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This article presents a new multiscale modeling approach proposed to predict the impact response of a biomedical niobium–zirconium alloy by incorporating both geometric and microstructural aspects. Specifically, the roles of both anisotropy and geometry-based distribution of stresses and strains upon loading were successfully taken into account by incorporating a proper multiaxial material flow rule obtained from crystal plasticity simulations into the finite element (FE) analysis. The simulation results demonstrate that the current approach, which defines a hardening rule based on the location-dependent equivalent stresses and strains, yields more reliable results as compared with the classical FE approach, where the hardening rule is based on the experimental uniaxial deformation response of the material. This emphasizes the need for proper coupling of crystal plasticity and FE analysis for the sake of reliable predictions, and the approach presented herein constitutes an efficient guideline for the design process of dental and orthopedic implants that are subject to impact loading in service.
The aim of this study is to assess the time-dependent mechanical properties of rat femoral cortical bone in a lifespan model from growth to senescence. New nanoindentation protocol was performed to assess the time-dependent mechanical behavior. The experimental data were fitted with an elastic–viscoelastic–plastic–viscoplastic mechanical model allowing the calculus of the mechanical properties. Variation of mechanical response of bone as a function of the strain rate and age were highlighted. The most representative variations of the mechanical properties with age were found to be statistically significant (P < 0.001) from 1 to 4 months for elastic properties, from 1 to 9 months for viscoelastic properties and during all lifespan for plastic and viscoplastic properties, highlighting different maturation ages for elastic, viscoelastic, plastic and viscoplastic behaviors. These results suggest that different physical–chemical and structural processes occur at different ages reflecting bone modeling and remodeling activities in the rat's whole lifespan.
Multilayer stereo micro/nanometer-sized porous surface structures were prepared by selective chemical etching of biphasic calcium phosphate (BCP) scaffolds with hydroxyapatite (HAP)/β-tricalcium phosphate (β-TCP) weight ratios of 90/10, 80/20, 70/30, 60/40, and 50/50 in phosphoric acid solution. The porous surface structures revealed periodic fluctuations in the observed heights of micro/nanometer-sized needles. And the average height increased from 0.59 ± 0.02 to 12.09 ± 0.03 μm when the β-TCP content in BCP scaffolds rose from 10 to 50%. In vivo cell tests using MG-63 cells (belonging to the human osteosarcoma cell line) revealed that micro/nanometer-sized pores on the scaffold surface could provide location for cell adhesion and migration and facilitate the formation of gap junction between cells. The BCP scaffold with 40% β-TCP exhibited the optimal surface structure for cell seeding and growth due to the largest number of micro/nanometer-sized pores on the surface. However, excessive β-TCP led to the damage of micro/nanometer-sized porous surface structure, which further impeded the cell interaction.
A novel thermosensitive core/shell microgel with carbon microspheres (CMSs) cores was prepared by three steps. First, oxidized-carbon microspheres were obtained by mixed-acid oxidization. Second, the silane agent of 3-(trimethoxysilyl)-propyl methacrylate was used to functionalize the oxidized-carbon microspheres so as to generate the vinyl groups on the microspheres. Thereafter, the as-synthesized particles were used as seeds in the precipitation polymerization of N-isopropylacrylamide to introduce a thermosensitive polymer microgel shell onto the surfaces of the silanized-CMSs in the presence of an initiator and a crosslinker. The morphology and thermosensitive properties of the composite microspheres were characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transformation infrared spectroscopy, thermogravimetry, and dynamic light scattering. Results indicate that the thickness of polymer layer could be adjusted by the crosslinking agent's concentration. The composite microgels had a low critical solution temperature at about 30 °C and exhibited strong thermosensitivity. The controlled release of a drug molecule (a model drug, acetosalicylic acid) was also investigated.
The infrared emissivity properties of carbon fibers with different treatments were investigated in the wave length range 6–15 μm from 1273 to 1873 K. The heat treatment affected the infrared emissivity of carbon fibers through the microstructure evolution. The Raman investigation about the microstructure indicated that the increase of the graphitization degree in carbon fibers degenerated the infrared emissivity of carbon fibers, especially under high temperatures. For the coated carbon fibers, the infrared emissivity properties were decreased for carbon fibers coated pyrolytic carbon (PyC) due to the lamellar structure of PyC and increased for carbon fibers deposited carbon nanotubes (CNTs) owing to the skeleton-like structure of CNTs. The study also illustrated that the PyC coating thickness from 0.5 to 1.0 μm had few effects on the infrared emissivity properties of carbon fibers.
Nearly dense and almost single-phase bulk (Cr1–xVx)2AlC (x = 0, 0.25, 0.5, 0.75, and 1.0) ceramics were successfully fabricated by in situ hot-pressing method using Cr, V, Al, and C powders as raw materials. A possible synthesis mechanism was proposed to explain the formation of (Cr1–xVx)2AlC solid solutions. The lattice parameters, microstructure, and mechanical properties of the (Cr1–xVx)2AlC ceramics were investigated in detail. The results indicated that the lattice parameters increased with the substitution of Cr by V and the aspect ratio of the grain changed from 1.4 to 3.2. The dependence of the mechanical properties on the V content was a single-peak type. The (Cr0.5V0.5)2AlC ceramic possessed the optimal mechanical performance and its Vickers hardness, flexural strength, and fracture toughness reached the maximum values of 5.18 GPa, 402 MPa, 5.91 MPa m1/2, respectively, due to the solid solution effect. The energy-consuming mechanisms of the material were also discussed.
SnZn(OH)6 (ZHS) hollow cubes were synthesized by a facile self-templated method at room temperature, and Ag/AgCl/ZHS particles were prepared by a photodepositing method. The crystalline structure and morphology of the prepared particles were characterized by x-ray diffraction, UV-vis diffuse reflectance spectroscopy, scanning electron microscopy, and N2 adsorption. The results indicated that the particles had almost uniform monoclinic geometry and size. The photocatalytic oxidation of Rhodamine B was used to evaluate the photocatalytic activity of the synthesized photocatalysts. It is found that the hollow Ag/AgCl/ZHS showed the highest catalytic performance under visible or UV light, which can be attributed to the synergetic effect of Ag, AgCl, and ZHS.
In this paper, we report the structural, electrical, and magnetic properties of polycrystalline La0.85–xSmxNa0.15MnO3 (x = 0.05, 0.1, 0.15) manganites. Rietveld refinement of x-ray data infers that doped manganite compounds possess a rhombohedrally distorted structure (space group $R\bar 3C$). Both lattice parameter and unit cell volume decrease and a systematic change in both Mn–O–Mn bond angle and tolerance factor is observed with Sm content. Resistivity measurements discern metal–insulator transition (TP). For x = 0.15 sample, a double metal–insulator transition with a single ferromagnetic transition is depicted. All samples exhibit extrinsic magnetoresistance (MR) effect. A large value of MR of 65% (253 K, 8 T) is associated with grain and grain boundary formation. The highest low-field MR of 23% (12 K, 2 T) and 35.2% (23 K, 2 T) for x = 0.05 and 0.1 is observed. The electronic and magnetic inhomogeneities induced by Sm and nonmagnetic metal Na phases account for MR properties.
A simple hydrothermal route to the eulytite phase of bismuth germanium oxide (E-BGO: Bi4(GeO4)3) that required no post-processing has been developed. The E-BGO material was isolated from a mixture of bismuth nitrate pentahydrate and a slight excess of germanium oxide in water under hydrothermal conditions (185 °C for 24 h). The resultant materials were characterized by powder x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and luminescence measurements to verify the particle's phase (eulytite), morphology, size, and response to a variety of excitation energy sources, respectively. Photoluminescence spectroscopic response from E-BGO pellets indicated that the samples exhibited a strong emission peak consistent with an x-ray induced luminescence of a E-BGO single crystal (500 nm excited at 285 nm). Cathodoluminescent properties of the E-BGO displayed a broadband spectrum with a maximum at 487 nm. The growth process was consistent with a standard Oswald ripening and LaMer growth processes.
The mechanical and thermal behavior of nanoglasses (NGs) were studied with a focus on the effect of the microstructure. The thermal expansion was measured to track changes in excess free volume during heating. It was found that the excess free volume, which is initially more dominant in the interphase region between the denser amorphous particles, is partially lost as well as redistributed during annealing. This relaxation during heating causes the nanoglass to behave like a melt-spun ribbon after heating while remaining amorphous. Nanomechanical tests were used to probe the local incipient plasticity and the influence of the interphase region. This interphase appears to affect the mechanical response of the NGs by inhibiting the propagation of shear bands and thus offers a novel approach for the introduction of plasticity in bulk metallic glasses. The results suggest that the NGs consist of two distinct amorphous phases with different glass transition temperatures.
It is widely accepted that oxygen will severely deteriorate the glass-forming ability (GFA) of an alloy. In this work, we report that the GFA of a Fe76Si9B10P5 glassy alloy can be significantly improved (the critical diameter for fully glass formation is increased from 1 to 3 mm) under oxygen casting atmosphere. Furthermore, the pressure of oxygen atmosphere gives an obvious enhancement in the critical diameter of Fe76Si9B10P5 glassy alloy. A dependence of GFA on casting atmosphere species (argon, nitrogen, air, and oxygen) is also observed for this glassy alloy, and its critical diameter is 1, 1.5, 2.5, and 3 mm, respectively. In addition, the Fe-based glassy alloy exhibits excellent soft magnetic properties regardless of the applied casting atmosphere. The mechanism for such an unusual oxygen effect on the GFA of Fe76Si9B10P5 glassy alloy is attributed to the reduced nucleation rate caused by the enhancement of surface tension of the alloy melt.
Al6061 and AZ31 plates were processed using accumulative roll bonding (ARB) method up to two passes to produce laminated composites. The sandwich stacks of Al6061/AZ31/Al6061 were held at 450 °C for 10 min in a cubical furnace and rolled together with reduction of 50% in one pass. The microstructural investigations were done using optical and scanning electron microscopes. The structures of the interface, mechanical and drop impact properties of the laminated composites after the first and second passes were investigated and compared with Al6061 and AZ31 alloy plates. It was found that Al6061 improved the elongation to failure property of AZ31 after the first pass of ARB process and the drop impact properties of AZ31 after the first and second passes. However, elongation to failure magnitude with the uniaxial tensile loading decreased with increase in the number of passes due to the formation of brittle intermetallic between the Al6061/AZ31 nonuniform interfaces.