Phase-field-crystal simulation of nano-single crystal microcrack propagation under different orientation angles

The propagation mechanism of microcracks in nanocrystalline single crystal systems under uniaxial dynamic and static tension is investigated using the phase-field-crystal method.Both dynamic and static stretching results show that different orientation angles can induce the crack propagation mode,microscopic morphology,the free energy,crack area change,and causing fracture failure.Crack propagation mode depends on the dislocation activity near the crack tip.Brittle propagation of the crack occurs due to dislocation always at crack tip.Dislocation is emitted at the front end of the crack tip and plastic deformation occurs,which belongs to ductile propagation.The orientation angles of 9°and 14°are brittleductile mixed propagation,while the orientation angles of 19°and 30°are brittle propagation and no dislocation is formed under dynamic tension.The vacancy and vacancy connectivity phenomenon would appear when the orientation angle is14°under static tension,and the crack would be ductile propagation.While the orientation angle is 19°and 30°,the crack propagates in a certain direction,which is a kind of brittle propagation.This work has some practical significance in preventing material fracture failure and improving material performance.

DOA and Subarray-Interval Estimation for Arbitrarily Distributed UAV Swarm System

In this paper,DOA and subarray-interval estimation are considered and applied to arbitrarily distributed unmanned aerial vehicle(UAV)swarm system,in which multiple small UAVs containing uniform linear array(ULA)are divided by unknown intervals because of dynamic moving.Three parameters are taken to indicate the steering vector,namely,the direction of arrivals(DOAs)of target users,the intervals of UAVs,and the orientation angles of UAVs.The orientation angles are first estimated with an auxiliary user and the DOAs are obtained through a search free rooting method,despite the intervals among the UAVs.Afterwards,the intervals among UAVs can also be calculated via exhaustive when the number of target users are no less than three.We further develop a low-complex method to reduce the computational complexity during subarray-interval estimation.The deterministic Cramér-Rao bound(CRB)of the DOA,orientation angle and subarray-interval can be inferred in a closed form.Eventually,numerical instances are cited to verify the research results.

Effect of Pore Morphology and Regional Distribution of Liquid Diffusion Directionality in Nonwoven Fabrics

The effect of pore morphology and regional distribution on liquid diffusion directionality in nonwoven fabrics was investigated in this study.Pore orientation angle(POA) and pore aspect ratio(PAR) were proposed to characterize the pore morphology,and α-region,β-region,and αβ-region were used to describe the characteristics of the pore regional distribution.The directional characteristics of macroscopic diffusion of liquid in nonwoven fabrics were characterized by the indicator of primary diffusion orientation angle(PDOA).Ten kinds of spunlaced nonwoven fabrics were selected.Firstly,the data of pore characteristic indices of each sample were obtained through scanning electron microscope(SEM) and the image processing technology as well,and the pore regional distribution map of each sample was further acquired.Then,the PDOA of each sample was obtained through the droplet method and image processing technology.Based on the data and statistical analysis,it was found that the PDOA of a certain volume of liquid in the nonwoven fabrics presented a significant linear relationship with the average POA of the nonwoven fabrics.And the characteristics of pore distribution affected the directionality of liquid diffusion in the nonwoven fabrics.The samples with a large proportion of α-region and good distribution had prominent liquid diffusion along the direction of laying-up,and the difference in liquid diffusion of the samples was more obvious between the directions of laying-up and vertical laying-up.

Content-Based Image Retrieval with Feature Extraction and Rotation Invariance

Over recent years, Convolutional Neural Networks (CNN) has improved performance on practically every image-based task, including Content-Based Image Retrieval (CBIR). Nevertheless, since features of CNN have altered orientation, training a CBIR system to detect and correct the angle is complex. While it is possible to construct rotation-invariant features by hand, retrieval accuracy will be low because hand engineering only creates low-level features, while deep learning methods build high-level and low-level features simultaneously. This paper presents a novel approach that combines a deep learning orientation angle detection model with the CBIR feature extraction model to correct the rotation angle of any image. This offers a unique construction of a rotation-invariant CBIR system that handles the CNN features that are not rotation invariant. This research also proposes a further study on how a rotation-invariant deep CBIR can recover images from the dataset in real-time. The final results of this system show significant improvement as compared to a default CNN feature extraction model without the OAD.

Reclined trend of alkyl chain of sodium dodecylbenzenesulfonate molecules induced by friction

Surfactants tend to adsorb on the surface/interface mostly in a directional manner.The alkyl chain orientation and conformation order for molecular monolayers of sodium dodecylbenzenesulfonate(SDBS)at low concentrations are studied by using the sum frequency generation vibrational spectroscopy(SFG-VS).The molecular arrangement of the surfactants adsorbed at the solid/liquid interface is further investigated.It is found that the arrangement of the SDBS at the interface becomes relatively ordered with increasing bulk concentration.Meanwhile,the orientation angle reduces gradually,and the molecules tend to be upright state.In addition,the effect of friction on the conformation order and orientation angle are also analyzed.The intensity of the SDBS vibrational contraction peak becomes lower after friction,which indicates that the anion has a reorientation process at the interface.The arrangement of molecules becomes more disordered due to friction.The orientation angle increases slightly,which indicates the monolayer has an inclined trend relative to the lateral direction on the interface.A modified adsorption model considering friction effect is proposed.This work may provide a reference for the further study of adsorption mechanism and application of surfactants.

Analysis of Localization of Mohr-Coulomb Strength Law with Damage Effect

The damage critical curved surface is derived by considering the related effect of isotropic damage and degradation of cohesion and internal friction angle of Mohr-Coulomb strength law.The characteristics of stress-displacement curve and networks of shear bands with the change of degree of damage,confining pressure and Poisson's ratio are investigated numerically by monitoring the stress-displacement values in the process of deformation of samples under plane strain and different initial conditions.The dependence of elastic-plastic response of localization is discussed.The non-uniqueness of the solution of equation is given.The orientation angle of shear band is derived by considering the related effect of isotropic damage and degradation of cohesion and internal friction angle.The orientation angle of shear band obtained by numerical simulation is contrasted to the orientation angle by measuring Mohr circle.It is shown that peak strength and residual strength depend on confining pressure.The networks of shear bands begin to appear in phaseⅡof elasticity and develop in soften phase,and the shear band is formed in the phase of residual strength.As the degree of damage increases,axial displacement at the points of bifurcation and shear band decreases.The orientation angle of shear band increases with the increase of the damage degree.The orientation angle of shear band obtained by numerical simulation and measuring Mohr circle is not much difference when the damage degree is equivalent.The Mohr-Coulomb theory may predict the localized instability of sample by considering the degradation of cohesion and internal friction angle.

Structural Optimization of Fiber-Reinforced Material Based on Moving Morphable Components (MMCs)

Fiber-reinforced composite materials have excellent specific stiffness,specific strength,and other properties,and have been increasingly widely used in the field of advanced structures.However,the design space dimensions of fiber-reinforced composite materials will expand explosively,bringing challenges to the efficient analysis and optimal design of structures.In this paper,the authors propose an explicit topology optimization method based on the moving morphable components for designing the fiber-reinforced material.We constrain the intersection area between components to guarantee the independence of each component and avoid the situation that one component is cut by other components.Adding the fiber orientation angle as a design variable,the method can optimize the structural layout and the fiber orientation angle concurrently under the given number of fiber layers and layer thickness.We use two classical examples to verify the feasibility and accuracy of the proposed method.The optimized results are in good agreement with the designs obtained by the 99-line code.The authors also popularize the proposed method to engineering structure.The results manifest that the proposed method has great value in engineering application.

Determination of Anisotropic Factors of Pyrolytic Carbon by Electron Diffraction

The preferred orientation of pyrolytic carbon coating is an important performance parameter for the safe use of artificial mechanical heart valve.In this paper,the selected area electron diffraction(SAED)analysis of pyrolytic carbon coating samples of artificial heart valve was carried out by transmission electron microscopy(TEM),and the experimental method of characterizing the preferred orientation of pyrolytic carbon by electron diffraction spectrum,namely bacon anisotropy factor(BAF),was described,and the orientation angle and BAF corresponding to the electron diffraction spectrum were measured.The results show that the BAF value can directly reflect the anisotropy of pyrolytic carbon in the selected area.The BAF value range is from 1 to infinity,and the higher the preferred orientation is,the greater the value is.The BAF value decreases exponentially with the increase of orientation angle.When the pyrolytic carbon tends to be isotropic,the orientation angle tends to 180 and the BAF value tends to 1.