In-situ formation of TiN-TiO2 composite layer on NiTi shape memory alloy via fluidized bed reactor

In this work, the NiTi alloy was oxynitrided in a fluidized bed reactor to attain an in-situ TiN-TiO₂ protective composite layer. Samples were treated at 540 ± 10 °C for various holding times ranging between 0 h and 8 h. Microstructural evolution on the surface was analyzed by scanning electron microscopy, X-ray diffraction, hardness test, electrochemical behavior, Ni ion release, and bioactivity. Quantitative phase analysis from X-ray diffraction pattern of the treated sample for 8 h showed that TiN (71.3%) and TiO₂ (23.0%) were dominant phases on surface. Hardness results revealed as the oxynitriding time increased from 0 h to 8 h, hardness values increased from 263.4 HV_0.1 to 1227.4 HV_0.1. Scanning electron microscopy observation and energy dispersive X-ray spectroscopy mapping micrographs showed that the grown of TiN with dendritic branches was hindered by Ni-rich regions. Electrochemical measurements using polarization and electrochemical impedance spectroscopy analysis revealed corrosion resistance of the oxynitrided samples was increased by ~170% from 173.3 kΩ cm² for the bare NiTi alloy to 473.1 kΩ cm² for the treated NiTi sample for 8 h. It was found that concentration of the released Ni ions decreased from 0.070 (bare NiTi) mg/l to 0.028 mg/l (treated for 8 h) after oxynitriding treatment. Enhanced biocompatibility of the surface treated sample for 8 h was explained by formation of thick and homogenous TiN-TiO₂ composite layer. Finally, bioactive behavior of the oxynitrided samples were studied using simulated body fluid.     

Acoustic emission analysis using Bayesian model selection for damage characterization in ceramic matrix composites

Acoustic emission (AE) during tensile testing of three-dimensional woven SiC/SiC composites was analyzed by a statistical modeling method based on a Bayesian approach to quantitatively evaluate the fracture process. Gaussian mixture models and Weibull mixture models were utilized as candidate models describing the AE time-series data. After fitting AE time-series data to these models with Markov Chain Monte Carlo (MCMC) methods, the model selection was conducted by stochastic complexity. Among the candidate models, the two-component Weibull mixture model was automatically selected. It was confirmed that the component distributions in the two-component Weibull mixture model were corresponding to the evolution of matrix cracking and fiber breakage, respectively. Since the proposed AE analysis method can determine the number of component distributions without the decision of researchers and inspectors, it is expected to be useful for an understanding of the fracture process in newly developed materials and the reliability assessment in service.     

Investigation of fracture behavior of cement-bonded corundum castables using wedge splitting test and digital image correlation method

To investigate the fracture behavior of cement-bonded corundum castables, various cement contents and pre-treating temperatures have been comparatively studied using the wedge splitting method and the digital image correlation technique. The results show that the microstructure enhances the mechanical properties, so the fracture energy and the maximum load as well as the fracture modes are affected correspondingly. The castables demonstrate the highest fracture energy and maximum load at 1600 °C with cement content of 10 wt% due to an appropriate amount of CA6. At the temperatures of 110 and 1100 °C, the crack propagation within the matrix and along the interface are dominated whereas within the aggregates significantly increased at 1600 °C, leading to the brittleness of materials. However, increasing the cement content can reduce their brittleness, caused by the maximum strain in thex-direction, largest length of the main crack, and high ratio of crack propagation in the matrix.     

低活化马氏体钢热变形行为及机理型本构建模研究

利用Gleeble-3500热模拟试验机研究了低活化马氏体钢在变形温度为850～950 ℃、应变速率为0.001～1 s^-1条件下的热变形行为。建立了流变应力本构方程，并评估了该方程的预测能力。绘制了低活化马氏体钢在不同应变下的热加工图。结果表明：在较高的应变速率条件下，该材料主要发生动态回复，在较高变形温度和较低应变速率下具有明显的动态再结晶特征；本构方程的预测结果与实验结果符合良好；变形温度870～930 ℃、应变速率0.001～0.01 s^-1和变形温度920～950 ℃、应变速率0.3～1 s^-1分别是真应变为0.4和0.6下最优的热加工区域。     

基于GFU和分层LSTM的组群行为识别研究方法

提出一种以"关键人物"为核心，使用门控融合单元（GFU，Gated Fusion Unit）进行特征融合的组群行为识别框架，旨在解决两个问题：①组群行为信息冗余，重点关注关键人物行为特征，忽略无关人员对组群行为的影响；②组群内部交互行为复杂，使用GFU有效融合以关键人物为核心的交互特征，再通过LSTM时序建模成为表征能力更强的组群特征.最终，通过softmax分类器进行组群行为类别分类.该算法在排球数据集上取得了86.7%的平均识别率.     

不同水针口径下的水辅助注射成型数值模拟

使用流体力学软件，对使用溢流法的三维120 °~150 °弯曲圆管件进行了水辅助注射成型可视化研究。分别改变水针口径尺寸、注水延迟时间、注水压力与熔体温度，分析其对制件内部水穿透行为的影响。结果表明，水针口直径为7 mm时，能显著增加制件的内部穿透长度并得到残余壁厚更薄的制件；受水针结构影响，注水延迟时间为1 s、注水压力为8 MPa、熔体温度为250 ℃时，水穿透长度最优能增长400 %，壁厚减少20 %；在注水延迟时间为1 s、注水压力为10 MPa、熔体温度为230 ℃时，穿透长度最大达到298 mm；注水延迟时间为1 s、注水压力为8 MPa、熔体温度为250 ℃时，比熔体温度为210 ℃和230 ℃的实验组受水针影响严重；缩短注水延迟时间、增加注水压力、升高熔体温度都能有效增大制件的中空率，成型出更薄的管件，但是水针对水辅助注射成型的影响不容忽视，其微小变化能极大地改变成型制件的内部型腔，有效提高水穿透行为的效率。     

Crystallization and spectroscopic properties in Er3+ doped oxyfluorogermanate glass ceramics containing Na

The Er³⁺ doped oxyfluorogermanate glasses, with a composition containing Na element, were synthesized by the conventional melting–quenching technique. When Na element was introduced into the composition of oxyfluorogermanate glass, the crystals behavior was investigated in details. Depending on the annealing procedure supplied, thermal annealing of precursor glasses in the system GeO₂/BaF₂/AlF₃/Na₂O/NaF/ZnO/GdF₃/ErF₃ led to the precipitation of different crystal phase nanocrystals. It was confirmed the nanocrystals in GC600 is orthorhombic NaBaAlF₆ which led to enhance obviously in the UC luminescence of Er³⁺. However, the nanocrystals in G585 led to decrease in the UC luminescence, which indicated few Er ions enter into the lattice of this nanocrystal phase. The reason of the decrease in UC emission intensity of GC585 was analyzed.     

An investigation of epoxy/thermoplastic blends based on addition of a novel copoly(aryl ether nitrile) containing phthalazinone and biphenyl moieties

In this paper, a novel soluble copoly(aryl ether nitrile) containing phthalazinone and biphenyl moieties (PPBEN) was synthesized for the first time to improve the impact resistance of tetraglycidyl 4,4'‐diaminodiphenylmethane epoxy resin cured with 4,4‐diaminodiphenylsulfone. Then a series of blends were prepared via solution blending with different contents of PPBEN. The thermal and mechanical properties and the micromorphology of the cured blends were investigated by differential scanning calorimetry, dynamic mechanical analysis (DMA), parallel plate rheometry, mechanical property tests and SEM analysis, respectively. The results indicated that the incorporation of thermoplastic PPBEN delayed the epoxy curing reaction, and the crosslinking density of epoxies was also reduced. The no‐notch impact strength of the cured blend with 15% PPBEN was up to 16.7 kJ m^?2, higher by about 104% than that of pure epoxy resin without sacrificing the modulus due to a specific sea‐island structure. All the blends showed two‐phase morphology characterized by DMA and SEM. The size of the thermoplastic morphology was only 70?80 nm, much less than that of commonly used thermoplastics, due to the special segment structure of PPBEN. © 2015 Society of Chemical Industry     

Evolutionary collective behavior decomposition model for time series data mining

In this research, we propose a novel framework referred to as collective game behavior decomposition where complex collective behavior is assumed to be generated by aggregation of several groups of agents following different strategies and complexity emerges from collaboration and competition of individuals. The strategy of an agent is modeled by certain simple game theory models with limited information. Genetic algorithms are used to obtain the optimal collective behavior decomposition based on history data. The trained model can be used for collective behavior prediction. For modeling individual behavior, two simple games, the minority game and mixed game are investigated in experiments on the real-world stock prices and foreign-exchange rate. Experimental results are presented to show the effectiveness of the new proposed model.