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0-3 composites containing high permittivity ceramic particles and high breakdown strength polymer have aroused extensive concern for energy-storage application. In this research, flexible composite films were fabricated through incorporating of strontium titanate (SrTiO3) platelets (P-ST) and poly(vinylidene fluoride) (PVDF), and the effect of P-ST content on the dielectric and energy storage performances were researched systematically. It was found that at the relatively low electric field of 350 MV/m, the composite with 1 wt% P-ST exhibited an increased discharged energy density of 9.48 J/cm3, exceeding most of the current reports at the same electric field. And the distribution of local electric field and local polarization of composite films were simulated by COMSOL Multiphysics. This work provided a reference for polymer-based composite films featuring high energy storage property at relatively low applied electric field, which could reduce the possibility of failure for capacitors.

The natural aging (NA) behaviors within 24 h of 7050 (Al-Zn-Mg-Cu) and 5A90 (Al-Mg-Li) aluminum (Al) alloys are investigated comparatively. The strikingly different evolution rules of mechanical properties and microstructures of the above two materials are characterized using tensile strength tests and high-resolution transmission electron microscopy (HRTEM), then the mechanisms are revealed based on the analysis of differential scanning calorimetry (DSC) and the calculation of precipitation activation energy. It is found that the NA rate of 7050 Al alloy is pronounced in the initial stage (after quenching), and decreases dramatically from 0 h to 20 h of NA, resulting in remarkable evolution of the microstructures and mechanical properties. In contrary, 5A90 Al alloy is stable and the effect of NA is not evident. DSC analysis indicates that the activation energy of the initial precipitate (GP zones) for 7050 Al alloy is nearly 74.3 KJ/mol, while that of the initial precipitate ( δ' phase) for 5A90 Al alloy is nearly 103.6 KJ/mol. Owing to the low activation energy, acicular GP zones precipitate in the matrix of 7050 Al alloy within the first 4 h of NA, causing a dramatic increase in strength. The precipitates continue to grow with increasing aging time, albeit at a slower rate and with reduced influence on mechanical strength. Whereas, the strength of the 5A90 Al alloy remains hardly changed due to the higher activation energy. It is noted that, for 7050 Al alloy, the NA induced decreasing of the solute atomic concentration makes the initial remarkable Portevin-Le Chatelier (PLC) effect weaken gradually with aging time. While for the 5A90 Al alloy, the PLC effect remains little changed all the time since NA phenomenon does not occur in this alloy. It is recommended that the as-quenched 7050 Al alloys should be exposed at room temperature for more than 20 h or refrigerated before practical processing.

The flow stress and microstructure evolution of Ti–6Al–4V alloy with annealing treatment are identified. Isothermal tensile tests of material, obtained with the various volume fraction of β-phase, were performed at 870 °C and the strain rate of 10−3/s. Stress hardening was found in the titanium alloys with annealing treatment. Subsequently, the microstructures were investigated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Electron Back-scattered Diffraction (EBSD) observation. Annealing treatment has little effect on the dislocation density of titanium alloy before tensile tests. Contrary to the initial material, the volume fractions of β-phase are higher in alloys with β-annealing treatment and lower for α-annealing. Significant grain growth related to heat treatment is detected. Especially, the static recrystallization and grain elongation are observed in β-annealed titanium alloy. In addition, a physic constitutive model based on the microstructure evolution is established, and an effective optimization method is applied to determine the material constants. The calculated results indicate that the effect of grain growth due to annealing treatment can't be ignored, and the static recrystallization is also an important mechanism in grain refinement for β-annealed titanium alloy. Besides, grain boundary sliding is still the dominant deformation mechanism in the Ti–6Al–4V with annealing treatment.

Free bending technology is a new bending process for manufacturing freeform tube products. When manufacturing a complex spatial product, the variation of bending curvatures and torsions will accompany with a frequent changing of forming parameters, which will increase the manufacturing difficulties greatly. Until now, there is no effective way for determining the forming parameters of a complex spatial product precisely. In this paper, the characters of stable elements and unstable elements are analyzed. A mathematical collection is established for describing the geometrical characters of unstable elements. By using the new describing method, it is possible for establishing the relationship between the characteristics of unstable elements and forming parameters. And then a knowledge base can be built for storing the relationships. Based on these researches, a procedure for acquiring the forming parameters of a complex spatial tube product in free bending technology is proposed. The procedure can be described as follows: (1) use the known unstable elements in knowledge base to converge a complex spatial tube; (2) acquire its preforming parameters through the knowledge base; (3) compensate the motion of clamp to acquire the optimized forming parameters. The strategy is successfully applied on a typical spatial tube product and the final optimized forming parameters are exhibited.

A comprehensive geometrical behavior against the multicomponent nano-activating flux, multi-walled carbon nanotubes-titanium oxide (MWCNTs-TiO2), was configured in this study. The specimens were investigated for macro-morphologies of the weld seams, distortions, weld depths, and depth to thickness (D/T) ratios. The scrutinized behavior of distortions has reported a decremented effect for every step addition of flux. The traveling trends of vertical distortions individually started from 5.334, 6.146, and 6.455 mm for without flux and eventually ended to 3.896, 4.112, and 4.713 mm respectively up to 2 wt% of MWCNTs-TiO2. A similar beneficial effect on weld depths of flux addition observed from optical micrographs, which revealed the radiating radii of semi-circular profiles with increasing penetration. The centripetal Marangoni convection (change in surface tension) and constriction of tungsten inert gas (TIG) welding arc column found responsible mechanisms for significant uplifting of geometrical behavior. However, the extended drive phenomenon due to the presence of TiO2 created electrical resistance effect, which provokes constricted droplet melting mode of filler. The use of MWCNTs provided heterogeneous nucleation that freezes the weld penetration along with limiting the distortion, attributed to the enormous mismatch of coefficient of thermal expansion (CTE) with AA6061. The experimental results also revealed the better performance of flux at higher welding current (200A), which triggered D/T >1 (at 1.5 wt% and 2 wt% MWCNTs-TiO2) in contrast to 160A and 180A.

Poly(lactide-co-glycolide) (PLGA) sponge was filled with fibrin gel, bone marrow mesenchymal stem cells (BMSCs) and transforming growth factor-β1 (TGF-β1) to obtain a construct for cartilage restoration in vivo. The PLGA sponge lost its weight steadily in vitro, but degraded much faster in the construct of PLGA/fibrin gel/BMSCs implanted in the full-thickness cartilage defects. The in vivo degradation of the fibrin gel inside the construct was prolonged to 12 wk too. The CM-DiI labeled allogenic BMSCs were detectable after transplantation (implantation) into the defects for 12 wk by small animal in vivo fluorescence imaging and confocal laser scanning microscopy. In vivo repair experiments were firstly performed by implantation of the PLGA/fibrin gel/BMSCs and PLGA/BMSCs constructs into full-thickness cartilage defects (3 mm in diameter and 4 mm in depth) of New Zealand white rabbits for 12 wk. The defects implanted with the PLGA/fibrin gel/BMSCs constructs were filled with cartilage-like tissue containing collagen type II and glycosaminoglycans (GAGs), while those by the PLGA/BMSCs constructs were filled with fibrous-like tissues. To repair the defects of larger size (4 mm in diameter), addition of growth factors was mandatory as exemplified here by further loading of TGF-β1. Implantation of the PLGA/fibrin gel/BMSCs/TGF-β1 constructs into the full-thickness cartilage defects for 12 wk resulted in full restoration of the osteochondral tissue. The neo-cartilage integrated well with its surrounding cartilage and subchondral bone. Immunohistochemical and GAGs staining confirmed the similar distribution of collagen type II and GAGs in the regenerated cartilage as that of hyaline cartilage. The quantitative reverse transcription-polymerase chain reaction (qRT-PCR) revealed that the cartilage special genes were significantly up-regulated compared with those of the TGF-β1 absent constructs.