High Load Applications Research Articles

A highly effective and simplified DPWM algorithm for NPC inverters for high power factor load applications

A highly effective and simplified DPWM algorithm for NPC inverters for high power factor load applications

Fabrication and Characterization of AA7050 Nano Composites by Enhancing Directional Properties for High Impact Load Applications

Fabrication and Characterization of AA7050 Nano Composites by Enhancing Directional Properties for High Impact Load Applications

Evaluating the effect of unidirectional loading on the piezoresistive characteristics of carbon nanoparticles

The piezoresistive effect of materials can be adopted for a plethora of sensing applications, including force sensors, structural health monitoring, motion detection in fabrics and wearable, etc. Although metals are the most widely adopted material for sensors due to their reliability and affordability, they are significantly affected by temperature. This work examines the piezoresistive performance of carbon nanoparticle (CNP) bulk powders and discusses their potential applications based on strain-induced changes in their resistance and displacement. The experimental results are correlated with the characteristics of the nanoparticles, namely, dimensionality and structure. This report comprehensively characterizes the piezoresistive behavior of carbon black (CB), onion-like carbon (OLC), carbon nanohorns (CNH), carbon nanotubes (CNT), dispersed carbon nanotubes (CNT-D), graphite flakes (GF), and graphene nanoplatelets (GNP). The characterization includes assessment of the ohmic range, load-dependent electrical resistance and displacement tracking, a modified gauge factor for bulk powders, and morphological evaluation of the CNP. Two-dimensional nanostructures exhibit promising results for low loads due to their constant compression-to-displacement relationship. Additionally, GF could also be used for high load applications. OLC’s compression-to-displacement relationship fluctuates, however, for high load it tends to stabilize. CNH could be applicable for both low and high loading conditions since its compression-to-displacement relationship fluctuates in the mid-load range. CB and CNT show the most promising results, as demonstrated by their linear load-resistance curves (logarithmic scale) and constant compression-to-displacement relationship. The dispersion process for CNT is unnecessary, as smaller agglomerates cause fluctuations in their compression-to-displacement relationship with negligible influence on its electrical performance.

Expression of semaphorin-3A in the joint and role in osteoarthritis.

Osteoarthritis (OA) is characterised by the deterioration of cartilage in the joints and pain. We hypothesise that semaphorin-3A (sema-3A), a chemorepellent for sensory nerves, plays a role in joint degradation and pain. We used the mechanical joint loading (MJL) model of OA to investigate sema-3A expression in the joint and examine its association with the development of OA and pain. We also analyse its effect on chondrocyte differentiation using the ATDC5 cell line. We demonstrate that sema-3A is present in most tissues in the healthy joint and its expression increases in highly innervated tissues, such as cruciate ligaments, synovial lining and subchondral bone, in loaded compared to nonloaded control joints. In contrast, sema-3A expression in cartilage was decreased in the severe OA induced by the application of high loads. There was a significant increase in circulating sema-3A, 6 weeks after MJL compared to the nonloaded mice. mRNA for sema-3A and its receptor Plexin A1 were upregulated in the dorsal root ganglia of mice submitted to MJL. These increases were supressed by zoledronate, an inhibitor of bone pain. Sema-3A was expressed at all stages of Chondrocyte maturation and, when added exogenously, stimulated expression of markers of chondrocyte differentiation. This indicates that sema-3A could affect joint tissues distinctively during the development of OA. In highly innervated joint tissues, sema-3A could control innervation and/or induce pain-associated neuronal changes. In cartilage, sema-3A could favour its degeneration by modifying chondrocyte differentiation.

High temperature tribological response of Fe-2Cu-0.8C-CaF2 self-lubricating composites at high speeds

In this work, Fe-2Cu-0.8C-CaF2 self-lubricating composites with calcium fluoride solid lubricant (3 □ 12 wt.%) were examined for their friction and wear at 5 and 10 m/s, at 500 °C. Addition of CaF2 decreased density and hardness of composites. During sliding, materials gained weight due to oxidation. Compared to the base matrix (Fe-2Cu-0.8C), composites showed lower weight gain and lower coefficient of friction. Increase in porosity with CaF2 content increased oxidation resulting in higher weight gain and increased friction due to wear debris abrasion. Increase in speed reduced weight gain due to higher material loss. Adhesion was the dominant wear mechanism in base matrix; delamination and wear debris abrasion in composites. Temperature rise at sliding surfaces was theoretically estimated. Increase in speed increased temperature, which reduced friction due to softening and shearing of solid lubricant. Composite with 3 wt.% CaF2 showed least surface damage and 6 wt.% showed lowest coefficient of friction, i.e., lower by 16% and 10% at 5, 10 m/s than base matrix. Tribological response of the composites to a broad range of applied parameters, viz. speed, load and temperature taken from earlier works and present work is briefly summarized. The study suggests the dominant role of CaF2 content and the wear debris in altering the tribological response. Further, the stability of the developed composites at high temperature and high load conditions was also established. The study suggests that the developed composites could serve high-load and high-temperature applications for heavy machinery such as bearings, shafts and gears.

Thermal fatigue response of W-EUROFER brazed joints by the application of High Heat Flux loads

Thermal fatigue response of W-EUROFER brazed joints by the application of High Heat Flux loads

Effects of the tool geometry, cutting and ultrasonic vibration parameters on the cutting forces, tool wear, machined surface integrity and subsurface damages in routing of glass-fibre-reinforced honeycomb cores

Honeycomb structured materials have been increasingly used for high-load applications; however, machining of the highly elastic honeycomb cores is still facing challenges from tool wear issues and degraded machined surface integrity. In this work, experimental evaluations were carried out in routing glass-fibre-reinforced honeycomb cores under the parametric control of tool geometries (straight and helical flutes), vibration amplitude (0–12 μm) and cutting speeds (30–120 m/min) in a full factorial design. The recorded cutting forces, cutting temperatures, tool wear and the machined surface integrity indicators were statistically tested and discussed, with their main effects and interactions. Executive findings indicated that the helical-flute routers in the oblique cutting produced lower cutting forces; in contrast, the straight-flute routers in the orthogonal cutting produced lower cutting temperatures. Moreover, the flank wear of the straight-flute routers decreased with the amplitude; whereas the flank wear of the helical-flute routers increased with the amplitude. The use of ultrasonic vibration-assisted energy would reduce propagations of cracks and pull-out fibres, compared to using conventional machining. Additionally, the internal damages such as out-of-plane cracks and fractures were characterised by their width and area via computed tomography scans. When routing at a high cutting speed (~90 m/min), the superimposed assisting energy coupled with the straight-flute routers could adversely convert the minor delamination into severe out-of-plane cracks. Causes and the underlying mechanisms are all discussed and detailed.

Towards Closed-Loop Recycling of Ceramic Particle-Reinforced Aluminium Alloys: Comparative Study of Resistance-Heating Sintered Primary and Solid-State Recycled Secondary SiCp/AlSi7Mg Composites

Particle-reinforced aluminium matrix composites (AMC) with a high-volume fraction of ceramic reinforcement (>30 vol.%) combine high specific strength and stiffness with good wear resistance and thermal stability, resulting in their increasing popularity in high-load applications, such as brake discs and bearings. It is hence assumed that AMC will accumulate as scrap in the near future. Appropriate recycling strategies must therefore be developed to maintain AMC’s inherent properties. Melt-metallurgical recycling routes bear the danger of dissolving the ceramic reinforcement in the liquid metallic matrix and contaminating primary melts or forming intermetallic phases in secondary melts. Here, a solid-state AMC recycling route with crushing and sintering is investigated, wherein all steps are carried out below the solidification temperature of the aluminium matrix. A sintered primary AMC is mechanically converted into a particulate/powdery secondary raw AMC in coarse, medium, and milled quality (i.e., with d ≈ 7–12 mm, d ≈ 3–7 mm, and d < 300 µm) and subsequently resistance heating sintered to a secondary AMC under a variation of the sintering pressure. The two AMC generations are analysed and discussed regarding their microstructure and mechanical properties. Since the secondary AMC show reduced the mechanical strength, the fracture surfaces are analysed, revealing iron contaminations from the mechanical processing.

Assessment of a high strength concrete using experimental and numerical methodologies for high strain rate ballistic impacts

The high compressive strength of concrete materials enables it to be implemented for many applications. Understanding its response under high strain rate loadings is especially important for some of these applications. This study investigates the high strain rate response of a high-performance concrete denoted as BBR9 under ballistic impact. This is conducted through both an experimentally and numerically based methodology. BBR9 targets are impacted with a spherical projectile at velocities ranging from 432 to 1459 m/s and three target thicknesses ranging from 25.4 to 58.1 mm. These impacts are studied numerically by formulating a finite element model corresponding to the experimental design in this study. The mechanical response of the concrete target is captured using the Holmquist-Johnson-Cook (HJC) concrete model with its parameters calibrated to confined compressive experiments of the BBR9 concrete. The simulations show good agreement with the kinetic experimental data with an average error across all simulation points of approximately 5%, thereby validating the HJC model for this concrete in these high strain rate loading applications.

ОРГАНИЗАЦИЯ ВИРТУАЛЬНОЙ ОБЛАЧНОЙ ЛАБОРАТОРИИ ДЛЯ РАЗВИТИЯ ПРОФЕССИОНАЛЬНЫХ КОМПЕТЕНЦИЙ В ОБЛАСТИ СЕТЕВОГО И СИСТЕМНОГО АДМИНИСТРИРОВАНИЯ ПРИ ПОДГОТОВКЕ БУДУЩИХ IT-СПЕЦИАЛИСТОВ

The article proves the importance of modern virtualization tools usage in professional education by modeling the cloud infrastructure of a corporate network for the student professional competencies development of the network and system administration. The use of the specially organized virtual cloud laboratory allows effectively developing not only theoretical, but also practical component in training future competitive IT specialists. It also helps to test technologies for ensuring reliable operation of a distributed, high-load web application in the private cloud service of a corporate computer network.

Impact Behaviour of Laminated Bamboo, E-Glass and Hybrid Bamboo/E-Glass Fibre Composites

Natural fibres are currently used as a mutually reinforcing fibre foundation. One of their prospects, particularly that which is said to be good in mechanical reinforcement, is bamboo fiber.This study focuses on developing a high-quality bamboo that can withstand high load and high impact application, that utilize and promote green technology and local crops production ofbamboo in Malaysia.The work scope was focusing onthe impact performance of bamboo fiber as natural fiber, E Glass fiber as synthetic fibers, and combination of both bamboos with E Glass Fiber as hybrid composites.The developedlaminated hybrid bamboo was hit by a hard object named impactorin the drop impact testing procedures. The analysisgives the sound of the impact properties thatcan be absorb with optimal load before the specimen penetrated or failures. Configuration of 6,12,18 layers of woven bamboo and 6,12,18 layers of woven E-Glass, in order of thicknesses 9 mm, 18 mm, 22 mm and 4 mm, 7 mm and 10 mm, respectively were fabricated by hand lay-up. The thickness of each and individual strips of woven bamboo and E-Glass used in the range of 1.5-2.5 mm thicknesses. The results showed that the impact performance of the hybrid bamboo/E-Glass had outperformedthe non-hybrid bamboo/E-Glass.The developed hybrid bamboo composites show highly potential use for ballistic application in replacing metal armor.

Study of ruthenium film grown in oxygen environment for x-ray optics application

Ru shows high damage threshold as compared to other standard materials Au, Rh and Pt for high heat load applications in high brilliance synchrotron radiation source and x-ray free electron laser. It is also a promising candidate to be used as a protective capping layer in multilayers for increasing their life time. In the present study, Ru thin films of 500Å thickness were deposited in oxygen environment at different substrate temperatures varying from 70°C to 500°C. In reactive ion beam sputtering process, the flow of Ar and reactive O2 gas was maintained in 4:1 ratio keeping total flow 3 SCCM constant. The deposited films were characterized using grazing incidence x-ray reflectivity (GIXRR), grazing incidence x-ray diffraction (GIXRD) and secondary ion mass spectroscopy (SIMS) techniques. A significant change in GIXRR profile was observed in the sample grown at 100°C and 500°C whereas the GIXRD measurements indicated no significant formation of ruthenium oxide at different temperatures. However, a strong peak of Ru2Si3 (222) at 500°C was observed indicating a strong interfacial reaction at ruthenium/ substrate interface.The experimental data suggested a weak signature of RuO2 phase in the films deposited at RT, 70°C and 100°C and therefore the effect of ruthenium oxide with 10% composition in pure ruthenium was calculated on optical performance in extreme ultra violet region of photon energy (85-115 eV).

Abrasive wear resistance of idler roll polymeric materials

Idler rolls are an integral part of belt conveyors. Recently, steel idler rolls have been replaced with polymeric ones in low to middle load applications, bringing several advantages due to the polymer’s lightweight and low abrasiveness in the conveyor belt. However, using polymeric material for high load application brings challenges, particularly presenting similar structural and abrasion resistance to steel. This work puts forwards a methodology using a rubber-wheel tribometer to evaluate the abrasion resistance of polymeric idler rolls in their most severe operating condition (halted idler roll) and defines a threshold limit based on the results obtained with steel idler rolls. The methodology was applied to 07 different polymeric materials. To further understand materials abrasions resistance, scratching tests were performed, and the main wear mechanisms, verified by scanning electron microscopy (SEM) and abrasion factor (FAB), were discussed along with the material properties. The main conclusions are: i) some polymeric materials present abrasion resistance similar to steel rolls; ii) the wear micromechanisms, verified by SEM and FAB, are good indicators of abrasion resistance of the materials but insufficient because they do not include temperature and fatigue effects resulting from multi abrasive events; iii) the additive fillers significantly altered the abrasive resistance of materials, although they do not change the material properties significantly.

Synthesis, Microstructure and Wear Analysis of Copper Alloy with Alumina and Graphene as Reinforcement

Hybrid copper alloy composites are widely used in numerous industrial applications, such as aeronautics and automobile, because of their wear resistance and excellent cast ability. They are widely used for high load and low speed application such as stone crushers and earth movers. The pin-on-disc dry sliding wear investigation and microstructure characterization of copper alloy reinforced with Al2O3 and graphene particulates were conducted. Stir casting technique is used to prepare the composites. Wear loss of hybrid composite (Cu alloy + 4wt.% Gr + 4wt.% Al2O3) is compared with Cu alloy, Cu alloy + 4wt.% Gr and Cu alloy + 4wt.% Al2O3. In microstructural analysis SEM and EDS images were assessed to know the distribution uniformness of reinforcement in copper alloy matrix. Dry wear test was carried on pin on disc machine. In the first trial, the sliding speed was kept as constant to 300 rpm and load was varied in range of 1 kg, 2 kg and 3 kg. In the second trial, the load was kept as constant and the sliding speed was varied in range of 100, 200 and 300 rpm. Results in both trials have shown that the wear resistance was increased and wear rate was very low in hybrid composite (Cu alloy + 4wt.% Gr + 4wt.% Al2O3) compared to the other compositions of the tested composites.

Graph-Based Dynamic Modeling of Two-Phase Heat Exchangers in Vapor Compression Systems

Vapor compression systems are a popular thermal management solution for high heat load applications because they benefit from the high heat transfer rate of two-phase fluid flow. However, model-based design and control of these systems proves challenging because of the complex and coupled hydro-thermal dynamics as the working fluid changes phase in the heat exchangers. When modeling these heat exchangers, there exists a strong tradeoff between model accuracy and computational complexity. While different techniques have aimed to reduce computational complexity of the model, they come at the cost of a decrease in accuracy. On the other hand, high fidelity models are computationally expensive to run. To bridge the gap between computational efficiency and accuracy, this work develops a novel multi-state graph-based dynamic modeling approach. The multi-state graph modeling approach is used to develop a dynamic model of a two-phase heat exchanger. The heat exchanger model is integrated into a vapor compression system model and the model behavior is verified against other models present in the literature. The results demonstrate that the multi-state graph model can accurately capture system dynamics within 1% of the current state of the art modeling approaches while providing valuable modularity for system level modeling. Additionally, the computational load can be made comparable to less accurate approaches.

Experimental investigations on indirect contact type liquid desiccant cooling systems for high latent heat load application

Heat driven sorption technologies are promising alternatives to traditional vapour compression based systems for comfort cooling. High latent heat load applications and improved indoor air quality are best accommodated by the various sorption technologies available and desiccant-based cooling systems. Liquid desiccant-based systems are preferred over solid desiccant-based systems due to lower pressure drop, the possibility of continuous operation, solar energy for regeneration, and the ease of storage of regenerated desiccant solution. This paper investigates the experimental performance of indirect contact type liquid desiccant cooling systems for applications involving a high latent heat load. An experimental test rig includes a dehumidifier, regenerator, and heat exchanger, all been developed, fabricated and connected to work as one unit. The dehumidifier and regenerator transfer the heat and mass from liquid desiccant to the air membrane making the arrangement an indirect contact type of heat exchanger. Lithium Chloride solution is used as a desiccant solution in experiments, and Polyvinylidene Fluoride is used as a membrane material. The effect on dehumidifier performance parameters like rate of moisture removal, sensible heat effectiveness, and latent heat effectiveness is studied for varying inlet air parameters as well as for various liquid desiccant operating parameters. The inlet air specific humidity ranges from 10 to 13 g/kg da, and the inlet air flow rate varies from 2 to 4.5 kg/hr. The inlet desiccant temperature supplied at 24–32 0C with desiccant concentration varied 30–42%, and the desiccant solution mass flow rate is supplied in the range of 3–11 kg/h. Various dehumidifier performance parameters like rate of moisture removed, latent heat effectiveness and sensible heat effectiveness are discussed. Based on the experimentation, utilizing the optimum values of inlet air parameters or optimum values of desiccant solution parameters has been recommended to achieve the cooling system's highest possible latent heat effectiveness.

Decarbonisation of heavy-duty diesel engines using hydrogen fuel: a review of the potential impact on NOx emissions

Hydrogen–diesel co-fuelling may reduce NOx and PM2.5 emissions if used in lower load construction machinery and HGVs. In high load applications such as electrical generators, emissions could be higher than pure diesel, unless further abated.

Performance of 3D printed topologically optimized novel auxetic structures under compressive loading: experimental and FE analyses

The auxetic structures, because of their negative Poisson's ratio, have a lot of potential applications in the aerospace and automobile industry due to their exceptional mechanical properties under bending, shear, and compression loads. In this study, three novel auxetic structures were prepared by creating modifications in the existing ones found in the literature. The in-plane mechanical performance of the novel structures under uniaxial compression loads was evaluated using experimentally validated finite element analysis (FEA) models. Moreover, their deformation and collapse behavior was also examined. It was found that all of the new auxetic structures possess higher Young's modulus and energy absorption capacities as compared to the conventional re-entrant structure. To further enhance their aforementioned properties, a topology optimization technique, i.e., shape optimization, whose effect on the mechanical performance of auxetic structures is not yet explored, was applied to the conventional and the new structures. The mechanical properties of shape-optimized structures were found to be significantly better than the un-optimized structures. Hence, auxetic structures, with compressive properties superior to the traditional ones were developed in this research which are favorable for high load applications. The modifications made to conventional structures, as well as the shape optimization technique utilized in this research, can be used as a guideline to produce other high-performance auxetic structures.

Application of a Rolling Bearing Life Model with Surface and Subsurface Survival to Hybrid Bearings in High-Load and High-Speed Applications

Application of a Rolling Bearing Life Model with Surface and Subsurface Survival to Hybrid Bearings in High-Load and High-Speed Applications

Wear resistant solid lubricating coatings via compression molding and thermal spraying technologies

This work combines two industrially friendly processing methods in order to create wear resistant and solid-lubricating composite coatings potentially suitable for high load applications. Layered composite coatings were fabricated over wrought stainless steel 444 (SS444) by compression molding a mixture of solid lubricant polymer, polytetrafluoroethylene (PTFE, 80 wt%), and wear resistant polymer, polyimide (PI, 20 wt%), onto iron aluminide (Fe3Al) thermal spray coatings without the need of either primers or adhesives. The fabrication process consisted of three main steps: deposition of the Fe3Al thermal spray coating onto a SS444 substrate and transfer into a metal mold; transfer, compress, and sinter mixed polymeric powder onto the thermal spray coating; and finally, sample cooling to room temperature. This method takes advantage of the high surface roughness of thermal spray coatings, which increases mechanical adhesion of slippery PTFE to the underlying metallic material. Coatings were produced with and without a small amount of graphite (5 wt%) to analyze its impact on sliding and wear properties. Unlike current coating technologies, the thickness of the coatings presented herein can be easily and quickly tailored by varying the amount of polymer powder added to the mold prior to compression or by grinding after fabrication. We produced and analyzed coatings ~1.3 mm in total thickness that portray coefficient of frictions ~0.1, similar to pure PTFE. The calculated wear rates for both coatings with and without graphite are an order of magnitude lower than what has been previously reported for coatings of similar composition. The influence of graphite on wear properties was found to be minimal due to the high content of self-lubricating PTFE yet can act as a way to lower material costs and increase the coatings load capacity.