Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.

X-Ray Diffraction

DAMASK – The Düsseldorf Advanced Material Simulation Kit for modeling multi-physics crystal plasticity, thermal, and damage phenomena from the single crystal up to the component scale

Electron and x-ray diffraction are well-established experimental methods used to explore the atomic scale structure of materials. In this work, a computational method is implemented to produce virtual electron and x-ray diffraction patterns directly from atomistic simulations without a priori knowledge of the unit cell. This method is applied to study the structure of [0 1 0] symmetric tilt low-angle and large-angle grain boundaries in Ni. Virtual electron diffraction patterns and x-ray diffraction 2θ line profiles show that this method can distinguish between low-angle grain boundaries with different misorientations and between low-angle boundaries with the same misorientation but different dislocation configurations. For large-angle Σ5 (2 1 0), Σ29 (5 2 0) and Σ5 (3 1 0) coincident site lattice [0 1 0] symmetric tilt grain boundaries, virtual diffraction methods can identify the misorientation of the grain boundary and show subtle differences between grain boundaries in the x-ray 2θ line profiles. A thorough analysis of the effects of simulation size on the relrod structure in the electron diffraction patterns is presented.

https://iopscience.iop.org/article/10.1088/0965-0393/21/5/055020/pdf

Virtual diffraction analysis of Ni [0?1?0] symmetric tilt grain boundaries

Mindlin's second strain gradient continuum theory for isotropic linear elastic materials is used to model two different kinds of size-dependent surface effects observed in the mechanical behaviour of nano-objects. First, the existence of an initial higher order stress represented by Mindlin's cohesion parameter, b0, makes it possible to account for the relaxation behaviour of traction-free surfaces. Second, the higher order elastic moduli, ci, coupling the strain tensor and its second gradient are shown to significantly affect the apparent elastic properties of nano-beams and nano-films under uni-axial loading. These two effects are independent from each other and allow for separated identification of the corresponding material parameters. Analytical results are provided for the size-dependent apparent shear modulus of a nano-thin strip under shear. Finite element simulations are then performed to derive the dependence of the apparent Young modulus and Poisson ratio of nano-films with respect to their thickness, and to illustrate hole free surface relaxation in a periodic nano-porous material.

Second strain gradient elasticity of nano-objects

Experimental characterization and crystal plasticity modeling of anisotropy, tension-compression asymmetry, and texture evolution of additively manufactured Inconel 718 at room and elevated temperatures

https://iopscience.iop.org/article/10.1088/0965-0393/23/6/065009/pdf

A FFT-based formulation for efficient mechanical fields computation in isotropic and anisotropic periodic discrete dislocation dynamics

https://publikationen.bibliothek.kit.edu/1000051831/3819006

In-situ neutron diffraction during biaxial deformation

A crystallographic extension to the Olson-Cohen model for predicting strain path dependence of martensitic transformation

Using a recent elasto-plastic theory of dislocation and disclination fields, a continuous representation of grain boundaries is introduced. Periodic arrays of wedge disclination dipoles, including those defined in the Disclination Structural Unit Model, are set-up as initial configurations in a dynamic model for symmetric tilt boundaries. These configurations are found to be unstable when the transport of disclinations is allowed. Driven by their self couple-stress field, the motion of disclinations leads to relaxation of the initial elastic curvature and stress fields and to nucleation and transport of relaxation dislocations, until an equilibrium configuration of lower energy is reached. Most of the residual elastic energy of grain boundaries is localized in a non-singular nanometric layer. This energy arises from alternative dilatation and contraction of the lattice around disclinations, and from lattice curvature and shear between disclination dipoles. By virtue of its continuous and dynamic character, the present theory allows modeling absolute misorientations and leads to energy density levels comparable to molecular statics findings.

Grain boundary modeling using an elasto-plastic theory of dislocation and disclination fields

https://www.dora.lib4ri.ch/psi/islandora/object/psi%3A4840/datastream/PDF/Upadhyay-2018-Mechanical_response_of_stainless_steel-%28published_version%29.pdf

M. V. Upadhyay

Papers

A FFT-based formulation for efficient mechanical fields computation in isotropic and anisotropic periodic discrete dislocation dynamics

In-situ neutron diffraction during biaxial deformation

A crystallographic extension to the Olson-Cohen model for predicting strain path dependence of martensitic transformation

Grain boundary modeling using an elasto-plastic theory of dislocation and disclination fields

Mechanical response of stainless steel subjected to biaxial load path changes:Cruciform experiments and multi-scale modeling