Modelling of shear stress field in glide plane in substitutional solid solutions

The formation of stochastic shear stress field in the glide plane in the substitutional solid solution was investigated by computer simulation. If the atoms in the crystal lattice nodes of the substitutional solid solution are considered as a kind of point defects in the virtual solvent medium, the shear stress distribution in the glide plane can be calculated based on the interaction of edge dislocation and such defects. For concentrated solid solutions, the shear stress will be a normally distributed random value with zero mathematical expectation. The standard deviation of this distribution will be the greater the greater the effective distortion of crystalline lattice of the alloy. In the case of dilute solid solution, where one of the components has a predominant content, the simulation gives shear stress distribution in the glide plane, where large peaks are separated from each other by wide areas of near-zero stresses. Thus, there are separate discrete obstacles in the form of large stress peaks for the edge dislocation in the glide plane in dilute solid solution, and the space between the peaks is practically stress-free. The average distance between large peaks correlates with the average distance between the atoms of those components that are few in solution, if total atomic fraction of these components is considered. Thus, the proposed modeling gives a very realistic shear stress distribution in the glide plane for concentrated and dilute substitutional solid solutions with fcc and bcc structures. This can be useful in further modeling the yield strength in multicomponent alloys. Keywords: dislocation, distorsion, shear stresses.

Behavior of Cell Under Wall Shear Stress in Flow Field: Comparison Among Cell Types

Does the hysteresis effect remain in each cell after division? In the present study, the cell activity has been investigated after division under a shear stress field. To apply the constant shear stress field on cells, a Couette type flow device has been manufactured: between parallel walls (a lower stationary culture disk, and an upper rotating disk) with a constant gap. The wall shear stress was controlled by the rotating speed of the upper disk. Four types of cells were used in the test: C2C12 (mouse myoblast cell line), HUVEC (Human Umbilical Vein Endothelial Cells), 3T3-L1 (mouse fat precursor cells), and L929 (mouse fibroblast connective tissue). After cultivation without flow for 24 hours for adhesion of cells on the lower plate, the shear stress of 1 Pa was continuously applied on cells for 7 days at 310 K. The behavior (alignment and deformation) of each cell was traced at the time lapse image observed by an inverted phase contrast microscope placed in an incubator. The experimental results show the following behavior of each type of cell: C2C12 tends to return to the same direction as that of before division. Deformed 3T3-L1 tends to tilt to the flow direction.

Shape of dislocation line in stochastic shear stress field

The shape of the dislocation line in the stochastic shear stress field in the glide plane was studied using the method of discrete dislocation dynamics. Stochastic shear stresses can occur due to the distortion of the crystal lattice. Such distortion may exist, for example, in a solid solution. Different atoms in a solid solution induce atomic size misfit and elastic modulus misfit into crystal lattice. These misfits result in crystal lattice distortions which varies spatially. The distortions are the origin of internal stresses in the lattice. Such internal stress in certain location has stochastic value normally distributed. The particular case of such stresses is shear stress distribution in the glide plane. The special method was developed to model such stress distribution. The stochastic shear stress field results in movement of different segments of dislocation line to form its equilibrium shape. The important characteristic parameters of the equilibrium shape can be measured by numerical methods. This shape also includes a "long-wavelength" component that has a non-zero amplitude and was formed without thermal activation. The shape of the dislocation line determines to some extent the yield strength of the material. Thus, the study of dislocation line shape and modeling its formation in the field of stochastic shear stresses can help to determine the yield strength of multicomponent alloys, especially multi-principal element alloys. Keywords: dislocation, discrete dislocation dynamics, shear stresses.

Continuous bubble streams for controlling marine biofouling on static artificial structures

Biofouling accumulation is not proactively managed on most marine static artificial structures (SAS) due to the lack of effective options presently available. We describe a series of laboratory and field trials that examine the efficacy of continuous bubble streams in maintaining SAS free of macroscopic biofouling and demonstrate that this treatment approach is effective on surface types commonly used in the marine environment. At least two mechanisms were shown to be at play: the disruption of settlement created by the bubble stream, and the scouring of recently settled larvae through shear stress. Field trials conducted over a one-year period identified fouling on diffusers as a major issue to long-term treatment applications. Field measurements suggest that noise associated with surface mounted air blowers and sub-surface diffusers will be highly localised and of low environmental risk. Future studies should aim to develop and test systems at an operational scale.

High-Throughput Production of Heterogeneous RuO2/Graphene Catalyst in a Hydrodynamic Reactor for Selective Alcohol Oxidation

We report on the high-throughput production of heterogeneous catalysts of RuO2-deposited graphene using a hydrodynamic process for selective alcohol oxidation. The fluid mechanics of a hydrodynamic process based on a Taylor–Couette flow provide a high shear stress field and fast mixing process. The unique fluidic behavior efficiently exfoliates graphite into defect-free graphene sheets dispersed in water solution, in which ionic liquid is used as the stabilizing reagent to prevent the restacking of the graphene sheets. The deposition of RuO2 on a graphene surface is performed using a hydrodynamic process, resulting in the uniform coating of RuO2 nanoparticles. The as synthesized RuO2/IL–graphene catalyst has been applied efficiently for the oxidation of a wide variety of alcohol substrates, including biomass-derived 5-hydroxymethylfurfural (HMF) under environmentally benign conditions. The catalyst is mechanically stable and recyclable, confirming its heterogeneous nature.

Morphology and rheology of PP/POE blends in high shear stress field

Polypropylene (PP)/polyolefin elastomer (POE; ethylene–octene copolymer) blends with varying weight percentages of POE were prepared in a twin-screw extruder and molded through high shear rate injection-molding process. The morphologies and rheology of the PP/POE blends were systematically investigated based on rheological data and experimental analysis. The results indicate that the polymer blends of plastic and rubber in a high shear stress field result in a multilayered microstructure, which can be divided into skin, transitional, shear, and core layers according to the morphology of the dispersed phase. The morphology formation of the dispersed phase depends on the shear field and temperature field in the processing. Morphological evolution of the dispersed POE phases in PP matrix was described and quantified. A dragging ellipsoid model and capillary number were employed to describe the morphological evolution of the dispersed phase, and the morphological parameters were obtained. The results show that the dragging ellipsoid model is well suited to explain the morphological evolution of the dispersed phase in polymer blends molded under high shear rate.