查看更多>>摘要：Engineered polymer matrix composite materials with designer electrical properties are important for a myriad of engineering applications including flexible actuators and wearable sensors. We use stereolithography in combination with ultrasound directed self-assembly to align electrically conductive microfibers in a photopolymer matrix. We relate the fabrication process parameters to the resulting filler material alignment and corresponding electrical conductivity using supervised machine learning methods and quantify the prediction accuracy of data-driven models derived from different interpretable and non-interpretable algorithms. We determine that decision tree and artificial neural network algorithms result in data-driven models with R-2 scores that are 79.8% and 83.2% higher, respectively, than a traditional multivariate regression analysis benchmark model in predicting the microfiber alignment. Similarly, random forest and artificial neural network algorithms result in data-driven models that predict composite material electrical conductivity 9.1% and 13.7% more accurately, respectively, than a logistic multivariate regression benchmark model. Relating the fabrication process parameters to the resulting electrical conductivity of the material is a crucial step towards fabricating polymer matrix composite materials with designer electrical properties for use in engineering applications.
Chen, Dian-TengCheng, H-p.Hennig, Richard G. G.Trickey, S. B....
13页
查看更多>>摘要：Current spin-crossover (SCO) energy calculations depend on nearly artisanal skill in picking quantum mechanical approximations and computational methods. That is incompatible with automated (work-flow-driven) screening. An acceptable methodology must be quantum mechanically sound, yield both basic structure and property values, and accurate delta E-HL without steering or tuning. Cost vs. accuracy causes focus on density functional theory (DFT). We show by a near-exhaustive study of schemes for calculating the basic molecular high-low spin energy difference, delta E-HL, that presently there is no combination of a constraint-based, non-empirical density functional approximation (DFA) and a set of well-defined semi-empirical corrections to it adequate for such a protocol. Somewhat successful hybrid DFA calculations of delta E-HL are too costly for high-throughput screening of condensed phases. Lower-cost alternatives combine a generalized gradient approximation (GGA) DFA with a Hubbard -U correction (DFT + U). But we show that neither U = 0 nor any currently available unsteered U calculation gives a decent delta E-HL value for [Mn(taa)] without also degrading molecular structure or property predictions. Moving to the SCAN meta-GGA does not solve the problem. The revised-restored SCAN (r(2)SCAN) meta-GGA together with its deorbitalized version r(2)SCAN-L give improved but not wholly satisfactory results. We also document and diagnose several non-obvious technical and procedural sensitivities and inter-code differences. In addition to being a formidable challenge to DFA development, the lack we delineate is a major impediment to progress in the development of quantum materials and spintronics.
查看更多>>摘要：Metals with fcc structure may exhibit deformation twinning under specific conditions, which is an interesting but somewhat elusive aspect of their deformation behavior. It is well acknowledged that the phenomenon occurs through the activities of twinning partial dislocations. However, the lack of a comprehensive understanding of their fundamental properties obstructs the development of detailed multiscale plasticity models for the fcc metals. Here, we explore the core-structures and lattice friction of twinning partials through atomistically informed numerical modeling. To this end, we choose four fcc crystals with widely differing stacking fault energies. Using the semi-discrete variational Peierls-Nabarro model with non-local and surface corrections, we compute the core-widths and Peierls stresses of edge and screw twinning dislocations. In particular, the alternate-shear mode of twinning has been considered in addition to the regular layer-by-layer mechanism. In the former case, the stable disregistry energy of the middle layer is observed to be significantly less than the unsheared configuration, which is enough to overcome the Peierls barrier spontaneously. This study also highlights the significance of incorporating the correction terms, the absence of which may lead to significant inaccuracy in estimating the intrinsic lattice resistance of the twinning partials.
Wang, ChaoKhan, Muhammad BilalWang, ShuaiChen, Shaohua...
8页
查看更多>>摘要：Nanoparticle-contained graphene foams (NP-GrFs) have been widely concerned and used in many practical applications in recent years. However, the mechanical property and its micro-mechanism of such a new com-posite material are still poorly understood. In this work, a coarse-grained NP-GrFs model is established to sys-tematically study the mechanical response of NP-GrFs under uniaxial tension as well as the size and volume fraction effects of nanoparticles. It is found that both the initial modulus and tensile strength depend on the size and volume fraction of NPs, both of which can increase by almost an order of magnitude. Furthermore, when the volume fraction of nanoparticles increases, the strain hardening phenomenon occurs. Two main enhancing mechanisms are found. One is the increased adhesion between neighbor sheets by NPs and the other is the homogenized stress due to the extrusion of NPs. The present results should be useful not only for understanding the microstructure-determined mechanical properties of NP-GrFs but also for the design of advanced functional materials or devices based on GrFs.
Rojas-Chavez, H.Miralrio, AlanCruz-Martinez, H.Martinez-Espinosa, J. A....
11页
查看更多>>摘要：This study has been designed with the aim to understand the stability of the as-milled PbSeO3 reaction product, which is considered the determining step associated with the mechanochemical synthesis of PbSe nanostructures. Herein, a detailed discussion of the transition pathway from PbSeO3 to PbSe nanostructures is proposed. Hence, the decomposition process of PbSeO3, during milling, is studied by X-ray diffraction. According to the Rietveld refinement, the largest PbSeO3 concentration is obtained after 2 h of milling; after that, it decreases as the milling time is increased. In addition, the chemical composition changes are studied via density functional theory (DFT) calculations because the changes have an impact on the electronic properties, especially the bandgap value (Eg) associated with the presence of oxygen. Furthermore, the DFT calculations are also used to understand the transition state (TS)-via the diffusion of O-atoms by the atomic layers-from PbSeO3 to PbSe. After the oxygen removal, an energetically expensive process of spatial rearrangement (similar to 26.97 kJ.mol(-1)) took place to obtain the ground state structure of PbSe. Therefore, this work provides a comprehensive understanding of the decomposition mechanism of PbSeO3 that allows to tune the electronic properties of devices based on PbSe nano structures, which are concerned with surface chemical composition changes.
NSTL
Elsevier