Force Measuring System for High-Precision Surface Characterization under Extreme Conditions

Force measuring is used in various surface characterization techniques such as indentation, scratch tests, tribological analysis, determination of gas content, etc. The main problems related with force measurement under extreme conditions have been analysed. A strategy that should be followed to solve these problems has been discussed and several examples of successive solutions that recently were developed by the authors are presented. The need to carry out the characterization under extreme conditions poses serious problems for the designers of the measuring systems that may include the incompatibility of the sensors with the test conditions, undesirable interactions with other components, stability, precision and uncertainty issues, the measurement range, etc. Resolving these problems must be based on a global approach in which the characterization system is considered as a whole, while the designer must analyse and solve the possible conflicts between the subsystems. The way how an appropriate force measuring system can be selected is described. The proposed method is illustrated by an example in which an indirect force measurement using optical fibre displacement sensor was used. Another example describes measuring system developed for vacuum high-temperature nanoindentation. At high temperature, proper heat management based on non-contact heating and laminar flow cooling system is mandatory to avoid experimental data being affected by external noise and thermal drift

Transient aspects of plasma luminescence induced by triboelectrification of polymers

Transient electric gas discharges that occur around sliding interfaces during contact electrification of polymers were studied at millisecond timescales and with micrometre resolution. Deduced vibrational temperatures indicate cold plasma resulting from positive corona discharge. At millisecond timescales, previously unseen rapid discharge events are observed, and modelling suggests that these result from streamer development, triggered by electron emission from the polymer surface. Those which occur over a period of several seconds are shown to be caused by competition between charge generation and the formation of polymer films. The findings explain the interplay between charging and plasma generation and their dependence on wear processes.UK Engineering and Physical Sciences Research Council (EP/J002100/1), Additional equipment funding provided by the Taiho Kogyo Tribology Research Foundation (11A01). Spanish Ministry of Economy, Industry and Competitivity through the grant BIA2016-79582-

Application of diamond-like carbon coatings to elastomers frictional surfaces

Nitrile-butyl rubber-like materials were coated with amorphous hydrogenated diamond-like carbon (DLC) coatings in order to modify their surface and tribological properties. Measurements of water contact angle were performed by the sessile drop method and showed that the coated samples are more hydrophobic with water contact angles up to 116°. The surface free energy of the elastomers was calculated by the acid-base regression method considering polar and dispersive contributions and the results were correlated with changes in the surface chemistry measured by X-ray photoelectron spectroscopy. It has been found that the lower presence of oxygen functional groups on the elastomer surfaces led to lower surface free energies, even though the polar contribution was not predominant. We also found that the DLC coatings led to a significant decrease of the surface free energy (up to 16%) and that there is a good correlation between the surface free energy values and the corresponding water contact angle values. The coefficient of friction was also measured and presented a significant decrease after coating with DLC. © 2008 Elsevier Ltd. All rights reserved.The authors acknowledge the financial support of the EU from the Sixth framework programme in the KRISTAL Project no. 515837-2. L. Martínez and Y. Huttel acknowledge the Spanish “Ministerio de Educación y Ciencia” for the “Juan de la Cierva” and “Ramón y Cajal” programmes, respectively. R. Nevshupa acknowledges the “Marie Curie” programme (MIF1-CT-2006-22067)

Triboemission: Unveiling hidden tribological processes

Resumen del trabajo presentado a Ibertriva (X Iberian Conference on Tribology / XI Iberian Vacuum Conference), celebrada en Sevilla (España) del 26 al 28 de junio de 2019.Injection of concentrated mechanical energy into materials at a tribological interface brings about a number of activated electronic and vibrational states, which trigger cascades of physico-chemical reactions including chemical reactions between the activated material and the environment. Many of these reactions end up emitting electrons, ions, gas molecules, electromagnetic radiation, etc. that is collectively known as triboemission. Born at the buried surfaces of a tribological interface triboemission carries valuable information about hidden tribological processes: energy dissipation, mechanical behaviour of materials (plastic flow, fracture, etc.) and tribochemical reactions (Fig. 1). This work summarizes the results of our recent studies of triboemission of gases, triboelectrification and triboluminescence aimed at establishing links between triboemission and material degradation, both structural and chemical. The research findings led us to the development of innovative methods for non-destructive in situ and real-time evaluation of integrity of tribological materials and coatings, characterization of tribochemical transformation of lubricants, as well as other characterization methods far beyond the tribology area

Development of a composite friction modifier with carbon nanotubes for applications at the wheel–rail interface

Wear of wheels and rails is a major problem in railway transportation industry. Solid lubricants constitute a cost-efficient alternative to control wear and friction at the wheel–rail interface, especially when a fine-tuned balance between traction force and energy consumption is sought. In this work, composite friction modifiers (CFMs) composed of a vinyl ester matrix reinforced with molybdenum disulfide and carbon nanotubes were developed. The total solid additive content was less than a half in comparison with a commercial product available on the market, which was used as a reference. A benchmarking study of the CFM was carried out by means of tribological tests in a twin-disc machine at a contact pressure of 1.1 GPa and different slip values. The results indicated that the developed CFM reduce coefficient of traction by 10% compared to unlubricated conditions that is similar to the reference. However, the total mass loss of steel components due to wear under CFM lubrication was lower than in the reference test

Data for: The effect of environmental variables on corrosion of high–strength low–alloy mooring steel immersed in seawater

Some results of immersion corrosion of R4 steel samples in synthetic seawater under various temperatures, salinity levels and dissolved oxygen concentration