PSI - Issue 50

A.A. Ushkanov et al. / Procedia Structural Integrity 50 (2023) 294–298 A.A. Ushkanov, A.A. Okhlopkova, A.P. Ammosova / Structural Integrity Procedia 00 (2022) 000 – 000

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Table 1. Results of the study of physicomechanical and tribological characteristics Composite, wt % σ t , MPa ɛ , % Е , MPa σ c , MPa I, mg/h f PTFE BF CF 100.0 - - 22 400 355 21 51.39 0.20 99.9 0.1 - 22 434 361 21 46.02 0.22 99.5 0.5 - 26 470 302 21 9.85 0.17 98.0 2 - 26 411 364 22 2.04 0.31 99.9 - 0.1 29 483 414 22 40.67 0.16 99.5 - 0.5 30 477 400 22 2.72 0.17 98.0 - 2 26 373 398 24 1.24 0.20

Note : σ t - tensile strength, MP а ; ɛ - elongation at break, %; E - modulus of elasticity, MPa ; σ c - compressive strength, MPa (25%); I – mass wear rate, mg/h; f – coefficient of friction.

As can be seen from the table, the tensile strength of the composites increased to 36% of the initial unreinforced. When the content of the filler in the amount of 2 wt %, on the contrary, there is a decrease in strength. For a more accurate and transparent picture, it was decided not to add an additional component. It is likely that it was its absence that led to the deterioration of the tensile strength values. However, this behavior is a characteristic phenomenon for polymeric materials and is explained by the weakening of the intermolecular bonds of PTFE. In other words, the higher the filler content, the weaker the bonds and the worse the strength of the material (Kirillina et al. (2013)). The relative elongation of PCM increases by more than 20%. Due to the fact that polymers cannot be strictly attributed to crystalline or amorphous substances, it is quite reasonable to assume that an increase in relative elongation occurs with an increase in the proportion of the amorphous phase. Amorphous regions of polymers, compared to crystalline regions, have the ability to form voids in the polymer matrix, which can eventually lead to looseness of the package (Pomogova (2019)). The modulus of elasticity of PCM is effectively improved by adding a reinforcing filler, regardless of the nature of the filler. In the case of adding carbon fiber up to 0.1 wt %, a greater effect on the modulus of elasticity is observed, since there is a noticeable increase in the modulus of elasticity of PCM up to about 483 MPa compared to the initial 355 MPa. The introduction of fibers into the polymer matrix from 0.1 to 2 wt % monotonically increases the compressive strength of composites up to 14% compared to the initial polymer. Consequently, the addition of basalt or carbon fiber to PTFE improved the performance obtained during the compression test. When fibers are added to the polymer matrix, there is a decrease in the friction coefficient of PCM up to 20% compared to PTFE, and at the same time, the mass wear rate is significantly reduced up to 41 times. Low friction coefficients exist at sliding speeds less than 0.01 m/s, and with an increase in sliding speed it increases noticeably and amounts to more than 0.3. Therefore, it can be assumed that the obtained values of f are within the acceptable range (Negrov and Putintsev (2021), Kurguzova (2014)). It can be seen that low mass wear rates are observed for composites containing 2 wt % fibers. The increase in wear resistance can be explained by a change in the supramolecular structure of the polymer, and at the same time by the reinforcing ability of the fibers, when the fibers, penetrating the polymer matrix, provide the formation of a reinforced structure. Such formation of a reinforced structure gives the composites rigidity and, as a result, high wear resistance (Okhlopkova et al. (2013)). For example, in the work by Vasilev (2018) it was found that up to 5 wt % BF is achieved by the optimal set of properties to improve the deformation-strength and tribological characteristics. From Fig. 1, fibers are clearly detected on the friction surface of the composites. Apparently, an increase in the wear resistance of PCM occurs due to the fact that the fibers, being localized on the surface layer of the polymer, protect it from destruction. When comparing the surfaces of composites, PCM is distinguished, containing 2 wt % BF (Fig. 1d), the friction surface of which is characterized by fractures and a large number of fractures.