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Micromechanical modeling of size-dependent crystal plasticity and deformation twinning
Citation Link: https://doi.org/10.15480/882.2370
Publikationstyp
Doctoral Thesis
Date Issued
2019
Sprache
English
Author(s)
Advisor
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2018-12-13
TORE-DOI
TORE-URI
Citation
Technische Universität Hamburg (2019)
The computational modeling and simulation of the deformation behavior of crystalline materials at the micron scale is the objective of this thesis. Numerous experimental studies have proven that small-scaled metallic probes behave mechanically different from their bulk counterparts, in particular, the yield strength and work hardening behavior is affected in the way that smaller single crystals behave stronger. This characteristic behavior opens up new design possibilities for further improvement of mechanical properties of engineering material systems. In view of high expenses for advanced and complex experimental work along with the inherent testing limitations, numerical methods offer a great option to validate experimental findings, support the development of suitable theories, and extend scientific investigations on a computer-aided basis.
A gradient crystal plasticity model is presented in this thesis and applied to selected scientific problems including the mechanical testing of single crystals via simulation of microcompression and microbending using a three-dimensional finite element framework. The model is implemented on an element basis and linked to the commercial finite element software Abaqus via the user subroutine UEL. Two major deformation mechanism are considered by the underlying model. Deformation via crystallographic slip is modeled in a non-local fashion allowing to account for gradient effects. Geometrically necessary dislocation (GND) densities associated with plastic slip gradients are introduced as additional nodal degrees of freedom while the actual plastic slip variables are handled as internal variables. Deformation twinning is accounted for in terms of a simple shear deformation associated with shear and shuffling of atoms. In addition, the twinning-induced reorientation of the crystal lattice is fully considered along with subsequent activation of slip modes within the twinned region. In accordance to the non-local crystal plasticity framework, the gradient of the twin volume fraction is introduced at the nodal level. The actual twin volume fraction is treated as an extended internal variable yielding a coupled system of highly non-linear equations at the local level. The competitive nature between slip deformation and deformation by twinning is addressed by physically motivated interaction relations. The characteristic features of the model are portrayed for a variety of micromechanical problems and in relation to experimental results.
A gradient crystal plasticity model is presented in this thesis and applied to selected scientific problems including the mechanical testing of single crystals via simulation of microcompression and microbending using a three-dimensional finite element framework. The model is implemented on an element basis and linked to the commercial finite element software Abaqus via the user subroutine UEL. Two major deformation mechanism are considered by the underlying model. Deformation via crystallographic slip is modeled in a non-local fashion allowing to account for gradient effects. Geometrically necessary dislocation (GND) densities associated with plastic slip gradients are introduced as additional nodal degrees of freedom while the actual plastic slip variables are handled as internal variables. Deformation twinning is accounted for in terms of a simple shear deformation associated with shear and shuffling of atoms. In addition, the twinning-induced reorientation of the crystal lattice is fully considered along with subsequent activation of slip modes within the twinned region. In accordance to the non-local crystal plasticity framework, the gradient of the twin volume fraction is introduced at the nodal level. The actual twin volume fraction is treated as an extended internal variable yielding a coupled system of highly non-linear equations at the local level. The competitive nature between slip deformation and deformation by twinning is addressed by physically motivated interaction relations. The characteristic features of the model are portrayed for a variety of micromechanical problems and in relation to experimental results.
Subjects
gradient crystal plasticity, deformation twinning, micromechanics, magnesium
DDC Class
600: Technik
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