Frictional Work Research Articles

ON-BOARD MONITORING OF TECHNICAL STATE FOR POWER UNITS OF WHEELED AND TRACKED VEHICLES

The paper considers new methodologies pertaining to on-board diagnosis of wear-out rate for friction linings of a clutch driven disk and friction discs of a hydraulic press clutch of transmission gear boxes which are based on physical process that uses friction work as an integrated indicator. A new methodology in determination of life-span rate for engine oil has been developed in the paper. The paper presents block schematic diagrams for on-board monitoring of technical state for power units of wheeled and tracked vehicles. Usage of friction work as an integrated indicator for determination of wear-out rate for friction linings of clutch driven disk and friction discs of a haydraulic press clutch makes it possible timely at any operational period of wheeled and tracked vehicles to determine their residual operation life and forecast their replacement.While taking volume of the used fuel for determination of engine oil life-span rate it permits quickly and effectively at any operational period of wheeled and tracked vehicles to determine residual useful life of the engine oil and also forecast its replacement.

Structural-Energy Characteristics of Tribotechnical Contact in Unsteady Operational Modes

The current tribological research is intended to achieve maximum wear resistance under the structural adaptability of tribocoupling elements, which requires application of means to reduce the activation of the metal surface layers, decrease in frictional work, regulation of passivation and temperature control. The aim of this study is to identify the patterns that influence the kinetics formation of the boundary layers of lubricating mineral gear oil on activated friction contact surfaces, and the increment of the friction specific work on wear-resistant steel 42Cr4 and 100Cr6 in frequent start and stop operation mode. Due to the activation of surface layers of metal in the non-stationary operating conditions of the contact surfaces, the gradual forming of the boundary lubricant adsorption layers with increased effective viscosity in contact occurs, exhibiting high adaptation ability, and the boundary layer thickness is from 0.2 to 4 microns. This research analyzed the lubricating ability of oil at the starting maximum torque of friction, showing that the thickness of the oil layer formed in contact had a dual nature—boundary and hydrodynamic. The pure rolling conditions promote localization of shear in the lubricating layers, and the high frictional properties of the transmission oil have been identified regardless of the hardness of the investigated surfaces.

MODELO DE ANÁLISIS Y VALIDACIÓN DE PROPUESTAS DE DISEÑO MEDIANTE PROTOTIPOS FLEXIBLES

In recent years, 3D printing is becoming a tool that will become as common as a conventional printer. The rapid expansion of these technologies both in dimensions and ease of management software and the use of different materials gives evidence of a long future, as well as its expansion, expansion that will change the concept of manufacturing, which will give more possibilities of creative freedom than traditional manufacturing technologies such as machining or injection. Within the framework of previous observations, it is considered that 3D reproduction with flexible materials can be interesting in phases of the product design with the aim of promoting the creativity and get so products with a higher degree of innovation. On the other hand, ergonomics is likely to be tested in a more precise way by the coefficient of friction of the product. This article investigates the possibility of realization of a model of analysis and validation by means of flexible prototypes made in a 3D printer. With this type of prototyping design aspect that is not possible with rigid materials, PLA, or ABS, can be checked. One example is checking the coefficient of friction, their ergonomics or own flexible working. You could say that elastic realities are printed. Several empirical studies studying the impact that has a flexible prototype in the evaluation and validation of a conceptual proposal for a design and demonstrate the reliability of the analysis model

Quantifying Degradation of Railway Ballast Using Numerical Simulations of Micro-deval Test and In-situ Conditions

Throughout the life of the track, ballast grains wear as a result of both the trains passing over the track and the maintenance operations (tamping). The morphology of the grains is changed: they lose angularity and fine particles are produced, causing a gradual loss of track performance. Eventually ballast renewal becomes necessary. In order to predict the evolution of this degradation, a multi-scale study is proposed. A comparison between discrete element method (DEM) simulations of Micro-Deval attrition test and of the passage of trains over a sleeper is performed in order to both detect the different loading and wearing mechanisms involved and quantify the amount of friction work produced, which is directly related to friction wear. The same numerical approach is also used with the simulations of the track to detect families of contacts in order to determine characteristic loading paths at the micro-scale. Loads and displacements of both systems are then compared in order to discuss the relevance of the Micro-Deval test.

Dynamics and Energy Conversion of Aircraft Landing Gears at Touchdown

Dynamics of aircraft landing gears with and without pre-rotation has been analysed. The ground friction work is been formulated which raises the temperature of touch point to the rubber smoke point. The sliding time, distance, power and energy released by the friction at touch point have been presented. Simulation of target speed has been shown for different levels of pre-rotation torque.

Instability analysis of friction oscillators with uncertainty in the friction law distribution

Despite substantial research efforts in the past two decades, the prediction of brake squeal propensity, as a significant noise, vibration and harshness (NVH) issue to automotive manufactures, is as difficult as ever. This is due to the complexity of the interacting mechanisms (e.g. stick-slip, sprag-slip, mode coupling and hammering effect) and the uncertain operating conditions (temperature, pressure). In particular, two major aspects in brake squeal have attracted significant attention recently: nonlinearity and uncertainty. The fugitiveness of brake squeal could be attributed to a number of factors including the difficulty in accurately modelling friction. In this paper, the influence of the uncertainty arising from the tribological aspect in brake squeal prediction is analysed. Three types of friction models, namely the Amonton-Coulomb model, the velocity-dependent model and the LuGre model, are randomly assigned to a group of interconnected oscillators which model the dynamics of a brake system. The complex eigenvalue analysis, as a standard stability analysis tool, and the friction work calculation are performed to investigate the probability for instability arising from the uncertainty in the friction models. The results are discussed with a view to apply this approach to the analysis of the squeal propensity for a full brake system.

Experimental and numerical studies of bolted joints subjected to axial excitation

The dynamic behaviour of bolted joints subjected to axial excitation is investigated using experimental and numerical methods. Firstly, the amount of reduction in clamp force is found by experiments. In addition, the damage of threads is analysed using scanning electron microscope (SEM) and Energy Dispersive X-ray (EDX). Secondly, by changing the tightening torque, the amplitude of the axial excitation, and coating lubricant (MoS2) on the threads, their effects on both the clamp load loss and the damage of threads are determined in experiments. It is found that the clamp force decreases rapidly in the early stage because of the cyclic plastic deformation, and then slowly because of fretting wear in the later stage. With the increase of the tightening torque and the decrease of the amplitude of the axial excitation, the clamp load loss decreases and the damage of threads becomes slight. The lubrication (MoS2) of bolt threads is useful to reduce bolt loosening and damage of threads.A three-dimensional finite element model used to simulate the bolted joint under axial excitation is created using ABAQUS, through which the frictional stress, slip amplitude and frictional work per unit area along two specified paths on the first thread are studied. It is found that the FE results agree with the experimental observations very well.

Investigations of critical cutting speed and ductile-to-brittle transition mechanism for workpiece material in ultra-high speed machining

This paper investigates the brittle removal mechanism of ductile materials in ultra-high speed machining (UHSM). Firstly, a predictive model of critical cutting speed for UHSM is proposed with the theory of stress wave propagation. The predicted critical cutting speed for ductile-to-brittle transition of ductile materials is then validated by machining experiments of 7050-T7451 aluminum alloy at the cutting speeds ranging from 50m/min to 8000m/min. The experimental results show that fragmented chips are produced above the critical cutting speed of 5000m/min for 7050-T7451 aluminum alloy. The scanning electron microscopic (SEM) images of chips, chip roots and finished workpiece surfaces are observed and analyzed. Large amounts of brittle cracks and cleavage steps are observed on the fragmented chip surface obtained under the ultra-high cutting speed. Due to the remained brittle cracks, the finished surface quality obtained with UHSM is worse than that obtained with high speed machining. Secondly, the specific energy models for the chip formation are proposed and validated by experiments under ductile regime machining and brittle regime machining, respectively. The specific energies consumed for continuous and serrated chip formation mainly include plastic deformation energy located in the primary shear zone, the friction work between the tool–chip interface, and the chip kinetic energy. The plastic deformation energy accounts for the largest proportion among the total specific energy. Comparatively, the specific energy consumed during fragmented chip formation mainly includes the local kinetic energy of fragments and fracture surface energy. When the chip morphology evolves from serrated to fragmented one, the specific energy consumed reduces substantially, which demonstrates that the UHSM is beneficial for the energy saving. Lastly, taking both of the material removal efficiency and machined surface quality into consideration, the UHSM is recommended to be applied in rough machining or semi-finishing, while high speed machining is recommended to be applied in finishing process. This research firstly reveals the control mechanism for ductile-to-brittle transition of ductile materials under critical cutting speed (i.e. critical strain rate) considering solid mechanics and metal cutting principles as well as energy consumption simultaneously. This paper is enticing from both engineering and analytical perspectives aimed at revealing the mechanism of UHSM and instructing the optimization of machining parameters.

Ubiquitous weakening of faults due to thermal pressurization

Faults weaken during earthquakes. Analysis of the amount of energy released during earthquakes globally suggests that heat-induced pressurization of pore fluids can weaken faults during earthquakes of all sizes. Laboratory simulations of earthquakes show that at high slip rates, faults can weaken significantly, aiding rupture1,2,3. Various mechanisms, such as thermal pressurization and flash heating, have been proposed to cause this weakening during laboratory experiments1,4,5,6, yet the processes that aid fault slip in nature remain unknown. Measurements of seismic radiation during an earthquake can be used to estimate the frictional work associated with fault weakening, known as an event’s fracture energy7,8,9. Here we compile new and existing8,9 measurements of fracture energy for earthquakes globally that vary in size from borehole microseismicity to great earthquakes. We observe a distinct transition in how fracture energy scales with event size, which implies that faults weaken differently during small and large earthquakes, and earthquakes are not self-similar. We use an elastodynamic numerical model of earthquake rupture to explore possible mechanisms. We find that thermal pressurization of pore fluid by the rapid shear heating of fault gouge can account for the observed scaling of fracture energy in small and large earthquakes, over seven orders of fault slip magnitude. We conclude that thermal pressurization is a widespread and prominent process for fault weakening.

Experimental and numerical study of frictional heating during rapid interactions of a Ti6Al4V tribopair

Frictional work dissipated into a pair of bodies in contact can lead to the generation of high temperatures at the interface. For extreme conditions, knowledge of such temperatures is indispensable for predicting material damage. Friction experiments have been performed for a Ti6Al4V tribopair on a ballistic bench at elevated sliding velocities and at high normal pressure (V0=43–65m/s and p=110MPa). A specific foil-workpiece thermocouple was developed to measure interface temperature; it was determined that such a sensor is particularly well-adapted to severe interaction conditions (very short response times, adhesive wear and high plastic strain). The experimental study shows that under such extreme conditions, sliding velocity effects on maximum temperatures reached are quite negligible. Using experimentally measured friction coefficients, thermal finite element simulations were performed to examine thermal fields along a sliding path. The temperature and thickness of the heat-affected zone are in good agreement with our postmortem SEM observations, indicating that wear phenomena do not modify the temperature field. A complex partition of heat flux is observed due to differences in the temperatures of the bodies in contact, being accentuated by temperature dependent thermal diffusivity of the Ti6Al4V alloy. Based on these partition coefficients, gradients of dissipated energy along the sliding path are determined.

Self-adaptive optimal control of dry dual clutch transmission (DCT) during starting process

An optimal control based on the minimum principle is proposed to solve the problems with the starting process of the self-developed five-speed dry dual clutch transmission (DCT). For the slipping phase, the minimum principle and improved engine constant speed control are adopted to obtain the optimal clutch and engine torques and their rotating speeds, with the minimum jerk intensity and friction work as optimization indices. For the stable running phase, the engine torque is converted to the driver׳s level of demand. The Matlab/Simulink software platform was used to simulate the DCT vehicle in the starting stage. The simulation and related analysis were conducted for different engine speeds and intentions of the driver. The results showed that the proposed clutch starting control strategy not only reduces the level of jerk and the frictional energy loss but also follows the different starting intentions of the driver. The optimum clutch engagement principle was transformed into the clutch position principle, and a test was carried out on the test bench to validate the effectiveness of the optimum clutch position curve.

Disc cutter wear prediction for a hard rock TBM cutterhead based on energy analysis

Disc cutter wear is a crucial problem that influences the working efficiency and security of hard rock tunnel boring machines (TBMs). This wear results from friction energy accumulation and conversion. In this study, the process of hard rock TBM disc cutter wear is identified and analyzed by quantifying the collective energy change. This study starts with an analysis of the friction process between the disc cutter and hard rock. The relationship between the rolling force work and thrust force work of the disc cutter is examined. As a result, the disc cutter energy equation is determined, and the meaning of the upper and lower bounds of this equation are discussed. Based on the above results, the hard rock TBM cutterhead energy equation is then deduced. A method to identify the friction work is developed. According to the energy wear theory, the cutter wear law on hard rock for a TBM cutterhead is revealed, and a method for predicting disc cutter wear for a hard rock TBM cutterhead is advanced. Furthermore, the validity of this prediction method is confirmed by utilizing data from project cases.

The influence of rail lubrication on energy dissipation in the wheel/rail contact: A comparison of simulation results with field measurements

This work investigates the energy dissipation in a wheel/rail system with field measurements and friction work modeling. Friction and contact conditions are measured and analyzed in order to calculate the power saving of one vehicle running over a curve of a metro line. For modeling the contact forces, creepages and spin between the wheels and rails are determined via simulations of a train traveling in a curve of the track. Next the contact stress and the micro-slip in the contact area are computed from the forces, creepages and spin as well as the measured friction coefficient and profiles of wheels and rail. Three friction conditions are tested: dry, lubricated with a friction modifier and a postlubricated condition. The total frictional work is obtained by integrating local frictional dissipation over the contact area. The wear is also analyzed according to the Tγ method including the spin, in combination with Kalker׳s simplified theory, assuming that the wear is proportional to the frictional work. The frictional work is then related to the energy consumptions under the different friction conditions, which allows evaluating the effectiveness of the friction modifier and its influence on the wear of the wheel/rail system.

Enhancement of Wear and Friction Characteristics of Epoxy Resin by Multiwalled Carbon Nanotube and Boron Nitride Nanoparticles

Epoxy resins are widely used in engineering applications. However, their low thermal stability limits their usage at high sliding velocities and loads. The mechanical properties and thermal stability of a machine element subjected to friction and wear are very important. In this study, friction and tribology behaviors of multiwalled carbon nanotubes (MWCNTs) and boron nitride (BN)-modified epoxy resin have been investigated. Epoxy resin modified by three different nanoparticle configurations, 0.3% MWCNT, 0.5% BN, and 0.5% MWCNT/0.3% BN, was investigated. The tribological characteristics of nanoparticle-modified epoxy resin were compared with properties of neat resin. The friction and tribological behavior of modified epoxy resin were tested using a ball-on-disc test stand at 1.2 and 1.5 ms−1 sliding velocities under 10 N applied load. The tests were done under dry condition and 1,800 m distance. The friction coefficient, wear loss, and temperature increase during testing were recorded and compared with that obtained for neat epoxy. It is observed that nanoparticle modification resulted in enhanced wear resistance and a reduction in friction coefficient and working temperatures.

Experimental Investigation on Sialon Ceramic Inserts for Ultra-high-speed Milling of Inconel 718

A series of milling aerospace material Inconel 718 experiments were conducted with a sialon ceramic tool to investigate chip evolution, cutting force, and tool wear at different cutting speeds. Round inserts were used at ultra-high-speeds under dry cutting conditions. A scanning electron microscopy and an optical microscope were used to observe the worn surfaces and to reveal the wear mechanisms of the inserts. The experiment results showed that the macroscopic shape of the chips was small scraps and fan-shaped. With the increase in the cutting speed, the plastic deformation of the chips was increasingly serious. The minimal average cutting forces were obtained at vc = 700 m/min. The rise of cutting temperature was resulted from the increase in cutting deformation work and friction work with cutting speed. The combined effect of thermal stress and mechanical stress contributed to the tool chipping, flaking, microcrack propagation, abrasion, and adhesion which were the primary reasons of the sialon ceramic tool wear.

Revisiting dissipative heating in tropical cyclone maximum potential intensity

In this study, we re‐examine the hypothesis of the dissipative heating in the tropical cyclone (TC) maximum potential intensity (MPI) proposed by Bister and Emanuel in 1998. By analysing an integral energy equation for an atmospheric domain that encloses all the TC Carnot legs, it is shown that the dissipative heating within the boundary layer is inherently contained in the energy budget so that there is no need to treat it separately. Due to the well‐mixed assumption, the net impact of the dissipative heating turns out to be negligible, resulting in the same MPI estimation as in Emanuel's 1986 article. Within the atmospheric surface layer, the dissipative heating comes at the expense of reduced internal kinetic energy in the boundary layer, which is not seen in Bister and Emanuel's formulation due to their assumption of constant wind speed within the atmospheric surface layer. Analysis of the energy distribution within the atmospheric surface layer shows that about 10–30% of the frictional work could be transferred to the ocean surface waves and oceanic well‐mixed layer, and the assumption that all frictional work is converted to the dissipative heating therefore needs to be revisited. Given further uncertainties in how the dissipative heating is distributed within the surface layer and how the atmospheric surface layer exchanges heat with the ambient environment, we recommend use of the original MPI formula obtained by Emanuel (1986) in which the impact of the dissipative heating within the surface layer can be effectively included in the bulk enthalpy flux parametrization instead of considering dissipative heating as an independent heat source as proposed by Bister and Emanuel.

RESEARCH OF THERMAL STATUS OF THREADING ZONE WITH THE HELP OF FULL FACTOR EXPERIMENT

Thermal processing zone status when threading in heatproof, high-strength and titanium alloys is a major problem in the general theory of metal cutting. Under other equal conditions temperature in the processing zone of these materials is higher than in cutting of carbon structural steels, as they have high strength and ductility, low thermal conductivity, that makes difficult the working conditions of the taps, increases the area of the tool contact with the workpiece, deteriorates lubrication and cooling of the cutting area because of the increased tendency of heatresistant materials for the curing. This causes an increase in the work and force of friction and as a consequence the rise of cutting temperature. Research of temperature state of the threaded coils formation zone with combined countersink tool-tap is one of the major challenges facing the authors of this work. When performing the work was used factorial experiment. The temperature in the cutting zone of the thread was determined by a built-in chromel-aluminum thermocouple with thermoelectrode cross-sectional area 0,23mm2 . Experiments were carried out using the apparatus of mathematical statistics. Studies have shown that the greatest impact on the temperature state of the cutting area has a tensile strength of the material. Effect of cutting speed in the studied variation range is relatively less noticeable. The explanation for this is a special scheme of cutting of combined countersink tap which allows significantly improve conditions in the cutting zone. The proposed design of the tap allows to reduce the temperature in the area of tapping for 20%.

Sliding mode control of shifting process based on throttle opening and vehicle mass variations

In order to reduce the friction work in the inertial phase of shifting process of heavy-duty vehicle (HDV), a complete vehicle model and a shifting process model are built firstly to analyse the dynamical character of automatic transmission (AT)'s shifting process. Then, throttle opening and vehicle mass are introduced as modification in the inertial phase control, and the friction elements' speed difference is treated as control objective. A sliding mode control (SMC) is adapted to realise this control, and shows a better target tracing feature than the conventional PID control. The results of real vehicle test verify the proposed control strategy, and the vehicle has a good shifting behaviour.

Experimental Setup for the Analysis of Vortices

This paper presents a specific experimental setup in which artificial vortices are successfully created and maintained under controlled conditions. The developed vortex simulation chamber is demonstrated to be crucial to the study of vortices and to improve the understanding of vortex nature and behaviour. Furthermore, the general simulation chamber characteristics, constructional details and working principle are elaborated in detail. Preliminary experimental results are also discussed. Specifically, the influence of the water vapour content on the pressure potential and the vortex stability has been analysed. The specific friction work in the vortex system has also been analysed ; the novel specific vortex efficiency factor has been introduced. The gained research results and conclusions are important to understand the complex nature of vortex systems, which can be useful for both meteorological purposes and energy concepts research, where convective vortices are assumed to be used as heat engines.

Process optimization of combined biomass torrefaction and pelletization for fuel pellet production – A parametric study

Torrefaction of plant biomass has the capacity to produce a fuel with increased energy density and homogeneity, but there are reports that it changes the pelletizing properties of the biomass, making it more difficult to obtain high quality pellets. A parametric study was therefore conducted in which three key qualitative parameters, degree of torrefaction (250–300°C), moisture content (0–10%) and pelletizing temperature (125–180°C), were varied according to a five level fractional factorial design, also including particle size as a qualitative parameter. Pelletizing at 300MPa (pellet densities: 1.0–1.2mg/mm3) was undertaken using a single pellet press and the responses recorded were compression work (Wcomp), maximal force to overcome static friction (Fmax), kinetic friction work (Wfric), single pellet dimensions and strength. Small particles reduced Wcomp and Fmax, but increased strength. As expected, all other parameters also had significant effects. In general, less energy was required for Wcomp, Wfric and Fmax at lower degrees of torrefaction and higher moisture contents and when pelletizing was conducted at higher temperatures. The process window to optimize pellet strength was narrow and, surprisingly, somewhat higher moisture content at higher degrees of torrefaction increased strength. This narrow production window in combination with feedstock variations may, in practical pelletizing situations, result in varying quality. Furthermore, the study illustrates that factorial experiments using single-pellet devices provide new insights that are of importance for the next generation of pelletizing of torrefied biomass.