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Gear failure modes and their underlying mechanisms are usually identified by visual inspection, which relies on the skills and experience of the human observer and hence is prone to subjectivity and bias. Therefore, it is essential to design and implement objective methods to improve the identification of gear failure modes. In the present study, the 3D topography of gear surfaces affected by different types of wear modes, i.e., micropitting, pitting, and scuffing, was measured by means of white light interferometry. The surfaces were evaluated in terms of height, spatial, and function roughness parameters, according to ISO 25178-2. Besides, a new roughness parameter, named surface motion orientation (S m o ), was proposed. Three features were found relevant to identify the differences between the gear surfaces affected by different failure modes: the shape of asperities distribution, the severity of damage, and the surface texture orientation with respect to the motion direction. The combination of the roughness parameters selected to quantify each of these features (S s k , S q , S m o ) resulted in an objective classification of the assessed gear failure modes. • 3D topography of gears with scuffing, micropitting and pitting were evaluated. • A new roughness parameter, named surface motion orientation (S m o ), was proposed. • The combination of S q , S s k and S m o enable the identification of gear failure modes. [ABSTRACT FROM AUTHOR]

The tribological behavior of new green friction materials with rice husk (RH) and rice husk ash (RHA) is discussed in the current paper. Two formulations developed, one with 6% RH and one with 6% RHA, were compared with a reference formulation with alumina under the AK Master test, through a braking tribometer. Formulation with RHA showed tribological performance equal to or better than the reference material, especially in high temperature applications where the RHA particles assisted in the building of the contact plateaus. Adding RH reduced the abrasive action of the composite, allowing the formation of a more homogeneous tribofilm on the disc than in the other formulations. • An eco-friendly brake friction material with rice husk ash was developed. • Rice husk ash led to a high percentage of contact plateaus in high temperature. • Rice husk ash had similar wear and friction performance as the reference material. • Rice husk had lower friction and promoted a more homogeneous tribofilm. • Rice husk ash showed great potential as reinforcement in brake materials. [ABSTRACT FROM AUTHOR]

The present paper addresses the tribological behaviour of new eco-friendly brake friction materials with rice husk (RH). Three formulations with different RH content (0%, 6% and 12%) were developed and subjected to the SAE J2522 test procedure, plus an extra high-temperature section, through a laboratory-scaled braking tribometer. At 300 °C, RH acted holding wear debris and improving wear resistance due to the formation of large contact plateaus. At 550 °C, RH's organic compounds degraded, leading to a greater material fade. Formulation 6% RH outperformed the others, showing the lowest wear. In this case, the effect of the hard and temperature resistant silica outweighed the degradation of the organic compounds. • Eco-friendly brake materials were developed with different amounts of rice husk. • Increasing the amount of rice husk increases wear resistance at low temperatures. • At high temperatures, the increase in rice husk led to a lower fade resistance. • At high temperatures, medium amounts of rice husk improved wear resistance. • Rice husk shows great potential as reinforcement in brake materials. [ABSTRACT FROM AUTHOR]

The present study examined the effect of temperature on Pressure-Velocity Limit (PVL) of a commercial polyacetal (POM-C) with carbon black. The polymer was rubbed against a gray cast iron counterpart (disc) through a pin-on-disc tribometer. The operating parameters of the wear tests included a fixed constant load, 3 different temperatures (30, 55 and 85 °C), and sliding velocities (v) varying from 1.2 to 2.0 m/s. At 30 °C, the PVL was 2.04 MPa m s−1 (at 1.8 m/s). At 55 °C, two distinct PVLs were identified: PVL 1 = 2.04 MPa m s−1 (v = 1.8 m/s) and PVL 2 = 2.26 MPa m s−1 (v = 2.0 m/s). Between the PVL 1 and PVL 2 at v = 1.9 m/s, the wear regime was mild due to the presence of a protective and uniform tribofilm on the surface of the disc. At 85 °C, no PVL was reached. The higher temperature of the tests softened the polymer in this case, easing its adhesion on the disc's surface. This in turn contributed to form a uniform and continuous tribofilm over the disc's surface, preventing the PVL and severe wear regime to occur. The wear mechanisms involved in the tests are described and discussed throughout the paper. • The highlights of the study are: • Pressure-velocity limit (PVL) of POM-C is strongly affected by temperature. • It was found a single PVL at 30°C, double PVLs at 55°C and none PVL at 85°C. • At 85°C, a uniform tribofilm prevented PVL and severe wear regime to occur. • In the PVL, wear of POM-C increased considerably due to adhesive wear mechanism. [ABSTRACT FROM AUTHOR]