A low constraint center cracked Brazilian disk specimen for ductile FCC single crystal

• Published in: International journal of fracture 2021-10, Vol.231 (2), p.147-167
• Main Authors: Deka, Nipal, Jonnalagadda, Krishna N.
• Format: Article
• Language: English
• Subjects: Aluminum; Automotive Engineering; Boundary layers; Characterization and Evaluation of Materials; Chemistry and Materials Science; Civil Engineering; Classical Mechanics; Crack tips; Ductile fracture; Edge dislocations; Energy release rate; Evaluation; Face centered cubic lattice; Finite element method; Fracture mechanics; Fracture toughness; J integral; Localization; Materials Science; Mechanical Engineering; Original Paper; Shear bands; Single crystals; Slip; Strain localization
• ISSN: 0376-9429; 1573-2673
• DOI: 10.1007/s10704-021-00570-7

In this work, the center cracked Brazilian disk (BD) geometry is proposed as a possible small-scale low crack tip constraint fracture specimen for ductile FCC single crystals. These low crack tip constraint conditions are frequently encountered where shallow cracks are present. The effect of in-plane and out-of-plane crack tip constraint on crack tip fields in a Brazilian disk geometry was analyzed for an aluminum single crystal. A simple stress difference method is proposed to evaluate the in-plane crack tip constraint, T -stress for any anisotropic FCC crystal. The magnitude of T -stress for the center cracked BD specimen was calculated to be much lower than that in other standard fracture specimens. Besides, the energy release rate, J -integral was also evaluated for this specimen using the domain integral method. Results obtained from the full 3D crystal plasticity finite element analysis agreed well with previously reported modified boundary layer analysis with negative crack tip constraint. The study primarily considered the specific crack orientation, { 010 } 101 . Two other crack orientations were also studied to analyze the different nature of strain localization in ductile single crystal. The forward localization band was observed to be significantly dominant over the other possible localization bands for all the crack orientations. However, the nature of localization varied from slip to kink in the forward band depending on the crack orientation. Under mixed mode I–II loading, localization bands not aligned with slip directions were observed with high local lattice rotation, suggesting possible existence of kink shear bands. Additionally, some important specimen details are reported, which would help in designing the small scale experiment on ductile single crystal, to measure crack tip constraint, and fracture toughness under low constraint condition.