2015-08-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/709580摘要：金屬玻璃是一種擁有優異機械性質的嶄新材料，然而，此種材料的形變常常會局限在很小範圍的剪切帶上。在室溫下，由於其塑性變形能力有限，這種材料會迅速的導致脆性斷裂。這種在面對形變時的不穩定性，限制了金屬玻璃在工程上的應用。此計畫是想要從基本上來了解剪切帶的形成機制，以及不同組剪切帶之間的交互作用。當建立起這些概念後，我們可藉此找到改善金屬玻璃延展性的方法。 由於剪切帶的形成主要是由剪應力所驅動，我們估計用剪刀來剪帶狀金屬玻璃就可以產生剪切帶，而這個假設也在初步研究中被我們證實。此計劃的目的為設計特殊的夾具，如「剪刀」以及「打洞機」之剪切模具，來有系統的探討剪切帶形成的機制。此外，溫度、應變速率、樣品厚度、以及顆粒強化等因素對剪切帶的影響，亦在我們探討的範圍。我們將運用有限元素法模擬在「剪刀」與「打洞機」之剪切下的應力場。所得到之應力場將配合Mohr–Coulomb模型以及Rudnicki–Rice模型，來分析不同剪切模式下，所形成不同剪切帶的方向。所得到之理論結果，將與實驗量測結果比對，由此可檢視模型的可行性，了解剪切帶的形成機制。這個計劃將會從機理的觀點來理解剪切帶的形成，並且提供有效的方法來提升金屬玻璃的延展性。 <br> Abstract: Although metallic glasses constitute a new class of metallic materials with attractive mechanical properties, they often deform by the formation of localized shear bands and display little plasticity before catastrophic fracture at room temperature. This inability to permanently deform limits the use of metallic glasses in engineering applications. The proposed project seeks fundamental understanding of formation of shear bands and interactions between sets of shear bands which, in turn, would lead to ways of improving the ductility of metallic glasses. Because the shear stress is the major driving force for shear band formation, it is expected that shear bands can be generated by simply cutting the metallic glass ribbon with a pair of scissors. This has been confirmed by our preliminary studies. The purpose of this proposal is to develop unique techniques of “scissor cutting” and “hole puncher” to systematically study the mechanism of shear band formation. The effects of temperature, strain rate, sample thickness, and particles reinforcement on the shear band formation will also be examined. Finite element analyses will be performed to simulate the stress fields resulting from “scissors cutting” and “hole puncher”, respectively. This would provide the insights for shear band formation. Using the stress fields obtained from finite element analyses, we will adopt both Mohr-Coulomb model and Rudnicki–Rice model to analyze the shear band orientation for “scissors cutting” and “hole puncture” tests. The results will be used to compare with the experimental measurements to justify the applicability of the model. This would lead to a mechanistic understanding of shear band formation and a predictable way of improving the ductility of metallic glasses.金屬玻璃剪切帶剪刀打洞機有限元素理論模型Metallic GlassShear BandScissors CuttingHole PuncherFinite Element AnalysisModeling