查看更多>>摘要：This paper presents an analytical study on the dynamic stability of carbon nanotubes (CNTs) reinforced functionally graded composite beams when subjected to axial excitation loading. The composite beams are functionally graded using a I-type CNTs reinforcement. The section properties of the non-uniform functionally graded composite beams are assessed using Halpin-Tsai model. The analysis of dynamic stability of the composite beams is performed by using Bolotin's method. Analytical expressions of determining free vibration frequency, critical buckling load, and excitation frequency of the non-uniform functionally graded composite beams are derived, in which both the shear deformation and rotary inertia effects are considered. The study demonstrates that the dynamic stability of the beam can be improved significantly when it is functionally graded using the I-type CNTs reinforcement.
查看更多>>摘要：In magnesium alloys, deformation twinning and its interactions with dislocation slip are responsible for a sigmoidal shape stress-strain behavior and an asymmetrical tension-compression yield strength in magnesium alloys. The sensitivity of twinning to the underlying microstructure renders the crystal plasticity method the most commonly adopted modeling approach for magnesium-twinning. This paper compares three state-of-the-art crystal plasticity-based twinning models from the literature, namely the elastic-viscoplastic self-consistent twinning-detwinning (EVPSC-TDT) model, crystal plasticity finite element model based on enhanced predomi-nate twin reorientation approach (CPFE-ePTR), and the crystal plasticity finite element model based on "discrete twinning " approach (CPFE-DT). A polycrystalline microstructure is simulated with all three methods to compare the resulting stress-strain curves and lattice strains to those from the experimentally measured data. All three methods showed the capability of capturing the experimental results with different levels of accuracy. The EVPSC-TDT method avoids solving the finite element matrices and showed the highest computational efficiency. The CPFE-ePTR model shows a higher accuracy in capturing the lattice strain. The CPFE-DT relies on high -resolution finite element mesh and is much slower than the other two methods, but it captured the local deformation concentration and stress reversal phenomena near the twin band, which was not possible with the other two methods. Based on the comparison, guidance for the selection of the appropriate model based on the specific modeling target is provided in this paper.
查看更多>>摘要：Using a trial and error method to measure amorphous forming ability in the experiment is a complex and timeconsuming process. Therefore, it is necessary to devise a method that can rapidly and accurately predict the amorphous forming ability. In this study, two models, artificial neural network and convolutional neural network, are proposed for the prediction of amorphous forming ability of various amorphous alloys. The prediction accuracy of the two models reached 0.77623 and 0.71693, respectively, both of which were more than 19% higher than the reported prediction accuracy of the 13 criteria. This result shows that artificial neural network and convolutional neural network models can accurately predict the amorphous forming ability of a variety of amorphous alloys and provide theoretical guidance for the development and preparation of amorphous alloys.
查看更多>>摘要：The phase-field dislocation dynamics (PFDD) method, originated in 2002, is a continuum dislocation model that uses order parameters to describe dislocation slips in crystalline materials. In the past two decades, and especially since it was last reviewed in 2016, PFDD was advanced significantly in terms of the mathematical formulation, numerical implementation, and applicability. The main purpose of this short review is to summarize recent progress made to improve the energy functional formulation and numerical techniques of PFDD as well as its recent applications. Some recommendations for future work to further extend the PFDD method are presented.
查看更多>>摘要：Based on the classical nucleation theory and the crystal-melt interface kinetic equation, a new method was proposed to compute the anisotropic free energy of the crystal-melt interface. The method stems from the fact that the interface stiffness, instead of the interface free energy, controls the morphologies of nuclei when they are in equilibrium with the surrounding melts. In addition, the interface stiffness has an anisotropy which is an order of magnitude higher than that of the interface free energy, and the anisotropies of these two quantities are related to each other. Mapping out the relation between the curvature radius on the local interface of the nucleus and the equilibrium undercooling temperature during molecular dynamics simulations, we are able to determine the interface stiffness, the interface free energy, and their anisotropy parameters. The new method was used to compute the anisotropy of interface free energy for pure Cu as an example, and the results are in good agreement with the data from experiments and existing simulations.
Rodrigues, Nailton M.Politi, Jose R. S.Martins, Joao B. L.
11页
查看更多>>摘要：Adsorption-based gas storage can be more efficient when porous structures such as MOFs are used as adsorbent material, while structural modifications of these materials can further maximize the application. It is known that MOF organic ligands are generally deficient adsorption sites. Thus, improvements in these ligands can increase the adsorption rate. In this work, modifications were made to the organic ligands of IRMOF-1 and IRMOF-6, generating new structures following a full factorial design 23. These modifications consist in decorating the aromatic ring with Al and substituting ligand hydrogen atoms bonded to the ring by donor and acceptor groups. As a result, the factorial design provided effects with 95% of confidence for the adsorption of CH4, H-2, and H2S gases. It was found that the inclusion of electron donor groups promotes increment in the CH4 and H-2 adsorption. The H2S molecules preferentially interact with electron acceptor groups, and the inclusion of Al atom increased the adsorption significantly, where these interactions have an electrostatic character.
查看更多>>摘要：We systematically study the stability, Gilbert damping parameters, electronic structure, exchange interaction and Curie temperature of CrYCoZ (Z = Al, Ga, In, Tl) alloys. Stability is estimated from the perspective of thermodynamics, dynamics and mechanics. Gilbert damping parameters are calculated by using the linear response formalism, and the values 0.6~& nbsp;4.1 x 10(-3) are observed at room temperature. Electronic calculations show that the CrYCoZ alloys are half-metallic ferrimagnets, and their integer magnetic moments follow the M-t = Z(t) - 18. Origin of gap is discussed by the hybridization, distribution and occupation of electronic states as well as the charge transfer. In addition, the effect of GGA+U on electronic structure is also discussed. Based on the Heisenberg model, we calculate the exchange interactions between atomic components, and analyze the competition and collaboration between d-d exchange, super-exchange and RKKY exchange, finally offer the dominant mechanism of appearance of ferrimagnetic order phase. Furthermore, we calculate the Curie temperatures of CrYCoZ alloys, which are much higher than room temperature. Overall, the CrYCoZ alloys can be considered as a prospective candidates in spintronics application.
查看更多>>摘要：Convolutional neural networks (CNNs) were used for the semantic segmentation of angular monocrystalline WC from NiCrBSi-WC optical microscopy images. This deep learning approach was able to emulate the laborious task of manual segmentation effectively, with a mean intersection over union (IOU) and a mean dice coefficient (DC) of 0.911 and 0.953, respectively, across the entire test dataset. From the model output, the carbide percent can be determined by dividing the area of positively labeled pixels by the total area of the image. Additionally, the mean free path can be quantified using the method described in ASTM STP 839, and by physically counting the black pixels (CPB) between the particles in the image. Comparing the models predictions to the ground truth, the carbide percent had an average difference of 1.2 area %, while the mean free path differed by 15.7 mu m for the ASTM method, and 24.8 mu m for the CPB method. The robustness of the model was tested on images containing both spherical eutectic WC and angular monocrystalline WC to determine whether the model was capable of accurately predicting the location of objects that were not part of the training dataset. The U-Net CNN was able to segment the spherical and angular WC with considerable accuracy. These results show that the application of computer vision models for microstructural characterization is not limited to complex imaging modalities, and can be applied to readily available methods such as optical microscopy.
查看更多>>摘要：The manufacturing process of multimaterial and multilayer assemblies involving pre-impregnated laminates consist of heating the composite structure at high temperature, typically of the order of 200 C, at which polymerization occurs. During the curing, a permanent deformation, called chemical shrinkage strain, is generated and may strongly influence the future flatness of the assembly. Moreover, the cooling generates additional thermal deformations, which also participate into the manifestation of flatness defects at room temperature. To predict warpage or flatness defects, the chemical shrinkage strain needs to be precisely determined.& nbsp;This work proposes an analytical approach dedicated to flatness prediction of multilayer composites taking into account shrinkage strain generated during processing. Our contribution also aims at predicting and analyzing stable and unstable solutions of flatness defects. The proposed analytical model, developed for any multilayer composite, is obtained from an extension of the classical laminate theory (CLT). Geometrical nonlinearities are also accounted for. The analytical approach relies on trial fields for strain and displacements, and on total potential energy minimization. The theory is applied to a bilayer laminate consisting of a cured layer made of epoxy/glass fiber composite and of a pre-impregnated one of the same material. Results obtained from the analytical modeling are validated by numerical simulations. Influence of material parameters is also analyzed for this configuration. Finally, from experimental measurements of curvatures on bilayer composite samples, an inverse method and a minimization procedure, the proposed analytical development provides an estimate of the effective shrinkage strain, which is responsible for the flatness defect. Illustration of this strategy is exemplified by considering a bilayer composite manufactured for this work.
Tang, XiaochuanThompson, Gregory B.Ma, KakaWeinberger, Christopher R....
16页
查看更多>>摘要：The thermodynamic stability of equiatomic mixed carbides, commonly referred to as high entropy carbides (HECs), is investigated via the CALculation of PHAse Diagrams (CALPHAD) approach for mixed carbides con-sisting of the group IVB and VB transition metal carbides as well as tungsten carbide. The Gibbs free energy of the B1-structured mixed carbides is computed using the compound energy formalism while that of the B-h-structured mixed carbides is evaluated using a point-defect model. The required thermodynamic data for the CALPHAD approach are obtained from density functional theory calculations and the Debye-Gruneisen model. The lower temperature limit at which the HECs mix in thermodynamic equilibrium is determined via numerical and analytical approaches. We find that enthalpy of mixing is at least as important as configurational mixing entropy in these mixed transition metal carbide compounds. The lower limit temperature where an equiatomic solid solution is present is largely independent of the number of components with the only exception being solutions containing tungsten carbide, where a weak temperature dependence is noted. Furthermore, the only equiatomic solid solutions that are thermodynamically stable below approximately 1000 K are those stabilized by enthalpy alone, indicating that many currently fabricated HECs are not at equilibrium at room temperature. Collectively, our results demonstrate that the formation of these carbides is controlled by the competition between entropy and enthalpy, or enthalpy alone, and thus these materials should be referred to as multi-principal component carbides since the former terminology can be misleading.
NSTL
Elsevier