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In order to find the variations of mechanical properties of millet stalk during dynamic cutting, a three-dimensional model of cutting parts and a double-layer flexible model of millet stalk were established in this study. The mechanical cutting properties of millet stalk at different cutting speeds and blade oblique angles were investigated based on ANSYS/LS-DYNA, while the verification tests were carried out based on the self-made cutting test bench. Simulation results showed that the maximum Von Mises stress was concentrated on the contact point of the stalk and the moving blade. The maximum Von Mises stress of stalk during extrusion, cutting, and after cutting were 60.03 MPa, 60.72 MPa, and 39.87 MPa, respectively, and the cutting energy of stalk epidermal tissue was greater than that of inner tissue. The cutting stress and the unit area cutting energy decreased first and changed steadily as cutting speed was increased when the cutting speed was 0.5-1.5 m/s. When the blade oblique angle was 0°-48°, the cutting stress decreased as the blade oblique angle was increased, while the unit area cutting energy decreased first and then increased. Verification tests showed that the cutting speed and the blade oblique angle had significant effects on the cutting mechanical properties (P < 0.05), which was consistent with the simulation test results. Research results can be used to optimize the cutting parameters of millet stalk

Honeycomb-like nitrogen-doped porous carbon (HNC) is prepared by using poly(2,6-diaminopyridine) as nitrogen-enriched precursor and silica as hard template. After carbonization and template removal, the obtained HNC possesses an interconnected 3D hierarchical porous structure and a nitrogen level up to 15.31 at.%. Owing to the hierarchical porous structure and abundant active sites in the carbon matrix, the HNC exhibits an excellent capacitive performance with a high specific capacitance of 398 F g−1 at a current density of 0.1 A g−1 and exceptional cycling stability (110.4% retention after 5000 cycles). This work provides a facile and efficient strategy for the large-scale production of nitrogen superdoped interconnected hierarchical carbon framework for high performance supercapacitors.

Carbonaceous material is considered as the most promising anode material for potassium ion batteries (KIBs) in the advantages of low price, stable physical/chemical properties, and renewable resources. However, the moderate capacity and sluggish kinetics cast a shadow over its application. Here, we synthesize multiple active sites decorated porous hollow carbon nanospheres (S/N-PHCs) by a one-step large scalable carbonization method with polypyrrole coated polystyrene and low-cost sulfur as precursors. The obtained S/N-PHCs exhibits an amorphous nanocarbon structure with high specific surface area (502.2 m2 g−1) and S, N content of 9.12 and 3.14 at.%, respectively. The porous hollow nanospheres structure promotes the fully utilization of multiple active sites and a capacitive-dominated K+ storage. Consequently, the S/N-PHCs electrode delivers an ultrahigh specific capacity of 460.6 mAh g−1 at a current density of 100 mA g−1 with an initial Coulombic efficiency of 67.7% and excellent rate capability of 228.1 mAh g−1 at 5000 mA g−1. Moreover, a high reversible capacity of 249.7 mAh g−1 can be retained over 1000 cycles at 1000 mA g−1 (83.4% of the initial specific capacity), demonstrating a remarkable cycle stability. This work provides a scalable and environmentally friendly strategy to achieve hierarchical amorphous carbon as superior anode for KIBs.

This paper develops a time-varying model for battery tabs based on the parametric excitation of Euler-Bernoulli beams. The instability caused by combination resonance under a high-frequency longitudinal load is considered. A Galerkin procedure is used to discretize the time-dependent problem into the Mathieu equation. The critical axial load is obtained from the transition curve of combination resonance. The effectiveness of the stability analysis was verified by numerical simulations involving longitudinal and bending loads.

Graphene oxide/amylose (GO/amylose) composite films with different amounts of graphene oxide (GO), glycerol and polyvinyl alcohol (PVA) were prepared by a solution casting method. The structure, morphologies, and properties of the films were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, UV–vis spectroscopy and tensile tests. The results indicated good dispersion of the GO nanosheets in the GO/amylose composite films and consequently a significant improvement in their mechanical properties. The addition of GO increased the tensile strength of the GO/amylose films, significantly. When glycerol was used as a plasticizer, the elongation at break of the films increased. When PVA was also added to the composite films, the films were mechanically strong and flexible. The incorporation of GO also decreased the moisture absorbability and UV transmittance of the films. The stability of the GO/amylose films in acidic and alkaline solutions was also studied and the films had excellent stability in both acidic and alkaline aqueous mediums.

Graphene oxide (GO) and reduced graphene oxide (RGO) foams were prepared using a unidirectional freeze-drying method. These porous carbon materials were characterized by thermal gravimetric analysis, differential scanning calorimetry, X-ray photoelectron spectroscopy and scanning electron microscopy. The adsorption behavior of the two kinds of foams for acetone was studied. The result showed that the saturated adsorption efficiency of the GO foams was over 100%, and was higher than that of RGO foams and other carbon materials.

Graphene oxide (GO) and reduced graphene oxide (RGO) 3D porous monoliths were prepared using a simple and green method, unidirectional freeze-drying method. Gold or silver nanoparticles were deposited on the GO nanosheets to form Au/GO and Ag/GO nanocomposites under the reducing action of GO without using any reducing agent or surfactant. The Au or Ag nanoparticles loaded GO 3D porous monoliths (Au/GO or Ag/GO 3D porous monoliths) prepared from Au/GO and Ag/GO nanocomposites by unidirectional freeze-drying method had an order (unidirectional) porous structure and high porosity. The Au/GO or Au/RGO 3D porous monoliths not only had high catalytic activity in the reduction of 4-nitrophenol and Suzuki–Miyaura coupling reaction, but also showed good recyclability.

Sodium alginate/graphene oxide (NaAlg/GO) fibers were prepared using a wet spinning method. Their structures and properties were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction and mechanical strength testing. The incorporation of GO significantly improved the strength of the NaAlg/GO fibers owing to the uniform distribution of the GO nanosheets in the NaAlg matrix. The maximum tensile strength and Young's modulus increased from 0.32 and 1.9 to 0.62 and 4.3 GPa, respectively, at 4 wt% GO loading. The composite fibers had an even higher strength when they were stretched. The tensile strength increased by 43% over the un-stretched fiber, and Young's modulus increased to 9.39 GPa. In aqueous solution, the GO/NaAlg fibers swelled to form hydrogel fibers that are nontoxic to cells which demonstrated the potential applications of the as-spun fibers in wound dressing materials.

Halloysite/potato starch composites were prepared by adding modified natural halloysite nanotubes into potato starch matrices to reenforce the mechanical properties of potato starch films. The halloysite/potato starch films were characterized by X-ray diffraction, scanning electron microscope and infrared spectrometry. Meanwhile, the mechanical properties and transparency of the films were studied. The results show that the modified halloysite nanotubes can be well distributed in the starch matrix and thus the tensile strength of the films was clearly enhanced. The flexibility of the films could be improved through adding glycerol although at the cost of reducing tensile strength. But incorporation of PVA could further improve the tensile strength of the halloysite/potato starch films.

The construction of inorganic bone fillers with a suitable degradation period to match the new bone growth is an urgent task since most bone fillers have an either too fast or slow degradation rate. Calcium sulfate, as a commonly used implanting material, shows good biocompatibility, biodegradability, osteoconductivity and mechanical properties. However, its degradation rate and the drug-release rate are too rapid to meet the requirements for clinical application. In this paper, calcium sulfate bead clusters (CSBC), with or without loaded drug, were prepared; and two kinds of coatings, porous or nonporous, were deposited on the surface of the beads to extend the degradation and the drug release period. The results show that poly(lactic acid-glycolic acid) (PLGA) coatings, incorporated with different porogens can form in situ porous coatings that obviously lengthen the degradation period of the beads from 30 days to around 60-90 days. Consequently, the drug-release rate was significantly reduced, and the release period increased from about 10 days to over 50 days.

Stable Bi2S3 colloidal nanocrystals with sphere or rod shape were synthesized through a "hot injection" method using organic molecules and macromolecules as ligands. The morphology of Bi2S3 nanocrystals is highly dependent on the experimental parameters, including the reaction temperature, reaction time, reactant ratio and ligands. Especially, adjusting the properties of ligands can lead to an obvious shape evolution of Bi2S3 nanocrystals. When polyvinylpyrrolidone is added as ligands before the reaction, a stable nanodot colloid is formed. While using polyvinylpyrrolidone and thioglycolic acid as mixed ligands benefits for the formation of Bi2S3 nanorods. The synthesized Bi2S3 nanorods were used as seeds in the second-step growing process to achieve a stable, shape and size controlled Bi2S3 nanocrystals. The Bi2S3 nanocrystals were characterized by XRD, UV-Vis and TEM.

Calcium sulfate (CaSO(4)), as a commonly used implanting material, shows good biocompatibility, biodegradability, osteoconductivity and mechanical properties. Studies about using CaSO(4) as bone filler for the treatment of bone defects are reported now and then, but the fabrication of injectable implant was hardly studied. In this study, calcium sulfate hemihydrate (CSH), as the basic material, was incorporated with a cellulose derivative, poly(ethylene glycol) (PEG), calcium sulfate dehydrate (CSD) crystal coated with PEG (P-CSD), and a certain amount of water to form injectable CaSO(4) bone fillers. The structure of the bone fillers with different compositions was analyzed with scanning electron microscopy (SEM), infrared spectroscopy (IR) and X-ray diffraction (XRD). The effects of additives such as P-CSD, CSD, PEG and cellulose derivative on setting time, water absorption ability, mechanical properties and structure of the injectable bone fillers were studied. The in vitro degradation test showed that the injectable bone fillers have appropriate degradation time in phosphate-buffered solution (PBS), and they can maintain integrity throughout the degradation process. In vitro cell culture and preliminary animal model experiments demonstrated that the bone fillers do not exhibit a deleterious effect on cell viability and can hasten bone growth in bone defect model.

Because of their poor rigidity, the deformation of thin-walled workpieces caused by cutting force in NC milling is the main factor that decreases machining precision and increases aeronautical product cost. The straight side walls of aluminum LY12CZ workpieces are machined on a vertical machining center THA5656 and their errors are analyzed. Based on orthogonal tests, the deformation characters of the thin-walled workpieces are discussed under different cutting conditions. The research can provide support for machining deformation control and machining simulation model verification.