的研究進展和應用現狀.最后,對韌性斷裂研究的發展趨勢進行了展望.本文可以為金屬韌性斷裂模型的選擇、應用及其開發提供有益參考.

     

    Abstract: 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.

     

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