5,559 research outputs found
Analysis of Piezoelectric Ceramic Multi-layer Actuators Basedon the Electro-mechanical Coupled Meshless Method
No full textThis paper presents an efficient meshless method for analyzing cracked piezoelectric structures subjected to mechanical and electrical loading. The method employs an element free Galerkin(EFG) formulation and an enriched basic function as well as special shape functions that contain discontinuous derivatives. Based on the moving least squares (MLS) interpolation approach, The EFG method is one of the promising methods for dealing with problems involving progressive crack growth. Since the method is meshless and no element connectivity data are needed, the burdensome remeshing procedure required in the conventional finite element method (FEM) is avoided. The numerical results show that the proposed method yields an accurate near-tip stress field in an infinite piezoelectric plate containing an interior hole. Another example is to study a ceramic multilayer actuator. The proposed model was found to be accurate in the simulation of stress and electric field concentrations due to the abrupt end of an internal electrode
Fracture mechanics of piezoelectric and ferroelectric solids
No full textFracture Mechanics of Piezoelectric and Ferroelectric Solids presents a systematic and comprehensive coverage of the fracture mechanics of piezoelectric/ferroelectric materials, which includes the theoretical analysis, numerical computations and experimental observations. The main emphasis is placed on the mechanics description of various crack problems such static, dynamic and interface fractures as well as the physical explanations for the mechanism of electrically induced fracture. The book is intended for postgraduate students, researchers and engineers in the fields of solid mechanics, applied physics, material science and mechanical engineering. Dr. Daining Fang is a professor at the School of Aerospace, Tsinghua University, China; Dr. Jinxi Liu is a professor at the Department of Engineering Mechanics, Shijiazhuang Railway Institute, China
Damage characterizations and simulation of selective laser melting fabricated 3D re-entrant lattices based on in-situ CT testing and geometric reconstruction
No full textIn recent years, metal additive manufacturing (AM) are widely employed for industrial applications, such as: biomedical, aerospace, automotive, marine and offshore sections. AM demonstrated superior manufacturing efficiencies and economic advantages for advanced lightweight industrial components with unlimited arbitrary topological layouts and complex internal microstructures, and are also employed for fabrication of auxetic materials and structures. In this paper, damage characterizations and mechanical behaviors of selective laser melting (SLM) fabricated 3D re-entrant lattices are investigated based on in-situ interrupted micro-CT test, and simulation based on geometric reconstructed models are performed for exploring the underlying failure mechanisms. Firstly, theoretical models for predicting the mechanical properties of 3D re-entrant lattice are developed, such as stiffness, Poisson's ratio and strength, etc. Secondly, the geometrical errors and fabrication defects of 3D reentrant lattices are analyzed based on 3D micro-CT scanning, in-situ micro-CT interrupted compression tests are performed for studying the deformation process and failure mechanisms. Finally, image finite element models with the detailed information of the shape, position and distribution of defects of the 3D reentrant lattices are constructed from 3D tomographic images, and numerical simulations are performed for studying the effects of the defects on the mechanical performances of the SLM additive manufactured 3D re-entrant lattice structures. It is shown that the failure behavior of the reentrant lattice is governed not only by its topology, but also by the geometric defects and surface defects. Moreover, the proposed interrupted in-situ micro-CT mechanical loading experiments and image finite element approaches can also shed lights on the relations between fracture failure around the edge and the powder adhesion. The damage evolution process is compared with the numerical simulation results to verify the materials failure modes
Fang Fang
No full textBiochemistry & Molecular BiologyCell BiologySCI(E)0EDITORIAL MATERIAL12R444-R4462
Does Downloading PowerPoint Slides Before the Lecture Lead to Better Student Achievement?: Reply
No full textThis reply responds to a comment by Cannon (2011) that opens the debate on consistency of the effect of downloading PowerPoint slides before lectures on students’ exam performance. Cannon (2011) points out potential endogeneity problems in Chen and Lin (2008) and attempts to explore the unconditional mean effect of downloading PowerPoint slides for the full sample. In this reply, we firstly argue that the estimates in our original article are consistent since the effect of interest is the “conditional†treatment effect but not the unconditional mean effect. We provide explanations for our rationale of estimating the “conditional†treatment effect. Secondly, we propose a modified downloading variable to replicate Cannon’s analysis. Our results suggest that downloading PowerPoint slides before the exam does not produce a significant effect on absent students’ exam performance which is different from the results in Cannon (2011). Our analysis does support Cannon’s argument that students fixed effects are different across different attendance status.
Preliminary Study on Ductile Fracture of Imperfect Lattice Materials
No full textThe ductile fracture behavior of two-dimensional imperfect lattice material under dynamic stretching is studied by finite element analyses (FEA). Three isotopic lattice materials, including the regular hexagonal honeycomb, the Kagome lattice and the regular triangular lattice, are taken into account, which are made of an elastic/visco-plastic metal material. Two typical imperfections (vacancy defect and rigid inclusion) are introduced separately. The numerical results reveal novel deformation modes and crack growth patterns in the ductile fracture of lattice material. Various crack growth patterns as defined according to their profiles, such as "X"-type, "Butterfly"-type, "Petal"-type. Crack propagation could induce severe material softening and plastic dissipation of the lattices. Subsequently, the effects of the strain rate, relative density, microstructure topology, and defect type on the crack growth pattern, the associated macroscopic material softening and the knock-down of total plastic dissipation are investigated.Materials Science, MultidisciplinaryMaterials Science, Characterization & TestingEICPCI-S(ISTP)
Tailoring diffusion-induced stresses of core-shell nanotube electrodes in lithium-ion batteries
No full textCarbon-coated electrode nanoparticles enhance the cycling stability of lithium-ion batteries due to their intrinsic electric conductivity and excellent tolerance to mechanical stress. To study diffusion-induced stresses of these nanocomposites, nanotube electrodes wrapped with carbon shells are investigated including the effects of surface stress. The results of our model show that diffusion-induced stresses strongly depend on the thickness of carbon layer, which should be tuned to endure material strengths, avoiding mechanical fracture. In addition, surface tension produces compressive stresses through the electrode materials, even a tensile state can turn into a state of compressive stress, which may become a resistance to brittle fracture. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4772963]Physics, AppliedSCI(E)EI3ARTICLE1null11
Modeling of magnetoelectric effects in flexural nanobilayers: The effects of surface stress
No full textA model is developed for the effects of surface stress on low-frequency magnetoelectric (ME) effects in flexural magnetostrictive-piezoelectric bilayers, and we further take cobalt ferrite and lead zirconate titanate (PZT) as a specific case. The results show that flexural deformation can suppress the ME voltage coefficient, especially for moderate PZT volume fraction. Owing to residual surface tension, the ME voltage coefficient should depend on magnetic field, and this tendency is weakened with increasing magnetic field. Interestingly, the size dependence of ME voltage coefficient is found when the thickness of bilayer reduces to nanoscale. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795167]Physics, AppliedSCI(E)EI6ARTICLE10null11
Mechanical deformation and fracture mode of polycrystalline graphene: Atomistic simulations
No full textMechanics of polycrystalline graphene are studied through molecular dynamics simulations. Local buckling forms the ridge or funnel centering on pentagon, and fluctuating stress occurs under small tensile strain due to out-of-plane distortion. In addition, brittle breaking is initialized from heptagons and ends with fracture of pentagons. (C) 2012 Elsevier B.V. All rights reserved.Physics, MultidisciplinarySCI(E)0ARTICLE24-251942-194737
Using Google Analytics for improving library website content and design: a case study
No full textGoogle Analytics is a free web analytics solution that provides webmasters with insightful information about how visitors find and interact with their websites. In this case study, we have experimented in using Google Analytics to analyze two of our websites: The Rutgers-Newark Law Library main website and The New Jersey Digital Legal Library website. It was used to monitor our visitors' browsing activities and viewing behaviors for three months. Based on our findings from Google Analytics reports, we have redesigned our website. Subsequent data collected by Google Analytics have confirmed that our new design better fits the information needs of our visitors and librarians. Google Analytics is very powerful and can be used for almost any website. We believe that other libraries will benefit from using Google Analytics as well. Limitations of Google Analytics are also discussed based on our experience with it.The published version of this article is available at: http://www.webpages.uidaho.edu/~mbolin/lpp2007.htm"June, 2007
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