PSI - Issue 28

7

Author name / Structural Integrity Procedia 00 (2019) 000–000

D.A. Bondarchuk et al. / Procedia Structural Integrity 28 (2020) 743–751

749

Fig. 7. G II after cure (a) and G II after cut (b) of sample depending on crack length.

The history of values G I and G II (obtained via FE simulation) over time for the specimen with [0°/90°] 12 layup and with the longest simulated crack (length of 6mm) is demonstrated in Fig.8.

Fig. 8. G II (a) and G II (b) for the specimen with [0°/90°] 12 layup and with crack length of 6mm.

Real composite structures can work under the cyclic loads. Under cycle loading the limiting critical energy release rates tend to decrease with increasing number of cycles. The change in the normalized fracture energy G max depending on the number of cycles obtained during the experimental study is shown for AS4/8552 material in Fig.9 (Argűelles A. et.al. (2011)). The fatigue limit obtained for 3 million load cycles is 50% of the static critical energy for material AS4/8552. With a subsequent increase in the number of cycles, there is the possibility of a further decrease in the critical energy value. The limit values of fracture toughness during fatigue loading are typically orders of magnitude higher than the values realized in the sample by the residual stress. Thus, the fatigue crack onset of the carbon-epoxy composites will not change due to the presence of residual stresses.