鎳鈦形狀記憶合金板材的張伸成形研究

Study on Stretch Forming of Ni-Ti Shape Memory Alloy Sheets

范光堯(Kuang-Jau Fann) ； 蘇哲雍(Jhe-Yung Su)

《鍛造》 26卷4期 (2017/12) Pp. 11-16

摘要

本研究嘗試將常溫為奧斯田相的富鎳之鎳鈦形狀記憶合金板材進行張伸成形試驗，探討該材料在雙軸拉伸應力狀態下的成形特性。研究令該材料先經800∘C固溶處理後，以半球形沖頭進行不同沖深的張伸成形。研究結果顯示常溫下為奧斯田相的材料具有超彈性，過小的張伸成形量易回彈，不易見出成形件的幾何輪廓，須有具塑性變形的張伸成形量，始可得出成形輪廓。同時結果亦顯示該固溶處理後的鎳鈦形狀記憶合金板材的成形特性不佳。此外，本文另藉商用有限元素分析軟體DEFORM 2D模擬鎳鈦形狀記憶合金板材張伸成形成形製程，其所需的材料特性曲線，則藉拉伸試驗取得。研究並嘗試使用彈塑性數值理論模擬鎳鈦形狀記憶合金的超彈性行為，獲致與實驗相符的成果。雖然有限元素分析得出張伸成形後的回彈特性與實現結果相近，但其負荷仍過高於實驗值，值得進一步探討，以提升模擬的準確度。

關鍵字

鎳鈦形狀記憶合金 ； 張伸成形 ； 有限元素分析 ； 拉伸試驗

並列摘要

This study attempted to investigate the properties of Ni-rich Ni-Ti shape memory alloy sheet parts for stretch forming process at room temperature, which is under bi-axial tensile stress state. After undergoing solid solution treatment at 800°C, shape memory alloy sheet is formed at room temperature by a hemispherical punch in different strokes. As a result, the sheet metal has austenitic phase at room temperature, which shows superelasticity. Too small forming amount causes severe springback and the form of the stretch formed sheet part is very hard to detect with the naked eye. Only if a forming amount beyond the critical value is applied, a form can be achieved on to the sheet part. Furthermore the Ni-Ti shape memory alloy sheet undergoing such solid solution treatment shows a low formability for cold forming. To detail the stretch forming process of the Ni-Ti shape memory alloy sheet, a Finite Element Analysis (FEA) with the commercial software DEFORM 2D was conducted in this study. The material data for FEA was acquired by the tensile test. This study tried to apply the already implemented mathematic model of classic elastic-plasticity in DEFORM to formulate the stress strain relation during the martensitic transformation in superelastic deformation. The results from FEA soundly agree those of experiment very well. Even the springback status obtained from FEA matches that from experiments very well, the loads obtained from FEA are much higher than those from experiments, which is worth in the future to further investigate to improve the accuracy of FEA.

並列關鍵字

shape memory alloy ； stretch forming ； Finite Element Analysis ； tensile test