RESUMO
Six-axis force/torque sensors are increasingly needed in mechanical engineering. Here, we introduce a flexure-based design for such sensors, which solves some of the drawbacks of the existing designs. In particular, it is backlash-free, it can be wirelessly monitored, it exactly enforces 90° angles between axes, and it enables visual inspection of the monitored system, thanks to its hollow structure. We first describe the generic design, implementation, and calibration procedure. We then demonstrate its capabilities through three illustration examples relevant to the field of tribology: low friction measurements under ultra-high vacuum, multi-directional friction measurements of elastomer contacts, and force/torque-based contact position monitoring.
RESUMO
Recent engine design and emission trends have led to the commercial use of Atmospheric Plasma Spray (APS) coatings for cylinder liner applications like the TiO2 APS coating. It was shown in our previous work that this type of coating showed better friction results compared to steel lubricated with MoDTC. To further investigate this feature, a parametric study was carried out involving the effect of MoDTC concentration, test temperature, Hertzian contact pressure and the change of counterpart materials from steel balls to ceramic balls (Al2O3 and ZrO2). Ball-on-flat tribotests were carried out on a reciprocating (ball-on-flat) tribometer lubricated with base oil containing MoDTC. Results show that for all the test conditions used including the concentration of MoDTC, test temperature and the contact pressure, lower friction and wear is observed for the TiO2 APS coating compared to reference steel. To explain the low friction behavior, tribofilm compositions were investigated and it was observed that MoS2 is always formed in the case of TiO2 APS with no oxysulphide species. For the reference steel, MoO x S y species are mainly detected in the tribofilms. XPS analyses performed on TiO2 APS flats when the counterpart material was changed from steel balls to ceramic balls suggested the formation of MoS2 (Mo in +iv oxidation state) and Mo-C (Mo in +iv or +ii oxidation state) species with a negligible amount of MoO3 (Mo in +vi oxidation state). It was also shown that a significant amount of molybdenum atoms inside the tribofilm, originating from MoDTC (Mo in +v oxidation state) were reduced in the tribological contact. A mechanism for the decomposition of MoDTC on the basis of tribocatalytic behaviour hypothesized in our previous work was proposed and discussed.
RESUMO
Amide molybdate has been recently introduced as a friction modifier for tribological applications. Combined with zinc dithiophosphate (ZDDP) and fatty amines, it provides an ultralow friction coefficient. The ultimate product of Mo compound transformations in tribological contact, due to frictional heating and shearing, as well as chemical interactions with oil additives, is molybdenum sulfide (MoS2). Understanding the decomposition of amide molybdate leading to MoS2 is of primary importance to the optimization of the design of lubricant formulations. This study focuses on the investigation by Raman spectroscopy of amide molybdate decomposition intermediates. Raman spectra of tribofilms, obtained after friction tests under different temperatures and pressures, revealed the formation of an amorphous MoS3 intermediate coexisting with MoS2. However, under severe conditions, the tribofilms are mostly composed of MoS2.