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

Engine life prediction has always been of interest in the automotive industry. Wear is the main factor in limiting the life of an engine. Wear is considered among the parts with a lot of reciprocating movement in the engine. Piston rings and liners with bearings are the most important wear parts in the engine. In this article, the wear pattern in the rings and cylinders of the same family of engines has been investigated after 500 hours of durability tests. The rating results of these parts after the durability test are considered wear criteria. Then, these qualitative data are related to the parameters of blowby and the amount of engine oil consumption in the last hours of the test by the fuzzy logic method. Finally, a criterion for measuring wear is provided without the need to disassemble and rate the engine. The application of this criterion is to plan future tests on used engines without disassembling them and according to their wear rate. The important achievement of this method is saving the cost and time of engine preparation according to the amount of wear.

Hybrid composite of aluminum base reinforced with alumina and graphite particles was prepared by vortex casting method along with centrifugal casting and its tribological behavior was investigated. The wear test was performed with a sliding speed of 60 cm/s and a force of N30. The results showed that by adding graphite and alumina to the aluminum base, the abrasion resistance of the hybrid composite increased. The amount of graphite in the hybrid composite had a great effect on the wear rate, and adding it to an optimal amount leads to a decrease in the wear rate and its further increase leads to an increase in the wear rate. With the presence of alumina particles, the hardness decreased less and the wear resistance increased. The Al-Al2O3-Gr hybrid composite showed a much better wear rate than the base alloy as well as the Al-Gr composite. Al-Gr composite had a higher wear rate than the base alloy due to the high amount of graphite and the absence of alumina particles. The scanning electron microscope investigations of the wear surfaces showed that in the base alloy, the wear mechanism is a combination of adhesive, scraping, and indentation mechanisms, while in composites, the dominant wear mechanism is scratching and indentation.

is In this research, the microstructure and wear behavior of high-strength AISI 4340 low-alloy steel coated using austenitic stainless steels ER309, ER312 and cobalt base steel stellite 6 were investigated by tungsten-gas arc welding method. Microstructural investigations were carried out by optical microscope and scanning electron microscope equipped with X-ray energy diffraction spectroscopy system.Hardness measurement was done by Vickers method with a load of 30kgf on the surfaces and Vickers microhardness in the transverse sections of the welds in zigzag form. Also, in order to evaluate the wear behavior, the wear test of the pin on the disc was used to identify the wear mechanism. By reducing the intensity of the current in the second layer and also by increasing the number of welding layers, the dilution and mixing of the sub-layer decreased and the hardness increased, and the highest hardness was 565 (HV) for stellite6. The results of the wear test showed that the highest friction coefficient was related to ER 309 weld metal has an average value of 0.68 and the lowest friction coefficient is related to stellite 6 weld metal with an average value of 0.53.

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.

Due to the high importance of manufacturing methods with metal powders such as aluminum, in this study, using pure aluminum powder, samples were made by two methods of powder metallurgy and spark plasma sintering, and then the samples in terms of microstructure, hardness. Abrasion resistance and corrosion resistance were evaluated. Spark plasma sintering method compared to powder metallurgy method shows significant improvement in hardness, microstructure density, increased wear resistance, and corrosion of aluminum. This improvement can be attributed to the high speed and temperature of the sintering process as well as the simultaneous application of force and temperature, resulting in a more complete density of the structure. The coefficient of wear and hardness increased from 0.9 and 43 Brinell in powder metallurgy method to 0.8 and 49.3 Brinell in spark plasma sintering method, respectively. Also, according to the results of corrosion test, the linear corrosion resistance of sintering-plasma-spark sample is higher than powder metallurgy sample.

The purpose of this research is to experimentally investigate the role of copper oxide nanoparticles in improving the tribological properties of the lubricant. This research consists of three stages. In the first stage, copper oxide nanoparticles with weight percentages of 0.1, 0.2 and 0.5 were added as an additive to Behran Super Turbo Diesel SAE 15W-40 oil. An ultrasonic bath was used to disperse the nanoparticles in the fluid, and span80 surfactant was used to stabilize the fluid and prevent solid nanoparticles from settling. In the second stage of the experimental tests, including the wear test using the pin-on-disk wear test device and the thermal conductivity test, were performed. In the third stage, the results of the analysis and the performance of the nano-fluid blends were compared with the base fluid. The results of this research showed a decrease in friction coefficient values, a decrease in wear rate and an increase in thermal conductivity of nano-lubricant blends compared to the base fluid. Based on the results, the lowest coefficient of friction, the lowest amount of wear and the highest coefficient of thermal conductivity are related to the nano-lubricant mixture containing 0.5% by weight of copper oxide nanoparticles. The friction coefficient reduction rate of this nano-lubricant mixture was 37.1% compared to the base oil, the wear reduction rate was 58.3% and the thermal conductivity increase rate was 3.84% compared to the base oil. The results show the positive role of copper oxide nanoparticles as an additive in improving the tribological properties of the working fluid.

Al-Si alloys are commonly used in the manufacture of auto parts, including pistons. Although this alloy offers desirable properties for use in pistons, several microstructural properties, such as the presence of needle-like silicones or dendrites, interfere with the performance of the components produced. In this study, ZrO2 reinforcing particles were used to produce metal-based composites by friction stir process. First, the microstructural characteristics of the stir zone (SZ) of the samples produced were studied using a optical microscope. The results showed that the friction stir process improves the microstructural properties of the base metal, including the size of the silicon particles, and the distribution of these particles in the base metal. Then the particle distribution and bond quality between ZrO2 and aluminum reinforcing particles were investigated using SEM. Then, hardness and wear tests were performed to determine the wear and hardness of the composites. Pin-on-disk wear tests were performed at speeds of 1 m / s and 2 m / s and normal applied loads of 5 N, 10 N and 20 N. The wear test results showed that the wear resistance of the produced composite was improved by about 172% compared to the base alloy.

1.4923 stainless steel is one of the options for producing Iranian gas turbine (IGT25) compressor blades and upgrading IGT25 +., as well as the importance of wear resistance in turbine parts and the small number of studies in the field of wear as a destructive mechanism of turbine parts, in this research the effect of residual stress caused by shot peening on the wear resistance of steel 1.4923 was investigated. To create the compressive residual stress, shot peening operations were used at 5, 10, 15 and 20 minutes. Microstructural studies by optical microscopy (OM) and scanning electron microscopy (SEM) showed that with increasing shot peening time, the thickness of the plastic deformation area increases so that the plastic deformation area can be divided into three plastic deformation areas. Severe, ordinary plastic deformation and the area affected by plastic deformation. Calculations on the results of X-ray diffraction (XRD) showed that with increasing shot peening time, the amount of compressive residual stress increases to 694 MPa. With increasing compressive residual stress on the surface, the wear resistance of the samples increased up to 90% due to the increase in the density of dislocations and grain refining.  Also, the investigation of worn surfaces by SEM showed that the wear mechanism in the samples is oxide adhesive wear and increasing the residual stress of the samples causes the transfer of the wear regime to mild wear abrasion with the appearance of crater areas.

In this research article, the effect of zeolite nanoparticles on the tribological properties of high molecular weight polyethylene, which are widely used in orthopedic implants, has been studied. Improving the tribological properties of this polymer is one of the medical industry challenges which has an important effect on the life-time of orthopedic implants. Nanocomposites based on ultra-high molecular weight polyethylene (UHMWPE) blend, containing 2 to 6 phr of nano-zeolite, were prepared via melt compounding followed by injection molding. The morphology was studied using scanning electron microscopy. The wear and temperature of specimens as well as friction coefficient were characterized by employing a pin on disk test under 50 N and sliding velocity of 0.5 m/s. The wear rates, temperature and friction coefficient of nanocomposite containing 4 phr of nano-zeolite, were 56, 32 and 26%, respectively, lower than those of neat UHMWPE. In contrast, the application of 6 phr of of nano-zeolite, led to agglomeration and increased wear, temperature and coefficient of friction compared to nanocomposite samples. In addition, the morphology of nanocomposite samples, after testing, revealed a smoother surface with the mild abrasion marks than that of of pure UHMWPE sample.

During the operation of rotating machines in large industries such as power plants, the journal bearing failures are numerous. In order to avoid catastrophic damages in bearings and reducing the causes, evaluation of the root causes of bearing failures is important. In this paper, we investigate the root causes of failure in journal bearings, using one of the powerful methods of maintenance fields, which has been named failure mode and effect analysis. In order to collect bearing failures data, have been referred to the six power plants and failures information is obtained. Using this data and charts related to the occurrence probability, detection probability and severity rates which are the main parameters of this method for determining the risk priority number, the failure mode and effect analysis method has been implemented. According to this method, the main failure has been identified as wear. Then, using the well-known model of bearing wear geometries and computational fluid dynamics analysis for solving Navier-Stocks equations, effects of wear on the bearing load capacity, maximum lubrication pressure, in the different locations of wear, in the lower half of the bearing, has been investigated. Finally, the results of the finite element analysis have been compared to the results of the theory and solving the Sommerfeld-Harrison equation for bearing without wear. Also, to reduce the effects of this failure, another bearing geometry has been proposed in a similar situation with a load capacity greater than the custom one.

In this paper, the slider-on-flat-surface (SOFS) test was used to study the galling in automobile body drawing dies (made of GGG60 alloy). The SOFS tests were conducted on the DC06 (EN 10130) and DC04 (MSC standard) alloy sheet metals; according to the following two approaches: in the first approach, the slider was forced to move in a single linear path, repeatedly. While, in the second approach, the slider was moved on separate parallel paths. The second approach was performed using both flat and curved surfaces of the slider to simulate galling conditions on flat and curved surfaces of the dies, respectively. Moreover, the effect of hardness, surface roughness, and mechanical properties of the DC04 and DC06 sheet materials on die galling was investigated. The galling tests’ results were in agreement with the galling wear that occurred in automobile body drawing dies. The results showed that forming DC04 sheet metal will lead to more galling wear. Furthermore, a qualitative coincidence was observed between the results of the aforementioned approaches. Nevertheless, in the first approach, wear emerged in a shorter period; while, in the second approach, the slider was moved on a much longer path for creating observable wear.

Lubrication is one of the most effective ways to reduce friction and reduce the excess heat generated in a mechanical system. Identifying the right additive to improve lubrication properties by additives that have features such as accessibility and higher quality performance is important. The aim of this study was to investigate the effect of silicon dioxide (SiO2) nanoparticles with different concentrations as additives on the thermal and anti-wear properties of lubricants. For this purpose, nanoparticles with concentrations of 0.2, 0.4 and 0.5 wt% were combined with oil. Span 80 surfactant, ultrasonic bath and high speed agitator were used to disperse the nanoparticles into the base fluid and achieve a stable nanofluid. The static stability of nanofluids was also visually investigated. The obtained results showed that the addition of nanoparticles to the oil does not cause any change in its state and over time no sedimentation and phase change was observed, which indicates the very good stability of this nanofluid. In the last stage, wear tests, determination of friction coefficient and thermal conductivity coefficient were performed on the samples. According to the results, the lowest amount of disc wear was related to the lubricating mixture with a concentration of 0.5% by weight. The weight loss of the discs due to wear for this mixture was 60.76%, the reduction of the coefficient of friction was 15.07% and the increase of the thermal conductivity was 2.4% compared to the base oil.

In this research, wear behavior of a TRIP steel and a DP steel from two different heat treatments was investigated on a high-strength low-alloy steel. Reciprocating wear tests were performed at a force of one kg with a constant linear velocity of 0.1 m/s. Wear samples were studied by SEM with point analysis. To study type of phases formed, XRD was used. The results showed that during the wear process, TRIP steel had more weight loss than DP steel, and in TRIP steel, the rate of change in weight decreased significantly during the wear process due to the transformation of the remaining austenite phase to martensite. In the DP steel, due to severe difference in ferrite and martensitic hardness, a more uniform wear surface was produced. Also, experiments showed that Fe2O3 oxide was formed in steel DP and Fe2O3 and Fe3O4 in steel TRIP, which increased the amount of iron oxide in steel TRIP compared to DP steel. Ultimately, the wear mechanism of both steel, delamination and oxidation wear were detected.

High corrosion resistance, proper mechanical properties, and biocompatibility of Ti-6Al-4V alloy make it suitable for medical (dentistry and orthopedic implants), military and electronic industries. The greatest disadvantages of this alloy are poor wear resistance, low fatigue strength and poor tribological properties. The aim of this study was to apply an adhesive coating to improve both corrosion and wear properties of the Ti-6Al-4V alloy. Surface modification of alloy was done by nitrogen plasma nitriding in both electrolyte plasma and atmosphere plasma environment. Finally, the TiN layer was coated on the modified samples, using cathodic arc evaporation technique. The microstructural investigation, surface morphology, and coating thickness were studied by field emission scanning electron microscope (FESEM) equipped with energy dispersive spectroscopy. The grazing incidence X-ray diffraction (GIXRD) was applied to study the phases in the coatings. The corrosion resistance was studied with potentiodynamic polarization and electrochemical impedance spectroscopy. The wear resistance and the coating coefficient of friction were tested with pin-on-disc machine. The corrosion resistance of the samples was improved by applying the coatings and the plasma-nitride/TiN double-layer coating showed the best corrosion resistance with current density of 1.46×10-7A/cm2 and corrosion potential of -0.3V. On the other hand, the lowest thickness reduction in wear test was observed in double-layer coatings, so that the thickness reduction for both double-layer coatings, was less than 4μm, after 300m sliding.

Nowadays, the increase in axial load and speed in railway transportation systems has increased the amount of pressure applied to the surface and energy loss, and has caused severe wear of turnout profiles, especially in turnout intersections. One of the major financial and physical losses to the country's railway is the train derailment in the turnout intersections. As mentioned above, due to the importance of turnout in this study, it has been tried to study the role of damages caused by turnout wear of railway system and explain the necessity for such research in this regard, particularly in Iran, by studying this phenomenon and examining the ruling theories as well as collecting information. In fact, these studies are the starting point for a more precise investigation into this phenomenon. In the following, the movement of train on a turnout is simulated in the "Universal Mechanism" software and the amount of force applied to the turnout and the wear energy is extracted. Furthermore, the effect of different parameters such as speed, axial load, friction coefficient, arc radius, and turnout profile on the rate of wear will be investigated. Then the turnouts are modeled on CATIA software and the forces extracted from the Universal Mechanism simulation are exerted to the turnout in the FEM software, and the stress, strain and deformation of the turnouts are investigated.

Commercial pure (CP) titanium has many applications in biomaterials especially in implants due to its excellent biocompatibility. Despite the importance of surface properties in bio-applications, limited research has been conducted to improve surface properties of CP titanium by improving the structure. Therefore, the purpose of this research is to improve the corrosion and wear properties of CP titanium by reducing grain size by multi-directional forging (MDF) process. For this purpose, annealed CP titanium samples were forged by MDF up to six passes at ambient temperature and 220°C. To investigate the corrosion properties of specimens, the tafel polarization test was performed in a simulated body fluid (SBF) solution. The tribological properties were also investigated by pins-on-disk test at sliding speed and applied stress of 0.2 (m/s) and 1MPa, respectively. The results of microstructure analysis of the samples using a scanning electron microscope (SEM) equipped with EBSD showed that the ultrafine grain structure was formed in titanium CP, after 6 passes of the MDF. The results of the investigation of the tafel polarization test showed that the corrosion resistance of the samples increased with applying MDF and increasing the pass number, regardless of the processing temperature. Also, the corrosion resistance of MDFed samples at 220°C temperature was higher than the MDFed samples at ambient temperature. Wear resistance of CP titanium was also increased, by decreasing the grain size. The results of the investigation of surface morphology of samples using a field-emission scanning electron microscope showed mainly the abrasive and delamination wear mechanisms.

Wear is one of the most detrimental mechanisms which can affect the performance of many industrial systems. TiN coating due to its unique properties such as resistance to wear, oxidation, and heat is widely used in mechanical elements. In this research, TiN coating has been coated on steel substrate using a physical vapor deposition method. The coating’s properties have been obtained using nano-indentation test. Pin on disk wear test has been conducted while the disks are coated. The tests are conducted under three different loads and different speeds. It was shown that the samples with thicker coating show a better tribological performance. In this study, the relationship between wear and entropy has been investigated in order to predict the wear rate for different materials by predicting temperature. Also, temperature changes over time were predicted in two states of with and without coating. It was also shown that the samples with thicker coating have better wear resistance. One of the innovations of this research is the ability to establishing a correlation between the wear rate and produced temperature.

Amorphous/ultrafine grained production method using friction stir processing under water is a novel method which uses a rotating tool to knead the base metal, and immediately after that, it is cooled by water to alter the crystalline structure in the next crystallization and change it into amorphous/ultrafine grained structure. In the present study, the applied metal was copper with purity of 99.8 percent. The properties of crystal structure before and after the test were examined. Examinations using optic microscope (OM) showed that the friction stir processing with higher rounds would decrease the tunnel defects and heterogeneity and cavities, and grain size of sample was reduced. Moreover, hardness test was conducted on samples in cross section and perpendicular to the process line. Results showed that making amorphous using friction stir processing can increase the sample hardness to 45 percent compared with the base metal. The structural properties of samples were examined using x-ray diffusion. Results showed that the peaks presented in diffusion pattern were decreased and their width were increased because of a severe change in plastic form and conducting the process under water which prevent the growth of grains and complete re-crystallization of microstructures. The main reason for reduction in peak intensities and increase in their height was the presence of ultrafine grained phase and extra fine granules. Moreover, the friction behavior of samples were examined using pin on disk method, and a reduction in the friction coefficient was found which was 48 percent compared with the base metal.

Journal bearings are vastly used in major industries such as power generation, oil and gas production, refineries, and the like. Thus, much investigation and study has taken place for more effective maintenance and fault detection of these bearings. An effective method in maintenance for these bearings is Root Cause Analysis (RCA) that tools like FMEA and FTA are used in it. In this paper, initially meanwhile investigation of journal bearing failures prioritizing of them have been down by using FMEA and FTA. For this purpose, expert opinion and field data collection were used in six gas power stations of country and by used them RPN are calculated for faults. Finally considering to RPN result and the importance of wear in journal bearing, this issue is simulated in COMSOL software and using Navier-Stokes equations and load capacity is investigated. At least some suggestions about geometry of journal bearing were presented to improve its performance