2. Fachtagung TestRig - September 2024 81 Tribological Investigations under Varying Pressure Atmosphere Felix S. M. Zak Optimol Instruments Prüftechnik GmbH, Munich, Germany * felix.zak@optimol-instruments.de Abstract The exploration of pressurized gas atmospheres within tribological investigations holds significant implications across diverse industrial sectors. This novel Tribotest option offering a specialized testing apparatus designed explicitly to operate under various pressurized gas atmospheres. This advancement aligns with the critical need to simulate real-world scenarios where materials and components undergo mechanical friction and wear within specific gas environments. By subjecting test samples to controlled gas atmospheres at different pressure levels, the Tribotest option emerges as a crucial tool for assessing material performance and durability under varied operating conditions. 1. Introduction Pressurized gas atmospheres are commonly encountered in aerospace, oil and gas, energy generation and various manufacturing processes. The behavior of materials and lubricants under elevated pressure conditions can signif-icantly impact the efficiency, safety, and reliability of these systems. However, traditional tribology test methods often fall short in accurately simulating the complex conditions found within pressurized gas environments. A novel option for tribotesting is presented, specifically designed to operate under different pressurized gas at-mospheres, especially hydrogen. By exposing test samples to controlled gas atmospheres at different pressure levels, the Tribotest option provides a valuable tool for evaluating the tribosystem in terms of per-formance and durability of materials under different op-erating conditions. 2. Design and Features The new Tribotest option presents an extension module of the SRV®5, an established testing machine for tribo-logical investigations. It retains the standard specifica-tions of the tribometer and additional adjustable parame-ters, like the pressure up to 100 bar The technical dependencies of set values, in the form of the tribological loading spectrum, give rise to several limitations. These dependencies require additional corrections within the regulation, such as compensating for force due to pressure differentials between the pressure chamber and the environment, necessary for normal force control. The option offers variable adjustment of the surrounding atmospheric pressure, capable of encompassing various gases, with a primary focus on hydrogen. Due to hydrogen’s unique properties, predominantly stemming from its small molecular size and associated hazards concerning its high energy density, specific design considerations are imperative. The small molecule size, governed by Graham’s law, results in a high diffusion rate. To counter this, aside from hermetic sealing, an additional protective gas layer is employed. This protective gas (ni-trogen) operates at the same pressure as the test gas, con-ferring advantages in terms of the system’s dynamic sealing. The pressure is measured in both circuits and controlled separately and also recorded for examination purposes. Given the hazards posed by different test gases, particularly hydrogen, an elaborate safety concept is pursued. This includes the utilization of external sensors for detection purposes and consideration of safety parameters, such as the maximum allowable temperature for sealing materials, through continuous monitoring and shutdown mechanisms. In addition to diffusion, other effects emerge when dealing with hydrogen, such as increased permeation and hydrogen embrittlement. These are mitigated through suitable material selection. For permeation, a specific polymer blend, verified through permeation testing, has been employed. The amalgamation of pressure tightness and the dynamic load from tribological investigations presents diverse challenges to individual components within the sealing concept. To counter these challenges, appropriate kinematics and well-chosen sealing methods have been implemented. No detectable leakage of the test gas is tolerated, while minimal leakage of the protective gas is accepted. Parasitic forces, like spring forces or damping forces resulting from the sealing components, are minimized through suitable calibration processes, corrections, and a deliberate distribution of stiffness and mass within the testing system. Despite the necessity for a substantially robust construction the Tribotest option offers temperature measurement close to the friction point for regulating the test body contact or measuring friction-induced temperature rise. Abb. 1: Design of Tribotest Option