PSI - Issue 40

I.A. Morozov et al. / Procedia Structural Integrity 40 (2022) 314–320 I.A. Morozov et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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According to the AFM measurements (Fig. 3a), the average thickness of the activated layer is 1.5 nm, increasing to 2 nm (or 3 nm) after Ar/C 2 H 2 treatment for 30 s (or 60...120 s). Significant dispersion of measurements is due to heterogeneous modification of the two-phase polymer. The surface elastic modulus (Fig. 3b) increases with treatment time, but the thickness does not change significantly: at the initial stage, separate islets of the future continuous coating are formed without increasing its thickness. after 120 s of treatment, the elastic modulus of the soft areas of the surface tends to hard ones - a solid homogeneous coating is formed.

Fig. 3. Thickness of the coating (a) and average values of the elastic modulus (b). Zero treatment time corresponds to argon-activated polyurethane. The inset in (a) shows a fragment of the AFM-image with indentation imprints, on the basis of which the thickness was evaluated. Fatigue uniaxial loading does not affect the surface structure of argon-activated polyurethane (Fig. 4a). The structure of surfaces treated in Ar/C 2 H 2 plasma for 30 or 60 seconds undergoes significant changes (Fig. 4b, c): local folds orthogonal to the axis of load appear on the unloaded surfaces (the result of non-uniform elastic-plastic deformation of the coating), as well as longitudinal folds associated with compression of the material in the transverse direction under tension. The initial random wrinkled structure of the surface after treatment for 60 s (Fig. 2c) is not restored. Fatigue loading smoothes the relief in the vicinity of the strain-induced folds (Fig. 4c). The same longitudinal and transverse folds are visible on the surface after 120 s (Fig. 4d), but in this case the original wrinkle structure is also partially preserved. A study of the materials under tension after fatigue loading showed the formation on the activated surface (Fig. 5a) folds co-directed to the axis of deformation, which disappear without a trace after the tension is removed (Fig. 4a). The submicron cracks are formed in stretched state on the surfaces after 30 s or 120 s treatment (Fig. 5b, d); the distance between crack tips is 20…500 nm and depth is 10...12 nm. The cracks appear predominantly in the lowlands of the relief: these are the open folds formed during fatigue loading (Fig. 4b, d). The nanosize of the observed cracks suggests that the modified surfaces have structural-mechanical nanodefects associated with inhomogeneities of the plasma coating at the initial stage of the treatment.