جستجوی مقالات مرتبط با کلیدواژه « سرعت دورانی » در نشریات گروه « مکانیک »

To fix the femoral neck fracture using screws, there are different opinions among orthopedic surgeons about screw placement. Also, the parameters of bone drilling, including the angle of the drill tip and the rotational speed of the drill, can also have an effect on the fixation strength. In this research, experimentally and with the help of simulation, the effect of three types of arrangement including triangle, inverted triangle and linear, and parameters of rotational speed and angle of the drill tip on the strength of femoral neck fracture fixation has been investigated for the first time. In experimental tests, the maximum force tolerated by for the inverted triangle arrangement is 25% and 37% higher than the triangle and linear arrangements, respectively. The rotational speed of the drill 2000 rpm compared to 1000 rpm and the tip angle of the drill 60° compared to 118° have increased the connection strength by 11 and 7.5 percent, respectively. The analysis of variance showed that the effect of the type of screw arrangement, respectively. the rotational speed of the drill and the angle of the drill tip on the fixation strength is 83.26, 6.98 and 3.24%, respectively. The results obtained from the numerical simulation showed that the proper arrangement is the inverted triangle with the drilling parameters of the rotational speed of the 2000 rpm and the tip angle of the 60°, which has endured N4782 force.

Composites reinforced with carbon fibers have various applications in different industries, due to their physical and mechanical properties. In this regard, multi-walled carbon nanotubes are used to strengthen the epoxy resin base, which is one of the emerging and important materials. Since machining is required to repair reinforced composite parts, in this research, the damages caused during the process should also be investigated and solutions should be provided. In this study, the delamination damage in the machining of composite parts of epoxy reinforced with carbon fibers and multi-walled carbon nanotubes has been discussed. In this regard, experiments have been conducted with a carbide end-mill at different cutting speeds and feed speeds. Then the delaminations created in these tests are studied. In the analysis of the results, by increasing the rotational speed from 500 to 2500, the amount of delamination increased by 25% and the force decreased by 87%. Also, solutions that include reducing the feed speed will have a significant effect on improving the final quality of the machined part.

Today, wooden products are widely spread in the industry of furniture, art boards, wooden dishes, etc. The traditional and manual manufacturing methods of producing these artefacts cannot compete with mechanized production methods, especially computer numerical control (CNC) machines. Therefore, using of these devices is always increasing. Nevertheless, one of the parameters that affect the production speed is the surface roughness, and the workshops have to spend a lot of time on polishing the products. For this reason, in the present research, the effect of machine parameters (feed speed, rotational speed and transverse step) and tool characteristics (diameter, number of cutting edge and type of cutting edge) on surface roughness of beech wood has been investigated. The outcomes demonstrated that cutting tools with two spiral cutting edges have a more favorable surface roughness than cutting tools with a straight cutting edge and one spiral cutting edge, and tools with a straight edge are not suitable for beech wood. It was also observed that by reducing the transverse step from 0.7D to 0.3D, a lower surface roughness is created. By reducing the tool diameter from 6 to 4 and 3 (mm), reducing the feed speed from 60 to 20 (mm/min) and increasing the rotational speed from 15000 to 25000 (rpm), the surface roughness of final product was improved, significantly.

The Fans are the beating heart of the system and play an important role in the production process in industry. The objective of this paper is the numerical study of flow through an axial fan and examining the effects of fan design parameters on the performance of the fan. Fan design is done with SolidWorks software and the SST-k-ω and k-ε turbulence models are applied in the simulation which are done using CFX software. In the study of pressure distribution and current separation, occurs at the back of the blade attack edge, and as we get closer to the tip of the blade, the vortices resulting from the separation of the flow become decreasing. The effect of changing the length of the blades and their angle has also been studied. The results show that at different rotational speeds, the optimal blade is different and with increasing fan speed, the maximum fan efficiency percentage occurs at a smaller attack angle. By increasing the blade length by 20% the fan output increases 47.5% and the fan power consumption increases by 53%.

Polishing using nanoscale magnetic field (NMAF) is a new method for surface coating with nanoscale roughness as a mechanical process and is done by abrasive powder abrasion as a tool. The force required to move the abrasive particles is provided by a magnetic field that has a relative motion to the workpiece. This method can be used for polishing non-magnetic metal parts or non-metallic parts. One of the special features of this method is the reduction of thermal stresses to the workpiece and the lack of restrictions on polishing surfaces of the workpiece, which due to their geometric shape, the ability to work with conventional tools is difficult. Such as polishing of superalloys and hard metals, as well as for surfaces with special forms that can not be achieved by other methods to an acceptable level of smoothness. In this paper, using the nano-polishing mechanism, the polishing of cylindrical external surfaces of Inconel superalloy is investigated, so that the surface quality is improved at the nanoscale. To create a magnetic field, variable magnets with the ability to adjust the current intensity of the magnetic field have been used. In this research, aluminum oxide and silicon-carbide abrasive particles have been used and their combination.

Single point incremental forming is one of the novel processes in forming of metallic sheets that has created high forming levels in sheet by local plastic deformation. In this paper, new tool based on incremental forming principles is introduced for production of cylindrical flange. Using this tool for forming of the flange, the manual milling machine is used instead of milling machine equipped with computer numerical control (CNC). Forming of flange wall is accomplished by a new tool that includes two forming punches. Tool shank is fixed on milling machine spindle and the value of eccentricity determines the final diameter of flange. Movement of rotary tool is simple and downward with defined step. The results show that flanges with specified diameters can be formed by using this method very fast. Increasing the diameter of the primary hole created on the sheet increases the flange height but also increases the thinning. Increasing rotational speed results in forming flanges with higher height but increasing vertical feed rate of tool decreases the flange height.

Friction stir process is one of the process that improve the mechanical and metallurgical properties of metals surface. One of the important parameters in this process which affect mechanical and metallurgical properties is rotational speed of shoulder and pin tool. In this study, unlike the other research a new tool was designed and manufactured in such a way that rotational speed of pin and shoulder is seperatable from each other and each one can adopt different speed. Friction stir process was done with constant rotational speed of shoulder (800 rpm) and different rotational speed of the pin(800, 1000 and 1250 rpm). Maximum temperature and mechanical properties of the samples was investigated. The results showed that the maximum temperature does not increase greatly with increasing the rotational speed of the pin (2% increase with 25% increase in the rotational speed of the pin). Mechanical properties of the samples increased with increasing the rotational speed of the pin. The ultimate stress was increased 18% when the rotational speed of the pin was changed from 800 rpm to 1250 rpm.

Due to the specific characteristics of composite wood plastic and increasing of this product due to its compatibility with the environment, the quality of the appropriate surface area during the various machining processes on this material has been considered more than before. In this study, after turning operation with self-rotary tool on samples by changing the parameters of spindle speed, the feed rate and cutting depth, to measure and compare the surface roughness of the turning surfaces, the surface quality assessment has been investigated by microscope as well as numerical analysis of the process. The results show that during turning with self-rotary tool, for the cutting depth of 1mm and the feed rate of 22.0mm/rev by increasing the spindle speed from 500 to 710rpm, the surface quality of about 17% improved that this amount compared with conventional turning is also Improved about 37%. Also, due to increasing machining forces, by increasing the feed rate from 22.0 to 44.0mm/rev, surface quality is reduced by about 21%. Comparing the obtained values for surface roughness showed that after the feed rate, the spindle speed had the highest impact on the quality and health of the turning surfaces. Also, comparing the roughness of the measured surfaces during the finite element method and the experimental method showed the proper accuracy and adaptability of these two methods.

Compared to the resistance spot welding (RSW) process, Friction stir spot welding (FSSW) is an ideal process for aluminum alloys. In this study, the effect of welding parameter such as tool penetration depth, tool rotational speed, tool penetration speed and the arrangement of aluminum alloy sheets of 7075-T6 and 2024-T3 on the shear strength of the joining zone in the friction stir spot welding process have been investigated. By properly choosing these parameters, the optimum shear strength of the joint can be attainable. The result of the shear test showed that the increase of tool rotational speed from 800 up to 1250 rpm caused the increase of shear force, However further increase up to at 1600 and 2000 rpm resulted in the decrease of the shear force. By increasing in tool penetration depth, shear force increases. If the alloy Al2024 -T3 is selected to be the upper plate, the connection will have better shear strength.

Friction Stir Welding is an appropriate method to connect different metals in temperatures below their melting point. In spite of this, the effect of thermal cycles causes the reduction in mechanical strength in different weldment regions. On the other hand, because of necessity of doing welding in submerged conditions like in navy industries it is of great importance to investigate and thermally modeling the submerged Friction Stir Welding. In this paper, finite element modeling of friction stir welding in the air and underwater were performed for Al6061-T6 alloys to control the thermal cycles. In addition to cooling effect, the influence of parameters such as welding speed and rotational speed on the maximum temperature in workpiece was investigated. The model results were then examined by experimental data and a reasonable agreement was observed. Results show that increasing rotational tool speed due to increasing in generating heat flux causes increasing in maximum temperature experienced by workpiece in different regions in both air and underwater welding. However, in underwater welding because of boiling water surrounding the tool, temperature drop is more greater than another one. The difference between maximum temperature in air and underwater welding is high. Reducing welding speed causes increasing the maximum temperature. This is due to reducing cumulative generated heat flux during welding. Increasing temperature during welding in air is more salient than doing welding in underwater. In the other word the effect of welding speed on maximum temperature in welding in air is more than underwater welding.

Rotational abrasive flow machining process (RAFM) is one of the modern surface polishing processes where in the material removal in micro and nano sizes is performed by tiny abrasive particles. Rotational abrasive flow machining is very effective in finishing of complex internal and external surfaces.in comparison with other finishing methods. In this study, the rotational abrasive flow machining process has been investigated in polishing of AISI H 13 hot work steel. The main objectives of workpiece rotation was increasing the material removal rate and decreasing the surface roughness of workpiece. So the effects of rotational speed and hardness of workpiece and the mesh size of abrasive particles as input variables on the output parameters including surface roughness and material removal rate have been studied. The results showed that applying of rotational speed of workpiece leads to higher material removal rate and lower surface roughness. Furthermore, the material removal rate is decreased and surface roughness is improved by increasing the mesh size of abrasive particles. Also, increasing the hardness of workpiece leads to decreasing the material removal rate, and in similar cutting conditions, the surface of workpiece with more hardness is better polished in comparison with the surface of workpiece with lower hardness.

In this paper, the effect of friction stir spot welding process parameters in AA 7075-T6 sheets has been investigated. Also, the effect of different rotational speeds and plunge depths of the tool with different backplate materials on shear failure load of the welding area has been studied. Joints were created in two rotational speeds of 800 and 1600 (rpm). Also, different plunge depths of 5/3, 5/5, 5/7 and 5/9 (mm) with two backplate of AA1100 and Ti6Al4V were used. Shear strength test was performed to evaluate the quality of the weld. Results indicated that the backplate material has a direct effect on the shear strength and geometry of the stir zone. In rotational speed of 1600 (rpm) and by using Ti6Al4V backplate with increasing plunge depth, upper sheet of the base metal zone has been teared. Also, it was found that high rotational speeds is caused a drop in shear strength of welds compared with low rotational speeds. Maximum load for shear failure obtained in 800 (rpm) and 5/9 (mm) with Al1100 backplate. Shear failure was observed in the joints because of propagation of crack in circumference of keyhole.

Friction stir extrusion (FSE) is a process based on the heat generated by friction between die and materials in which a sample is produced through consolidation and extrusion of precursor materials such as metal chips. In this paper, the wire samples produced by friction extrusion of aluminum alloy AA7022 chips are investigated. The samples were extruded at different rotational speeds and extrusion forces, and impacts of these two parameters were studied. At first, structural properties of samples were studied using optical microscopy and scanning electron microscopy (SEM). The result showed that the samples produced at higher rotational speeds and lower forces had a far better surface quality and lower surface crack were seen on them. On the other hand, the temperature of process and grain size were increased with rise of rotational speed. The SEM micrographs showed that by changing rotational speed and extrusion force, the amount of adhesion and sintering between aluminum particles change and by optimizing these parameters can decrease wire’s internal defects and pits. In the following, to study mechanical properties, micro hardness and compression tests were used. The values of hardness and yield stress of samples were decreased with increasing rotational speed and increasing the extrusion force to a certain extent caused increase in yield stress of material.

In this paper, the effect of different workpiece geometries on the properties of welded Al-7075-T6 parts in rotational friction welding process has been investigated by using experimental and finite element approaches. Welding process is continuous drive friction welding. In this research, the samples diameter were selected equal to 25 mm and the samples length were selected equal to 75 mm. The process variables such as friction time (t1), forging time (t2), friction pressure (P1) and forging pressure (P2) where assumed to be constant, whereas, rotational speeds were variable and selected equal to 2000 rpm and 2500 rpm. Three cylindrical parts with different cross sectional geometries were adopted as three samples. Finally, to verify the accuracy of numerical analysis, the experimental and thermo-mechanical simulation results were compared and found a good agreement between them. Since, an experimental test is a time consuming and a costly process activity, it was decided to get more results by using an alternative method such as finite element simulation technique. Results of this study showed that changing in front geometric of workpiece is an effective factor for tensile strength, length of workpiece and generated flash in welded area and by changing this factor, properties of welded area can be improved.

In this study, the stability of deionized water based copper oxide nanofluid with weight concentration of 0.1 percent is investigated experimentally. The experiments are designed to investigate the influence of rotational speed and dispersion time of nanoparticles in the base fluid, ultrasonic waving time, type and concentration of surfactants and pH on the nanofluid stability and achieve to an optimal stability condition. The results are statistically analysed using Taguchi method by implementing Qualitek-4 software. Furthermore, nanofluid stability is evaluated by investigation of sedimentation photographs also, zeta potential method. The results showed that using sodium dodecyl sulphate with weight concentration of 0.1 percent, ultrasonic waving by ultrasonic probe device for an hour and changing the pH to 10.72, provide the best conditions for dispersing copper oxide nanoparticles in deionized water. In this condition, prepared nanofluid is maintained it̕s stability with no trace of sedimentation of nanoparticles for forty days at least.

In the present paper, a three-dimensional thermo-mechanical model for friction stir welding is presented. Friction stir welding (FSW) is a relatively new welding process that may have significant advantages compared to the fusion processes. Although originally intended for aluminium alloys, reach of FSW has now extended to a variety of materials including steels and polymers. This study aims to numerically explore the thermal histories and temperature distributions in a work piece during a friction stir welding process involving the butt joining of aluminum 6061-T6. In this regard ABAQUS commercial software was utilized. The process is solid state and as such, temperatures experienced near the weld are lower than those experienced during fusion welding and there are no large density changes due to a solid-liquid transformation.

In the last two decades of the twentieth century, using of hydraulic micro turbines has been wide attention globally. Due to the global move towards decentralization of electric energy production, by using of micro hydropower plants, a comprehensive program for the development of micro turbines compatible with the geographical conditions of Iran was proposed. Hydrocoil is one of the selected turbines of this program. Hydrocoil is a portable axial turbine with low head and flow. In general, the Hydrocoil is designed and built inspired by Archimedes screw pump. Currently, only one manufacturer in the world produce Hydrocoil and Technical information related to it is exclusively at the discretion of this manufacturer. In this paper, in order to achieve the operating Characteristic of the turbine, constant blade pitch hydrocoil , has been studied numerically. Under similar conditions, this results were compared with the results obtained by the University of Pennsylvania. This comparison proves the accuracy of the results. Furthermore, this study was to determine and analyze the behavior of turbines in various conditions in order to achieve working characteristics, main characteristics and constant efficiency characteristics of hydrocoil. These results provide necessary background to build and optimization of hydrocoil.

The aircraft aluminum alloys generally present low weldability by traditional fusion welding process. The development of the friction stir welding has provided an improved way of producing aluminum joints. In this present work the influence of process and tool parameters on strength properties of AA7075-T6 joints produced by friction stir welding was analyzed. Joints were fabricated by varying process parameters and tool parameters. Strength properties of the joints were evaluated and correlated with the microstructure and hardness of weld nugget. This investigation demonstrates, Joints fabricated at rotational speed of 1400 rpm and welding speed of 60 mm/min using the tool with 15mm shoulder diameter, 5mm pin diameter and 45 HRc tool hardness, yielded higher strength properties.

The piston scuffing is a major failure of an internal combustion engine. This failure occurs due to loss of the oil film between the piston and the cylinder liner. The piston scuffing investigation by the acoustic emission (AE) method is a new study. Because this failure occurs randomly، it is an online detection which is very difficult. The goal of this paper is to study the ability of the AE method to be applied to the piston scuff detection. In addition record of the AE signal behaviour، before and after the piston scuffing is another new purpose. To this order، in an experimental set-up، two AE sensors was installed on the cylinder head and the engine block of a diesel engine. We know that the blow-by is directly affected by the piston scuffing failure. Therefore، it was measured as a base parameter. The creation of intended piston scuff conditions is very difficult. Therefore، a special test was designed to make it artificially. Results show that the best AE parameter for the piston scuff detection is the AE root mean square and the AE energy. Based on the present method، we can find the location of the event in the cylinder head or in the engine block.