جستجوی مقالات مرتبط با کلیدواژه « Friction » در نشریات گروه « مکانیک »

In this study, the performance of biochar and titanium dioxide nanoparticles in combination with epoxidized soybean oil as a biolubricant is investigated. biochar nanoparticles were produced from sugarcane bagasse coal using the ball mill. Then, after the production of biochar nanoparticles, in order to check their quality and size, samples are photographed using a scanning electron microscope. Titanium dioxide nanoparticles were also prepared commercially. In the next step, nanoparticles with weight percentages of 0.1, 0.2, and 0.5 were combined with biological fluid, after ensuring the stability of the nanofluid, the prepared samples were tested to determine the wear and friction properties. The results show the friction coefficient changes for nano titanium dioxide fluids are better than nano biochar lubricants. At the concentration of 0.1, the average friction coefficient of titanium dioxide nanoparticles was recorded as 0.092 and nano biochar as 0.115. For titanium dioxide and nano-biochar with a concentration of 0.2, it is 0.067 and 0.143, respectively, and for a concentration of 0.5, it is 0.064 and 0.111, respectively. The results of the wear test also show the wear rate of nano-lubricant discs with concentrations of 0.1, 0.2, and 0.5 containing titanium dioxide compared to nanobiochar 24.65, 35.43, and 85.48% is decreased respectively.

Friction and wear are ubiquitous, from nano-electro-mechanical systems in biomedicine to large-scale integrated electric propulsion in aircraft carriers. Applications of nanomaterials as lubricating oil additives have achieved great advances, which are of great significance to control friction and wear. This review focuses on the applications of nanomaterials in lubricating oil and comprehensively compares their tribological characteristics as lubricating oil additives. Finally, suggestions for future research on nanomaterials as lubricating oil additives are proposed. Hence, this review will promote a better fundamental understanding of nanomaterials for lubricating oil application and help to achieve the superior design of nanoadditives with outstanding tribological performances.

Split Hopkinson pressure bar apparatus (SHPB) is used commonly for determining high strain rate material properties. The validity of the SHPB test results depend on many parameters. In this paper, the effect of specimen dimension (aspect ratio) as well as friction on test results is studied both numerically and experimentally. ABAQUS/Explicit is used for numerical study. To this end, the signals at strain gage positions (on input and out bars) are extracted and stress-strain curve of the specimen is determined using wave propagation analysis. By comparing these stress-strain curves for different states of friction and specimen dimensions, the validity of the experimental and numerical results are checked. By increasing friction, the stress increase and strain decrease in the output stress-strain curve and the best result is for no friction condition. Its is observed that by increasing the aspect ratio, the discrepancy of the results for different friction conditions decreases. Specifically, in simulation results, the difference between maximum stresses of with and without lubrication for aspect ratios 0.25, 0.5, 1.0 and 1.5 are 58%, 18%, 9% and 5%, respectively which is in agreement with experimental trends. In other words, different stress-strain curves are obtained for different aspect ratios in the presence of friction which is mainly due to the friction effect rather than strain rate effect. As the friction increases, the error will reduce the overall strain of the sample and increase the yield stress.

Modeling of processes and systems is very essential step in control engineering. This paper considers a two-degree-of-freedom launcher which can move in Azimuth and Elevation directions and presents a model of the system. In this model, the relationships between inputs and outputs of the system and their interactions are carefully derived. In addition to the effect of controlled inputs, all other effective factors such as friction and backlash on the behavior of the system are considered. For this purpose, two types of Viscous and Coulomb frictions have been considered in different parts of the launcher, and a model of them is presented. Furthermore, in order to use this modeling in control procedure, a single-input single-output approach (SISO) is presented. In other words, using this view, both Azimuth and Elevation direction of the launcher are considered independent of each other, and the interferences between these two directions are considered as disturbance inputs.

The phenomenon of abrasion and friction in mechanical mechanism and the ways to reduce them have been highly regarded. One of these methods is surface texturing, which can be accomplished using a laser with high speed and accuracy. In this study, a precise numerical model is developed to investigate the frictional behavior of the dimple transient film formation effect. Then the effect of laser made textures on a ST37 steel disc is studied experimentally in linear contact situation in the mixed lubrication regime. In this study, the friction coefficient is measured after 100m distance for different input important parameters of velocity and vertical load. Results have shown that friction coefficient decreases with increasing speed and decreasing applied force. Comparison of the results between the textured and smooth discs showed that the friction coefficient decreased by 12 to 23% in the experimental study, while numerical estimates of the possibility of a decrease of between 25 and 40% were also predicted. At high velocities, the numerical model estimates and the results of the experiment are very close.

Aluminum extrusion processes is a common method for production of prismatic aluminum profiles with identical cross-section. In extrusion process, friction is one of the most important factors and it plays a crucial role in this process. Friction affects the output profile shape, temperature distribution, extrusion load and etc. One of the best methods to control and reduce the friction between different surfaces during extrusion process is using a lubricant. The aim of this paper is studying the effect of lubricant in aluminum extrusion process of the AA6082 alloy by employing the varying friction coefficient between interfaces. For this purpose the finite element analysis has been adopted by using the commercial DEFORM 3D finite element software and in order to verify the obtained results, the experimental results which are available in the literature have been used.The results show that, the friction reduction decreases the required extrusion force and maximum temperature of work piece significantly. In addition, by reducing the amount of friction between interfaces, the more uniform velocity distribution at the output profile is obtained which leads to improvement in the output profile shape and reduction in the dead metal zones.