23rd International Colloquium Tribology - January 2022 507 Upscaling Materials Performance Ulrike Cihak-Bayr AC2T research GmbH, Wiener Neustadt, Austria Corresponding author: franz.pirker@ac2t.at Marin Herr, Franz Pirker AC2T research GmbH, Wiener Neustadt, Austria 1. Introduction The design process of tribological systems usually involve expensive and time-consuming experimental tests on full component scale to ensure efficient and reliable operation on system scale. Within the European test-bed project i-TRIBOMAT („Intelligent Open Test Bed for Tribological Materials Characterisation“) we present an approach to upscale material performance from simple model tests to component scale behaviour and predict the product performance at an early development stage and significantly reduce costs and time-to-market for new materials. The current study investigates the influence of the tribological properties of self-lubricating polymer seals on system performance of a pneumatic actuator and represents one of three i-TRIBOMAT use cases. 2. Digital Services The centrepiece of the digital service provided by i-TRI- BOMAT are numerical simulations predicting material performance. Figure 1 shows the simulation for reciprocating seals under dry conditions, exemplarily. The simulation is fed with the mechanical material models taken from an extensive database including the tribological properties of the material of interest in an appropriate tribological model test. The requirements of the industrial system, where the seal is meant to operate, define the boundary conditions of the upscaling simulation, such as environmental temperature, velocity profile, and chamber pressure. Thus, the simulation expert, who designs the new component, can consult the database (service 2) for model-test results fulfilling these requirements. If some additional parameter variations of the model test are needed, these will be performed within the service 1, the shared tribological test infrastructure. Figure 1: Overview services and integrated workflow The target values of the upscaling simulation such as frictional force and wear volume indicate the new seal material performance in terms of efficiency and reliability of the system. 3. Trusted input data Flexibly, new materials can be characterised in the standardized model set-up and be evaluated for their performance in the up-scaling simulation. This requires absolute control of the input data quality. While the mechanical testing procedure is quite straight forward, the tribological testing remains a challenge and slightly different testing procedures [1] and different evaluation processes [2] lead to a significant variation of the final result. To ensure stable conditions at model tests and reliable results the test was standardized during the i-TRIBOMAT project to provide trusted experimental data for the up-scaling from model test to component performance. The validation of the model with the results from component test-rig on system level (Figure 2) ensures trustworthy up-scaling model simulation outputs. Figure 2: Component test-rig on system level 508 23rd International Colloquium Tribology - January 2022 Upscaling Materials Performance 4. Workflow The workflow starts with the industrials users` needs with a new material and the operation conditions (Figure 3). In order to find the appropriate model test parameters, the simulation model is used to “down-scale” the operational conditions on component level to an appropriate model test set-up and parameter field. So, the input conditions such as chamber pressure, ambient temperature, velocity, and stroke determine the range of contact pressure, velocity, and temperature for the model test. At the end of the down-scaling process it is possible to define a tribological test matrix for the standardized model test that will closely represent conditions in the contact on component level. The results of the model tests are subsequently used as input values in the up-scaling model to predict target values like frictional force on system level and change of the seal profile due to wear. Figure 3: Workflow of the upscaling simulation model 5. Influence of tribological input parameters on seal upscaling model A sensitivity study is the basis to detect the essential level of accuracy of the experimental input data to ensure robust predictions on friction and wear on the system level. Figure 4 shows the results of a parameter study performed with a wide range of CoF input-values, ranging from typically suggested values of 0.2 to values obtained in tribological tests for the current material in contact with a given counter-body surface. The diagram in Figure 4 shows the frictional force for a chamber pressure of 0, 10 and 60 bar. The frictional force does not relate linearly to the coefficient of friction but increases following a power law relation. The red circle in Figure 4 shows a CoF value typically suggested in the simulation community. If the predicted frictional forces are compared with the measured CoF of 0.6 for the current seal material (see green circle in Figure 4), there will be a deviation between predicted friction of 75 % compared to the values based on an assumed CoF taken e. g. from literature. Figure 4: Influence of coefficient of friction (CoF) on frictional force of seal model Figure 5 shows the cross section of the seal in operation with different values for CoF and chamber pressure. In specific operation conditions the seal loses its grip to the housing, which leads to an increased contact area between seal and shaft. Naturally, the seal cannot operate under such unstable conditions and is prone to early failure. These fatal conditions are difficult to predict experimentally on system level beforehand but can reset the whole design process back to its start. Figure 5: Contour plots of seal for different chamber pressures and coefficient of frictions 6. Conclusion The presented materials upscaling model can predict the system performance of self-lubricating seals based on well-designed model tests. The sensitivity study reveals a strong dependence on the CoF value chosen as input parameter. As small changes in the model test-set up or evaluation process can have significant influence on the results, a standardization of the model test is done. With a strong linkage between simulation and experimental tribological testing of the material and full control over the quality of the data i-TRIBOMAT provides a platform for prediction of material performance on system level. 23rd International Colloquium Tribology - January 2022 509 Upscaling Materials Performance i-TRIBOMAT captures the industrial need for drastically reduced development processes by providing validated numerical up-scaling models, an extensive material library, and tribological testing service on a web-based platform. Thus, the optimal material solution can be determined at an early stage of the development, which significantly reduces the costs and time to market. References [1] Gee, M. G. “VAMAS report: Towards standardization for friction and wear testing.” Tribology International 26.2 (1993): 143-146. [2] Llavori, I., et al. “Critical analysis of coefficient of friction derivation methods for fretting under gross slip regime.” Tribology International 143 (2020): 105988. 7. Acknowledgement This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 814494, project i-TRIBO- MAT. More details: https: / / www.i-tribomat.eu/ .