The stress increments depend not only on the plastic strain but also on the gradient of plastic strain, when the characteristic length scale associated with non-uniform plastic deformation is on the order of microns. ...
The stress increments depend not only on the plastic strain but also on the gradient of plastic strain, when the characteristic length scale associated with non-uniform plastic deformation is on the order of microns. In the present research, the Taylor-based nonlocal theory of plasticity (TNT plasticity), with considering both geometrically necessary dislocations and statistically stored dislocations, is applied to investigated the effect of particle shapes on the strain gradient and mechanical properties of SiC particle reinforced aluminum composites (SiC/Al composites). Based on this theory, a two-dimensional axial symmetry cell model is built in the ABAQUS finite element code through its USER-ELEMENT (UEL) interface. Some comparisons with the classical plastic theory demonstrate that the effective stress predicted by TNT plasticity is obviously higher than that predicted by classical plastic theory. The results also demonstrate that the irregular particles cause higher effective gradient strain which is attributed to the fact that angular shape particles give more geometrically.
Strain gradient theories have been considered to be an effective means for capturing the size effects on ceramic particle-reinforced metal-matrix composites (MMCp), but the results predicted by them are significantly ...
Strain gradient theories have been considered to be an effective means for capturing the size effects on ceramic particle-reinforced metal-matrix composites (MMCp), but the results predicted by them are significantly lower than the corresponding experimental data. One reason might be, that the thermal residual stresses caused by thermal contraction mismatch between the metal matrix and the ceramic particle were neglected in the numerical models. By incorporating the Taylor-based nonlocal theory (TNT) of plasticity, the finite element method (FEM) is applied in the present research, to investigate the effect of thermal residual stresses on the yield stress and average axial stresses of the aluminium matrix reinforced by silicon carbide particles (SiCp/Al). The elements of the matrix have been implemented in the ABAQUS finite element code through its USER-ELEMENT (UEL) interface for TNT plasticity. Some comparisons with the associated literature demonstrate that the numerical model with the thermal residual stresses is more in agreement with the experimental results.
Based on microstructure evolution of Mg-20Al-0.8Zn magnesium alloys realized by semisolid isothermal heat-treatment(SSIT),we obtained the non-dendrite or spherical grains microstructure under the suitable technologica...
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Based on microstructure evolution of Mg-20Al-0.8Zn magnesium alloys realized by semisolid isothermal heat-treatment(SSIT),we obtained the non-dendrite or spherical grains microstructure under the suitable technological parameters that isothermal temperature is 495 and holding time is 120 min.℃ With the help of special experimental equipment,the semisolid die-casting process has been studied and the specimens have been *** effects of different parameters as injection speed and pressure on tensile strength,elongation rate,hardness,etc have been *** results indicate that tensile strength was improved along with increasing injection speed and ***,excessive speed will involve gas,which formed defects and reduced the mechanical *** the injection pressure is 40MPa and injection speed is 4m/s,the tensile strength and elongation rate can reach maximal 220MPa and 5.63% *** fracture mechanism was intercrystalline cracking.
Tin bronze wires were produced by dieless drawing. The effects of heating power, the distance between cooler and heater as well as feeding speed on the diameter, the temperature field, and the deformation region profi...
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Tin bronze wires were produced by dieless drawing. The effects of heating power, the distance between cooler and heater as well as feeding speed on the diameter, the temperature field, and the deformation region profile of the wires were investigated. The results indi-cated that each processing parameter exhibited both lower and upper limits of stable deformation based on the criterion of stable deformation with the diameter fluctuation of ±0.05 mm. Both the temperature and its gradient of the deformation region increased with increasing heating power under stable deformation, but decreased with an increase in feeding speed. As the distance between cooler and heater increased, the temperature of the deformation region increased and the slope of the deformation region profile decreased. The processing limit map of sta-ble deformation exhibited a closed curve and the unstable deformation consisted of wire breakage and diameter fluctuations.
This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO2, HfO2 and rutile TiO2 （001） by using classical molecular dynamics. It is found that these three surfaces re...
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This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO2, HfO2 and rutile TiO2 （001） by using classical molecular dynamics. It is found that these three surfaces relax instead of reconstruction at 0 K, and have little possibility to reconstruct below 40 K. Above 40 K, surface reconstructions take place as collective atomic motion which can be speeded by higher temperature or compressed strain. Several reconstruction patterns with approximate surface energies are found, and electrostatic potentials on them are also provided in comparison with possible microscopic results.
The photocatalytic degradation of *** membrane cell by ZnO nanowires was studied using field-emission scanning electron microscope（FE-SEM）,fluorescence microscopy,and Attenuated total reflection fourier transform in...
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The photocatalytic degradation of *** membrane cell by ZnO nanowires was studied using field-emission scanning electron microscope（FE-SEM）,fluorescence microscopy,and Attenuated total reflection fourier transform infrared（ATR-FTIR）.The outer membrane of *** was removed completely in the presence of ZnO nanowires under UV irradiation,and the cells became twisted shapes without a mechanically strong *** ZnO nanowires photocatalysis,the permeability of the treated cells increased to some degree that could be confirmed by quantum dots labeling *** changes in the cell wall membrane were revealed by the decay of the characteristic groups bands in ATR-FTIR spectra.
Dominant heat-carrying modes in skutterudites are associated with vibrations of the pnicogen rings. Apart from filling the structural cages with foreign species, disrupting the pnicogen ring structure by substitutiona...
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Dominant heat-carrying modes in skutterudites are associated with vibrations of the pnicogen rings. Apart from filling the structural cages with foreign species, disrupting the pnicogen ring structure by substitutional alloying should be an effective approach to reduce thermal conductivity. In this paper we explore alloying configurations of pnicogen rings (Sb rings in the case of CoSb3) that yield particularly low values of the thermal conductivity. We find that IV-VI double substitution (replacing two Sb atoms with one atom each from the column IV and column VI elements to achieve an average charge of two Sb atoms) is a very effective approach. Our ab initio calculations, in combination with a cluster expansion, have allowed us to identify stable alloy configurations on the Sb rings. Subsequent molecular and lattice dynamics simulations on low energy configurations establish the range of atomic displacement parameters and values of the thermal conductivity. Theoretical results are in good agreement with our experimental thermal conductivity values. Combining both approaches of compensated double substitution and filling of structural cages should be an effective way of improving the thermoelectric figure of merit of skutterudites.
Anchored periplasmic expression (APEx) technology aims to express and localize proteins or peptides in the Escherichia coli periplasm. Some reports have suggested that transmembrane segments of integral membrane prote...
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Anchored periplasmic expression (APEx) technology aims to express and localize proteins or peptides in the Escherichia coli periplasm. Some reports have suggested that transmembrane segments of integral membrane proteins can be used as membrane anchors in the APEx system. In this study, a series of hydrophobic anchors derived from the first putative transmembrane helix of a Bacillus subtilis integral membrane protein, MrpF, and its truncated forms were investigated for anchored periplasmic expression of alkaline phosphatase (PhoA) in E. coli. Anchoring efficiency of hydrophobic anchors was evaluated by monitoring the expression and activity of anchored PhoA. The length of hydrophobic anchors was found to be critical for anchoring proteins to cell membranes. This study may open new avenues for applying transmembrane segments derived from native membrane proteins as membrane anchors in the APEx system.
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