Search

• Presents a fully resolved, three-dimensional computational characterization of the interaction effects between grain size and initial texture strength on the orientation-dependent macroscopic mechanical responses of magnesium alloy. • Offers insights into microstructure-property linkages. • Makes projections of the grain size and texture dependent net plastic anisotropy on the possible ductile failure by porosity evolution. This work systematically investigates the microstructure-property relationship in Mg alloys. Emphasis is placed on understanding, through high resolution crystal plasticity modeling, how grain size and texture collectively impact material strengthening and hardening, net plastic anisotropy, and tension-compression asymmetry. To achieve this, 528 fully three-dimensional finite element calculations are performed, which comprise eleven textures, four grain sizes, six loading orientations, and two uniaxial loading states (tension and compression). The grain size effect follows Hall-Petch relation that depends on both, loading orientation and initial texture. The reduction in extension twinning with grain size refinement is influenced by texture as well. Below a threshold textural strength, grain size refinement leads to an appreciable reduction in the net plastic anisotropy at yield, quantified using Hill anisotropy, and reduced tension-compression asymmetry. Using a micromechanical basis, the effect of grain size and texture on material ductility is predicted to be non-monotonic. The computational predictions serve as synthetic data sets for experimental validation and reduced-order modeling. [ABSTRACT FROM AUTHOR]

• Effect of temperature on the CRSSs of slips and twinning is evaluated in Mg single crystals. • Slips traces are used specially to define various deformation modes of Mg. • VPSC-GA modeling is proved to be effective to obtain the CRSSs of Mg. Magnesium (Mg) single crystal specimens with three different orientations were prepared and tested from room temperature to 733 K in order to systematically evaluate effects of temperature on the critical resolved shear stress (CRSS) of slips and twinning in Mg single crystals. The duplex non-basal slip took place in the temperature range from 613 to 733 K when the single crystal samples were stretched along the <0 1 ¯ 10> direction. In contrast, the single basal slip and prismatic slip were mainly activated in the temperature range from RT to 733 K when the tensile directions were inclined at an angle of 45° with the basal and the prismatic plane, respectively. Viscoplastic self-consistent (VPSC) crystal modeling simulations with genetic algorithm code (GA-code) were carried out to obtain the best fitted CRSSs of major deformation modes, such as basal slip, prismatic slip, pyramidal II , {10 1 ¯ 2} tensile twinning and {10 1 ¯ 1} compressive twinning when duplex slips accommodated deformation. Additionally, CRSSs of the basal and the prismatic slip were derived using the Schmid factor (SF) criterion when the single slip mainly accommodated deformation. From the CRSSs of major deformation modes obtained by the VPSC simulations and the SF calculations, the CRSSs for basal slip and {10 1 ¯ 2} tensile twinning were found to show a weak temperature dependence, whereas those for prismatic , slip and {10 1 ¯ 1} compressive twinning exhibited a strong temperature dependence. From the comparison of previous results, VPSC-GA modeling was proved to be an effective method to obtain the CRSSs of various deformation modes of Mg and its alloys. [ABSTRACT FROM AUTHOR]

{ 10 1 ¯ 2 } twins were introduced into the magnesium (Mg) plate AZ31 via pre-rolling along its transverse direction. The plates, both with and without the pre-induced { 10 1 ¯ 2 } twins, were subjected to uniaxial tension along different directions. Using crystal plasticity modeling, we found that the strengthening effect of the pre-induced { 10 1 ¯ 2 } twins on the macroscopic flow stress primarily arised from the increased slip resistance caused by the boundaries, rather than the orientation hardening due to the twinning reorientation (although the latter did make its contribution in some specific loading directions). Besides, the pre-existing { 10 1 ¯ 2 } twins were found, by both experiments and simulation, to promote the activity of prismatic 〈a〉 and pyramidal in the parent matrix of the material. Further analysis showed that the enhanced non-basal slip activity is related to the { 10 1 ¯ 2 } twin boundaries' low micro Hall-Petch slope ratios of non-basal slips to basal slip. With the critical resolved shear stress (CRSS) obtained from crystal plasticity modeling and the orientation data from EBSD, a probability-based slip transfer model was proposed. The model predicts higher slip transfer probabilities and thus lower strain concentration tendencies at { 10 1 ¯ 2 } twin boundaries than that at grain boundaries, which agrees with the experimental observation that the strain localization was primarily associated with the latter. The present findings are helpful scientifically, in deepening our understanding of how the pre-induced { 10 1 ¯ 2 } twins affect the strength and slip activity of Mg alloys, and technologically, in guiding the design of the pre-strain protocol of Mg alloys. [ABSTRACT FROM AUTHOR]

Present work focuses on analysis of the stress and strain fields inside and around the individual {10–12} twin in magnesium alloy. The 3D crystal plasticity model represents twin as an ellipsoidal inclusion surrounded by the matrix. Five different twin thicknesses and three different lateral twin lengths are used for stress/strain analysis. The simulations are complemented with experimental observations using high-resolution electron backscattered diffraction. The simulations and experiments show a similar distribution of the shear stress and the spatial activity of individual slip systems (basal, prismatic, pyramidal). Plasticity induced inside the twin is dominantly caused by the prismatic dislocations slip and does not influence twin back stress which is identical to pure elastic twin. The twin with larger lateral dimension requires lower equilibrium stress which suggests anisotropic twin propagation and increased thickness of such twins. The lateral twin propagation is mostly influenced by prismatic and pyramidal slip in the twin vicinity. The twin thickness can reach a maximal level that is driven by the critical resolved shear stress values for dislocation slip with the significant influence of basal slip. [ABSTRACT FROM AUTHOR]

A multiscale crystal plasticity model accounting for temperature-dependent mechanical behaviors without introducing a larger number of unknown parameters was developed. The model was implemented in elastic-plastic self-consistent (EPSC) and crystal plasticity finite element (CPFE) frameworks for grain-scale simulations. A computationally efficient EPSC model was first employed to estimate the critical resolved shear stress and hardening parameters of the slip and twin systems available in a hexagonal close-packed magnesium alloy, ZEK100. The constitutive parameters were thereafter refined using the CPFE. The crystal plasticity frameworks incorporated with the temperature-dependent constitutive model were used to predict stress–strain curves in macroscale and lattice strains in microscale at different testing temperatures up to 200 °C. In particular, the predictions by the crystal plasticity models were compared with the measured lattice strain data at the elevated temperatures by in situ high-energy X-ray diffraction, for the first time. The comparison in the multiscale improved the fidelity of the developed temperature-dependent constitutive model and validated the assumption with regard to the temperature dependency of available slip and twin systems in the magnesium alloy. Finally, this work provides a time-efficient and precise modeling scheme for magnesium alloys at elevated temperatures. [ABSTRACT FROM AUTHOR]

Due to their low symmetry in crystal structure, low elastic modulus (∼45 GPa) and low yielding stress, magnesium (Mg) alloys exhibit strong inelastic behaviors during unloading. As more and more Mg alloys are developed, their unloading behaviors were less investigated, especially for rare-earth (RE) Mg alloys. In the current work, the unloading behaviors of the RE Mg alloy ZE10 sheet is carefully studied by both mechanical tests and crystal plasticity modeling. In terms of the stress–strain curves, the inelastic strain, the chord modulus, and the active deformation mechanisms, the substantial anisotropy and the loading path dependency of the unloading behaviors of ZE10 sheets are characterized. The inelastic strains are generally larger under compressive Loading–UnLoading (L–UL) than under tensile L–UL, along the transverse direction (TD) than along the rolling direction (RD) under tensile L–UL, and along RD than along TD under compressive L–UL. The basal slip, twinning and de-twinning are found to be responsible for the unloading behaviors of ZE10 sheets. [ABSTRACT FROM AUTHOR]

This research aims to make simple modeling of the crystal structure of carbon tetrachloride, diamond, and fullerenes using molymod. The method used is a descriptive quantitative with the research stages including the selection, making, and testing the feasibility of crystal structure. The feasibility of the crystal structure was assessed using a product feasibility test sheet and analyzed using the ideal standard mean equation. The development of a crystal structure model was carried out using a simple and easy method to obtain equipment in the form of molymod. The results of this research indicate that the crystal structure of carbon tetrachloride, diamond, and fullerenes can be interpreted significantly and easily with the help of molymod. The simple model of the crystal structure is also suitable for use as a physics learning medium that can help students understand abstract crystal structure material. [ABSTRACT FROM AUTHOR]

In vitro ‒ in vivo correlation (IVIVC) of solid dosage forms should be established basically between in vitro and in vivo dissolution of active pharmaceutical ingredients. Nevertheless, in vivo dissolution profiles have never been accurately portrayed. The current practice of IVIVC has to resort to in vivo absorption fractions (F a). In this proof-of-concept study, in vivo dissolution of a model poorly water-soluble drug fenofibrate (FNB) was investigated by fluorescence bioimaging. FNB crystals were first labeled by near-infrared fluorophores with aggregation-caused quenching properties. The dyes illuminated FNB crystals but quenched immediately and absolutely once been released into aqueous media, enabling accurate monitoring of residual drug crystals. The linearity established between fluorescence and crystal concentration justified reliable quantification of FNB crystals. In vitro dissolution was first measured following pharmacopoeia monograph protocols with well-documented IVIVC. The synchronicity between fluorescence and in vitro dissolution of FNB supported using fluorescence as a measure for determination of dissolution. In vitro dissolution correlated well with in vivo dissolution, acquired by either live or ex vivo imaging. The newly established IVIVC was further validated by correlating both in vitro and in vivo dissolution with F a obtained from pharmacokinetic data. Authentic in vitro ‒ in vivo correlation should be established between in vitro dissolution and in vivo dissolution which however has never been determined accurately. This study provides proof of concept of in vivo dissolution based on live imaging of fluorescently hybridized crystals of a model poorly water-soluble drug fenofibrate. [Display omitted] [ABSTRACT FROM AUTHOR]

Elementary processes during the oxidation of single crystal Co/Ni-base model alloys between 800 °C and 900 °C were investigated in the present study. The influence of the base element (Co or Ni) on the oxidation rate was elucidated by continuous thermogravimetry in synthetic air for 100 h. After exposure, the multilayered oxide scales were characterized by scanning electron microscopy combined with electron probe micro analysis. The substitution of Co by Ni caused reduced oxidation rates at 900 °C. At lower temperatures an inverse trend with Co-rich alloys demonstrating lower mass gains was observed. The development of diffusion-limiting scale sections that lead to overall thinner oxide layers could be proved for the Co-base superalloy without Ni at 800 °C and 850 °C. The growth of AlN as well as the unwanted phase transformation of the ?/?' microstructure into Co3W persisted in alloys with high Co levels for all investigated temperatures. Material transport at 900 °C was elucidated by two-stage oxidation experiments in normal oxygen and 18O-enriched atmospheres. Transport of O2 via microchannels could be concluded for all compositions. The provided insights contributed to deeper understanding of essential processes during the formation of barrier layers in the scale. [ABSTRACT FROM AUTHOR]

In the stores of museums and university departments of mineralogy and crystallography, there are collections of sets of models of crystal shapes. Representing the external form of natural specimens, their use was for identification and demonstration purposes, by scientists, teachers and students from the late eighteenth century onwards. Whilst studying crystal model collections at the National Museums Scotland in Edinburgh, I came across the illustration work of Miss Delvalle Lowry. Her name, along with that of her father Wilson, appeared on plates illustrating an 1820 textbook by Nathaniel Larkin, a London teacher of solid geometry. Miss Lowry married the painter John Varley in 1825 and wrote a number of mineralogical texts that were reprinted through the first half of the nineteenth century. Delvalle Lowry was able to enjoy this career not least as a result of her ability to draw. The role of the Society of Arts in encouraging both drawing and the study of crystallography may well have been a feature of her success. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Shift of chemical shielding studied. • It alters for trimer. • It is stable for pentamer. A computational investigation has been performed without any symmetry constraints at the B3LYP/6-31++G** level for the evidencing of hydrogen bonding interactions in the real crystalline structure of Leflunomide (LFM) via chemical shielding (CS) tensors at the site of 14C, 17O, 15N, 1H nucleus. In this study, one molecule (monomer), three molecules (trimer), and five-molecules (cluster) of Leflunomide's conformer have been modeled by accessible crystal coordinates. The CS tensors have been computed for 3 models of structure to indicate the effects of the hydrogen bonding interactions on the parameters of NMR. The evaluated NMR parameters of 14C, 17O, 15N, 1H nuclei of Leflunomide show specific tendencies from the monomer to the target molecule in the cluster as a result of the involvement in the intermolecular C O...H N type of hydrogen bonding interaction. Chemical shift of 14C, 17O, 15N, 1H nuclei significantly alter from monomer to the target molecule in trimer because of formation of inter-molecular C O...H N kind of the hydrogen bonding interaction whereas this alternation was insignificant via the target molecule in trimer to pentamer as a result of do not change numbers and types of the hydrogen bonding interactions. [ABSTRACT FROM AUTHOR]

Natural hydroxyapatite provides certain strength and stiffness to biological bones, and most of the studies on the strength of bone tissues have been carried out on hydroxyapatite (HAP). However, the Ca/P ratio of hydroxyapatite in bones is actually about 1.50, and the natural hydroxyapatite belongs to calcium-deficient hydroxyapatite (CDHA) with Ca vacancy defects. Therefore, this work focused on the effect of Ca vacancy defects on CDHA crystals through investigating the generation and expansion of microcracks under uniaxial tensile loading by combining molecular dynamics and first principles method. A series of crystal models with different Ca vacancy ratios are constructed and find that Ca vacancies degrade the mechanical properties of hydroxyapatite. Meanwhile the fracture behavior of crystals is detailed and find that the cracks arise at vacancies and extend along the direction of vacancies. Also, first-principles calculation is performed to reveal the mechanism of crack formation in MD simulations. It is found that the decrease of Ca–O bonding of CDHA causes the decrease of the stability of the crystal structure by analyzing the DOS of HAP and CDHA, and the cracks originate from Ca vacancies. This work performs more realistic simulations of CDHA with calcium vacancy defects in actual bone tissue and directly reveals the development and progression of bone fragility at the nanometer scale. [ABSTRACT FROM AUTHOR]

This article describes a low-cost crystal-structure model, which is used to represent atomic positions in different types of unit cell. It consists of a wooden base with holes drilled on both sides. These holes can receive dowels on to which balls (commercial or home-made) can be fitted. The model's use for modelling different types of packing in crystals, and the structure of metals, non-metals, ionic compounds, etc., is explained, with examples. This model is not only easy to operate and inexpensive, but has pedagogical advantages too, as the student can visualise many salient features of the crystal structure. A list of activities that can be performed with this model is included, based on a learning cycle for conceptual understanding. [ABSTRACT FROM AUTHOR]

Illustrates how to make an accurate three-dimensional model of any crystal. Drawing and model-making setup; Construction of a crystal model of vesuvianite; Obtaining angular data on crystals.