## 4 Discussion
12.5\(\longrightarrow\) 4.9%), and 2.05 (13.8/12.8\(\longrightarrow\) 7.8%). The first number is the pressure according to the presented method, the second is the pressure according to the FEM in the indicated work, and the third is the convergence of the pressures. The convergence of the results depends on the amount of radial clearance. On the other hand, the mean pressures \(p\), calculated using (11), reached a value of 3.1 MPa. This indicates a lack of reliability of the assessment of pressures using the conventional method. The following quantitative and qualitative effects of the load; sleeve thickness; types of tribopolymer and filler materials; Young's modulus; and wear resistance indices \(B_{1}\), \(m_{1}\), and \(t_{10}\) of the sleeve tribopolymers on the durability \(t\) of the bearings were determined (Figures 4 and 5). When the bushing thickness \(S\) decreased from 6 to 2 mm, the bearing durability \(t\) decreased by 1.14 times for all the types of polymeric materials. The bearing with a PET+20 PTFE bushing had the longest durability, and the bearing with a PA6+30 GF bushing had the shortest durability. The ratio of their durability values was 5.33 at \(N\) = 1500 N and 5.7 at \(N\) = 3000 N. Bearings with a bushing made of PA6+MoS2, PA6+oil, and PET had approximately the same durability at \(N\) = 1500 N. At a load of \(N\) = 3000 N, the durability was the same for bushings made of PA6+MoS2 and PA6+oil and slightly higher than that of PET. The lowest durability of the bearings made of PA6, PA6+30 GF, and PEEK at \(N\) = 1500 N were similar, and at \(N\) = 3000 N, the bearings made of PA6+30 GF and PEEK had the lowest durability. The durability of the bearings with PA6+30 CF and PEEK+30 GF bushings were somewhat higher. Depending on the type of polymeric material used for the bushing, the durability \(t\) of the MP bearings increased in the following order: PA6+30 GF \(\rightarrow\) PEEK \(\rightarrow\) PA6 \(\rightarrow\) PEEK+30 GF \(\rightarrow\) PA6+30 CF \(\rightarrow\) PA6+oil \(\rightarrow\) PA6+MoS2 \(\rightarrow\) PET \(\rightarrow\) PTFE+10C+10 GF \(\rightarrow\) PTFE+15C+5 MoS2 \(\rightarrow\) PET+20 PTFE. The wear resistance of the tribopolymers and the level of specific friction force \(\tau=fp_{max}\) at the tribocontact (see Equation (4)) [19], rather than the contact pressures \(p_{\max}\), had a decisive influence on the durability. In the authors' methodology for testing the kinetics of material wear under sliding friction [19], it is assumed that the material wear rate is functionally related to the level of the friction force. The increase in the linear wear resistance characteristic \(B_{1}\) of the polymeric materials was in the following order: PA6 \(\rightarrow\) PEEK \(\rightarrow\) PA6+30 GF \(\rightarrow\) PA6+MoS2 \(\rightarrow\) PEEK+30 GF \(\rightarrow\) PA6+30 CF \(\rightarrow\) PET \(\rightarrow\) PA6+oil \(\rightarrow\) PET+20 PTFE \(\rightarrow\) PTFE (Tables 1-3). On the other hand, the trend in the change in the unit value of the frictional force in the tested MP bearings with different polymers was different: PA6+MoS2 \(\rightarrow\) PTFE+15C+5 MoS2 \(\rightarrow\) PA6+oil \(\rightarrow\) PTFE+10C+10 GF \(\rightarrow\) PET \(\rightarrow\) PA6 \(\rightarrow\) PET+20 PTFE \(\rightarrow\) PA6+30 CF \(\rightarrow\) PEEK \(\rightarrow\) PEEK+30 GF \(\rightarrow\) PA6+30 GF. At the same time, the trend in the changes in the value of the specific friction force \(\tau\) in the studied MP bearings with different polymers was also different: PA6+MoS2 \(\rightarrow\) PTFE+15C+5 MoS2 \(\rightarrow\) PA6+oil \(\rightarrow\) PTFE+10C+10 GF \(\rightarrow\) PET \(\rightarrow\) PA6 \(\rightarrow\) PET+20 PTFE \(\rightarrow\) PA6+30 CF \(\rightarrow\) PEEK \(\rightarrow\) PEEK+30 GF \(\rightarrow\) PA6+30 GF.