Issue 41

L. Patriarca et alii, Frattura ed Integrità Strutturale, 41 (2017) 277-284; DOI: 10.3221/IGF-ESIS.41.37 283 (a) (b) Figure 7 : Simulation results of the residual strain field: (a) strain field over the whole crystal plasticity area; (b) focus on the area close to the notch and identification of the crystallographic orientations of the grains showing average local deformations higher than   0.2% . The model was loaded to reproduce the experimental conditions where the crack was loaded to reach a nominal stress intensity factor of 20 MPa√m. Fig. 7a shows the results of the simulation in terms of the extension of the residual strain field generated at the crack tip. Focusing on the crack tip region (Fig. 7b), the grains showing average strain localization higher than   0.2% were selected (those contained in the area delimited with the white dashed contour). Fig. 7b also shows the crystallographic orientations of the selected active grains in the stereographic triangle. The main outcome of this analysis is that those grains showing high plastic deformations do not have a preferential texture, while the crack tip singularity dictates the deformation. The main result coming from the simulations, if compared with the DIC, is the agreement with the extension of the strain field. In addition, most of the grains with active slip systems are reproduced. The main difference with DIC is the presence of high concentrated strains at the crack tip. This feature may be related to the hypothesis made of considering the crack front extended through the thickness, while compression pre-cracking usually involves only the surface regions of the specimen. Another important point of discussion is the approximation introduced with the definition of the CPFE model. The EBSD map characterizes the grain orientation and morphology at the observed surface, but no microstructural information are available along the thickness of the specimen. The CPFE model is then reconstructed extruding the 2D EBSD map, this represents an approximation of the real material microstructure. Studies on 3D grain geometries [16] showed that differences may occur in surface localizations. These differences may affect simulations results while reproducing material behavior under cyclic test, where no discontinuities like cracks, are included and the strain filed is mainly influenced by crystals’ orientations and geometries. The introduction of discontinuities localizes the deformation in confined areas and the 3D structure of the grains assume a secondary role in the prediction of the deformation field. C ONCLUDING R EMARKS he proposed work presents the preliminary results obtained by simulating a stationary crack inside a polycrystalline aggregate with a crystal plasticity model. The simulation was successively compared with the experimental observations obtained by means of digital image correlation. This result was achieved reproducing a quasi-static test where the crack was statically loaded. The analysis of the residual strain field shows a good agreement on the extension of the localizations area. Moreover, the study shows that the crack tip stress singularity dictates the deformation of the surrounding grains without preferential orientations. T 