镍钛铌形状记忆合金特性的试验与本构模型研究

发布时间：2018-11-02 07:06

【摘要】：形状记忆合金因其独特的伪弹性和形状记忆效应,近几十年来受到了广泛关注。NiTiNb形状记忆合金作为NiTi基合金的重要成员,在一定的温度(Ms+30oC)下经历一定的预变形(约16%)后可获得宽的相变滞后效应和较好的形状记忆效应,使该材料制作而成的管接头等连接件能够在常温下运输和储存,从而大大方便了应用。另一方面,随着科技的发展,材料与结构的使役条件日益苛刻,形状记忆合金实际使用过程中不可避免的卷入塑性变形,而塑性变形对形状记忆合金的逆相变应力和滞后温度有着显著的影响。为了更好的利用这种材料,国内外的学者对其热力学特性进行了大量的研究工作。本文在系统地分析国内外有关形状记忆合金试验和本构行为研究现状的基础上,结合近年来有关Ni47Ti44Nb9形状记忆合金试验及本构模型的发展,对Ni47Ti44Nb9形状记忆合金的热—力学特性进行了较为系统的试验研究,在此基础上提出了一种考虑塑性变形影响和片层状微结构的跨层次形状记忆合金本构模型及Ni47Ti44Nb9形状记忆合金的细观力学模型。取得了以下进展:1、对Ni47Ti44Nb9形状记忆合金进行了系统的试验研究:运用微观观测手段观察了合金的微观组织结构并测量了其各组成成分;运用DSC和XRD方法测量了合金的特征相变温度点和组织状态,在此基础上进行了不同温度条件下合金的单轴拉伸试验和纯扭转试验及其升温回复特性研究;研究了Ms+30oC温度下不同拉扭比例的比例加载、先拉后扭和先扭后拉三种典型路径下的力学响应及相应的升温回复特性的比较;利用XRD方法测量了不同加载路径条件下材料内部激活的不同变体。试验结果表明,常温下基体材料由细条状的奥氏体组成,富Nb相颗粒弥散分布在NiTi基体中;材料在拉伸和扭转变形下的响应具有显著差异,包括应力应变曲线及试件表面形貌,但其相变应力都随着环境温度的升高而升高;双轴路径下材料的力学响应及升温回复特性强烈的依赖于加载路径,并在应变空间中沿最短路径回复;单轴拉伸和纯扭转加载方式在材料内部激活的马氏体变体不同,而拉—扭二维加载路径下激活的变体是二者的叠加。2、基于非经典塑性理论建立了各相本构模型并改进了相变控制方程:将形状记忆合金看作马氏体相和奥氏体相的混合物,将马氏体相考虑成弹性-相变(重取向)-塑性三个部分组成,将奥氏体相考虑成弹性-塑性两个部分,基于非经典塑性理论建立了马氏体相和奥氏体相本构模型。考虑到塑性变形对材料逆相变应力和相变滞后温度的影响,对Tanaka相变控制方程进行了改进。3、建立了考虑塑性变形和材料微结构的形状记忆合金本构模型:基于试验观察到的形状记忆合金片层状微结构,将其考虑成马氏体薄片和奥氏体薄片相互叠合而成的代表性体积单元,马氏体片和奥氏体片的本构关系采用前一部分建立的本构方程,通过内部应力应变的协调关系建立了代表性体积单元的本构关系。将形状记忆合金多晶考虑为沿正二十面体面法向进行取向平均后的代表性单元组集而成,利用Hill自洽方法,得到了考虑塑性影响和材料微结构形式的跨层次形状记忆合金本构模型。利用该模型对形状记忆合金的铁弹性和伪弹性进行了模拟,计算结果与试验结果吻合较好;对不同应变幅值塑性变形对逆相变应力进行了数值模拟,与试验结果的比较表明,模型能够很好地描述塑性变形的影响。4、初步发展了NiTiNb形状记忆合金细观本构模型:以考虑塑性的马氏体相和奥氏体相本构关系为基础,首先利用voigt假设建立了形状记忆合金两相本构模型,以此作为NiTi基体相的本构模型,同时将Nb相考虑成弥散分布在基体上的球形夹杂,利用Mori-Tanaka方法,初步发展了NiTiNb形状记忆合金细观本构模型。利用该模型研究了不同体积分数弹性夹杂、弹塑性夹杂对材料整体和基体的影响,结果显示模型能够很好的描述其响应规律;最后对NiTiNb形状记忆合金在不同温度下纯扭转和单轴拉伸的响应,不同拉扭比例的比例加载、先拉后扭和先扭后拉三种不同路径下材料响应进行了模拟,通过数值计算结果和试验结果比较,表明发展的模型能够较好的描述试验现象。
[Abstract]:Shape memory alloys have been widely paid attention in recent decades due to its unique pseudoelasticity and shape memory effect. The NiTiNb shape memory alloy is an important member of the NiTi-based alloy, and undergoes a certain pre-deformation (about 16%) at a certain temperature (Ms + 30oC), so that a wide phase change hysteresis effect and a better shape memory effect can be obtained, and the connecting piece such as a pipe joint made of the material can be transported and stored at normal temperature so as to greatly facilitate the application. On the other hand, with the development of science and technology, the service conditions of materials and structures are increasingly harsh, and the deformation of the shape memory alloy is inevitably involved in the actual use of shape memory alloy, and the plastic deformation has a significant influence on the inverse phase change stress and the hysteresis temperature of the shape memory alloy. In order to make better use of this material, scholars at home and abroad have carried out a lot of research work on their thermodynamic characteristics. Based on the systematic analysis of the present research situation of shape memory alloy test and the structure behavior of Ni47Ti44Nb9 shape memory alloy in recent years, the mechanical properties of Ni47Ti44Nb9 shape memory alloy have been studied systematically. Based on this, a micro-mechanical model of shape memory alloy and Ni47Ti44Nb9 shape memory alloy considering plastic deformation effect and lamellar microstructure are proposed. The following progress has been made: 1. The experimental study of Ni47Ti44Nb9 shape memory alloy was carried out: the microstructure of the alloy was observed by means of micro-observation and its components were measured. The characteristic phase transformation temperature and tissue state of the alloy were measured by DSC and XRD. On this basis, the uniaxial tensile test and the pure torsion test of the alloy under different temperature conditions and the research on the temperature-raising response characteristics of the alloy were carried out, and the proportional loading of different pull-out ratios under the temperature of Ms + 30oC was studied. The mechanical response of three typical paths and the comparison of the corresponding temperature rise response characteristics were carried out firstly, and the different variants of the internal activation of materials under different loading paths were measured by XRD. The experimental results show that the matrix material is composed of fine strip-shaped austenite, and the Nb-rich phase particles are dispersed in the matrix. The response of the material under tensile and torsional deformation has a significant difference, including the stress-strain curve and the surface topography of the test piece. However, the phase change stress increases with the increase of the ambient temperature; the mechanical response and the temperature rise response of the material under the biaxial path strongly depend on the loading path and recover along the shortest path in the strain space; The single-axis tension and pure torsion loading are different from the martensitic variants activated in the interior of the material, while the variants activated under the two-dimensional loading path of the pull-and-twist two-dimensional loading path are the superposition of the two. the shape memory alloy is regarded as a mixture of a martensite phase and an austenite phase, the martensite phase is taken into consideration as an elastic-phase change (re-orientation)-plastic three parts, the austenite phase is considered to be two parts of an elastic-plastic phase, The structure model of martensite phase and austenite phase was established based on the non-classical plasticity theory. Considering the effect of plastic deformation on the material inverse phase change stress and the phase change lag temperature, the Tanaka phase change control equation was improved. 3. The shape memory alloy model considering plastic deformation and material microstructure was established: the layered microstructure of shape memory alloy sheet was observed based on the experiment. Considering the structure equation set up by the former part, the structure relation of the representative volume unit is established by the coordination relation of internal stress and strain. In this paper, the shape memory alloy polycrystal is considered as a representative cell group set which is oriented with average orientation along the positive twenty-face decent method, and a cross-level shape memory alloy model is obtained considering plastic influence and material microstructure form by using Hill self-consistent method. The elasticity and pseudoelasticity of shape memory alloy were simulated by using the model, and the calculated results agree well with the experimental results. The influence of plastic deformation can be well described. The microstructure model of NiTiNb shape memory alloy is preliminarily developed. Based on the relationship between the martensite phase and austenite phase, the structure model of shape memory alloy is firstly established by using void hypothesis. The microstructure model of NiTiNb shape memory alloy was initially developed by using the method of Mori-Tanaka. The effects of different volume fraction elastic inclusions and elastic-plastic inclusion on the whole and matrix of materials are studied. The results show that the model can describe its response law very well, and finally, the pure torsion and uniaxial tension response of NiTiNb shape memory alloy under different temperatures are studied. In this paper, the material response of three different paths is simulated by the proportional loading of different pull-and-twist ratio, the first pull-back and the first twist, and the experimental results show that the development model can describe the experimental phenomenon better by comparing the numerical results and the experimental results.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG139.6

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