PSI - Issue 37

Oleg Staroverov et al. / Procedia Structural Integrity 37 (2022) 804–810 Oleg Staroverov, Dmitrii Lobanov/ Structural Integrity Procedia 00 (2019) 000 – 000

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After each impact, specimens were visually inspected. Micro-structural studies and analysis of fracture images of test specimens in case of complex impact and cyclic loading were done using Carl Zeiss SteREO Discovery V12 stereo microscope (Fig. 4).

original

e ’ = 0,33

e ’ = 0,5

e ’ = 0,66

e ’ = 0,75

e ’ = 0,8

e ’ = 0,9

e ’ = 1

e ’ = 1

Fig. 4. Photographs of CFRP specimens after impact tests according to the three-point bending by a falling weight on carbon fiber specimen in impact tests according to the three-point bending

In cases of impacts with energy e’ = 0.33 near the impacted surface, fractures were formed due to contact with the striker, while there were no cracks, dents, shears and other types of damages on the front and rear side of specimens which could be found by visual inspection. Impacts with the energy within e’ = 0.5 to e’ = 0.66 resulted in fractures near the rear side (relative to the impact point). When the impact energy increased, lamination defects were formed. Further load falling with the intensity of e ’ = 0.75 to e’ = 0.9 caused mixed types of damages in the form of laminations and fractures in the transverse direction with the local failure of fibers. Visual inspection showed fractures with residual bending on the front and rear side of the specimens. Images of fractures of the specimens tested for failure at three- point bending by falling load e’ = 1 show multiple breaks of fibers and laminations in the longitudinal direction relative to the orientation of reinforcement layers.. This resulted in experimental dependencies of effects of various intensities of impact bending on residual fatigue life of carbon fiber specimens (Fig. 5). The diagrams are constructed similarly to the fatigue sensitivity diagrams by Wildemann et al(2018). The Experimental studies in the framework of the description of the mechanical behavior of structurally inhomogeneous materials were conducted within the State Assignment of the Ministry of Science and Higher Education of the Russian Federation (№ FSNM -2020-0027).