- 标题
- 摘要
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- 实验方案
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Hyperelastic material modeling of graphene based on density functional calculations
摘要： A new parameter set for the graphene material model of [1] is obtained. The material model is anisotropic hyperelastic and calibrated by a trial dataset generated by density functional theory (DFT). The DFT experiments are one pure dilatation test and two uniaxial stretch tests along the armchair and zigzag directions. The strain energy is computed from ab-initio simulations and used to calibrate the parameters of the hyperelastic model. The strain energy and stresses from the new parameter set are calculated and verified with the results of [1].
关键词： density functional theory,hyperelastic material model,DFT,anisotropic,strain energy,graphene
更新于2025-09-04 15:30:14
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Pipeline leakage identification and localization based on the fiber Bragg grating hoop strain measurements and particle swarm optimization and support vector machine
摘要： A pipeline's safe usage is of critical concern. In our previous work, a fiber Bragg grating hoop strain sensor was developed to measure the hoop strain variation in a pressurized pipeline. In this paper, a support vector machine (SVM) learning method is applied to identify pipeline leakage accidents from different hoop strain signals and then further locate the leakage points along a pipeline. For leakage identification, time domain features and wavelet packet vectors are extracted as the input features for the SVM model. For leakage localization, a series of terminal hoop strain variations are extracted as the input variables for a support vector regression (SVR) analysis to locate the leakage point. The parameters of the SVM/SVR kernel function are optimized by means of a particle swarm optimization (PSO) algorithm to obtain the highest identification and localization accuracy. The results show that when the RBF kernel with optimized C and γ values is applied, the classification accuracy for leakage identification reaches 97.5% (117/120). The mean square error value for leakage localization can reach as low as 0.002 when the appropriate parameter combination is chosen for a noise‐free situation. The anti‐noise capability of the optimized SVR model for leakage localization is evaluated by superimposing Gaussian white noise at different levels. The simulation study shows that the average localization error is still acceptable (≈500 m) with 5% noise. The results demonstrate the feasibility and robustness of the PSO–SVM approach for pipeline leakage identification and localization.
关键词： pipeline leakage localization,method of characteristics (MOC),FBG hoop strain sensor,support vector regression (SVR),particle swarm optimization (PSO) algorithm,support vector machine (SVM)
更新于2025-09-04 15:30:14
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Local Strain and Crystalline Defects in GaN/AlGaN/GaN(0001) Heterostructures Induced by Compositionally Graded AlGaN Buried Layers
摘要： Plastic strain relaxation in epitaxial layers is one of the crucial factors that limit the performance of III-nitride-based heterostructures. In this work, we report on strain relaxation and crystalline defects in heterostructures consisting of compositionally graded AlGaN epitaxial layers tensile-strained between a GaN-buffer and a GaN-cap. We demonstrate the effects of Al concentration and the shape of the concentration-depth profile in the buried graded layers on the accumulated elastic strain energy and how this influences the critical thickness for crack generation or fracture. It is shown that this fracture leads to the formation of partially relaxed regions with their degree of strain relaxation directly related to the density of cracks. Nevertheless, even though the in-plane coherency between the AlGaN layer and the GaN-buffer is broken, the in-plane coherency within the AlGaN layer is preserved for all regions. Furthermore, the tensile strain released in the buried graded AlGaN layers is consistent with compressive strain induced in the GaN-cap layers. Finally, the localized stress and the densities of threading dislocations are correlated with the features of the resulting fractured heterostructures. These results are important towards the control of complex plastic strain relaxation and further facilitate the growth of high quality compositionally graded AlGaN-based devices.
关键词： X-ray diffraction,cracks,graded layers,epitaxy,strain relaxation,AlGaN
更新于2025-09-04 15:30:14
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Strain-Mediated Substrate Effect on the Dielectric and Ferroelectric Response of Potassium Sodium Niobate Thin Films
摘要： If piezoelectric thin films sensors based on K0.5Na0.5NbO3 (KNN) are to achieve commercialization, it is critical to optimize the film performance using low-cost scalable processing and substrates. Here, sol–gel derived KNN thin films are deposited using a solution with 5% of potassium excess on Pt/TiO2/SiO2/Si and Pt/SrTiO3 substrates, and rapid thermal annealed at 750 ?C for 5 min. Despite an identical film morphology and thickness of ~335 nm, an in-plane stress/strain state is found to be tensile for KNN films on Pt/TiO2/SiO2/Si, and compressive for those on Pt/SrTiO3 substrates, being related to thermal expansion mismatch between the substrate and the film. Correspondingly, KNN films under in-plane compressive stress possess superior dielectric permittivity and polarization in the parallel-plate-capacitor geometry.
关键词： stress/strain,ferroelectric hysteresis,dielectric properties,KNN thin films,sol–gel,thermal expansion
更新于2025-09-04 15:30:14
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Three-Dimensional Imaging of Phase Ordering in an Fe-Al Alloy by Bragg Ptychography
摘要： We show three-dimensional images of phase ordering in a Fe55Al45 alloy obtained by coherent x-ray diffraction Bragg ptychography. Fe-Al alloys display ordered phases where the atoms organize on sublattices resulting in the emergence of otherwise forbidden superlattice reflections. The degeneracy of the ordering results in antiphase domain boundaries that, in addition to the general lattice strain, provide phase shifts of the diffracted beam depending on the reflection. The reconstructed phase images can be separated into components originating from B2 phase domains and lattice strain by performing Bragg ptychography on both the (002) fundamental and the (001) superlattice reflections.
关键词： lattice strain,three-dimensional imaging,antiphase domain boundaries,Fe-Al alloy,Bragg ptychography,phase ordering
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 7th Global Conference on Consumer Electronics (GCCE) - Nara, Japan (2018.10.9-2018.10.12)] 2018 IEEE 7th Global Conference on Consumer Electronics (GCCE) - Blood Circulation Based on PPG Signals for Thermal Comfort Evaluation
摘要： This paper presents a new index for monitoring transition of blood circulation from Photoplethysmogram (PPG) signals for thermal comfort evaluation of users. Heat dissipation reaction through the dilation of blood vessels is person's intrinsic ability to control the thermal comfort. When body temperature is higher than normal temperature, blood circulation changes according to the dilation of blood vessels in distal end of the extremities. Blood circulation is often evaluated by an index of peripheral resistance corresponding to changes in blood flow velocity such as systolic/diastolic ratio (S/D) of flow velocities, resistance index and the pulsatility index. Unfortunately, such an index cannot be utilized in daily life for healthcare with using fitness trackers since the blood flow velocity is measured by either an ultrasonic Doppler blood flowmeter (UDF) or a Laser-Doppler flowmeter. Therefore, we propose a new index which is easily acquirable from PPG signals. First, a couple of variables correlating to the blood flow velocity is calculated from a rate of volumetric strain of Photoplethysmogram signals. Then the new index can be obtained as difference of these variables. Experimental results show the effectiveness of this index by confirming high correlation with S/D of UDF.
关键词： Peripheral blood circulation,volumetric strain,blood flow velocity,Photoplethysmogram signals
更新于2025-09-04 15:30:14
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Formation mechanism of twin domain boundary in 2D materials: The case for WTe2
摘要： Our scanning tunneling microscopy (STM) study observes, for the first time, twin domain boundary (TDB) formations on the surface of WTe2 single crystal, which is glued by solidifying indium to Si substrate. In these TDB regions, a large inhomogeneous strain field, especially a critical shear strain of about 7%, is observed by geometric phase analysis. This observation does not obey the old believe that a small mechanical stress is sufficient to drive thermally-induced TDB formations in two-dimensional materials. To resolve the contradiction, we perform density functional theory calculations combined with elasticity theory analysis, which show that TDBs on WTe2 are entirely displacement-induced, for which a critical strain is necessary to overcome the onset barrier.
关键词： WTe2,twin domain boundary,density functional theory,strain,scanning tunneling microscopy (STM)
更新于2025-09-04 15:30:14
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APPLICATION OF OPTICAL METHOD IN MEASURING MECHANICAL VIBRATIONS IN A CANTILEVER BEAM
摘要： The pertinent literature discloses a family of optical profile measuring techniques highlighting the moiré methods. The Moiré technique is based on the interference of two superimposed optical grids which produce fringe patterns which can be processed to analyze the DYNAMIC MEASUREMENT IN MATERIALS mechanical behavior. The goal of this research is to experimentally determine the mechanical displacement of a slim cantilever beam by means of Moiré technique with Phase Shift. Photomechanical experimental arrangement included a digital camera, a multimedia projector and a PC. The occurrence of oscillations has been adequately analyzed. The results showed data from which useful information can withdraw, being of great importance to support agricultural machinery projects and development.
关键词： Deformation,Agricultural Machinery,Moiré Technique,Strain,Material Mechanical Behavior Analysis
更新于2025-09-04 15:30:14
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Fracture behaviors of a piezoelectric-piezomagnetic sandwich structure under electromechanical loads: plane problem
摘要： The fracture behaviors of a piezoelectric-piezomagnetic sandwich structure with an eccentric internal crack subjected to two kinds of in-plane electromechanical loads have been studied in this paper. A singular integral equation with Cauchy kernel is obtained by means of Fourier transform and further solved by using Gauss-Chebyshev technique. Then the stress intensity factors are obtained and some numerical results are presented to show the e?ects of the material properties, structure geometries, electromechanical loads and the crack location on the stress intensity factors. The conclusions of the present paper may be useful for the design and fracture prediction of layered piezoelectric-piezomagnetic structures.
关键词： sandwich structure,stress intensity factor,plane strain problem,integral transformation,Piezoelectric-Piezomagnetic composite
更新于2025-09-04 15:30:14
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Influência do Strain e da Intera??o Spin-órbita em um Ponto Quantico Cilíndrico
摘要： In this work study how the strain and spin-orbit Rashba interaction type affect the energy levels of the conduction band in a cylindrical quantum dot, using the 2x2 method k●p. The results show that the spin-orbit interaction strongly influences the energy levels of lifting the degeneracy even in zero magnetic field, while the strain compressing the levels enhance the Rashba interaction effects. In this context, the intraband optic absorption becomes a useful tool to study the effects of spin-orbit interaction and the strain on the electron energy levels.
关键词： k●p method,Conduction Band,Quantum dots,Strain,Spin-orbit Rashba interaction
更新于2025-09-04 15:30:14