Localization in NiTi tubes under bending
Localization in NiTi tubes under bending
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DOI：
10.1016/j.ijsolstr.2013.11.023
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发表时间：
2014-03-01
影响因子：
3.6
通讯作者：
Kyriakides, Stelios
中科院分区：
文献类型：
--
作者：
Bechle, Nathan J.;Kyriakides, Stelios
近等原子NiTi可以表现出伪弹性行为，由于可逆的固体到固体的应力诱导相变在室温下。在张力下，转变导致几个百分比的局部变形，其倾向于在几乎恒定的应力下扩展。卸载后变形恢复，同时再次表现出局部变形。在压缩下，虽然仍然是伪弹性的，但转换应变较小，应力较高，响应是单调的，并且变形基本上是均匀的。这项研究探讨了这种纹理驱动的，复杂的材料不对称性如何影响一个简单的结构：弯曲的管。为此，NiTi管在旋转控制和等温条件下在定制的四点弯曲设施中弯曲。相变导致由加载和卸载力矩平台组成的闭合力矩-转动滞后。在加载期间，马氏体的局部成核导致管的经转变的区段的高曲率和未转变的区段的低曲率。对应于较高曲率区域的马氏体逐渐扩展，而力矩几乎保持恒定。马氏体的成核是以倾斜于管的轴的带的形式，其在结构的张紧侧上将自身组织成菱形变形图案。这些图案与用Luders带弯曲钢管时观察到的图案相似，然而，对于NiTi，由于材料不对称，它们仅在拉伸侧上发展。一个较低的力矩平台被跟踪卸载后，类似的局部弯曲和擦除的金刚石变形模式。这种复杂的行为被发现重复的伪弹性制度的NiTi的力矩旋转滞后移动到更高或更低的时刻水平取决于温度的温度。(C)2013爱思唯尔有限公司保留所有权利。
Nearly equiatomic NiTi can exhibit pseudoelastic behavior due to reversible solid-to-solid stress induced phase transformation at room level temperatures. In tension, the transformation leads to localized deformation of several percent that tends to spread at nearly constant stress. The deformation is recovered upon unloading while again localized deformation is exhibited. Under compression, while still pseudoelastic, the transformation strains are smaller, the stress is higher, the response is monotonic, and the deformation is essentially homogeneous. This study examines how this texture-driven, complex material asymmetry affects a simple structure: the bending of a tube. To this end, NiTi tubes are bent in a custom four-point bending facility under rotation control and isothermal conditions. The phase transformations lead to a closed moment-rotation hysteresis comprised of loading and unloading moment plateaus. During loading, localized nucleation of martensite results in a high curvature for the transformed sections of the tube and low curvature for the untransformed. Martensite, which corresponds to the higher curvature regime, spreads gradually while the moment remains nearly constant. The nucleation of martensite is in the form of bands inclined to the axis of the tube that organize themselves into diamond shaped deformation patterns on the tensioned side of the structure. The patterns are similar to those observed in bending of steel tubes with Luders bands, however, for NiTi they develop only on the tensioned side due to the material asymmetry. A lower moment plateau is traced upon unloading with similar localized bending and the erasure of the diamond deformation patterns. This complex behavior was found to repeat for a number of temperatures in the pseudoelastic regime of NiTi with the moment-rotation hysteresis moving to higher or lower moment levels depending on the temperature. (C) 2013 Elsevier Ltd. All rights reserved.