The interface between rock-concrete under high water pressure may lead to concrete leaching, which is crucial to the safety of concrete gravity dams. However, the mechanism of concrete leaching in the micro pore-structure is not well understood. Thus, this study aims to investigate the effect of concrete leaching on the microstructure and permeability of the rock-concrete interfacial transition zone (ITZ).First, rock-concrete specimens were subjected to an accelerated leaching process using ammonium chloride. Subsequently, the micro pore-structure, calcium compound, and micro-morphology of the degraded rock-concrete interface were analyzed by nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Permeabilities of the ITZ under different dissolution times were measured by the steady-state method. The above results indicate that the cement slurry dissolves most rapidly in the ITZ, forming a dominant leakage channel. The seepage characteristics of the ITZ are primarily determined by the micro pore-structure. As the dissolution process progresses, the increase in capillary pores enhances the permeability. Finally, considering the penetration of cement slurry, a novel mathematical model of permeability evolution in ITZ was proposed. Compared with experimental results, it shows that this mathematical model can predict the deterioration of permeability in ITZ.
Retaining elongated grain microstructure during thermo-mechanical processes would be attractive for obtaining high-strength aluminium alloys with good toughness. A small Zr addition promotes the formation of Al 3 Zr dispersoids to inhibit the recrystallisation. Since the dispersoids precipitate directly from castings, their inhomogeneous distribution reduces the effectiveness on the recrystallisation resistance. This paper systematically summarised the theoretical and experimental contributions to optimise the distribution of dispersoids in the Zr-containing aerospace Al alloys including Al–Cu–Li and Al–Zn–Mg alloys. It is concluded that improving the distribution of dispersoids across a grain can be effectively realised by refining the homogenisation conditions such as lowering ramp heating rate, two-step homogenisation, etc., and by controlling the concentrations of the dispersoid-forming elements such as Zr, Mn, Sc, etc.
In order to get rid of the pollution to environment by acidic electrolytes, an electrolyte system of NaOH and Na2SiO3 was used to prepare micro arc oxidation (MAO) coating on the surface of ZK60 Mg alloy.The effect of the concentration of electrolyte ingredients on the corrosion-resistance of the MAO coating was investigated.Results show that the MAO coating obtained at a lower concentration of NaOH is more smooth and uniform , and has better corrosion resistance.At the same time, with the increase of the concentration of Na2SiO3 the coating thickness increases and corrosion current density decreases, while its corrosion resistance is increased.
Drift has long been an issue in atomic force microscope (AFM) systems and limits their ability to make long time period measurements. In this study, a new method is proposed to directly measure and compensate for the drift between AFM cantilevers and sample surfaces in AFM systems. This was achieved by simultaneously measuring z positions for beads at the end of an AFM colloidal probe and on sample surface through an off-focus image processing based visual sensing method. The working principle and system configuration are presented. Experiments were conducted to validate the real time drift measurement and compensation. The implication of the proposed method for regular AFM measurements is discussed. We believe that this technique provides a practical and efficient approach for AFM experiments requiring long time period measurement.
The massive amounts of dust formed during bamboo CNC milling presents serious risks to human health and equipment. The present study aimed to determine the particle size distribution (PSD) and shape characteristics of bamboo milling dust derived from different average chip thicknesses. Spindle speed and feed rate were varied in combination, in setting up two experimental groups having the same average chip thicknesses. Sieving and flatbed scanning image analyses were collectively utilized for the morphological analysis of bamboo dust. The results showed that less than 5% of the particles were below 100 μm in terms of mass, but represented more than 83% in number. Average chip thickness was positively correlated with a mass proportion of bamboo dust with large size, which was preferably generated when reducing spindle speed instead of increasing feed rate. Spindle speed and feed rate individually affected the particle size and particle size distribution instead of average chip thickness. The aspect ratio, roundness and convexity of bamboo milling dust were augmented with a reduction in particle size, indicating that bamboo milling dust with smaller size had more a regular shape, a smoother profile and fewer corners. These findings provide a theoretical basis for better understanding bamboo milling dust and its related control in the bamboo processing industry.
The flyer velocity is one of the critical parameters for welding to occur in laser impact welding (LIW) and plays a significant role on the welding mechanism study of LIW. It determines the collision pressure between the flyer and the target, and the standoff working distance. In this study, the flyer velocity was measured with Photon Doppler Velocimetry under various experimental conditions. The laser energy efficiency was compared with measured flyer velocity for various laser energy and flyer thickness. In order to reveal the standoff working window, the peak flyer velocity and flyer velocity characteristic before and after the peak velocity and the flyer velocity was measured over long distance. In addition, the rebound behavior of the flyer was captured to confirm the non-metallurgical bonding in the center of the weld nugget in LIW. Furthermore, the flyer size and confinement layer effect on the flyer velocity were investigated.
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