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slip irreversibility twin Sehitoglu, Huseyin Chowdhury, Piyas 2012-02-01T00:54:12Z 2014-02-01T11:00:22Z 2011-12 2012-02-01T00:54:12Z 2011-12 A combination of molecular dynamics and dislocation dynamics simulations is performed to model fatigue crack growth (FCG) in a nano-twinned nickel single crystal. Molecular dynamics simulations are employed to investigate the irreversible interaction of crack-tip emitted dislocations with nano-twins in the vicinity of the crack upon cyclic loading. A method is developed to quantify the irreversibility of slip, and calculate it as a function of the twin lamella thickness and crack-tip to twin lamella spacing. Subsequently, atomistically calculated slip irreversibility is utilized in dislocation dynamics crack growth simulations to understand the role of thickness of the nano-twins as well as the crack-tip to twin spacing on da/dN. In molecular dynamics simulations, in order to study the cyclic slip-twin interactions, the nano-twinned single grain specimen is set up such that it favors two separate cases comprising pure screw and pure edge dislocation nucleation from the crack-tip. Both screw and edge dislocations demonstrate a cyclic steady-state interaction mechanism with the nano-twin under strain control loading. The da/dN formulations, based on discrete dislocation dynamics, are derived for the cases ranging from single to multiple screw or edge dislocations emission from the crack-tip over cycles. The molecular dynamics slip irreversibility is incorporated into the dislocation dynamics based da/dN calculations. An implementation of these formulations demonstrates that both for the cases of decreasing nano- twin thickness or lowering of crack-tip to twin spacing, da/dN also decreases complying with some recent experimental findings in literature. Item withdrawn by Mark Zulauf (zulauf@illinois.edu) on 2011-12-08T14:39:34Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 2 Chowdhury_Piyas.doc: 22433792 bytes, checksum: 3ab2921e542073155e9a04a3c5a9cb98 (MD5) Chowdhury_Piyas.pdf: 3304547 bytes, checksum: 02b569aa07b9e6a1c3aab2221a4d1186 (MD5) Made available in DSpace on 2012-02-01T00:54:12Z (GMT). No. of bitstreams: 2 chowdhury_piyas.pdf: 3232245 bytes, checksum: d3bb2707c1ef61940ee2dd694edd92ba (MD5) license.txt: 4065 bytes, checksum: 63a33943f49816d2e68fdfb6f9bffa24 (MD5) Item marked as restricted to the 'Administrator' Group (id=1) by William Ingram (wingram2@illinois.edu) on 2012-02-01T00:57:04Z Item is restricted until 2014-02-01T00:56:58Z Item reinstated by Sarah Shreeves (sshreeve@illinois.edu) on 2014-02-01T11:00:21Z Item was in collections: Graduate Theses and Dissertations at Illinois (ID: 204) Dissertations and Theses - Mechanical Science and Engineering (ID: 675) No. of bitstreams: 3 chowdhury_piyas.pdf.txt: 111943 bytes, checksum: 4d16e61a02da4901597afd128d9fa8bd (MD5) chowdhury_piyas.pdf: 3232245 bytes, checksum: d3bb2707c1ef61940ee2dd694edd92ba (MD5) license.txt: 4065 bytes, checksum: 63a33943f49816d2e68fdfb6f9bffa24 (MD5) Item released from any restrictions by Sarah Shreeves (sshreeve@illinois.edu) on 2014-02-01T11:00:22Z http://hdl.handle.net/2142/29530 en Copyright 2011 Piyas Chowdhury Fatigue crack growth nano-obstacle molecular dynamics Fatigue crack growth (FCG) modeling in the presence of nano-obstacles Dissertation / Thesis text Mechanical Sci & Engineering 1917 Mechanical Engineering 0133 University of Illinois at Urbana-Champaign Thesis M.S. PHD:Mechanical Enginerng -UIUC 10KS0133PHD