Abstract Thermally sprayed coatings have residual stresses due to the processing techniques where the particles go through thermal softening / melting, high velocity impact and rapid solidification. The nature and magnitude of residual stresses in these coatings determine the bond strength and failure mechanisms. This investigation thus involves a non-destructive neutron diffraction residual stress evaluation of suspension high-velocity oxy-fuel (S-HVOF) thermal sprayed alumina and YSZ coatings onto 304 stainless steel substrates. SHVOF spray is a high deposition efficiency process to deposit coatings from sub-micron or nanometric feedstock particles. Neutron diffraction measurements were performed at the UK ISIS facility, using ENGIN-X pulsed neutron diffractometer to obtain through thickness residual stress profiles. The Z-scanning method was used to avoid pseudo-strains in the neutron diffraction measurements near the coating surface whereby the incident neutron beam/gauge volume was partially submerged and traversed vertically out of the horizontal coating surface. The residual stress in the alumina coating was compressive across the whole thickness while the stress changed from tensile to compressive in the YSZ coatings. The residual stress measurements were complemented by lab based X-ray diffraction residual stress measurement techniques. Depth sensing indention of the coatings were also performed to gain a comprehensive understanding of the stresses in SHVOF sprayed ceramic coatings.
The nanomechanical properties of polymers that contained (styrene–methyl methacrylate) copolymer (PS-PMMA) composites with reduced graphene oxide sheets (RGO) prepared by (i) in situ bulk polymerization and (ii) a microwave irradiation (MWI) method were compared. The nanomechanical properties such as the hardness and elastic modulus of these copolymers were analyzed using Berkovich nanoindentation. The results indicate that the composite obtained using the MWI method exhibited a better morphology and increased dispersion with enhanced thermal stability. As a result, the mechanical properties also improved due to increased mechanical interlocking between the graphene oxide (GO) nanofillers and the PS-PMMA matrix, which improved the mechanical strength. An average increase of 136% in hardness and 76% in elastic modulus were achieved through the addition of only 2.0 wt % of RGO composite obtained via the MWI method.
A finite element analysis (FEA) based wear algorithm model is presented to predict sliding wear behavior of a composite cobalt-based (Stellite 6) alloy. This study aims to provide an understanding of FEA model behavior using: (a) free-mesh, (b) composite material microstructure, and (c) wear test conditions of loading and geometry which are consistent with ASTM G133-02. Results indicate that the wear model using free-mesh is able to predict wear in composite alloy within the limits of experimental deviation using a suitable kD (wear-rate) value. The rationale for the differences in the experimental setup and FEA model calculations is discussed in terms of the role of wear debris, wear mechanisms, and ball wear.
Abstract Purpose: The purpose of the study is to investigate the dispersion of droplet nuclei/aerosol which are produced during coughing and continuous talking in order to quantify the risk of infection due to airborne disease transmission. Methods: A three-dimensional modelling of aerosol transport due to human respiratory activities such as coughing and talking within a room environment has been simulated using CFD technique. An inert scalar transport equation was used to represent aerosol cloud, while turbulence was modelled with the \(k-ϵ\) turbulence model. A modified Wells-Riley equation was used to calculate the risk of infection based on quanta emission concept. Results The spatial and temporal distribution of aerosol cloud within the room is initially driven by the upward flowing thermal plume surrounding the human, but later driven by the flow field constrained by the walls and cooler air movement. While the cough generated aerosols are concentrated in a smaller space within the room, the continuous talk generated aerosols are distributed throughout the room. Conclusion Within an indoor environment, 2m distancing will not be enough to protect healthy people from aerosols coming from an infected person due to continuous talking with prolonged exposure.
The geological storage of carbon dioxide (CO2), also referred to as CO2 geosequestration, represents one of the most promising options for reducing greenhouse gases in the atmosphere. However, most of the time, CO2 is captured with small amounts of other industrial gases such as sulphur dioxide (SO2) and hydrogen sulphide (H2S), which might be compressed together and stored in depleted petroleum reservoirs or aquifers. Moreover, during CO2 geosequestration in reservoirs, pressure variations during injection could force some amount of CO2 (with or without other acid gas impurities) into the caprock; thereby, altering the petrophysical, geochemical, and geomechanical properties of the caprock. Thus, the brittleness index of the reservoir and caprock might be impacted during CO2 geosequestration due to the chemical reactions between the rock minerals and the formation fluid. Furthermore, to meet the world net-zero carbon target, the promotion of CO2 utilization is paramount. This could be possible by developing an effective technology for cyclic CO2 geosequestration (with or without gas impurities). Therefore, studies on the co-injection of CO2 with other acid gases from industrial emissions, their withdrawal from the porous medium, and their impact on reservoir and caprock integrity are paramount. In this study, a dual-tubing string well completion technology was designed for cyclic injection and withdrawal of CO2 (with or without another acid gas), and numerical simulations were performed using TOUGHREACT codes, to model the cyclic process and investigate the co-injection of SO2 and H2S (separately) with CO2 in sandstone formations overlain by shale caprock. A novel technique of converting the volume fraction of minerals to their weight fraction was developed in this study, to evaluate the brittleness index of the sandstone reservoir and shale caprock during CO2 geosequestration. The findings of the study indicate that the porosity and permeability increase for the CO2 only and CO2-H2S injection cases, in the shale caprock; while for the CO2-SO2 injection case, porosity and permeability only decreased in the layers of the shale caprock contacted by SO2 and due to anhydrite precipitation. In all the injection cases, the porosity and permeability of the sandstone reservoir decreased in a few layers directly below the perforation interval of the production zone. However, in other regions in the sandstone reservoir, the porosity and permeability increased for the CO2 only and CO2-H2S injection cases. In contrast, for the CO2-SO2 co-injection case, porosity and permeability decreased in the layers of the sandstone rock contacted by SO2. In all the CO2 geosequestration cases, the brittleness of the shale and sandstone rocks investigated decreased slightly, except in the CO2-SO2 co-injection case where the brittleness of the sandstone rock decreased significantly. Based on the mineralogical composition of the formations in this study, co-injection of SO2 gas with CO2 gas, only decreased the brittleness index of the shale caprock slightly, but significantly decreased the brittleness of the sandstone reservoir.
Nanoscale impact fatigue tests were conducted to comprehend the relative fatigue performance and failure modes of 100 nm thick diamondlike carbon (DLC) film deposited on a 4 in. diameter Si (100) wafer of 500 μm thickness. The nanofatigue tests were performed using a calibrated TriboIndenter equipped with Berkovich indenter in the load range of 300–1000 μN. Each test was conducted for a total of 999 fatigue cycles (a low cycle fatigue test). Contact depth in this load range varied from 10 to 30 nm. An integrated contact stiffness and depth sensing approach was adapted to understand the mechanisms of fatigue failure. The contact depth and stiffness data indicated some peculiar characteristics, which provided some insights into the mechanisms of cohesive and adhesive failure in thin films. Based on the contact stiffness and depth data, and surface observations of failed DLC films using atomic force microscope and scanning probe microscopy, a five-stage failure mechanism is proposed. The failure of films starts from cohesive failure via cracks perpendicular to the film/substrate interface, resulting in a decrease in contact depth with number of fatigue cycles and no appreciable change in contact stiffness. This is followed by film delamination at the film/substrate interface and release of elastic stored energy (residual stress) resulting in an increase in contact stiffness. Finally, as the film breaks apart the contact stiffness decreases with a corresponding increase in contact depth.
In this paper, we investigate the aerosol cloud flow physics during three respiratory actions by humans (such as coughing, talking, and breathing). With given variables (i.e., velocity, duration, particle size and number of particles, and ambient conditions), the standoff safe distance during coughing, talking, and breathing should be the distance where virus-laden droplets and aerosols do not have significant transmission to another person. However, at a critical distance, the aerosol cloud flux can still be extremely high, which can immediately raise the transmission in a localized area to another person during a static condition. In this study, computational fluid dynamics analysis of selective respiratory actions has been carried out to investigate the effect of the standoff distance and assess the importance of social distancing in indoor places. The prediction of the aerosol transport due to flow generated from coughing, talking, and breathing was obtained by applying the Eulerian–Lagrangian approach. From the simulation results, it can be concluded that the aerosols released due to continuous talking travel a similar distance to that released due to sudden coughing. On the other hand, aerosols exhaled from breathing do not travel a long distance but float in air for a long time.
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