Slow crack growth resistance of electrically conductive zirconia-based composites with non-oxide reinforcements

Slow crack growth (SCG) behavior of four zirconia-based composites reinforced with 40 vol% WC, TiC, NbC or TiCN were studied by means of double-torsion testing. Compared to monolithic zirconia, the composites had a higher resistance to fast fracture, i.e., higher fracture toughness. The extent of toughening depended on the reinforcement type, shifting the V-K_I (crack velocity versus stress intensity factor) curve parallel to higher K_I values. More importantly, these composites were less sensitive to SCG. Identical V-K_I/K_IC curves with steeper slopes compared to monolithic zirconia were observed for the investigated composites, independent on the reinforcement type. No rising R-curve was measured, at least in the crack-size domain investigated by SCG. Therefore, the higher SCG resistance of the composites was due to the intrinsic stress-assisted corrosion resistance of the covalent non-oxide secondary phase.     

Ageing under oscillatory stress: Role of energy barrier distribution in thixotropic materials

In this work the ageing dynamics of soft solids of aqueous suspension of laponite has been investigated under the oscillatory stress field. We observed that, at small stresses elastic and viscous moduli showed a steady rise with the elastic modulus increasing at a faster rate than the viscous modulus. However, at higher stresses both the moduli underwent a sudden rise by several orders of magnitude with the onset of rise getting shifted to a higher age for a larger shear stress. We believe that the observed behavior is due to interaction of barrier height distribution of the potential energy wells in which the particle is trapped and strain induced potential energy enhancement of the particles. Strain induced in the material causes yielding of the particles that are trapped in the shallower wells. Those trapped in the deeper wells continue to age enhancing the cage diffusion timescale and consequently the viscosity, which lowers the magnitude of strain allowing more particles to age. This coupled dependence of strain, viscosity and ageing causes forward feedback for a given magnitude of stress leading to sudden rise in both the moduli. Changing the microstructure of the laponite suspension by adding salt affected the barrier heights distribution that showed a profound influence on the ageing behavior. Interestingly, this study suggests a possibility that any apparently yielded material with negligible elastic modulus may get jammed at a very large waiting time.     

Effect of protein degradation in the axon on the speed of the bell-shaped concentration wave in slow axonal transport

This paper investigates the effect of degradation of proteins transported by means of slow axonal transport (due to enzyme-mediated breakdown of proteins) on the speed of the bell-shaped wave of protein concentration propagating toward the synapse of the axon. Another issue investigated in this paper is the effect of protein degradation on the traffic jam caused by a decay of microtubule tracks at a certain location in the axon. The decay of microtubule tracks may be caused by misregulation of microtubule-associated proteins resulting from an imbalance in intracellular signaling or by mutations of these proteins. Axonal swellings caused by such traffic jams hinder axonal transport; they are a likely cause of various neurodegenerative diseases, including Alzheimer's and Parkinson's diseases and the Down syndrome.     

Effect of different microstructural features on the hydrogen embrittlement susceptibility of alloy 718

Due to its high strength and acceptable corrosion resistance, Alloy 718 is a viable material for the use in subsea applications. The alloy's susceptibility to hydrogen embrittlement is however limiting its viability. In this work the effect of microstructure on the hydrogen embrittlement susceptibility of Alloy 718 was examined by the use of slow strain rate testing on three different heat treatments. Cathodic pre-charging and polarization during testing were used to introduce hydrogen into the samples. A severe reduction in the ductility of the alloy due to the precipitation phases γ″ and γ′ were found. In addition, one of the heats had a continuous film of a Nb and C rich phase on the grain boundary giving an intergranular fracture mechanism. This intergranular fracture mode was further enhanced by the presence of hydrogen. In the solution annealed condition, the presence of hydrogen reduced the dimple size on the fracture surface.     

时域分析技术在机械设备故障诊断中的应用

低速重载的一些机械设备,由于频率较低,故受振动诊断分析仪器功能的限制,频谱分析方法效果不太理想。经过现场的长期监测及诊断分析,几个典型案例说明了对于低速重载的机械设备,时域分析是最有效的故障诊断方法之一。     

A subspace ensemble regression model based slow feature for soft sensing application

A novel adaptive subspace ensemble slow feature regression model was developed for soft sensing application. Compared to traditional single models and random subspace models, the proposed method is improved in three aspects. Firstly, sub-datasets are constructed through slow feature directions and variables in each sub-datasets are selected according to the output related importance index. Then, an adaptive slow feature regression is presented for sub-models. Finally, a Bayesian inference strategy based on a slow feature analysis process that monitors statistics is developed for probabilistic combination. Two industrial examples were used to evaluate the proposed method.     

Slow and fast dynamics of a natural gas hydrogen reformer

It has been known for some time that fuel cells operate in multiple time scales due to phenomena of different nature that govern their dynamics (electrical, chemical, mechanical, electrochemical, thermodynamic). It is expected that multi-time scales will be presented in the hydrogen gas reformer (produces hydrogen from hydrogen rich fuels) due to its complex chemical and physical nature. In this paper, we show how to present a linearized hydrogen gas reformer dynamic model in the coordinates in which slow and fast variables are explicitly defined and exactly separated. This result is important in its own right to get a better understanding of slow and fast dynamics of particular variables, study their interactions, and as well for designing reduced-order controllers and estimators for the hydrogen gas reformer that will independently operate in different time scales.     

区分快慢变子系统的柔性机械臂控制方法

为了提高柔性机械臂控制精度、抑制柔性机械臂末端振动,提出了区分快慢变子系统的组合控制方法。使用拉格朗日方程和假设模态法建立了柔性机械臂动力学方程,利用奇异摄动原理将柔性机械臂系统分解为快变子系统和慢变子系统;鉴于慢变子系统的强非线性和参数不确定性,将反演控制和滑膜变结构相结合,提出了基于反演滑模变结构控制方法的慢变子系统控制;鉴于快变子系统模型不准确问题,而模糊控制对模型精度没有要求,因此设计了快变子系统模糊控制器。经仿真验证可以看出,与传统PID控制相比,机械臂转角最大误差由4.1°下降为0.04°,稳定时间由10s下降为2.5s,末端振动最大值由0.081m下降为0.021m,极大地提高了柔性机械臂控制精度。     

The role of aluminum in slow sand filtration

Engineering enhancement of slow sand filtration has been an enigma in large part because the mechanisms responsible for particle removal have not been well characterized. The presumed role of biological processes in the filter ripening process nearly precluded the possibility of enhancing filter performance since interventions to enhance biological activity would have required decreasing the quality of the influent water. In previous work, we documented that an acid soluble polymer controls filter performance. The new understanding that particle removal is controlled in large part by physical chemical mechanisms has expanded the possibilities of engineering slow sand filter performance. Herein, we explore the role of naturally occurring aluminum as a ripening agent for slow sand filters and the possibility of using a low dose of alum to improve filter performance or to ripen slow sand filters.     

Important parameters for the manufacture of slow-release matrix pellets with an aqueous dispersion of quaternary poly(meth)acrylates in the rotary fluidized bed

The manufacture of slow-release matrix pellets with an aqueous dispersion of quaternary poly(meth)acrylates was investigated in the rotary fluidized bed. By considering the moisture content of the fluidized bed to be the key process parameter, it was measured on-line throughout the whole manufacturing process. A specially designed sampling device opened new ways to apply NIR spectrometry in laboratory scale processes. It was shown that reproducibly improved pellet properties can be achieved by reproducing the moisture content of the (rotary) fluidized bed. Moisture plateaus proved to be a suitable way to optimize the sphericity of the pellets. Premoisturizing was found to be a very effective tool to achieve slow-release dissolution of the model drug theophylline.