NiTi形状记忆合金宏细观热—力耦合循环本构模型研究

发布时间：2018-01-20 15:10

  本文关键词： NiTi形状记忆合金 功能性劣化 热力耦合 本构模型 宏观 细观　出处：《西南交通大学》2015年博士论文　论文类型：学位论文

【摘要】：NiTi形状记忆合金以其优越的超弹性、形状记忆特性、生物相容性以及高阻尼特性,被广泛地应用在航空航天、生物医学工程、土木工程等领域。NiTi形状记忆合金作为结构中的关键元件,在服役过程中常常受到循环热-力荷载的作用。在NiTi形状记忆合金的循环变形过程中,功能性劣化(超弹性和形状记忆效应的劣化)和热-力耦合效应是两个不可忽略的重要因素,并且相互作用和影响。因此,很有必要建立考虑功能性劣化特性和热-力耦合效应的本构模型来描述和预测NiTi形状记忆合金结构和器件在各种复杂热-力荷载作用下的循环变形特性。近年来,已有不少学者基于实验现象在不同尺度上建立了NiTi形状记忆合金的本构模型。在宏观尺度上,已有的模型仅仅考虑了功能性劣化特性或热-力耦合效应中的一种,对功能性劣化特性的描述采用唯象方法,缺乏相应的物理机理。在细观尺度上,已有的模型仅仅关注NiTi形状记忆合金在一个加-卸载下的热-力学响应,由于尚未考虑到材料功能性劣化所对应的内在机制,无法对NiTi形状记忆合金循环变形特性给出合理的描述。可见,已有的本构模型还不够完善,仍有较大的局限性。针对以上不足,本文将在不同尺度下建立NiTi形状记忆合金的热力耦合循环本构模型,开展的创新性工作如下：(1)在宏观尺度下,通过对已有宏观-微观实验现象的总结,提出了NiTi形状记忆合金在循环变形过程中超弹性劣化的物理机理,即马氏体相变和缺陷的交互作用。基于热力学框架,针对超弹性NiTi形状记忆合金建立了一个能够同时描述其超弹性劣化和率相关变形行为的热-力耦合循环本构模型。通过模拟和预测超弹性NiTi形状记忆合金在不同加载率下的循环变形特性,验证了该模型的预测能力。进一步,采用该模型预测了超弹性NiTi形状记忆合金温度相关的循环变形特性。(2)在单晶代表性体积单元上,通过确定的晶体学位向关系引入多种非弹性变形机制,即马氏体相变、马氏体重定向、马氏体解孪、奥氏体塑性和马氏体塑性,基于热力学框架在单晶尺度下建立了热-力耦合本构模型。通过显式过渡准则和温度均匀性假设,将单晶模型过渡到了多晶。通过对多晶NiTi形状记忆合金在不同温度、不同加载率、不同应力水平下的单轴和非比例多轴热-力耦合变形特性的描述和预测,验证了模型的合理性和全面性。(3)通过总结已有的宏观-微观实验观察,提出了一种新的非弹性变形机制,即马氏体重定向诱发塑性。在工作(2)建立的晶体塑性模型基础上,进一步在单晶代表性体积单元上定量引入和NiTi形状记忆合金功能性劣化相关的非弹性变形机制,即相变诱发塑性、重定向诱发塑性和残余马氏体的累积,进而基于热力学框架在单晶尺度下建立了热-力耦合本构模型。通过显式过渡准则和温度均匀性假设,将单晶模型过渡到多晶。通过对多晶NiTi形状记忆合金在不同温度下的单轴、非比例多轴以及率相关循环变形行为进行了模拟和预测,验证了模型的预测能力。(4)在单晶代表性体积单元上,考虑马氏体相变和相变诱发塑性两种非弹性变形机制。将24个马氏体处理成形态相同、但晶体学位向不同的椭球形夹杂镶嵌在弹性各向异性的奥氏体基体中,并进一步采用Mori-Tanaka均匀化方法得到奥氏体和每个马氏体变体中的平均应力场。基于马氏体瞬间扩展假设,提出相变诱发塑性应变及位错密度的正向、逆向继承概念,在热力学框架下建立了单晶细观循环本构模型。通过对单晶各向异性循环变形特性的描述和预测,验证了模型的正确性。
[Abstract]:NiTi shape memory alloy with excellent superelasticity and shape memory properties, biocompatibility and high damping properties, is widely used in aerospace, biomedical engineering, civil engineering and other fields of.NiTi shape memory alloy as a key element in the structure, are often served in cyclic thermo mechanical loads in the process. In the NiTi shape memory alloy during cyclic deformation, functional deterioration (degradation of super elasticity and shape memory effect) effect of coupling and thermal stress are two important factors that can not be ignored, and the interaction and influence. Therefore, it is necessary to consider the establishment of functional coupling effect and thermal degradation characteristics mechanical constitutive model to describe and predict NiTi shape memory alloy structures and devices in various complex thermo mechanical load under cyclic deformation characteristics. In recent years, many scholars have been based on experimental phenomena in different scales On establishing the constitutive model of NiTi shape memory alloy. On the macroscopic scale, the model only considers the coupling effect of a functional deterioration or thermal stress of the functional deterioration is described by phenomenological method, the lack of corresponding physical mechanism in meso scale. The existing models, focus only on NiTi shape memory alloy in a loading unloading under thermo mechanical response, due to the inherent mechanism of the corresponding functional material deterioration has not yet, not for NiTi shape memory alloy cyclic deformation characteristics is given a reasonable description. Thus, some have constitutive model is still not perfect, still there are many limitations. In view of the above shortcomings, this paper will establish a thermodynamic coupling of NiTi shape memory alloy under different scale cyclic constitutive model, innovative work carried out as follows: (1) at the macro scale, through the macroscopic and microscopic experiment In summary, NiTi shape memory alloy on the physical mechanism of super elastic cyclic deformation deterioration is proposed, namely the martensitic transformation and defect interaction. Based on the thermodynamic framework for superelasticity of NiTi shape memory alloy can also set up a description of its super elastic deterioration and rate dependent deformation behavior of thermal stress the coupled constitutive model. Through the simulation and prediction of superelastic NiTi shape memory alloy under different loading rate under cyclic deformation characteristics, verify the prediction ability of the model. Further, the prediction model of superelastic NiTi shape memory alloy temperature cyclic deformation characteristics. (2) in a single representative volume element on the introduction of a variety of non elastic deformation mechanism to determine the degree of the relationship between the crystal and the martensitic transformation, martensite reorientation, Martensite Twin solution plastic and martensite austenite, plastic, based on thermodynamic Study in the framework of the single crystal scale established under thermal stress coupling constitutive model. The explicit transition criterion and the temperature uniformity assumption, crystal transition to the polycrystalline model. The polycrystalline NiTi shape memory alloy at different temperature and different loading rate, different description and prediction of properties under uniaxial stress and the non proportional multiaxial thermal stress coupling deformation, verify that the model is reasonable and comprehensive. (3) by summarizing the macroscopic and microscopic observation, we propose a new non elastic deformation mechanism, namely Markov reorientation induced plasticity in the work. (2) the establishment of crystal plasticity on the basis of the model, further in a single representative volume element on the introduction of quantitative and NiTi shape memory alloy functional deterioration of non elastic deformation mechanism, namely the transformation induced plasticity, redirect induced plasticity and residual martensite accumulation, and thermal mechanical framework based on Single crystal scale was established under the thermal stress coupling constitutive model. The explicit transition criterion and the temperature uniformity assumption, single crystal model transition to polycrystalline. Based on polycrystalline NiTi shape memory alloy at different temperatures under uniaxial and multiaxial cyclic deformation behavior and the rate was simulated and predicted to verify the prediction ability of the model. (4) in a single representative volume element, the martensitic transformation and transformation induced plastic deformation mechanism of two kinds of non elastic. 24 martensite into the same shape, but the crystal degree to ellipsoidal inclusions embedded in the austenite matrix of elastic anisotropy in different, and further using Mori-Tanaka homogenization method to get the average stress of austenite and martensite in each field. Based on the assumption of instantaneous expansion of martensitic transformation induced plasticity, put forward strain and dislocation density, reverse the concept of inheritance, A single crystal mesoscopic cyclic constitutive model is established under the framework of thermodynamics. The correctness of the model is verified by describing and predicting the anisotropic cyclic deformation characteristics of single crystal.

【学位授予单位】：西南交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG139.6
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本文编号：1448653