PSI - Issue 25

Sergey Smirnov et al. / Procedia Structural Integrity 25 (2020) 209–213 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Experiment and results Originally, we obtained mechanical characteristics for the coatings in the initial state, not subjected to thermal effects. A load of 1 N and a loading time of 40 s were selected as the loading parameters. The values of Martens hardness and the normal elastic modulus for the unmodified lacquer coating amount to 260 N/mm 2 and 7.3 GPa, respectively. Titanium dioxide has been found to increase Martens hardness by 5% as compared to that of the unmodified lacquer. In turn, the introduction of zinc oxide and silicon dioxide reduces HM by 4% and 5.5%, respectively. The value of for the coating modified with titanium dioxide increases by 15% as compared to the pure epoxy lacquer to become 8.4 GPa. For the coatings filled with zinc oxide, the value of the contact elastic modulus is 7.4 GPa, thus remaining on the level with the values for the pure epoxy lacquer. In turn, for the coating containing silicon dioxide, the value of decreases by 6% to become 6.9 GPa. Most likely, the obtained results are explained by the influence of the size of the filler particles and agglomerates; namely, the smaller the size, the higher the elastic modulus. Besides, the observed phenomena testify to the fact that the oxide modifier in the epoxy resin manifests itself as a reactive component forming a certain set of intermolecular interactions, including covalent interaction. A load F of 1 N, a loading time of 40 s, and a holding time t h under a load of 0, 20, 40, and 60 s were selected as loading parameters to study creep. Figure 1a shows the average values of for each sample at various values of t h . The behavior of as dependent on the holding time is qualitatively the same for all the samples tested. For the filled lacquer samples, the values of decrease on the average by 15%. The obtained data testify to the absence of significant effect of modifiers on the viscous properties of the polymer, obviously, due to the low content of oxides in the coating. Figure 2 shows the obtained values of HM and for the samples subjected to thermocycling. The values of Martens hardness and the normal elastic modulus for the unmodified lacquer coating decrease smoothly with the increasing number of thermocycling cycles. Thus, HM decreases by 10% after 5 cycles and by 14% after 10 cycles from the initial hardness value. In turn, decreases first by 5% and then by 10% from the value of the modulus corresponding to the material not subjected to thermocycling. For the coating modified with zinc oxide, the hardness decreases by 7% within 5 cycles, whereas the HM values remain invariable with the further effect of cyclic temperatures. For the lacquer doped with ZnO, decreases by 5% after 5 cycles and by 15% after 10 cycles as compared to the value for the non-thermocycled coating ZnO. For the coating doped with silicon dioxide, the values of Martens hardness for the initial state and after thermocycling are on the level with those for the ZnO-doped lacquer. The elastic modulus value for this dope is initially the lowest; it decreases by 15% after 5 cycles and remains unchanged after 10 cycles. Thermocycling has most noticeable effect on the coating containing titanium dioxide. Initially, this coating is the hardest, with its hardness value falling from 270 N/mm 2 to 220 N/mm 2 , i.e. by 20%, after 5 cycles of thermocycling. After 10 cycles, the value of HM increases to 260 N/mm 2 , thus exceeding the HM values of the other samples, but

c

a

b

Fig. 1. Average

values for each sample at various t h for the epoxy lacquer samples with different volume contents of the fillers after 0 (a),

5 (b), and 10 (c) thermocycling cycles.