Optimal configuration of Energy-Efficient Ethernet

The IEEE 802.3az standard provides a new low power mode that Ethernet network interfaces can use to save energy when there is no traffic to transmit. Simultaneously with the final standard approval, several algorithms were proposed to govern the physical interface state transition between the normal active mode and the new low power mode. In fact, the standard leaves this sleeping algorithm unspecified to spur competition among different vendors and achieve the greatest energy savings. In this paper, we try to bring some light to the most well known sleeping algorithms, providing mathematical models for the expected energy savings and the average packet delay inflicted on outgoing traffic. We will then use the models to derive optimum configuration parameters for them under given efficiency constraints.     

Microstructure and mechanical properties of in-situ MC-carbide particulates-reinforced refractory high-entropy Mo0.5NbHf0.5ZrTi matrix alloy composite

Refractory high-entropy Mo_0.5NbHf_0.5ZrTi alloy matrix composite with MC-carbide particulates-reinforced was prepared by arc melting. It is found that Mo_0.5NbHf_0.5ZrTiC_0.1 and Mo_0.5NbHf_0.5ZrTiC_0.3 alloys consist of one disordered body-centered cubic (BCC) solid solution phase as the matrix phase and MC carbide phase. MC carbide is enriched with Zr and Hf due to the higher binding strength and without any Mo. Noticeable strengthening from the carbide is not observed for C_0.1 and C_0.3 alloys while the compressive plasticity is improved slightly due to the decrease of solution strengthening for the matrix BCC disordered solid solution phase.     

Physical metallurgy of concentrated solid solutions from low-entropy to high-entropy alloys

The alloy world could be divided into low-entropy (LEAs), medium-entropy (MEAs) and high-entropy alloys (HEAs) based on the configurational entropy at the random solution state. In HEAs, four core effects, i.e. high entropy, sluggish diffusion, severe lattice distortion and cocktail effects, are much more significant than low-entropy alloys in affecting phase transformation, microstructure and properties. In fact, the degree of the influence from these core effects more or less increases with increased mixing entropy. The trend is gradual from low-entropy alloys to high-entropy alloys. In this article, physical metallurgy of HEAs is discussed with the bridge connected to that of conventional alloys. As disordered and ordered solid solutions are the main constituent phases of alloys, the understanding of solid solutions is fundamental for the understanding of alloys. In addition, as dilute solid solutions have been well treated in current physical metallurgy, concentrated solid solutions from low-entropy to high-entropy alloys are focused in this article. Physical properties are especially emphasized besides mechanical properties.     

The mechanical properties of natural fibre based honeycomb core materials

This paper investigates the compression properties of square and triangular honeycomb core materials based on co-mingled flax fibre reinforced polypropylene (PP) and polylactide (PLA) polymers. Initial testing focused on investigating the sensitivity of the tensile properties of the composites to variations in processing conditions. Following this, a range of triangular and square honeycomb structures were manufactured using a simple slotting technique. These structures were tested in compression at quasi-static rates of strain and their strength and specific energy absorption characteristics were determined. Finally, a finite element analysis was undertaken to accurately predict the strength, energy-absorbing characteristics, buckling behaviour and failure modes of these natural fibre based core materials.     

Phase formations in low density high entropy alloys

Phase formations in high entropy alloys (HEAs) with at least two light elements in literature are predicted by CALPHAD (CALculation of PHAse Diagrams) thermodynamic calculations and the results are compared with experimental observations. The comparison suggests that the applicability of traditional CALPHAD calculations depends on the manufacturing processes of HEAs. Factors such as solute trapping, energies of defects need to be considered while predicting phases in HEAs prepared by non-equilibrium processes. The effects of light elements (Al, Ti, Si, alkali and alkaline earth metals) on the phase formations in HEAs are discussed. Especially, intermetallics predicted for Si-containing HEAs by traditional CALPHAD calculation can be suppressed in rapid solidification process, due to the solute trapping effect. Mg or other alkali and alkaline earth metals can lead to the formations of various intermetallics in HEAs prepared by conventional casting, but could be dissolved into solid solutions by non-equilibrium processes such as mechanical alloying. It is proposed that non-equilibrium processes may be an effective way to introduce light elements Si, alkali and alkaline earth metals into HEAs.     

Uniaxial and biaxial failure behaviors of aluminum alloy foams

Combined shear–tensile test have been performed on a closed-cell aluminum alloy foams with three relative densities over a wide range of loading rates in order to probe their failure behaviors under biaxial loading conditions. Quasi-static uniaxial compressive and tensile tests have also been conducted to investigate uniaxial failure behaviors of the aluminum alloy foams. The materials exhibit uniaxial failure stress asymmetry due to different failure mechanism in the uniaxial tensile and compression. Comparison is made between three phenomenological failure criteria and the measured failure stresses under different loading conditions to verify these criteria. The experimental failure surfaces of the aluminum alloy foams provide support for the three phenomenological failure criteria when suitable Poisson’s ratio is employed. The shape of the experimental failure surface in principal stress plane was not significantly influenced by variation in the relative density. The slight expansion of the failure surfaces with loading rate happened to be isotropic for this investigated closed-cell aluminum alloy foams in combined shear–tensile testes.     

Nanoindentation characterised plastic deformation of a Al0.5CoCrFeNi high entropy alloy

Abstract

The plastic deformation of a high entropy alloy Al_0.5CoCrFeNi was investigated by instrumented nanoindentation over a broad range of strain rates at room temperature. Results show that the creep behaviour depends on the strain rate remarkably. In situ scanning images showed a significant pile up around the indents, demonstrating that a highly localised plastic deformation occurred in the process of nanoindentation. Under different strain rates, contact stiffness and elastic modulus basically remain unchanged. However, the hardness decreases as indentation depth increases due to indentation size effect. For the same maximum load, serrations became less prominent as the loading rate of indentation increased. Similar serrations have been observed in the current alloy upon quasi-static compression.     

Effect of heavy cryo-rolling on the evolution of microstructure and texture during annealing of equiatomic CoCrFeMnNi high entropy alloy

The effect of cryo-rolling on the evolution of microstructure and texture during annealing was investigated in equiatomic CoCrFeMnNi high entropy alloy. For this purpose the alloy was cold- and cryo-rolled to 90% reduction in thickness followed by annealing at temperatures ranging from 700 °C to 1200 °C. The two alloys showed the development of predominantly brass type deformation texture consistent with profuse nano-twin formation reported in this alloy. The cryo-rolled material showed significantly finer grain size after different annealing treatments as compared to the cold-rolled alloy. This could be attributed to finer microstructure in the cryo-rolled material providing greater number of available sites for nucleation. The recrystallization texture of cold- and cryo-rolled materials showed the presence of similar texture components indicating that cryo-rolling had limited effect on the formation of annealing texture. The volume fractions of different texture components did not reveal significant dependence on the annealing temperature. The evolution of texture could be explained on the basis of absence of strong preferential nucleation and growth during annealing.     

Elevated temperature low cycle fatigue of grey cast iron used for automotive brake discs

This paper evaluates the fatigue life properties of low carbon grey cast iron (EN-GJL-250), which is widely used for automotive brake discs. Although several authors have examined mechanical and fatigue properties at room temperatures, there has been a lack of such data regarding brake discs operating temperatures. The tension, compression and low cycle fatigue properties were examined at room temperature (RT) and at brake discs’ working temperatures: 500 °C, 600 °C and 700 °C. The microstructure of the material was documented and analysed. Tensile stress–strain curves, cyclic hardening/softening curves, stress–strain hysteresis loops, and fatigue life curves were obtained for all the above-mentioned temperatures. It was concluded, that Young’s modulus is comparable with both tension and compression, but yield its strength and ultimate strength are approximately twice as great in compression than in tension. All the mechanical properties remained quite stable until 500 °C, where at 700 °C all deteriorated drastically. During fatigue testing, the samples endured at 500 °C on average at around 50% of cycles at room temperature. Similar to other materials’ properties, the cycles to failure have dropped significantly at 700 °C.     

Mechanical properties of functionally graded 2-D cellular structures: A finite element simulation

Functionally graded cellular structures such as bio-inspired functionally graded materials for manufacturing implants or bone replacement, are a class of materials with low densities and novel physical, mechanical, thermal, electrical and acoustic properties. A gradual increase in cell size distribution, can impart many improved properties which may not be achieved by having a uniform cellular structure.The material properties of functionally graded cellular structures as a function of density gradient have not been previously addressed within the literature. In this study, the finite element method is used to investigate the compressive uniaxial and biaxial behavior of functionally graded Voronoi structures. Furthermore, the effect of missing cell walls on its overall mechanical (elastic, plastic, and creep) properties is investigated.The finite element analysis showed that the overall effective elastic modulus and yield strength of structures increased by increasing the density gradient. However, the overall elastic modulus of functionally graded structures was more sensitive to density gradient than the overall yield strength. The study also showed that the functionally graded structures with different density gradient had similar sensitivity to random missing cell walls. Creep analysis suggested that the structures with higher density gradient had lower steady-state creep rate compared to that of structures with lower density gradient.