Graphene fiber-based supercapacitors (SCs) are rising as having the greatest potential for portable/wearable energy storage devices. However, their rate performance is not well pleasing, which ...greatly impedes their broad practical applications. Herein, three-dimensional porous carbon nanotube/reduced graphene oxide fibers were prepared by a nonsolvent-induced rapid phase separation method followed by hydrazine vapor reduction. Benefitting from their three-dimensional porous structure, large specific surface area, and high conductivity, the fabricated SC exhibits a high volume capacitance of 54.9 F cm–3 and high energy and power densities (4.9 mW h cm–3 and 15.5 W cm–3, respectively). Remarkably, the SC works well at a high scan rate of 50 V s–1 and shows a fast frequency response with a short time constant of 78 ms. Furthermore, the fiber-shaped SC also exhibits very stable electrochemical performances when it is subjected to mechanical bending and succeeding straightening process, indicating its great potential application in flexible electronic devices.
Ultra-high strength steels are the crucial irreplaceable materials in the fields of aerospace, national defense and military industries. Unfortunately, it is challenging to achieve the requirements ...of vital components because of the strength-toughness trade-off of ultra-high strength steels. In this review, three types of conventional ultra-high strength martensitic steels are systematically summarized. These are: (i) low alloy ultra-high strength steels; (ii) ultra-high strength maraging steels; and (iii) Co–Ni secondary hardening steels. The main influencing factors of mechanical properties of ultra-high strength steels and the exploration on strengthening/toughening are discussed. In particular, the design concept based on the synergistic precipitation of low lattice misfit nano-particles and the formation of martensite matrix with high-density dislocations is a promising approach to develop novel ultra-high strength steels. Finally, some suggestions on the traditional design methods and future development of ultra-high strength steels are put forward and an outlook on future work is offered. This provides guidance for the development of novel ultra-high strength steels with excellent comprehensive performance.
In this paper, Ti-6Al-4 V (TC4 titanium alloy) specimens were prepared by a new process, the variable parameter forming process (VPFP) of selective laser melting (SLM) technology. The surface ...morphology, tensile properties, and microstructure of the TC4 titanium alloy specimen were investigated. The test results showed that within the 250–300 W of laser power, the tensile strength of VPFP was larger than the quantitative parameter forming process (QPFP). However, the elongation was decreased. By decreasing the index of the hierarchy, the tensile strength increases, reaching 1190.84 MPa. Compared with the specimen without heat treatment, the elongation increases to more than 200%, and the maximum elongation reached 13%. By increasing the heat treatment temperature, the fracture gradually changes from brittle fracture to ductile fracture, and the main metallographic structure of the specimen was gradually transformed from acicular martensite α′ to α phase. This study provides new processes for SLM.
In this paper, five grading functional gradient lattice structures with a different density perpendicular to the loading direction were proposed, and the surface morphology, deformation behavior, and ...compression properties of the functional gradient lattice structures prepared by selective laser melting (SLM) with Ti-6Al-4V as the building material were investigated. The results show that the characteristics of the laser energy distribution of the SLM molding process make the spherical metal powder adhere to the surface of the lattice structure struts, resulting in the actual relative density of the lattice structure being higher than the designed theoretical relative density, but the maximum error does not exceed 3.33%. With the same relative density, all lattice structures with density gradients perpendicular to the loading direction have better mechanical properties than the uniform lattice structure, in particular, the elastic modulus of LF, the yield strength of LINEAR, and the first maximum compression strength of INDEX are 28.99%, 16.77%, and 14.46% higher than that of the UNIFORM. In addition, the energy absorption per unit volume of the INDEX and LINEAR is 38.38% and 48.29% higher, respectively, than that of the UNIFORM. Fracture morphology analysis shows that the fracture morphology of these lattice structures shows dimples and smooth planes, indicating that the lattice structure exhibits a mixed brittle and ductile failure mechanism under compressive loading. Finite element analysis results show that when the loading direction is perpendicular to the density gradient-forming direction, the higher density part of the lattice structure is the main bearing part, and the greater the density difference between the two ends of the lattice structure, the greater the elastic modulus.
The quality of ensemble forecasting is seriously affected by sample quality. In this study, the distributions of ensemble members based on the observed track and intensity of tropical cyclones (TCs) ...were optimized and their influence on the simulation results was analyzed. Simulated and observed tracks and intensities of TCs were compared and these two indicators were combined and weighted to score the sample. Samples with higher scores were retained and samples with lower scores were eliminated to improve the overall quality of the ensemble forecast. For each sample, the track score and intensity score were added as the final score of the sample with weight proportions of 10 to 0, 9 to 1, 8 to 2, 7 to 3, 6 to 4, 5 to 5. These were named as “tr”, “91”, “82”, “73”, “64”, and “55”, respectively. The WRF model was used to simulate five tropical cyclones in the northwestern Pacific to test the ability of this scheme to improve the forecast track and intensity of these cyclones. The results show that the sample optimization effectively reduced the track and intensity error, “55” usually had better performance on the short-term intensity prediction, and “tr” had better performance in short-term track prediction. From the overall performance of the track and intensity simulation, “91” was the best and most stable among all sample optimization schemes. These results may provide some guidance for optimizing operational ensemble forecasting of TCs.
Soil fauna can sensitively respond to alterations in soil environment induced by land-use changes. However, little is known about the impact of urban land-use changes on earthworm communities. In ...this study, three land-use types (i.e., forest, nursery and abandoned lands) were chosen to identify differences in diversity, abundance and biomass of earthworm community in Kunming City. Urban land-use had a pronounced difference in species composition, evenness and diversity of earthworm communities. Forest land had the highest density, biomass and diversity of the earthworm communities. Total abundance was dominated by endogeic species in nursery land (70%) and abandoned land (80%), whereas in the forest land, the earthworm community comprised epigeic, endogeic and anecic species. Temporal changes in earthworm density and biomass were also significantly affected by land-use change. Total density and biomass of earthworms in the forest and nursery lands were highest in September, but highest in the abandoned land in October. The influence of soil physicochemical properties on the earthworm density and biomass also varied with land-use types. Soil temperature significantly affected earthworm density and biomass in the three land-use types. Soil pH was positively correlated with earthworm biomass in the forest land, but negatively associated with earthworm density in the abandoned land. Soil organic matter was positively correlated only with density and biomass of earthworms in the nursery and abandoned lands. Our results suggest that the species composition, abundance and biomass of earthworm communities can be determined by the modification of soil properties associated with urban land-use type.
A series of UV-curable fluorinated polycarbonate polyurethanes (FCPUAs) were synthesized by modifying polycarbonate polyurethane with 2-(perfluorohexyl)ethanol (PFHE) and glycidyl methacrylate (GMA). ...The structures of FCPUAs were analyzed with
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H NMR and FTIR. Different contents of FCPUAs were blended into non-fluorinated polycarbonate polyurethane as fluorinated additives. The water and oil contact angles of the films were investigated by contact angle measurement, and the results indicated that an extremely low concentration of FCPUAs could produce a highly hydrophobic and oleophobic coating. The X-ray photoelectron spectroscopic analysis showed that the coating surface was rich in fluorinated species. Besides, the films containing FCPUAs also had great tensile strength, hardness and adhesion.
This paper studies the effects of different combinations of scanning strategies between layers on the surface quality, tensile properties, and microstructure of samples in a laser beam powder bed ...fusion (L-PBF) formation experiment of Ti-6Al-4V titanium alloy. The purpose of this experiment was to improve the comprehensive performance of the piece by selecting the optimal combination of scanning strategies. The results show that the surface roughness of the L-PBF specimen was the lowest under the combination of the CHESS scanning strategy, reaching 14 μm. The surface hardness of the samples was generally higher with the LINE scanning strategy and the angle offset of 90°, reaching 409 HV. The overall density of the samples was higher under the combination of CHESS scanning strategies, reaching 99.88%. Among them, the CHESS&45° sample had the best comprehensive properties, with a density of 99.85%, a tensile strength of up to 1125 MPa, a yield strength of 912 MPa, and an elongation of 8.2%. The fractured form was a ductile fracture, with many dimple structures. Compared with the CHESS scanning strategy, the tensile properties of the CHESS&45° samples were improved by 12.8%. The microstructure of the L-PBF sample was mainly composed of the primary β phase and α’ martensite phase. The upper surface of the CHESS scanning strategy combination sample had a clear melt channel, and the distribution of each phase was uniform. A certain number of columnar β crystals were distributed in the longitudinal section of the sample, which was paralleled to the build direction. The columnar β crystals of CHESS&45° were relatively coarse, which enhanced the tensile properties of the sample.
This paper presents an in-depth study of the variable reference process to improve the organization and properties of selective laser melting TC4 specimens. A relationship equation between body ...energy density and stratification is proposed. This study aimed to look into how layer and volume energy density affect the surface, tensile characteristics, and microstructure of specimens. The test findings demonstrated that specimen densities rise as the power index falls, with the most excellent density reaching 99.42%. The number of secondary α’ phases declined as the energy density of the laminae slowed down. The tensile strength of these specimens reached 1190.84 MPa, and the yield strength came at 1103.87 MPa with the same interval of variable laser power. This offers a fresh avenue for research into SLM to enhance the specimens’ overall performance.
Using finite element analysis software and based on the Johnson–Cook failure criterion, a 3D printing workspace model with collapse, powder sticking, and cavity defects was established under the ...selective laser melting (SLM) forming process. The simulation analysis of milling holes was carried out, and the relationship between cutting speed and material-removal rate on tool wear and entrance burr was derived. The hole-milling experiment was carried out to verify the dimensional accuracy and surface appearance of the hole under the two processes of SLM direct forming and re-milling after forming; the inhibition effect of re-milling after forming on collapse, powder sticking, and cavity defects in hole forming were studied, and the formation mechanism of various defects such as burrs, scratches, and hole-wall cracks in the hole-milling process was analyzed. The Kistler9129A dynamometer was used to measure the cutting forces of re-milling holes and direct milling holes, and a comparative analysis was carried out. The influence of cutting speed, hole diameter, and material-removal rate on the axial force of milling holes was explored. The experiment results were consistent with the simulation cutting model, and the model’s accuracy was verified.
