Increasing the load capacity and rigidity of roller–screw mechanisms by adjusting the screw surfaces

A method is proposed for increasing the load capacity and rigidity of roller–screw mechanisms by adjusting the screw surfaces. That permits the design of compact mechanisms such as automobile steering assemblies.     

On the role of sliding load and heat input conditions in friction stir processing on tribology of aluminium alloy–alumina surface composites

ABSTRACT

Aluminium (AA5083)-alumina surface composites are prepared by friction stir processing in two conditions of heat input. The low heat (LH) input conditions is achieved at a rotational speed of 710?rpm and a traverse speed of 100?mm/min, and high heat (HH) input conditions are achieved at a rotational speed of 1400?rpm and a traverse speed of 40?mm/min. The tribological characteristics of aluminium alloy, friction stir processed (FSPed) alloy and FSPed surface composites against steel ball are studied at 5, 10 and 20?N load. While no significant influence is found on frictional behaviour, wear resistance of FSPed composites is superior to FSPed alloys. FSPed composites fabricated at HH input conditions exhibited improved wear resistance as compared to LH input condition. Adhesion and delamination are dominant wear mechanisms at 20?N. Debris particles are reduced in size and hydroxidated in sliding of surface composites.     

The influence of friction and wear on the generation of surface microprofile of steel–sintered friction powder based on copper in the course of operation in lubricated medium

The development of new compositions of sintered friction powders based on copper that operate in lubricated states should be based on deep knowledge of peculiar features of break-in and wear mechanisms of both counterbody and friction material. The obtained data have enabled the determination of the existence of the transferred bronze layer of friction material, the peculiarities of the generation of the surface microprofile of the counterbody during operation, these data can be useful upon assessing the thermal loading of the friction zone.     

Analysis of stir die cast Al–SiC composite brake drums based on coefficient of friction

The work reported here is to analyze the suitability of Aluminum alloy–Silicon Carbide MMC (Al–SiC MMC) in the automobile brake drum applications in comparison with cast iron (CI) brake drum. A brake drum dynamometer test rig was developed for the purpose. Al–SiC MMC was reinforced with 10% and 15% SiC particle by weight. The effect of heat treatment of the Al–SiC MMC brake drum was also studied. Performance was mainly evaluated on the basis of brake drum coefficient of friction (μ). Scanning electron microscope was also used to study the effect of braking on the sliding surface of the brake drum.     

Tribological characterisation of epoxy–graphene–liquid filler composite coatings on steel under base oil external lubrication

In our earlier study, epoxy-based composites with graphene (10?wt-%) and in situ liquid fillers (base oil SN150 or perfluoropolyether at 10?wt-%) were found to provide low friction and highly wear durable as thin coatings on the steel substrate in dry interfacial state. In this present work, we have tested this composite in the presence of an external lubricant (base oil SN150). The lowest coefficient of friction was recorded as 0.04 and the lowest specific wear rate was measured as 9.8?×?10^?7?mm^3?Nm^?1 for the composites without any failure of the coating up to 200,000 sliding cycles. It is shown that such polymeric coatings can be an excellent boundary film in both dry and lubricated conditions for various bearings.     

I–V curve characteristics of solar cells on composite substrate under mechanical loading

This research is aimed to conduct a characterization of I–V (current-voltage) curve changes in order to interpret the effects of physical defects such as microcracks of solar cells installed over structures to which mechanical load is applied on the power generation performance of solar cells, as well as to conduct fractography to interpret causes for reducing the power generation performance of the cells. To accomplish this, tensile specimens to which a mechanical load would be applied were produced using composite materials, which are representative light materials and solar cells that were attached to the specimens using the adhesive property of EVA film. In the experiment, mono-crystalline silicon solar cells were used, which are breakable and whose efficiency is approximately 24.2% (lab.). Also, in order to evaluate the power generation performance of solar cells under mechanical loading in real-time, a measuring device was designed to compare and evaluate the time point and property of fracture under mechanical loading. Moreover, fractography was conducted to analyze and consider causes for reducing the efficiency of solar cells. As a result of the experiment, it was found that the mechanical load applied to solar cells caused cracks to the surface and interior of the cells, which in turn reduced the I_sc value and the V_oc value of the I–V curve. The present study provides an initial set of valuation parameters in the maintenance and management of installed solar cells when applying solar cell technology to dynamic structures.     

Role of thermal,mechanical and oxidising treatment on structure and chemistry of carbon black and its impact on wear and friction: Part 2 – Boundary lubrication condition

Mineral oil formulations with zinc dialkyl dithiophosphate (ZDDP) and dispersant (poly isobutylene succinimide ashless dispersant or ‘PIBSA’) and fully formulated oils with and without carbon black were subjected to thermal and mechanical treatment and tribologically tested on TE 77 (high frequency reciprocating rig or ‘HFRR’) machine to examine the frictional performance during the test. These results were compared to oils without carbon black and oils with diesel soot. Results indicate that oils with just ZDDP and dispersant had the highest friction that remains constant for the duration of the test while oils with carbon black in the milled and oxidised condition had the lowest coefficient of friction and the smallest surface roughness in the tribofilm. The mechanism of wear with treated carbon black and diesel soot was found to be polishing wear as evidenced by the scanning probe microscopy images of the tribofilms. Tribofilms were analysed with X-ray absorption near edge structure (XANES) and it was seen that oils without carbon black or even with untreated carbon black had sulphates at the surface, while the oils with carbon black that were treated had a higher proportion of sulphides. A combination of both FeS and ZnS was found in the tribofilms along with short chain phosphates of Zn.     

Comparison between rubber–ice and sand–ice friction and the effect of loose snow contamination

The application of sand particles is a common method to improve the friction of aircraft tires on snow or ice covered runways. Hence, an understanding of the prevailing rubber–ice and sand–ice friction mechanisms is of practical interest. Rubber–ice and sand–ice friction measurements were made with a British Pendulum Tester at temperatures between ?22 and 0 °C and the effect of loose snow contamination on top of the ice was investigated. The results (the response of the instrument) were expressed in a sliding length averaged friction coefficient μ_BP. Close to the melting point the friction of rubber on ice was low and increased with decreasing ice temperature. Below ?5 °C, reasonably high friction levels (0.2<μ_BP<0.5) were obtained between rubber and ice, but the friction level dropped drastically by the presence of a very thin layer of snow. The sand–ice friction level was less dependent on ice temperature and clearly not as much affected by the presence of snow, compared to rubber–ice friction. The micromechanisms involved in rubber–ice and sand–ice frictions were investigated by the application of etching and replicating technique (ERT) developed for the examinations of the dynamics of dislocations in ice during deformation.     

The friction and sliding wear of unlubricated 316 stainless steel in air at room temperature in the load range 0.5–90 N

The reciprocating self-wear of 316 stainless steel in air and at room temperature has been investigated in the load range 0.5–90 N. Above approximately 40 N the debris was metallic, indicating a severe wear mode. The wear volume was a linear function of the sliding distance and the specific wear rate was independent of load.Below the 40 N load, after an initial severe stage, a transition occurred with a decrease in wear rate by up to an order of magnitude. The specific wear rate in both wear stages decreased with decreasing load, showing no indication of saturating at low loads. The load dependence of the wear volume V per unit sliding distance was of the form V = kLⁿ where n ≈ 1.8 for both pre- and post-transition stages.The transition and the decreasing specific wear rates with decreasing load are thought to be associated with an increasing proportion of asperity interactions' being elastic rather than involving plastic deformation. It is proposed that wear occurs by a multistage mechanism of metal transfer to form prows, prow oxidation in the post-transition stage and prow breakdown. The transition is associated with a change in the rate-limiting step. This is believed to be the metal transfer step in the pre-transitional stage and the prow breakdown step in the post-transitional stage. Only a tentative correlation could be made between the onset of a wear transition and changes either in the friction behaviour or in the appearance of oxide in the wear debris. The friction data suggest that wear in the post-transition stage is a cyclic process of prow breakdown, prow re-formation by further metallic transfer, prow embrittlement by oxidation leading once again to breakdown and the formation of oxide-containing wear debris.     

The influence of the valena metal-plating additive on tribotechnical characteristics of the Steel–Bronze tribological system

The paper considers a change in the coefficient of friction and the temperature distribution in the contact zone of the steel–bronze tribosystem. Investigations were carried out by the shaft–bushing system for three values of the load in the mixed-to-boundary lubrication regime with SAE 80W transmission oil without and with Valena additive. It is found that the additive presence in oil decreases the coefficient of friction by 11–21%, depending on the applied load. At the same time, the maximum decrease in the coefficient of friction is observed at a maximum applied load of 1500 N.     

Dry sliding wear characteristics of glass–epoxy composite filled with silicon carbide and graphite particles

The dry sliding wear characteristics of a glass–epoxy (G–E) composite, filled with both silicon carbide (SiC_p) and graphite (Gr), were studied using a pin-on-disc test apparatus. The specific wear rate was determined as a function of sliding velocity, applied load and sliding distance. The laminates were fabricated by the hand lay-up technique. The volume percentage of filler materials in the composite was varied, silicon carbide was varied from 5 to 10% whereas graphite was kept constant at 5%. The excellent wear resistance was obtained with glass–epoxy containing fillers. The transfer film formed on the counter surface was confirmed to be effective in improving the wear characteristics of filled G–E composites. The influence of applied load is more on specific wear rate compared to the other two wear parameters. The worn surfaces of composites were examined with scanning electron microscopy (SEM) to investigate the probable wear mechanisms. It was found that in the early stage of wear, the fillers contribution is significant. The process of transfer film, debris formation and fiber breakage accounts for the wear at much later stages.     

Research on ball valve and misaligned guide vane devices to improve the “S” characteristics of a pump turbine

“S”characteristics of a pump turbine may result in certain problems, such as excessive water hammer pressure, unstable no-load operation, and difficulty in synchronization. Accordingly, a new start-up strategy based on the partial opening of a ball valve is proposed, and the calculation model of the hydraulic transition process with misaligned guide vane devices (MGV) and a ball valve is established. The emergency shutdown and turbine start-up conditions are simulated and analyzed. The ball valve can more effectively reduce the maximum inlet pressure of the volute and increase the minimum inlet pressure of the draft tube during the shutdown process compared with the MGV devices. The newly proposed strategy can also effectively reduce the amplitude of pressure fluctuation at the volute and draft tube, shorten the synchronization time, and reduce the speed overshoot during the start-up process. The ball valve can effectively improve the operating quality of the unit in the S-shaped area.

     

Modeling and analysis of the effects of processing parameters on the performance characteristics in the high pressure die casting process of Al–SI alloys

The high pressure die casting (HPDC) process has achieved remarkable success in the manufacture of aluminum–silicon (Al–SI) alloy components for the modern metal industry. Mathematical models are proposed for the modeling and analysis of the effects of machining parameters on the performance characteristics in the HPDC process of Al–SI alloys which are developed using the response surface methodology (RSM) to explain the influences of three processing parameters (die temperature, injection pressure and cooling time) on the performance characteristics of the mean particle size (MPS) of primary silicon and material hardness (HBN) value. The experiment plan adopts the centered central composite design (CCD). The separable influence of individual machining parameters and the interaction between these parameters are also investigated by using analysis of variance (ANOVA). With the experimental values up to a 95% confidence interval, it is fairly well for the experimental results to present the mathematical models of both the mean particle size of primary silicon and its hardness value. Two main significant factors involved in the mean particle size of primary silicon are the die temperature and the cooling time. The injection pressure and die temperature also have statistically significant effect on microstructure and hardness.     

Operational damage to the structure and failure of the KAMAZ truck spring in the temperature–load conditions of the North

Forecasting of the residual life of machine and structure elements requires consideration of the changes of the metal condition until it achieves its critical states. The failure of the KAMAZ truck spring during the cold operation period under the climatic and natural conditions of the North was studied taking the metal degradation in the zones of different loading into account. The structural damage was estimated using the microhardness and porosity parameters. The physical mechanisms that change the microhardness and the formation of the pore system in the spring steel were analyzed. It is shown that a deviation of the value of the metal microhardness from the normal distribution law is observed in the zone of development of a fatigue crack in the spring. Satisfactory resistance of the spring material to the development of a failure is revealed under the considered temperature–load conditions. A materials-engineering analysis confirmed the role of the road conditions as a more significant destructive factor during the working of the spring in the permafrost zone compared to the factor of the low temperatures.     

Influence of the electromagnetic gap in gas–magnetic bearings on the output characteristics of high-speed rotor systems

The electromagnetic gap in gas–magnetic bearings has a considerable influence on the output load and rigidity characteristics of high-speed rotor systems, as shown by experiments and simulation.     

Influences of lubrication conditions and blank holder force on micro deep drawing of C1100 micro conical–cylindrical cup

Lubrication conditions and blank holder force (BHF) are two key processing parameters in deep drawing. This is more obvious in micro forming because of the miniaturization of the specimen size. Micro conical–cylindrical cups with internal conical bottom diameter of only 0.4 mm were well formed. The influences of lubrication conditions and BHF on micro deep drawing of micro conical–cylindrical cups were investigated using a micro blanking–deep drawing compound mold. Pure copper C1100 with a thickness of 50 μm, which was annealed at 450 °C for 2 h in vacuum condition, was chosen as the specimen material. The experiments were conducted on a universal testing machine with a forming velocity of 0.05 mm/s under 4 kinds of lubrication conditions and BHF. The experimental results showed that a micro conical–cylindrical cup with internal conical bottom diameter of only 0.4 mm was well formed, and the limiting drawing ratio (LDR) reached 2.1. The polyethylene (PE) film, which decreased the drawing force and increased the drawing ratio (DR), was superior to castor oil, petroleum jelly and dry friction, and can be chosen as a proper lubricant for micro deep drawing. The rim of the micro cup seriously wrinkled when BHF was less than 4.2 N. The bottom of the micro cup cracked when the BHF was larger than 5.6 N.     

Prediction of friction and heat flow in machining incorporating thermophysical properties of the coating–chip interface

This paper deals with an experimental and analytical investigation into the thermodynamically activated effects influencing the behaviour of the multi-layered coated tool rake face during orthogonal cutting of ferromagnetic and paramagnetic steels. Temperature measurements on the tool rake face using a thermocouple-based technique and identification of the contact zone by means of computer image processing were carried out. New methodology for assessing friction and the amount of thermal energy generated when machining with a coated tool insert with natural and restricted contact coupled with a metallic chip, using thermophysical properties of the sliding materials is developed in this study. The dependence of the material properties on the contact temperature makes the predictive models more realistic. It was proven, based on the heat flux analysis, that the use of advanced coatings with an intermediate Al₂O₃ layer could substantially improve the heat flow into the chip at distinctly lower temperatures than other commercially available coatings. The data obtained can be used for the optimisation of tool selection with respect to friction and heat transfer and for maintaining the recommended contact temperature.     

A numerical study on the transient aspects of porous flows and the applicability of Darcy’s friction flow relation

In recent developments of shale reservoirs, it is important to estimate the permeabilities of hydraulic fractures accompanying the Non- Darcy effects and geometric changes. Accordingly, a new permeability estimation method that considers the varying geometric features under different flow regions is demanded. To this end, the present study introduces the generalized Darcy’s friction flow relation, especially for examining the friction factor-Reynolds number (f · Re) relationship of porous flow, which is originally used in general internal friction flow analyses. Moreover, simple hydraulic fractures comprising structured microbeads are simulated via computational fluid dynamics during fracture aperture variations under different flow conditions from laminar to turbulent. Frictional flow features, e.g., the preservation characteristics of f · Re values, are examined under different geometry and flow conditions, and the transient flow characteristics are investigated using streamline analyses. Consequently, it is verified that the f · Re values vary slightly in proportion to the geometric changes caused by aperture reduction in each medium. Even though the variations in the f · Re values are much smaller than the permeability variations, it seems to be contrary to our expectation. Otherwise, the almost linear-variation aspects of f · Re values were observed in both directional flow cases. The linear-variation aspect of f · Re values is expected to be useful in the permeability-variation estimations in porous media with changing basic geometric factors, such as hydraulic fracture closing. Moreover, it is demonstrated that regardless of aperture reduction in the same type of medium, each porous flow has a very similar power-law relation between f and Re values when the flow velocity changes from the laminar to the turbulent condition. This aspect can be effectively used for obtaining permeability estimations of the varied media, particularly under different flow conditions.     

Wear of the Counterbody at the Research Friction on Carbon Coating–Orientant in Lubricant Environments

The profile wear scars on steel balls are analyzed upon their friction in lubricant against steel coated with monocrystalline carbon doped by tungsten. Bond of ball wear with the lubricant composition and the range of test loads has been established.     

Optimization of the EDM parameters on machining Ti–6Al–4V with multiple quality characteristics

In this paper, parameter optimization of the electrical discharge machining process to Ti–6Al–4V alloy considering multiple performance characteristics using the Taguchi method and grey relational analysis is reported. Performance characteristics including the electrode wear ratio, material removal rate and surface roughness are chosen to evaluate the machining effects. The process parameters selected in this study are discharge current, open voltage, pulse duration and duty factor. Experiments based on the appropriate orthogonal array are conducted first. The normalised experimental results of the performance characteristics are then introduced to calculate the coefficient and grades according to grey relational analysis. The optimised process parameters simultaneously leading to a lower electrode wear ratio, higher material removal rate and better surface roughness are then verified through a confirmation experiment. The validation experiments show an improved electrode wear ratio of 15%, material removal rate of 12% and surface roughness of 19% when the Taguchi method and grey relational analysis are used.