On the formation of adiabatic shear bands in textured HCP polycrystals

AbstractAdiabatic shear band (ASB) formation in textured HCP polycrystals has been investigated under regimes of high rate compression and shear loading using dynamic thermo-mechanically coupled, dislocation-based crystal plasticity modelling. The balance between rate of plastic dissipation leading to internal heat generation versus rate of thermal diffusion at a crystallographic length scale has been shown to be pivotal for the formation or otherwise of ASBs. Micro-texture has been found to have a key role in both advancing and inhibiting shear band growth, and its control offers the possibility of new alloys with higher impact strength over strain rate range1 × 10−2 to 1 × 105 s−1. Texture has been found to lead to wide variations in applied macroscopic strain at which ASB formation occurs, such that strain level in isolation is inappropriate as a universal indicator of ASB onset.High-rate shear loading is found to lead to lower onset strains for ASBs compared to high rate compression, but the dependence of both on texture leads to considerable variation in strain level for ASB formation. A preliminary map demarcating ASB onset has been established over regimes of applied strain and texture for dynamic shear and compression

The effect of the beta phase on the micromechanical response of dual-phase titanium alloys

This paper investigates the role of beta phase on the micro-mechanical behaviour of dual-phase titanium alloys, with particular emphasis on the phenomenon of cold dwell fatigue, which occurs in such alloys under room temperature conditions. A strain gradient crystal plasticity model is developed and calibrated against micro-pillar compression test data for a dual-phase alpha-beta specimen. The effects of key microstructural variables, such as relative beta lath orientation, on the micromechanical response of idealised alpha-beta colony microstructures are shown to be consistent with previously-published test data. A polycrystal study on the effects of the calibrated alpha-beta crystal plasticity model on the local micromechanical variables controlling cold dwell fatigue is presented. The presence of the alpha-beta phase is predicted to increase dwell fatigue resistance compared to a pure alpha phase microstructure

DEPURADORA. SARDINA DEL NORTE [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201

Twin nucleation and variant selection in Mg alloys: An integrated crystal plasticity modelling and experimental approach

Extension twin nucleation and variant selection in magnesium alloy WE43 is investigated in experimentally characterised and deformed microstructures replicated in crystal plasticity models. Total stored (dislocation) energy density is found to identify the experimentally observed locations of twins which are not otherwise explained by global Schmid factors or local resolved shear stress criteria. A critical total stored energy of the order 0.015 Jm-2 is determined below which twin nucleation does not occur. The total stored energy density explains the locations of the observed twins and the absence of twins in parent grains anticipated to be favourable for twin nucleation. Twin variant selection has been shown to be driven by minimising locally stored shear energy density, while the geometric compatibility and strain compatibility factors only aid in partial prediction. All experimentally observed variants were correctly determined

Multiscale modelling of layered-silicate/PET nanocomposites during solid-state processing

This work aims to develop a continuum, multi-scale, physically-based model of the forming process for layered-silicate nanocomposites based on poly(ethylene terephthalate) (PET) matrices, as might be used for packaging. This challenge is tackled using: (1) a physically-based model of PET implemented into the FEM-based code ABAQUS, (2) RVEs with prescribed morphologies reflecting TEM images, and (3) nonlinear computational homogenisation. As a result, 2-D two-scale FEM-based simulations under biaxial deformations (constant width) enabled the extraction of macroscopic stress-strain curves at different silicate contents and processing temperatures. In particular, interesting features in terms of morphology changes and its impact on the macroscopic stress response were captured: (a) morphology change by particle re-orientation and pronounced bending, (b) macroscopic strain hardening due to platelet re-orientation and local strain stiffening, (c) facilitated platelet alignment, and platelet delamination in tactoids through sheardominated deformations and increasing temperature

Crystal plasticity and high-resolution electron backscatter diffraction analysis of full-field polycrystal Ni superalloy strains and rotations under thermal loading

Electron backscattered diffraction (EBSD) has been employed to study a polycrystalline nickel superalloy containing a complex non-metallic agglomerate under thermal loading. Heterogeneous distributions of elastic strains are observed near the inclusion due to its complex geometry and these have been quantified. Lattice rotations were also related to geometrically necessary dislocation (GND) density (View the MathML source), indicating the development of localized plasticity arising from the mismatch in thermal expansivity between the Ni polycrystal and the inclusion. A crystal plasticity finite-element (CPFE) model which explicitly represents the full detail of the complex microstructure was developed to interpret the experimental measurements, and good quantitative and qualitative agreement has been obtained. However, a limitation of the EBSD technique when investigating polycrystal systems is that full-field, transgranular strain measurement remains difficult due to the necessity to reference a lattice spacing within a grain for strain calculation. An inverse reference shifting methodology has been developed using CPFE modeling to overcome this problem, thereby allowing like-for-like and grain-by-grain strain comparisons to be made. The method, in conjunction with high-resolution EBSD, shows promise for the determination of full-field strains and rotations in polycrystalline materials, and provides key information for fatigue nucleation in these material systems

Investigation of slip transfer across HCP grain boundaries with application to cold dwell facet fatigue

<p>Data for "Investigation of slip transfer across HCP grain boundaries with application to cold dwell facet fatigue"<br> http://dx.doi.org/10.1016/j.actamat.2017.01.021</p> <p>This Data folder contains 4 data files:<br> (1) Data_for_Figure_3.xlsx<br> (2) Data_for_Figure_4.xlsx<br> (3) Data_for_Figure_9.xlsx<br> (4) Data_for_Figure_13.xlsx</p> <p>-<br> If readers need further information, please feel free to contact:<br> [email protected]</p

Типология малых городских поселений Беларуси как центров туризма

The previous small urban settlements (SUS) typologies experience is being analyzed. Base principles SUS typology building are being formulated. SUS typology is being carried out, taking in account 5 leading factors, and three original SUS «portraits» description is being given. The strategy of the SUS development is determined. = Анализируется опыт существующих типологий малых городских поселений Беларуси. Формулируются основные принципы построения типологии МГП как центров туризма. Проводится типология МГП на основании 5 ведущих факторов и дается описание трех типизированных «портретов» МГП с определением стратегии их дальнейшего развития

Determination of ti-6242 α and β slip properties using micro-pillar test and computational crystal plasticity

Data for "Determination of ti-6242 α and β slip properties using micro-pillar test and computational crystal plasticity" http://dx.doi.org/10.1016/j.jmps.2016.06.007 Zhen Zhang, Tea-Sung Jun, T. Benjamin Britton and Fionn P.E. Dunne Department of Materials, Imperial College London, Prince consort Road, London, SW7 2AZ, UK -- This experimental data folder contains 3 subfolders: (1) Micropillar compression videos (2) Simulation data (3) Data for Figure 4 (4) Data for Figure 6 -- The simulation data in (2) is ABAQUS input deck containing an example finite element representation of an alpha-beta titanium micropillar subjected to compression loading. This model was calibrated against the experimental data using the first 60s of the stress relaxation period. -- If readers need further information, please feel free to contact: [email protected]