Adaptive concurrent atomistic-continuum simulation of the deformation behavior of materials with microstructure complexities

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Phan, Thanh
Major Professor
Xiong, Liming
Bastawros, Ashraf
Collins, Peter
Ho, Kai-Ming
Levitas, Valery
Sheidaei, Azadeh
Committee Member
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Aerospace Engineering
In the search of high-performance materials, one strategy is to introduce interfaces, such as grain boundaries (GBs), twin boundaries, phase boundaries, and so on. This strategy is always accompanied by a decrease in material ductility, although it does lead to a significant enhancement in strength. In the past decades, many strategies have been invented to overcome this strength-ductility trade-off dilemma. For instance, inspired by the nature of biological materials such as nacre and dental enamel, an amorphous/crystalline metallic composite (A/C-MC), which combines amorphous metallic glasses with crystalline metals introduces the amorphous-crystalline interfaces (ACIs) to absorb dislocations instead of blocking them. Similarly, another strategy involves a gradient nanograined (GNG) polycrystalline in which the grain size increases from nanoscale on the surface to microscale in the core. This GNG structure under deformation can simultaneously activate both softening in the nanograined skin as well as hardening in the coarse-grained core towards a strength-ductility synergy. Despite the great potential of these strategies in expanding the strength-ductility envelope, a design of them through a manipulation of their microstructure is, however, still at a “trial and error” stage. One reason is due to the lack of a simulation tool that can predict the overall performance of such materials by accommodating the atomic-scale structure evolution at the interface together with the microscale plasticity away from the interface within one framework. To meet this need, one main goal of this dissertation research is to establish an adaptive concurrent atomistic-continuum (A-CAC) simulation tool that can: (i) enable a smooth dislocation slip from the atomistic to the continuum domain by furnishing the existing CAC with an adaptive finite element (FE) splitting algorithm; (ii) probe the mechanisms underlying the slip-interface reaction and the subsequent structure changes; and most importantly, (iii) predict how the complex material microstructure responds to the stresses without smearing out the atomistic nature underlying it. In this dissertation, I present the theoretical foundation, numerical algorithms, and applicability of A-CAC with a focus on demonstrating its applicability in: (a) eliminating the FE mesh-induced overhardening issue in existing CAC simulation tools; (b) interpreting the experimental observations through simulating the reaction between the microscale dislocation slip and the atomically structured GBs in polycrystalline alloys; and (c) characterizing the interplay between microscale dislocation slip and nanoscale shear transformation zones in polycrystalline A/C-MCs. The limitations, future development, and potential applications of A-CAC in a rational design of high-performance A/C-MCs and GNG will be also discussed in this dissertation.
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