Shi Feng Huang

Influence of Source Distance on the Characteristics of AE Signal from Cement-Based Materials

The influence of source distance on the characteristics of acoustic emission (AE) signals from mortar and normal concrete were investigated in this research. To collect AE signals of high signal to noise, which can be used in AE research for cement-based materials, the influence of source distance on the characteristics of AE signal were analyzed. The results showed that distance made a significant influence on the characteristics of AE signal from cement-based material, such as rise time, counts, peak amplitude and average frequency.

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.

Effect of Sr/Ba Ratio on Dielectric Properties of BSTN Ceramics

The phase composition of (1-x)BaO·xSrO·0.7TiO2·0.3Nb2O5 (BSTN) composite ceramics was analyzed by XRD, and the effect of Sr/Ba ratio on the dielectric properties of BSTN was investigated by impedance analyzer. The results showed that any sample with different x value contained two phases-the perovskite phase and the tungsten bronze phase. The dielectric constants of BSTN basically decreased while the tanδ increased with the increase in x value. Both dielectric constant and tanδ decreased with the applied frequency increased for the same x value. There were two Curie points for BSTN composite ceramics. The first one belonging to the perovskite phase decreased with the increase in x value, but the second one belonging to the tungsten bronze phase kept almost constant at about 300°C.

Study on Acoustic Emission of 1-3 Orthotropic Cement Based Piezoelectric Sensors

1-3 orthotropic cement based piezoelectric composites were fabricated by cut-filling and arrange-filling technique, using PZT-51 ceramic as functional material and cement as passive matrix. 1-3 orthotropic cement based piezoelectric composites were prepared into Acoustic Emission (AE) sensors, the attenuation of AE signal on the concrete and the response of different sensors on the concrete with increasing distance were researched. The results showed that the signal strength received by sensing element increases with the increasing PZT volume fraction; signal peaks and amplitude decrease gradually when the testing distance increases; signal strength received on the ceramic title is stronger than on the concrete; the attenuation of signal wave shape received on the concrete is much slower when compared with ceramic title.

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.

Temperature and boundary influence on cement hydration monitoring using embedded piezoelectric transducers.

In this study, the hydration process was monitored using embedded ultrasonic transducers. It was found that the ultrasonic amplitude decreased and fluctuated at the very early age, several hours after the beginning of fast hydration. The embedded transducers are very different from the surface coupled ones for they were directly influenced by the cement paste, such as the varying temperature and the boundary condition. Experiments were carried out to find out which factor result in such decrease and fluctuation. Test results showed that both the temperature and boundary conditions affect the ultrasonic measurement. When the hydration progressed under constant temperature, the amplitude of the ultrasonic wave decreased smoothly during certain period. When the hardened specimen was tested, it was found that the amplitude would decrease obviously with the increasing of temperature and vice versa. The findings could be used to interpret the amplitude plot obtained in the normal hydration monitoring using embedded transducers.

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.

Influence of Base Thickness on Performance of 1-3-2 Piezoelectric Composite

Sulphoaluminate cement and Lead Niobium-Magnesium Zirconate Titanate ceramic [P(MN)]ZT were used as matrix and functional phase respectively to fabricate 1-3-2 cement-based piezoelectric composites by dice and filling technique. The influences of base thickness on piezoelectric properties, electromechanical properties and acoustic impedance properties of the composites were discussed. The results show that as the base thickness increases, the piezoelectric stain factor d33 increases gradually, while the piezoelectric voltage factor g33 decreases. The planar electromechanical coupling coefficient Kp exhibits the trend of decrease, while the thickness electromechanical coupling coefficient Kt and acoustic impedance show the increasing trend. The mechanical quality factor Qm reaches the minimum (1.49) when base thickness is 2.00 mm. The results reveal that the 1-3-2 piezoelectric composite will be suitable for application by changing the base thickness.

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.