## 4 Discussion  
The quantitative and qualitative results of the influence of the load, sleeve thickness, type of tribopolymer material, filler, and [PERSON]'s modulus on the value of maximum contact pressures \(p_{max}\) were obtained (Figures 2 and 3). Reducing the bushing thickness \(S\) from 6 to 2 mm resulted in a 1.126-fold increase in the \(p_{max}\), regardless of the type of polymeric material used for the bushing. The bushing thickness \(S=2\) mm for a shaft diameter \(D_{2}=30\) mm is indicated for the IGUS deep-groove  
Figure 6: Contact pressures (**a**) and durability (**b**) of deep-groove bearings: black colour—\(S=6\), 4, 2 mm, \(f=0.35=\) const; light green—\(S=6\) mm, blue—\(S=4\) mm, red—\(S=2\) mm, \(f\
eq 0.35\). bearings Iglidur J, Iglidur G, and Iglidur W300. The contact pressures in deep-groove bearings increased in the following order depending on the type of polymeric material used for the bushing: PTFE \(\rightarrow\) PA6+MoS2 \(\rightarrow\) PA6+oil \(\rightarrow\) PA6 \(\rightarrow\) PET+20 PTFE \(\rightarrow\) PET \(\rightarrow\) PA6+30 GF \(\rightarrow\) PA6+30 CF \(\rightarrow\) PEEK+30 GF \(\rightarrow\) PEEK. The Young's modulus of the polymers also increased in this order (Figure 7). The fillers had a different effect on the change in contact pressures compared to the unfilled (basic) polymeric materials. Fiberglass and carbon fiber in the polyamide group caused the contact pressures to increase because they increased the Young's modulus of the composite compared to that of PA6 (Table 1). The MoS2 filling reduced the pressures, while the oil filling did not change them. With the introduction of fillers into PA6, the change in the \(p_{max}\) increased up to 1.4 times. The filling of PTFE with polyetheretherketone or PET did not affect the \(p_{max}\). In the case of filling polyethylene terephthalate and PEEK with glass fiber, the \(p_{max}\) slightly decreased (by a factor of 1.045). The Young's modulus \(E_{2}\) had a significant effect on the maximum contact pressure. In polyamides, it increased by up to 2-fold (PA6+MoS2 \(\rightarrow\) PA6+30 CF), which led to a 1.4-fold change in the \(p_{max}\). In the studied polymers, the \(p_{max}\) increased by 4.29 times (PTFE \(\rightarrow\) PEEK+30 GF) (Tables 2 and 3). From the analysis of Figures 2 and 3, it can be seen that in this case, the \(p_{max}\) increased by about 1.86 times (1.86-1.88 times at \(N=1500\) N, and 1.85-1.86 times at \(N=3000\) N). According to the criterion of a minimal contact pressure (\(p_{max}\)), the bearings with a bushing made of PTFE+10C+10 GF or PTFE+15C+5 MoS2 are optimal compared to the other groups of polymers with a bushing made of PA6+MoS2, PET, or PEEK+30 GF. As mentioned above, there are no effective calculation methods in the literature for estimating contact pressures in MP plain bearings. On the other hand, in designing metal plain bearings, the bearing load-carrying capacity is calculated based on the average pressure \(p\) that is uniformly distributed over the contact surface \(2R_{2}l\), i.e.,  
\[p=\frac{F}{2R_{2}l}=\frac{N}{D_{2}}\leq[p] \tag{11}\]  
where \([p]\) is the permissible contact pressure of the less durable material of the bearing elements. The significant disadvantage of this conventional method is that it does not take into account the radial clearance in the joint, which must be greater than zero for normal bearing operation. It also does not take into account the elastic characteristics \(E\) and \(\
u\) of the shaft and sleeve materials. However, these parameters of the tribosystem and its materials have a decisive influence on the value of the contact parameters (maximum  
Figure 7: Modulus of elasticity of tribopolymers. contact pressure and the contact zone). In the indicated conventional calculation, the contact arc has a constant length of \(2\alpha_{0}R_{2}=D_{2}\) and a correspondingly constant contact angle of 114.6\({}^{\circ}\). A modified formula for calculation \(p_{max}\) is also known [32].