高强度纤维素双网络导电水凝胶制备及其应变感应特性研究

将微晶纤维素(MCC)-氢氧化钠/尿素溶液通过乙醇蒸气诱导形成纤维素一级网络,以丙烯酸(AA)和丙烯酰胺(AM)为原料,N,N′-亚甲基双丙烯酰胺(MBAA)为交联剂,过硫酸铵(APS)为引发剂构建二级网络,随后采用浸泡法引入氯化铁,构筑了多交联的纤维素/聚丙烯酰胺-聚丙烯酸/铁离子(C/PAMAA/Fe^(3+))水凝胶,并对水凝胶的力学性能及电化学性能进行了探究。研究结果表明:Fe^(3+)与—COO^(-)形成的配位键在形变时作为牺牲键断裂,这有助于C/PAMAA/Fe^(3+)机械性能的提升,水凝胶的韧性和抗拉强度分别达到17.13 MJ/m^(3)和4.59 MPa。循环拉伸测试的结果显示:随着Fe^(3+)浓度的增加,C/PAMAA/Fe^(3+)水凝胶的能量耗散效率增加,从56.86%增加到75.17%,且第二次循环后弹性恢复率接近85.0%。随着Fe^(3+)用量的增加,离子电导率增大,Fe^(3+)浓度为0.2 mol/L的C/PAMAA/Fe^(3+)水凝胶电导率为1.03 S/m。将C/PAMAA/Fe^(3+)水凝胶组装为应变感应器,感应器的灵敏度为4.0,其拉伸递增和拉伸循环的电阻变化结果表明该应变感应器具有较好的稳定性;实时监测关节活动的结果表明该感应器具有稳定的应变响应性。

DISTRIBUTED MICROBEND FIBER-OPTIC STRAIN SENSOR

The distributed strain sensor has significant application in real time measurement of strain status for large and important engineering structures such as aircraft, bridge and dam. In this paper, a quasi distributed optical fiber strain sensor system is set up using optical time domain reflect technique. The local strain sensors based on a novel microbend configuration are designed and applied to measure local strains along the optical fiber. As the result of the experimental research, the microbend sensors show high sensitivity, good linearity and repeatability in certain operation range.

Structural Stress Identification Using Fuzzy Pattern Recognition and Information Fusion Technique

In order to ensure the service security of space structures under wind load, the stress identification method based on the combination of fuzzy pattern recognition and information fusion technique is proposed, in which the measurements of limited strain sensors arranged on the structure are used. Firstly, the structure is divided into several regions according to the similarity and the most unfavorable region is selected to be the key region for stress identification, while the different numbers of the strain sensors are located on the key region and the normal regions; secondly, the different stress distributions of the key region are obtained based on the measurements of the strain sensors located on the key region and the normal regions separately, in which the fuzzy pattern recognition is used to identify the different stress distributions; thirdly, the stress distributions obtained by the measurements of sensors in normal regions are selected to calculate the synthesized stress distribution of the key region by D-S evidence theory; fourthly, the weighted fusion algorithm is used to assign the different fusion coefficients to the selected stress distributions obtained by the measurements of the normal regions and the key region, while the synthesized stress distribution of the key region can be obtained. Numerical study on a lattice shell model is carried out to validate the reliability of the proposed stress identification method. The simulated results indicate that the method can improve identification accuracy and be effective by different noise disturbing.

Design and validation of wireless strain test system for bridge based on the resistance strain sensor

In order to achieve an access to strain sensor data with wireless transmission in bridge engineering structure testing, a wireless strain test system is presented based on the resistance strain sensor of networks. The wireless bridge strain test system composed of master station and substation adopts the wireless method to realize the high accuracy data acquisition between the master station and the substation under a reliable communication protocol. The system has been tested in contrast with the present strain apparatus. Results show that the wireless system is high-reliable, and has many characteristics such as high efficiency, good precision, high stability with low cost, and good flexibility, without using the present communication network.

Facile preparation and high performance of wearable strain sensors based on ionically cross-linked composite hydrogels

Flexible sensors that can respond to multiple mechanical excitation modes and have high sensitivity are of great significance in the fields of electronic skin and health monitoring.Simulating multiple signal responses to skin such as strain and temperature remains an important challenge.Therefore,new multifunctional ion-crosslinked hydrogels with toughness and conductivity were designed and prepared in this work.A chemical gel with high mechanical strength was prepared by cross-linking acrylamide with N,N’-methylenebisacrylamide and ammonium persulfate.In addition,in order to enhance the conductive properties of the hydrogel,Ca^(2+),Mg^(2+)and Al^(3+)ions were added to the hydrogel during crosslinking.The double-layer network makes this ionic hydrogel show excellent mechanical properties.Moreover,the composite hydrogel containing Ca^(2+)can reach a maximum stretch of 1100%and exhibits ultra-high sensitivity(Sp=10.690 MPa^(-1)).The obtained hydrogels can successfully prepare wearable strain sensors,as well as track and monitor human motion.The present prepared multifunctional hydrogels are expected to be further expanded to intelligent health sensor materials.

Eggshell-inspired membrane—shell strategy for simultaneously improving the sensitivity and detection range of strain sensors

The tradeoff between sensitivity and detection range(maximum and minimum stretchability)is a key limitation in strain sensors;to resolve this,we develop an efficient and novel strategy herein to fabricate a highly sensitive and stretchable strain sensor inspired by the membrane-shell structure of poultry eggs.The developed sensor comprises a soft and stretchable surface-grafting polypyrrole(s-PPy)film(acting as the membrane)and a brittle Au film(acting as the shell),wherein both films complement each other at the electrical and mechanical levels.Au forms cracks under strain contributing to its high sensitivity and low detection limit,and s-PPy can bridge Au cracks and increase stretchability which has not been used in strain sensors before.The surface-grafting strategy not only enhances interface adhesion but also tunes the brittle property of native PPy to render it stretchable.Utilizing the synergetic effect of the membrane-shell complementary structure,the strain sensors achieve ultrahigh sensitivity(>10^(7)),large stretchability(100%),and an ultralow detection limit(0.1%),demonstrating significant progress in the field of strain sensors.The membrane-shell(Au/s-PPy)-structured strain sensor can successfully detect finger motion,wrist rotation,airflow fluctuation,and voice vibration;these movements produce strain in the range of subtle to marked deformations.Results evidence the ultrahigh performance and bright application prospects of the developed strain sensors.

Application of aluminum foil for “strain sensing” at fatigue damage evaluation of carbon fiber composite

Surface layer of a loaded solid is an individual structural level of deformation that was shown numerously within concept oI physical mesomechanics. This gives rise to advance in its deformation development under loading as well as allows using this phenomenon to sense the strain induced structure changes. It is of specific importance for composite materials since they are highly heterogeneous while estimating their mechanical state is a topical applied problem. Fatigue tests of carbon fiber compo- site specimens were carried out for cyclic deformation estimation with the use of strain sensors made of thin （80 jam） alumi- num foil glued to the specimen＇s surface. The surface images were captured by DSLR camera mounted onto an optical micro- scope. Strain relief to form during cyclic loading was numerically estimated using different parameters： dispersion, mean square error, universal image quality index, fractal dimension and energy of Fourier spectrum. The results are discussed in view of deformation mismatch in thin foil and bulk specimen and are offered to be applied for the development of Structural Health Monitoring （SHM） approach.

Constructing hydrophobic protection for ionic interactions toward water,acid,and base-resistant self-healing elastomers and electronic devices

Dynamically crosslinked materials generally lose their self-healing ability and mechanical robustness in aqueous,acidic,and basic environments due to disruption of their dynamic interactions and bonds.Herein,a micelle-like structure with a hydrophobic outer layer is used to protect ionic interactions.This structure ensures the self-healing and long-term stability of the ionically crosslinked elastomers in aqueous,acidic,and basic environments.The elastomer possesses a tensile strength of 6.7 MPa and a strain at break of 1400%,which is superior to the existing waterproof selfhealing elastomers.The strain sensors and dielectric actuators based on the elastomer are highly stable and self-healable,even in extremely harsh environments.This design strategy of hydrophobic protection for dynamic interactions is quite general,allowing it to be extended to other self-healing materials.

High-Strain Fiber Bragg Gratings for Structural Fatigue Testing of Military Aircraft

This paper reports on an experimental program of work which investigates the reliability, durability, and packaging of fiber Bragg gratings （FBGs） for application as distributed strain sensors during structural fatigue testing of military platforms. The influence of the FBG fabrication process on sensor reliability is investigated. In addition, methodologies for broad-area packaging and surface-mounting of FBG sensing arrays to defense platforms are developed and tested.

Study on the spectral response of fiber Bragg grating sensor under non-uniform strain distribution in structural health monitoring

Many theoretical studies have been developed to study the spectral response of a fiber Bragg grating (FBG) under non-uniform strain distribution along the length of FBG in recent years. However, almost no experiments were designed to obtain the evolution of the spectrum when a FBG is subjected to non-uniform strain. In this paper, the spectral responses of a FBG under non-uniform strain distributions are given and a numerical simulation based on the Runge-Kutta method is introduced to investigate the responses of the FBG under some typical non-uniform transverse strain fields, including both linear strain gradient and quadratic strain field. Experiment is carried out by using loads applied at different locations near the FBG. Good agreements between experimental results and numerical simulations are obtained.

Application of Brillouin Optical Correlation Domain Analysis for Crack Identification in Concrete Structure

This paper investigates the application of distributed optical fiber strain sensors to civil engineering structures, because no other tool can satisfactorily detect the location of the unpredictable phenomenon. In fact, the locations of cracks in the concrete structure are unknown a priori; therefore, a fully distributed sensor is necessary to detect them. The Brillouin optical correlation domain analysis （BOCDA）, which offers high spatial resolution by using stimulated Brillouin scattering along the whole length of the optical fiber, is used in a wide range of civil engineering applications, and the same has undergone significant development over the last decade. In this paper, it is demonstrated how a BOCDA-based strain sensor can be employed to monitor cracks in concrete. Crack monitoring on the surface of the concrete member provides useful information for evaluating stiffness and durability of the structure, particularly for early detection of tiny cracks, which is essential for preventing crack growth and dispersion. The crack-induced strain distribution was analytically investigated, and it was proved that BOCDA can identify even a small crack before its visual recognition by a beam test. Moreover, periodical crack monitoring was successfully executed on a pedestrian deck for five years.

Piezoresistive effect in MoO3 nanobelts and its application in strain-enhanced oxygen sensors

MoO3 nanobelts （NBs） having different properties have been synthesized via a physical vapor deposition （PVD） method. The crystallographic structures and morphologies of the NBs were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. Electrical measurements were performed and the profound piezoresistive effect in MoO3 experimentally studied and verified. Factors that influence the gauge factor, such as NB size, doping concentration and atmosphere composition, are discussed and analyzed. Gas sensing performance was also tested in devices and it was demonstrated that by applying strain to the gas sensor, its sensing performance could be effectively tuned and enhanced. This study provides the first demonstration of significant piezoresistivity in MoO3 NBs and the first illustration of a generic mechanism by means of which this effect can be coupled with other electronic modulation measures to afford better device performance and broader material functionality.

Coordinated motion of molecular motors on DNA chains with branch topology

To understand the macroscopic mechanical behaviors of responsive DNA hydrogels integrated with DNA motors,we constructed a state map for the translocation process of a single FtsKc on a single DNA chain at the molecular level and then investigated the movement of single or multiple FtsKc motors on DNA chains with varied branch topologies.Our studies indicate that multiple.FtsKc motors can have coordinated motion,which is mainly due to the force-responsive behavior of individual FtsKc motors.We further suggest the potential application of motors of FtsKc,together with DNA chains of specific branch topology,to serve as strain sensors in hydrogels.