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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.

High-temperature dielectric composite films of all-organic PVDF/ABS were fabricated. The composites possessed excellent temperature stability. Ultrahigh Udischarged (11.42 J cm−2) and high efficiency (75.8%) at 100 °C were simultaneously achieved.

The activated slip system of Ti-6Al-4V alloy during the superplastic forming (SPF) was investigated by the in-grain misorientation axes analysis (IGMA), and the mechanisms of slip system activation have been discussed. Depending on the distribution of IGMA, one significant discovery from this study is that all the basal, prismatic, and pyramidal slip systems would be activated. Considering the effective slip systems, Schmid factors, and the Euler angles together, it is suggested that the dominant slip systems not only desired the largest Schmid factors but strongly demand continuous Schmid factors among the adjacent grains. Meanwhile, the estimated critical resolved shear stress (CRSS) on basal and prismatic at the temperature of 920 °C with the strain rate of 10−3 s is given. An original method of roughly estimating dominant slip systems with Euler angles has been introduced, which predicts that grain rotation may change the slip system. Furthermore, the crystal plasticity finite element method (CPFEM) is employed to simulate the evolution of Euler angles, and the grain orientation presents the largest set of significant clusters around the (1¯100) after deformation. Besides, the continuity of the Schmid factor assumption for the activated slip system has also been verified by CPFEM. In addition, the eigenvector corresponding to the eigenvalue λ1 = 1 of Euler angle rotation matrix is calculated to be aligned with the grain rotation axis, which can be applied to describe the grain rotation.

Purpose With the discussion on the linear relationship of determined material parameters, this study aims to propose a new method to analyze the deformation mechanism. Design/methodology/approach A modified constitutive model based on the hyperbolic sine Arrhenius equation has been established, which is applied to describe the flow behavior of Ti-6Al-4V alloy during the superplastic forming (SPF). Findings The modified constitutive model in this work has a good ability to describe the flow behavior for Ti-6Al-4V in SPF. Besides, a deformation map of titanium material is obtained based on the parameters. As the supplement, finite element models of high-temperature tensile tests are carried out as the application of the constitutive model. Originality/value The relationship between constitutive model parameters and forming mechanism is established, which is a new angle in rheological behavior research and constitutive model analysis.

A novel functionalized tannin-chitosan bentonite composite (TCBC) was successfully synthesized. The formation of the composite was confirmed by the X-ray diffraction (XRD) patterns and Fourier transform infrared spectroscopy (FT-IR) analysis. The pHpzc of TCBC was 3.38. The influences such as pH, dosage of TCBC, temperature and initial Cr(VI) concentration on adsorption capacity were investigated. The experimental data indicated that the almost saturated adsorption of the TCBC towards Cr(VI) in 100 min. The maximum adsorption capacity was 262.08 mg/g at 333 K with initial pH = 2.5. The adsorption kinetics of Cr(VI) on TCBC followed the pseudo-second-order kinetics model. The isothermal data were well described by the models of Langmuir, Freundlich and Temkin. The results revealed that the adsorption of Cr(VI) on TCBC existed comprehensive effects and mainly belong to the chemisorption. The TCBC could keep good performances (q e = 192.17 mg/g) in five runs, 1 M NaOH was used as eluent for desorption, which showed a high desorption efficiency. Studies showed TCBC prepared with low cost and green raw materials, and simple green preparation technology had high adsorption capacity, good reusability and acidic tolerance. By exploring the Cr(VI)-Cr(III) hybrid system, part of Cr(VI) was reduced to Cr(III) and adsorbed by TCBC. The optimal adsorption pH of Cr(III) was 5.0.

The flow behavior of Ti-6Al-4V alloy in superplastic forming (SPF) is studied, and a simple constitutive model is established based on the hyperbolic-sine equation. The constant strain rate high temperature tensile tests were performed at 890, 920, and 950℃, the selected strain rates are 10-2, 10-3, and 10-4/s. The calculation results of strain rate sensitivity index (m) indicates there are two dominant mechanisms of deformation: (i) grain boundary sliding (GBS) when the temperature is below 920℃ or strain rate is above 10-3/s; (ii) GBS and diffusion creep if the temperature is above 920℃ and strain rate is below 10-3/s. Besides, the higher temperatures or the lower strain rates, the smaller void volume fraction. The genetic algorithm (GA) is applied to optimize the parameters in the constitutive model, the average absolute relative error (AARE) between the prediction results and experimental data of stress is reduced from 11.10% to 5.52%. A new modeling method of strain compensation is provided, which is based on stress hardening and softening. The term K is introduced to describe the effects of strain on flow behavior in SPF, and a good agreement between the predicted results and experimental data can be obtained. In summary, the simple hyperbolic-sine constitutive model established in this work with parameter optimization can achieve high prediction accuracy.

Bending-twisting process can be used for manufacturing complex spatial tube products. To describe the relationship between the torsion of tube axis and the twisting angle, torsion adjustment index is introduced in existing literatures. However, a puzzling problem is that the torsion adjustment index varies nonlinearly in a large range. Until now, this phenomenon has not been explained properly. In this paper, three loading models are introduced to investigate the springback behavior of tube element in bending-twisting deformation, including synchronous loading model, asynchronous loading model, and multiple loading model. Equations are established to describe the relationship between torsion and twisting angle for the three loading models separately. By comparison, it is found that the relationships among bending radii, twisting angles, residual radii, and residual angles are only a little different for the three loading models above, while a distinguished relationship between torsion and twisting angle exists obviously. The multiple loading model is better for describing the inconformity between twisting angle and torsion in bending-twisting process. The executed work shows that the inconformity between twisting angle and torsion occurs before springback. There exists twisting deformation in feeding phase, but no torsion is generated. Twisting deformation in feeding phase only influences the torsion during springback. The enhanced twisting angle in bending phase is a key factor in torsion generation. The enhanced twisting angle can be influenced by the mobile die position and torque on clamp. Finally, the springback is also a factor in torsion variation.

This article focuses on the prediction of forming trajectory and process optimization during the forming process for the variable curvature tubes. Firstly, through cubic B-spline interpolation, the geometric characteristics of the axis of the target tube are obtained. An overall tube is "separated and then integrated", and the relationship between geometric parameters and processing parameters is established to obtain the initial process parameters. Based on the Extended Kalman Filter (EKF) algorithm, the motion model and observation model of tube forming using simulation are presented section by section, and the relevant calculation and analysis are carried out. The forming trajectory has been predicted and the processing parameters are optimized during the processing process, in which the effectiveness of the processing optimum scheme is illustrated.

Purpose When manufacturing an arc-shaped tube product using push bending process, the transition zone and outfeed zone will inevitably occur. Transition zone and outfeed zone are caused by the kinematical motion of mobile tools. The existence of transition zone and outfeed zone will lead to a big deviation between the forming product and desired shape. To improve the forming quality of arc-shaped products in push bending, the transition zone and outfeed zone are investigated in this paper. Design/methodology/approach A piecewise function is used to describe the bending characteristics along bending line, in which a series of vibration parameters are extracted and considered as control values. Findings The new strategy is helpful for finding the relationship between tools motion and curvature distribution and improving the bending lines design procedure in flexible push bending. Originality/value The new strategy is helpful for finding the relationship between tools motion and curvature distribution and improving the bending lines design procedure in flexible push bending.

During creep aging (CA), through-thickness heterogeneity and in-plane anisotropy in creep and mechanical properties affect the shape forming and performance tailoring. The specimens are first machined from the surface (t1), subsurface (t2) and center (t3) layers along the thickness direction of the 7050 Al alloy plate. Then in the rolling plane of each layer, the specimens are taken along the angles of 0° (L0), 45° (L45) and 90° (L90) to the rolling direction. After CA, the creep strain shows the trends of t1 > t2 > t3 along the thickness direction and L45 > L90 > L0 for in-plane directions, while the yield strength (YS) shows t1 > t3 > t2 and L90 > L0 > L45, respectively. Before CA, the low-angle grain boundaries (LAGBs) increase along the thickness direction, leading to a reduced creep strain. After CA, through-thickness heterogeneous LAGBs contributes to the above trend of YS. After L45 and L90 loading, S, Brass and Copper textures are obviously weaker than that under L0 loading, and show the largest equivalent Schmid factor (ESF) for L45 loading, and that for L0 and L90 conditions are approaching; while the equivalent slip system number (ESSN) shows L90 > L0 > L45. Both ESF and ESSN determine the in-plane anisotropy by affecting dislocation slip, but ESF plays a dominant role.

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.

An investigation of flow behavior and the deformation mechanism for Ti-6Al-4V alloy during the superplastic deformation process is presented in this paper. Constant strain rate tensile tests were performed at 890–950 °C and strain rates of 10−2, 10−3, and 10−4/s. Then, surface observation by Optical Microscope (OM), Scanning Electron Microscopy (SEM), and Electron Back-scattered Diffraction (EBSD) was applied to obtain the microstructure mechanism. With pole figure maps (PF) for α-phase, obvious texture gradually changed in the main deformation direction. For the titanium alloy, the evolution of texture in deformed samples was attributed to grain rotation (GR). Significant grain rearrangement occurred between grains after deformation. A complete grain rotation accommodated grain boundary sliding (GBS) deformation mechanism is proposed, which can explain texture evolution without grain deformation.

A physically based constitutive model with internal state variables (ISVs) is established, it is used to describe the flow stress and microstructure evolution of Ti–6Al–4V alloy in the superplastic forming (SPF). The ISVs in the constitutive model includes the dislocation density, grain size, and the volume fraction of dynamic recrystallization. The flow stress consists of σfd, σta, and σGB, which are related to forest dislocation, thermal activation, and grain boundary sliding (GBS), respectively. The material constants of the constitutive model are determined, and the genetic algorithm (GA) optimization. A modeling method path to optimize the flow stress model is established, which is on the basis of the errors between the predicted and experimental flow stresses. In the modified flow stress constitutive model, the grain rotation (GR) is applied as a hardening mechanism, and the void is treated as a softening mechanism. A new GR model is proposed to describe the flow stress which is related to the GR. The modified constitutive model can accurately predict the evolution of yield stress, grain size and flow stress in SPF. With the calculation results of the multi-scales constitutive model, the mechanism of Ti–6Al–4V in SPF is discussed, and a new deformation map with dominant mechanisms for Ti–6Al–4V is obtained.

In order to capture the directed relationship between nodes more accurately, this paper proposed a novel network embedding model called BDNE. The model adds the bi-directional distance while preserving the co-occurrence frequency of the nodes within a context window, which is of great significance in some applications of social networks, such as public opinion monitoring and control, and group discovery. Experimental results show that the embedding results of our model as features in the node classification task are better than DeepWalk, Node2Vector and Line on real data sets of different types and sizes.

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.

Combination of gene therapy with tissue engineering can enhance the interplay between cells and matrix, leading to better restoration and regeneration of tissues and organs in vivo. In this study the PLGA/fibrin gel hybrids were employed to load lipofectamine/pDNA-TGF-β1 complexes and mesenchymal stem cells (MSCs) (experimental group), acting as a cartilage-mimetic tissue platform. The gene complexes distributed more evenly in the hybrid scaffolds, whereas they adhered onto the pore walls of the PLGA sponges. The filled fibrin gel rendered gene release in a slower manner, too. Moreover, the fibrin gel entrapped MSCs and contributed to a higher cell loading density in the hybrid constructs. In vivo assay showed that in the defects implanted with the experimental constructs both gene and protein expression levels of TGF-β1 were significantly higher than those of the fibrin-free group at weeks 1, 3, and 6 after surgery. The full articular cartilage defects repaired by the experimental group for 12 w were resurfaced by neo-tissues with a similar thickness, cell arrangement, and color to the normal neighboring cartilage and abundant glycosaminoglycans.

The poly(lactide-co-glycolide) (PLGA, LA/GA 75/25) sponges with different weight average molecular weights (Mw 52, 122, and 177 kDa) were fabricated and were used to build the constructs of PLGA/fibrin gel/mesenchymal stem cells (MSCs)/transforming growth factor-β1 (TGF-β1). The PLGA 177 with the highest Mw (177 kDa) had the fastest degradation rate at the initial stage, whereas the PLGA 122 had the moderate degradation rate and smallest mass loss. After implantation in rabbit knees for 12 weeks, the full-thickness defects (both cartilage and subchondral bone were destroyed with a diameter and depth of 4 mm) repaired by the PLGA 122 group had formed a hyaline cartilage-like tissue with abundant glycosaminoglycans on the top layer and subchondral bone on the bottom layer. The group also achieved the best macroscopic (11.3 ± 0.8) and histological scoring (Wakitani, 0.5 ± 0.6). To unveil the mechanism of the cartilage repair outcome and the PLGA degradation behaviors, the chondrogenesis-related genes, inflammatory cytokines, and matrix metalloproteinase (MMP) activity were analyzed by quantitative reverse transcription-polymerase chain reaction at week 1, 3, and 6 postsurgery. At each time point, the regenerated tissues by the PLGA 122 group had the highest mRNA expression of SOX9 and collagen type II, but the smallest mRNA expression of interleukin-1β and tumor necrosis factor α, and MMP-13 and MMP-3. In summary, as a scaffolding matrix, the PLGA with different Mw shows a huge difference in cartilage regeneration in vivo. The one with a moderate Mw (122 kDa) causes the weakest inflammatory response and results in the best cartilage regeneration.

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.

This work provides a comprehensive investigation of multi-walled carbon nanotubes (MWCNTs) inducement in weldment and their apparent effect on the microstructure, %elongation and ultimate fracture behavior of Al-Mg-Si alloy referring modified tungsten inert gas (TIG) welding joints. Serious experimental work is carried out at 1 wt%, 1.5 wt%, and 2 wt% of MWCNTs to provide a gradually increasing heterogeneous nucleation. The behavior of grain morphology showed the pure field of epitaxial growth without MWCNTs, and the forestry type morphology for 1 wt% MWCNTs at low welding currents (160 A), though there was a noticeable conversion into equiaxed (EQZ) grains filled with inter-dendritic particles at high welding currents (180 A and 200 A) for 1.5 wt% and 2 wt% of MWCNTs. Moreover, the formation of a cellular type network above the fusion line predominated initially at all parameters. Conversely, fine EQZ grains were formed as they moved upward into the welded zone (WZ) explicitly at a high heat input. A conceptual pictorial model is presented in the study which summarized the behavior of morphological changes at the utilized parameters. The welded joints have demonstrated an increasing trend of strength and %elongation in contrast to joints without added MWCNTs. Comparative results have shown an exceptional increment of 71 to 76% and 67 to 75% of elongation up to ultimate tensile strength (UTS), and a fracture point that was clinched for 1 wt% and 1.5 wt% MWCNTs at 180A. From macro to micro-examination of the fracture surfaces, pure ductile modes constituting elliptical cup and cone type isotropic flow was evident in all specimens. Detailed confirmation of the pull-out fracture mode of MWCNTs has highlighted in the scanning electron microscope (SEM) images that intimated a methodical contribution in load-transfer from matrix to the fiber under axial load. Overall, a concise en-route for MWCNTs inducement is well-appointed through tube fillers along with an activating facilitator (TiO2) in contrast to stereotype fillers for improved behavior termed as modified TIG welding joint process in study.

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.

A poly (lactide-co-glycolide) (PLGA) scaffold filled with fibrin gel, mesenchymal stem cells (MSCs) and poly(ethylene oxide)-b-poly (L-lysine) (PEO-b-PLL)/pDNA-TGF-β1 complexes was fabricated and applied in vivo for synchronized regeneration of cartilage and subchondral bone. The PEO-b-PLL/pDNA-TGF-β1 complexes could transfect MSCs in vitro to produce TGF-β1 in situ and up regulate the expression of chondrogenesis-related genes in the construct. The expression of heterogeneous TGF-β1 in vivo declined along with the prolongation of implantation time, and lasted for 3 and 6 weeks in the mRNA and protein levels, respectively. The constructs (Experimental group) of PLGA/fibrin gel/MSCs/(PEO-b-PLL/pDNA-TGF-β1 complexes) were implanted into the osteochondral defects of rabbits to restore the functional cartilages, with gene-absent constructs as the Control. After 12 weeks, the Experimental group regenerated the neo-cartilage and subchondral bone with abundant deposition of glycosaminoglycans (GAGs) and type II collagen. The regenerated tissues had good integration with the host tissues too. By contrast, the defects were only partially repaired by the Control constructs. qRT-PCR results demonstrated that expression of the chondrogenesis-marker genes in the Experimental group was significantly higher than that of the Control group, and was very close to that of the normal cartilage tissue. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A: 3097–3108, 2013.