PSI - Issue 59

Valerii Kobzar et al. / Procedia Structural Integrity 59 (2024) 344–351 Valerii Kobzar and Oleh Derkach / Structural Integrity Procedia 00 (2023) 000 – 000

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twill CFRP along the weft, the dependence of the logarithmic decrement of vibrations on the amplitude of cyclic strain exhibited a local maximum at small values ( ε = 1∙ 10 – 4 ... 3∙ 10 – 4 ). This indicates an increase in dry friction in the damaged area. However, for samples with a 45 deg fiber orientation, an increase in damping capacity was observed without significant changes in the amplitude dependency of the logarithmic decrement of vibrations. As shown in Fig. 6, the presence of local damage in the cantilever beams (0 deg fiber orientation), resulted in a more significant relative change in the normalized logarithmic decrement 0     ( δ 0 is the logarithmic decrement for intact specimen), compared to the decrease in the main frequency of the beam flexural vibrations ( 0 p p p  is the normalized frequency, where p 0 is the main frequency for intact specimen). Therefore, the change in vibration damping is a more sensitive vibrodiagnostic indicator of the presence of local damage in the composite beam compared to the natural frequency.

Fig. 6. Dependence of the normalized natural frequency ( 〇 ) and logarithmic decrement ( ⨉ ) of vibrations on the local damage parameter D of the specimen.

Fig. 5. Dependence of the logarithmic decrement of vibrations on the amplitude of the relative cyclic deformation under the conditions of bending vibrations of the cantilever sample made of woven CFRP along the weft (solid lines) and 45 deg (dashed lines): (1) intact D = 0; and damaged (2) D = 0.06; (3) D = 0.13.

Additionally, it was experimentally found that the effect of the location of the dissipative section on the damping capability increase Δ δ for the cantilever beam has a cubic character (Fig. 7). Thus, the logarithmic decrement of vibrations is sensitive to damage located at one-third of the cantilever beam length.

Fig. 7. Dependence of the relative change logarithmic decrement of vibrations on the location of damage area in the cantilever beam specimen.