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铁磁智能材料力磁耦合行为研究
作者姓名：裴永茂
论文题目：铁磁智能材料力磁耦合行为研究
作者简介：裴永茂，男，1979年3月出生，2002年9月师从于清华大学方岱宁教授，于2007年7月获博士学位。
中文摘要
铁磁智能材料，包括稀土超磁致伸缩材料和铁磁形状记忆合金，同时具有感知和驱动功能，即材料自身能感知环境变化，并作出相应的响应，因此在航空航天、
MEMS、信息存储及医疗器械等技术领域有广阔的应用前景，越来越受人们的关注。这些材料往往工作在磁场、应力场等多场耦合环境中，其在多场耦合环境下的磁学、机械等物理力学性能表征以及检测至关重要。因为铁磁智能材料在磁场、应力场及耦合场作用下具有复杂的非线性响应，不同应力状态下的矫顽场、饱和磁化强度、磁导率、磁致伸缩效应，以及不同磁场作用下的弹性模量、应变导数、阻尼等材料性能均会产生明显的差异。然而迄今为止，由于铁磁智能材料的力磁耦合行为的复杂性，这方面的研究成果仍很缺乏，尤其是缺少检测铁磁智能材料力磁耦合性能技术方法及设备，限制了相关的研究进展。这一领域的研究对铁磁智能材料物理力学性能的表征、检测及多场耦合下的非线性行为、滞后响应的基础研究具有重要的意义，对智能材料和结构器件的设计具有指导作用，将在一定程度上促进电磁固体力学的发展。
本文从实验和理论两个方面深入研究了铁磁智能材料力磁耦合行为。我们自行研制了多轴多功能全自动力磁耦合加载与测量系统，能够同时产生强磁场和高机械载荷，实现了高精度全自动测量和控制，为研究铁磁智能材料的力磁耦合行为奠定了基础。该发明技术和设备具有多功能，高载荷，强磁场，高精度和全自动的技术特点，代表了目前国内外发展的新趋势，具有很强的国内外市场竞争力。并利用该设备，系统的实验研究了超磁致伸缩材料在多轴力磁耦合场作用下的本构行为，在国际范围内首次发现了超磁致伸缩材料的巨大受迫体磁致伸缩，磁致伸缩的“回落”现象等。在理论研究方面，提出了一个唯象的磁畴旋转模型，定量的描述了力磁耦合场作用下的磁致伸缩和磁滞回线行为;在热力学框架基础上，通过引入Preisach函数来描述畴变过程，从而提出了唯象的畴变拟弹性模型来描述超磁致伸缩材料的畴变拟弹性行为;并且利用磁致应力和机械应力的等效原则，将磁场作用引入相变动力学，提出了一个简单的唯象磁致应变模型来描述铁磁形状记忆合金的磁致应变行为。本论文从实验和理论两方面系统研究了铁磁智能材料在耦合场下的非线性滞后行为，成功的解释了其物理机制。在这些工作中，我们取得了以下创新性成果：
1.
自行研制了多轴多功能全自动力磁耦合加载与测量系统，解决了同时产生高磁场和高载荷的难题，在极头直径为100mm，极间距为100mm时，最大磁场强度能够达到1910kA/m;最大载荷可以达到2000kg;设计了小型化的液压驱动加载装置，能够在磁场均匀区旋转成任意角度，从而实现多轴力磁耦合场;当电磁铁产生巨大电磁吸引力时，由伺服电机自动实时调控极头间距，避免了手动锁定极头造成损坏极头或者压碎试件;采用绝缘和屏蔽技术，实现了电磁铁设备与液压驱动系统的结合，并自行研发了力磁耦合测控软件，实现了全自动化高精度的控制和测量;开发了多种力磁耦合实验功能，包含力磁耦合的磁致伸缩，磁滞回线，应力退磁化行为，畴变拟弹性行为和磁致断裂行为等。
2.
系统的实验研究了超磁致伸缩材料在高载荷、强磁场、多轴力磁耦合场作用下的磁弹性行为，包括磁致伸缩、磁滞回线、应力应变和应力退磁化等。在国际范围内首次研究和发现[110]定向多晶Tb0.3Dy0.7Fe1.95合金在力磁耦合场作用下的巨大的受迫体磁致伸缩;磁致伸缩的“回落”现象;弹性模量的各向异性行为;路径依赖效应;擦除特性和同余特性;并研究了其拟弹性行为，首次提出了畴变拟弹性的概念。
3.
提出了唯象的各向异性磁畴旋转模型。在实验的基础上，提出能量分布参数为预应力的线性函数，该模型定量的预测了超磁致伸缩材料在力磁耦合场下的非滞后的非线性行为，理论预测与实验结果吻合很好;并且假设能量分布参数为磁化状态的函数，引入了耗散参数，描述了磁滞回线和磁致伸缩曲线，在低应力和高应力区域均很好的预测了超磁致伸缩材料的磁滞现象，理论预测与实验结果吻合的很好。该模型物理意义明确，表述简单。
4.
提出了一个基于热力学框架的畴变拟弹性唯象模型，通过对畴变过程的分析和简化，给出了一个合适的Gibbs自由能;并引入Preisach函数描述在力磁耦合场作用下畴变演化过程，它满足实验发现同余性和擦除特性，具有明显的磁滞特征;通过对实验过程分析，确定Preisach函数为高斯分布形式;最后将理论预测和实验结果对比，发现仅采用无磁场作用时测量得到的材料参数，该理论模型即可较好的描述在不同恒定磁场作用下的畴变拟弹性变形过程。
5.
提出了一个铁磁形状记忆合金的唯象磁致应变模型，通过修改传统形状记忆合金的相变动力学公式来描述马氏体变体择优取向过程;提出了反指数形式的单一磁化曲线假设来描述易轴和难轴方向的磁化曲线的非线性;并基于磁致应力和机械应力的等效原则，将磁场的作用引入相变动力学公式，理论预测了铁磁形状记忆合金的磁致应变行为。通过理论预测与实验结果的对比发现，该模型理论预测磁化曲线，应力应变曲线和磁致应变曲线均与实验结果吻合较好。
注：需要指出的是自主发明的高载荷强磁场多轴力磁耦合自动加载与测量方法与技术及设备，经教育部成果鉴定，鉴定委员会一致认为：自行研制的全自动力磁耦合加载与测量设备，填补了国内空白，达到国际领先水平。该设备对研究磁性材料的力磁耦合行为，磁致失效行为以及无损检测技术具有重要的意义(鉴字
[教NF2006] 第030 号)。并获得2007年度高等学校科学技术奖(技术发明)一等奖。目前已获得授权中国发明专利5项，已申报受理中国发明专利1
项，获得软件著作权1
项。在国家工业部门和国防装备建设以及许多国内外高校和研究部门得到了推广应用，为其提供了多场耦合复杂环境下物理力学性能检测有效的技术手段，取得了显著的经济效益和社会效益。主要工程应用单位包括中国计量院、北京赛迪机电新技术开发公司、陕西省长安钢厂、海军XXX
舰队基地装备部、美国阿诺德磁材公司等工业企业与国防部门，提高了其物理力学检测评价水平，为指导产品设计和保证产品质量提供了实质性贡献，由此带来显著的经济效益。主要科研应用单位有清华大学、西安交通大学、兰州大学、香港大学、湘潭大学、北京理工大学、石家庄铁道研究院、澳大利亚伍伦贡大学、太原科技大学、装甲兵工程学院，有效地提升了这些单位的实验装备水平和技术手段，增强了研究能力，取得了一批学术研究成果，由此获得几千万元科研课题项目经费。同时，北京航空航天大学、同济大学、韩国高等科学技术研究员(KAIST)等单位也准备购置，并为北京航天航空大学、中科院物理所和浙江大学材料系进行新型磁材的物理力学性能检测，取得了一批科研成果，推动了该领域的科学进展。
关键词：
超磁致伸缩材料;铁磁形状记忆合金;力磁耦合;本构关系;
Study on the Magnetomechanical Behavior of
Ferromagnetic Smart Materials Pei Yongmao
ABSTRACT
Ferromagnetic smart
materials, including rare-earth giant magnetostrictive materials and
ferromagnetic shape memory alloys, can exhibit sensation and activation
simultaneously. It means it can not only detect the ambient variation but also
show the corresponding response. Therefore, it has attracted more and more
attentions because of its promising applications in aeronautics and
astronautics, MEMS, information storage, medicine and so on. There materials are
always subjected to magnetic fields besides stresses. It is particular important
to characterize and measure their properties of magnetism and mechanics under
magnetomechanical loading. Ferromagnetic smart materials present complicated
nonlinear responses under the application of stress, magnetic field and
magnetomechanical field. For example, coercive field, saturation magnetization,
permeability, and magnetostriction will change obviously under different
stresses. Elastic modulus, strain derivative and damping capacity are sharply
dependent on magnetic fields. However, until now it is still lack to study on
the magnetomechanical coupled behaviors of ferromagnetic smart materials due to
its complexity. Another critical reason is that it needs to develop the
experimental technique, method and instruments to measure the magnetomechanical
properties of ferromagnetic smart materials. It is very important to measure and
characterize their physical and mechanical performances, particular the
nonlinear, coupled magnetic and mechanical behaviors at strong mechanical and
magnetic loading. The research is very useful for the design of smart materials
and structure devices. In this dissertation, the experimental and theoretical
studies of the magnetomechanical behavior of ferromagnetic smart materials have
been carried out. A multiaxial and multifunctional automatic loading and
measuring apparatus for carrying out magnetomechanical experiments has been
constructed by ourselves. It can provide strong magnetic field and mechanical
loading and allow the automatic measurement and control with high accuracy.
Employing this apparatus, the systematical experiments have been carried out to
investigate the magnetoelastic behavior of the giant magnetostrictive materials
in the multiaxial intense magnetic field-large stress space, such as the
magnetostriction, magnetic hysteresis, stress-strain behavior, stress
demagnetization effect, damping property and so on. The phenomenon of the giant
forced volume magnetostriction, the “drop” of the magnetostriction, the
anisotropy of the Young’s modulus, the path-dependent effect, congruency and
wiping-out properties has been reported. In theoretical research, a
phenomenological anisotropic domain rotation model has been proposed, which can
quantitatively predict the magnetostriction and magnetic hysteresis of giant
magnetostrictive materials under the application of the magnetomechanical
loading. Based on the thermodynamic framework, the Preisach function with
magnetic hysteretic characters is introduced to describe the domain switch
process under the application of the magnetomechanical loading, which can
satisfy the congruency and wiping-out properties at the same time. Then, a
domain switch pseudoelasticity phenomenological model has been proposed to
predict the domain switch pseudoelasticity. At last, a model on the basis of
transformation kinetics is developed, in which the magnetic-field-induced stress
is introduced and the equivalence principal is employed for the mechanical and
magnetoelastic deformation. It can be used to describe the magnetic field
induced strain for the ferromagnetic shape memory alloys. In this dissertation,
we have systematically study the nonlinear hysteretic behavior under a
multiaxial magnetomechanical space as well as the physical mechanism. In these
works, some creative achievements are obtained. 1. A multiaxial and
multifunctional automatic loading and measuring apparatus for carrying out
magnetomechanical experiments has been constructed by ourselves. It can provide
strong magnetic field and large mechanical load, which is very difficult to
realize because the limit of space. It combines a hydraulically driven
mechanical loading system with a dipole electromagnet, which is capable of
producing mechanical forces up to 2000kg and magnetic fields up to 1910kA/m with
a pole gap of 100mm. And the mechanical force can be applied in any angle with
the magnetic field because the mechanical loading device can be rotated in the
pole gap. Thus, the multiaxial stress-magnetic field can be realized. To
eliminate the effect of the high magnetic force on the electromagnet gap and
avoid the damage of the pole and the sample, a system with a servo-motor driven
by the feedback encoding is designed to keep the pole gap constant. To combine
the electromagnetic device and the hydraulically driven system perfectly, the
insulation and shield technique is adopted. The software developed allows the
automatic measurement of magnetomechanical parameters under on-line computer
control of both the magnetic field and the mechanical force, so that the
magnetostriction, magnetic hysteresis, stress demagnetization effect, domain
switch pseudoelasticity and magnetic induced fracture can be carried out under
the application of magnetomechnical coupled field. 2. The systematical
experiments have been carried out to investigate the magnetoelastic behavior of
the giant magnetostrictive materials in the multiaxial intense magnetic
field-large stress space, such as the magnetostriction, magnetic hysteresis,
stress-strain behavior, stress demagnetization effect, damping property and so
on. The phenomenon of the giant forced volume magnetostriction, the “drop” of
the magnetostriction, the anisotropy of the Young’s modulus, the path-dependent
effect, congruency and wiping-out properties has been firstly studied and
reported for the [110] oriented polycrystalline Tb0.3Dy0.7Fe1.95 alloys in the
multiaxial magnetomechanical space. And a domain switch pseudoelasticity concept
has been proposed based on the experimental results. 3. A phenomenological
anisotropic domain rotation model has been proposed. On the basis of the
experimental results, it is assumed that the energy distribution parameter is a
linear function of the pre-stress. Then the anhysteretic behavior of giant
magnetostrictive materials under the application of the magnetomechanical
loading has been predicted quantitatively. Further more, we assume that the
energy distribution parameter is the function of the magnetization state. Thus a
dissipation parameter is introduced to describe the magnetic hysteresis and
magnetostriction. A good agreement between the model and the experimental
results in low and high stress regions is obtained. It has the clear physical
meaning and simple express. 4. On the other hand, based on the thermodynamic
framework, a domain switch pseudoelasticity phenomenological model has been
proposed. A Gibbs free energy is obtained by the analysis and simplification of
the domain switch process. Then, a Preisach function with magnetic hysteretic
characters is introduced to describe the domain switch process under the
application of the magnetomechanical loading, which can satisfy the congruency
and wiping-out properties at the same time. Based on the experimental process, a
Gauss distribution is adopted to represent the Preisach function. At last,
materials parameters obtained easily under zero magnetic field are used to
describe the domain switch pseudoelastic deformation behavior under different
magnetic fields. A good agreement between the model and the experimental results
is obtained. 5. A model on the basis of transformation kinetics is developed to
describe the martensite variants preferred reorientation for the ferromagnetic
shape memory alloys. An inverse exponential expression is given to describe the
field dependence of magnetization for martensitic variants. The
magnetic-field-induced stress is introduced into transformation kinetics and the
equivalence principal is employed for the mechanical and magnetoelastic
deformation. The experimental results including the magnetization, stress-strain
and magnetic-field-induced strain are all predicted well. Key words: Giant
magnetostrictive material; Ferromagnetic shape memory alloy; Magnetomechanical;
Constitutive relation;
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