Abstract
We examine the nucleation of a crack from a notch under a dominant shear loading in Al 6061-T6. The specimen is loaded in nominally pure shear over the gage section in an Arcan specimen configuration. The evolution of deformation is monitored using optical and scanning electron microscopy. Quantitative measurements of strain are made using the 2nd phase particles as Lagrangian markers which enable identification of the true (logarithmic) strains to levels in the range of two. Electron microscopy reveals further that the 2nd phase particles do not act as nucleation sites for damage in the regions of pure shear deformation. The initial notch is shown to “straighten out”, forming a new, sharper notch and triggering failure at the newly formed notch. Numerical simulations of the experiment, using the conventional Johnson–Cook model and a modified version based on grain level calibration of the failure strains, reveal that it is necessary to account for large local strain levels prior to the nucleation of a crack in order to capture the large deformations observed in the experiment.
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Notes
The compliance of the loading system has not been removed; therefore the slope of the linear region is significantly smaller than the slope of the specimen alone and the normalized displacements should not be compared directly to those determined in the simulations reported later in Sect. 4. Macroscopic scale digital image correlation (DIC) could provide adequate measurements to prescribe realistic boundary conditions arising from the loading system compliance, but this was not considered essential to the objectives of the present work.
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Acknowledgments
This work was performed during the course of an investigation into ductile failure under two related research programs funded by the Office of Naval Research: MURI project N00014-06-1-0505-A00001 and FNC project: N00014-08-1-0189. This support is gratefully acknowledged.
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Ghahremaninezhad, A., Ravi-Chandar, K. Crack nucleation from a notch in a ductile material under shear dominant loading. Int J Fract 184, 253–266 (2013). https://doi.org/10.1007/s10704-013-9883-7
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DOI: https://doi.org/10.1007/s10704-013-9883-7