5 research outputs found
Prevalence and some psychosocial characteristics of social anxiety disorder in an urban population of Turkish children and adolescents
Purpose: To define the prevalence and some of the psychosocial characteristics of social anxiety disorder (SAD) in an urban population of Turkish children and adolescents
A finite element method to calculate geometrically necessary dislocation density: accounting for orientation discontinuities in polycrystals
Strain gradients have been used to link various microscale deformation phenomena to the mechanical response of a polycrystalline material, revealing sub-crystal deformation structures. The strain gradients are computed in terms of the orientation gradients and then converted to geometrically necessary dislocation densities, a quantity considered important to explain flow stress and strain hardening behaviour. In this study, a unique method has been developed to compute the orientation gradients by finite element method while enforcing orientation continuity inside the grains and allowing sharp gradients at the grain boundaries by a global minimization approach. The method is showcased on an exemplar electron backscatter diffraction datasets of a stainless type of steel. The energy minimization method (Demir et al., 2009) reveals geometrically necessary dislocation densities that are an order of magnitude lower than those calculated using the widely accepted Least-Squares minimization approach (Arsenlis et al., 1999). The proposed approach successfully eliminates sharp orientation gradients at grain boundaries, removing the artificially high dislocation densities near orientation discontinuities that is characteristic to the finite difference-based approaches
Exploring 3D X-Ray Diffraction Method to Validate Approaches in Materials Modelling
Cyclic high temperature deformation, which is a precursor to creep-fatigue damage is one of the main life limiting factors in thermal power plants. Microstructurally informed models such as crystal plasticity have shown great promise in predicting cyclic plasticity and creep deformation; however, further validation of predicted meso-scale deformation is required to ensure accurate damage calculations. Here, a novel 3D X-ray diffraction (3DXRD) experiment was performed to resolve and investigate the response of individual grains within a polycrystalline material under loading at elevated temperature. Specimens were made from 316H stainless steel, which is an alloy commonly used for critical structural components in thermal power generation plants. The 3DXRD experiments were conducted at the UK national synchrotron facility, Diamond Light Source. The measurements provided positions, strain tensors, and orientations of individual grains within a gauge volume. The data generated from 3DXRD was used both as an input and for the validation of a crystal plasticity finite element model (CPFE). The results provided demonstrate the importance of microstructural information in materials modelling.<br/