PSI - Issue 81

Andrii Gypka et al. / Procedia Structural Integrity 81 (2026) 478–485

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b

а

Fig. 1. General view of the friction testing machine (a) general view of the friction unit (b).

The open design of the friction unit enables convenient visual monitoring of its operation, lubrication regime, natural cooling of the frictional contact zone, replacement of tribological pair components, and integration of measuring equipment. The schematic representation of the friction unit and the loading mechanism is shown in Fig. 2.

Fig. 2. Schematic diagram of the friction unit and loading mechanism.

The loading mechanism of the friction unit consists of the lever (12), which is pivotally connected to the stationary support (1). Counterweights (5) are mounted on one end of the lever to ensure its balance, while the opposite end is connected to the piston rod of the hydraulic cylinder (13). A segmented plate (10) is rigidly attached to the lever. The lever arm ratio L1:L2=1:5. The spherical surface of the plate (10) is in contact with bearings (9), through which the load is transmitted to the specimen (21), which is in contact with the counter-specimen (19). To record the friction torque, a strain-gauged beam (18) equipped with strain gauges (2) is used, with their output terminals connected to the input module of the strain amplifier. The strain-gauged beam (18) with the mounted strain gauges (2) is installed in a clamp (17), which is fixed on the support (1). During the calibration procedure, the left end of the rod (7), which passes through an opening in the upper part of the strain gauged beam (18), is connected to a guide sleeve (8). Two bearings (3) are mounted on the left end of the rod and pressed against the strain-gauged beam by a nut (4). The right end of the rod (11) is pivotally connected to a tension cable (15), which is routed over a pulley (14) and equipped with a flange for mounting calibration weights (16). To limit the deformation of the strain-gauged beam (18), an adjustable stop (20) is used. When the tribological pair transitions to a seizure mode of the contacting surfaces, the machine is automatically shut down by a limit switch (6). During the investigation of friction and wear processes, the following parameters were measured: wear rate I, friction coefficient μ , contact electrical resistance (CER, R ) of the tribological pair, as well as criteria of the structural state of the friction surface materials of the tested specimens (DSS type). The structural analysis and chemical examination of the friction surfaces were carried out using a CamScan 4DV microscope and a Link 860 analytical system. Materials of the tribological pair components: counter specimen made of steel 30Kh3MFSA (HRC 52 – 56); tested specimens made of steel 45, steel 30Kh3MFSA, bronze BrAZh 9-4; and lubricating environments: inactive vaseline oil, chemically neutral to metals, diesel fuel, and motor oil MT-16p. A universal additive “Anglamol 99” was used as a friction modifier. Lubricants and diesel fuel were supplied to the friction contact zone by a droplet feed system (≈10 d rops/min), controlled by a metering valve to ensure a constant lubrication regime. The friction coefficient was determined by measuring the friction torque (force) based on the deformation of an elastic element equipped with strain gauges (Fig. 3). The wear of the tested specimens was measured gravimetrically using an analytical balance VLR-200 (measurement accuracy 0.01 mg). The run-in specimens were cleaned and degreased before and after the experiment. The schematic diagram for measuring the friction coefficient and controlling the sliding speed is shown in Fig. 3.