Smart yarns and textiles are an active field of researches nowadays due to their potential applications in flexible and stretchable electronics, wearable devices, and electronic sensors. Integration ...of ordinary yarns with conductive fillers renders the composite yarns with new intriguing functions, such as sensation and monitoring of strain and stress. Here we report a low cost scalable fabrication for highly reliable, stretchable, and conductive composite yarn as effective strain sensing material for human motion monitoring. By incorporating highly conductive single-wall carbon nanotubes (SWCNTs) into the elastic cotton/polyurethane (PU) core-spun yarn through a self-designed coating approach, we demonstrated that the yarn is able to detect and monitor the movement of human limbs, such as finger and elbow, and even the wink of eyes. By virtue of the covered structure of the cotton/PU yarn and the reinforcement effect of SWCNTs, the composite yarn can bear up to 300% strain and could be cycled nearly 300,000 times under 40% strain without noticeable breakage. It is promising that this kind of conductive yarn can be integrated into various fabrics and used in future wearable devices and electronic skins.
Since the damage of the bridge structure may cause great disasters, it is necessary to monitor its health status, especially the bridge bearing, the important connecting component of the bridge's ...upper and lower structures. Nowadays, manual inspection is the main method to get the information of the bridge bearings' work status. However, occasional damage of bridge bearing may not be detected in time, and sometime the installation position of the bearing makes the manual inspection on bridge bearing difficult and even impossible. Therefore, in order to know the work status of the bridge bearings timely, an intelligent remote monitoring system for the bridge bearing is developed. A 32-channel real-time acquisition system is designed by using an AD7768-1 analog-to-digital converter and Xilinx Spartan-6 Field Programmable Gate Array for interface stress continuously acquired in the bridge bearing. To assure the good linearity and low noise performance of the monitoring system, the data acquisition card is meticulously designed to reduce noise from both hardware and software and realize high-precision acquisition. Through the establishment of the monitoring server, the compressive stress data can be displayed synchronously and the overpressure situation can be alarmed in real-time. The experimental results show that the accuracy of the calibrated sensor is within 1.6%, and the detection error of the acquisition board is less than 200 μV. The acquisition system is deemed to have considerable advantages in accuracy and applicability.
The aim of this study is to find out the degradation of dynamic behaviour of bridge girders with trapezoidal profiled webs when subjected to different vehicle moving loads. Finite element modelling ...based parametric analysis is demonstrated to be desirable in capturing the dynamic deflection and stress state of critical structural details of girders. The model is validated in the modal analysis through a comparison with theoretical eigenfrequencies. The vibration characteristics are shown to be significantly affected by the corrugation details. The structural service life results of analysed bridge girders are in close agreement with experimental data. It is shown that the dynamic nodal velocity and deflection of analysed bridge girders are greatly affected by the magnitude of the load corresponding to the overload of the vehicle in contrast to the vehicle travel speed. Similar observations can be made for the fatigue life prediction analysis related to the crack initiation when unfavourable effects of the overload vehicle are concerned. Presented analytical results using a fracture mechanics approach could be taken as a good basis for the service life assessment of related bridges with the desired level of performance or functionality.
In the fields of electronic skin and soft wearable sensors, intrinsically stretchable conductors undergo rapid development; however, practical applications of artificial skinlike materials/devices ...have not been realized because of the difficulty in combining the electromechanical properties and sensing performance. Contrarily, insoluble inorganic conductive domains in the hydrogel matrix are generally incompatible with surrounding elastic networks, decreasing the mechanical strength. Usually, the hydrogels are vulnerable either to severe mechanical stimuli or large deformation, especially when notches are induced. In this study, based on an energy-dissipative dual-crosslinked conductive hydrogel, a mechanically durable and super-tough strain sensor was developed. The highly soft yet dynamically tough hydrogel demonstrated high ionic conductivity (30.2 mS cm
−1
), ultrastretchability (>600% strain), and superior linear dependence of strain sensitivity with a maximum gauge factor of 1.2 at 500% strain. Because of these advantageous synergistic effects, the resultant hydrogel strain sensor demonstrated reliable and stable detection of a large range of human motion and subtle vibrations. Moreover, it impressively exhibited super toughness that could endure consecutive treading pressure and even retain normal operation after 20 times of car run-over on the road. These demonstrations highly confirm the sensor’s superior mechanical durability and reliability, displaying great potential in developing next-generation mechanically adaptable sensors.
This paper presents an experimental study on the fatigue life estimation of off-centrally cracked aluminum plates. Typical theoretical equations for off-central, central and edge cracks were reviewed ...and compared in terms of their sensitive parameters and applicability. A finite element model has been validated in its capacity in modelling the influences of eccentricity and crack size on the boundary correction coefficients. The Forman equation has been employed along with numerical results for the prediction of fatigue lives. Based on the test data, the fatigue life results of aluminum plates with and without patched laminate repair have been compared with codified fatigue classes. It is demonstrated that the repair at the crack tip close to the plate edge is effective in the fatigue life improvement for off-centrally crackedaluminum plates.
Capacitive‐type strain sensors based on hydrogel ionic conductors have undergone rapid development benefited from their robust structure, drift‐free sensing, higher sensitivity, and precision. ...However, the unsatisfactory electro‐mechanical stability of the conventional hydrogel conductors, which are normally vulnerable to large deformation and severe mechanical impacts, remains a challenge. In addition, there is not enough research regarding the adhesiveness and mechanical properties of the dielectric layer, which is also critical for the mechanical adaptability of the whole device. Here, a dynamically super‐tough capacitive‐type strain sensor based on energy‐dissipative dual‐crosslinked hydrogel conductors and an organogel dielectric with high adhesive strength is developed. Combining with the mechanical advantages of the hydro/organo‐gels, the capacitive strain sensor exhibits high stretchability and superior linear dependence of sensitivity with a gauge factor of ≈0.8% at 100% strain. Moreover, the sensor displayed ultrastability against various severe mechanical stimuli that can even survive unprecedentedly from extremely catastrophic car run‐over by 20 times. With these synergistic mechanical advantages, the capacitive strain sensor is successfully applied as a highly‐reliable wearable sensing system to monitor diverse faint physiological signals and large‐range human motions.
A super‐tough capacitive strain sensor is developed based on energy‐dissipative dual‐crosslinked hydrogel conductors, which display excellent stretchability, broad‐range sensing, and pronounced operational stability for monitoring faint physiological signals and large‐range human motions.
•Two 1:5 scale models of composite beams with CSWs and trusses are tested.•The effects of bottom trusses and concrete in steel tubes are examined.•Finite element simulation is used to simulate the ...full behavior of tested specimens.•Theoretical model is developed to predict the nonlinear behavior.
The composite box girder with corrugated steel webs (CSWs) and trusses is a bridge structure developed on the basis of traditional box girders with CSWs. In this research, experimental, numerical and analytical studies were carried out to investigate the flexural performance of simply supported composite box girders with CSWs. Two 1:5 scale models of a real bridge were fabricated and tested, including one with concrete filled steel tubes and another with hollow steel tubes. The test results show that the two specimens have good ductility and failed in a ductile manner. The concrete filled inside steel tubes reduces the deflection and increases the yield load. The cross sections of the two specimens basically satisfy the “plane section assumption”. Finite element models were also developed for the two specimens and validated based on the experimental results. Afterwards, a parametric study was carried out with the validated finite element models, which shows that the steel ratios and the structure of bottom trusses strongly influences the flexural behavior. At last, a theoretical model is developed to calculate the bending moment of composite beams at the ultimate load.
Concrete-filled galvanized helical corrugated steel tubes (CFCSTs) are newly proposed for strengthening the corrosion resistance, ductility, and constructability of traditional RC structures. Their ...composite effectiveness and basic compressive, bending, and shear properties have been investigated previously. However, the unique spiral shape and lock-seam connections of the helical CST may lead to complex torsional responses, which have not been studied. This paper, therefore, attempts to present static experiments for the CFCSTs subjected to pure torsion and combined compression-torsion loads. The main test variables are the member types, loading directions, boundary conditions, and axial compression ratios. The static loading test set-up and instruments have been introduced in detail. The torsional working mechanisms are discussed carefully with the analysis of failure modes and torques versus torsional angle curves. The direct and indirect contributions in torsional resistances of the helical CST have been analysed and calculated through elastic-plastic stress/strain analysis. Finally, the applicability of the existing design methods for the torsional bearing capacity of CFCSTs is examined.
•Eight specimens tested under pure torsion and combined compression-torsion loads.•Loading test set-up for realizing pure torsion condition and instruments for torsional angles and torques.•Torsional working mechanism and torsional contributions of helical CST.•Examination of the applicability of existing design methods for the torsional bearing capacity.
•The shear-lag effect of CBGB-CSWTs are studied.•The concrete filled in bottom steel tubes has little influence on the shear-lag effect.•The width-to-span ratio is an important influencing factor of ...the shear-lag effect.•Analytical equations are developed to calculate the shear-lag coefficient.
The composite box girder bridge with corrugated steel webs and trusses is a recently proposed enhanced composite box girder bridge structure. The shear-lag effect of this kind of structure is studied in detail in this research. Two 8.744 m-long test beams with and without concrete filled in the bottom steel tubes were constructed and tested. The non-uniform distribution of cross-sectional stress in the top concrete slab was captured. The filling of concrete inside the bottom steel tubes is shown not to have a great influence on the shear-lag effect. Numerical parametric studies were carried out to study the influence of various factors on the shear-lag effect of this kind of structure. The numerical results indicate that the magnitude of the shear-lag effect increases with the width-to-span ratio and the suspension ratio. Analytical equations were derived to calculate the shear-lag coefficient for composite box girders with corrugated steel webs and trusses based on the energy variational principle. The experimental and numerical validation indicates that the proposed equations can be well applied in engineering practice.
Abstract
Acoustic emission technology, as a nondestructive real-time monitoring technique, has been proven to be an effective method for monitoring dynamic damage of materials. The prestressing ...strand material used for constructing bridge ties is the focus of this study. This paper reports the experiment setup in detail. This test uses an oil pump to load the prestressing strand at a uniform rate for the tensile breakage test. Real-time signal acquisition of the strand damage during the tensile test was performed using acoustic emission equipment. The preliminary analysis of the data was used to determine the effect of amplifier and transducer type on signal acquisition.
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