Construction of extrusion limit diagram for AZ31 magnesium alloy by FE simulation

The maximum speed at which magnesium can be extruded is considerably slower than that of many common aluminium extrusion alloys. This affects both the economies of production and the final mechanical behaviour. The present work quantifies the limiting extrusion speeds and ratios of magnesium alloy AZ31 as a function of billet temperature. This is done by combining hot compression test results, FE simulations and extrusion trials. Hot working stress–strain curves displayed a distinct dynamic recrystallisation peak. These data were used as a “look-up” table for the FE simulations in which the cracking limit was assumed to occur when the surface temperature reaches the incipient melting point. The maximum extrusion ratio predicted using FE analysis dropped from 90 to 40 when the extrusion ram speed was raised from 5 to 50 mm/s. The predicted limits agree well with the occurrence of cracking in both a laboratory and a commercial extrusion trial.

Expanding the extrusion limits of wrought magnesium alloys

Consumption of wrought magnesium products wax reduced by half between 1971 and the 1990s. To increase the use of wrought magnesium, several challenges must be overcome: its formability at room temperature is lower than steel or aluminum; its productivity is lower than steel or aluminum; and extruded magnesium exhibits a marked anisotropy of yield when comparing tension and compression. This article describes research on the rapid evaluation of the extrusion behavior of wrought magnesium alloys. The work aims to establish a methodology for rapid prototyping of alloys and to assess the effects of aluminum on the behavior of AZ-series magnesium alloys.

Antioxidant defences and homeostasis of reactive oxygen species in different human mitochondrial DNA-depleted cell lines

Three pairs of parental (ρ+) and established mitochondrial DNA depleted (ρ0) cells, derived from bone, lung and muscle were used to verify the influence of the nuclear background and the lack of efficient mitochondrial respiratory chain on antioxidant defences and homeostasis of intracellular reactive oxygen species (ROS). Mitochondrial DNA depletion significantly lowered glutathione reductase activity, glutathione (GSH) content, and consistently altered the GSH2 : oxidized glutathione ratio in all of the ρ0 cell lines, albeit to differing extents, indicating the most oxidized redox state in bone ρ0 cells. Activity, as well as gene expression and protein content, of superoxide dismutase showed a decrease in bone and muscle ρ0 cell lines but not in lung ρ0 cells. GSH peroxidase activity was four times higher in all three ρ0 cell lines in comparison to the parental ρ+, suggesting that this may be a necessary adaptation for survival without a functional respiratory chain. Taken together, these data suggest that the lack of respiratory chain prompts the cells to reduce their need for antioxidant defences in a tissue-specific manner, exposing them to a major risk of oxidative injury. In fact bone-derived ρ0 cells displayed the highest steady-state level of intracellular ROS (measured directly by 2',7'-dichlorofluorescin, or indirectly by aconitase activity) compared to all the other ρ+ and ρ0 cells, both in the presence or absence of glucose. Analysis of mitochondrial and cytosolic/iron regulatory protein-1 aconitase indicated that most ROS of bone ρ0 cells originate from sources other than mitochondria.

Constitutive modelling of drawing and extrusion with cyclic torsion

In the current work, constitutive models are developed to describe the cyclic hardening and softening led by the strain path chaneg.  The contribution of deformation conditions such as drawing and extrusion speed, cyclic rotating angle on the drawing and extrusion force will be investigated.  The development of such constitutive models will provide insight into the optimization of operation conditions to explore the potential of industrial applications.

Using immune genetic algorithm to optimize the reactive power

A novel algorithm, immune genetic algorithm (IGA) is proposed for reactive power optimization of power system. While retaining excellent characteristics of genetic algorithm (GA), through imitating the biological immune system, the algorithm evaluates and selects the optimal solutions by the affinities between antigens and antibodies. With the regulation of the activating and suppressing of antibodies, IGA can achieve the dynamic balance between individual diversity and population convergence, and avoid getting into the local optimal solution. The proposed IGA is applied to the IEEE 30-bus system, and the results show that it is superior to the GA with good population convergence and fast computing speed.

Nanostructures and nanoporosity in thermoset epoxy blends with an amphiphilic polyisoprene-block-poly(4-vinyl pyridine) reactive diblock copolymer

Nanostructured thermoset blends were prepared based on a bisphenol A-type epoxy resin and an amphiphilic reactive diblock copolymer, namely polyisoprene-block-poly(4-vinyl pyridine) (PI-P4VP). Infrared spectra revealed that the P4VP block of the diblock copolymer reacted with the epoxy monomer. However, the non-reactive hydrophobic PI block of the diblock copolymer formed a separate microphase on the nanoscale. Ozone treatment was used to create nanoporosity in nanostructured epoxy/PI-P4VP blends via selective removal of the PI microphase and lead to nanoporous epoxy thermosets; disordered nanopores with the average diameter of about 60 nm were uniformly distributed in the blend with 50 wt% PI-P4VP. Multi-scale phase separation with a distinctly different morphology was observed at the air/sample interface due to the interfacial effects, whereas only uniform microphase separated morphology at the nanoscale was found in the bulk of the blend.

Application of the strain localization CAFE model to investigate extrusion with various die shapes

Multi scale CAFE model for the prediction of initiation and propagation of the micro shear bands and shear bands in metallic materials subjected to plastic deformation is presented. The CAFE approach is the combination of the Cellular Automata (CA) and the Finite Element (FE) methods. The application of the developed CAFE model to analyze material flow during extrusion is the objective of the present work. The proposed CAFE approach is applied in this work to simulation of the extrusion with flat face and convex dies and to investigate differences in the material flow. The initial FE meshes with the set of the CA point are generated for the numerical tests and the results of the metal flow predicted by the CAFE method are presented in the paper.

Effects of leveling agent on the uptake of reactive dyes by untreated and plasma-treated wool

Atmospheric-pressure plasma treatment of wool fabric produced a significantly higher level of adsorbed fiber-reactive dye when applied at 50 °C (pH 3.0–6.0) in the absence of any organic leveling agent. In addition, color yields indicated that dye was more uniformly adsorbed by the plasma-treated fabric compared with the untreated material. When untreated fabric was dyed in the presence of a leveling agent (Albegal B), the extent and levelness of dye sorption were enhanced. These enhancements were, however, relatively small on the plasma-treated wool compared with those on untreated wool. A ‘surface’ mechanism, similar to that proposed when plasma-treated wool is dyed in the absence of leveling agent, can explain the leveling ability of Albegal B under adsorption conditions. Increasing the dyebath temperature to 90 °C resulted in dye penetration of the fibers. Under these conditions, any enhancements of dye uptake produced by the plasma treatment, as well as the use of Albegal B, were relatively small, in contrast to the behavior at 50 °C. Improvements in the uniformity of dye sorption observed at 50 °C were, however, maintained at the higher temperature. It is concluded that the inability of reactive dyes to migrate (and so promote leveling and uniformity) once they have reacted with the fiber, means that differences in the uniformity of dye sorbed at 50 °C are still apparent at equilibrium.

Reactive system model for building fault-tolerant distributed applications

The development of fault-tolerant computing systems is a very difficult task. Two reasons contributed to this difficulty can be described as follows. The First is that, in normal practice, fault-tolerant computing policies and mechanisms are deeply embedded into most application programs, so that these application programs cannot cope with changes in environments, policies and mechanisms. These factors may change frequently in a distributed environment, especially in a heterogeneous environment. Therefore, in order to develop better fault-tolerant systems that can cope with constant changes in environments and user requirements, it is essential to separate the fault tolerant computing policies and mechanisms in application programs. The second is, on the other hand, a number of techniques have been proposed for the construction of reliable and fault-tolerant computing systems. Many computer systems are being developed to tolerant various hardware and software failures. However, most of these systems are to be used in specific application areas, since it is extremely difficult to develop systems that can be used in general-purpose fault-tolerant computing. The motivation of this thesis is based on these two aspects. The focus of the thesis is on developing a model based on the reactive system concepts for building better fault-tolerant computing applications. The reactive system concepts are an attractive paradigm for system design, development and maintenance because it separates policies from mechanisms. The stress of the model is to provide flexible system architecture for the general-purpose fault-tolerant application development, and the model can be applied in many specific applications. With this reactive system model, we can separate fault-tolerant computing polices and mechanisms in the applications, so that the development and maintenance of fault-tolerant computing systems can be made easier.

Reactive ball milling to produce nanocrystalline ZnO

Ball milling of zinc powders in oxygen atmosphere leads to nanocrystalline ZnO. The average grain size has a value of 9 nm. The zinc oxidation proceeds gradually. It is compared with the combustion oxidation reactions of metals (Zr, Ti, Fe and Sn) reported previously. We propose a new parameter ΔH/C_p(metal) instead of simplified adiabatic temperature to judge if the mechanochemical oxidation of a particular metal happens via gradual or combustion reaction.

Solid state recycling of 5083 Al alloy by hot extrusion

The machined chips of 5083 Al alloy were recycled by hot extrusion at 723 K with an extrusion ratio of 44:1 in air. Corrosion and mechanical properties of the recycled specimens have been compared with those of a virgin extrusion which was processed from the ingot block. As a result of salt immersion tests, mass loss of the recycled specimen was not less than twice of that of the virgin extrusion. The deterioration in corrosion properties for the recycled specimen was attributed to the excessive contamination of Fe which promoted galvanic corrosion. As a result of tensile tests, the recycled specimen exhibited a good combination of high strength and high elongation to failure at room temperature. The excellent mechanical properties for the recycled specimen were attributed to the refined microstructure. However, the elongation to failure of the recycled specimen at elevated temperatures more than 573 K was lower than that of the virgin extrusion. The contamination of oxide particles is likely to be responsible for the lower elongation in the solid recycled specimen.

Extrusion properties of a Zr-based bulk metallic glass

The extrusion behavior of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 metallic glasses in the supercooled liquid region was investigated. Good extrusion formability was observed under low strain rates at temperatures higher than 395 °C. The metallic glasses were fully extruded without crystallization and failure within the range of T=395–415 °C under strain rates from 5×10⁻³ s⁻¹ to 5×10⁻² s⁻¹, and the deformation behavior of the metallic glasses during the extrusion was found to be in a Newtonian viscous flow mode by a strain rate sensitivity of 1.0.

Compression and extrusion of metals using rotating dies

Experimental and theoretical investigations of compression and extrusion of metals with steadily or cyclically rotating dies were carried out. Reasonably simple models were produced by classical plasticity theory and analytical equations were developed to establish a theoretical basis for the associated phenomena. Analytical solutions agreed well with the experimental results.