## 3 Research Results and Discussion  
### Measurement of the Shaft Sleeve Pressing and Removal Forces  
The correct tolerance value is a decisive factor for the value of surface pressures, which translates into the appropriate joint strength and stability. As a result of the joint assembly or disassembly process, elastic-plastic or plastic deformations may take place in the top layer of the elements joined together. That situation will occur especially in the actual contact zone of the mating surfaces. The outcome of top-layer destruction is that the value of the actual surface pressure is smaller in relation to the structural value, which may lead to joint disconnection in the course of its operation. As indicated by the results of research undertaken by other authors, whereas joint strength clearly increases when elastic joint deformation occurs, growth strength intensity in the elastic-plastic and plastic deformation area diminishes when the tolerance grows. The measurement of the force needed for forced-in joint assembly and disassembly demonstrated the varying values of the maximum force, depending on the fatigue cycles. The highest value of the force needed for pressing the sleeve onto the shaft was measured at the beginning of fatigue tests during the first installation of the sleeve on the shaft (for 0 fatigue cycles). After the next stages of fatigue tests, it was noted that a smaller force was needed to create a joint between the elements. It is as late as after the third fatigue cycle that the need for a greater force was noted compared to the previous test stages. The maximum value of that force did not, however, exceed the value noted during the first assembly. The detailed values of the maximum forces needed for pressing the sleeve onto the shaft and for the sleeve removal from the shaft are compiled in Table 4, and the pattern of the shaft sleeve pressing force after each fatigue cycle is shown in Figure 4.  
In the case of joint disassembly, varying maximum values of the forces needed to remove the sleeve from the shaft are also noted. The lowest value was recorded after the first fatigue cycle. After the successive fatigue cycles, greater forces were required to disconnect the joint. However, the difference between the maximum forces in the second and third fatigue cycles is insignificant and amounts to 0.2 kN only. Diagrams showing the shaft sleeve removal forces are presented in Figure 5.  
The process of forcing the sleeve onto the shaft results in shearing and crushing the microirregularities present on the surface of the elements joined together. Shearing intensity on those irregularities depends mainly on the tolerance value and the physical and chemical properties of the materials joined together. Adhesion-related damage may also arise. The greatest deformation occurs at the contact surfaces at the beginning of the hub and at the end of the axle seat. This results in uneven contact over the joint length and in the related uneven distribution of surface pressures. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Name** & **First Joint Assembly** & **First Fatigue Cycle** & **Second Fatigue Cycle** & **Third Fatigue Cycle** \\ \hline Number of fatigue cycles & 0 & 10,000 & 100,000 & 1,000,000 \\ \hline Pressing & 3.875 & 2.370 & 1.414 & - \\ \hline Removal & - & 1.387 & 4.952 & 5.159 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Value of the maximum force needed for joint assembly and disassembly [kN]. Figure 4: Sleeve pressing force pattern after the successive fatigue cycles. Based on the information above and on the results of the measurements presented in this work, it may be concluded that the maximum force needed to press the sleeve onto the shaft and to remove the sleeve from the shaft strongly depends on surface roughness and on the presence of wear products between the surfaces joined together. The greatest maximum pressing force was necessary to assemble the joint for the first time because the joint surfaces have low initial roughness.