Search

Dry sliding wear tests were performed on Mg97Zn1Y2 alloy at various temperatures of 20, 50, 100, 150 and 200 °C using a pin-on-disc wear testing machine in order to reveal mild-severe (M-S) wear transition mechanism during elevated-temperature wear testing. It was shown that at each test temperature, the wear rate increased with increasing load, and all wear rate-load curves demonstrated two distinct stages i.e. mild and severe wear stages. The predominant wear mechanisms operating in mild and severe wear stages were analyzed, and they were indicated in the mild and severe wear regimes of a wear mechanism transition map, respectively. M-S wear transition mechanism was analyzed by comparison of microstructure transformation and hardness change in subsurfaces of samples tested in mild and severe wear stages, from which M-S wear transition mechanism was confirmed as softening of surface material arising from dynamic recrystallization (DRX) microstructure transformation. The M-S wear transition load was found to have a linear relationship with test temperature, and decreased with rising test temperature. M-S wear transition obeyed a critical surface DRX temperature (SDT) criterion under given conditions, and the transition loads were estimated at various test temperatures by using the criterion.

In this work, the droplet evaporation rate and ignition probability of biodiesel of neem and karanja were investigated and modelled using RSM. The biodiesel from neem and karanja oil were prepared using trasesterification. Thermo-physical properties of fuels was tested. Further, a test rig was fabricated to find out the rate of evaporation of fuel droplet as well as the ignition probability of the biodiesel and comparison was done so as to find out the feasibility for combustion application. It was concluded that the ignition probability and evaporation rate of karanja biodiesel was better than neem biodiesel. Also, evaporation rate and ignition probability above critical surface temperature (450 °C) drastically increased for all fuel. The model of ER and IP was found statistically significant and predict responses accurately at any surface temperature.

The article presents the results of an experimental study to determine the dependence of the critical surface density of heat flux from wind influence. The convergence of the obtained experimental data in each of the individual experiments was investigated. The dependence of the critical surface heat flux density on wind influence is established and the regression is defined, which describes such dependence with the corresponding coefficients.

Let $$x:M \to \mathbb{S}{^{n + p}}(1)$$ be an n-dimensional submanifold immersed in an (n + p)-dimensional unit sphere $$\mathbb{S}{^{n + p}}(1)$$ . In this paper, we study n-dimensional submanifolds immersed in $$\mathbb{S}{^{n + p}}(1)$$ which are critical points of the functional $${\cal S}(x) = \int_M {{S^{{n \over 2}}}} dv$$ , where S is the squared length of the second fundamental form of the immersion x. When $$x:M \to \mathbb{S}{^{2 + p}}(1)$$ is a surface in $$\mathbb{S}{^{2 + p}}(1)$$ , the functional $${\cal S}(x) = \int_M {{S^{{n \over 2}}}} dv$$ represents double volume of image of Gaussian map. For the critical surface of $${\cal S}(x)$$ , we get a relationship between the integral of an extrinsic quantity of the surface and its Euler characteristic. Furthermore, we establish a rigidity theorem for the critical surface of $${\cal S}(x)$$ .

With the advancement of modern enabling technologies, surfaces of high value-added products are changing from traditional simple geometries to complex geometries that feature freeform shapes. The analysis of topographical features on freeform surfaces is challenging because surface shapes are no longer planar and measurement data often require surface description in the form of triangular meshes. An approach is proposed to extend the watershed segmentation from planar surfaces to freeform surfaces. Surface topography is first extracted from measured surfaces (mesh surfaces) using proper mathematical operations, e.g. fitting and filtration. The watershed segmentation based on Maxwell's theory is extended to 3D triangular meshes and applied to the extracted surface topography defined as a scalar function associated with the vertices of the mesh surface. Critical surface points such as peaks, pits and saddles are identified to construct a Pfaltz graph. Ridge lines and course lines are then traced starting from saddles and following the steepest uphill and downhill paths to peaks and pits, respectively. Wolf pruning of the change tree is employed to merge over-segmented regions. The extended watershed segmentation method is applied to segment surface topography of the additively processed scaffold and lattice surfaces.

Thermal-runaway propagation in battery systems can escalate the battery fire hazard and pose a severe threat to global users. In this work, the thermal-runaway propagation over 18650 cylindrical lithium-ion battery was tested in the linear-arranged module with a 3-mm gap. State of charge (SOCs) from 30% to 100%, ambient temperatures from 20°C to 70°C, and three tab-connection methods were investigated. Results indicate that the battery thermal-runaway propagation speed was about 0.35 ± 0.15 #/min, which increased with SOC and ambient temperature. The critical surface temperature of thermal runaway ranged from 209°C to 245°C, which increased with ambient temperature while decreased with SOC. Compared to the open-circuit module, the flat tab connection could cause an external short circuit to accelerate the thermal-runaway propagation, and the non-flat tab connection was more likely to trigger an explosion. A heat transfer analysis was proposed to qualitatively explain the speed and limiting conditions of thermal-runaway propagation, as well as the influence of SOC, ambient temperature, and tab connection. This work reveals the thermal-runaway propagation characteristics under well-controlled environments, which could provide scientific guidelines to improve the safety of the battery module and reduce battery fire hazards.

Hydrogen adatoms are a critical surface species for several reactions catalyzed by Fe surfaces, such as Fischer-Tropsch synthesis, ammonia synthesis, and the hydrodeoxygenation of biomass-derived o...

Theory and modeling are combined to reveal the physical and dynamical processes that control Saharan dust transport by amplifying African easterly waves (AEWs). Two cases are examined: active transport, in which the dust is radiatively coupled to the circulation, passive transport, in which the dust is radiatively decoupled from the circulation. The theory is built around a dust conservation equation for dust-coupled AEWs in zonal-mean African easterly jets. The theory predicts that, for both the passive and active cases, the dust transports will be largest where the zonal-mean dust gradients are maximized on an AEW critical surface. Whether the dust transports are largest for the radiatively passive or radiatively active case depends on the growth rate of the AEWs, which is modulated by the dust heating. The theoretical predictions are confirmed via experiments carried out with the Weather Research and Forecasting model, which is coupled to a dust conservation equation. The experiments show that the meridional dust transports dominate in the passive case, while the vertical dust transports dominate in the active case.