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In diesem Beitrag wird der Einfluss der Umgebung auf das Reibungs- und Verschleißverhalten von Polymerwerkstoffen präsentiert. Dabei wurden reine und mit Graphit gefüllte Polymere an Luft, im Vakuum und in einer Wasserstoffumgebung bei Raumtemperatur sowie in flüssigem Wasserstoff bei – 253°C untersucht.
The effects of weathering exposure on unfilled and filled thermoplastic polyurethanes (TPU) materials are described as performed under different humidity conditions. For this purpose, a weathering device was used with UV-A 340 nm lamps at a constant temperature of 40 °C. The effects of environmental (UV and humidity condition) degradation on the frictional properties of TPU materials are presented along with surface analyses to characterize the chemistry of the degradative process. Photooxidative degradation of unfilled polymer leads to deterioration of physical and mechanical properties, which affects its tribological behavior significantly. Due to crosslinking, the stiffness of the material increases, reducing drastically the friction coefficient of unfilled TPUs. The frictional behavior of glass fiber reinforced TPU is less affected by radiation.
The effects of UV radiation and humidity condition on the frictional properties of TPU materials are presented in this paper.
Photooxidative degradation of polymer leads to deterioration of physical and mechanical properties, which affect its tribological behavior significantly.
Unfilled TPUs lose their anti-slip properties.
The effects of UV radiation and humidity condition on the frictional properties of TPU materials are presented in this paper.
Photooxidative degradation of polymer leads to deterioration of physical and mechanical properties, which affect its tribological behavior significantly.
Unfilled TPUs lose their anti-slip properties.
Effect of high-pressure hydrogen environment on the physical and mechanical properties of elastomers
(2024)
This study presents the influence of high-pressure hydrogen environment on the physical and mechanical properties of two types of cross-linked hydrogenated acrylonitrile butadiene rubbers. Based on the CSA/ANSI standard, static exposures in hydrogen experiments were performed up to 100 MPa at 120 °C. Characterization before and after exposure was conducted by means of density and hardness measurements, dynamic mechanical analysis (DMA), tensile tests, compression set, FT-IR and AFM analyses to assess effects after decompression. While the effect of high-pressure exposure is significant immediately after exposure, most of the physical and mechanical properties recover after 48 hours. FT-IR, AFM, SEM and compression set results indicate, however, permanent effects.
Le secteur automobile doit faire face actuellement à de nouveaux challenges au niveau de la construction allégée, des économies de carburant et des coûts. Ces exigences motivent la mise au point de tribosystèmes pouvant résister à des pressions de contact de plus en plus élevées avec de faibles coefficients de frottement. L'optimisation de systèmes existants par l'application de revêtements de surface performants représente une alternative intéressante. Ce texte présente les performances de couches minces dans des conditions d'essais de slip-rolling (roulement à composante de glissement) en présence de lubrifiants liquides. Après une première sélection à température ambiante, les revêtements les plus performants ont été testés à 120 °C. Il s'agit de revêtements DLC en carbone hydrogéné (a-C:H) et en carbone tétraédrique (ta-C) de dernières générations ainsi qu'un nouveau système « revêtement/substrat ». Certains des revêtements DLC développés récemment sont résistants en slip-rolling au moins jusq'à 10 millions de cycles à 120 °C dans l'huile moteur sous des pressions hertziennes de contact de P0max = 2600 / 2940 MPa. De plus, le nouveau système revêtement Zr(C,N)x/substrat peut résister au moins à 1 million de cycles sous des pressions hertziennes initiales de contact allant jusqu'à P0max = 3500 MPa et à des températures de lubrifiant d'au moins 120 °C. -----------------------------------------------------------------------------------------------------------------------------------------------
The light-weight approach and fuel economy targets in today's automotive engineering require tribosystems, which can withstand higher contact pressures associated with low coefficients of friction. The application of surface coatings represents one approach among others. This paper presents thin film coatings performances in a bench mark test procedure exerting slip-rolling conditions in the presence of liquid lubricants. After a first selection at room temperature, the most resistant coatings were evaluated at 120 °C. These are newly developed DLC coatings (a-C:H & ta-C) as well as a novel coating-substrate system. Some of the newly developed DLC-coatings are slip-rolling resistant for at least up to 10 million cycles at 120 °C oil temperature) under Hertzian contact pressures of P0max = 2600 / 2940 MPa. Furthermore, this novel Zr-based thin film coating can withstand at least 1 million cycles under initial Hertzian contact pressures of up to P0max = 3500 MPa and oil temperatures of at least 120 °C associated with low coefficients of friction under mixed/boundary conditions.
The development of hydrogen technologies entails high safety requirements in distribution and dispensing infrastructure. Therefore, it is necessary to pursue research on material compatibility in hydrogen, especially for critical parts with tribological issues.
The focus of this study is to evaluate the influence of hydrogen on a wider range of commercially available polymer materials. Thereby, the friction and wear behavior of different grades of TPE, POM, PA66, PA12, PPA, PEEK, PPS, PTFE, PAI, PI and PBI were investigated against a rotating steel disk (AISI 304). Filled and unfilled polymers from different suppliers were evaluated at room temperature in air, vacuum and hydrogen gas (H2) as well as in liquid hydrogen at - 253°C (LH2).
The sliding behavior of the polymer materials is discussed by means of surface analyses, whereby special attention is paid to the formation of a transfer film.
According to the results at ambient temperature, the effect of hydrogen environment on the tribological behavior of neat polymers may be related to lack of moisture, but also to saturated hydrocarbons in gaseous hydrogen. In liquid hydrogen, the best tribological performances were achieved with neat PA polymers as well as PPS and PI composites.
This chapter deals with the development of polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE)-based composites, optimized for low friction and low wear performance under extreme environments. It is demonstrated that the incorporation of a harder polymer component into PTFE (such as PEEK particles), a short fiber reinforcement (e.g. carbon fibers (CFs)) and internal lubricants (e.g. PTFE particles) helps to reduce the friction and to improve the wear resistance over a very wide temperature range.