PSI - Issue 2_A

M. Wicke et al. / Procedia Structural Integrity 2 (2016) 2643–2649 M. Wicke et al./ Structural Integrity Procedia 00 (2016) 000–000

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in Fig. 6 for both shrinkage pores. For the sake of clarity only the nodes in the front surface – represented by the red points – are displayed while further nodes are covered by the geometry.

Fig. 6. Highly stressed regions on the contour of the (a) first and (b) second shrinkage pore The elastic stress concentration factor ܭ ௧ , which is defined as the ratio between peak von Mises stress and nominal stress, ranged between 4.73 and 14.56 for the first shrinkage pore (Fig. 6a) and from 7.63 to 19.91 for the second one (Fig. 6b) with an average value of 7.85 and 9.88 respectively. As it can be observed in Fig. 6, the peak stress concentration was located in a hole on the geometry of both pores. Since more than half of the orientations of the first pore and over one-third of the second one exhibit the maximum ܭ ௧ in these regions, the holes can be identified as hot spots. A reason for the increased number of highly stressed regions in the second pore model is in the morphological variation. In contrast to the relative regular-shaped first pore, the latter is complex in shape with multiple branches acting as stress concentrators in dependency of the load direction. The present data are compared to the previous study by Nicoletto and coworkers [Nicoletto et al. (2012)], where a similar approach was used. A quasi-gas pore as well as a shrinkage pore was rotated around two axes, separately, within an FE model of a cylindrical volume in the range 0-90° to assess the combined influence of pore morphology and loading direction on the stress concentration factor. In that case of a simulated push-pull test, the ܭ ௧ of the shrinkage pore was found to range from 3.0 to 3.5 with an average value of 3.28. These low ܭ ௧ results compared to those presented here are likely caused by the local pore geometry. While in the present work the by far highest values of ܭ ௧ could be localized in a hole on the defect surface, the shrinkage pore reconstructed in [Nicoletto et al. (2012)] does not contain such a characteristic according to the author’s knowledge. In consideration of the simultaneous rotation of each pore around all coordinate axes in the range 0-360°, the present treatment is possibly more appropriate for identifying hot spots on the contour of casting defects. Due to the automatization of the numerical process from the defect import to the visualization of the results using python scripts, further pores revealed by μ-CT can now readily be assessed in terms of local stress concentration after applying suitable mesh parameters. The identified regions of elevated stress could subsequently be used for a fracture mechanics assessment. 4. Conclusion A partly automated treatment on the basis of micro-computed tomography (μ-CT) and elastic finite element analysis (FEA) has been developed to identify local stress concentration on the contour of casting pores. Highly stressed regions can readily be localized by the appropriate visualization of the numerical results. Microtomography was applied to reconstruct the morphology of pores in a cast Al-Si-Cu alloy. The geometry of these defects ranged from small and relatively regular in shape exhibiting only a few branches to elongated with some