Xinchun Guan

Nanomaterials-Enabled Multifunctional Concrete and Structures

Nanomaterials-enabled multifunctional concrete that has self-sensing ability and high mechanical properties is attractive for guaranteeing the safety of infrastructure. Self-sensing ability of nanoconcrete which is based on its piezoresistivity is obtained by adding appropriate concentration of nano-carbon black into concrete. Effect of various loading states on pieroresistivity of nanoconcrete was studied experimentally, and a theoretical model was proposed to predict and modify the strain gauge factor of nanoconcrete under various loading or environmental conditions. Effect of moisture on resistance of nanoconcrete was studied and a water-proof method was proposed to eliminate the unfavorable effect of polarization on resistance measurement. Finally, a cement-based strain sensor was fabricated and used in monitoring the strain of concrete column. Other benefits from inclusion of nanomaterials in concrete include enhancement in mechanical properties, including strength, abrasion resistance and fatigue properties. Microstructures of nanoconcrete was studied with help of SEM pictures, which showed that the hydration product of nanoconcrete was more uniform and compact than that of normal concrete.

Experimental investigation on vibration control of one stay cable using one magnetorheological fluid damper

An experimental study on vibration control of one stay cable using a magnetorheological fluid (MR) damper is described in the paper. A 14m-long stay cable model, which is a 1:16 scale model of a 220m-long prototype stay cable in the actual structure, is established for the experimental investigation.The planar sinusoidal excitations with the resonant frequencies are generated by the exciter installed perpendicular to the stay cable model at a point near the low anchorage. The modal testing on the unimpeded stay cable is first performed to identify the actual modal properties and the dynamic performances. Then a series of vibration control tests are conducted on the stay cable incorporated with a small-size MR damper near the low anchorage under the sinusoidal excitations with the first two modal resonant frequencies. The control efficacies and the dynamic performances of the combined cable/MR damper system corresponding to the different current inputs to the MR damper and the semi-active MR damper are investigated comparatively. The experimental results of the vibration control of the stay cable model indicate that the semi-active MR damper can achieve much better control efficacy than the passive MR dampers supplied with constant currents, and the reason can be attributed to the pseudo-negative stiffness generated by the semi-active MR damper.

A novel electric current sensor based on Fiber Bragg gratings and magnetostrictive composites

A novel electric current sensor based on FBG and magnetostrictive composites, which is made from epoxy resin and Terfenol-D particulates, was fabricated. The relationship between the strain of the sensing head and the magnetic field intensity was obtained. The new sensor exhibited a good linearity and repeatability, which indicates its potential to be a practical electric current sensor.

An experimental study of magnetorheological fluid dampers for vibration control of one offshore platform

The possibility of reducing offshore structural response under strong external excitations such as wind storm, sea ice and earthquake via control systems is attracting the interest of a large number of researchers. Up to now, lots of dampers have been installed on different offshore platforms. As one new kind of effective semi-active device, magnetorheological fluid (MRF) damper has been used in the field of mechanical equipment, automobile and civil buildings, however, the practical application for vibration control of offshore platform has not seen before. In this paper, 8 MRF dampers with maximum damping force of 100kN for vibration control of one offshore platform with total weight of 650t have been manufactured and tested. The general situation of MRF damper system and the offshore platform include manufacturing issues, powering, range of variability of the mechanical parameters and response time are introduced.

Field Tests of Vibration Control of Stay Cables by Using Magnetorheological Fluid Dampers

Shandong Binzhou Yellow River Highway Bridge is a three-tower, cable-stayed bridge in Shandong, China. Because the stay cables are prone to vibration, 40 MR dampers are attached at the 20 longest cables of this bridge to suppress their possible vibration. An innovative control algorithm based on measurable acceleration response at limited locations along a cable is proposed. And then a series of field tests are carried out to investigate the control effectiveness in cable vibration achieved by semi-active MR dampers, passive-off MR dampers and passive-on MR dampers. The damping ratio of the cables incorporated with MR dampers are also obtained from the test. The semi-active MR dampers more efficiently reduce the vibration of cables than both of the passive-off MR dampers and passive-on MR dampers and the reason can be attributed to the negative stiffness provided by semi-active MR dampers

Experiment study of large-scale magnetorheological fluid damper

Due to their character of low power requirement, rapid-response and large force, the dampers that made based on the special rheologic performance of magnetorheological fluid (MRF) have shown to be one kind of ideal semi-active vibration control devices for civil engineering structures and vehicles. In this paper, the character of magnetic circuit of MRF damper was firstly studied; based on above results, a large-scale MRF damper whose adjustable multiple is about 16 and maximum damping force is about 170kN was then designed and tested. Experimental results show that, under lower electrical current, same or opposite of electric current direction of multi-coils winding on the piston do not influence damping performance of MRF damper; however, under higher electrical current, inverse connecting of adjacent coils is apt to improve damping force of MRF damper.

Thick-film resistors on glass ceramic substrates as smart strain sensing aggregates for SHM

Thick film resistors (TFRs) were screen-printed and fired on fluorophlogopite glass ceramic (FGC) and alumina ceramic substrate as smart aggregates. Performances of smart aggregates under compressive load were tested before and after embedded in mortar specimens. Compared to alumina ceramic substrate, the TFRs on FGC shows better compatibility and matching performance, the matching error between sensor and mortar decreased from 0.734 to 0.187, the output strain ratio between sensor and mortar increased from 0.0837 to 0.421, and the test results confirmed the theoretical calculation results. When embedded in mortar, the TFRs on FGC shows better repeatability than that on alumina ceramic under repeated compressive load.

A practical design method for TEP-GT MRFD

To provide a practical design method for Magnetorheological fluid damper (MRFD), mechanical model is established for two-exserted-pole gap type (TEP-GT) MRFD and the relationship between damping force and internal sizes is given. The magnetic circuit is studied and the materials and structures of main components are discussed. A practical design method for TEP-GT MRFD is obtained and several key expressions are provided. A kind of TEP-GT MRFD for the cable-stayed vibration control system is designed and manufactured.

Effect of soft magnetic materials blend on the properties of polymer-bonded Terfenol-D composites

In recent years, influence of volume, size and shape of particulate, stiffness of the polymeric matrix and mechanical preload on the magetostrictive property of polymer-bonded Terfenol-D composites have been investigated by several papers, however, few studies on the effects of the blending soft magnetic particles. In this study, polymer-bonded Terfenol-D composites composed with 20% volume fraction of Terfenol-D particulate and different volume percentage of carbonyl iron particle (i.e. 0, 10%, 20%, 30% and 40%) are fabricated. The changes of magnetostriction and magnetic permeability with changing applied field are tested. The experimental results indicate that with increases of fraction of carbonyl iron particle, the permeability of the composites increases, but the magnetostrictive property declines. The change of permeability is explained based on two ideal models, while the change of magnetostriction is explained from the perspective of energy transforming and mechanical property of matrix.

Design and fabrication of a novel settled and laminated testing instrument for magnetorheological fluid

As having ability of changing its apparent viscosity in presence of magnetic field in millisecond, magnetorheological fluids (MRF) exhibit widely potential application in devices or systems for controlling vibration and noise. In addition to shear stress strength, another import performance index of MRF is its stability under long time static state. For most applied conditions, without hard agglomeration is more important than higher shear stress strength. However, up to now, only a few reports pay attention to evaluate method of MRFs settling. This make it is difficult to optimize manufacturing technique of MRF and study its principle. A novel testing instrument, which made based on theory of that varying magnetic particles volume content of MRF would induce its correspondingly changing of magnetic conductivity, designed and fabricated. And settling state of several MRF were tested by that instrument, factors which influence accuracy of that instrument is also discussed. Research shows that, the novel settled and laminated testing instrument (NSLTI) is potential to be used to evaluate settling stator and monitor settling process of magnetic particles. Moreover, study also shows that strength of magnetic field, position of magnetic field sensor, sensitivity of Tesla meter, type of MRF and testing time may influence accuracy of NSLTI.