On the Effects of High and Ultra-High Rotational Speeds on the Strength, Corrosion Resistance, and Microstructure during Friction Stir Welding of Al 6061-T6 and 316L SS Alloys

In this study, under the conditions of using tools at a high rotational speed (HRS) of 10,000 rpm and an ultra-high rotational speed (ultra-HRS) of 18,000 rpm, the produced welding heat input was utilized to weld two specimens of Al alloy 6061-T6 with 1.0 mm thickness and 316L SS with 0.8 mm thickness. The microstructural characteristics, mechanical properties, and electrochemical corrosion properties of the aluminum alloy–steel joints were analyzed. The higher tool offset forms an intermetallic compound layer of less than 1 µm at the Fe-Al interface on the advancing side (AS) at different speeds. This results in a mixed zone structure. The lower tool offset forms intermetallic compounds of only 2 µm. The formation of a composite material based on aluminum alloy in the weld nugget zone improves the hardness value. The intermetallic compounds are Fe3Al and FeAl3, respectively. It was observed that the formation of intermetallic compounds is solely related to the rotational speed, and the iron-rich intermetallic compounds produced under ultra-HRS parameters have higher corrosion resistance. When the tool offset is 0.55 mm, using the HRS parameters, the tensile strength is 220.8 MPa (about 75.9% of that of the base metal).

DETERMINATION OF DESIGN PARAMETERS OF A STEP DISK MILL

The calculation of the design parameters of a disc mill equipped with a feeder made in the form of a conical hopper is given. For shredders of the disintegrator type, it is very important to ensure the uniformity of loading of the crushed material of the working zone of active impact on particles. In addition, the most important factor is the throughput capacity of all sections of the grinding plant. The throughput should be determined by the design and technological parameters of the working chamber of the mill. Its overload can lead to a blockage of the working chamber, and insufficient throughput will negatively affect the intensity and effectiveness of the impact on the particles of the material. For example, insufficient concentration of particles in the secondary zone of the grinding chamber leads to a decrease in the efficiency of mutual abrasion. The article attempts to determine the design and technological parameters in the loading and accelerating parts of the disk mill. At the same time, it is necessary to coordinate the throughput of the disk spreader and the volumetric flow rate of the material particles flowing from the hopper. In this case, it is advisable to take into account that as a result of a rather high rotational speed and the size of the initial particles, with the wrong height of the radial blade of the spreader, material particles can roll over the radial blades, which leads to a delay of the material in the zone of the spreading disc. Therefore, it is necessary to determine the calculation formulas for finding the required height of the radial blade of the spreading disc, depending on the size of the initial particles. The formula demonstrates that the height of the separating blade depends on the particle size, the speed of rotation of the disks and the distance to the point of meeting of the particle with the radial blade.

DETERMINATION OF DESIGN PARAMETERS OF A STEP DISK MILL

The calculation of the design parameters of a disc mill equipped with a feeder made in the form of a conical hopper is given. For shredders of the disintegrator type, it is very important to ensure the uniformity of loading of the crushed material of the working zone of active impact on particles. In addition, the most important factor is the throughput capacity of all sections of the grinding plant. The throughput should be determined by the design and technological parameters of the working chamber of the mill. Its overload can lead to a blockage of the working chamber, and insufficient throughput will negatively affect the intensity and effectiveness of the impact on the particles of the material. For example, insufficient concentration of particles in the secondary zone of the grinding chamber leads to a decrease in the efficiency of mutual abrasion. The article attempts to determine the design and technological parameters in the loading and accelerating parts of the disk mill. At the same time, it is necessary to coordinate the throughput of the disk spreader and the volumetric flow rate of the material particles flowing from the hopper. In this case, it is advisable to take into account that as a result of a rather high rotational speed and the size of the initial particles, with the wrong height of the radial blade of the spreader, material particles can roll over the radial blades, which leads to a delay of the material in the zone of the spreading disc. Therefore, it is necessary to determine the calculation formulas for finding the required height of the radial blade of the spreading disc, depending on the size of the initial particles. The formula demonstrates that the height of the separating blade depends on the particle size, the speed of rotation of the disks and the distance to the point of meeting of the particle with the radial blade.

Investigation of Gyroscopic Effect on the Stability of High Speed Micromilling via Bifurcation Analysis

Catastrophic tool failure due to the low flexural stiffness of the micro-tool is a major concern for micromanufacturing industries. This issue can be addressed using high rotational speed, but the gyroscopic couple becomes prominent at high rotational speeds for micro-tools affecting the dynamic stability of the process. This study uses the multiple degrees of freedom (MDOF) model of the cutting tool to investigate the gyroscopic effect in machining. Hopf bifurcation theory is used to understand the long-term dynamic behavior of the system. A numerical scheme based on the linear multistep method is used to solve the time-periodic delay differential equations. The stability limits have been predicted as a function of the spindle speed. Higher tool deflections occur at higher spindle speeds. Stability lobe diagram shows the conservative limits at high rotational speeds for the MDOF model. The predicted stability limits show good agreement with the experimental limits, especially at high rotational speeds.

Investigation into Mechanical Properties and Sliding Wear Behavior of Friction Stir Processed Surface Composite Material

One of the different and pioneering solid-state techniques, friction stir processing (FSP), is employed for the production of surface composites. In this research, the matrix selected was copper-nickel (CuNi) with hard boron carbide particle as reinforcement. The objective of the current research work is to produce reinforced 90/10 copper-nickel surface composites reinforced with B4C fabricated via FSP. The influence of tool rotational speed on macrostructure, microstructure, grain size analysis, microhardness, and wear studies of friction stir processed (FSPed) CuNi/B4C surface composites was assessed. For high rotational speed (1400 rpm) of stir tool, the modified surface area found is a maximum of 44.4 mm2 with uniform dispersion of hard particle reinforcement. The presence of hard particle in the surface area is revealed through the electron imaging and the spectroscopic results. Spectra mapping shows the uniform distribution of hard particle over the FSPed area, and the evidence is obtained with XRD analysis. From the experimentation, it is interesting to report that the reinforcements have decreased the surface hardness for an increased rotational speed of stir tool. The hardness recorded for minimum rotational speed is 223 HV which has gradually decreased to 178 HV for 1300 rpm. It has directly influenced the wear rate of modified FSPed, as hardness is directly proportional to wear behavior. The worn surface and fractured morphology of the CuNi/B4C surface composites were also studied using Field Emission Scanning Electron Microscope (FESEM).

Specifics of turbo-alternator design with a high rotational speed of 6000 rpm

Object and purpose of research. The object under study is a 36 МW turbo-alternator (TA) with electromagnetic excitation and a high rotational speed of 6000 rpm, which can be used as an option for ac electric power source of 100 Hz in ship electric power systems with a turbo-alternator plant. The purpose is to perform electromagnetic calculations to determine TA main data and technical characteristics, including the stator and rotor pack, their design, mass of active materials, etc. for comparison with a TA of the same power but 3000 rpm. Materials and methods. The studies are based on research and engineering data about investigations and design of double-pole industrial TA of 50 Hz as well as TA with a high current frequency (100 Hz and higher). For this purpose, the known formulas were used to estimate the size of TA active elements, excitation forces of stator and rotor windings, as well as methods for calculation of main TA parameters and technical characteristics. Main results. Design specifics of TA with a high rotational speed of 6000 rpm is identified, and results of electromagnetic estimations are obtained for a specific 36 MW turbo-alternator of 100 Hz with a forced close cycle cooling and better mass and size characteristics. Conclusions. The obtained results are of practical value, showing feasibility of developing a version of 36.0 МW TA with a rotational speed of 6000 rpm and significantly reduced specific mass and size characteristics – tentatively by 35–40 % as compared to the existing TA of the same power but with a speed of 3000 rpm.

Design and Experimental Investigation of Composite Automotive Drive Shaft

Replacing composite bodies by the conventional metallic bodies have many advantages because of high specific strength and high specific stiffness of the composite materials. As compared to the conventional drive shafts, Composite drive shafts have the potential of lighter and longer life with high rotational speed. Nowadays drive shafts are used in two pieces. However, the main advantage of the current design is that only one piece of composite drive shaft is possible that fulfils all the drive shaft requirements. The torsional strength, torsional buckling and bending natural frequency are the main basic requirements considered here. This work is all about the replacing the conventional two-piece steel drive shaft with a one-piece carbon/epoxy. Design of composite drive shaft Classical Lamination Theory is used for the design of composite drive shaft. Finite element analysis (FEA) was used to design composite drive shafts incorporating carbon within an epoxy matrix. From experimental results, it was found that the developed one-piece automotive composite drive shaft had 64% mass reduction, 74% increase in torque capability compared with a conventional two-piece steel drive shaft. It also had 6380 rpm of natural frequency which was higher than the design specification of 3050 rpm. Index Terms: Bending frequency, Composite Materials, Drive shaft, Finite Element Analysis (FEA), Power transmission, Torsion, Torsional buckling.

Study of dynamic and ecological properties of automotive bi-fuel engine

Gaseous fuels are increasingly used to power internal combustion engines. Spark-ignition engines are fuelled with liquefied petroleum gas. Engines powered by gaseous fuels are characterized by good ecological properties due to the emission of pollutants. The paper presents the results of empirical tests of two passenger cars with spark-ignition engines powered alternatively: with gasoline and LPG fuel. The engines were equipped with fifth generation LPG fuelling systems. The tests were performed on a chassis dynamometer in tests used in approval procedures in Europe (NEDC test) and in the United States of America (FTP-75 test). These tests were the basis for determining the average specific distance emission of pollutants (carbon monoxide, hydrocarbons, nitrogen oxides and carbon dioxide) during the tests. The engines were also tested in the conditions of the external speed characteristics while accelerating the car in third gear. It was found that the type of fuelling the engines with both fuels has little influence on the dynamic properties of the engine due to the effective power. The tests clearly showed a decrease in specific distance emission of carbon monoxide and carbon dioxide. The relative reduction in specific distance emission of carbon monoxide was in the order of (45–65)%, and carbon dioxide—about 10%. For hydrocarbons, there was an increase in specific distance emission of hydrocarbons for the fuelling of engines with LPG, while for hydrocarbons, there was a large difference in the value of the relative specific distance emission difference for both tests. (The relative difference was from 25 to 175%.) Specific distance emission of nitrogen oxides turned out to be significantly higher when running engines with LPG. The reason for this is leaning of the fuel mixture at high rotational speed during acceleration of the car, which may result from insufficient conversion efficiency of engine control algorithms in the LPG fuel mode.

Loss assessment of the NASA SDT configuration using URANS with phase-lagged assumption

This paper presents the study of the Source Diagnostic Test fan rig of the NASA Glenn (NASA SDT). Numerical simulations are performed for the three different Outlet Guide Vane (OGV) geometries (baseline, low-count and low-noise) and three rotational speeds. Unsteady Reynolds Averaged Navier Stokes (URANS) approach is used. The in- and out-duct flow including the nacelle are considered in the numerical simulations and results are compared against available measurements. Due to the blade count of the fan and OGVs, the simulation can only be reduced to half the full annulus simulation domain using periodic boundary conditions that still represents a significant cost. To alleviate this issue, a URANS with phase-lagged assumption is used. This method allows to perform unsteady simulations on multistage turbomachinery configurations including multiple frequency flows with a reduced computational domain composed of one single blade passage for each row. The large data storage required by the phase-lagged approach is handled by a compression method based on a Proper Orthogonal Decomposition. This compression method improves the signal spectral content especially at high frequency. Based on the numerical simulations, the flow field is described and used to assess the losses generated in the turbofan architecture based on an entropy approach. The results show different flow topologies for the fan depending on the rotational speed with a leading edge shock at high rotational speed. The fan boundary layer contributes strongly to losses with the majority of the losses being generated close to the leading edge.

Effect of High Rotational-Speed Friction-Stir Welding on Microstructure and Properties of Welded Joints of 6061-T6 Al Alloy Ultrathin Plate

The butt joint of an Al alloy ultrathin plate with a thickness of 0.5 mm is realized by a high rotational-speed friction-stir welding process. It overcomes the welding difficulty that the ultrathin plate is often torn, and it cannot be formed by conventional friction-stir welding. The results show that the weld surface is well-formed at a high-rotational speed (more than 8000 rpm), and there are no obvious defects in each area of the joint section. The nugget zone (NZ) is a recovery recrystallization structure dominated by large-angle grain boundaries, with a grain size of about 4.9 μm. During grain growth, the texture is randomly and uniformly distributed, and the strength is balanced. The microhardness of the NZ increases significantly with the increase in rotational speed, and the fluctuation range of hardness value is small. The NZ β–Mg2Si is finer and significantly less than the base metal (BM). The heat dissipation of the thin plate is fast, so a Cu plate is used as the backing plate to slow down the steep temperature-drop process in the weld area. Compared with a low rotational speed, the precipitation amount of brittle phase Al–Cu–Mg–Cr and Al–Fe–Si–Mn is significantly reduced, which is conducive to improving the mechanical properties of the joint. At a high rotational speed, 12,000 rpm, the best tensile strength of the joint is 220 MPa, which is about 76% of the BM (290 MPa), and the highest elongation is 9.3%, which is about 77.5% of the BM (12%). The fracture mode of the joint is a typical plastic fracture.