Emerging Trends in Damage Tolerance Assessment:A Review of Smart Materials and Self-Repairable Structures

The discipline of damage tolerance assessment has experienced significant advancements due to the emergence of smart materials and self-repairable structures.This review offers a comprehensive look into both traditional and innovative methodologies employed in damage tolerance assessment.After a detailed exploration of damage tolerance concepts and their historical progression,the review juxtaposes the proven techniques of damage assessment with the cutting-edge innovations brought about by smart materials and self-repairable structures.The subsequent sections delve into the synergistic integration of smart materials with self-repairable structures,marking a pivotal stride in damage tolerance by establishing an autonomous system for immediate damage identification and self-repair.This holistic approach broadens the applicability of these technologies across diverse sectors yet brings forth unique challenges demanding further innovation and research.Additionally,the review examines future prospects that combine advanced manufacturing processes with data-centric methodologies,amplifying the capabilities of these‘intelligent’structures.The review culminates by highlighting the transformative potential of this union between smart materials and self-repairable structures,promoting a sustainable and efficient engineering paradigm.

APPLICATIONS OF PIEZOELECTRIC MATERIAL SENSORS IN SMART STRUCTURES

The use of piezoelectric material sensors in smart composite structures is investigated. An experimental structure bonded with lead zirconate titanate piezoelectric ceramic(PZT) sensors is developed. These bonded sensors are employed to monitor load variations and transient impacts in the structure. Incorporated with pattern recognition approach, PZT sensors have succeeded in detecting the onset and location of damages.

4D printing: interdisciplinary integration of smart materials, structural design,and new functionality

Four-dimensional printing allows for the transformation capabilities of 3D-printed architectures over time,altering their shape,properties,or function when exposed to external stimuli.This interdisciplinary technology endows the 3D architectures with unique functionalities,which has generated excitement in diverse research fields,such as soft robotics,biomimetics,biomedical devices,and sensors.Understanding the selection of the material,architectural designs,and employed stimuli is crucial to unlocking the potential of smart customization with 4D printing.This review summarizes recent significant developments in 4D printing and establishes links between smart materials,3D printing techniques,programmable structures,diversiform stimulus,and new functionalities for multidisciplinary applications.We start by introducing the advanced features of 4D printing and the key technological roadmap for its implementation.We then place considerable emphasis on printable smart materials and structural designs,as well as general approaches to designing programmable structures.We also review stimulus designs in smart materials and their associated stimulus-responsive mechanisms.Finally,we discuss new functionalities of 4D printing for potential applications and further development directions.

Smart Property of Homogeneous Electrorheological Fluid and Its Application in Reducing Seismic Responses of Engineering Structures

The smart properties of homogeneous electrorheological fluid (HERF) containing side-chain type liquid crystalline polymer were studied and an actual HERF damper with an adjustable viscosity was produced.A mechanical model of the HERF smart damper was established on the basis of experiment and theoretical analysis.Then a controlled equation of SDOF structure by HERF damper was derived and a semi active control strategy based on optimal sliding displacement of damper was presented.The simulation results for a single story frame structure indicate that HERF,which may avoid some defects of common particles suspended ER fluids,is an excellent smart material with better stability.Using the semi active control strategy presented,HERF smart damper controlled could effectively reduce seismic responses of structures and keeps the control stable at all times.

Smart epidermal electrophysiological electrodes:Materials,structures,and algorithms

Epidermal electrophysiological monitoring has garnered significant attention for its potential in medical diagnosis and healthcare,particularly in continuous signal recording.However,simultaneously satisfying skin compliance,mechanical properties,environmental adaptation,and biocompatibility to avoid signal attenuation and motion artifacts is challenging,and accurate physiological feature extraction necessitates effective signal-processing algorithms.This review presents the latest advancements in smart electrodes for epidermal electrophysiological monitoring,focusing on materials,structures,and algorithms.First,smart materials incorporating self-adhesion,self-healing,and self-sensing functions offer promising solutions for long-term monitoring.Second,smart meso-structures,together with micro/nanostructures endowed the electrodes with self-adaption and multifunctionality.Third,intelligent algorithms give smart electrodes a“soul,”facilitating faster and more-accurate identification of required information via automatic processing of collected electrical signals.Finally,the existing challenges and future opportunities for developing smart electrodes are discussed.Recognized as a crucial direction for next-generation epidermal electrodes,intelligence holds the potential for extensive,effective,and transformative applications in the future.

Neural Network Signal Processing Approach for Damage Assessment in Fiberoptic Smart Material Systems and Structures

An approach by using neural network signal processing in associate with embedded fiberoptic sensing array for the newly developed “smart material systems and structures” is discussed in this paper.The principle,structure of this approach and suitable neural network algorithms are described.The results of simulation experiments are also given.

Smart heat isolator with hollow multishelled structures

Safe, green and efficient industrial production has always been the pursuit of the chemical industry. Since thermal energy is the driving force for most of chemical reactions, an ideal reaction tank would have the capacity to automatically regulate heat conduction rate. In detail, this reaction tank should endow an ability that resists the heat loss when the reaction temperature is lower than the target, while accelerating the heat dissipation when the system is overheated. In this case, this smart reactor can not only minimize energy consumption but also reduce safety risks.Hollow structures are known to reduce heat conductivity. Particularly, the hollow structure with multishells can provide more interfaces and thus further inhibit heat transmission, which would be more favorable for heat isolation. Step forward, by coupling HoMSs with temperature-sensitive polymer, a smart heat isolation material has been fabricated in this work. It performs as a good heat isolator at a relatively lower temperature. A heat insulation effect of 6.5℃ can be achieved for the TSPU/3S–TiO_(2)HoMSs with a thickness of 1 mm under the temperature field of 50℃.The thermal conductivity of composite material would be raised under overheating conditions. Furthermore, this composite displays an unusual two-stage phase transformation during heating. Benefiting from the unique multishelled structure, energy is found to be gradually guided into the hollow structure and stored inside. This localized heat accumulation enables the composite to be a potential coating material for intelligent thermal-regulator and site-defined micro-reactor.

埋入式光纤模式功率调制传感原理及实验研究——航天smart结构

对 Smart材料 /结构中的光纤传感原理进行了探讨 ,并进行了实验研究。这种新研制的传感器工作原理是基于模式功率调制。远场光强将反映结构内的变形场 ,亦即光纤受到外界加载或扰动后所产生的变形。最后提出了应用多模光纤在编织复合材料 Smart结构中进行远场光强测量的方案 ,建立了实验装置 ,给出了实验结果并进行了讨论。

埋入式光纤传感原理及实验研究——航天Smart结构

对Ｓｍａｒｔ材料／结构中的光纤传感原理进行了探讨，并进行了实验研究。首先介绍了Ｓｍａｒｔ结构中常见的埋入式光纤传感器的特点及其工作原理，然后提出了应用多模光纤在编织复合材料Ｓｍａｒｔ结构中进行应变场测量的方案，建立了实验装置，给出了实验结果并进行了讨论。

Smart结构——用压电材料抑制结构振动研究之一

指出了Ｓｍａｒｔ材料及结构在航天技术发展中的重要作用，并从常用的Ｓｍａｒｔ材料－压电材料的本构方程出发，着重探讨了由压电驱动器组成的ＲＣ电路和ＬＲＣ电路在抑制结构振动中的应用；最后通过实验验证了ＲＣ电路的振动抑制性能；为航天Ｓｍａｒｔ结构的深入研究做必要的准备。

The Third-Order Viscoelastic Acoustic Model Enables an Ice-Detection System for a Smart Deicing of Wind-Turbine Blade Shells

The present work is based on the third-order partial differential equation (PDE) of acoustics of viscoelastic solids for the quasi-equilibrium (QE) component of the average normal stress. This PDE includes the stress-relaxation time (SRT) for the material and is applicable at any value of the SRT. The notion of a smart deicing system (SDS) for blade shells (BSs) of a wind turbine is specified. The work considers the stress in a BS as the one caused by the operational load on the BS. The work develops key design issues of a prospective ice-detection system (IDS) able to supply an array of the heating elements of an SDS with the element-individual spatiotemporal data and procedures for identification of the material parameters of atmospheric-ice (AI) layer accreted on the outer surfaces of the BSs. Both the SDS and IDS flexibly allow for complex, curvilinear and space-time-varying shapes of BSs. The proposed IDS presumes monitoring of the QE components of the normal stresses in BSs. The IDS is supposed to include an array of pressure-sensing resistors, also known as force-sensing resistors (FSRs), and communication hardware, as well as the parameter-identification software package (PISP), which provides the identification on the basis of the aforementioned PDE and the data measured by the FSRs. The IDS does not have hardware components located outside the outer surfaces of, or implanted in, BSs. The FSR array and communication hardware are reliable, and both cost- and energy-efficient. The present work extends methods of structural-health/operational-load monitoring (SH/OL-M) with measurements of the operational-load-caused stress in closed solid shells and, if the prospective PISP is used, endows the methods with identification of material parameters of the shells. The identification algorithms that can underlie the PISP are computationally efficient and suitable for implementation in the real-time mode. The identification model and algorithms can deal with not only the single-layer systems such as the BS layer without the AI layer or two-layer systems but also multi-layer systems. The outcomes can be applied to not only BSs of wind turbines but also non-QE closed single- or multi-layer deformable solid shells of various engineering systems (e.g., the shells of driver or passenger compartments of ships, cars, busses, airplanes, and other vehicles). The proposed monitoring of the normal-stress QE component in the mentioned shells extends the methods of SH/OL-M. The topic for the nearest research is a better adjustment of the settings for the FSR-based measurement of the mentioned components and a calibration of the parameter-identification model and algorithms, as well as the resulting improvement of the PISP.

Smart structures with embedded flexible sensors fabricated by fused deposition modeling-based multimaterial 3D printing

Smart structures have the advantages of high system integrity and diverse sensing capabilities.However,the labor-intensive and timeconsuming fabrication process hinders the large-scale adoption of smart structures.Despite recent attempts to develop sensorembedded structures using 3D printing technologies,the reported smart structures generally suffer from the complex fabrication process,constrained part size,and limited sensing modality.Herein,we propose a workflow to design and fabricate novel smart structures via multi-material fused deposition modeling(FDM)-based 3D printing.More specifically,conductive filaments with tailorable mechanical and elec-trical properties,e.g.piezoresistive effects,were developed.Additionally,the printing process was optimized for processing soft filaments with Young’s modulus around 2 MPa,resolving the issue of filament buckling.Furthermore,the potential applications of the proposed workflow were showcased using three design cases,i.e.biaxial strain sensor,smart tire,and cable-driven soft finger with multiple sensing capabilities.This workflow provides a cost-effective and rapid solution for developing novel smart structures with soft materials.

Encryption/decryption and microtarget capturing by pH-driven Janus microstructures fabricated by the same femtosecond laser printing parameters

Several natural organism can change shape under external stimuli. These natural phenomena have inspired a vast amount of research on exploration and implementation of reconfigurable shape transformation. The Janus structure is a promising approach to achieve shape transformation based on its heterogeneous chemical or physical properties on opposite sides.However, the heterogeneity is generally realized by multi-step processing, different materials,and/or different processing parameters. Here, we present a simple and flexible method of producing p H-sensitive Janus microactuators from a single material, using the same laser printing parameters. These microactuators exhibit reversible structural deformations with large bending angles of ~31°and fast response(~0.2 s) by changing the p H value of the aqueous environment. Benefited from the high flexibility of the laser printing technique and the spatial arrangements, pillar heights, and bending directions of microactuators are readily controlled,enabling a variety of switchable ordered patterns and complex petal-like structures on flat surfaces and inside microchannels. Finally, we explore the potential applications of this method in information encryption/decryption and microtarget capturing.

Vibration shape testing of space sheet structure

The space sheet for a solar array structure is large in dimension, and flexible to induce complex distortion. It is difficult to measure the distortion. A large-scale flexible test prototype system is built for sheet structure vibration monitoring based on the vibration information of the solar array in space. The system provides an intelligent test method for flexible space structure with embedded sensors and non-visualization reinstruction. Multiple fiber Bragg grating （FBG） sensors are packaged and embedded into the structure with spatial division multiplexing （SDM） and wavelength division multiplexing （WDM）. The sensor interrogator distinguishes wavelength shifts that can be turned into curvature of the curve. The structure shape is reconstructed based on the curvature information and the arc-length, and then displayed. The experiment shows that the system has a high FBG sensitivity. The reconstruction algorithm is fast with high precision. The system has great potential for use in health monitoring of the space sheet structure.

Origami-Based Design for 4D Printing of 3D Support-Free Hollow Structures

The integration of additive manufacturing(AM)in design and engineering has prompted a wide spectrum of research efforts,involving topologically optimized solid/lattice structures,multimaterial structures,bioinspired organic structures,and multiscale structures,to name a few.However,except for obvious cases,very little attention has been given to the design and printing of more complex three-dimensional(3D)hollow structures or folded/creased structures.One of the main reasons is that such complex open or closed 3D cavities and regular/freeform folds generally lead to printing difficulties from support-structure-related issues.To address this barrier,this paper aims to investigate four-dimensional(4D)printing as well as origami-based design as an original research direction to design and build 3D support-free hollow structures.This work consists of describing the rough 3D hollow structures in terms of two-dimensional(2D)printed origami precursor layouts without any support structure.Such origami-based definitions are then embodied with folding functions that can be actuated and fulfilled by 3D printed smart materials.The desired 3D shape is then built once an external stimulus is applied to the active materials,therefore ensuring the transformation of the 2D origami layout to 3D structures.To demonstrate the relevance of the proposal,some illustrative cases are introduced.

具有智能蒙皮潜质的磁流变弹性体磁力学特性

变体飞机的难点之一在于变形机翼,而变形机翼的难点之一在于变形蒙皮,其中后者的研究难度长期以来被忽视。以往很多变形翼蒙皮的研究与设计中,一般更加关注基于力学特征的智能材料。本文从变体结构中的变形蒙皮特性与需求出发,简述了变形蒙皮的研究进展,论述了磁流变弹性体(MRE)的概念、材料组成以及功能等内容,以及磁流变弹性体磁力学的相关表征。

光纤光栅传感器研发及其在土木工程中的应用进展

从传感器类型出发介绍了表贴式、纤维增强聚合物式、管式和内嵌式封装光纤布拉格光栅传感器的结构型式、实施方式和关键技术,简述了各种封装方式传感器的工作原理、技术研发及工程应用进展,总结了不同封装方式传感器的优势和不足。然后,简要介绍了光纤布拉格光栅传感器在桥梁结构状态监测或检测中的典型工程应用案例。最后,指出了光纤布拉格光栅传感器在土木工程领域中的工艺工法、耐久性和分布式测量以及未来推广应用有待解决的关键问题等,为光纤布拉格光栅传感器技术优化及其在土木工程中的推广应用提供参考。

柔性变形翼结构设计、建模与分析研究进展

未来飞行器设计将面临空域、速域不断扩大、任务适应性要求不断提高的严峻挑战,变体飞行器可为提高飞行性能、扩大飞行包线提供新思路与新方法。采用柔性蒙皮配合相应的支撑结构成为克服传统变体飞行器缺点的主要解决方案。本文首先综述了柔性蒙皮、蜂窝支撑结构、新型智能材料在变体飞行器设计中的研究现状,然后对现有文献中柔性变形翼结构设计、建模与分析方法进行讨论。最后提出现有柔性变形翼结构设计、建模与分析方法存在的问题,以及未来可能的研究方向。

基于“一平三端”的工程材料智慧课堂教学方法

为了提高学生的自主学习能力,使用超星平台、教室端、移动端、管理端开展工程材料智慧课堂教学,在课前预习、课堂学习、课后作业三个阶段实施智慧教学的课程改革模式。基于项目引导式的课程内容改革,建立题库,在课堂上充分利用课堂签到、线上测验、互动等智慧应用。实践证明,该方法能够激发学生的自主学习性,具有较好的教学效果。

仿生土木工程研究进展与展望

随着城镇化水平不断提升,中国每年新增建筑面积约20亿m2,大规模基础设施建设对土木工程理论和技术创新的要求越来越高。学者们通过研究自然界的增强增韧、水下黏合、钻孔掘进和轻质高强等现象发现,生物体具有独特的外部形态和组织结构,通过模仿生物体的外部形态、结构特征或运动机理可为土木工程技术创新和可持续发展提供新思路、新原理和新理论。从仿生材料、仿生结构和仿生机械与构筑物3个方面阐述仿生学在土木工程中的应用,列举典型的应用案例,并对仿生土木工程进行总结和展望,为未来的研究提供基础材料。作为新兴的研究方向,仿生土木工程基础理论尚不完善,仿生土木工程涉及生物、材料、结构等多学科的交叉,需要开展不同领域间的协同合作研究。