190 research outputs found
Damage identification in beams based on the observation of frequencies and modal curvatures
No full textThis work investigates numerically and experimentally the dynamic response of a free-free beam in its undamaged and damaged states, in terms of natural frequencies and modal curvatures. The damage consists of a height reduction extending to all the base of the cross section, and is described by three parameters, that are: depth of the height reduction, extension, location of its axis of symmetry along the beam axis. The resulting direct problem is solved via a 2D plane-stress finite element analysis, covering a dense grid of the three damage parameters. Several experimental tests are conducted on steel beams, covering selected values of damage parameters, and using strain gauges with grids of different lengths to understand how this sensor characteristic affects the measurement of the strain. The natural frequencies and modal curvatures obtained from the solution of this direct eigenvalue problem are compared to their experimental counterpart to evaluate the capability of the model to describe real data. Furthermore, the solution of the inverse problem of damage identification is carried out, providing some insight into the identifiability of the three damage parameters. The solution of the inverse problem is approached minimizing objective functions that measure the differences between numerical and pseudo-experimental and experimental variations of natural frequencies and/or of modal curvatures in the undamaged and damaged states
The effect of uniformly distributed carbon nanotubes and rotation on the frequencies of fiber metal laminated cylindrical shells
No full textIn this manuscript, the effects of carbon nanotubes and rotation on the free vibration of fiber metal laminated circular cylindrical shell based on Love’s first approximation theory have been studied. The representative volume element is consisting of four phases: fiber, carbon nanotubes (CNTs), polymer matrix and metal. Initially, the CNTs have been added to the matrix and then the fiber phase has been reinforced by them. Finally, the adhesive fiber prepreg has been combined with the thin metal layers. The generated cylindrical shell can be named CNT/fiber/polymer/metal laminates (CNTFPMLs) cylindrical shell. The effects of different parameters such as lay-ups, volume fractions of metal and composite sections, mass fraction of CNTs on the frequencies of CNTFPMLs cylindrical shell with respect to rotational speed have been considered. The results demonstrated that the frequency changes of CNTFPMLs cylindrical shell are different with growing for various volume fraction of fiber. The difference between backward and forward modes for different mass fractions increase with growing th
Agglomeration effects on the vibrations of CNTs/fiber/polymer/metal hybrid laminates cylindrical shell
No full textThis work studies the agglomeration effect of continuously graded single-walled carbon nanotubes (SWCNTs) on the vibration of SWCNTs/fiber/polymer/metal laminates cylindrical shell. The strain-displacement relations are applied according to the Kirchhoff Love’s first approximation shell theory, whereas the dimensionless frequencies of the structure are obtained by means of the beam modal function model. Fiber, carbon nanotubes (CNTs), polymer matrix and metal are four phases constituting the agglomerated CNTs/fiber/polymer/metal laminate (CNTFPML) cylindrical shell. In the first step, we introduce the CNTs randomly within the matrix, such that the volume fraction can be assumed to be continuously graded in the thickness direction. We determine the effect of the CNTs agglomeration on the elastic properties of CNT-reinforced composites, by means of the Eshelby-Mori-Tanaka approach here applied on an equivalent fiber. In the second step, the fiber is introduced as reinforcement phase in the CNT-reinforced composite. Finally, the adhesive fiber prepreg is combined with the thin metal layers. Thus, we study the sensitivity of the vibration behavior of the cylindrical shell to the following input parameters, namely: the CNTs agglomeration and distribution, the mass and volume fractions of the fiber, the boundary condition and lay-ups
Modeling creep behavior of carbon nanotube/fiber/polymer composite cylinders
No full text In this research, the effects of multi-walled carbon nanotubes on the distribution of long-term creep strains in thick-walled multi-walled carbon nanotube/fiber/polymer three-phase laminated composites are studied. In the first step, micromechanical models are developed to calculate the elastic properties of multi-walled carbon nanotube/vinylester and multi-walled carbon nanotube/E-glass fiber/vinylester composites. Using classical lamination plate theory, equilibrium and compatibility equations and strain–displacement relations, the distribution of effective stresses is considered. Moreover, utilizing Schapery single-integral model for nonlinear viscoelastic materials, Prandtl–Reuss relations and Mendelson’s approximation method, not only the distribution of circumferential and radial strains is investigated but also the effects of fiber orientation and weight fraction (wt.%) of the multi-walled carbon nanotubes on the way of distribution are studied. The results demonstrated that the addition of the multi-walled carbon nanotube to the vinylester can reduce absolute values of the radial and circumferential creep strains and dimensionless effective stresses. Moreover, most reduction occurred in the inner wall of the cylindrical shell when fiber orientation was α = 90°. </jats:p
DR. TAHIR TAUNSVI'S WORK ON MASOOD HASSAN RIZVI ADEEB
No full textDr. Tahir Taunsvi is a well-known and acclaimed researcher, critic, and poet of Urdu language and literature. His, more than seventy remarkable books (compilations and compositions) are a great contribution to Urdu research and criticism. He has also written more than three hundred valuable research articles. He introduced many literary personalities to the arena of the Urdu language and literature. Prominent Indian researcher and critic Syed Masood Hassan Rizvi Adeeb and his literary dimensions are an important field of Dr. Tahir Taunsvi’s research work. In this article, the authors have presented an analytical study of the following four research books of Dr. Tahir Taunsvi. Masood Hassan Rizvi Adeeb: Hayat Aur Karnamay, Lakhnawyat_e _Adeeb, Razm Nama Anees O Dabeer Taaruf O Taqabal, Masood Hassan Rizvi Adeeb, Kitabyaat. In these detailed and comprehensive research books, the author has unfolded the life history, different literary dimensions (especially, as a critic, researcher, and poet), and the worth of literary achievements of Syed Masood Hassan Rizvi Adeeb. This study not only unveils the salient features of these exceptional research books of Dr. Tahir Taunsvi but also throws light on the multidimensional literary aspects of renowned writer Masood Hassan Rizvi Adeeb
Four kilobyte memory array for Magnetic Random Access Memory development
No full textThesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 129-131).The circuits for a A 4kb array of Magnetic Tunnel Junctions (MTJs) have been designed and fabricated in a 0:18¹m CMOS process with three levels of metal. Support circuitry for addressing, reading, writing, and test mode probing enables the characterization of the switching of a thin-film ferromagnetic layer in the MTJs. Specifically, novel mechanisms involving spin-transfer or thermal assistance can be studied and compared to current MRAM designs that switch the MTJ with current-induced magnetic fields. Using this array design, both high speed digital and quasi-static dI/dV experiments can be conducted to investigate the nature of the MTJ resistance hysteresis and process variation in addition to the switching behavior under both polarities of current.by Masood Qazi.M.Eng
Free vibration analysis of rotating fiber–metal laminate circular cylindrical shells
No full text In this article, free vibration of rotating fiber–metal laminate thin circular cylindrical shells has been analyzed. Strain–displacement relations have been obtained based on Love’s first approximation shell theory. The variations of frequencies of the fiber–metal laminate cylindrical shell with rotational speeds for different axial and circumferential wave numbers, L/R ratios, metal thicknesses and volume fractions of metal have been presented. Also, free vibrations of the rotating fiber–metal laminate shell have been studied for carbon/epoxy, glass/epoxy and aramid/epoxy composite materials combining thin aluminum layers. The results showed that with increasing rotating speed, the gap between backward and forward waves frequencies increased. </jats:p
مختار مسعود کی تحریروں میں فلیش بیک کی تکنیک
No full textVarious stylistic techniques are used by the writers to illuminate their text as well as to convey the essence of their works to the readers. "Flash back" is one of these techniques. The famous urdu writer Mukhtar Masood has also used this very technique in a successful manner. In this article, the author has ciritically analysed the used of the said technique in the works of Mukhtar Masood
A Design Tool for Passive Wrist Support
No full textA design tool for passive wrist support using compliant spatial beams as gravity balancer is presented. The aim of this assistive device is to reduce required effort for pronation-supination and flexion-extension by 70% to help patients with muscular weakness keeping their hand’s posture and doing daily tasks, while the forearm is rested. To reach this goal, a setup with three connection points to the user’s hand, and two optimized spatial beams as elastic gravity compensators, are developed. The overall shape and cross-sectional dimensions of the compliant beams are attained using an optimization technique. The objective is reaching a desired endpoint kinetostatic behaviour which is determined based on the hand’s weight and available muscular forces. A design case is presented to show the ability of the method, and the final errors from the desired behaviour are clarified. In the end, possible further applications of the design tool are discussed.Accepted Author ManuscriptMechatronic Systems DesignPrecision and Microsystems Engineerin
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