【作者】 马志超；

【导师】 周晓勤； 赵宏伟；

【作者基本信息】 吉林大学 ， 机械制造及自动化， 2013， 博士

【摘要】 研制能够对材料性能进行多种载荷作用下微观力学性能原位（In situ）测试的仪器装备并据此获得的材料性能数据，将是材料研制、结构与制品设计、寿命预测和可靠性评估的重要基础，具有重要的科学意义，也将产生重大的社会效益和经济效益。原位拉伸-疲劳测试是可对材料微观变形损伤、组织结构变化进行可视化监测的最为典型的静、动态原位测试技术之一。目前针对块体材料的原位拉伸测试多借助商业化的原位拉伸测试仪，该类仪器功能确定，不易于进行功能扩展；而现有的原位疲劳测试多利用压电驱动与液压驱动方式分别对微尺度构件和块体材料开展测试，且分别存在加载行程有限和测试频率不足的问题。此外，现有原位力学测试技术较少涉及多种载荷的复合载荷测试模式。据此，本文针对块体材料的微观力学性能测试及表征，开展了原位力学测试装置及其控制系统的研制，提出了三种用于修正力学参数的算法，对拉伸-疲劳原位测试装置性能进行了较为系统的测试分析，并开展了基于拉伸模式的复合载荷测试的理论与试验研究。主要研究工作可概述为：（1）原位拉伸测试装置及其控制系统的设计分析提出了基于大减速比减速机构的“超低速准静态”加载方法，利于SEM等装备对材料微观变形损伤的高分辨率成像，并可实现测试装置的紧凑化和轻量化。提出了基于夹具体与试件夹持部分等宽约束的夹持方法。进一步，搭建了基于载荷/位移传感器模拟量反馈和编码器数字量反馈的闭环控制系统。在此基础上，开展了测试装置与SEM的兼容性测试。此外，针对小真空腔体SEM或光学成像条件下的成像工作距离要求，研制了将试件置高布置的非标准布局型测试装置，以实现其与各类成像系统的广泛兼容性，并对该装置的传动误差和固有频率等进行了测试。（2）拉伸测试结果的修正算法针对表征材料力学性能的重要参数，如弹性模量和伸长率等的测试准确性，本文对小型化原位拉伸测试装置进行了系统的理论与试验研究。首先，就不同夹持位置对弹性模量计算的影响，提出了计算试件标距部分实际应变的理论模型，建立了检测位移与实际应变间的理论模型，采用原位观测图像对模型可行性进行了验证。其次，针对试件置高布置的非标准布局型测试装置，系统研究了因传动单元间隙及传感器倾覆导致的系统刚度弱化问题，提出了对试件全量程范围的应力和应变进行修正的算法。最后，对于试件轴线与拉伸方向的空间不同轴问题，提出了基于水平面剪切变形分量和竖直面弯曲变形分量的解析方法，结合挠曲线计算，可对试件的实际应力-应变曲线进行准确计算。（3）原位拉伸-疲劳装置性能测试分析许多构件的损伤失效形式往往归因于静、动态载荷的耦合作用，采用直流伺服电机与压电驱动器耦合驱动的方法，可开展大范围应力比模式下的原位疲劳测试。通过对压电叠堆温升和电荷释放行为的研究，确定了原位疲劳测试的合理连续循环周数和间隔时间。本文系统研究了不同初始静载荷下压电驱动器的动态输出特性，以及不同加载频率下压电驱动器的有效行程，并就交变载荷对应力松弛进程的加速作用进行了研究。（4）典型材料的原位拉伸测试试验与循环应力-应变曲线预测利用研制的测试装置，本文对铜铝复合材料的断裂机制进行了研究，对其颈缩行为开展的SEM下观测结果表明：复板层（C11000铜）先于基板层（1060铝）发生断裂，基板层的主要断口形貌为撕裂韧窝，而复板层韧性断口主要为纯剪切型断口。对锌对铜锌合金低周疲劳性能的影响发现：基于相同的应变幅，含锌量增加后，铜锌合金在每次循环过程中消耗的塑性功更多，疲劳过渡寿命更短。此外，本文还针对具有典型循环硬化行为的材料，提出了单轴应力-应变曲线及循环应力-应变曲线的拟合方法，并据此提出了利用单轴拉伸应力-应变曲线预测出强化应变范围内的循环应力-应变曲线的方法。（5）拉伸-剪切复合载荷加载与解耦方法以及预载荷对力学性能的影响利用集成改进型Arcan夹具的测试装置开展了AZ31B变形镁合金的单轴拉伸、纯剪切及偏移角为45°的拉伸-剪切复合载荷测试并发现：材料断裂时的塑性功消耗并无显著变化，这表明材料在无预应力作用下的断裂发生所需的累积功消耗对受载形式并不敏感。进一步，提出了该复合加载模式下拉伸应力-应变与切应力-应变曲线的解耦模型。此外，本文还研究了拉伸预应变和弯曲预挠度对AZ31B变形镁合金弯曲、拉伸性能的影响并发现：在弹性阶段，塑性预应变对试件弹性行为的影响并不显著；在过渡强化阶段，预应变越大，试件的应变硬化行为越显著；而在大应变软化阶段或颈缩阶段，随着预应变的增加，材料表现出应变软化行为。总之，本文的研究工作不仅是对现有原位力学测试技术的扩展，也是对力学性能参数准确修正和复合载荷耦合加载与解耦理论的进一步深化。本文有关原位力学测试装置的研制方法及理论解析将为原位力学测试技术及装备提供理论基础并开辟新的应用途径。更多还原

【Abstract】 Developping the in situ testing instruments based on various loads types to researchon various materials and accordingly obtaining testing data of material performance wouldbe the important foundation to materials development, the designing of structures andproducts, life prediction and reliability evaluation. Therefore, the developping of in situtesting instruments has important scientific significance, prominent social and economicbenefits.In situ tensile and fatigue testing are considered as one of most typical static anddynamic technologies to visually supervise the micro deformation, damage and structureschanges of materials. Currently, the primary method of in situ tensile testing of bulkmaterials mostly depends on commercial in situ tensile testers. However, these instrumentspresent specific function and function expansion is confined. The existing in situ fatiguemechanical testing mostly relies on the piezoelectric driving or hydraulic driving methodsto carry out the relevant tests on microscale specimen or bulk materials, however, thedriving methods respectively present problems of limited testing stroke and frequency.Furthermore, the current in situ testing methods have not involved combined loads testingbased on multiple loading modes and relevant decoupling methods. Therefore, accordingto the micro-mechanical properties testing and characterization of bulk materials,corresponding in situ testing devices and control system were developed in this paper. Andthree algorithms for correcting the mechanical parametres were proposed. On this basis,the in situ tensile-fatigue testing device was also systematically and deeply tested. Thetheories and experimental researches on the combined loads testing of bulk materials werealso carried out. The main research works of this paper could be summarized as follows:(1) Design and analysis of in situ tensile device and control systemThe ultra-low speed quasi-static loading mode was proposed by adopting thereducing mechanism with large reduction ratio, the loading mode could not only achievethe functions of reducing speed and increasing torque, but also effectively meet therequirement of high resolution imaging of materials’ deformation process by SEM.Addtionally, the loading mode could also achieve the compacting and lightweight oftesting devices. A self-positioning gripping method was also proposed based onequi-width constraint of the gripper and specimen’s gripping section. Furthermore, basedon the calibration of displacement sensor and load sensor, the author constructed aclosed-loop control system based on analog signal feedback of the load/displacement sensors and digital signal feedback of the encoder. The compatibility testing with SEMwas also conducted. On the basis, to achieve imaging depth requirements of SEM withsmall vacuum chamber or optical imaging conditions, a non-standard layout type deviceby layouting the specimen on the top horizontal plane was also developed to achieve thebroad compatibility with various types of imaging systems. The transmission error andnatural frequency of the device were also tested.(2) Correction methods of tensile testing dataAs for the important parameters for the characterization of material’s mechanicalproperties, such as the testing accuracy of elastic modulus, yield strength and elongation,systematically theoretical and experimental investigations on miniaturized in situ tensiletesting devices were carried out. Firstly, for the influences of various gripping positions onelastic modulus calculations, this paper proposed a theoretical model for calculating theactual strain of the specimen’s gripping section, and theoretical model between measureddisplacement and actual strain was also established. In addition, in situ observation imageswas adopted to verify the feasibility of the proposed model. Secondly, for the non-standardlayout device by layouting the specimen on the top horizontal plane, this papersystematically investigated the weakening of system stiffness caused by the transmissionchain gap and the overturn of load sensor, and proposed an algorithm which could correctthe stress and strain of full scale range. Finally, for the dimensional misaligment issuebetween the specimen’s axis and tensile direction, this paper proposed an analyticalmethod based on horizontal shear deformation component and vertical bendingdeformation component. Combined with the calculation of deflection curve, thespecimen’s actual stress-strain curve could be accurately calculated.(3) Tests and analysis on in situ tensile-fatigue deviceFor many components, the materials’ failure is often attributed to the coupled effectsof static and dynamic loading. By using the coupling driving method integrating the DCservo and piezoelectric actuator, fatigue testing with variable frequencies and wide stressratio could be carried out. By investigating the temperature rise and charge releasebehaviors of piezoelectric stacks, the rational number of cycles and interval time wereobtained. This paper also studied the dynamic output performance of piezoelectric actuatorbased on different initial static loads, and the effective stroke of piezoelectric actuatorbased on various testing frequency. The aggravation effects of alternating load on thetensile stress relaxation was also investigated.(4) In situ tensile testing of typical materials and prediction of cyclic stress-straincurveWith the aid of developed devices, the fracture mechanism of Cu-Al compositematerial was investigated, the necking process was observed by SEM and the testingresults showed: the plate layer (C11000copper) fractured antecedent to substrate layer (1060aluminum), the main fracture morphology of plate layer and substate layer wererespective tear toughening nest and pure shear typies. The research on the effect of alloycomposition Zn on the low cycle fatigue properties of copper-zinc alloy showed that basedon the identical strain amplitude, as the content of Zn increased, the copper-zinc alloyconsumed more irreversible plastic work during each cycle and presented shortertransition life. In addtion, for the bulk materials with typical cyclic hardening behaviors,an accurate prediction method of cyclic stress-strain curves at the materials’ strengthenstrain range was also proposed and investiagted based on uniaxial tensile stress-straincurve.(5) Combined loading and decoupling method of tensile-shearing mode and effects ofpre-loads on mechanical propertiesBy using a modified Arcan fixture, the uniaxial tensile, pure shear andtensile-shearing combined loading tests based on an offset angle of45°of AZ31Bmagnesium alloy were carried out. The results showed that the total consumed plasticwork did no significantly change, this indicated that the plastic work consumptionrequired for material fracturing without pre-stress was not sensitive with the loading typies.Furthermore, the decoupled model of the tensile stress-strain and shear stress-straincurves under tensile-shearing combined loads was proposed. Besides, the effects of tensilepre-strain and bending pre-deflection on the bending and tensile properties of AZ31Bextruded magnesium alloy were investigated. Specifically, in the elastic stage, the effectsof plastic prestrain on specimen’s elastic behavior were not obvious, in the transitionalhardening stage, as the prestrain increased, the specimen presented more obvioushardening behavior, in the large strain softening stage or necking stage, as the prestrainincreased, the softening behavior of specimen presented more obvious trend.In conclusion, this study is not only the expansion of the existing in situ tensiletesting technology, but also the further understand of the accurate correction of mechanicalproperties and combined loads coupling and decoupling theories and technologies. Thedevelopment of serialized in situ mechanical testing devices and the theoretical analysiswill provide a theoretical foundation and open up new avenues for developing in situmechanical testing technologies and equipments.更多还原