Acoustic Matching Characteristics of Annular Piezoelectric Ultrasonic Sensor

Using intelligent materials and sensors to monitor the safety of concrete structures is a hot topic in the field of civil engineering. In order to realize the omni-directional monitoring of concrete structural damage, the authors of this paper designed and fabricated an embedded annular piezoelectric ultrasonic sensor using the annular piezoelectric lead zirconate titanate (PZT) ceramic as a sensing element and epoxy resin as the matching and the backing layers. The influence of different matching and backing layers thickness on the acoustic characteristic parameters of the sensor were studied. The results show that the resonant frequency corresponding to the axial mode of annular piezoelectric ceramics moves toward the high frequency direction with the decrease of the height of piezoelectric ceramics, and the radial vibration mode increases as well as the impedance peak. With the thickness of the backing layer increases from 1 mm to 2 mm, the radial resolution of the annular piezoelectric ultrasonic sensor is enhanced, the pulse width is reduced by 39% comparing with the sensors which backing layer is 1 mm, and the head wave amplitude and −3 dB bandwidth are increased by 61% and 66%, respectively. When the matching layer thickness is 3 mm, the sensor has the highest amplitude response of 269 mV and higher sensitivity

Influence of backing layer on the non-metallic encapsulated acoustic emission sensor for concrete monitoring

Use acoustic emission sensors to monitor the acoustic emission phenomenon of concrete materials after being loaded has always been a hot spot in the field of civil engineering. Currently, the mixture of tungsten powder and epoxy resin was commonly used as the backing layer of acoustic emission sensors. Therefore, the influence of tungsten powder content on backing layer and acoustic emission sensor was studied. The backing layer of air has the largest acoustic reflection coefficient, and the mixture of epoxy resin and tungsten powder has the largest acoustic attenuation performance, which is benefit to improve the bandwidth of the acoustic emission sensor. As the content of tungsten powder increases, the acoustic reflection coefficient of the mixture of tungsten powder and epoxy resin gradually decreases, the acoustic impedance gradually increases, and the resolution of the acoustic emission sensor increases, both the resonant frequency and electrical impedance of the sensor gradually decrease. When the tungsten powder content in the backing layer reaches 50% of the total mass, the optimal backing layer of the sensor was prepared, and the fabricated sensor exhibits a higher peak-to-peak value of 7.5 V and a larger first wave amplitude of 3.4 V. It also possesses the widest − 3 dB bandwidth of 7 kHz. The uniaxial compression experiment of concrete with equal strain rate was carried out. According to the variation law of acoustic emission characteristic parameters, the compression characteristics of concrete in uniaxial compression test were divided into three stages

Effect of Paste Fluidity and Paste-to-Aggregate Ratio on the Strength and Permeability of Porous Mortar from Manufactured Sand

Many places in the world suffer from a shortage of river sand because of population growth and environmental protection, and people have to replace river sand with manufactured sand (M-sand). In this study, M-sand was adopted as aggregate and the effect of the mix design (paste fluidity (PF) and paste-to-aggregate ratio (P/A)) on the properties of porous mortar was investigated through a combined experimental, statistical and response surface method (RSM). By including variations in both P/A (0.16–0.26) and PF (160–200 mm), the method was utilized to develop ANOVA models and construct response surface and contour lines. The experimental results revealed that the compressive strength of the porous mortar increased by 62.3% to a value of 34.1 MPa while the PF increased to 190 mm from 160 mm at a P/A of 0.20, and the water permeability coefficient was 7.2 mm/s under the same conditions. In addition, the ANOVA analysis of the measured properties revealed a strong interactive effect of the paste-to-aggregate ratio and paste fluidity on the porous mortar properties, and the developed relationship models between the variables and responses were accurate. A porous mortar with a compressive strength over 30 MPa and a permeability coefficient over 7 mm/s could be conveniently designed by RSM. Additionally, the compressive strength of the porous concrete reached more than 40 MPa at a P/A of 0.26

Early-age hydration characteristics and kinetics of Portland cement pastes with super low w/c ratios using ice particles as mixing water

The liquid water was replaced by ice particles for preparing homogenous structural Portland cement (PC) pastes at super low w/c ratios from 0.08 to 0.16. For introducing the process of PC hydration, a sophisticated conduction calorimeter was adopted to measure the early-age hydration heat evolution. The hydration kinetic parameters were determined by Krstulovic–Dabic model based on data of hydration heat evolution. The concentrations of K+ and Na+ of the pore solution were measured by ICP-OES. Experimental results showed that the acceleration period of the hydration process of PC paste was improved by increasing w/c ratio due to the improvement of space available for hydration product growth. The hydration mechanism of PC paste changed to nucleation and crystal growth (NG) - diffusion (D) when its w/c ratio below 0.16, representing a more intense hydration reaction than that of PC with a normal w/c ratio of 0.30. The concentrations of K+ and Na+ of pore solution of hydrated PC paste decreased with the increase of w/c ratios, which led to the alkalinity of that decreased with the increase of w/c ratios. In addition, the mechanical properties of hardened PC pastes were enhanced by increasing w/c ratios from 0.08 to 0.16, which could be attributed to the decrease of porosities of hardened pastes.This article is published as Li, Laibo, Mingxu Chen, Xiangyang Guo, Lingchao Lu, Shoude Wang, Xin Cheng, and Kejin Wang. "Early-age hydration characteristics and kinetics of Portland cement pastes with super low w/c ratios using ice particles as mixing water." Journal of Materials Research and Technology 9, no. 4 (2020): 8407-8428. DOI: 10.1016/j.jmrt.2020.05.082. Copyright 2020 The Author(s). Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Posted with permission

In Vitro Bioactivity Study of RGD-Coated Titanium Alloy Prothesis for Revision Total Hip Arthroplasty

Total hip arthroplasty (THA) is a common procedure for the treatment of end-stage hip joint disease, and the demand for revision THA will double by 2026. Ti6Al4V (Titanium, 6% Aluminum, and 4% Vanadium) is a kind of alloy commonly used to make hip prothesis. To promote the osseointegration between the prothesis and host bone is very important for the revision THA. The peptide Arg-Gly-Asp (RGD) could increase cell attachment and has been used in the vascular tissue engineering. In this study, we combined the RGD with Ti6Al4V alloy using the covalent cross-linking method to fabricate the functional Ti6Al4V alloy (FTA). The distribution of RGD oligopeptide on the FTA was even and homogeneous. The FTA scaffolds could promote mouse osteoblasts adhesion and spreading. Furthermore, the result of RT-qPCR indicated that the FTA scaffolds were more beneficial to osteogenesis, which may be due to the improvement of osteoblast adhesion by the RGD oligopeptide coated on FTA. Overall, the FTA scaffolds developed herein pave the road for designing and building more efficient prothesis for osseointegration between the host bone and prothesis in revision THA

Effect of Tartaric Acid on the Printable, Rheological and Mechanical Properties of 3D Printing Sulphoaluminate Cement Paste

Rapid setting and low viscosity of sulphoaluminate cement (SAC) make it difficult to be extruded by 3D printing (3DP) technique. In this study, the effect of tartaric acid (TA) on printability, rheology and mechanical property of 3DP SAC paste is investigated. The experimental results indicate that the setting time, hydration evolution and apparent viscosity of SAC paste can be well controlled by adding a proper amount of TA to satisfy the requirements of 3DP. An excellent structure of SAC paste with the ultimate deformation rate less than 10% can be printed without compromising mechanical strength

Comparative Study on Laser Welding Thick-Walled TC4 Titanium Alloy with Flux-Cored Wire and Cable Wire

In the welding process of thick-walled titanium alloys, the selection of the wire type is one of the critical factors affecting the welding quality. In this paper, flux-cored and cable wires were used as filler materials in the welding of thick-walled titanium alloys. The macrostructure, microstructure, texture, and grain size of both welded joints were compared by employing an optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM), and the tensile and impact properties were also evaluated. The comparison result showed that the fusion zone microstructure of both welded joints was dominated by a basketweave structure composed of interwoven acicular α′ martensite, whereas the microstructure of flux-cored wire welded joints was finer, and the degree of anisotropy was low. The strength of both welded joints was higher than that of the base metal, ensuring that fracture occurred in the base metal area during tension. The Charpy impact energy of the flux-cored wire welded joint was 16.7% higher than that of the cable wire welded joint, indicating that the welded joint obtained with the flux-cored wire performed better in the welding process of thick-walled titanium alloys