查看更多>>摘要：This study integrates 3D printing and finite element analysis (FEA) to investigate the effect of micro-architectural characteristics on the mechanical properties of porous scaffolds. The studied characteristics include the thickness of the scaffold walls and the number of domains at the cross-section. We use 3D printing to fabricate scaffolds of deliberately designed microstructures to enable strict architecture control of the scaffolds. The longitudinal compressive properties of different scaffolds are first analyzed through experimental testing. Then, FEA is conducted to investigate the mechanical properties and the deformation mechanisms of the scaffolds. We find that decreasing wall thickness leads to failure mechanism transition from wall compression failure to buckling instability. For scaffolds with different wall thicknesses, the failure mechanisms and the critical loads are evaluated using the theory of thin plate buckling. For the characteristic of the number of domains, both experimental and FEA results show increasing effective stiffness with increasing domains. Interestingly, we find that with the material properties extracted from a single wall scaffold, the computational models tend to overestimate the effective compression modulus of scaffolds with larger numbers of walls or domains than the experimental data. This observation indicates possible size-dependent material properties in 3D printed structs. Our study demonstrates that integrating experiments and computational modeling can provide fundamental insights into the mechanical properties and deformation mechanisms of micro-architectured scaffolds and unveil unique small-scale material behaviors.
Patel, Anand, VHou, TaoBeltran Rodriguez, Juan D.Dey, Tamal K....
10页
查看更多>>摘要：Tomography is a widely used tool for analyzing microstructures in three dimensions (3D). The analysis, however, faces difficulty because the constituent materials produce similar grey-scale values. Sometimes, this prompts the image segmentation process to assign a pixel/voxel to the wrong phase (active material or pore). Consequently, errors are introduced in the microstructure characteristics calculation. In this work, we develop a filtering algorithm called PERSPLAT based on topological persistence (a technique used in topological data analysis) to improve segmentation quality. One problem faced when evaluating filtering algorithms is that real image data in general are not equipped with the 'ground truth' for the microstructure characteristics. For this study, we construct synthetic images for which the ground-truth values are known. On the synthetic images, we compare the pore tortuosity and Minkowski functionals (volume and surface area) computed with our PERSPLAT filter and other methods such as total variation (TV) and non-local means (NL-means). Moreover, on a real 3D image, we visually compare the segmentation results provided by our filter against TV and NL-means. The experimental results indicate that PERSPLAT provides a significant improvement in segmentation quality.
Kim, NamhoonBlankenau, Brian J.Su, TianyuPerry, Nicola H....
10页
查看更多>>摘要：Owing to the challenges in obtaining realistic atomic configurations in large chemical phase spaces, it is not straightforward to describe structure-property relations in materials exhibiting configurational disorder. One example is iron-substituted strontium titanate (SrTi1-xFexO3-d, STF), a promising perovskite-derivative cathode material in solid oxide fuel cells that exhibits full solid solubility 0 <= x <= 1 and a tendency to exhibit short-range order. Here we demonstrate a multisublattice cluster expansion (CE) framework and apply it to STF across the full composition range. The CE approach is distinct from more traditional CE formulations in that clusters are defined explicitly by the chemical species distributed among multiple sublattices, rather than via cluster functions of occupation variables with decoration. The modified CE approach makes it easy to distinguish meaningful chemical interactions that are harder to extract from conventional CE, since for the latter chemical identity in a cluster is expressed as a product of site occupations. The least absolute shrinkage and selection operator (LASSO) is implemented as a regression analysis tool to select key clusters and avoid overfitting. We demonstrate this formulation on STF, and show that it can accurately predict configurational energies in comparison to conventional CE. From the key clusters, we identify that short-range ordering between substitutional Fe and oxygen vacancies (V-O) results in the formation of Fe-V-O strings. In addition, we consider the stability of STF through CE-based Monte Carlo (MC) simulations and confirm the presence of superstructures that were previously observed in transmission electron microscopy. Analysis of atomic configurations from MC samples reveals variations in the oxidation state of Fe atoms, which can be explained by the ordering tendency of Fe and V-O. The cluster description and selection formalism described here may be applied to other disordered multisublattice systems for accurate and efficient material modeling.
查看更多>>摘要：A systematic study of geometries, formation energies, and electronic structures has been carried out for LiF considering monodoping with Mg and Ti at the interstitial, and lattice site positions, codoping in equal and different proportions, and vacancy defects in absence and presence of foreign elements using hybrid density functional. This study reveals that, both Mg and Ti, show preference for the Li lattice sites over interstitial sites. Li-poor condition is energetically more preferable over Li-rich condition, and codoping is found to be more stable over individual doping. Under this condition, formation of Li-vacancy in codoped system is found to be spontaneous. The presence of only Li vacancy results negligible changes on LiF electronic structure. Interestingly, in presence of Mg, and Ti, it plays an important role by modifying the band gap. Present results provide important insights to tune optical properties of LiF through the rational design of defect-controlled synthetic conditions.
Sarkar, AbhishekShrotriya, PranavNlebedim, Ikenna C.
9页
查看更多>>摘要：We report the impact of the temperature-driven synergistically-coupled anodic degradation mechanisms on the electrochemical performance of lithium batteries with graphite anode over multiple cycles. Temperature dependence of electrochemical reactions and damage mechanisms, such as solid electrolyte interface (SEI) growth, lithium plating/stripping, dead lithium storage/dissolution, and film cracking are incorporated into the degradation model. Results of a parametric analysis are presented, evaluating the effects of charging rates (1-6 C), operating temperatures (-15 - 45 degrees C) and electrode design parameters, on the relative performance fade in the lithium-ion battery. Thermo-electrochemical process maps are developed to provide insights into the relationship between electrode performance and failure mechanisms. The simulation results predict a severe capacity loss due to lithium plating at low temperatures, which is further aggravated at high charging rates. A common strategy for mitigating lithium plating, through charging at high temperatures, also results in rapid capacity loss due to accelerated SEI formation. Simulation results are used to identify the combination of operating conditions and electrode design parameters that improve the electrochemical performance of the battery. These results demonstrate an opportunity to design safe and high-performance lithium-ion batteries, guided by anodic degradation models.
查看更多>>摘要：In this work, based on the modified Bethe lattice method and excluded volume theory, a conductivity prediction model was proposed for ternary nanocomposites such as carbon nanotubes, graphene nanoplatelet and epoxy, and the influence trend of filler size change on the overall conductivity was also analyzed. The synergy effect was then analyzed based on the above model, and it can be concluded that the enhanced synergy effect between carbon nanotubes and graphene nanosheets is the result of the competition between the geometric synergy effect (whether enhanced or not) and the electrical conductivity of the filler. Moreover, based on this prediction model, we extended a piezoresistive model under tensile strain and explored the effects of filler dosage, size and work function of polymer matrix on piezoresistive effect. It is found that the ternary conductive polymer with enhanced synergy in conductivity also has the chance to have a higher gauge factor, which is valuable for the application of flexible pressure sensors. Although our discussion focuses on the two fillers of carbon nanotubes and graphene, this heuristic prediction model can also be applied to other ternary nanocomposites.
查看更多>>摘要：Multi-principal element alloys (MPEAs) are alloys that form solid solution phases and consist of three or more principal elements. Fundamental to the numerical study of mechanical properties of MPEAs are the calculations of their basic structural parameters such as lattice parameter and elastic constants. Due to the presence of multiple elements, calculation of each quantity should ideally consider multiple atomic configurations for each MPEA. However, direct calculations are sometimes expensive, and so some studies in the literature either considered only one atomic configuration or used an indirect method to provide an estimation. In this paper, we calculate the lattice parameters, cohesive energies, and elastic constants of 42 equal-molar refractory MPEAs using small atomistic models. For each quantity in each MPEA, four approaches are used: multiple direct calculations using the alloy potential, a single direct calculation using the A-atom potential, as well as estimations using two rules of mixtures. It is shown that the coefficient of variation based on the first approach positively scales with the lattice distortion of MPEAs. In addition, taking the mean values obtained via the first approach as references, we find that the other three approaches can overestimate or underestimate the basic structural parameters.
查看更多>>摘要：We explore the photocatalytic ability of honeycomb lattice of borocarbonitride (BC6N), investigating its optoelectronic properties and band-edge alignment based on hybrid density functional theory. We observe that along with pronounced visible absorbance, BC6N exhibits a good reducing ability. It is capable of depositing heavy metal ions, hydrogen fuel generation and carbon dioxide sequestration through photoelectrocatalysis. To broaden its applicability we further tune its redox ability using biaxial strain. We observe even a slight expansion makes this material capable of performing simultaneous oxidation and reduction, which is essential for waste management and hydrogen generation through spontaneous water splitting. In this study, we propose BC6N to be a promising potential candidate as metal-free two-dimensional (2D) photocatalyst and show ways to tune its applicability to address multiple environmental crises.
查看更多>>摘要：Based on first-principles calculations, we studied the band gap, work function and effective mass of two dimensional (2D) PbSe by using applied external in-planed strain. Our results show a linearly decrease trend of band gap under both compressive and tensile axial strain. However, the typical character of direct band gap of 2D PbSe has been changed to indirect with a minimum value about 0.3 eV. In contrast, under biaxial compression, the original type of direct band gap is kept. Under biaxial compression strain, we predict that the optical absorption coefficient of 2D PbSe in the ultraviolet region has significant enhancement. Moreover, we found that the work function of 2D PbSe is sensitive and can be tuned between 3.60 eV and 5.31 eV by applying biaxial strain. In addition, we predict that the decrease of the effective mass of electrons or holes along with the compressive strain can promote the carrier mobility in PbSe monolayer. These results imply that 2D PbSe has potential applications in optoelectronic devices.
NSTL
Elsevier