In this paper, TiB2 particle-reinforced Cu and Cu–Cr composites were prepared by the vacuum arc melting technique. The tensile strength, electrical conductivity and wear properties of the composites ...were tested. The microstructure and wear morphology of the composites were characterized by SEM. The results showed that microscale TiB2 particles were dispersed uniformly in copper matrix, and the interface between the TiB2 particles and matrix was clean and well bonded. Nanoscale Cr particles were dispersed in the copper matrix. The friction coefficient and wear rate of the composites increased with increasing current. The dual-scale TiB2/Cu–Cr composites with nanoscale Cr particles and microscale TiB2 particles possessed a high strength and hardness, that was conducive to improving the wear resistance. Compared with the wear rate for composites prepared with powder metallurgy, when the current was 50 A, the wear rate of TiB2 particle-reinforced Cu and Cu–Cr composites prepared by vacuum arc melting decreased by 9.3% and 55.3%, respectively. The Cr particles strengthened the copper matrix and the TiB2 particles supported the friction process. The synergistic effect improved electrical wear resistance of the TiB2/Cu–Cr composite. Microstructural observations revealed that the main wear mechanisms of the composites were adhesive wear, abrasive wear and arc erosion.
•In this study, TiB2 particle reinforced Cu/Cu–Cr composites were prepared by vacuum arc melting.•The dual-scale TiB2/Cu–Cr composites with nanoscale Cr particles and microscale TiB2 particles possessed a high strength.•Cu/Cu–Cr composite has the best wear resistance.•The wear mechanisms of Cu/Cu–Cr composites were proposed.
Hybrid copper matrix composites reinforced by TiB whiskers and TiB2 particles were fabricated by in situ mixing casting in combination with rolling and annealing. During turbulent mixing and copper ...mold casting processes, the in situ reactions carried out completely, and the macrosegregation of reinforcements in the composites was overcome efficiently. By controlling the rolling and annealing parameters, unfavorable casting defects, including “chain-type” reinforcement clusters and shrinkage porosities that formed during the end stage of solidification, were eliminated. Accordingly, the uniform distribution of hybrid reinforcements in the as-annealed composites provided good comprehensive performance. Compared to the 2.6 wt%TiB2p/Cu composite, the (1.0 wt%TiB2p-0.9 wt%TiBw)/Cu hybrid composite exhibited both higher strength (492 MPa) and higher electrical conductivity (85.5% International Annealed Copper Standard). Therefore, the hybrid effect in the copper matrix composites can be explained by the fact that a better strengthening effect was achieved by adding less hybrid reinforcement, which helped maintain the electrical conductivity at a relatively high level.
•TiB whiskers and TiB2 particles distribute uniformly in copper matrix.•The strength of composites is improved by adding less hybrid reinforcement.•Low hybrid reinforcement concentration leads to a high electrical conductivity.•A positive hybrid effect is achieved in comprehensive properties of CMCs.
Salmonella is one of the most common causes of food-associated disease. An electrochemical biosensor was developed for Salmonella detection using a Salmonella-specific recognition aptamer. The ...biosensor was based on a glassy carbon electrode modified with graphene oxide and gold nanoparticles. Then, the aptamer ssDNA sequence could be linked to the electrode. Each assembly step was accompanied by changes to the electrochemical parameters. After incubation of the modified electrode with Salmonella, the electrochemical properties between the electrode and the electrolyte changed accordingly. The electrochemical impedance spectrum was measured to quantify the Salmonella. The results revealed that, when more Salmonella were added to the reaction system, the current between the electrode and electrolyte decreased; in other words, the impendence gradually increased. A detection limit as low as 3cfu/mL was obtained. This novel method is specific and fast, and it has the potential for real sample detection.
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•An aptamer-based electrochemical biosensor for Salmonella detection was constructed.•Graphene oxide and gold nanoparticles were modified on the glassy carbon electrode to enhance the electron transfer properties.•The biosensor method for Salmonella detection could be realized as low as 3cfu/mL.
Rocks in underground projects at great depth, which are under high static stresses, may be subjected to dynamic disturbance at the same time. In our previous work (Li et al. Int J Rock Mech Min Sci ...45(5):739–748,
2008
), the dynamic compressive behaviour of pre-stressed rocks was investigated using coupled-load equipment. The current work is devoted to the investigation of the dynamic tensile behaviour of granite rocks under coupled loads using the Brazilian disc (BD) method with the aid of a high-speed camera. Through wave analyses, stress measurements and crack photography, the fundamental problems of BD tests, such as stress equilibrium and crack initiation, were investigated by the consideration of different loading stresses with abruptly or slowly rising stress waves. The specially shaped striker method was used for the coupled-load test; this generates a slowly rising stress wave, which allows gradual stress accumulation in the specimen, whilst maintaining the load at both ends of the specimen in an equilibrium state. The test results showed that the tensile strength of the granite under coupled loads decreases with increases in the static pre-stresses, which might lead to modifications of the blasting design or support design in deep underground projects. Furthermore, the failure patterns of specimens under coupled loads have been investigated.
The fabrication of carbon nanotubes (CNTs)-reinforced copper matrix composites with excellent performances is a challenging task because of the weak interfacial bonding between CNTs and copper ...matrices. In the present work, an alloying element—titanium—was intentionally added to the bonding interfaces of laminated CNTs/Cu composites via the flake powder metallurgy method. Due to the in situ formed intermediate layer of TiC and Cu3Ti particles, the interfacial bonding of the composites was significantly improved. In combination with the architecture design, the locally alloyed 0.2 wt% CNTs/Cu-0.5Ti composite exhibits both improved ultimate tensile strength (407 ± 22 MPa) and ductility (9.7%) compared with the unalloyed composite containing the same CNT concentration. Since titanium was locally added solely to the interface, the inclusion of titanium had a negligible effect on the lattice parameters of the copper matrix, and the electrical conductivities of the bulk composites were maintained at a relatively high level.
•A 3D Microstructure-based finite element modeling of TiB2/Cu composites was established.•Numerical evaluation and experimental verification of mechanical properties and fracture behavior for TiB2/Cu ...composites are implemented.•It provides useful guidelines for optimum composite structures design in TiB2/Cu composites.
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In this paper, according to the geometric characteristics of TiB2 particle acquired from the scanning electron microscopes (SEM), computational structural modeling of TiB2/Cu composites is performed, in which the size, shape, position, volume fraction and proportion of TiB2 particles are numerically reproduced to be similar to those of the actual micro-structures of TiB2/Cu composites. The ductile damage and failure behaviors for matrix, the elastic brittle failure for the particle reinforcement, and the traction-separation for interface, were independently simulated in this model. Four evaluation indexes such as elastic modulus, yield strength, tensile strength and elongation are used to assess the comprehensive mechanical properties of composites. Load-bearing capability of the TiB2/Cu composites is investigated by analyzing the stress and strain distribution of particles, interface and matrix. The validity of the simulation results is verified by the agreement of the experimental stress-strain curve and the morphology of fracture section. The effects of particle size, shape, volume fraction and proportion of TiB2 particles on the mechanical behavior are presented. The present work may provide useful guidelines for optimum composite structures design and industrial applications.
This paper presents the design of a fast and accurate control system using electric cylinder for the automated measurement of bearing shell crush height, which is an important parameter for quality ...control and needs to be measured in a particular test loading according to ISO3548-3:2012 standard. A test bench has been developed and an electric cylinder is used to provide the required test loading pressure with the LabVIEW platform. In order to meet the demands for high accuracy, fast speed, and stability, the control method of electric cylinder has been designed for industrial applications based on PLC. The control methods include automatic origin seeking and reset when powering up, fast and accurate pressure loading, generating control parameters by self-learning, and returning to the origin and pressure calibration. The fast and accurate pressure loading process consists of position preloading, pressure preloading, pressure coarse loading, and pressure fine loading. The experimental results have shown that the election cylinder can meet the application requirements, the control methods for pressure loading are accurate and fast, and the control system is stable and reliable. They will have potentials for wide industrial applications.
Monitoring mollusk biodiversity is a great challenge due to their large diversity and broad distribution. Environmental DNA (eDNA) technology is increasingly applied for biodiversity monitoring, but ...relevant studies on marine mollusks are still limited. Although previous studies have developed several pairs of primers for mollusk eDNA analyses, most of them targeted only a small group of mollusks. In this study, seven primers were designed for the mollusk community and validated and compared with eight pairs of published primers to select the best candidates. After in silico test, MollCOI154 and MollCOI255 primers showed non-specific amplification, and same results were also obtained in published primers (COI204, Sepi, and veneroida). Moll12S100, Moll12S195 and Moll16S primers failed to amplify across all genomic DNA from selected mollusk. Except Moll16S, all developed and two published (unionoida and veneroida) primers were successfully amplified on four eDNA samples from Yangtze River estuary. After annotation of the amplified sequences, MollCOI253 showed higher annotation of the amplification results than the other primers. In conclusion, MollCOI253 had better performance in terms of amplification success and specificity, and can provide technical support for eDNA-based research, which will be beneficial for molluscan biodiversity investigation and conservation.
The TiB2p/Cu composites were prepared by current-assisted vacuum hot pressing (CAVHP) combined with rolling using in-situ spherical TiB2p/Cu composite powder as raw material. The effects of rolling ...deformation on the microstructure and properties of the sintered TiB2p/Cu composite were investigated. The results show that CAVHP leads to a rapid densification of the composite powder compact, and the subsequent rolling deformation is able to eliminate the unclosed pores and achieve a uniform distribution of TiB2p. The dynamic recrystallization during cold rolling refines the Cu matrix grains to ultrafine grains with an average grain size of 0.47 μm. The cold rolled TiB2p/Cu composite obtains a remarkable comprehensive performance with ultimate tensile strength, yield strength and electrical conductivity of 621 MPa, 567 MPa and 86.3% IACS, respectively. In addition, the strengthening and fracture mechanism of the cold rolled TiB2p/Cu composite are analyzed. This work will explore a new technological solution for the preparation of high-performance Cu matrix composites.
Background: Vegetation roots are considered to play an effective role in controlling soil erosion by benefiting soil hydrology and mechanical properties. However, the correlation between soil ...hydrology and the mechanical features associated with the variation root system under different vegetation types remains poorly understood. Methods: We conducted dye-tracer infiltration to classify water flow behavior and indoor experiments (including tests on soil bulk density, soil organic carbon, mean weight diameter, soil cohesion, root density, etc.) to interpret variation patterns in three forest systems (coniferous and broad-leaved mixed forest, CBF; coniferous forest, CF; Phyllostachys edulis, PF) and fallow land (FL). Results: Based on the soil dye-tracer infiltration results, the largest dyeing area was observed in CF (36.96%), but CF also had the lowest infiltration rate (60.3 mm·min−1). The soil under CBF had the highest shear strength, approximately 25% higher than other vegetation types. CF exhibited the highest aggregate stability, surpassing CBF by 98.55%, PF by 34.31%, and FL by 407.41%, respectively. Additionally, PF forests showed the greatest root biomass and length. The results of correlation analysis and PCA reveal complex relationships among hydrological and mechanical soil traits. Specifically, soil cohesion does not exhibit significant correlations with hydrological traits such as the dyeing area, while traits like MWD and PAD show either positive or negative associations with hydrological traits. Root traits generally exhibit positive relationships with soil mechanical traits, with limited significant correlations observed with hydrological traits. Conversely, we found that root biomass contributes significantly to the dyeing area (accounting for 51.48%). Conclusions: Our findings indicate that the reforestation system is a successful approach for conserving water and reducing erosion by increasing soil-aggregated stability and shear strength, causing water redistribution to be more homogenized across the whole soil profile.
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