## 3 Experimental Results and Discussion
### Tribological Properties
Based on the same considerations, the elongation at break value was assumed to be 300%. This was 37% less than that of neat UHMWPE. However, the achievement of such a strain level was a clear indicator of the structure homogeneity and the composite viscosity. An increase in strength of the composites by reinforcement was typically accompanied by a decrease in their impact toughness (as characteristics of dynamic fracture toughness). The Charpy impact toughness value of neat UHMWPE was \(A_{\mathrm{K}}\geq 150\) kJ\(\cdot\)m\({}^{-2}\) (without fracture). Since such (dynamic) loads were rare under the operating conditions of the metal-polymer tribological units, the authors considered taking the \(A_{\mathrm{K}}\geq 90\) kJ\(\cdot\)m\({}^{-2}\) value as a threshold level. This was 60% lower than that of neat UHMWPE, but higher than even a perfectly acceptable two-fold decrease \(A_{\mathrm{K}}\geq 75\) kJ\(\cdot\)m\({}^{-2}\). The friction coefficient value did not particularly affect wear resistance under the \"moderate\" conditions of tribological loading, when wear was mainly \"controlled\" by the fatigue mechanism (in this case, heating of the contacting parts was negligible). Therefore, 0.12 was chosen as a threshold value of the friction coefficient, which was only 0.02 higher than that of neat UHMWPE. From the point of view of setting the threshold level, the most critical was the wear rate parameter (namely, \"net\" wear, measured considering elastic recovery according to the \"block-on-ring\" scheme under the \"moderate\" conditions). This was chosen equal to that of neat UHMWPE, since it was the properties of pure polymer that was required to be surpassed. For this reason, the wear factor (WF) \(\leq 0.49\times 10^{-6}\) mm\({}^{3}\cdot\)N\({}^{-1}\cdot\)m\({}^{-1}\) condition was predefined. The surfaces of the tribomechanical properties were drawn on the basis of the previously obtained experimental data and assigned threshold levels (Figure 14). Figure 14: Cont. Figure 14: Isoline patterns on the operational properties of the UHMWPE-based composites: elastic modulus \(E\), MPa (**a,b**); ultimate tensile strength \(\sigma_{\rm U}\), MPa (**c,d**); elongation at break \(\epsilon\), % (**e,f**); impact toughness \(a_{\rm k}\), kJ-m (**g.h**); the friction coefficient\(f\) (**l,g**); and wear rate \(\rm I\), \(\rm 10^{-6}\) mm\({}^{3}\)-N\({}^{-1}\)-m\({}^{-1}\) (Load = 140 N, Velocity = 0.5 m\(\cdot\)s\({}^{-1}\)) (**k,l**). The range of the control parameters ensuring the correspondence of the tribomechanical properties of the material to the given boundaries is shown in Figure 15. Only a small region in the upper right corner filled in green satisfied all predefined requirements. It corresponded to the maximum both filler content of 23 wt. % and yield strength (with the same filling degree) of 25.4 MPa. It should be noted that not all material properties used in the analysis had an effect on the region formation. This was evidenced by a fairly small number of isolines limited it. In addition, a region limited on all sides would be more convincingly obtained in terms of the composite design. Highly likely in this case that a further increase in the filler content was useful to achieve (and possibly even exceed) the required levels of the threshold values. However, the experimental data analysis unequivocally testified to the fact that an increase in the wollastonite content over 23 wt. % was impractical, since the composite structure, as well as the mechanical and tribological properties worsened. Computational Design of the UHMWPE-Based Composite for the \"Severe\" Conditions of the Metal-Polymer Tribological Loading  
In this section, the threshold values of the tribomechanical properties of the UHMWPE-based composite loaded with 10 wt. % wollastonite were predefined for use in the \"severe\" conditions of the metal-polymer tribological loading. This implied both an increase in load and a high level of wear rate.