- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Fiber Path Optimization in a Variable-Stifness Cylinder to Maximize Its Buckling Load Under External Hydrostatic Pressure
摘要： The optimum paths and orientations for curvilinear and straight fibers in composite cylindrical shells of variable and constant stiffness under external hydrostatic pressure are obtained and compared. The optimization was performed for several length-to-diameter ratios of the shells. Results showed that the buckling pressure of the variable-stiffness shell was by about 30% higher than that of the constant-stiffness one. This increase in the buckling pressure was obtained by locating fibers in the hoop direction in the middle of the cylinder and orienting the fibers toward the longitudinal direction on cylinder edges.
关键词： variable stiffness,cylindrical shell,external hydrostatic pressure,buckling,curvilinear fiber
更新于2025-09-23 15:23:52
-
Size-Dependent Buckling and Vibrations of Piezoelectric Nanobeam with Finite Element Method
摘要： In the present paper, a finite element method is used to study the vibrations and buckling of a piezoelectric nanobeam. The beam theory used here is Bernoulli–Euler model. In order to achieve the goal, first, the governing equations of the piezoelectric nanobeam were obtained via the Hamilton principle, based on the higher-order theory such as modified couple stress. The shape functions were embedded in these equations, and the matrix form of the equations was obtained. In other words, the governing equations were discretized by the finite element method. By calculating the matrix form of equations, mass matrices, mechanical stiffness and electrical stiffness of the beam were obtained. It should be noted that when calculating stiffness matrices, first, the definition of a new element must be added to the effects of the electric field in the elements of the beam, and the effects of the gradient of strain should be added in the form of non-classical matrix to the stiffness matrix. With the aid of these critical load matrices, the buckling force and voltage and the natural frequency of the piezoelectric nanobeam have been calculated. Numerical results show that this method can involve the size effects.
关键词： Size effect,Piezoelectric,Buckling voltage,Couple stress theory,Free vibration,Buckling load
更新于2025-09-23 15:22:29
-
Single-Layer Ag <sub/>2</sub> S: A Two-Dimensional Bidirectional Auxetic Semiconductor
摘要： Two-dimensional auxetic materials have attracted considerable attention due to their potential applications in medicine, tougher composites, defense and so on. However, they are scare especially at low dimension, as auxetic materials are mainly realized in engineered materials and structures. Here using first-principles calculations, we identify a compelling two-dimensional auxetic material, single-layer Ag2S, which possesses large negative Poisson’s ratios in both in-plane and out-of-plane directions, but anisotropic ultra-low Young’s modulus. Such a coexistence of simultaneous negative Poisson’s ratios in two directions is extremely rare, which is mainly originated from its particular zigzag-shaped buckling structure. In addition, contrary to the previously known metal-shrouded single-layer M2X (M = metal, X = nonmetal), single-layer Ag2S is the first nonmetal-shrouded M2X. Electronic calculations show that it is an indirect-gap semiconductor with gap value of 2.83 eV, and it can be turned to be direct with strain. These intriguing properties make single-layer Ag2S a promising auxetic material in electronics and mechanics.
关键词： ultra-low Young’s modulus,two-dimensional,buckling structure,auxetic material
更新于2025-09-23 15:22:29
-
[IEEE 2019 IEEE International Symposium on Applications of Ferroelectrics (ISAF) - Lausanne, Switzerland (2019.7.14-2019.7.19)] 2019 IEEE International Symposium on Applications of Ferroelectrics (ISAF) - Vibrating Piezoelectric Energy Conversion Efficiency of Sol-Gel PZT Films with Various Crystal Orientations on MEMS Buckled Diaphragm Structures
摘要： Vibrating energy conversion efficiency was investigated on piezoelectric transducers fabricated on MEMS buckled diaphragm structures from the viewpoint of crystal orientation of sol-gel derived lead-zirconate-titanate (PZT) films. The crystal orientation dominates in-plane stress and spontaneous polarization direction of the PZT films. The in-plane stress affects the static buckling of the diaphragm where a large convex buckling results in a high mechanical conversion efficiency from the flexural vibration to the in-plain vibration. The polarization direction affects the intrinsic piezoelectric conversion efficiency. The crystal orientation of the sol-gel PZT was controlled through pyrolysis temperature between 250?C and 350?C, resulting in a texture variation from (100)-oriented films to (111)-oriented ones. Highly (111)-oriented films showed large polarizations but small buckling deflections, while highly (100)-oriented films showed vice versa. Intermediately textured films with 40–45% (111)-orientation index showed the highest conversion efficiency.
关键词： Piezoelectric,Sol-gel,Residual stress,Buckling,PZT,Polarization,Energy conversion,Diaphragm
更新于2025-09-19 17:13:59
-
Interface Stress for Bidirectional Frequency Tuning of Prebuckled Vanadium Dioxide MEMS Resonators
摘要： Interface stress between structural materials and thin film coatings has a significant influence on the resonant frequency of microelectromechanical system (MEMS) resonators. In this work, the axial stress on different types of buckled bridge MEMS resonator structures is controlled through the solid-to-solid phase transition of a VO2 thin film coating. The devices have identical dimensions, but different buckling orientations and profiles due to the combined effect of overetching and residual thermal stress mismatch. Thermal actuation is used to tune the resonant frequency of the device, but the changes in frequency are found to be dependent on the type of buckling for the device. Thermal actuation is achieved by applying an electrical current to integrated heaters, or by uniform substrate heating. Bidirectional tunability is found when substrate heating is used, while Joule heating shows a monotonic change in frequency. This phenomenon can be attributed to the transition in boundary conditions, where the turning points are indicated by the prominent changes in buckling amplitude. In addition, devices with opposite buckling orientations exhibit different tuning behaviors which can be explained by different bending moments induced by beam stress interface modification.
关键词： MEMS resonators,interface stress,buckling,vanadium dioxide,resonant frequency tuning
更新于2025-09-19 17:13:59
-
Buckled Conductive Polymer Ribbons in Elastomer Channels as Stretchable Fiber Conductor
摘要： Conductors that can sustain large strains without change in resistance are highly needed for wearable electronic systems. Here, the fabrication of highly stretchable coaxial fiber conductors through self-buckling of conductive polymer ribbons inside thermoplastic elastomer channels, using a “solution stretching–drying–buckling” process, is reported. The unique hierarchically buckled and conductive core in the axial direction makes the resistance of the fiber very stable, with less than 4% change when applying as much as 680% strain. These fibers can then be directly used as stretchable electrical interconnects or wearable heaters.
关键词： resistance change,conductive polymers,buckling,stretchable fiber conductors,coaxial fibers
更新于2025-09-16 10:30:52
-
Size-dependent instability of organic solar cell resting on Winkler-Pasternak elastic foundation based on the modified strain gradient theory
摘要： The present study employs the modified strain gradient theory (MSGT) in conjunction with the refined shear deformation plate theory to explore the buckling behaviour of simply supported and clamped OSC. The Winkler-Pasternak elastic foundation is implemented to idealise the foundation. The size-dependent effect of the OSC is captured by the three length scale parameters within the MSGT. The Hamilton principle is used to derive the equations of motion and the boundary conditions, and the Galerkin procedure is subsequently implemented to obtain the critical buckling load. Subsequently, the framework is extended to the thermally induced buckling behaviour, and three types of temperature rise patterns, namely uniform, linear and nonlinear temperature variations, along the thickness of the OSC are considered. Several verification studies are conducted to illustrate the accuracy of the present method. Besides, size-dependent material properties are taken into consideration during the numerical experiments. Thorough studies are conducted to demonstrate the difference between critical buckling loads and temperature variations obtained from the MSGT, the modified couple stress theory (MCST), and the classical plate theory (CPT) models. Furthermore, the effects of length scale parameter (hl), the aspect ratio (ab), the length-to-thickness ratio (ah) and the Winkler-Pasternak elastic foundation parameters on the buckling behaviour of the OSC are also revealed by the numerical results.
关键词： Refined shear deformation plate theory,Strain gradient elasticity theory,Thermal buckling,Organic solar cell,Mechanical buckling,Elastic foundation
更新于2025-09-12 10:27:22
-
A Resonant Gas Sensor Based on Multimode Excitation of a Buckled Microbeam
摘要： We report a new gas sensing technique based on the simultaneous tracking of multiple modes of vibration of an electrothermally heated bridge resonator operated near the buckling point. The proposed technique maximizes the sensitivity of the sensor to changes in gases concentrations. We demonstrate a 200% frequency shift in contrast to 0.5% resistance change using the conventional resistive technique. The method also demonstrates selective identification for some gases without the need for surface functionalization of the microstructure. The proposed method is simple in principle and design and is promising for achieving practical low-cost gas sensors.
关键词： buckling point,multimode,Gas sensor,heated microbeam
更新于2025-09-12 10:27:22
-
Atomic and electronic structure of the Si(331)-(12 × 1) surface
摘要： We report on the investigation of the atomic and electronic structures of a clean Si(331)-(12 × 1) surface using a first-principles approach with both plane wave and strictly localized basis sets. Starting from the surface structure proposed by Zhachuk and Teys [Phys. Rev. B 95, 041412(R) (2017)], we develop significant improvements to the atomic model and localized basis set which are critical for the correct description of the observed bias dependence of scanning tunneling microscopy (STM) images. The size mismatch between the Si pentamers from the surface model and those seen by STM is explained within the context of the Tersoff-Hamann model. The energy barriers that separate different Si(331) buckled configurations were estimated, showing that the surface structure is prone to dynamic buckling at room temperature. It is found that empty electronic states on Si(331) are essentially localized on the pentamers with interstitials and under-coordinated Si sp2-like atoms between them, while filled electronic states are localized on under-coordinated Si sp3-like atoms and dimers on trenches. The calculated electronic density of states exhibits two broad peaks in the fundamental bandgap of Si: one near the valence band top and the other near the conduction band bottom. The resulting surface bandgap of 0.58 eV is in an excellent agreement with spectroscopy studies.
关键词： scanning tunneling microscopy,Si(331)-(12 × 1) surface,first-principles approach,electronic density of states,Tersoff-Hamann model,atomic and electronic structures,dynamic buckling
更新于2025-09-10 09:29:36
-
Nonlinear torsional buckling and postbuckling analysis of cylindrical silicon nanoshells incorporating surface free energy effects
摘要： In the present study, a size-dependent shell model is developed which can afford to describe the nonlinear torsional buckling and postbuckling characteristics of cylindrical nanoshells in the presence of surface stress effects. To accomplish this purpose, the Gurtin–Murdoch theory of elasticity together with the von Karman geometric nonlinearity is implemented into the ?rst-order shear deformation shell theory. A linear variation through the thickness is considered for the normal stress component of the bulk to satisfy the balance conditions on the free surfaces of the nanoshell. By means of the virtual work principle, the non-classical governing differential equations are constructed in which the transverse displacement and Airy stress function are considered as independent variables. Thereafter, a boundary layer theory is employed including the effect of surface stress in conjunction with the nonlinear prebuckling deformations and the large postbuckling de?ections. Subsequently, an ef?cient solution methodology based on an improved perturbation technique is put to use to obtain the size-dependent critical torsional buckling loads and the associated postbuckling equilibrium paths. It is observed that the torsional load exhibits a signi?cant increase after reaching the minimum postbuckling load. Also, it is revealed that the effect of surface stress becomes negligible at high values of the de?ection.
关键词： First-order shear deformation shell theory,Nonlinear torsional buckling,Postbuckling analysis,Surface free energy effects,Cylindrical silicon nanoshells,Gurtin–Murdoch theory,von Karman geometric nonlinearity
更新于2025-09-10 09:29:36