PSI - Issue 18

Staroverov Oleg A. et al. / Procedia Structural Integrity 18 (2019) 757–764 Staroverov O.A., Wildemann V.E., Tretyakov M.P., Yankin A.S./ Structural Integrity Procedia 00 (2019) 000–000

759

3

molding method. The mechanical properties of the composite were determined by quasi-static tension tests, considering the recommendations of ASTM D 3039. The tests were carried out on an Instron 5882 electromechanical system, the speed of movement of the crosshead was 2 mm/min. To measure the longitudinal deformation of the samples, a hinged displacement and deformation sensor with a measuring base of 50 mm was used. The method of cyclic testing at elevated temperatures complied with the recommendations of ASTM D3479 standard. Fatigue tests were performed on an Instron Electropuls E10000 electrodynamic testing system. The method of experimental investigation of the influence of preliminary shock impacts of different intensity on the nature of the destruction of carbon-plastic composites was based on the standards ASTM D7136 and ASTM D7137. The object of the study was the sample plate with spatial reinforcement layouts with dimensions of 150×100×4 mm. For the application of impact damage to samples of the materials studied, a vertical Instron CEAST 9350 type pile driver with a spherical tip 16 mm in diameter was used. Quasi-static compression after impact was performed on an Instron 5982 electromechanical testing system. Tests on uniaxial compression were carried out at a speed of movement of the loading beam 2 mm/min until failure or loss of stability of the sample. 3. The processes of deformation and destruction of fiberglass specimens with different layouts The experimental research method consisted of the installation tests for quasi-static tension with the determination of strength ( σ B ) and stiffness ( E ) characteristics of the samples. Further, the fatigue life (N max ) was determined from cyclic tensile tests with a frequency ν=20 Hz, an asymmetry coefficient R=0.1, and a maximum stress value in the cycle σ max =0.5∙σ B . For samples with layouting [±45], fatigue failure with such parameters occurred over 1000–1500 cycles, so the stress value in the cycle was selected in the linear part of the strain diagram and was σ max =0.35∙σ B (Fig. 1).

Fig. 1. Characteristic deformation diagrams of fiberglass specimens with different laying angles of reinforcing layers

Experimental data on the study of the processes of change in residual strength after preliminary cyclic loads are presented in the form of a fatigue sensitivity diagram (Fig. 2) Wil'deman et al. (2018). The values of K Bn ’=1 with n’=0 are obtained from experiments on quasi-static stretching, K Bn ’=0; n’=1 – fatigue failure. Intermediate points obtained during tensile tests after preliminary cycling of various duration. For samples with laying angles [0/90] and [0/30/0/60], three zones can be distinguished in the fatigue sensitivity diagram: initial, stabilization, and exacerbation of fatigue sensitivity. The change in the residual strength characteristics for samples with the laying of reinforcing layers [±45] occurred in two stages, without a part of the initial fatigue sensitivity. It should be noted that the initial sensitivity for samples [0/90] was (0–0.3)∙n’, stabilization (0.3–0.6)∙n’, exacerbations (0.6–1)∙n’; for samples [0/30/0/60], the area of initial sensitivity (0–0.2)∙n’, stabilization (0.2–0.7)∙n’, exacerbations (0.7–1)∙n’.