Effect of velocity on roll/slip for low and high load conditions in polymer composite

In the last decade polymer composites are often used without lubrication on both low and high speed applications. Some of the application areas are marine, automotive and agriculture used as bearings and cams where roll-slip is the dominant mechanism. Limited studies are made for composites relating such applications where rolling/sliding condition influences the tribological behavior of the material. Investigating the roll-slip phenomenon for identifying the influence of velocity on frictional behavior can mark a boundary to map the use of composites with respect to its application. Moreover, the design of the material can be optimized to match the operating conditions. In the current research the polymer composite (with polyester matrix) has been tested under rolling-sliding condition for two different loads with 61N and 210N and with different speeds ranging from 10 rpm to 700 rpm. Ideal conditions in terms of roughness, slip ratio, surface temperature and ambient temperature were maintained to reduce the frictional heating. Using a 20% slip ratio the behavior of the material was observed for the tribological characteristics where the rate of increase of friction force follows a exponential pattern with increasing speeds. Nevertheless, on testing with high speeds a steady rate of increase in the friction curve was observed. Friction behavior of composites under different speeds is briefed with the microstructural characteristics for low and high loads

Tribological behaviour of the low and high viscosity peek against steel using different contact pressures

In the market of polymers for tribological applications polyetheretherketone (PEEK) are often used for satisfying requests coming from industry regarding enhanced properties such as, thermal stability, friction and wear resistance. These properties promote the material to be used in so called high performance tribological applications. However, fundamental mechanisms governing friction and wear are not yet fully understood and neither is the influence of composition parameters. An important parameter is PEEK’s viscosity during manufacturing process which is heated up to semi-solid state, between its glass transition and melting temperature. This paper studies the friction and wear performance of low and high viscosity PEEK and pure PEEK under dry reciprocating sliding contact. The tests were performed in large scale specimens under flat-on-flat configuration to determine the transitions in tribological behaviour at different contact pressures. Tests were carried out at controlled atmosphere with 25 °C and a relative humidity of 50%. Contact pressures parameters were 4, 8 and 10 MPa used at a sliding speed of 20 mm/s. Post mortem analyses were carried out by means of 2-D surface topography and optical microscopy. The results show that the pure PEEK exhibits low coefficient of friction and wear rate when the contact pressure increase and similar behave for high and low viscosity PEEK

Friction torque, temperature and roughness in roll-slip phenomenon for polymer–steel contacts

The current study gives an insight of the roll-slip phenomenon of polymer-metal pair where priority is given to measurement techniques, test duration and the behavior of the polymer. A systematic tribological measurement was used to identify the friction torque from polymer –metal pairs where the friction torque from contact is obtained by subtracting the base torque of the test rig to exploit the absolute results. Base torque of the machine is almost constant, the changing can describe with linear trend line which is less than 0,5% per ten minutes. Measurements made for 3 hours shows that the friction force between the polyamide 6 (NaPA6) and structural steel (S33J2) has a polynomial of degree two with a function ( Ff = −1.5549 ⋅T 2 + 9.4031⋅T +13,126 ). Micrographs from the contact surface revealed the damage of roughness peaks during the course of testing. The involved wear mechanisms was investigated with roughness measurements and microscopy. The roughness plots also correlates with the micrograph where the rate of decrease in Ra in the initial stage is higher followed by a linear increase in the later stage. This can describe using polynomial function of degree as ( Ra = 0.029 ⋅T 2 + 0.3695⋅T + 2.4967 )

A novel measuring technique to evaluate frictional characteristics of roll-slip contacts in polymer-metal pairs

Tribology research is aimed for desirable frictional characteristic; especially in rolling/sliding of polymer-metal contacts which helps smooth operations and energy savings. Conventional roll-slip tests for few million cycles have significant deposit of polymer transfer layer on counterface, thus having a polymer-polymer contact instead of polymer-metal contact. Besides, backtransfer affecting the friction force was never explored. Studying these phenomenon individually and characterizing frictional property without the presence of transfer layer helps for a better understanding of the combined system. A new procedure for measuring friction torque at 20% slip ratio is adapted for varying speeds from 10 to 500 rpm. The observed friction-force increases rapidly at low-speeds and becomes linear at high-speeds. The micrographs of the contact surface prove no trace of transfer layer was found in the newly developed measuring process. Also specimen surface temperature never reached the effective level to affect friction properties

The impact of fuel and CO2 prices on electricity power plans

The increasing uncertainty surrounding the electricity generating sector has implications on the forecasting accuracy and makes sensitivity analysis an essential tool for electricity power planning. The fuel price volatility and the emissions trading schemes represent major sources of uncertainty, as the relative economic interest of thermo power plants and of renewable energy sources largely depends on these two factors. In this paper, an electricity planning model will be used to analyse both these aspects, identifying the relative importance and sensitiveness of the optimal electricity power plans to changes on these parameters.peer-reviewe

Tribological behaviour of polymer filled with nanoparticles at various testing scales

Nowadays, high potential polymers have been applied as structural materials in the aerospace, automotive and chemical industries. Nevertheless, new high performance applications can be established with the appropriated combination of polymer and nanocomposites fillers; thus providing lower weight alternatives to metallic materials. The research is focused to address the understanding of the wear behaviour of high performance thermoplastic materials and to identify the possibilities to enhance the mechanical properties, wear resistance at large scale test rig. All investigations will be done on high performance PEEK polymers unfilled and filled with nanocomposites. Reciprocating sliding test have been performed in PEEK polymer and PEEK with nanocomposite using flat-on-flat configuration and medium scale tribotester (MSF) under different contact pressures (4, 8, and 10 MPa) and two speeds (20 and 50 mm/s), respectively. It has been found that friction and wear of the PEEK polymer filled with nanocomposites presented low friction but high wear resistance with increase the contact pressure and the speed. Post-mortem analysis will be carried out by means of scanning electron microscopy (SEM) and X-ray Diffraction (XRD) on the worn and counter surfaces to determine the compatibility of the contact bodies, transfer film formation and the type of wear debris in the sliding interface. An analytical wear model will be developed with different test parameters and the obtained results. Wear and friction results obtained at large and small scale experiments are going to be compared, introducing a macroscopic geometrical scaling parameter in an attempt to match both steady-state sliding conditions. Special attention will be given to the sliding stability during the running-in period under high contact pressures. It should be verified if large-scale tests at extremely high load conditions can be equivalent with small scale tests at high sliding velocities and temperature

Tribological behaviour of the low and high viscosity peek at various testing scales

Polyetheretherketone (PEEK) has become most attractive as a sliding bearing material in industrial applications, due to its excellent thermal stability, good friction and wear resistance. These properties promote the material to be used in so called high performance tribological applications. However, fundamental mechanisms governing friction and wear are not yet fully understood and neither is the influence of composition parameters. An important parameter is PEEK’s viscosity during injection moulding which is heated up to semi-solid state, between its glass transition and melting temperature. It is not known to what extent the injection viscosity, related to the applied temperature profile, affects subsequent tribological features. This paper studies the friction and wear performance of low and high viscosity PEEK under dry reciprocating sliding contact. The tests were performed with small and large scale specimens under pin-on-plate and flat-on-flat configuration, respectively; to determine the transitions in tribological behaviour at different scales and to identify the applications limits. Tests were carried out at controlled atmosphere with 25 °C and a relative humidity of 50%. Parameters such as contact pressures and sliding speed were limited at 10 MPa and 20 mm/s, respectively; post mortem analyses were carried out by means of 2-D surface topography and optical microscopy. The results show that PEEK injected at high viscosity exhibits a tribological performance with a relatively high coefficient of friction and high wear rate compare to PEEK injected at low viscosity

Sustainable public transportation from a total cost of ownership perspective

Green transportation advocates decreasing use of private motor cars, the increasing use of walking, bicycle and public transport. Since the main factors for people who desire to travel are cost and time, the use of private cars has increased with significant negative impacts on environment. Total Cost of Ownership (TCO) is an analysis meant to uncover all the lifetime costs that follow from owning certain kinds of assets. In the near future, more people will be challenged to use a combined set of transports to minimize total transportation costs. In this study, a set of combined types of transportation (private cars, train and bus) was simulated by using a traffic simulation software and the TCO for a case of a route in the North of Portugal was calculated. Criteria for the evaluation of the different types of transportation included conventional cost of traveling (internal) and value of travel time and value of environmental aspects proceed by the CO2 emissions (external costs), all translated in monetary values using estimations of the value of time and of environmental impacts. The results showed the importance of the value of time estimation and confirmed public transportation as the best option under both conventional and extended TCO point of view