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The flow behavior and microstructure evolution of a near α titanium alloy with nonuniform microstructure during hot deformation were studied by isothermal compression test and electron backscatter diffraction technique. It is found that the nonuniform microstructure prior to deformation consists of equiaxed α, lamellar α in the colony form and β phase, and the α colony keeps the Burgers orientation relationship with β phase. The flow stress of nonuniform microstructure exhibits significant flow softening after reaching the peak stress at a low strain, which is similar to the lamellar microstructure. Nevertheless, the existence of equiaxed α in nonuniform microstructure makes its flow stress and softening rate be lower than the lamellar microstructure. During deformation, the lamellar α undertakes most of the deformation and turns to be rotated, bended and globularized. Moreover, these phenomena exhibit significant heterogeneity due to the orientation dependence of the deformation of lamellar α. The continuous dynamic recrystallization and bending of lamellar α lead to the “fragmentation” during globularization of lamellar α. The bending of lamellar α is speculated as a form of plastic buckling, because the bending of lamellar α almost proceed in the manner of “rigid rotation” and presents opposite bending directions for the adjacent colonies.

Insulin injection is a definitive therapy for diabetic patients, but mismatched dosage and untimely intervention lead to wide fluctuations in blood sugar levels. Therefore it is essential to combine exogenous insulin and intelligent carriers, which is promising to normalize glucose concentrations. The temperature and glucose dual-responsive materials bearing poly(N-isopropylacrylamide) (PNIPAAm) and phenylboronic acid (PBA) have been confirmed for insulin-controlled release in experimental stages. The recent progress on different types of smart PNIPAAm and PBA-containing carriers is summarized in this review. The new challenges and future direction regarding the studies on elaborate insulin-controlled-release systems are also proposed.

Predicting and controlling the forming defects in transitional region are two key problems needed to be solved in the isothermal local loading forming of Ti-alloy rib-web component. To this end, the authors have conducted systematic works, which are reviewed here. First, according to the structural features of large-scale rib-web component, the finite element (FE) model of transitional region was established and validated by physical experiment. Then, the material flow and deformation inhomogeneity of transitional region are quantitatively studied by the FE model. In addition, the formation mechanisms of forming defects were revealed. Subsequently, an adaptive folding index was proposed to measure the severity of folding defect, based on which a quick prediction model of the folding defect was developed. Finally, the forming limit considering the forming defects in transitional region was determined by the stepwise searching method combined with the defect prediction model.

In order to establish the constitutive model to predict deformation behavior during quenching process, uniaxial tension behaviors of an as-quenched AA2219 sheet were investigated over a wide temperature range (298-773K) at different strain rates (0.001-1s-1) in quasi-static regime. The experimental results show that the flow stress is closely related to temperature and strain rate. The material exhibits negative strain rate sensitivity (SRS) that the flow stress decreases with increase of strain rate below a critical temperature of Tc. A model established by Kabirian et al. (Kabirian, F., Khan, A.S., Pandey, A. Int. J. Plast. 2014, 55) based on the KHL model considering the negative to positive SRS shows successful prediction of the flow stress in a temperature range of 296-473K. However, at higher temperatures (473-773K) the measured SRS deviates from the calculated values of Sigmoidal function given by Kabirianet al. with the increase of temperature. Therefore, in this paper, based on an extended Sigmoidal function and a proposed relation between flow stress and the coupling effects of strain and temperature, a modified Johnson-Cook model is proposed to describe the quasi-static stress-strain responses over a wider temperature range. Correlations using the modified model show good agreement with the experimental results.

It is critical to precisely control the tri-modal microstructure during the isothermal local loading forming of titanium alloy to obtain high-performance components. To this end, the effect of local loading processing parameters on the development of tri-modal microstructure were experimentally investigated. The key influence factors and laws are revealed as follows. In the first loading step, the deformation temperature plays a decisive role in the volume fraction of equiaxed α, which decreases with the increase of temperature. While, the deformation amount and cooling mode present little effects on the microstructure evolution. In the second loading step, the deformation temperature and amount mainly influence the volume fraction, spatial orientation distribution and globularization of lamellar α. The volume fraction of lamellar α increases with the temperature decreasing. The spatial orientation distribution of lamellar α gradually changes from homogeneous distribution to concentrated distribution with the increase of deformation amount. Besides, the dynamic globularization fraction of lamellar α producing in the second loading step increases with the deformation amount, and their relationship can be well fitted by Avrami type equation. Moreover, higher temperature in the second loading step is beneficial to decrease the critical strain for the initiation of dynamic globularization and promote the kinetic rate of dynamic globularization. On the other hand, the deformation amount of the second loading step has after-effects on the static globularization of lamellar α in the annealing treatment. If the deformation amount exceeded the critical strain for the initiation of dynamic globularization, the static globularization of lamellar α would produce in the annealing, and the static globularization fraction increases with the deformation amount of the second loading step.

Volume fraction of primary alpha is an important microstructure feature and can be changed by controlling its diffusive growth during heat treatment of two-phase Ti-alloys. A model for predicting its growth is urgently needed to realize microstructure control. Classical diffusion model based on additivity rule causes a significant underestimation of volume fraction of primary alpha phase. In present work, a diffusion-controlled growth model is developed to predict the evolution of phase fraction with temperature in the finite beta matrix, by solving the 3-dimensional diffusion equation with moving boundary conditions. By introducing a thermal history-related function and considering soft impingement, the prediction precision of present model is improved notably. Moreover, by considering the effect of secondary alpha precipitation on the far-field matrix composition and thus matrix supersaturation, the maximum error is almost one third of that by classical diffusion model when applied to TA15 and Ti-6Al-4V alloys. The results show that the volume fraction of primary alpha phase is overestimated in the later stage due to the effect of secondary alpha which is not captured by classical model. Combining the calculated length of diffusion field with metallographic analysis, the present model slightly underestimates the volume fraction of primary alpha in the initial stage due to the overestimation of soft impingement.

A near isothermal forming technique was proposed to manufacture titanium alloy component, aiming to save the cost and obtain specific microstructure. In the near isothermal forming, the dies are heated to a temperature about 150℃ lower than that of workpiece. The relative low die temperature increases the die strength and decreases the hot corrosion of die. Meanwhile, the workpiece can be formed without significant die chilling and the tri-modal structure can be obtained by the coupling of deformation and phase transformation in non-isothermal forming. To obtain the objective microstructure, an analog experiment was carried out to investigate the effect of deformation parameters in the near-β phase field on microstructure morphology in the controlled cooling process. The evolution about phase volume fraction of primary and secondary alpha phase is obtained by quantitative metallographic analysis during cooling following hot deformation. The results show that the microstructure morphology can be changed by control the strain rate and thermal path. This will provide guidance for microstructure optimization in the near isothermal forging of titanium alloy large-scale integral components.

Poly(N-isopropylacrylamide) (PNIPAAm) is a typical thermoresponsive polymer used widely and studied deeply in smart materials, which is attractive and valuable owing to its reversible and remote “on–off” behavior adjusted by temperature variation. PNIPAAm usually exhibits opposite solubility or wettability across lower critical solution temperature (LCST), and it is readily functionalized making it available in extensive applications. Cell culture is one of the most prospective and representative applications. Active attachment and spontaneous detachment of targeted cells are easily tunable by surface wettability changes and volume phase transitions of PNIPAAm modified substrates with respect to ambient temperature. The thermoresponsive culture platforms and matching thermal-liftoff method can effectively substitute for the traditional cell harvesting ways like enzymatic hydrolysis and mechanical scraping, and will improve the stable and high quality of recovered cells. Therefore, the establishment and detection on PNIPAAm based culture systems are of particular importance. This review covers the important developments and recommendations for future work of the preparation and characterization of temperature-responsive substrates based on PNIPAAm and analogues for cell culture applications.

A highly sensitive, specific and simple LC-MS/MS method for quantification of capmatinib (INC280) in rat plasma was presented. The LC-MS/MS method was validated in terms of specificity and selectivity, linearity, accuracy and precision, matrix effect, extraction recovery, dilution integrity, carryover and stability as per the US Food and Drug Administration's bioanalytical method validation guideline. The validated assay was applied for quantification of capmatinib from a pharmacokinetic study in rats following oral administration at the doses of 1.0, 3.0 and 9.0 mg/kg. The calibration curve ranges from 1 to 2000 ng/ml with desirable linearity and r2 > 0.99. The intra- and inter-batch accuracies were within 99.24-103.59 and 97.76-102.83% with coefficients of variation 5.08-7.36 and 3.18-4.99%, respectively. No significant interference was observed by endogenous peak at the retention time of capmatinib and IS. The assay was free from any matrix effect and showed precise recovery across the calibration curve range, and samples were stable under all experimental conditions. The validated assay was successfully applied to analyze plasma samples of pharmacokinetic study in rat to determine the concentration of capmatinib. In summary, a novel method for analyzing capmatinib in rat plasma has been successfully validated and is now being utilized for quantification of capmatinib from pre-clinical studies.

Strain localization, a cross-scale issue degrading homogeneity and formability during hot working of TA15 titanium alloy, is complicated by lamellar microstructure for hierarchical feature, spatial morphology, and orientation relationship. In this work, by taking advantage of hat-shaped specimens to maintain deformation mode, the effect of heterogeneous lamellar microstructure on strain localization is accessible and visualized by cross-section comparison enlightened by cake cutting. Moreover, the evolution behavior and mechanism are also investigated by the two-scale crystal plasticity model. The mechanism of strain localization during hot working of lamellar microstructure is re-recognized as the structural softening governed by an abrupt phase interface weakening and continuous geometrical softening. The driving force of strain localization is the ‘collapse’ of the stress gradient between constituent phases intensified by the progression of compelled uniformed deformation. The key to microstructure-dependent strain localization is the influence of lamellar orientation on germination and colony interface on intensification. Colonies with lamellar orientation deviated 45 o from the direction of maximum shear stress are endowed with the intrinsic potential of strain localization. Large-size and strongly-orientated colony interfaces intensify strain localization. These findings provide new insights into microstructure-dependent strain localization supporting a more efficient design of processing routing to control localization powerfully.

The correlation between lamellar globularization and deformation modes during the primary hot processing of titanium alloy was evaluated by means of uniaxial compression, tension, torsion and plane strain compression tests. The microstructure evolution features and underlying globularization mechanisms were comparatively studied via Electron Backscattered Diffraction technique. Noticeable divergences of globularization response are captured in different deformation modes, especially for the globularized fractions and the critical strain. In the face of the strain applied is less than the critical globularization value (0.4−0.63) under uniaxial compression, the lamellae can be still globularized under tension or torsion deformation. But the growth rate of globularized fraction is more sluggish under tension than that under torsion deformation. The lamellae separation at early tension deformation preferentially occurs at junctions of lamellae without destroying Burgers Orientation relationship and significant orientation fluctuation. Shear deformation can facilitate the formation of intra-α boundaries and its distribution uniformity, which could make the lamellae grow up into globularized particles and improve the globularization heterogeneity. It is envisaged that the results obtained can provide guidance for the technology scheme and route design of primary hot working of titanium alloy aiming at the homogeneous equiaxed grains.

Uniaxial compression is widely employed to investigate the constitutive behavior and microstructural developments of metallic materials at elevated temperatures. However, the heat exchange between work-piece and anvils leads to temperature gradient and inhomogeneous deformation within the work-piece, which weakens the reliability of the testing method. The problem is more serious for titanium alloys due to the poor thermal conductivity and high sensitivity of deformation resistance on temperature. To quantify the effect of temperature gradient, a coupled thermo-electric-mechanical FE model is developed for hot compression of TA15 titanium alloy with a Gleeble thermal simulator. The precise temperature control is achieved via a negative feedback control algorithm. It is found that the temperature gradient prior to deformation is sensitive to the electrical contact conductance between specimen and anvils as well as the heat transfer between the anvil and anvil base. Bulging is sensitive to temperature gradient rather than interfacial friction. The measured flow stress is smaller than the true value at large strain for the titanium alloy, which is contrary to conventional perception. Thus, the traditional flow stress correction method degrades the accuracy of flow stress measurement. A correction procedure is developed based on inverse analysis of the FE simulation. The results can reduce the systematic error of flow stress measurement of titanium alloys with Gleeble system.

The large temperature gradient resulted from rapid heat dissipation and a long process period in the hot deformation of aluminum alloy causes complex microstructure evolutions. Accurate constitutive models describing the evolution of the microstructures over a wide temperature range are acquired. Thus, a physically-based continuous dynamic recrystallization constitutive model combined with grain fragmentation and subgrain rotation was established in this investigation. Uniaxial hot compression tests for aluminum alloy 2219 were conducted at temperatures of 250 °C–450 °C and the evolution of microstructures were analyzed via metallographic technique. Then internal state variables were proposed to describe the migration of grain boundary, dislocation density, average grain boundary misorientation, and subgrain/grain size. The net torque on the grain is introduced to precisely describe the progressive subgrain rotation mechanism. Moreover, geometrically necessary dislocations are considered to reasonably simulate the rise in flow stress associated with grain fragmentation. The results show that continuous dynamic recrystallization (CDRX) and dynamic recovery are the main softening mechanisms. The CDRX mechanism is gradually changed from grain fragmentation to subgrain rotation due to the increase in temperature. The new constitutive model may precisely predict the flow stresses, subgrain/grain size, and average misorientation in the wide temperature range. Comparing with the existing continuous dynamic recrystallization model which only considers subgrain rotation, the overestimate of the grain size in the low-temperature range is avoided in the new constitutive model. Furthermore, the contributions of the grain fragmentation to the increase in strain hardening can reasonably be covered.

The hot compressions in (α + β) region were conducted on β wrought TA15 titanium alloy, so as to investigate the effect of β working on the flow behavior and dynamic globularization of lamellar microstructure. The results indicated that initial β grain size had no significant influence on flow stress. The dynamic globularization rate of α laths in smaller β grains was higher due to the difference in lamellar length. β predeformation would decrease the flow stress of (α + β) deformation. Most of α laths in the microstructure after β predeformation were short with a geometric orientation vertical to β grain boundary and rotated together during compression, which would promote the formation of α/α substructures, thus highly enhanced the dynamic globularization rate of α laths. While β heat treated microstructure had long α lamellae with a random orientation, which tended to become kinked first and then break up into short ones, resulting in the delay of dynamic globularization. In addition, prior β deformation changed the initial α phase texture and dynamic globularization rate would be affected by strain path. When the compressive direction in (α + β) region was vertical to that of β predeformation, the globularized fraction of α lamellae was apparently high. Keywords: TA15 titanium alloy, β working, (α + β) deformation, Flow behavior, Dynamic globularization

The conventional Kalman filter (KF) which uses the current measurement to estimate the current state is a posterior estimation. KF is identified as the optimal estimation in linear models with Gaussian noise. However, the performance of KF with incomplete information may be degraded or diverged. In order to improve the performance of KF, an Amended KF (AKF) is proposed by using more posterior measurements. The principle, derivation and recursive process of AKF are presented. The differences among Kalman smoother, adaptive fading method and AKF are analyzed. The simulation results of target tracking with different covariance of motion model indicate the high precision and robustness of AKF.

The deformation inhomogeneity of transitional region plays a great role in both the macro and micro forming qualities in the local loading forming. In this work, the dependence of deformation inhomogeneity of transitional region on the die parameters in the local loading forming of Ti-alloy rib-web component was studied based on finite element (FE) simulation. To evaluate the deformation inhomogeneity, an area-weighted strain inhomogeneity index was employed, which is calculated through the user subroutine of FE software (DEFORM-2D). It is found that there exist two kinds of strain concentration areas contributing to the deformation inhomogeneity of transitional region. One kind is the almost symmetric strain concentration area at the non-partitioned ribs, which is essentially related to the filling of rib. Another kind is the slant strain concentration area at the partitioned rib, which is caused by the multi-step loading during local loading forming. Besides, the effects of die parameters on the deformation inhomogeneity of transitional region were studied by the combination of orthogonal experiment design and FE simulation. The results suggest that the draft angle of the right rib is the most significant factor for both the deformation inhomogeneities of the partitioned rib region and whole transitional region. And, these two deformation inhomogeneities both decrease with the draft angle of the right rib decreasing. Furthermore, the relationship between die parameters and deformation inhomogeneity of transitional region is developed using the response surface methodology (RSM). Based on the RSM model, the die parameters were optimized to improve the deformation homogeneity of transitional region. The results will provide basis for the design of die parameters to improving the deformation and microstructure homogeneities in the isothermal local loading forming of Ti-alloy rib-web component.

The characteristics of two-phase pressure drop for steam condensation in trapezoidal microchannels with different cross-sectional geometries via novel experimental facility and specific analytical method were investigated in this study. Three types of multi-port trapezoidal microchannels with hydraulic diameter range of 134–166 μm and aspect ratio range of 3.1–6.7, were employed. The pressure drop was determined under steam mass flux between 130 and 340 kg m−2 s−1 accompanied with various cooling water volume flow rate ranging from 20 to 40 L h−1. The results showed that the total frictional, deceleration and contraction pressure drop were more obvious than other local pressure drop. It also presented that not only the steam mass flux, steam quality, cooling water volumetric flow rate and hydraulic diameter but also the aspect ratio had a significant influence on the two-phase frictional pressure drop. The comparison between the experimental data and existing models were finally carried out to verify their predictive accuracy for steam condensing flows in microchannels, and accordingly a modified Friedel model was proposed. The model considering the effect of geometrical parameters of microchannels, the forces acting on fluid and fluid properties, can be available to predict the steam condensing two-phase flow pressure drop multiplier for liquid flowing alone.

Dynamic and post dynamic recrystallization in primary working of a coarse grained two-phase TA15 titanium alloy were investigated. It is found that in β deformation, dynamic recrystallization (DRX) can be triggered at a low strain. The low nucleation rate retards DRX. It is prone to producing a duplex grain structure. During post-deformation holding, both meta-dynamic recrystallization (MDRX) and static recrystallization (SRX) occur. The average recrystallized grain size increases sharply in the early stage of holding due to MDRX but varies slightly after SRX occurs. Post dynamic recrystallization can be finished in a short time and additional β annealing after deformation is unnecessary. Refining the initial structure can accelerate recrystallization and decrease the recrystallized grain size.

To study the effect of deformation mode together with loading path on the microstructure evolution of 2219 aluminium alloy at elevated temperature, plane strain compression (PSC) and uniaxial compression (UC) along different loading paths (rolling direction (RD), transverse direction (TD) and normal direction (ND)) as well as equal-channel angular pressing (ECAP) along RD were performed on the cubic and cylindrical samples cut from thick plate. Detailed microstructure evolution was characterized by optical microscope and electron backscattered diffraction (EBSD). The results indicate that the PSC deformation shows a higher stress level than UC and an increasing discrepancy in flow softening occurs with the increasing strain during PSC along different loading paths. The volume fraction of dynamic recrystallization (DRX) after RD-UC is higher than that of RD-PSC, while the grain refinement level is the lowest in the one pass ECAP. DRX is the main grain refinement mechanism for RD-UC, while deformation bands (DBs) are dominant in RD-PSC and ECAP. Due to the grain morphology anisotropy, a significant microstructural difference was exhibited in the PSCed samples along different loading paths. The grain refinement in hot working of 2219 aluminium alloy plate is greatly related to the deformation modes and loading paths in view of the brick-like grains.

The aim of this study is to investigate the impact of social integration and socioeconomic status on immigrant health in China. Taking the framework of social determinants of health (SDH) as the theoretical starting point, this paper uses the Hangzhou sample of the 2018 Survey of Foreigners in China (SFRC2018) to explore two core factors affecting the health inequality of international migrants in China: the level of social integration following settlement, and socioeconomic status before and after coming to China. The results show that having a formal educational experience in China helped improve both the self-rated health status and self-assessed change in health of international migrants, that the socioeconomic status of an emigrant’s home country affected self-rated health, and that the self-assessed change in health of immigrants from developing countries was significantly higher than those from developed countries. This study concludes that the health inequalities of immigrant populations in China must be understood in the context of China’s specific healthcare system and treatment structure.

Flow forming was employed to manufacture the 2219 aluminium alloy thin-walled tubular parts with cross inner ribs (longitudinal and transverse inner ribs, LTIRs) integrally, which have been widely used in the aviation and aerospace fields. Electron backscattered diffraction (EBSD) examination along with micro-hardness tests was conducted on the typical zones of the flow formed part, thus to make a detailed study on the deformation modes as well as strain gradient induced heterogeneous microstructure and mechanical property. The wall thickness thinning is dominant at non-rib zone, while it is the die filling that mainly prevails at TIR and LIR zones, resulting in the occurrence of three different deformation modes. The plane strain deformation contributes to the severe fragmentation of ribbon-like grains at non-rib zone, while the axial tensile strain during longitudinal inner rib (LIR) forming and small radial tensile strain during transverse inner rib (TIR) forming cannot make the large ribbon-like grains refined effectively. In order to refine the microstructure and obtain uniform mechanical property, modifying the initial microstructure and changing the strain types at rib zones by full die filling, as well as subsequent annealing treatment should be considered.

Kaji-ichigoside F1, a pentacyclic triterpenoid saponin, exhibits various beneficial pharmacological effects. In this study, a simple, rapid, and specific high-performance liquid chromatography-tandem mass spectrometry method for rapid quantification of kaji-ichigoside F1 in rat biological matrix was developed. Plasma was prepared by a single-step protein precipitation followed by separation of the analyte using an Inertsil ODS-3 column with a gradient mobile phase. Positive ion electrospray was used and selected reaction monitoring transitions were m/ z 673.27 → 511.15 for kaji-ichigoside F1 and m/ z 429.19 → 267.29 for morroniside, respectively. The developed method was validated with linear range of 20 to 10 000 ng/mL. All validation parameters were well within the acceptance limit based on the guidance of FDA. The validated method was successfully applied to analyze samples from the in vivo and in vitro pharmacokinetic studies in rats.

Using a diagonal reference model to analyze data from three waves of Chinese General Social Surveys conducted between 2006 and 2012, we examine how social mobility affects political participation in urban China. We classify political participation into three main categories: voting participation (grassroots elections in the People's Congress and neighborhood committees); voluntary participation (civic activities in social organizations and NGOs); and mixed participation (activities in state corporatism organizations). Our findings demonstrate that there is an asymmetry effect of social mobility in voluntary participation in which the upwardly mobile tend to adapt more to their destinations, while the downwardly mobile tend to adhere more to their origins. But in both voting and mixed participation, political behaviors are more influenced by destination effect. These findings suggest that despite increased civic engagement in NGOs and nonprofit organizations as a mode of voluntary participation, identification with the party apparatus still remains an important factor in explaining the political behaviors of the upwardly mobile in China. When people rise in class status, they tend to be more politically conservative and to build alliances with state agencies by participating in party-sponsored political initiatives.

Temperature rise is a significant factor influencing microstructure during (α + β) deformation of TA15 titanium alloy. An experiment was designed to explore microstructure evolution induced by temperature rise due to deformation heat. The experiment was carried out in (α + β) phase field at typical temperature rise rates. The microstructures of the alloy under different temperature rise rates were observed by scanning electron microscopy (SEM). It is found that the dissolution rate of primary equiaxed α phase increases with the increase in both temperature and temperature rise rate. In the same temperature range, the higher the temperature rise rate is, the larger the final content and grain size of primary equiaxed α phase are due to less dissolution time. To quantitatively depict the evolution behavior of primary equiaxed α phase under any temperature rise rates, the dissolution kinetics of primary equiaxed α phase were well described by a diffusion model. The model predictions, including content and grain size of primary equiaxed α phase, are in good agreement with experimental observations. The work provides an important basis for the prediction and control of microstructure during hot working of titanium alloy.

The under-filling defect is prone to occur in the forging of large-scale titanium alloy rib-web components (LTRC). A rigorous preform design with accurate volume distribution is required for a desirable LTRC. The unequal thickness billet (UTB) design divides the preform into multiple regions of varying thickness and can not only adjust the volume distribution effectively but also control forming defects with low cost and high efficiency. The purpose of this paper is to attain LTRC without any under-filling defects using the UTB methodology. Firstly, cross sections are extracted from a desirable LTRC so as to create the initial UTB according to the calculated neutral layer of material flow between ribs. Then a finite element (FE) model is established, using the Deform-3D software for the isothermal closed-die forging to study the material flow and die cavity filling. Finally, three schemes to modify the initial UTB are proposed for those areas where there is under-filling: (I) increase the number of regions in affected areas, (II) adjust the size parameters of the regions around affected areas, and (III) increase the thickness of the regions in affected areas. In conclusion, it is found that scheme I and scheme II are based on the constancy of volume principle and can be adopted if the distribution of the ribs on those affected areas is quite simple. However, scheme I increases the complexity of the UTB, so scheme II is preferred. Alternatively, if the distribution of ribs on those regions is more complicated, scheme III can be adopted. Although the volume of the UTB is increased slightly, all ribs can be completely filled, allowing the most accurate LTRC to be produced.

Forming quality of transitional region determines the performance of titanium alloy large-scale rib-web component under isothermal local loading forming. As folding defect is the most sensitive defect in transitional region, its prediction is very critical to the precision shape forming in isothermal local loading forming. In this paper, a quick prediction model for the folding defect in transitional region was established to replace the traditional defect prediction method by time-consuming FE simulation. First of all, the FE model of local eigen model of transitional region during local loading forming of large-scale rib-web component was established and validated by physical experiment. Then, an adaptive folding index was proposed to measure the possibility and severity of folding defect based on the mechanism that there exists a local increase of strain rate when a folding tends to appear. Availability of the adaptive folding index was checked by large numbers of uniform experiments designed by the space-filling Maximin Latin hypercube designs (maximin LHDs). Furthermore, a judging criterion for folding defect based on the folding index was developed and validated by random samples. Subsequently, the folding index was correlated with the geometrical characteristic parameters of transitional region model by RSM model, through which the folding index can be predicted quickly without the time-consuming FE simulation. Finally, a quick prediction model was established for folding defect judgment under various geometrical parameters by combination of the RSM model for folding index and proposed judging criterion. Prediction results are quite consistent with the results of FE simulation and experiment. The folding prediction model can greatly facilitate the design space exploration and engineering design thereby providing guideline to the precision shape forming. Besides, the adaptive folding index and corresponding judging criteria for folding defect put forward in this work have reference significance to the study on folding defect in other forging processes.

The forming quality in the transitional region largely determines the formability of local loading forming of the large-scale rib-web component. Thus, it is very critical to determine the forming limit considering defects in the transitional region during local loading forming. In this paper, the stepwise searching method based on Kriging metamodels of defect indexes is adopted to determine the above forming limit. First, the finite element (FE) simulation of the transitional region during local loading forming and the evaluation indexes for folding and cavum defects are introduced. Then, the Kriging metamodels of defect indexes are developed based on quantities of FE simulation results under various geometry parameters. During Kriging metamodeling, in order to guarantee the accuracy of the metamodel in the global design space and interesting region simultaneously, the space-filling maximin Latin hypercube designs (maximin LHDs) and sequential sampling approach are employed to design sample points. After metamodeling, extra random samples designed within the whole space are simulated to validate the developed Kriging metamodels. At last, the method of determining the forming limit considering defects in the transitional region is presented and applied to two specific transitional region models. It is realized through stepwise searching based on Kriging metamodels of defect indexes. The application results show that the proposed method is an effective and reliable method to determine the forming limit considering defects in the transitional region. It would provide an important guideline in the processing design of local loading forming of titanium alloy large-scale rib-web components.

The effect of initial structure on phase evolution in continuous heating of a near-α TA15 titanium alloy (Ti-6Al-2Zr-1Mo-1V) was experimentally investigated. To this end; three microstructures were obtained by multiple heat treatment: I-bimodal structure with 50% equaixed α, II-bimodal structure with 15% equiaxed α, III-trimodal structure with 18% equiaxed α and 25% lamellar α. Differential scanning calorimetry (DSC), dilatometry and quantitative metallography were carried out on specimens with the three initial structures at heating rates from 5 to 40 °C/min. The transformation kinetics was modeled with the Johnson–Mehl–Avrami (JMA) approach under non-isothermal condition. It was found that there exists a four-stage transformation for microstructures I and III. The secondary and third stages overlap for microstructure II. The four stages of phase transformation overlap with increasing heating rate. In the presence of α laths, the phase transformation kinetics is affected by the composition difference between lamellar α and primary equiaxed α. Phase transformation is controlled by the growth of existing large β phase.

Characterizing the video diffusion in online social networks (OSNs) is not only instructive for network traffic engineering, but also provides insights into the information diffusion process. A number of continuous-time diffusion models have been proposed to describe video diffusion under the assumption that the activation latency along social links follows a single parametric distribution. However, such assumption has not been empirically verified. Moreover, a user usually has multiple activated neighbors with different activation times, and it is hard to distinguish the different contributions of these multiple potential sources. To fill this gap, we study the multiple-source-driven asynchronous information diffusion problem based on substantial video diffusion traces. Specifically, we first investigate the latency of information propagation along social links and define the single-source (SS) activation latency for an OSN user. We find that the SS activation latency follows the exponential mixture model. Then we develop an analytical framework which incorporates the temporal factor and the influence of multiple sources to describe the influence propagation process. We show that one’s activation probability decreases exponentially with time. We also show that the time shift of the exponential function is only determined by the most recent source (MRS) active user, but the total activation probability is the combination of influence exerted by all active neighbors. Based on these discoveries, we develop a multi-source-driven asynchronous diffusion model (MADM). Using maximum likelihood techniques, we develop an algorithm based on expectation maximization (EM) to learn model parameters, and validate our proposed model with real data. The experimental results show that the MADM obtains better prediction accuracy under various evaluation metrics.

The forming quality of transitional region plays a key role in the performance of titanium alloy large-scale rib-web component under isothermal local loading forming. In this work, a local eigen model of transitional region in the local loading forming of large-scale rib-web component is extracted so as to catch the detail-forming characteristics of transitional region with low computation time in simulation and experiment cost. Then, based on the local eigen model, the mechanism of forming defects in transitional region and their dependence on processing parameters are studied by the combination of physical experiment and verified finite element (FE) simulation. It is found that the second loading step can be divided into two forming stages according to the material flow pattern: (1) the transverse flow stage and (2) the stable forming stage. In the transverse flow stage, there exists long-range transverse flow of web material and excessive transverse flow would lead to the formation of folding and cavum defects. Moreover, the severities of defects are well correlated with the quantity of material transferred into the first-loading region in this stage. For a certain reduction amount, decreasing spacer block thickness and increasing friction both can decrease the quantity of transferred material and then suppress the development of folding and cavum defects, while the deformation temperature and loading speed have little effect on the quantity of transferred material and defects. In the end, an effective way is put forward to suppress and prevent the defects in transitional region during the local loading forming of titanium alloy large-scale rib-web component.

The material flow in transitional region plays an important role in the forming quality of transitional region in the isothermal local loading forming of titanium alloy large-scale rib-web component. To study the material flow in transitional region, the finite element (FE) model of transitional region was established based on DEFORM-2D software and validated by physical experiment. Then, a quick and easy method, which can measure the area of different local regions of forged part in DEFORM-2D via user subroutine, was proposed to achieve the quantitative analysis of material flow mechanism. This technique can also be used in the analysis of other forming process, such as the calculation of fill ratio in forging process. The material flow pattern of transitional region during local loading forming was analyzed step by step and compared with integral forming. The results show that the material flow of transitional region during local loading process can be divided into six stages according to the material flow pattern and load-time curve. Twice transverse material flow with opposite directions occurred in the first and second loading steps sequentially, which does not exist in the integral forming. Four characteristic values evaluating the transverse flow of material, which are associated with the formation of defects and their severities, are defined and quantitatively measured at various processing conditions. It is found that decreasing the spacer block thickness and increasing friction both can decrease the four characteristic values, thus weaken the transverse material flow, which are helpful to improve the forming quality in transitional region. However, the transverse flow of material is little affected by the loading speed.

In this paper, a set of physically based constitutive model coupling microstructure evolution was developed for unified prediction of flow stress and globularization evolution during hot working of two-phase titanium alloys with initial lamellar microstructure. The dislocation density variation, dynamic globularization and effect of Hall–Petch strengthening were considered in the microstructure model. The dynamic globularization was modeled by two parts: critical strain for initiation of globularization and globularization rate, both of which are function of processing conditions (temperature and strain rate); In the modeling of Hall–Petch strengthening, the dependence of Hall–Petch coefficient on processing conditions were considered and the loss of Hall–Petch strengthening with deformation process was molded. The microstructure model was implemented to a physically based constitutive model, composed of a thermally activated stress and an athermal stress, to realize the unified prediction of flow stress and globularization evolution. The material parameters were determined by calibration using the experimental flow stress and globularization fraction in isothermal compression tests through the genetic algorithm based optimization method. Based on the set of constitutive models, flow stress and globularization evolution of Ti–6Al–4V and TA15 alloys at different temperatures and strain rates were predicted. Good agreements between the experimental and computed results were obtained.

Understanding the mechanism of high temperature deformation is important for controlling the forming quality of the titanium alloy forgings. In the present work, the flow softening mechanism in subtransus deformation of titanium alloys with equiaxed structure was investigated by interrupted isothermal compression tests. The results show that limited strain hardening followed by continuous flow softening occurs in high temperature deformation of a two-phase TA15 titanium alloy. The flow softening can not be rationalized by dynamic recrystallization. Instead, the increase of mobile dislocations during deformation is an important reason for flow softening. The grain boundaries (including the α-β interfaces) act as an important source for the generation of mobile dislocations. The continuous flow softening results from the significant deformation heterogeneity in subtransus working.

Multicopy utility-based forwarding algorithms are popular in opportunistic mobile networks. They aim to gain high system throughput while keeping the cost low. However, most of them ignore the fairness issue on the successful delivery rate among users. In this paper, we analyze the fairness evaluation of the success rate distribution, and we propose a new fair packet-forwarding strategy based on packet priority. We formulate the opportunistic packet-forwarding process as a discrete-time Markov chain and deduce a stationary probability distribution vector. Instead of taking the hill-climbing heuristic on utility comparison, we introduce a lower utility tolerance mechanism for the decision-making process of each node, and we theoretically demonstrate that the proposed mechanism may be used to control the success rate of packet delivery by changing a simple parameter. In addition, we adopt a message-duplication restricting mechanism to adjust the number of replications based on packet priority. Our proposed protocol can work as a plug-in for traditional utility-based forwarding algorithms. The performance is compared with several well-known opportunistic routing protocols via both a synthetic model and real human mobility traces. The results show that our protocol improves the fairness in successful delivery rates among users while maintaining almost the same system throughput. Moreover, it reduces the cost of traditional utility-based forwarding algorithms, rendering our proposed scheme not only fair but efficient as well.

The intrinsic multi-heat unequal deformation behavior of the local loading forming requires a through-process macro–micro model to characterize the microstructure evolution during the forming process. In the present work, the phenomena and mechanisms of microstructural developments in local loading forming of titanium alloys are summarized. Mechanism-based unified material models, which characterize the through process microstructure evolution, are developed for integrated prediction of constitutive behavior and microstructure. A through-process macro–micro finite element model is established for the local loading forming of large scale complex titanium alloy component. The model can predict the microstructure evolution as well as macroscopic deformation in multi-step local loading forming process. Model predictions are in good agreement with experimental results. The microstructure evolution in local loading forming is investigated by the established finite element model. It is found that the thermo-mechanical processing route greatly affects the volume fraction of primary alpha but has little influence on the grain size in local loading forming

To control the microstructure and performance of large scale complex titanium alloy component by local loading forming, the effect of processing on microstructure in local loading forming was investigated by a through-process finite element model. It is found that the volume fraction of primary equiaxed α decreases with temperature, deformation speed and loading pass. The distribution of α fraction becomes more uniform with decreasing temperature and increasing deformation speed and loading pass. The α grain size increases with temperature and loading pass but decreases with deformation speed. The homogeneity of the grain size can be improved by increasing deformation temperature and loading pass, or decreasing loading speed.

The isothermal local loading forming technology provides a feasible way to form Ti-alloy large-scale rib-web components in aerospace and aviation fields. However, the local loading process forming limit is restricted by forming defects in the transitional region. In this work, the feasibility of controlling forming defects and improving the process forming limit by adjusting die parameters is explored through finite element (FE) simulation. It is found that the common cavum and folding defects in the transitional region are significantly influenced by the fillet radii of left rib and middle rib, respectively. The cavum and folding defects can be effectively controlled by increasing the fillet radii of left rib and middle rib, respectively. The process forming limits considering forming defects in the transitional region are determined by the stepwise searching method under various die parameters. Moreover, the relationship between the process forming limit and die parameters is developed through the response surface methodology (RSM). The developed RSM models suggest that increasing the fillet radii of left and middle ribs is effective to improve the process forming limit during local loading forming of rib-web components. The results will provide technical basis for the design of die parameters and the reduction amount, which is of great importance to control forming defects and improve the process forming limit in local loading forming of Ti-alloy large-scale rib-web components.

The role of subtransus hot working on microstructure morphology of TA15 titanium alloy plate with elongated α phases was studied by quantitative metallography on different sections. The results show that the microstructure morphology is mainly affected by loading direction. When the sample is compressed along normal direction, microstructure on the section vertical to normal direction has equiaxed primary α phase but microstructure on the section vertical to rolling direction has strip primary α phase with long axis along tangential direction. When the sample is compressed along rolling direction, microstructure on the section vertical to normal direction has strip primary α phase elongated along tangential direction but microstructure on the section vertical to rolling direction consists of strip and irregular broad-band primary α phase. The strip primary α phase aspect ratio is smaller at lower temperature due to the dynamic break-down of α phase. The difference on primary α phase aspect ratio between different sections decreases after compression along distinct directions in two loading passes, suggesting the improvement of equiaxity of primary α phase.

The condensation liquid was pulled into the corner of the noncircular microchannels due to the effect of surface tension. The thickness in the meniscus region increased along the channel with the decrease of the thin-liquid film region. The condensation annular flow completed when the short side wall of the microchannel was entirely covered by the meniscus region. At this point, the vapor liquid interface presented a circular shape, and the transition flow occurred. The location of transition flow depends on the short side length and the meniscus area ratio (MAR) at the breakup point under the same experimental conditions. The location of the transition flow moves toward the outlet with the increase of the short side length and decrease of the aspect ratio in the rectangular and trapezoidal microchannels. The transition flow occurs further downstream, and the annular flow regime is expanded in the trapezoidal and triangular microchannels compared with the rectangular microchannel with the same hydraulic diameter. The analysis was compared with the experimental data for different cross section shape microchannels. Most predicted values provided good predictions of the experimental data with a MRD of 30.50% and a MAD of 5.15 mm. Based on the numerical results, a dimensionless correlation with a new parameter MAR was also introduced to predict the transition flow location at different cross section shape microchannels.

A new method for separating complex touching equiaxed and lamellar alpha phases in the optical micrograph of titanium alloy was proposed for quantitative characterization. This new method involves three steps. First, concave points of the microstructural feature are identified with a threshold of the concaveness of the corner points which are extracted from the binarized image. Secondly, concave points pairs are selected from the concave points group established by means of marker circle or distance. Third, whether a candidate separation line which connects two concave points within a pair can be accepted or not is determined by the proposed four rules. The obtained results show that this method is effective on separating complex touching microstructural features.

Identity-based signcryption which guarantees the confidentiality and authentication of message is suitable for the key management of Ad Hoc network due to its low computation cost. Aiming at the deficiencies of the existing identity-based signcryption algorithms, this paper proposes an efficient grid-based identity signcryption algorithm which adopts a low overhand, high expandability and high connectivity grid as the logical structure. By using this signcryption algorithm in the key management scheme of Ad Hoc network, the communication and computation cost of key management is reduced and the safety and efficiency of the key management scheme is enhanced. The analyses show that the Ad Hoc network has a good ability of resistance to the attack when the new signcryption algorithm is used in key management.

In this paper, the microstructure evolution and processing–microstructure relationship in the non-isothermal local loading forming of TA15 titanium alloy were studied through an analog experiment. Some new microstructural mechanisms are found, which are different from those under isothermal local loading forming. In the non-isothermal local loading forming, the tri-modal microstructure consisted of equiaxed primary α, lamellar α and β transformed matrix is achieved. The lamellar α, not produced under isothermal condition, is generated by β → α transformation due to the decrease of component temperature. With the same processing parameters, the volume fraction and grain size of primary α are both greater than those processed isothermally. The content of lamellar α decreases with heating temperature decreasing and little lamellar α can be found when the heating temperature drops to 930 °C. Under small deformation degree, the lamellar α distributes randomly in each feature region. As deformation increases, the lamellar α in transitional region and second-loading region present a preferred orientation perpendicular to the compression direction. The primary α content almost decreases linearly with heating temperature, which is different from the regular that under isothermal condition. Non-isothermal local loading forming with a higher heating temperature (near-β region) offers a cost-efficient way for the manufacture of TA15 titanium alloy large-scale integral components.

The static globularization behavior and mechanism of transformed structure during heat-treatment of hot worked TA15 alloy were investigated. It is found that boundary splitting and microstructure coarsening are two competing mechanisms for static globularization. Boundary splitting is significant in the initial stage of annealing while coarsening occurs throughout the annealing process. Static globularization kinetics increases with annealing temperature and prestrain, but is independent on strain rate. The rate of static globularization kinetics decreases with annealing time. The asymptotic equation can be used to model the static globularization kinetics.

The cooling rate has a strong influence on the volume fraction, size and distribution of primary α phase of TA15 titanium alloy, which play a decisive role in the properties of the material. Thus, the purpose of this paper is to quantitatively investigate the effect rules of the cooling rate on the primary α phase of TA15 titanium alloy by the α/β heat treatment experiment and the mathematical modeling based on a diffusion model. The obtained results show that: (1) the final volume fraction and size of the primary α phase both increase due to more growth time of the primary α phase resulting from the decrease of the cooling rate; (2) the growth rate of primary α phase increases with cooling rate because of the larger supersaturation under higher cooling rate, and the growth rate increases first and then decreases at a certain cooling rate; and (3) the final size distribution of the primary α particles becomes more uniform with the decrease of cooling rate.