PSI - Issue 28

D.A. Bondarchuk et al. / Procedia Structural Integrity 28 (2020) 743–751 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The cut process was realized by special modeling technique by deactivating interaction between two parts after cure cycle simulation using an additional step of the analysis. 5. Modelling results The results of finite element modelling - the distribution of residual stresses for the obtained sample without crack and with initial crack of 6 mm in length before and after cut are presented in Fig. 4 and Fig.5 respectively.

Fig. 4. Stress distribution (Pa) in a sample with [0°/90°] 12 layup without crack after polymerization and after cutting(on a scale of displacements x0.01).

Due to cutout, the effect of the concentration of maximum stresses in the local zones of the free edge region arises. In the Fig. 4, Fig. 5 it is shown that the absolute maximum stress in the longitudinal direction is mainly concentrated in a small region at the free edge and is close to the ultimate stress of the composite material. It should be noted that the stress in the longitudinal direction ( σ 33 ) is also close to the ultimate value after a mechanical cut in a small area at the crack tip. Thus there is a possibility of formation of micro cracks in sample during manufacturing or at low applied load, which confirms the conjecture about the reduction of mechanical performance, especially for matrix-dominated properties by residual stresses. As the next step of research, the history of energy release rates under mode I, II ( G I , G II ) were analyzed over time during process of polymerization and free edge cut appearance. The values of G I and G II depending on the length of the crack after polymerization of the sample and after an ideal cutout are shown in Fig. 6 and Fig. 7 respectively. It should be noted, that the length of the initial defect in the sample does not significantly and not quite explicitly affect the energy release rate G I and G II , with the exception of the energy release rate under Mode I, during the manufacturing process. To assess the possible further growth of cracks, we analyzed the changes in fracture criteria f I and f II over time for a specimen with a crack of 6 mm. Values of critical energy release rates for AS4/8552 composite are presented in study, conducted by Soroush M. et.al. (2018), Coronado P. et.al. (2018), and provided in Table 1.