PSI - Issue 45

Dylan Agius et al. / Procedia Structural Integrity 45 (2023) 4–11 Dylan Agius et al. / Structural Integrity Procedia 00 (2019) 000 – 000 microstructure where the top left prior grain has an average strain per grain of 0.0264 and standard deviation of 0.00819, compared to the top right and bottom prior grain which have an average strain per grain of 0.0256 and 0.0248 respectively and a standard deviation of 0.00727 and 0.00516 respectively. The results suggest that on average, grains within the top left prior grain accumulate the most strain in addition to having more grains accumulating higher magnitudes of strain than the other two large prior grains. To examine the slip banding further, two grains were extracted (Grain 1 in Fig. 3 (a) and Grain 2 in Fig. 3 (b)). In these grains, the DIC results show intense slip band formation. Using SSLIP developed by (Vermeij, Peerlings et al. 2023), the active slip systems contributing to the localisation observed from the DIC results were identified. For Grain 1 and Grain 2, the slip systems contributing most significantly to this localisation are basal ((1 1 -2 0)[0 0 0 1]) and pyramidal 〈 + 〉 ((-1 -1 2 -3)[0 1 -1 -1]) in Grain 1 and pyramidal 〈 + 〉 ((-1 0 1 1)[-1 -1 2 -3]) in Grain 2. The orientation of these slip systems is provided next to each grain in Fig. 3 (as a combination of a red line for the slip plane and an arrow for the slip direction). This initial slip trace analysis indicates for the two grains studied, the local slip system activity does not correspond to the slip mode with the most favourable Schmid factor. This suggests that the local environment is influencing the slip system activity, which supports the findings of Lunt, Thomas et al. (2021). These observations are valuable for computational model development as they provide a means of validating the capability of the model to capture the interactions between neighbouring grains. 9 6

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Fig. 3 Selected grains (Grain 1 (a) and Grain 2(b)) from the microstructure used to examine the slip systems contributing the localisation observed from the DIC results. The slip system orientation and direction contributing to this localisation is indicated by the red lines and arrows. 6. Simulation results and discussion The simulated ROI is provided in Fig. 2(b) and compared against the experimental DIC results. What is initially evident from the simulation is the significant slip band formation. Further examination of the model’s ability to capture the influence of the local environment on slip system activity involved analysing the slip systems contributing to the strain localisation within the simulated results for Grain 2 against experimental results. Using SSLIP (Vermeij, Peerlings et al. 2023), two slip systems were found to be contributing to the localisation apparent in Grain 2. As was the case in the experimental results, the significant localisation was associated with pyramidal 〈 + 〉 ((-1 0 1 1)[-1 - 1 2 -3]) slip. It was the activity of this slip system which had the most influence on the strain localisation in the direction of the black arrow in Fig. 4 (a). The pyramidal 〈 + 〉 ((0 1 -1 -1)[-1 -1 2 -3]) slip system was also identified to be contributing to localisation. The deformation in the direction of the blue arrow in Fig. 4 (a) (not seen experimentally) is not due to slip band formation but instead kink band formation. This is confirmed from Fig. 4 (b) which provides the lattice rotation field across Grain 2. From Fig. 4 (b), the bands of strain localisation in the direction of the blue arrow in Fig. 4 (a) are lattice rotation bands and are therefore associated with kink bands. The same slip system in both the experimental and simulation results contributing to the most significant strain localisation is an encouraging finding. It suggests that the influence of the local grain environment on slip system activity in Grain 2 is being recognised. However, the issue of inaccurate kink band formation still plagues the simulation accuracy, even with the implementation of the mitigation efforts proposed by Marano, Gélébart et al. (2021).