Papers by Author: Dong Yu Xu

Abstract: 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.

Abstract: 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.

Abstract: The piezoelectric ceramics Pb_0.94Sr_0.06(Zr_0.53Ti_0.47)O₃+(Ni₂O₃+Cr₂O₃)0.1wt% + x wt%MnO₂ + y wt%CeO₂ (abbreviated as PCrNi-4) were prepared by a traditional ceramics process in this paper. The influences of MnO₂ and CeO₂-doping and sintered temperature on matrix material properties were studied by orthogonal tests. The effects of different inducing factors on the microstructure and dielectric loss were analyzed by means of XRD, SEM and electric measurement. The results indicate that the optimum process conditions are w(MnO₂)= 0.1%, w(CeO₂)= 0.3% and the sintering temperature 1280°C. The property parameters of samples are: d₃₃=304.8pC/N, Kp=0.6113, ε^T₃₃=1520, tanδ=0.00289, d₃₃×g₃₃=61.12×10^-12CVm/N.

Abstract: 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 g_h and hydrostatic figures of merit d_h·g_h of the composite decrease, while the relative dielectric constant ε_r increases. The hydrostatic piezoelectric strain d_h 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.

Abstract: The influences of particle size and mixing content of coarse cement on the self-healing ability of concrete were researched by ultrasonic method. Damaged degree was measured through the decrease of ultrasonic head wave amplitude (UHA) before and after loading. The relationship between damaged degree and self-healing ratio of concrete was built based on the experimental results as well as the relationship between cement diameter and self-healing ratio of concrete. Analyzing results show that UHA can evaluate the damaged degree of concrete clearly. There exists a damaged threshold of the concrete during loading. Under the same mixing content of coarse cement, when the damaged degree is higher than the threshold, the self-healing ratio of concrete decreases with the increase of damaged degree and increases with the increase of coarse cement diameter, however, while the damaged degree is less than the threshold, the self-healing ratio of concrete increases with both the increase of damaged degree and coarse cement diameter.

Abstract: 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, Poisson's ratio, and reducing the Yang's modulus, the relative dielectric constant.

Abstract: Periodic and non-periodic 1-3 type cement based piezoelectric composites were fabricated by cut and filling technique, using P(MN)ZT ceramic as functional material and cement as matrix. The influences of periodicity of piezoelectric ceramic rods in the composites on electrical properties of all the composites were discussed. The results show that the non-periodic composites have larger dielectric factor and piezoelectric strain constant than those of the periodic composite. The impedance-frequency spectra analysis indicates that the non-periodic arrangement of ceramic rods can effectively restrict the lateral structural mode of the composite, accordingly reduces the coupling resonant between the thickness resonant mode and lateral resonant mode. The thickness electromechanical coupling coefficient of non-periodic composites is larger than that of the periodic composite. With increasing the non-periodic level of P(MN)ZT ceramic in the composites, the mechanical quality factor of the composites increases gradually. Therefore, 1-3 type cement based piezoelectric composites with different special abilities can be obtained by varying the periodic arrangement of P(MN)ZT ceramic rods in the composites.

Abstract: In this paper, the 1-3-2 piezoelectric composites were fabricated by the cut-filling technique using P(MN)ZT piezoelectric ceramic as functional materials and polymer as matrix. The effects of ceramic volume fraction on the electrical properties of the composites were studied. The results indicate that as the ceramic volume fraction increases, the piezoelectric stain factor d33 increases evidently, while the piezoelectric voltage factor g33 decreases. Besides, the planar electromechanical coupling factor Kp and mechanical quality factor Qm of the composite are also less than those of the pure ceramic, while the thickness electromechanical coupling factor Kt is larger than that of the ceramic.

Abstract: 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.

Abstract: 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.