Orientation dependence of cyclic deformation behavior and dislocation structure in Ti–5at.% Al single crystals

Cyclic deformation behavior and substructure in single crystal Ti–5at.% Al alloy with different orientations fatigued at Δε_t/2=0.4% were examined. The selected loading orientation includes: single prism slip, A; double prism slips [$\text{2}\text{1}\text{̄}\text{1}\text{̄}\text{0}$], B; pyramidal slip, C; and twinning [0001], D. The testing results show that the crystallographic orientation has a strong effect on the cyclic stress response and the plastic deformation mode of Ti–5at.% Al single crystals. The crystals displayed an initial cyclic hardening followed by a striking softening period, and then a saturation stage was reached in specimens A and B. In contrast, an obvious cyclic saturation stage was obtained after first cyclic hardening until to fracture in specimens C and D. Trace analysis on the surface of specimens with an optical microscope shows that the ($\text{1}\text{1}\text{̄}\text{00}$) single prism slip was operated in specimen A during cycling. The ($\text{10}\text{1}\text{̄}\text{0}$) and ($\text{1}\text{1}\text{̄}\text{00}$) double prism slips can be distinguished from the traces on the (0001) surface in specimen B. The ($\text{1}\text{1}\text{̄}\text{01}$) pyramidal slip and the ($\text{1}\text{1}\text{̄}\text{00}$) prism slip were activated simultaneously in specimen C. Twinning is the primary plastic deformation mode in specimen D. The twinning type includes: {$\text{11}\text{2}\text{̄}\text{1}$}, {$\text{10}\text{1}\text{̄}\text{1}$}, {$\text{11}\text{2}\text{̄}\text{2}$} and {$\text{10}\text{1}\text{̄}\text{2}$}. The substructure in the fatigued specimens was examined using TEM. Typical dislocation configuration is well developed saturation bundle structure (SBS) in specimen A, while it is the planar edge dislocations which are tangled on the primary ($\text{10}\text{1}\text{̄}\text{0}$) plane and arranged parallel to the [0001] direction in specimen B. Fully developed loop patches were formed in specimen C. Typical deformed structure was the twin bundles and dislocations among twins in specimen D. The effects of plastic deformation mode on the cyclic stress response and the corresponding dislocation configuration of Ti–5at.% Al single crystals are then discussed.     

Survey of experimental data and assessment of calculation methods of properties for the air–water mixture

Thermodynamic properties of the air–water mixture at elevated temperatures and pressures are of importance in the design and simulation of the advanced gas turbine systems with water addition. In this paper, comprehensive available experimental data and calculation methods for the air–water mixture were reviewed. It is found that the available experimental data are limited, and the determined temperature is within 75 °C. New experimental data are needed to supply in order to verify the model further. Three kinds of models (ideal model, ideal mixing model and real model) were used to calculate saturated vapor composition and enthalpy for the air–water mixture, and the calculated results of these models were compared with experimental data and each other. The comparison shows that for the calculation of saturated vapor composition, the reliable range of the ideal model and ideal mixing model is up to 10 bar. The real model is reliable over a wide temperature and pressure range, and the model proposed by Hyland and Wexler is the best one of today. However, the reliability of the Hyland and Wexler model approved by experimental data is only up to 75 °C and 50 bar, and it is necessary to propose a new predictive model based on the available experimental data to be used up to elevated temperatures and pressures. In the calculation of enthalpy, compared to the ideal model, the calculated results of the ideal mixing model are closer to those of real model.     

On the real singularities points of cycloids,epi- and hypocycloids

This work considers the continuous transition between singular points of cycloids with help of complex parameters.     

Research of Stamp Forming Simulation Based on Finite Element Method

We point out that the finite element method offers a great functional improvement for analyzing the stamp forming process of an automobile panel. Using the finite element theory and the simulation method of sheet stamping forming, the element model of sheet forming is built based on software HyperMesh,and the simulation of the product′s sheet forming process is analyzed based on software Dynaform. A series of simulation results are obtained. It is clear that the simulation results from the theoretical basis...     

Preparation and alkaline stability of polyethylene composite hydroxide exchange membranes with different cations

Hydroxide exchange membrane fuel cells (HEMFCs) are a cost-effective alternative to proton exchange membrane fuel cells due to the advantages on fast oxygen reduction reaction kinetics, low cost and weak corrosion. Hydroxide exchange membrane (HEM) is the core component for HEMFC. At present, lacking highly robust and chemically stable HEMs is the main challenge to realizing durable HEMFCs. Polyethylene composite HEMs are considered as the-state-of-the-art HEM candidates due to their excellent mechanical properties, thus allowing for the use of ultrathin HEMs in HEMFCs to achieve a high cell and stack performance. Yet, the chemical stability of polyethylene composite HEM still needs to be improved for more durable HEMFC. In this study, we report that the preparation and chemical stability understanding of three polyethylene composite HEMs (named AEH-TMA, AEH-DMP and AEH-TMI) functionalized with trimethylamine (TMA), N-methylpiperidine (DMP) and 1, 2, 4, 5-tetramethylimidazole (TMI), respectively. We find that AEH-TMI exhibits a low conductivity and inferior chemical stability in comparison to AEH-TMA and AEH-DMP. To gain insight into chemical stability behavior, we have also prepared three organic chemicals (named Bn-TMA, Bn-DMP and Bn-TMI) as cations model by reacting benzyl chloride with TMA, DMP and TMI cations and elaborately studied their chemical stability in various water content systems. The results show that the overall chemical stability of cations can be strongly improved with increasing the surrounding water, and Bn-TMI suggests a lower chemical stability than Bn-TMA and Bn-DMP at high water content condition.