PSI - Issue 81

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

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At minimal loading of the tested specimen, the CER R value i s 80 Ω. With an increase in contact pressure to 2.8 MPa, the CER R value rapidly drops to 6 – 13 Ω and stabilizes after 45 – 65 minutes. Further increase of the contact pressure to 10 MPa reduces the CER R value practically to zero, and it remains at this level until the end of the experiment at P = 18 MPa. The initial friction coefficient μ at the mentioned value of P is μ=0.39, and at P = 2.5 MPa it decreases to μ=0.3. With further increase of P up to 18 MPa, the friction coefficient stabilizes at 0.26 – 0.28. Fig. 9 presents similar experimental results for the tribological pair consisting of the tested specimen made of bronze BrAZh9-4 and the counter-specimen made of steel 30Kh3MFSA in pure diesel fuel. In general, the behavior of the parameters μ and CER R as a function of contact pressure is similar to that in Fig. 8.

Fig. 8. Graphs of the dependence of the friction coefficient μ and contact electrical resistance R for the tribological pair: specimen made of bronze BrAZh 9-4, counter-specimen made of steel 30Kh3MFSA, on contact pressure P in pure diesel fuel.

Increasing the contact pressure to 1 MPa results in a rapid drop of CER R from 280 Ω to 55 Ω and a smoother decrease of μ . Further increase in contact pressure up to 7 MPa gradually decreases CER R , and at P = 7 MPa, CER R becomes zero, while μ reaches its minimum value of 0.15 – 0.17 at P=3.6 MPa, followed by its subsequent increase. Based on the comparison of the obtained experimental data presented in Figs. 7 and 8, it can be seen that the use of bronze BrAZh9-4 as the specimen material leads to stabilization of CER R at a higher level with a significantly lower value of the friction coefficient μ . The tribological pair bronze BrAZh9-4 – steel 30Kh3MFSA, in comparison with the steel 30Kh3MFSA – steel 30Kh3MFSA tribological pair, is characterized by superior antifriction properties due to the formation of DSS type II on the friction surface of the specimen and DSS type I on the friction surface of the counter-specimen. In the case of the steel 30Kh3MFSA – steel 30Kh3MFSA tribological pair, DSS type I forms on both friction surfaces, which results in inferior antifriction performance of the pair. In the next series of experimental studies of the bronze BrAZh9-4 – steel 30Kh3MFSA tribological pair, diesel fuel was replaced with motor oil MT-16p, which significantly influenced the values of CER R and μ and the nature of their variation with contact pressure (Fig. 9).

Fig. 9. Graphs of the dependence o f the friction coefficient μ and contact electrical resistance R for the bronze BrAZh9-4 – steel 30Kh3MFSA tribological pair on contact pressure P in motor oil MT-16p.

At minimal loading of the tested specimen, the CER R value is 5000 Ω. A further increase in contact pressure to 2 MPa causes a sharp decrease of CER R to 1000 Ω, and at a pressure of 3.5 MPa it increases to 1500 Ω. In the contact pressure range of 3.5 – 7.5 MPa, CER R decreases sharply to 250 Ω, and with further increase in pressure up to 15 MPa, it gradually approaches zero. The optimal (minimal) and stable friction coefficient μ=0.0 9 – 0.11 is observed in the pressure range of 2.5 – 12.5 MPa. Thus, for the same tribological pair bronze BrAZh9-4 – steel 30Kh3MFSA, replacing diesel fuel with motor oil MT-16p provides a wider