【作者】 王亚芳；

【导师】 岳珠峰；

【作者基本信息】 西北工业大学 ， 固体力学， 2007， 博士

【摘要】 NiTi形状记忆合金是智能材料中最先应用的一种驱动元件。因为具有良好的超弹性和形状记忆效应，从而得到广泛的应用。迄今为止，对NiTi合金的研究主要集中在一维状态。实际上，由于几何形状的复杂性以及载荷的复合作用，大多数零构件是处于复杂应力状态下工作的，因此很有必要从试验以及理论方面，对NiTi合金在复合加载下的力学性能进行研究。本论文采用理论分析、计算模型、实验考核与验证相结合的方法，研究了NiTi合金的超弹性性能。主要的工作总结如下：1．通过试验，研究了温度、循环加载—卸载、加载速率以及应力幅值对近等原子比NiTi合金丝材的超弹性性能以及疲劳寿命的影响。2．通过试验，研究了NiTi合金薄壁圆筒在单轴拉伸、纯扭转、双轴比例以及非比例加载下的疲劳行为，分析了相同应变幅值下，不同加载方式以及非比例相位差对NiTi合金双轴疲劳寿命的影响。3．在原有Gall等人提出的模型基础上，提出了一种新的改进的微观力学模型，并将这一模型移植到ABAQUS的用户子程序UMAT中。通过比较数值模拟结果与试验结果表明，模型基本可以描述NiTi合金的超弹性性能的主要特征。由于交互矩阵H^mm中的两个参数是从分析的角度估算来的，分析了H^mm的取值不同对多晶体应力-应变关系的影响，通过与试验结果相比较，确定了参数C和I。4．应用现有的本构模型，通过有限元模拟计算，研究材料织构对NiTi合金在拉伸和压缩载荷作用下力学响应不对称性的影响。同时，分析了四种不同温度下，多晶NiTi合金在双轴拉伸（压缩）加载下以及薄壁圆筒在拉伸（压缩）—扭转比例加载下的相变情况，以确定在应力平面上的马氏体相变初始曲线，同时也研究了材料织构对马氏体相变初始面的影响。5．应用已建立的本构模型，研究了四种不同表面粗糙度对NiTi合金超弹性性能的影响。为了比较，也对光滑模型以及单个缺口模型进行了模拟计算。6．通过试验，对形状记忆合金薄壁圆筒在拉伸—扭转双轴加载下的超弹性性能进行了研究，并与数值模拟计算结果进行了比较。结果表明，这一模型可以很好的模拟双轴加载下形状记忆合金的整个加载—卸载过程。并且从试验和数值模拟结果可以看出，不同的双轴加载路径下，材料的超弹性响应有很大的不同。更多还原

【Abstract】 NiTi shape memory alloy is one of the most developed driving components in intelligent materials. They have wide applications due to their unique shape memory effect and superelastic properties. Up to now, a lot of work about NiTi has been undertaken, but most found in literatures has been performed only on wires and thus are one-dimension. In fact, because of the complexities of geometric configures and the recombination actions of loading, engineering components are often in multi-axial loading condition, therefore, it is necessary to study the mechanical properties of NiTi alloy under complex loading.In the thesis, theoretic analysis, numerical model, model verified by experiments were employed to carry out some researches on the superelasticity. They are as follows:1. Based on a series of experiments, the effects of testing temperature, cyclic loading-unloading, displacement rates and stress amplitude on the superelasticity and the fatigue life of the nearly equi-atomic NiTi alloy have been studied.2. The biaxial fatigue behaviors of NiTi thin-walled tubes under uniaxial tension, pure torsion, biaxial proportional loading and nonproportional loading with the different phase angles have been studied. With the same axial and shear strain level, the influences of different loading mode and phase angle on the biaxial fatigue life of NiTi alloy have been analyzed.3. Based on the model of Gall et al, a new modified model has been developed, and the model has been implemented into the finite-element program ABAQUS/standard. Comparing the experimental and numerical results, it can be concluded that the model can capture the essential features of our SMA. In addition, because the only parameters estimated from an analytical standpoint are the terms in interaction energy matrix, H^mn, the effect of varying H^mn on the predicted polycrystalline stress-strain behaviors has been studied. Through discussion, the values C and I are chosen. 4. Using the current model, the influence of crystallographic texture on the stress-strain asymmetric behavior of polycrystalline NiTi shape memory alloy under tension and compression has been researched. Furthermore, a series of calculations of biaxial tension （compression） and proportional tension （compression）-torsion for the NiTi polycrystalline has been performed to determine the initial surface of phase transformation in the stress space which determines the onset of stress induced martensitic phase transformation. The main purpose of this study is to numerically illustrate the effects of crystallographic texture.5. Based on the new developed model, the effect of surface roughness on the superelastic behaviors of NiTi alloy has been studied. Periodic surface notches with four different notch depths as surface roughness were introduced into the models. For comparison, simulations were also performed on smooth models and models with a single notch.6. The model has been used to predict the superelastic response of the thin-walled NiTi tubes under combined tension-torsion loading. In order to validate the model, thin-walled tube has been tested under biaxial loading. From the comparison between the simulated and experimental results, it is found that the model is quite good in predicting the overall loading-unloading process of the SMA. Both the experimental and simulated results demonstrate the significant differences in the superelastic responses under different biaxial loading paths.更多还原