Dong Yu Xu

Influence of Slag and Fly Ash on the Self-Healing Ability of Concrete

The influence of slag and fly ash on the self-healing ability of concrete was researched by strength measurement and SEM analysis. The self-healing ratio was measured by the increase of compressive strength before and after self-healing. The optimal mixing amount of slag and fly ash were determined, and the reasonable sand ratio was obtained. Analyzing results show that the self-healing ability of concrete was the strongest when the mixing content of slag and fly ash were 30% and 40% respectively. The appropriate sand ratio was also obtained, when the sand ratio is 33%, the self-healing ability of concrete is the strongest.

Influence of Thickness Parameters on 2-2 Cement Based Piezoelectric Composite

2-2 cement based piezoelectric composite was fabricated using sulphoaluminate cement and lead magnesium niobate-lead zirconate-lead titanate ceramic (P(MN)ZT) by dice-and-fill technique. The effects of composite thickness on dielectric, piezoelectric and electromechanical properties of the composite were analyzed, respectively. The results show that the increase of composite thickness will improve the piezoelectric strain factor d33 of the composite, while decreases the piezoelectric voltage factor g33 of the composite. The relative dielectric factor εr as well as the dielectric loss tan δ of the composite also increases with increasing the thickness. The electromechanical analysis results show that the thickness electromechanical coupling coefficient Kt of the composite increases obviously with decreasing the thickness, meanwhile the mechanical quality factor Qm of the composite shows the increasing trend, thus, the receiving piezoelectric transducers can be fabricated by decreasing the thickness.

Effects of PMN Volume Fraction on the Damping Properties of 1-3 Piezoelectric Damping Composites

1-3 piezoelectric-damping composites were fabricated using piezoelectric ceramic as functional filler and epoxy resin as matrix by cut-filling method. The fabrication procedure of the composites was introduced. The effect of ceramic volume fraction on the damping behavior and the piezoelectric strain factor d33 were studied. The results show that the damping property was firstly improved, and then decreased with the increase of the ceramic volume fraction. An optimal ceramic volume fraction of 15% was shown. TA increased from 29.78 to 32.34. The piezoelectric strain factor d33 reached 323pC·N-1.

Effect of Backing Materials on the Performance of Cement-Based Piezoelectric Ultrasonic Sensors

In order to increase the sensitivity, frequency bandwidth and longitudinal resolution of the 1-3 cement-based piezoelectric ultrasonic sensor, different metal powder/epoxy resin composite materials were used to make backing layer, and the performances of sensors were evaluated and compared. The results indicated that the increase of the sensitivity and the frequency bandwidth, as well as a decrease of the pulse wave number can be observed when the backing materials of metal powder/epoxy resin composite materials were added to the sensor. A 42%-increase of the maximum peak-to-peak value of the echo pulse response, a 52%-reduction of the ring down time and a 200%-increase of the bandwidth can be achieved by using the backing material.

Performance Analysis of the 1-3 Piezoelectric Composites and Transducer Fabrication

1-3 polymer-based piezoelectric composites were fabricated using epoxy as the matrix by the cut-filling method. The influences of PMN volume fraction on the piezoelectric and dielectric properties of the composite were analyzed, and then the piezoelectric composite was fabricated to transducer whose properties were also analyzed. The results indicate that with increasing the PMN volume fraction, both the hydrostatic piezoelectric voltage gh and hydrostatic figures of merit dh·gh of the composite decrease, while the relative dielectric constant εr increases. The hydrostatic piezoelectric strain dh has the optimum value in the PMN volume fraction range of 40%-60%. The resonant frequency of transducer in water is 306.5 kHz and anti-resonant frequency is 352.6 kHz.

FEM Analysis of 1-3 Cement Based Piezoelectric Composites

The simulating software ANSYS is applied to carry out the coupling analysis of the 1-3 cement based piezoelectric composites. The interior displacement and strain distribution were obtained and discussed. The influences of material parameters such as thickness, relative dielectric constant, Poisson’s ratio and Yang’s modulus on the composites were analyzed based on the FEM model. The results indicate that active strain and displacement of the 1-3 cement based piezoelectric composites is mainly concentrated on the piezoelectric ceramic rods. The performance of the 1-3 cement based piezoelectric composites can be improved efficiently by increasing the thickness, Poissons ratio, and reducing the Yangs modulus, the relative dielectric constant.

Non Destructive Evaluation Based on Impedance Method Using Embedded PZT Sensor

The structural damage of mortar caused by simulated crack was evaluated using embedded PZT sensor combining with dynamic electromechanical impedance technique. The influence of embedded PZT sensors layout on detecting structural damage induced by the simulated cracks was also investigated. The results indicate that with increasing the simulated crack depth, the impedance real part of PZT sensors shift leftwards accompanying with the appearance of new peaks in the spectra. When more simulated cracks occur, the shift of the impedance curve becomes more obvious, and the amounts of new peaks in the impedance spectra also increase. RMSD indices of the structures with PZT sensors embedded in them with different layout can show the structural incipient damage clearly. With increasing more simulated cracks in the mortar structures, RMSD values of the structures with different PZT sensors layout become larger, under the same depth, RMSD indices of the structures with PZT sensor embedded transversely and horizontally in them show the increasing trend.

Fabrication of 1-3 Cement-Based Piezoelectric Ultrasonic Sensors for NDE Applications

This paper described fabrication and comparison of embedded ultrasonic sensors for NDE applications. A 1-3 cement-based piezoelectric composite was used as the sensing element of the ultrasonic sensor. As a front matching layer between test material and piezoelectric materials, cement/epoxy resin was selected. In order to make the backing materials for sensors had enough acoustic attenuation performance, the backing material of sensors doped with tungsten powder. When the mass ratio of tungsten/cement backing was two and the thickness of cement/epoxy resin front-face matching was 3mm, the 1-3 cement-based piezoelectric ultrasonic sensor showed a significant enhancement in both relative pulse-echo sensitivity and-6dB bandwidth. These promising results suggested the great potential for developing high-performance ultrasonic sensors using the 1-3 cement-based piezoelectric composite.

Concrete Damage Detection Based on Embedded Acoustic Emission Sensors

A new kind of embedded acoustic emission (AE) sensor has been developed and it was made up of 1-3 cement-based piezoelectric composites. Compared with those sensors which were traditionally affixed to concrete structures, the embedded AE sensors could minimize the leakage of AE hits and improve the accuracy of data acquisition. The AE thresholds of the sensors are 45dB and they can perceive the position of source and crack extending areas in concrete. Because of the low operation cost, the admirable compatibility with concrete and the excellent durability, the sensors could be widely used in the monitoring of civil structure.

Effect of Poling Temperature on the Barium Ferrite Modified 0-3 Cement-Based Piezoelectric Composites

A barium ferrite modified 0–3 cement-based piezoelectric composite was fabricated with piezoelectric ceramic [0.08Pb(Li1/4Nb3/4)O•0.47PbTiO3•0.45PbZrO3], sulphoaluminate cement and barium ferrite by compressing technique. It is well known that in the process of making piezoelectric composites，polarization is very critical, which is the process of domain structures motion and development in a piezoelectric composites. Without the polarization, the composites will have no piezoelectric properties. So the influences of poling temperature on the piezoelectric and dielectric properties, electromechanical coupling property and acoustic impedance were investigated. And the poling temperature were selected at 30°C、50°C and 80°C. The results showed that the optimum poling temperature were 80°C.