智能结构中光纤智能夹层力学特性的实验研究

根据光纤自诊断系统模块化、集成化要求,制作出光纤智能夹层,它可以铺设于复合材料结构表面或埋入复合材料结构内部。对智能夹层试件的轴向拉伸试验和层间拉伸试验表明,光纤智能夹层的埋入对复合材料结构的强度性能无显著影响,可以埋入复合材料结构内部并实施健康监测。试验还表明,在一定应变范围内,单膜交错光纤中光强—应变之间具有良好的线性关系,可以在埋入复合材料之前进行标定。     

SMA智能混凝土材料裂缝监测与修复机理和试验研究

混凝土材料的裂缝产生与扩张一直是土木工程领域亟待解决的难点问题之一.论文将形状记忆合金(SMA)材料植入混凝土材料中,构成一种基于SMA驱动的智能混凝土材料.通过对SMA材料的电阻变化和混凝土裂缝大小的关系进行讨论,建立了SMA智能混凝土材料的裂缝监测理论模型;对SMA试件在初始状态为奥氏体情况下所展示的形状记忆效应进行理论和试验分析,给出了SMA智能混凝土材料的裂缝修复理论模型;最后通过试验测试,讨论了不同尺寸试件的裂缝修复过程和裂缝修复程度.论文研究可为形状记忆合金智能混凝土材料的进一步优化设计和工程应用提供理论指导.     

结构健康监测技术及其在航空航天领域中的应用

对飞行器结构中的裂纹、腐蚀、脱层、材料性能退化及其它损伤进行及时且准确的检测是确保服役飞行器安全可靠运行的必要手段。结构健康监测是确定结构完整性的革命性创新技术,它在飞行器的结构设计、飞行及维护过程中都可发挥重要作用,它的使用可以提高飞行安全性、降低维护成本。本文简要介绍结构健康监测的系统组成、基本原理及关键技术,并通过实例阐述了基于智能层的结构健康监测技术在飞行器上的应用情况。     

振动工程中智能结构的研究进展

介绍了智能结构的概念,评述了近年来用于振动工程中的智能结构所研究的几个基本问题：传感器,作动器,智能结构动力学建模及其振动控制,传感／作动器在结构中的优化配置,并提出了建议研究的几个问题：作动／传感材料的研究、集成技术的研究、控制器的研究和结构控制一体化优化技术     

水凝胶多场耦合计算力学

作为一种具有多场耦合特性的智能柔体材料,水凝胶的制备技术、性能表征与结构应用得到迅速发展。本文在分析水凝胶本构理论和结构设计的基础上,提出了水凝胶多场耦合计算力学的基本方法和范式,包括微观粗粒化分子动力学模拟和宏观耦合有限元方法等,计算了化学-力学耦合作用下水凝胶材料与结构的变形和应力,给出了多个数值算例与结果比较。研究指出多场耦合计算力学将成为水凝胶材料和结构分析的主要手段,并推动水凝胶等这类智柔材料的性能设计与工程应用。     

基于认知技术的Lamb波结构损伤检测

在雷达领域最新技术进展的启发下,提出了一种新的概念——认知结构健康监测。认知结构健康监测是一种可以智能处理环境变化引起影响的结构健康监测系统:在先验知识及智能推理的基础上,通过调整系统输入及输出功能实现智能处理。并在此基础上提出了一种基于认知的Lamb波结构损伤检测方法,通过仿真进行了验证。铝板上的仿真结果表明,该方法能够在温度变化等干扰下准确地提取出与边界反射波混叠的损伤反射波,从而实现对边界附近损伤的检测。     

智能结构梁传递驱动模型

基于结性应变假设,提出了考虑粘贴层影响的智能结构梁分布模型。通过对双面粘压电驱动器的智能结构梁的数值模拟,得到了应变分布假设对压电驱动顺驱动性能影响的规律。结果表明：忽略粘贴层的影响,将过高地估计压电片产生的驱动力;考虑粘贴层影响的智能结构梁分布力模型更符合实际情况,具有广泛的普遍性。     

基于光纤智能夹层传感结构的应力测量研究

制作了一种模块化的光纤传感夹层,对夹层内的光纤传感器的应力特性进行了实验研究。分析了应变对传感系数的影响,对埋入到光纤智能夹层中的两种光纤传感器的输出特性进行了比较。实验结果表明:光纤Bragg光栅传感器的波长漂移与应变之间具有理想的线性关系,但应变灵敏度由1.2pm/με降至1.15pm/με;由于制作工艺的局限,对于非本征F-P光纤传感器,当应变达到350με后,应变与载荷具有较好的线性响应。与非本征F-P光纤传感器相比,光纤Bragg光栅传感器是光纤智能夹层首选的应变传感器。将埋入了Bragg光栅传感器的智能夹层粘贴于某型飞机的翼-身连接构件内部进行监测,实验结果为光纤智能夹层应用于复合材料结构的应变监测提供了参考。     

二维共振结构板波动调控研究进展

薄板结构是航空航天器、舰艇、高铁等现代工程装备上广泛应用的结构,其波动性能的优劣关系到设备综合性能及整体技术升级．在制备或复杂工况,结构的几何完备性会产生一些缺陷或参数扰动,会降低基于精准设计的波动调控性能．基于工程应用技术需求,二维共振结构板的高鲁棒性、高品质因子束缚态等波动特性研究不断发展．本文首先介绍了二维共振结构板波动调控发展历程,主要阐述了平面波展开法、多重散射法等二维共振结构波动表征基本理论．简述了二维共振结构板在波导与传感、鲁棒能量采集以及按需智能设计等最新研究成果．最后对二维共振结构板目前的局限性做了总结并对未来的理论研究进行探讨.     

面向压电智能结构精确变形的协同优化设计方法

智能结构集智能材料与传统材料于一体,能够实现结构的主动控制,在航空航天等领域具有巨大的应用潜力.由于其系统复杂且具有多场耦合效应,智能结构的整体式优化设计方法成为结构控制技术研究的关键之一.为了提高压电智能结构的整体性能和变形精度,提出了同时考虑压电驱动器布局(分布位置及角度)和基体结构拓扑构型的协同优化设计新方法.采用多点约束方法 (multi-point constraints,MPC)建立压电驱动器和基体结构的连接,定义一种与测量点目标位移相关的权重函数,以实现结构的精确变形控制.通过协同优化设计,压电驱动器可以获得最优的分布位置及角度,同时基体结构获得最优的拓扑构型,从而提升了压电智能结构系统的整体驱动性能和变形精度.通过进一步分析,研究了精确变形、体分比约束与结构优化构型和整体刚度的关系,以及优化结果中可能存在的传力路径畸变现象.数值算例的设计结果表明,采用协同优化设计方法,能够扩大结构的寻优空间,有效减小变形误差,实现压电智能结构的精确变形控制.     

厚度振动模式下背衬结构PZT的声能特性

为了充分利用埋入混凝土中压电陶瓷所激励的声能,采用了一种在压电陶瓷圆片结构的一面设置金属背衬的方法将压电陶瓷双侧的声能集中到一侧,提高了声指向性和声能。实验表明:该方法能使同距离下压电陶瓷圆片轴向声能提高10倍以上,并且得到了声能的相对增量随背衬厚度和声激励频率之积变化的特性曲线。声信号的谱分析还表明:背衬没有改变声信号的主频和主峰区间的频率带宽;当声激励频率为谐振频率79kHz时,最优背衬厚度为2.4mm;当声激励频率f为60kHz～100kHz时,接收端声能相对较大,适合用于实际的压电埋入式超声无损检测。     

Micromechanics and structural response of functionally graded,particulate-matrix,fiber-reinforced composites

Reinforcement of fibrous composites by stiff particles embedded in the matrix offers the potential for simple, economical functional grading, enhanced response to mechanical loads, and improved functioning at high temperatures. Here, we consider laminated plates made of such a material, with spherical reinforcement tailored by layer. The moduli for this material lie within relatively narrow bounds. Two separate moduli estimates are considered: a “two-step” approach in which fibers are embedded in a homogenized particulate matrix, and the Kanaun–Jeulin (Kanaun, S.K., Jeulin, D., 2001. Elastic properties of hybrid composites by the effective field approach. Journal of the Mechanics and Physics of Solids 49, 2339–2367) approach, which we re-derive in a simple way using the Benveniste (1988) method. Optimal tailoring of a plate is explored, and functional grading is shown to improve the performance of the structures considered. In the example of a square, simply supported, cross-ply laminated panel subjected to uniform transverse pressure, a modest functional grading offers significant improvement in performance. A second example suggests superior blast resistance of the panel achieved at the expense of only a small increase in weight.     

Acoustic emissions from reinforced concrete

Acoustic emissions from reinforced-concrete beams, reinforcing bars and plain concrete cylinders were monitored. Acoustic-emission events were used in a study of source locations, frequency characteristics, and other analytical methods that have found use in the past for evaluating acoustic-emission data in other fields of engineering. Tests were done on reinforced-concrete beams under flexural loading, individual reinforcing bars under pure tension, concrete cylinders under compression, and reinforcing bars subject to pullout tests.The experimental data were first analyzed with conventional acoustic-emission methodology. A critical look at many acoustic-emission techniques currently used in other materials (metals, composites, etc.) demonstrated some of the difficulties of applying the same techniques to reinforced concrete. More importantly, it illustrated the limitations of signal processing and parameter estimation of acoustic-emission events as viable nondestructive-evaluation (NDE) techniques for reinforced-concrete structures. Subsequently, on the basis of the experimental results, some of the more promising aspects of developing acoustic emission into a structural monitoring tool are discussed.     

土木工程结构健康监测系统的研究状况与进展

土木工程结构健康监测的研究是近年来国际学术研究的热点问题之一,涉及许多不同的研究领域,如数据采集系统、信号处理、结构分析等.阐述了实施土木工程结构健康监测的必要性和迫切性,介绍了结构健康监测系统的概念、组成及其应用,分析研究了结构健康监测系统的各个子系统的功能、特点和实现方法,重点讨论了实现各子系统的理论、方法和存在的若干力学问题,论述了结构健康监测在国内外土木工程领域的应用状况,最后对结构健康监测领域的几个重要问题做了展望.      

DETERMINATION OF INTERNAL STRAIN IN 3-D BRAIDED COMPOSITES USING OPTIC FIBER STRAIN SENSORS

A reliable understanding of the properties of 3-D braided composites is of primary importance for proper utilization of these materials. A new method is introduced to study the mechanical performance of braided composite materials using embedded optic fiber sensors. Experimental research is performed to devise a method of incorporating optic fibers into a 3-D braided composite structure. The efficacy of this new testing method is evaluated on two counts. First, the optical performance of optic fibers is studied before and after incorporated into 3-D braided composites, as well as after completion of the manufacturing process for 3-D braided composites, to validate the ability of the optic fiber to survive the manufacturing process. On the other hand, the influence of incorporated optic fiber on the original braided composite is also researched by tension and compression experiments. Second, two kinds of optic fiber sensors are co-embedded into 3-D braided composites to evaluate their respective ability     

Piezoelectric wafer active sensor embedded ultrasonics in beams and plates

In this paper we present the results of a systematic theoretical and experimental investigation of the fundamental aspects of using piezoelectric wafe active sensors (PWASs) to achieve embedded ultrasonics in thin-gage beam and plate structures. This investigation opens the path for systematic application of PWASs forin situ health monitoring. After a comprehensive review of the literature, we present the principles of embedded PWASs and their interaction with the host structure. We give a brief review of the Lamb wave principles with emphasis on the understanding the particle motion wave speed/group velocity dispersion. Finite element modeling and experiments on thin-gage beam and plate specimens are presented and analyzed. The axial (S ₀) and flexural (A ₀) wave propagation patterns are simulated and experimentally measured. The group-velocity dispersion curves are validated. The use of the pulse-echo ultrasonic technique with embedded PWASs is illustrated using both finite element simulation and experiments. The importance of using high-frequency waves optimally tuned to the sensor-structure interaction is demonstrated. In conclusion, we discuss the extension of these results toin situ structural health monitoring using embedded ultrasonics.     

Adsorption removal of sulfamethoxazole from water using UiO-66 and UiO-66-BC composites

The adsorption removal of anti-inflammatory drugs from water by diverse materials has drawn great attention. This study investigated the adsorption of sulfamethoxazole (SMX) by two types of materials, UiO-66 and UiO-66-BC composites. Highly porous MOF composites with functional groups were synthesized by combining UiO-66 with corncob-based biochar at different molar ratios. SEM results showed that macroporosity of UiO-66-BC composites was increased by increasing the ratio of biochar. It was found that UiO-66-BC composites displayed highly improved adsorption performance of SMX relative to pristine UiO-66. UiO-66-BC (5%) had the highest SMX adsorption capacity, about 2.4 times those of pristine UiO-66. It was the high surface area of UiO-66 and redundant functional groups of biochar that increased the adsorption performance of composites. Moreover, UiO-66-BC can be reused and displayed the competitive adsorption efficiency after successive adsorption, which made it a potential adsorbent for the removal of SMX from water.     

Research progress on thermal protection materials and structures of hypersonic vehicles

Hypersonic vehicles represent future trends of military equipments and play an important role in future war. Thermal protection materials and structures, Which relate to the safety of hypersonic vehicles, are one of the most key techniques in design and manufacture of hypersonic vehicles. Among these materials and Structures, such as metallic temperature protection structure, the temperature ceramics and carbon/carbon composites are usually adopted in design. The recent progresses of research and applica- tion of ultra-high temperature materials in preparation, oxidation resistance, mechanical and physical characterization are summarized.