Stressing state characteristics of reinforcement concrete box-girders strengthened with carbon fiber reinforced plastic

This paper investigates structural performance of five reinforcement concrete (RC) box-girders under a combination loading of bending, shear and torsion, applying the structural stressing state theory. The measured strain data is modeled as generalized strain energy density (GSED) to characterize the structural stressing state mode. Then the Mann-Kendall (M-K) criterion is innovatively applied to detect the leap characteristics of RC box-girders’ stressing state from the E’-T curves, deriving the new definition of structural failure load. Furthermore, the reinforcement effects of different Carbon Fiber Reinforced Plastic (CFRP) wrapping schemes on the behaviors of experimental RC box-girders are revealed through comparing strain modes of stirrup and longitudinal reinforcement. Finally, the method of numerical shape function is applied to reasonably expand the limited strain data for further exploring the strain distribution of cross section and analyzing the stressing state characteristics of the RC box-girders. The research results provide a new angle of view to conduct structural analysis and a reference to the improvement of reinforcement scheme. First published online 29 November 201

Effect of graphene orientation on microstructure and mechanical properties of silicon nitride ceramics

Mechanical properties and microstructure of graphene platelets reinforced Si3N4 composites have been investigated and compared to monolithic Si3N4. The microstructure shows that graphene platelets are parallel to each other and perpendicular to the hot pressing direction. Fracture toughness and flexural strength of composite with 1 wt.% graphene measured on polished surface perpendicular to hot pressing direction are 8.7 MPa·m1/2 and 892 MPa, respectively, which are increased about 14.5% and 20.2% compared with that parallel to hot pressing direction. The anisotropy of microstructure and mechanical properties of composites can be explained by the intrinsic anisotropy of graphene as well as the crack deflection energy release rate and the weak boundary bonding between graphene and Si3N4 caused by the thermal expansion mismatch

Comparative Study on the Dry Sliding Friction Properties of In-Situ Micron and Submicron (Ti-V)C Reinforced Fe-Based Laser Cladding Layers

By optimising the particle size of cladding alloy powders, in situ micron and submicron (Ti-V)C reinforced Fe-based laser cladding layers were prepared and the dry sliding friction properties were comparatively studied. Results showed that there were same phases of α-Fe, γ, TiC, and TiVC2 in the two cladding layers. The average grain size of the Fe-based matrix was 3.46 μm and 3.37 μm, the microhardness was 731 HV0.2 and 736 HV0.2, and the area ratio of carbides was 11.14% and 11.02%, respectively. The dry sliding wear resistance of the cladding layer reinforced by 1.95 μm carbides was 2.76 times higher than that of the 0.49 μm carbides. The failure mechanism of the cladding layer with the micron carbides was mainly caused by plastic deformation of the cladding layer matrix, whereas that of the submicron carbides involved both the plastic deformation of the cladding layer matrix and the abrasion that was caused by the peeled carbides

Lubrication Performance of Graphene as Lubricant Additive in 4-n-pentyl-4′-cyanobiphyl Liquid Crystal (5CB) for Steel/Steel Contacts

The lubrication performance of graphene used as additive in 4-n-pentyl-4′-cyanobiphyl liquid crystal (5CB) for steel/steel contacts was studied on a ball-on-plate tribotester. The friction test results show that when the graphene content in the 5CB was 0.15 wt.%, and the lubricant and friction pairs were heated to 44⁻46 °C before friction tests, the lubrication performance of the 5CB was most improved. Compared with pure 5CB, 5CB+0.15 wt.% graphene suspension reduced the friction coefficient and wear scar diameter by up to 70.6% and 41.3%, respectively. The lubrication mechanisms have been tentatively proposed according to the test results. We speculate that the excellent lubrication performance of graphene/5CB suspensions may be attributed to the low shear resistance adsorption layer formed by graphene and 5CB molecules on the sliding surfaces. As the protective layer, it not only prevents direct contact between the rough sliding surfaces but also is easy to slide

Pd-Free Activation Pretreatment for Electroless Ni-P Plating on NiFe2O4 Particles

A Pd-free activation pretreatment process was developed for electroless Ni-P plating on NiFe2O4 particles. The main influencing factors, including NiCl2·6H2O concentration, pH of electroless bath and temperature, were investigated. Microstructures of the coating layers were characterized by scanning electron microscopy. It was found that a more uniform and compact Ni-P coating layer was successfully formed by electroless plating via Pd-free activation pretreatment than Pd as sited plating. The coating layers plated by Pd-free activation pretreatment were thicker than those by the sensitization and activation pretreatment on average (9 vs. 5 μm). The new process did not need conventional sensitization or activation pretreatments, because the Ni particles dispersed uniformly on the NiFe2O4 substrate became catalytic activation sites for nickel electroless plating. Such improvement was beneficial to shortening the preparation process and reducing the production costs with the use of noble metal Pd

Effects of pulsed frequency on the microstructure characteristics and properties of Ti6Al4Vlaser melting deposition additive manufacturing parts

Laser melting deposition–produced Ti6Al4V additive manufacturingparts tend to manifest as coarse columnar grains. This paper optimises the laser pulse frequency to manage the microstructuralcharacteristics of Ti6Al4V parts and enhance their tensile properties and corrosion resistance. A fiber laser processing equipment with a laser power of 1200 W and a spot diameter of 2.0 mm was employed for all experiments, which provides pulsed lasers at 4, 40, 400, and 4000 Hz at a scanning speed of 8 mm/s and a duty cycle of 95 % for comparative research.The findings demonstrated that increasing the pulse frequency improved the deposition efficiency.An appropriate pulse frequency could promote the refinement and columnar-to-equiaxed transition (CET) of primary β grains.At 400 Hz, the Ti6Al4V-deposited parts yielded refined equiaxed grains.The average grain size in the middle of the sample was about 206.8 μm,and the microstructure mainly comprised fine α-laths in a lamellar structure, which yielded the best overall performance of the parts, with the ultimate tensile strength and elongation reaching 1083 MPa and 4.09 %, respectively.Therefore, improvingthe structural properties of partsby regulating the deposition process, which is conducive to the online regulation of the forming quality of laser deposition parts, is an effective and feasible approach

Impact of microstructure evolution on the corrosion behaviour of the Ti–6Al–4V alloy welded joint using high-frequency pulse wave laser

In this work, a high-frequency pulsed laser-welding process was successfully implemented to fabricate a Ti–6Al–4V alloy butt joint. The microstructure of each zone of the welded joint was systematically characterized by carrying out scanning electron microscopy and electron backscatter diffraction measurements. In addition, the corrosion resistance of the welded joint was tested using traditional electrochemical and local electrochemical methods, while the main factors affecting corrosion resistance and the mechanism of the galvanic corrosion were also thoroughly investigated. From the acquired results, it was demonstrated that the α′ martensitic phases constituted the microstructure in the fusion zone (FZ), where the grain size, grain orientation, and misorientation distribution of the different zones varied, and the α′ martensitic and bulk α covered the heat-affected zone (HAZ). The corrosion resistance in the HAZ was slightly better than that in the base material, and both were worse than that of the FZ, which was related to the phase type. In addition, the corrosion current density values of FZupper were about 1/4.6 and 1/2.6 those of FZmiddle and FZdown, respectively, which was attributed to differences in the grain size and grain orientation. The FZ was protected as a cathode during galvanic corrosion, which is of great importance for ensuring the service life of the component during practical applications

Mechanical Properties and Microstructures of Al2O3/TiC/TiB2 Ceramic Tool Material

In order to develop a new ceramic tool material with self-repairing capability, Al2O3/TiC/TiB2 ceramic tool material was prepared by vacuum hot-pressure sintering method. The toughening and strengthening mechanism of TiB2 on Al2O3/TiC substrate was analyzed. The results show that the ceramic tool material has good comprehensive mechanical properties when the TiB2 content is 10 vol.%. Its flexural strength was 701.32 MPa, hardness was 18.3 GPa, and fracture toughness was 6.2 MPa·m1/2, which were improved by 11.6%, 2.2% and 16.1% respectively, compared with the Al2O3/TiC tool material. Fracture surfaces of the Al2O3/TiC/TiB2 ceramic tool material were characterized by SEM, EDS and XRD. The results showed that the fracture mode was a mixture of transgranular fracture and intergranular fracture. The growth of Al2O3 and TiC grains can be effectively inhibited by adding appropriate amount of TiB2, and the internal grains of the material can be refined. The TiB2 has a uniform distribution in the matrix and acts as a diffusion toughening agent. The cutting performance of Al2O3/TiC/10 vol.%TiB2 tool material was further investigated. Experiments conducted on tools made of Al2O3/TiC and Al2O3/TiC/TiB2 materials showed that the main forms of wear for both tools were abrasive wear and bonded wear. The friction coefficient of Al2O3/TiC/TiB2 tools was reduced by 10.77% compared to Al2O3/TiC tools

Accurate Cutting-Force Measurement with Smart Tool Holder in Lathe

Cutting force in lathe work is closely related to tool wear and affects the turning quality. Direct measurement of the cutting force by measuring the strain of the tool holder is challenging because the tool holder design aims to be highly rigid in order to undertake large cutting forces. Accordingly, the most popular dynamometer designs modify the standard tool holder by decreasing the structural rigidity of the holder, which reduces the machining precision and is not widely accepted. In order to solve the issue of the low stiffness of the dynamometer reducing the machining precision, in this paper, the ultra-low strain on the tool holder was successfully detected by the highly sensitive semiconductor strain gauges (SCSG) adjacent to the blade cutting insert. However, the cutting process would generate much heat, which increases the force measuring area temperature of the tool holder by about 30 °C. As a result, the readout drifted significantly with the temperature changes due to the high temperature coefficient of SCSG. To solve this problem, the temperature on the tool holder was monitored and a BP neural network was proposed to compensate for temperature drift errors. Our methods improved the sensitivity (1.14 × 10−2 mV/N) and the average relative error of the BP neural network prediction (≤1.48%) while maintaining the original stiffness of the tool holder. The smart tool holder developed possesses high natural frequency (≥6 kHz), it is very suitable for dynamic cutting-force measurement. The cutting experiment data in the lathe work show comparable performance with the traditional dynamometers and the resolution of the smart tool holder is 2 N (0.25% of total range)