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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preliminary impact using three-point bending pattern and further cyclic tension by Staroverov et al (2019). Research using a similar technique were carried out by Mohammad R. Hosseini A. et al(2019). In their work, the authors consider the change in the residual strength life of a composite structure in the form of grid under quasi-static bending and after a transverse impact by a dropping weight. To implement preliminary impact conditions of various intensity, Instron CEAS 9350 electrodynamic impact testing machine was used with the potential energy range of 0.7 to 1800 J (Fig.2 a). Cyclic tests were done using Instron 8850 servo-hydraulic testing system that allowed for loading specimens at elongating forces up to 100 kN and frequency up to 100 Hz (fig.2 b). Nominal values of the ultimate strength were determined based on tests for quasi static elongation using Instron 5882 electromechanical system (Fig.2 c). The provided testing equipment allows implementing complex conditions of mechanistically action within a wide range of loads.

Fig. 2. Photo of experimental testing systems Instron (a) CEAST 9350; (b) 8850.(c) 5882

3. Influence of preliminary impact according to the three-point bending on the fatigue life of CFRP samples In accordance with the developed method, the ultimate strength ( σ U) was found for the studied carbon fiber from quasi-static elongation tests. The nominal value of fatigue design life (Nmax) was obtained from tests at parameters with maximum stress in the cycle of σmax = 0.75∙σ U, asymmetry coefficient R=0.1 and frequency of ν = 20 Hz. For installation tests, the frequency and amplitude of loading were selected such that the specimen heating would not exceed 20˚С as compared to the start of the test. Potential energy ( Е max) observed during failure of specimens was found from impact bending experiments. This was followed by preliminary impact tests using three-point bending pattern within 0.3 to 0.9 of failure energy (e’). Single impacts were done along the entire width of specimens (Fig. 3).

Fig. 3. Photo of an installed carbon fiber specimen in impact tests according to the three-point bending