International Nuclear Information System (INIS)
Bennett, J.G.; Fly, G.W.; Baker, W.E.
1984-01-01
The Steel Containment Buckling program is in its fourth phase of work directed at the evaluation of the effects of the structural failure mode of steel containments when the membrane stresses are compressive. The structural failure mode for this state of stress is instability or buckling. The program to date has investigated: (1) the effect on overall buckling capacity of the ASME area replacement method for reinforcing around circular penetrations; (2) a set of benchmark experiments on ring-stiffened shells having reinforced and framed penetrations; (3) large and small scale experiments on knuckle region buckling from internal pressure and post-buckling behavior to failure for vessel heads having torispherical geometries; and (4) buckling under time-dependent loadings (dynamic buckling). The first two investigations are complete, the knuckle buckling experimental efforts are complete with data analysis and reporting in progress, and the dynamic buckling experimental and analytical work is in progress
Habibi, M.; Rahmani, Y.; Bonn, D.; Ribe, N.M.
2010-01-01
Under appropriate conditions, a column of viscous liquid falling onto a rigid surface undergoes a buckling instability. Here we show experimentally and theoretically that liquid buckling exhibits a hitherto unsuspected complexity involving three different modes—viscous, gravitational, and
Buckling of Bucket Foundations
DEFF Research Database (Denmark)
Madsen, Søren; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo
2012-01-01
In this paper, the risk of structural buckling during installation of large-diameter bucket foundations is addressed using numerical methods. Imperfect geometries are introduced based on the pre-buckling mode shapes from a linear Eigenvalue buckling analysis. Various imperfect geometries are intr...
Shama, Mohamed
2013-01-01
Buckling of Ship Structures presents a comprehensive analysis of the buckling problem of ship structural members. A full analysis of the various types of loadings and stresses imposed on ship plating and primary and secondary structural members is given. The main causes and consequences of the buckling mode of failure of ship structure and the methods commonly used to control buckling failure are clarified. This book contains the main equations required to determine the critical buckling stresses for both ship plating and the primary and secondary stiffening structural members. The critical buckling stresses are given for ship plating subjected to the induced various types of loadings and having the most common boundary conditions encountered in ship structures. The text bridges the gap existing in most books covering the subject of buckling of ship structures in the classical analytical format, by putting the emphasis on the practical methods required to ensure safety against buckling of ship structur...
Shell Buckling Knockdown Factors
National Aeronautics and Space Administration — The Shell Buckling Knockdown Factor (SBKF) Project, NASA Engineering and Safety Center (NESC) Assessment #: 07-010-E, was established in March of 2007 by the NESC in...
International Nuclear Information System (INIS)
Stone, C.M.; Nickell, R.E.
1977-01-01
Because of the characteristics of LMFBR primary piping components (thin-walled, low pressure, high temperature), the designer must guard against creep buckling as a potential failure mode for certain critical regions, such as elbows, where structural flexibility and inelastic response may combine to concentrate deformation and cause instability. The ASME Boiler and Pressure Vessel Code, through its elevated temperature Code Case 1592 (Section III, Division 1) provides design rules for Class 1 components aimed at preventing creep buckling during the design life. A similar set of rules is being developed for Class 2 and 3 components at this time. One of the original concepts behind the creep buckling rules was that the variability in creep properties (especially due to the effects of prior heat treatment), the uncertainty about initial imperfections, and the lack of confirmed accuracy of design analysis meant that conservatism would be difficult to assure. As a result, a factor of ten on service life was required (i.e. analysis must show that, under service conditions that extrapolate the life of the component by ten times, creep buckling does not occur). Two obvious problems with this approach are that: first, the creep behavior must also be extrapolated (since most creep experiments are terminated at a small fraction of the design life, extrapolation of creep data is already an issue, irrespective of the creep buckling question); second the nonlinear creep analysis, which is very nearly prohibitively expensive for design life histograms, becomes even more costly. Analytical results for an aluminum cylindrical shell subjected to axial loads at elevated temperatures are used to examine the supposed equivalence of two types of time-dependent buckling safety factors - a factor of ten on service life and a factor of 1.5 on loading
Cellular buckling in long structures
Hunt, G.W.; Peletier, M.A.; Champneys, A.R.; Woods, P.D.; Wadee, M.A.; Budd, C.J.; Lord, G.J.
2000-01-01
A long structural system with an unstable (subcritical)post-buckling response that subsequently restabilizes typically deformsin a cellular manner, with localized buckles first forming and thenlocking up in sequence. As buckling continues over a growing number ofcells, the response can be described
Creep buckling of shell structures
International Nuclear Information System (INIS)
Miyazaki, Noriyuki; Hagihara, Seiya
2015-01-01
The present article contains a review of the literatures on the creep buckling of shell structures published from late 1950's to recent years. In this article, the creep buckling studies on circular cylindrical shells, spherical shells, partial cylindrical shells and other shells are reviewed in addition to creep buckling criteria. Creep buckling is categorized into two types. One is the creep buckling due to quasi-static instability, in which the critical time for creep buckling is determined by tracing a creep deformation versus time curve. The other is the creep buckling due to kinetic instability, in which the critical time can be determined by examining the shape of total potential energy in the vicinity of a quasi-static equilibrium state. Bifurcation buckling and snap-through buckling during creep deformation belong to this type of creep buckling. A few detailed descriptions are given to the bifurcation and snap-through type of creep buckling based on the present authors' works. (author)
International Nuclear Information System (INIS)
Butler, T.A.; Baker, W.E.
1987-01-01
Two aspects of buckling of a free-standing nuclear containment building were investigated in a combined experimental and analytical program. In the first part of the study, the response of a scale model of a containment building to dynamic base excitation is investigated. A simple harmonic signal was used for preliminary studies followed by experiments with scaled earthquake signals as the excitation source. The experiments and accompanying analyses indicate that the scale model response to earthquake-type excitations is very complex and that current analytical methods may require that a dynamic capacity reduction factor be incorporated. The second part of the study quantified the effects of framing at large penetrations on the static buckling capacity of scale model containments. Results show little effect from the framing for the scale models constructed from the polycarbonate, Lexan. However, additional studies with a model constructed of the prototypic steel material are recommended. (orig.)
International Nuclear Information System (INIS)
Butler, T.A.; Baker, W.E.
1986-01-01
Two aspects of buckling of a free-standing nuclear steel containment building were investigated in a combined experimental and analytical program. In the first part of the study, the response of a scale model of a containment building to dynamic base excitation is investigated. A simple harmonic signal was used for preliminary studies followed by experiments with scaled earthquake signals as the excitation source. The experiments and accompanying analyses indicate that the scale model response to earthquake-type excitations is very complex and that current analytical methods may require a dynamic capacity reduction factor to be incorporated. The second part of the study quantified the effects of framing at large penetrations on the static buckling capacity of scale model containments. Results show little effect from the framing for the scale models constructed from the polycarbonate, Lexan. However, additional studies with a model constructed of the prototypic steel material are suggested
Thermal ratcheting and progressive buckling
International Nuclear Information System (INIS)
Lebey, J.; Brouard, D.; Roche, R.L.
1983-01-01
Pure elastic buckling is not a frequent mode of failure and plastic deformations often occurs before buckling - like instability does. Elastic-plastic buckling is very difficult to analyse. The most important difficulty is the material modeling. In the elastic plastic buckling phenomena, small modifications of the material constitutive equation used are of great influence on the final result. When buckling cannot occurs, it is well known that distortion due to applied loads is greatly amplified when there is also some cyclic straining (like thermal stresses). This effect is called ratcheting - and thermal ratcheting when caused by cyclic thermal transients. As cyclic thermal stresses can be applied in addition of load able to cause buckling failure of a component, the question arise of the effect of cyclic thermal stresses on the critical buckling load. The aim of the work presented here is to answer that question: 'Is the critical buckling load reduced when cyclic straining is added'. It seems sensible to avoid premature computation based only on arbitrary assumptions and to prefer obtaining a sound experimental basis for analysis. Sufficient experimental knowledge is needed in order to check the validity of the material modeling (and imperfections) used in analysis. Experimental tests on buckling of compressed columns subjected to cyclic straining have been performed. These experiments are described and results are given. The most important result is cyclic straining reduces the critical buckling load. It appears that distortion can be increasing progressively during cyclic straining and that buckling can happen at last at compressive loads too small to cause buckling in the absence of cyclic straining. (orig./RW)
Energy Technology Data Exchange (ETDEWEB)
Yang, Dian; Whitesides, George M.
2017-12-26
A soft actuator is described, including: a rotation center having a center of mass; a plurality of bucklable, elastic structural components each comprising a wall defining an axis along its longest dimension, the wall connected to the rotation center in a way that the axis is offset from the center of mass in a predetermined direction; and a plurality of cells each disposed between two adjacent bucklable, elastic structural components and configured for connection with a fluid inflation or deflation source; wherein upon the deflation of the cell, the bucklable, elastic structural components are configured to buckle in the predetermined direction. A soft actuating device including a plurality of the soft actuators and methods of actuation using the soft actuator or soft actuating device disclosed herein are also described.
Computerized Buckling Analysis of Shells
1981-06-01
Simple Examples to Illu-trate Various Types of Buckling Column Buckling In order to make the discussion of the basic concepts introduced in connec...the optimum design of a square box column obtained from an "* analysis in which the effective width concept is used and collapse is assumed to occur...nology, Delft., pp 335-344 (1969). 120 Save, M., "Verification experimentale de l’analyse limite plastique des plaques et des coques en acier doux
Creep buckling analysis of shells
International Nuclear Information System (INIS)
Stone, C.M.; Nickell, R.E.
1977-01-01
The current study was conducted in an effort to determine the degree of conservatism or lack of conservatism in current ASME design rules concerning time-dependent (creep) buckling. In the course of this investigation, certain observations were made concerning the numerical solution of creep buckling problems. It was demonstrated that a nonlinear finite element code could be used to solve the time-dependent buckling problem. A direct method of solution was presented which proved to be computationally efficient and provided answers which agreed very well with available analytical solutions. It was observed that the calculated buckling times could vary widely for small errors in computed displacements. The presence of high creep strain rates contributed to the prediction of early buckling times when calculated during the primary creep stage. The predicted time estimates were found to increase with time until the secondary stage was reached and the estimates approached the critical times predicted without primary creep. It can be concluded, therefore, that for most nuclear piping components, whose primary creep stage is small compared to the secondary stage, the effect of primary creep is negligible and can be omitted from the calculations. In an evaluation of the past and current ASME design rules for time-dependent, load controlled buckling, it was concluded that current use of design load safety factors is not equivalent to a safety factor of ten on service life for low creep exponents
Radiologic Findings in Hydrated Hydrogel Buckles
International Nuclear Information System (INIS)
Lee, Sung Bok; Lee, Nam Ho; Jo, Young Joon; Kim, Jung Yeul; Lee, Yeon Hee; Kim, Song Soo
2008-01-01
Hydrogel buckles, which are used in scleral buckling surgery for retinal detachment, have been associated with late complications after successful retinal reattachment surgery, including strabismus, extraocular motility restriction, extrusion through the eyelid or conjunctiva, intraocular erosion, and scleral erosion. Hydrogel buckles sometimes appear as well-marginated, circumferential, lobulating, contoured cystic masses mimicking orbital cysts on orbital CT or MRI. We report the radiologic findings in 5 patients whose hydrogel buckles needed to be differentiated from orbital cysts
Radiologic Findings in Hydrated Hydrogel Buckles
Energy Technology Data Exchange (ETDEWEB)
Lee, Sung Bok; Lee, Nam Ho; Jo, Young Joon; Kim, Jung Yeul; Lee, Yeon Hee; Kim, Song Soo [Chungnam National University, Daejeon (Korea, Republic of)
2008-11-15
Hydrogel buckles, which are used in scleral buckling surgery for retinal detachment, have been associated with late complications after successful retinal reattachment surgery, including strabismus, extraocular motility restriction, extrusion through the eyelid or conjunctiva, intraocular erosion, and scleral erosion. Hydrogel buckles sometimes appear as well-marginated, circumferential, lobulating, contoured cystic masses mimicking orbital cysts on orbital CT or MRI. We report the radiologic findings in 5 patients whose hydrogel buckles needed to be differentiated from orbital cysts.
Buckling feedback of the spectral calculations
International Nuclear Information System (INIS)
Jing Xingqing; Shan Wenzhi; Luo Jingyu
1992-01-01
This paper studies the problems about buckling feedback of spectral calculations in physical calculations of the reactor and presents a useful method by which the buckling feedback of spectral calculations is implemented. The effect of the buckling feedback in spectra and the broad group cross section, convergence of buckling feedback iteration and the effect of the spectral zones dividing are discussed in the calculations. This method has been used for the physical design of HTR-10 MW Test Module
Buckling of Aluminium Sheet Components
Hegadekatte, Vishwanath; Shi, Yihai; Nardini, Dubravko
Wrinkling is one of the major defects in sheet metal forming processes. It may become a serious obstacle to implementing the forming process and assembling the parts, and may also play a significant role in the wear of the tool. Wrinkling is essentially a local buckling phenomenon that results from compressive stresses (compressive instability) e.g., in the hoop direction for axi-symmetric systems such as beverage cans. Modern beverage can is a highly engineered product with a complex geometry. Therefore in order to understand wrinkling in such a complex system, we have started by studying wrinkling with the Yoshida buckling test. Further, we have studied the buckling of ideal and dented beverage cans under axial loading by laboratory testing. We have modelled the laboratory tests and also the imperfection sensitivity of the two systems using finite element method and the predictions are in qualitative agreement with experimental data.
Buckling a Semiflexible Polymer Chain under Compression
Directory of Open Access Journals (Sweden)
Ekaterina Pilyugina
2017-03-01
Full Text Available Instability and structural transitions arise in many important problems involving dynamics at molecular length scales. Buckling of an elastic rod under a compressive load offers a useful general picture of such a transition. However, the existing theoretical description of buckling is applicable in the load response of macroscopic structures, only when fluctuations can be neglected, whereas membranes, polymer brushes, filaments, and macromolecular chains undergo considerable Brownian fluctuations. We analyze here the buckling of a fluctuating semiflexible polymer experiencing a compressive load. Previous works rely on approximations to the polymer statistics, resulting in a range of predictions for the buckling transition that disagree on whether fluctuations elevate or depress the critical buckling force. In contrast, our theory exploits exact results for the statistical behavior of the worm-like chain model yielding unambiguous predictions about the buckling conditions and nature of the buckling transition. We find that a fluctuating polymer under compressive load requires a larger force to buckle than an elastic rod in the absence of fluctuations. The nature of the buckling transition exhibits a marked change from being distinctly second order in the absence of fluctuations to being a more gradual, compliant transition in the presence of fluctuations. We analyze the thermodynamic contributions throughout the buckling transition to demonstrate that the chain entropy favors the extended state over the buckled state, providing a thermodynamic justification of the elevated buckling force.
Plastic buckling of cylindrical shells
International Nuclear Information System (INIS)
Bandyopadhyay, K.; Xu, J.; Shteyngart, S.; Eckert, H.
1994-01-01
Cylindrical shells exhibit buckling under axial loads at stresses much less than the respective theoretical critical stresses. This is due primarily to the presence of geometrical imperfections even though such imperfections could be very small (e.g., comparable to thickness). Under internal pressure, the shell regains some of its buckling strength. For a relatively large radius-to-thickness ratio and low internal pressure, the effect can be reasonably estimated by an elastic analysis. However, for low radius-to-thickness ratios and greater pressures, the elastic-plastic collapse controls the failure load. in order to quantify the elastic-plastic buckling capacity of cylindrical shells, an analysis program was carried out by use of the computer code BOSOR5 developed by Bushnell of Lockheed Missiles and Space Company. The analysis was performed for various radius-to-thickness ratios and imperfection amplitudes. The purpose of the analytical program was to compute the buckling strength of underground cylindrical tanks, that are used for storage of nuclear wastes, for realistic geometric imperfections and internal pressure loads. This paper presents the results of the elastic-plastic analyses and compares them with other available information for various pressure loads
Buckling shells are also swimmers
Quilliet, Catherine; Dyfcom Bubbleboost Team
We present an experimental and numerical study on the displacement of shells undergoing deformations in a fluid. When submitted to cycles of pressure difference between outside and inside, a shell buckles and debuckles, showing a succession of shapes and a dynamics that are different during the two phases. Hence such objects are likely to swim, including at low Reynolds (microscopic scale). We studied the swimming of buckling/debuckling shells at macroscopic scale using different approaches (force quantization, shape recording, displacement along a frictionless rail, study of external flow using PIV), and showed that inertia plays a role in propulsion, even in situations where dimensionless numbers correspond also to microswimmers in water. Different fluid viscosities were explored, showing an optimum for the displacement. Interestingly, the most favorable cases lead to displacements in the same direction and sense during both motor stroke (buckling phase) and recovery stroke (de-buckling phase). This work opens the route for the synthesis with high throughput of abusively simple synthetic swimmers, possibly gathered into nanorobots, actuated by a scalar field such as the pressure in echographic devices. Universite Grenoble Alpes, CNRS, European Research Council.
Buckling Analysis of Edge Cracked Sandwich Plate
Directory of Open Access Journals (Sweden)
Rasha Mohammed Hussein
2016-07-01
Full Text Available This work presents mainly the buckling load of sandwich plates with or without crack for different cases. The buckling loads are analyzed experimentally and numerically by using ANSYS 15. The experimental investigation was to fabricate the cracked sandwich plate from stainless steel and PVC to find mechanical properties of stainless steel and PVC such as young modulus. The buckling load for different aspect ratio, crack length, cracked location and plate without crack found. The experimental results were compared with that found from ANSYS program. Present of crack is decreased the buckling load and that depends on crack size, crack location and aspect ratio.
Simplified dynamic buckling assessment of steel containments
International Nuclear Information System (INIS)
Farrar, C.R.; Duffey, T.A.; Renick, D.H.
1993-01-01
A simplified, three-degree-of-freedom analytical procedure for performing a response spectrum buckling analysis of a thin containment shell is developed. Two numerical examples with R/t values which bound many existing steel containments are used to illustrate the procedure. The role of damping on incipient buckling acceleration level is evaluated for a regulatory seismic spectrum using the two numerical examples. The zero-period acceleration level that causes incipient buckling in either of the two containments increases 31% when damping is increased from 1% to 4% of critical. Comparisons with finite element results on incipient buckling levels are favorable
Elastic plastic buckling of elliptical vessel heads
International Nuclear Information System (INIS)
Alix, M.; Roche, R.L.
1981-08-01
The risks of buckling of dished vessel head increase when the vessel is thin walled. This paper gives the last results on experimental tests of 3 elliptical heads and compares all the results with some empirical formula dealing with elastic and plastic buckling
A practical rule for progressive buckling
International Nuclear Information System (INIS)
Clement, G.; Acker, D.; Lebey, J.
1989-01-01
Thin structures submitted to compressive loads must be carefully designed to avoid any risk of failure by buckling. When cyclic loadings are concerned, the question to assess their possible detrimental effect on the buckling resistance of thin structures arises. The aim of this paper is, first, to evidence that the critical buckling load may be notably lowered when cyclic strains are added to the compressive load and, secondly, to propose a practical rule of prevention against the failure due to the progressive buckling phenomenon. This rule is validated by the results of numerous tests related to the entire range of modes of buckling (i.e. from fully plastic to fully elastic). Practical cases of interest for its use would mainly be those where cyclic thermal stresses are involved. (orig.)
Review of strain buckling: analysis methods
International Nuclear Information System (INIS)
Moulin, D.
1987-01-01
This report represents an attempt to review the mechanical analysis methods reported in the literature to account for the specific behaviour that we call buckling under strain. In this report, this expression covers all buckling mechanisms in which the strains imposed play a role, whether they act alone (as in simple buckling under controlled strain), or whether they act with other loadings (primary loading, such as pressure, for example). Attention is focused on the practical problems relevant to LMFBR reactors. The components concerned are distinguished by their high slenderness ratios and by rather high thermal levels, both constant and variable with time. Conventional static buckling analysis methods are not always appropriate for the consideration of buckling under strain. New methods must therefore be developed in certain cases. It is also hoped that this review will facilitate the coding of these analytical methods to aid the constructor in his design task and to identify the areas which merit further investigation
Local buckling of composite channel columns
Szymczak, Czesław; Kujawa, Marcin
2018-05-01
The investigation concerns local buckling of compressed flanges of axially compressed composite channel columns. Cooperation of the member flange and web is taken into account here. The buckling mode of the member flange is defined by rotation angle a flange about the line of its connection with the web. The channel column under investigation is made of unidirectional fibre-reinforced laminate. Two approaches to member orthotropic material modelling are performed: the homogenization with the aid of theory of mixture and periodicity cell or homogenization upon the Voigt-Reuss hypothesis. The fundamental differential equation of local buckling is derived with the aid of the stationary total potential energy principle. The critical buckling stress corresponding to a number of buckling half-waves is assumed to be a minimum eigenvalue of the equation. Some numerical examples dealing with columns are given here. The analytical results are compared with the finite element stability analysis carried out by means of ABAQUS software. The paper is focused on a close analytical solution of the critical buckling stress and the associated buckling mode while the web-flange cooperation is assumed.
Macro stress mapping on thin film buckling
Energy Technology Data Exchange (ETDEWEB)
Goudeau, P.; Villain, P.; Renault, P.-O.; Tamura, N.; Celestre, R.S.; Padmore, H.A.
2002-11-06
Thin films deposited by Physical Vapour Deposition techniques on substrates generally exhibit large residual stresses which may be responsible of thin film buckling in the case of compressive stresses. Since the 80's, a lot of theoretical work has been done to develop mechanical models but only a few experimental work has been done on this subject to support these theoretical approaches and nothing concerning local stress measurement mainly because of the small dimension of the buckling (few 10th mm). This paper deals with the application of micro beam X-ray diffraction available on synchrotron radiation sources for stress mapping analysis of gold thin film buckling.
Elastic buckling strength of corroded steel plates
Indian Academy of Sciences (India)
structural safety assessment of corroded structures, residual strength should be ... Rahbar-Ranji (2001) has proposed a spectrum for random simulation of ... The main aim of the present work is to investigate the buckling strength of simply ...
Scleral buckle infection with Alcaligenes xylosoxidans
Directory of Open Access Journals (Sweden)
Chih-Kang Hsu
2014-01-01
Full Text Available We describe a rare case of extraocular inflammation secondary to scleral buckle infection with Alcaligenes xylosoxidans. A 60-year-old female with a history of retinal detachment repair with open-book technique of scleral buckling presented with purulent discharge and irritation in the right eye that had begun 4 weeks earlier and had been treated ineffectively at another hospital. Conjunctival erosion with exposure of the scleral buckle was noted. The scleral buckle was removed and cultured. The explanted material grew gram-negative rod later identified as A. xylosoxidans. On the basis of the susceptibility test results, the patient was treated by subconjunctival injection and fortified topical ceftazidime. After 4 weeks of treatment, the infection resolved.
FLEXURAL, TORSIONAL AND DISTORTIONAL BUCKLING OF ...
African Journals Online (AJOL)
ABSTRACT. Instability is an important branch of structural mechanics which examines alternate ... equations in V and V representing flexural buckling about the two axis of symmetry; a fully. 4 ..... of Thin-Walled Space Systems, First. Edition ...
Computational modelling of buckling of woven fabrics
CSIR Research Space (South Africa)
Anandjiwala, RD
2006-02-01
Full Text Available for reducing unit production cost is critically important if garment industries in developed countries are keen to improve their competitiveness vis-à-vis low labour cost countries. The mechanics of the buckling behaviour of woven fabric started... of woven fabric. INTRODUCTION The buckling, bending and drape behaviours of a woven fabric influence its performance during actual use and during the process of making-up into the end product. These properties are important, particularly when the fabric...
Buckling Behavior of Substrate Supported Graphene Sheets
Directory of Open Access Journals (Sweden)
Kuijian Yang
2016-01-01
Full Text Available The buckling of graphene sheets on substrates can significantly degrade their performance in materials and devices. Therefore, a systematic investigation on the buckling behavior of monolayer graphene sheet/substrate systems is carried out in this paper by both molecular mechanics simulations and theoretical analysis. From 70 simulation cases of simple-supported graphene sheets with different sizes under uniaxial compression, two different buckling modes are investigated and revealed to be dominated by the graphene size. Especially, for graphene sheets with length larger than 3 nm and width larger than 1.1 nm, the buckling mode depends only on the length/width ratio. Besides, it is revealed that the existence of graphene substrate can increase the critical buckling stress and strain to 4.39 N/m and 1.58%, respectively, which are about 10 times those for free-standing graphene sheets. Moreover, for graphene sheets with common size (longer than 20 nm, both theoretical and simulation results show that the critical buckling stress and strain are dominated only by the adhesive interactions with substrate and independent of the graphene size. Results in this work provide valuable insight and guidelines for the design and application of graphene-derived materials and nano-electromechanical systems.
Dynamic buckling of inelastic structures
International Nuclear Information System (INIS)
Pegon, P.; Guelin, P.
1983-01-01
The aim of this paper is to provide research engineers with a method of approach, qualitative feature and order of magnitude of the relevant parameters in the field of dynamic buckling of structures exhibiting constitutive irreversibility and geometrical, constitutive or loading imperfections. It is difficult to adjust some of the classical analysis of the quasi-static elastic case. There remain also some difficulties in justifying the choice of constitutive schemes and in dealing with general kinematic formulation. Moreover, the interpretation of dynamical experimental data is not an easy matter. Consequently, the attempts described here use a simple symbolic model including all essential physical aspects. This symbolic model, of discrete character, is an n-hinged strut with masses located at each n+1 joint. The constitutive properties of the strut and hinge are defined using the same method: a dash-pot is in parallel with a two fold element (spring and friction-slider in series). The intrinsic restrictions are: the two dimensionality assumption, however no additional hypothesis are made concerning the kinematic of the constitutive elements; the use of simple sources of intrinsic dissipation. The relevant question of the longitudinal-transverse coupling effects is studied. Then, after various validation, we verify that a Lagrange resolution of this n+1 body problem gives physical relevant qualitative results concerning rods and cylindrical shells subjected to impact loading. (orig./RW)
An experimental and theoretical investigation of creep buckling
International Nuclear Information System (INIS)
Ohya, H.
1977-01-01
The purpose of the present paper is to investigate creep buckling phenomena and the methods of analysis. Creep buckling experiments were performed on aluminum alloy 2024-T4 cylindrical shells having radius to thickness ratios of 16, 25, 50 and 80, in single, double and triple step axial compression at 250 0 C. It was observed that buckling occurred at one of the edges and the buckling mode depended on the radius to thickness ratio and also on the applied stress level. Thicker cylinders buckled in axisymmetric mode. Thinner ones under higher applied stress levels buckled in the asymmetric mode, whereas they under lower applied stress levels buckled in the axisymmetric mode. Creep buckling times were obtained from end shortening record of the cylinders. Experimental results were compared with theoretical values obtained by the following two methods. One is a simplified method to estimate buckling times, proposed by Gerard et al., Papirno et al. and others. The method is based on the fact that the creep buckling solutions are analogous to those of plastic buckling under a certain assumption. It was found that the bukling times could be reasonably estimated by this simplified method. The other is a finite element computer program for axisymmetric thin shells. This program is based on the incremental theory and can treat thermoelastoplastic creep analysis of axisymmetric thin shells with large deflection. Creep deformation behavior of cylindrical shells under axial compression and buckling times were calculated by the program and the effects of plasticity on buckling times were also investigated
Creep buckling problems in fast reactor components
International Nuclear Information System (INIS)
Ramesh, R.; Damodaran, S.P.; Chellapandi, P.; Chetal, S.C.; Bhoje, S.B.
1995-01-01
Creep buckling analyses for two important components of 500 M We Prototype Fast Breeder Reactor (PFBR), viz. Intermediate Heat Exchanger (IHX) and Inner Vessel (IV), are reported. The INCA code of CASTEM system is used for the large displacement elasto-plastic-creep analysis of IHX shell. As a first step, INCA is validated for a typical benchmark problem dealing with the creep buckling of a tube under external pressure. Prediction of INCA is also compared with the results obtained using Hoff's theory. For IV, considering the prohibitively high computational cost for the actual analysis, a simplified analysis which involves only large displacement elastoplastic buckling analysis is performed using isochronous stress strain curve approach. From both of these analysis is performed using isochronous stress strain curve approach. From both of these analysis, it has been inferred that creep buckling failure mode is not of great concern in the design of PFBR components. It has also been concluded from the analysis that Creep Cross Over Curve given in RCC-MR is applicable for creep buckling failure mode also. (author). 8 refs., 9 figs., 1 tab
The cutting of metals via plastic buckling
Udupa, Anirudh; Viswanathan, Koushik; Ho, Yeung; Chandrasekar, Srinivasan
2017-06-01
The cutting of metals has long been described as occurring by laminar plastic flow. Here we show that for metals with large strain-hardening capacity, laminar flow mode is unstable and cutting instead occurs by plastic buckling of a thin surface layer. High speed in situ imaging confirms that the buckling results in a small bump on the surface which then evolves into a fold of large amplitude by rotation and stretching. The repeated occurrence of buckling and folding manifests itself at the mesoscopic scale as a new flow mode with significant vortex-like components-sinuous flow. The buckling model is validated by phenomenological observations of flow at the continuum level and microstructural characteristics of grain deformation and measurements of the folding. In addition to predicting the conditions for surface buckling, the model suggests various geometric flow control strategies that can be effectively implemented to promote laminar flow, and suppress sinuous flow in cutting, with implications for industrial manufacturing processes. The observations impinge on the foundations of metal cutting by pointing to the key role of stability of laminar flow in determining the mechanism of material removal, and the need to re-examine long-held notions of large strain deformation at surfaces.
Post-buckling analysis of composite beams: A simple intuitive ...
Indian Academy of Sciences (India)
and lateral displacement functions at any discrete location of the beam. ..... shells under combined axial compression and radial pressure. ... Razakamiadana A and Zidi M 1999 Buckling and post-buckling of concentric cylindrical tubes under.
Buckling of paramagnetic chains in soft gels
Huang, Shilin; Pessot, Giorgio; Cremer, Peet; Weeber, Rudolf; Holm, Christian; Nowak, Johannes; Odenbach, Stefan; Menzel, Andreas M.; Auernhammer, Günter K.
We study the magneto-elastic coupling behavior of paramagnetic chains in soft polymer gels exposed to external magnetic fields. To this end, a laser scanning confocal microscope is used to observe the morphology of the paramagnetic chains together with the deformation field of the surrounding gel network. The paramagnetic chains in soft polymer gels show rich morphological shape changes under oblique magnetic fields, in particular a pronounced buckling deformation. The details of the resulting morphological shapes depend on the length of the chain, the strength of the external magnetic field, and the modulus of the gel. Based on the observation that the magnetic chains are strongly coupled to the surrounding polymer network, a simplified model is developed to describe their buckling behavior. A coarse-grained molecular dynamics simulation model featuring an increased matrix stiffness on the surfaces of the particles leads to morphologies in agreement with the experimentally observed buckling effects.
Sensitivity study of buckling strength for cylindrical shells
Energy Technology Data Exchange (ETDEWEB)
Kato, Hideo; Sasaki, Toru [Institute of Nuclear Safety System Inc., Mihama, Fukui (Japan)
2001-09-01
Aiming at making clear buckling behavior of cylindrical shells under earthquake loadings, we investigated procedure of recent elastic-plastic buckling analysis by finite element method (FEM). Thereby it is confirmed that the buckling strength becomes as well as that of a shell with a cross section of a perfect cylinder, if we apply the first buckling eigenvector to imperfection mode and assume the maximum imperfection amplitude to be 1% of the wall thickness. And then, by carrying out sensitivity study of buckling with geometrical parameters, such as length (L), radius (R), wall thickness (t), and load parameter, such as pressure, we obtained several characteristics about buckling strength and buckling mode for cylindrical shells. From the geometrical parameter analysis, it is seen that bending buckling occurs for small R/t (thick wall) and elastic buckling occurs for 2{<=}L/R{<=}4 and R/t{>=}400. And from the load parameter analysis, it is shown that hoop stress caused by the inner pressure increases shear buckling strength but decreases bending buckling strength, and hoop stress by hydrostatic pressure changes buckling mode and generates local deformation. (author)
Scleral Buckle Infection With Pseudallescheria boydii.
Law, Janice C; Breazzano, Mark P; Eliott, Dean
2017-08-01
Pseudallescheria boydii is a ubiquitous fungus that infects soft tissues and is known to cause ocular disease, including keratitis and endophthalmitis, in rare cases. In immunocompromised hosts, P. boydii can disseminate to or from the eye and other organs with lethal consequences. Postoperative P. boydii infections have, in rare cases, complicated several types of ocular surgeries in immunocompetent patients, but never for a scleral buckle. The authors present the first case of an infected scleral buckle from P. boydii. [Ophthalmic Surg Lasers Imaging Retina. 2017;48:676-678.]. Copyright 2017, SLACK Incorporated.
Buckling driven debonding in sandwich columns
DEFF Research Database (Denmark)
Østergaard, Rasmus Christian
2008-01-01
results from two mechanisms: (a) interaction of local debond buckling and global buckling and (b) the development of a damaged zone at the debond crack tip. Based on the pronounced imperfection sensitivity, the author predicts that an experimental measurement of the strength of sandwich structures may......A compression loaded sandwich column that contains a debond is analyzed using a geometrically non-linear finite element model. The model includes a cohesive zone along one face sheet/core interface whereby the debond can extend by interface crack growth. Two geometrical imperfections are introduced...
Design rules against buckling of dished heads
International Nuclear Information System (INIS)
Roche, R.L.; Alix, M.; Autrusson, B.
1984-01-01
The aim of this paper is to present the validation of the rules of the French code of presure vessels CODAP. First, it is shown that the theories of buckling cannot give alone a sufficient base of validation and that the experimental justification is necessary. Then, the admissible pressure values corresponding to the CODAP formules are compared with the experimental results. This comparison furnishes the safety margins given by the CODAP formules. Finally, buckling tests of torispherical shells carried out at the CEA Saclay (France) are presented. The results obtained can be represented by a simple semi-empiric formula [fr
Scleral buckle infection by Serratia species
Directory of Open Access Journals (Sweden)
Ramesh Venkatesh
2017-01-01
Full Text Available We describe a rare case of scleral buckle (SB infection with Serratia species. A 48-year-old male with a history of retinal detachment repair with scleral buckling presented with redness, pain, and purulent discharge in the left eye for 4 days. Conjunctival erosion with exposure of the SB and scleral thinning was noted. The SB was removed and sent for culture. Blood and chocolate agar grew Gram-negative rod-shaped bacillus identified as Serratia marcescens. On the basis of the susceptibility test results, the patient was treated with oral and topical antibiotics. After 6 weeks of the treatment, his infection resolved.
Scleral buckle infection by Serratia species.
Venkatesh, Ramesh; Agarwal, Manisha; Singh, Shalini; Mayor, Rahul; Bansal, Aditya
2017-01-01
We describe a rare case of scleral buckle (SB) infection with Serratia species. A 48-year-old male with a history of retinal detachment repair with scleral buckling presented with redness, pain, and purulent discharge in the left eye for 4 days. Conjunctival erosion with exposure of the SB and scleral thinning was noted. The SB was removed and sent for culture. Blood and chocolate agar grew Gram-negative rod-shaped bacillus identified as Serratia marcescens . On the basis of the susceptibility test results, the patient was treated with oral and topical antibiotics. After 6 weeks of the treatment, his infection resolved.
Mechanical model for filament buckling and growth by phase ordering.
Rey, Alejandro D; Abukhdeir, Nasser M
2008-02-05
A mechanical model of open filament shape and growth driven by phase ordering is formulated. For a given phase-ordering driving force, the model output is the filament shape evolution and the filament end-point kinematics. The linearized model for the slope of the filament is the Cahn-Hilliard model of spinodal decomposition, where the buckling corresponds to concentration fluctuations. Two modes are predicted: (i) sequential growth and buckling and (ii) simultaneous buckling and growth. The relation among the maximum buckling rate, filament tension, and matrix viscosity is given. These results contribute to ongoing work in smectic A filament buckling.
Thermal-buckling analysis of an LMFBR overflow vessel
International Nuclear Information System (INIS)
Severud, L.K.
1983-01-01
During a reactor scram, cold sodium flows into the hot overflow vessel. The effect on the vessel is a compressive thermal stress in a zone just above the sodium level. This condition must be sufficiently controlled to preclude thermal buckling. Also, under repeated scrams, the vessel should not suffer thermal stress low cycle fatigue. To evaluate the closeness to buckling and satisfaction of ASMA Code limits, a combination of simple approximations, detailed elastic shell buckling analyses, and correlations to results of thermal buckling tests were employed. This paper describes the analysis methods, special considerations, and evaluations accomplished for this FFTF vessel to assure satisfaction of ASME buckling design criteria, rules, and limits
Buckling Pneumatic Linear Actuators Inspired by Muscle
Yang, Dian; Verma, Mohit Singh; So, Ju-Hee; Mosadegh, Bobak; Keplinger, Christoph; Lee, Benjamin; Khashai, Fatemeh; Lossner, Elton Garret; Suo, Zhigang; Whitesides, George McClelland
2016-01-01
The mechanical features of biological muscles are difficult to reproduce completely in synthetic systems. A new class of soft pneumatic structures (vacuum-actuated muscle-inspired pneumatic structures) is described that combines actuation by negative pressure (vacuum), with cooperative buckling of beams fabricated in a slab of elastomer, to achieve motion and demonstrate many features that are similar to that of mammalian muscle.
Dynamic Pulse Buckling--Theory and Experiment
1983-02-01
34Buckling of Bars Subject to Axial Shock," Studii si Cercetari de Mecanica Applicata (Roumania), 7, 1, pp. 173-178, January 1956. 26. A.F. Schmitt, "A...Procopovici, "Transverse Deformation of an Elastic Bar Subjected to an Axial Impulsive Force," Studii si Ceretari de Mecanica Applicata. 8, 3, pp. 839
Buckling determination in reflected systems, program FLUXFIT
Energy Technology Data Exchange (ETDEWEB)
Sotic, O [Boris Kidric Institute of Nuclear Sciences Vinca, Beograd (Yugoslavia)
1971-07-01
An improvement in accuracy of determining radial and axial buckling from foil activation distributions measured in reflected cylindrical systems is given. resultant activities are fitted to radial and axial spatial functions derived from homogeneous diffusion theory. A Fortran program FLUXFIT based on the derived method is included. (author)
Method for Predicting Thermal Buckling in Rails
2018-01-01
A method is proposed herein for predicting the onset of thermal buckling in rails in such a way as to provide a means of avoiding this type of potentially devastating failure. The method consists of the development of a thermomechanical model of rail...
Phenomenology and control of buckling dynamics in multicomponent colloidal droplets
Pathak, Binita; Basu, Saptarshi
2015-06-01
Self-assembly of nano sized particles during natural drying causes agglomeration and shell formation at the surface of micron sized droplets. The shell undergoes sol-gel transition leading to buckling at the weakest point on the surface and produces different types of structures. Manipulation of the buckling rate with inclusion of surfactant (sodium dodecyl sulphate, SDS) and salt (anilinium hydrochloride, AHC) to the nano-sized particle dispersion (nanosilica) is reported here in an acoustically levitated single droplet. Buckling in levitated droplets is a cumulative, complicated function of acoustic streaming, chemistry, agglomeration rate, porosity, radius of curvature, and elastic energy of shell. We put forward our hypothesis on how buckling occurs and can be suppressed during natural drying of the droplets. Global precipitation of aggregates due to slow drying of surfactant-added droplets (no added salts) enhances the rigidity of the shell formed and hence reduces the buckling probability of the shell. On the contrary, adsorption of SDS aggregates on salt ions facilitates the buckling phenomenon with an addition of minute concentration of the aniline salt to the dispersion. Variation in the concentration of the added particles (SDS/AHC) also leads to starkly different morphologies and transient behaviour of buckling (buckling modes like paraboloid, ellipsoid, and buckling rates). Tuning of the buckling rate causes a transition in the final morphology from ring and bowl shapes to cocoon type of structure.
A strategy to compute plastic post-buckling of structures
International Nuclear Information System (INIS)
Combescure, A.
1983-01-01
All the methods presented here give in some cases, some interesting computed solutions. It has been remarked that the different strategies do not always give the same post buckling path. More foundamentally, it has been observed that the post buckling path, when buckling is unstable, is characterized by a dynamic movement. All inertial effects are neglected in all the approaches presented here. So that the post buckling load deflections curve is valid only if there is a very little kinetic energy associated with the post buckling. The method is also, as it is presented, limited to a load depending of a simple parameter lambda. The case of more than one parameter is not very clear yet. In conclusion, the method presented here gives a way to solve class of the post buckling behavior of a structure. If the post buckling occurs with a small kinetic energy (displacement controlled buckling) and if the loads depend of only one parameter. These methods should give good results even into the plastic range. If the buckling is unstable and that a large kinetic energy is involved with the post buckling these methods are not realistic. (orig./RW)
An experimental and theoretical investigation of creep buckling
International Nuclear Information System (INIS)
Ohya, H.
1977-01-01
Creep buckling is one of the failure modes which must be taken into consideration for the design of structures exposed to elevated temperatures. And, rules are provided in ASME Boiler and Pressure Vessel Code Case 1592 to prevent the creep buckling. However, methods of analysis are not provided in Code Case, and selecting the methods of analysis is left to owners and manufacturers. The purpose of the present paper is to investigate creep buckling phenomena and the methods of analysis. Creep buckling experiments were performed on aluminum alloy 2024-T4 cylindrical shells having radius to thickness ratios of 16, 25, 50 and 80, in single, double and triple step axial compression at 250 0 C. It was observed that buckling occurred at one of the edges and the buckling mode depended on the radius to thickness ratio and also on the applied stress level. Thicker cylinders buckled in axisymmetric mode. Thinner ones under higher applied stress levels buckled in the asymmetric mode, whereas under lower applied stress levels they buckled in the axisymmetric mode. Creep buckling times were obtained from end shortening record of the cylinders. Experimental results were compared with theoretical values obtained by two methods. (Auth.)
Shear buckling of cylindrical vessels benchmark exercise
International Nuclear Information System (INIS)
Dostal, M; Austin, N.; Combescure, A.; Peano, A.; Angeloni, P.
1987-01-01
In Liquid Metal Fast Breeder Reactors (LMFBR) potential shear buckling failures of the primary vessel, induced through seismic excitations, have to be considered. The problem is particularly severe in pool type reactors due to their large size, radius of approximately 10 m, coupled with small wall thicknesses of 50 mm and less. The object of this paper is to provide a comparison of three different computer codes capable of performing buckling analyses and to demonstrate on practical problems the level of accuracy that may be expected in design analyses. Three computer codes were examined ABAQUS, CASTEM (INCA/BILBO) and NOVNL and the computer results were compared directly with experimental data and other commonly used empirical formula. The joint effort was co-ordinated through the CEC Working Group on Codes and Standards AG2. (orig./GL)
On the dynamic buckling of thin shells
International Nuclear Information System (INIS)
Combescure, A.; Hoffmann, A.; Homan, R.
1986-10-01
The shells of a pool type reactor like Super Phenix 1 or the Super Phenix 2 project are relatively thin compared to the diameter. Normal loads and mainly seismic loads due to strong fluid-structure interaction and giving pressure of the same order then static collapse pressure. This is a main difficulty for a good and safe design of LMFBR. The paper describes the experimental results obtained at CEA-DEMT on the seismic buckling of structures filled with fluid. A general tendency is given on all experimental results. The experimental results are analysed by two simple models and the main results are explained. A strategy to design a structure against dynamic buckling is then presented. 7 refs
Yield stress independent column buckling curves
DEFF Research Database (Denmark)
Stan, Tudor‐Cristian; Jönsson, Jeppe
2017-01-01
of the yield stress is to some inadequate degree taken into account in the Eurocode by specifying that steel grades of S460 and higher all belong to a common set of “raised” buckling curves. This is not satisfying as it can be shown theoretically that the current Eurocode formulation misses an epsilon factor......Using GMNIA and shell finite element modelling of steel columns it is ascertained that the buckling curves for given imperfections and residual stresses are not only dependent on the relative slenderness ratio and the cross section shape but also on the magnitude of the yield stress. The influence...... in the definition of the normalised imperfection magnitudes. By introducing this factor it seems that the GMNIA analysis and knowledge of the independency of residual stress levels on the yield stress can be brought together and give results showing consistency between numerical modelling and a simple modified...
Micro-buckling in the nanocomposite structure of biological materials
Su, Yewang; Ji, Baohua; Hwang, Keh-Chih; Huang, Yonggang
2012-10-01
Nanocomposite structure, consisting of hard mineral and soft protein, is the elementary building block of biological materials, where the mineral crystals are arranged in a staggered manner in protein matrix. This special alignment of mineral is supposed to be crucial to the structural stability of the biological materials under compressive load, but the underlying mechanism is not yet clear. In this study, we performed analytical analysis on the buckling strength of the nanocomposite structure by explicitly considering the staggered alignment of the mineral crystals, as well as the coordination among the minerals during the buckling deformation. Two local buckling modes of the nanostructure were identified, i.e., the symmetric mode and anti-symmetric mode. We showed that the symmetric mode often happens at large aspect ratio and large volume fraction of mineral, while the anti-symmetric happens at small aspect ratio and small volume fraction. In addition, we showed that because of the coordination of minerals with the help of their staggered alignment, the buckling strength of these two modes approached to that of the ideally continuous fiber reinforced composites at large aspect ratio given by Rosen's model, insensitive to the existing "gap"-like flaws between mineral tips. Furthermore, we identified a mechanism of buckling mode transition from local to global buckling with increase of aspect ratio, which was attributed to the biphasic dependence of the buckling strength on the aspect ratio. That is, for small aspect ratio, the local buckling strength is smaller than that of global buckling so that it dominates the buckling behavior of the nanocomposite; for comparatively larger aspect ratio, the local buckling strength is higher than that of global buckling so that the global buckling dominates the buckling behavior. We also found that the hierarchical structure can effectively enhance the buckling strength, particularly, this structural design enables
Using Euler buckling springs for vibration isolation
Winterflood, J; Blair, D G
2002-01-01
Difficulties in obtaining ideal vertical vibration isolation with mechanical springs are identified as being due to the mass of the elastic element which is in turn due to its energy storage requirement. A new technique to minimize this energy is presented - being an Euler column undergoing elastic buckling. The design of a high performance vertical vibration isolation stage based on this technique is presented together with its measured performance.
Using Euler buckling springs for vibration isolation
International Nuclear Information System (INIS)
Winterflood, J; Barber, T; Blair, D G
2002-01-01
Difficulties in obtaining ideal vertical vibration isolation with mechanical springs are identified as being due to the mass of the elastic element which is in turn due to its energy storage requirement. A new technique to minimize this energy is presented - being an Euler column undergoing elastic buckling. The design of a high performance vertical vibration isolation stage based on this technique is presented together with its measured performance
Buckling of stiff polymers: Influence of thermal fluctuations
Emanuel, Marc; Mohrbach, Hervé; Sayar, Mehmet; Schiessel, Helmut; Kulić, Igor M.
2007-12-01
The buckling of biopolymers is a frequently studied phenomenon The influence of thermal fluctuations on the buckling transition is, however, often ignored and not completely understood. A quantitative theory of the buckling of a wormlike chain based on a semiclassical approximation of the partition function is presented. The contribution of thermal fluctuations to the force-extension relation that allows one to go beyond the classical Euler buckling is derived in the linear and nonlinear regimes as well. It is shown that the thermal fluctuations in the nonlinear buckling regime increase the end-to-end distance of the semiflexible rod if it is confined to two dimensions as opposed to the three-dimensional case. The transition to a buckled state softens at finite temperature. We derive the scaling behavior of the transition shift with increasing ratio of contour length versus persistence length.
Buckling of Carbon Nanotubes: A State of the Art Review
Shima, Hiroyuki
2011-01-01
The nonlinear mechanical response of carbon nanotubes, referred to as their “buckling" behavior, is a major topic in the nanotube research community. Buckling means a deformation process in which a large strain beyond a threshold causes an abrupt change in the strain energy vs. deformation profile. Thus far, much effort has been devoted to analysis of the buckling of nanotubes under various loading conditions: compression, bending, torsion, and their certain combinations. Such extensive studies have been motivated by (i) the structural resilience of nanotubes against buckling and (ii) the substantial influence of buckling on their physical properties. In this contribution, I review the dramatic progress in nanotube buckling research during the past few years. PMID:28817032
Circumferential buckling instability of a growing cylindrical tube
Moulton, D.E.
2011-03-01
A cylindrical elastic tube under uniform radial external pressure will buckle circumferentially to a non-circular cross-section at a critical pressure. The buckling represents an instability of the inner or outer edge of the tube. This is a common phenomenon in biological tissues, where it is referred to as mucosal folding. Here, we investigate this buckling instability in a growing elastic tube. A change in thickness due to growth can have a dramatic impact on circumferential buckling, both in the critical pressure and the buckling pattern. We consider both single- and bi-layer tubes and multiple boundary conditions. We highlight the competition between geometric effects, i.e. the change in tube dimensions, and mechanical effects, i.e. the effect of residual stress, due to differential growth. This competition can lead to non-intuitive results, such as a tube growing to be thinner and yet buckle at a higher pressure. © 2011 Elsevier Ltd. All rights reserved.
Buckling instability in amorphous carbon films
Energy Technology Data Exchange (ETDEWEB)
Zhu, X D [CAS Key Laboratory of Basic Plasma Physics, Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Narumi, K [Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan); Naramoto, H [Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan)
2007-06-13
In this paper, we report the buckling instability in amorphous carbon films on mirror-polished sapphire (0001) wafers deposited by ion beam assisted deposition at various growth temperatures. For the films deposited at 150 deg. C, many interesting stress relief patterns are found, which include networks, blisters, sinusoidal patterns with {pi}-shape, and highly ordered sinusoidal waves on a large scale. Starting at irregular buckling in the centre, the latter propagate towards the outer buckling region. The maximum length of these ordered patterns reaches 396 {mu}m with a height of {approx}500 nm and a wavelength of {approx}8.2 {mu}m. However, the length decreases dramatically to 70 {mu}m as the deposition temperature is increased to 550 deg. C. The delamination of the film appears instead of sinusoidal waves with a further increase of the deposition temperature. This experimental observation is correlated with the theoretic work of Crosby (1999 Phys. Rev. E 59 R2542)
Buckling instability in amorphous carbon films
International Nuclear Information System (INIS)
Zhu, X D; Narumi, K; Naramoto, H
2007-01-01
In this paper, we report the buckling instability in amorphous carbon films on mirror-polished sapphire (0001) wafers deposited by ion beam assisted deposition at various growth temperatures. For the films deposited at 150 deg. C, many interesting stress relief patterns are found, which include networks, blisters, sinusoidal patterns with π-shape, and highly ordered sinusoidal waves on a large scale. Starting at irregular buckling in the centre, the latter propagate towards the outer buckling region. The maximum length of these ordered patterns reaches 396 μm with a height of ∼500 nm and a wavelength of ∼8.2 μm. However, the length decreases dramatically to 70 μm as the deposition temperature is increased to 550 deg. C. The delamination of the film appears instead of sinusoidal waves with a further increase of the deposition temperature. This experimental observation is correlated with the theoretic work of Crosby (1999 Phys. Rev. E 59 R2542)
Progressive buckling under both constant axial load and cyclic distortion
International Nuclear Information System (INIS)
Clement, G.; Acker, D.; Lebey, J.
1988-09-01
Thin structures submitted to compressive loads must be carefully designed to avoid any risk of ruin by buckling. The aim of this paper is, first, to evidence that the critical buckling load may be notably lowered when cyclic strains are added to the compressive load and, secondly, to propose a practical rule of prevention against the ruin due to the progressive buckling phenomenon. This rule is validated by the results of numerous tests related to the entire range of modes of buckling (i.e. from fully plastic to fully elastic). Practical cases of interest for its use could mainly be those where cyclic thermal stresses are involved
Method for studying the plastic buckling of shells. Testing
International Nuclear Information System (INIS)
Alix, M.; Combescure, A.; Hoffmann, A.; Roche, R.
1980-05-01
In this article a description is given of the method selected for studying the elasto-plastic buckling of shells of any shape. The emphasis is mainly on three points: the difficulty in making a strict formulation with respect to plasticity, the model selected (MOTAN model) is presented; the effect of so called 'non conservative' forces; and the effect of great deformations that might precede the buckling. The method is compared to tests: basket handle buckling of bottoms, buckling of elliptical bottoms under internal pressure, of compresses thin tubes, of metal drums, spherical diaphragm, shearing rings [fr
Uncertainty modelling of critical column buckling for reinforced ...
Indian Academy of Sciences (India)
Buckling is a critical issue for structural stability in structural design. In most of the buckling analyses, applied loads, structural and material properties are considered certain. However, in reality, these parameters are uncertain. Therefore, a prognostic solution is necessary and uncertainties have to be considered. Fuzzy logic ...
Circumferential buckling instability of a growing cylindrical tube
Moulton, D.E.; Goriely, A.
2011-01-01
A cylindrical elastic tube under uniform radial external pressure will buckle circumferentially to a non-circular cross-section at a critical pressure. The buckling represents an instability of the inner or outer edge of the tube. This is a common
Post-Buckling Strength of Uniformly Compressed Plates
Bakker, M.C.M.; Rosmanit, M.; Hofmeyer, H.; Camotim, D; Silvestre, N; Dinis, P.B.
2006-01-01
In this paper it is discussed how existing analytical and semi-analytical formulas for describing the elastic-post-buckling behavior of uniformly compressed square plates with initial imperfections, for loads up to three times the buckling load can be simplified and improved. For loads larger than
Buckling of shells under internal pressure, practical formulas for sizing
International Nuclear Information System (INIS)
Roche, R.; Alix, M.; Perez, A.; Autrusson, B.
1983-10-01
For metallic dished heads which have great diameter/thickness ratio, elastic plastic internal pressure buckling may occur. Recently, the French Pressure Vessel Code (CODAP) made available rules to assist the designer with this buckling problem. The aim of this paper is to give a comparison between these rules and available experimental results [fr
Dynamic shear-bending buckling experiments of cylindrical shells
International Nuclear Information System (INIS)
Hagiwara, Y.; Akiyama, H.
1995-01-01
Dynamic experimental studies of the plastic shear/bending buckling of cylindrical shells were performed. They clarified the inelastic response reduction and the seismic margin of FBR reactor vessels. The test results were incorporated into the draft of the seismic buckling design guidelines of FBR. (author). 15 refs., 3 figs
The status of experimental buckling investigations of shells
International Nuclear Information System (INIS)
Singer, J.
1982-01-01
The recent developments in shell buckling experiments are surveyed and related to a review of the progress in the seventies. Model fabrication, imperfection measurements, boundary conditions, nondestructive testing, combined loading, postbuckling behavior, composite shells and other aspects of shell buckling tests are discussed. The motivation for experiments and the conclusions drawn in the previous review are reassessed. (orig.)
Post buckling of three dimensional shells
International Nuclear Information System (INIS)
Hoffman, A.; Combescure, A.; Verpeaux, A.
1984-01-01
The paper presented here gives a general description of the methods currently used in the CEASEMT System Computer Codes for the non linear analysis of thin shells. For post buckling two methods are presented: the first one is a controlled step by step calculation in order to obtain the load-displacement curve. The second consist of the calculation of a global parameter based on energetic consideration, which can be easily interpreted as a time of collapse of the structure. Some examples are given and compared with experimental values. (Author) [pt
Bending energy of buckled edge dislocations
Kupferman, Raz
2017-12-01
The study of elastic membranes carrying topological defects has a longstanding history, going back at least to the 1950s. When allowed to buckle in three-dimensional space, membranes with defects can totally relieve their in-plane strain, remaining with a bending energy, whose rigidity modulus is small compared to the stretching modulus. In this paper we study membranes with a single edge dislocation. We prove that the minimum bending energy associated with strain-free configurations diverges logarithmically with the size of the system.
Post buckling of three dimensional shells
International Nuclear Information System (INIS)
Hoffmann, A.; Combescure, A.; Verpeaux, A.
1984-10-01
The paper presented here gives a general description of the methods currently used in the CEASEMT System Computer Codes for the non linear analysis of thin shells. For post buckling two methods are presented: the first one is a controlled step by step calculation in order to obtain the load-displacement curve. The second consist of the calculation of a global parameter based on energetic consideration, which can be easily interpreted as a time of collapse of the structure. When dynamic loads are concerned like seismic loads this parameter can be very useful. Some examples are given and compared with experimental values
Buckling strength of spherical shells under combined loads
International Nuclear Information System (INIS)
Nagashima, H.; Kokubo, K.; Takayanagi, M.; Hayasaka, Y.; Kume, T.; Nagata, T.
1995-01-01
Many studies on buckling of cylindrical shells have been conducted, and many buckling evaluation equations have been proposed for actual plant designs; however, buckling of spherical shells under combined horizontal and vertical loads cannot be evaluated due to insufficient data. There is a particular lack of buckling data for spherical shells under lateral loads. To establish a method for estimating the buckling strength of spherical shells, we investigate the interactions between horizontal and vertical (compressive tensile) loads by conducting buckling tests. Applying several combinations of these loads in tests and using computer linear analysis, we obtain interaction curves. This study reports on the buckling tests conducted using spherical shell 1120 mm in dia., 0.7 mm thick and 696 mm high, which are shaped individually by press-forming and finally joined together by four meridional welds, using a specially made jig. Initial imperfections before testing and local deformations after each loading increment during testing are measured with special measuring equipment, and the interaction curve of horizontal and vertical loads and effect of imperfection on the buckling strength of spherical shells are obtained. Nonlinear FEM programs are developed using an 8-node isoparametric shell element and a four-node quadrilateral element of C 0 type with reduced integration based upon a Mindlin-Reissner theory which includes transverse shear. Actual initial imperfections are generally in irregular patterns. Thus, there may be several definitions of the equivalent magnitudes of initial imperfections related to buckling loads. Equivalent magnitudes have no practical meaning unless they can be obtained easily not only for small structures such as test shells but also for large actual structures. In the present study, we define the equivalent magnitude of initial imperfections as the maximum local ruggedness measured radially from a circular temperature having a radius equal
Experimental study on dynamic buckling phenomena for supercavitating underwater vehicle
Directory of Open Access Journals (Sweden)
Minho Chung
2012-09-01
Full Text Available Dynamic buckling, also known as parametric resonance, is one of the dynamic instability phenomena which may lead to catastrophic failure of structures. It occurs when compressive dynamic loading is applied to the structures. Therefore it is essential to establish a reliable procedure to test and evaluate the dynamic buckling behaviors of structures, especially when the structure is designed to be utilized in compressive dynamic loading environment, such as supercavitating underwater vehicle. In the line of thought, a dynamic buckling test system is designed in this work. Using the test system, dynamic buckling tests including beam, plate, and stiffened plate are carried out, and the dynamic buckling characteristics of considered structures are investigated experimentally as well as theoretically and numerically.
Endoilluminator-assisted scleral buckling: Our results
Directory of Open Access Journals (Sweden)
Varun Gogia
2014-01-01
Full Text Available Aims: The aim was to evaluate the long-term surgical outcomes of endoillumination assisted scleral buckling (EASB in primary rhegmatogenous retinal detachment (RRD. Methods: Twenty-five eyes of 25 patients with primary RRD and proliferative vitreoretinopathy ≤C2 where any preoperative break could not be localised, were included. All patients underwent 25 gauge endoilluminator assisted rhegma localisation. Successful break determination was followed by cryopexy and standard scleral buckling under surgical microscope. Anatomical and functional outcomes were evaluated at the end of 2 years. Results: At least one intraoperative break could be localized in 23 of 25 (92% eyes. Median age of these patients was 46 years (range: 17-72. Thirteen eyes (56.52% were phakic, 8 (34.78% were pseudophakic and 2 (8.6% were aphakic. Anatomical success (attachment of retina was achieved in 22 (95.63% of 23 eyes with EASB. All eyes remained attached at the end of 2 years. Significant improvement in mean visual acuity (VA was achieved at the end of follow-up (1.09 ± 0.46 log of the minimum angle of resolution [logMAR] compared with preoperative VA (1.77 ± 0.28 logMAR (P < 0.001. Conclusion: EASB can be considered an effective alternative to vitreoretinal surgery in simple retinal detachment cases with the added advantage of enhanced microscopic magnification and wide field illumination.
Modeling shape selection of buckled dielectric elastomers
Langham, Jacob; Bense, Hadrien; Barkley, Dwight
2018-02-01
A dielectric elastomer whose edges are held fixed will buckle, given a sufficiently applied voltage, resulting in a nontrivial out-of-plane deformation. We study this situation numerically using a nonlinear elastic model which decouples two of the principal electrostatic stresses acting on an elastomer: normal pressure due to the mutual attraction of oppositely charged electrodes and tangential shear ("fringing") due to repulsion of like charges at the electrode edges. These enter via physically simplified boundary conditions that are applied in a fixed reference domain using a nondimensional approach. The method is valid for small to moderate strains and is straightforward to implement in a generic nonlinear elasticity code. We validate the model by directly comparing the simulated equilibrium shapes with the experiment. For circular electrodes which buckle axisymetrically, the shape of the deflection profile is captured. Annular electrodes of different widths produce azimuthal ripples with wavelengths that match our simulations. In this case, it is essential to compute multiple equilibria because the first model solution obtained by the nonlinear solver (Newton's method) is often not the energetically favored state. We address this using a numerical technique known as "deflation." Finally, we observe the large number of different solutions that may be obtained for the case of a long rectangular strip.
Buckling Optimization of Thick Stiffened Cylindrical Shell
Directory of Open Access Journals (Sweden)
Qasim Hassan Bader
2016-03-01
Full Text Available In this work the critical pressure due to buckling was calculated numerically by using ANSYS15 for both stiffened and un-stiffened cylinder for various locations and installing types , strengthening of the cylinder causes a more significant increase in buckling pressures than non reinforced cylinder . The optimum design of structure was done by using the ASYS15 program; in this step the number of design variables 21 DVs. These variables are Independent variables that directly affect. The design variables represented the thickness of the cylinder and( height and width of 10 stiffeners. State variables (SVs, these variables are dependent variables that change as a result of changing the DVs and are necessary to constrain the design. The objective function is the one variable in the optimization that needs to be minimized. In this case the state variable is critical pressure (CP and the objective function is the total (volume of the structure. The optimum weight of the structure with reasonable required conditions for multi types of structure was found. The result shows the best location of stiffener at internal side with circumferential direction. In this case the critical pressure can be increased about 18.6% and the total weight of the structure decreases to 15.8%.
International Nuclear Information System (INIS)
Hagiwara, Yutaka; Yamamoto, Kohsuke; Kawamoto, Yoji; Nakagawa, Masaki; Akiyama, Hiroshi
1998-01-01
Plastic shear-bending buckling under seismic loadings is one of the major problems in the structural design of FBR main vessels. Pseudo-dynamic and dynamic buckling tests of cylinders were performed in order to study the effects of nonlinear seismic response on buckling strength, ductility, and plastic response reduction. The buckling strength formulae and the rule for ductility factors both derived from static tests were confirmed to be valid for the tests under dynamic loads. The displacement-constant rule for response reduction effect was modified by acceleration amplification factor in order to maintain applicability for various spectral profiles of seismic excitations. The response reduction estimated by the proposed rule was reasonably conservative for all cases of the pseudo-dynamic and the dynamic tests. Finally, a seismic safety assessment rule was proposed for plastic shear-bending buckling of cylinders, which include the proposed response reduction rule. (author)
Distortional buckling modes of semi-discretized thin-walled columns
DEFF Research Database (Denmark)
Andreassen, Michael Joachim; Jönsson, Jeppe
2012-01-01
buckling, distortional buckling and local buckling are given and it is shown how the novel approach may be used to develop signature curves and elastic buckling curves. In order to assess the accuracy of the method some of the results are compared to results found using the commercial FE program Abaqus...
Elastic Buckling Behaviour of General Multi-Layered Graphene Sheets
Directory of Open Access Journals (Sweden)
Rong Ming Lin
2015-04-01
Full Text Available Elastic buckling behaviour of multi-layered graphene sheets is rigorously investigated. Van der Waals forces are modelled, to a first order approximation, as linear physical springs which connect the nodes between the layers. Critical buckling loads and their associated modes are established and analyzed under different boundary conditions, aspect ratios and compressive loading ratios in the case of graphene sheets compressed in two perpendicular directions. Various practically possible loading configurations are examined and their effect on buckling characteristics is assessed. To model more accurately the buckling behaviour of multi-layered graphene sheets, a physically more representative and realistic mixed boundary support concept is proposed and applied. For the fundamental buckling mode under mixed boundary support, the layers with different boundary supports deform similarly but non-identically, leading to resultant van der Waals bonding forces between the layers which in turn affect critical buckling load. Results are compared with existing known solutions to illustrate the excellent numerical accuracy of the proposed modelling approach. The buckling characteristics of graphene sheets presented in this paper form a comprehensive and wholesome study which can be used as potential structural design guideline when graphene sheets are employed for nano-scale sensing and actuation applications such as nano-electro-mechanical systems.
International Nuclear Information System (INIS)
Kim, D. H.; Ko, K. H.; Lee, J. H.
2002-01-01
This work was done as one of the pre-research of buckling behavior for LMR reactor vessel. For the reduced scale buckling test, the three types of test specimen(slenderness ratio 1.0, 2.0, 4.8) was selected. Using the buckling formulae by Okada and the elastic-plastic finite element method, the buckling characteristics are investigated. From the results of buckling load evaluations, as the slenderness ratio decreases, the buckling load increases and a deflection shape approaches shear buckling mode. As the slenderness increases, the deflection approaches bending buckling mode. In comparison of buckling loads, the calculated buckling loads by the elastic-plastic finite element method are in good agreement with those of the evaluation formulae considering with plastic effect
Elastic torsional buckling of thin-walled composite cylinders
Marlowe, D. E.; Sushinsky, G. F.; Dexter, H. B.
1974-01-01
The elastic torsional buckling strength has been determined experimentally for thin-walled cylinders fabricated with glass/epoxy, boron/epoxy, and graphite/epoxy composite materials and composite-reinforced aluminum and titanium. Cylinders have been tested with several unidirectional-ply orientations and several cross-ply layups. Specimens were designed with diameter-to-thickness ratios of approximately 150 and 300 and in two lengths of 10 in. and 20 in. The results of these tests were compared with the buckling strengths predicted by the torsional buckling analysis of Chao.
Dynamic plastic buckling of rings and cylindrical shells
International Nuclear Information System (INIS)
Jones, N.; Okawa, D.M.
1975-01-01
A theoretical analysis is developed to predict the dynamic plastic buckling of a long, impulsively loaded cylindrical shell. This theoretical work is used to examine various features of plastic buckling and to assess the importance of several approximations which previous authors have introduced in dynamic plastic buckling studies. In particular, the influence of a time-dependent circumferential membrane force, the sharpness of the peaks in the displacement and velocity amplification functions, the restrictions which are implicit when employing the Prandtl-Reuss equations in this class of problems, and the limitations due to elastic unloading are examined in some detail. (Auth.)
On the buckling of an elastic rotating beam
DEFF Research Database (Denmark)
Furta, Stanislaw D.; Kliem, Wolfhard; Pommer, Christian
1997-01-01
problem is integrated and this results in a second order differential equation of the Fuchs type, which allows an asymptotic expansion of the buckling equation. By means of Lyapunov and Chetaev functions, a rigorous proof is given that the loss of stability of the trivial equilibrium shape occurs for any......A nonlinear model is developed, which describes the buckling phenomena of an elastic beam clamped to the interior of a rotating wheel. We use a power series method to obtain an approximate expression of the buckling equation and compare this with previous results in the literature. The linearized...
Evaluation of design safety factors for time-dependent buckling
International Nuclear Information System (INIS)
Stone, C.M.; Nickell, R.E.
1977-02-01
The ASME Boiler and Pressure Vessel Code rules concerning time-dependent (creep) buckling for Class 1 nuclear components have recently been changed. Previous requirements for a factor of ten on service life have been replaced with a factor of safety of 1.5 on loading for load-controlled buckling. This report examines the supposed equivalence of the two rules from the standpoint of materials behavior--specifically, the secondary creep strain rate exponent. The comparison is made using results obtained numerically for an axially-loaded, cylindrical shell with varying secondary creep exponents. A computationally efficient scheme for analyzing creep buckling problems is also presented
WELWING, Material Buckling for HWR with Annular Fuel Elements
International Nuclear Information System (INIS)
Grosskopf, O.G.P.
1973-01-01
1 - Nature of the physical problem solved: WELWING was developed to calculate the material buckling of reactor systems consisting of annular fuel elements in heavy water as moderator for various moderator to fuel ratios. The moderator to fuel ratio for the maximum material buckling for the particular system is selected automatically and the corresponding material buckling is calculated. 2 - Method of solution: The method used is an analytical solution of the one-group diffusion equations with various corrections and approximations. 3 - Restrictions on the complexity of the problem: Up to 32 different materials in the fuel element may be used
Evaluation of buckling on containment metallic vessels
International Nuclear Information System (INIS)
Silveira, Renato Campos da; Mattar Neto, Miguel
2000-01-01
The buckling analysis represents one of the most important aspects of the structural projects of nuclear power plants containment metallic vessels and in this work the Case N-284-1 ASME Code is used for evaluation of those structures submitted to this failure mode. From the stress analysis, performed by using finite element method on discrete structures with shell elements, the procedure of the Code Case are applied to the evaluation of the containment metallic vessel of the Angra 2 nuclear power plant submitted to the own weight, seismic loads and uplift in case of accident. A study of pressure vessel reinforced by rings submit ed to the external pressure. Conclusions and commentaries are established based on the obtained results
Buckling and stretching of thin viscous sheets
O'Kiely, Doireann; Breward, Chris; Griffiths, Ian; Howell, Peter; Lange, Ulrich
2016-11-01
Thin glass sheets are used in smartphone, battery and semiconductor technology, and may be manufactured by producing a relatively thick glass slab and subsequently redrawing it to a required thickness. The resulting sheets commonly possess undesired centerline ripples and thick edges. We present a mathematical model in which a viscous sheet undergoes redraw in the direction of gravity, and show that, in a sufficiently strong gravitational field, buckling is driven by compression in a region near the bottom of the sheet, and limited by viscous resistance to stretching of the sheet. We use asymptotic analysis in the thin-sheet, low-Reynolds-number limit to determine the centerline profile and growth rate of such a viscous sheet.
Compressive buckling of a rectangular nanoplate
Bochkarev, A. O.
2018-05-01
This paper considers the constitutive relations of the nanoplate theory with surface stresses taken into account according to the original or complete Gurtin-Murdoch (GM) model and according to the simplified strain-consistent GM model (which does not include any non-strain terms in the surface stress-strain relation). It is shown that the potential energy of a deformed nanoplate according to both GM models preserves the classical structure using the redefined elastic moduli (effective tangential and flexural elastic properties, which contain the characteristics of bulk phase and a surface). This allows to apply the known solutions and methods from macroplates to nanoplates. As example, it is shown that the critical load of the compressive buckling of a nanoplate according to the complete and strain-consistent GM models has the difference between two solutions no more than 1.5%.
Buckling Response of Thick Functionally Graded Plates
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BOUAZZA MOKHTAR
2014-11-01
Full Text Available In this paper, the buckling of a functionally graded plate is studied by using first order shear deformation theory (FSDT. The material properties of the plate are assumed to be graded continuously in the direction of thickness. The variation of the material properties follows a simple power-law distribution in terms of the volume fractions of constituents. The von Karman strains are used to construct the equilibrium equations of the plates subjected to two types of thermal loading, linear temperature rise and gradient through the thickness are considered. The governing equations are reduced to linear differential equation with boundary conditions yielding a simple solution procedure. In addition, the effects of temperature field, volume fraction distributions, and system geometric parameters are investigated. The results are compared with the results of the no shear deformation theory (classic plate theory, CPT.
Buckling localization in a cylindrical panel under axial compression
DEFF Research Database (Denmark)
Tvergaard, Viggo; Needleman, A.
2000-01-01
Localization of an initially periodic buckling pattern is investigated for an axially compressed elastic-plastic cylindrical panel of the type occurring between axial stiffeners on cylindrical shells. The phenomenon of buckling localization and its analogy with plastic flow localization in tensile...... test specimens is discussed in general. For the cylindrical panel, it is shown that buckling localization develops shortly after a maximum load has been attained, and this occurs for a purely elastic panel as well as for elastic-plastic panels. In a case where localization occurs after a load maximum......, but where subsequently the load starts to increase again, it is found that near the local load minimum, the buckling pattern switches back to a periodic type of pattern. The inelastic material behavior of the panel is described in terms of J(2) corner theory, which avoids the sometimes unrealistically high...
Uncertain Buckling Load and Reliability of Columns with Uncertain Properties
DEFF Research Database (Denmark)
Köylüoglu, H. U.; Nielsen, Søren R. K.; Cakmak, A. S.
Continuous and finite element methods are utilized to determine the buckling load of columns with material and geometrical uncertainties considering deterministic, stochastic and interval models for the bending rigidity of columns. When the bending rigidity field is assumed to be deterministic, t....... for structural design, the lower bound is of crucial interest. The buckling load of fixed-free, simple-supported, pinned-fixed, fixed-fixed columns and a sample frame are calculated....
Benchmark study of shear buckling of a cylindrical vessel
International Nuclear Information System (INIS)
Dostal, M.; Austin, N.M.; Peano, A.; Combescure, A.; Bastien, R.; Carnoy, E.G.
1986-01-01
The possibility of a buckling failure of the primary vessel subjected to seismic excitation has been considered, by all major designers of loop and pool type liquid metal cooled fast breeder reactors. The problem is particularly onerous in this type of reactor due to their large size, coupled with small wall thicknesses. This report details the results of the first phase in a joint European code validation exercise on the static shear buckling behaviour of thin, low aspect ratio stainless steel cylinders. Linear and non-linear finite element analyses were performed by four organizations using three different computer codes, i.e. NNC (UK)-ABAQUS, ISMES (Italy)-ABAQUS, CEA (France)-BILBO/INCA and NOVATOME (France)-NOVNL. The computed results were compared directly with experimental results. It was discovered that refined finite element models were essential if accurate buckling loads were to be calculated. Buckling analyses in 3D were therefore computationally expensive and 2D analyses, where applicable, proved an useful alternative. Traditional linear (Euler) bifurcation analysis seriously over-estimated the buckling loads by around 50 %. Extrapolation techniques can however be used to reduce this discrepancy. Elasto-plastic bifurcation analysis predicted conservative buckling loads close to the experimental value. Non-linear, large displacement analyses were performed on the vessel. The effect of geometrical imperfections in the vessel was considered. These analyses all over-estimated the experimental buckling load by 10 %-25 % and appeared to be largely insensitive to the initial imperfection size. Each of the codes appeared to predict reasonably well the final buckled geometry although the analytical load-deflection estimate did not agree exactly with the experiment
Thermal buckling comparative analysis using Different FE (Finite Element) tools
Energy Technology Data Exchange (ETDEWEB)
Banasiak, Waldemar; Labouriau, Pedro [INTECSEA do Brasil, Rio de Janeiro, RJ (Brazil); Burnett, Christopher [INTECSEA UK, Surrey (United Kingdom); Falepin, Hendrik [Fugro Engineers SA/NV, Brussels (Belgium)
2009-12-19
High operational temperature and pressure in offshore pipelines may lead to unexpected lateral movements, sometimes call lateral buckling, which can have serious consequences for the integrity of the pipeline. The phenomenon of lateral buckling in offshore pipelines needs to be analysed in the design phase using FEM. The analysis should take into account many parameters, including operational temperature and pressure, fluid characteristic, seabed profile, soil parameters, coatings of the pipe, free spans etc. The buckling initiation force is sensitive to small changes of any initial geometric out-of-straightness, thus the modeling of the as-laid state of the pipeline is an important part of the design process. Recently some dedicated finite elements programs have been created making modeling of the offshore environment more convenient that has been the case with the use of general purpose finite element software. The present paper aims to compare thermal buckling analysis of sub sea pipeline performed using different finite elements tools, i.e. general purpose programs (ANSYS, ABAQUS) and dedicated software (SAGE Profile 3D) for a single pipeline resting on an the seabed. The analyses considered the pipeline resting on a flat seabed with a small levels of out-of straightness initiating the lateral buckling. The results show the quite good agreement of results of buckling in elastic range and in the conclusions next comparative analyses with sensitivity cases are recommended. (author)
Strengthening of Steel Columns under Load: Torsional-Flexural Buckling
Directory of Open Access Journals (Sweden)
Martin Vild
2016-01-01
Full Text Available The paper presents experimental and numerical research into the strengthening of steel columns under load using welded plates. So far, the experimental research in this field has been limited mostly to flexural buckling of columns and the preload had low effect on the column load resistance. This paper focuses on the local buckling and torsional-flexural buckling of columns. Three sets of three columns each were tested. Two sets corresponding to the base section (D and strengthened section (E were tested without preloading and were used for comparison. Columns from set (F were first preloaded to the load corresponding to the half of the load resistance of the base section (D. Then the columns were strengthened and after they cooled, they were loaded to failure. The columns strengthened under load (F had similar average resistance as the columns welded without preloading (E, meaning the preload affects even members susceptible to local buckling and torsional-flexural buckling only slightly. This is the same behaviour as of the tested columns from previous research into flexural buckling. The study includes results gained from finite element models of the problem created in ANSYS software. The results obtained from the experiments and numerical simulations were compared.
On buckling of double-shell-stiffened cylindrical steel structures
International Nuclear Information System (INIS)
Chen, S.J.; Chiu, K.D.; Odar, E.
1981-01-01
Buckling analysis methods and acceptance criteria for single shells of various configurations are well documented and adequately covered by many codes. There are, however, no guidelines or criteria for large Double-Shell-Stiffened (DSS) structures, which have been used recently in nuclear power plant applications. The existing codes for buckling analysis cannot be directly utilized because of the uniqueness of structural configuration and complexity of loading. This paper discusses a method for determining the critical buckling loads for this type of structure under a multitude load and suggests buckling criteria for the design of DSS structures. The method commonly used to determine the critical buckling loads for a single shell with or without stiffeners applies reduction factors to the theoretical results. The capacity reduction factors, which are often obtained from experimental results, include plasticity corrections and account for the difference between actual and theoretical buckling loads resulting from the effects of imperfections and nonlinearities. The interaction formulas derived from experimental results can be used to compute the interaction effects of three stress components. This paper extends these concepts and discusses their applicability to a DSS cylindrical structure. (orig./HP)
Buckling instability in ordered bacterial colonies
Boyer, Denis; Mather, William; Mondragón-Palomino, Octavio; Orozco-Fuentes, Sirio; Danino, Tal; Hasty, Jeff; Tsimring, Lev S.
2011-04-01
Bacterial colonies often exhibit complex spatio-temporal organization. This collective behavior is affected by a multitude of factors ranging from the properties of individual cells (shape, motility, membrane structure) to chemotaxis and other means of cell-cell communication. One of the important but often overlooked mechanisms of spatio-temporal organization is direct mechanical contact among cells in dense colonies such as biofilms. While in natural habitats all these different mechanisms and factors act in concert, one can use laboratory cell cultures to study certain mechanisms in isolation. Recent work demonstrated that growth and ensuing expansion flow of rod-like bacteria Escherichia coli in confined environments leads to orientation of cells along the flow direction and thus to ordering of cells. However, the cell orientational ordering remained imperfect. In this paper we study one mechanism responsible for the persistence of disorder in growing cell populations. We demonstrate experimentally that a growing colony of nematically ordered cells is prone to the buckling instability. Our theoretical analysis and discrete-element simulations suggest that the nature of this instability is related to the anisotropy of the stress tensor in the ordered cell colony.
Buckling instability in ordered bacterial colonies
International Nuclear Information System (INIS)
Boyer, Denis; Mather, William; Mondragón-Palomino, Octavio; Danino, Tal; Hasty, Jeff; Orozco-Fuentes, Sirio; Tsimring, Lev S
2011-01-01
Bacterial colonies often exhibit complex spatio-temporal organization. This collective behavior is affected by a multitude of factors ranging from the properties of individual cells (shape, motility, membrane structure) to chemotaxis and other means of cell–cell communication. One of the important but often overlooked mechanisms of spatio-temporal organization is direct mechanical contact among cells in dense colonies such as biofilms. While in natural habitats all these different mechanisms and factors act in concert, one can use laboratory cell cultures to study certain mechanisms in isolation. Recent work demonstrated that growth and ensuing expansion flow of rod-like bacteria Escherichia coli in confined environments leads to orientation of cells along the flow direction and thus to ordering of cells. However, the cell orientational ordering remained imperfect. In this paper we study one mechanism responsible for the persistence of disorder in growing cell populations. We demonstrate experimentally that a growing colony of nematically ordered cells is prone to the buckling instability. Our theoretical analysis and discrete-element simulations suggest that the nature of this instability is related to the anisotropy of the stress tensor in the ordered cell colony
Buckled two-dimensional Xene sheets.
Molle, Alessandro; Goldberger, Joshua; Houssa, Michel; Xu, Yong; Zhang, Shou-Cheng; Akinwande, Deji
2017-02-01
Silicene, germanene and stanene are part of a monoelemental class of two-dimensional (2D) crystals termed 2D-Xenes (X = Si, Ge, Sn and so on) which, together with their ligand-functionalized derivatives referred to as Xanes, are comprised of group IVA atoms arranged in a honeycomb lattice - similar to graphene but with varying degrees of buckling. Their electronic structure ranges from trivial insulators, to semiconductors with tunable gaps, to semi-metallic, depending on the substrate, chemical functionalization and strain. More than a dozen different topological insulator states are predicted to emerge, including the quantum spin Hall state at room temperature, which, if realized, would enable new classes of nanoelectronic and spintronic devices, such as the topological field-effect transistor. The electronic structure can be tuned, for example, by changing the group IVA element, the degree of spin-orbit coupling, the functionalization chemistry or the substrate, making the 2D-Xene systems promising multifunctional 2D materials for nanotechnology. This Perspective highlights the current state of the art and future opportunities in the manipulation and stability of these materials, their functions and applications, and novel device concepts.
Critical thickness ratio for buckled and wrinkled fruits and vegetables
Dai, Hui-Hui; Liu, Yang
2014-11-01
This work aims at establishing the geometrical constraint for buckled and wrinkled shapes by modeling a fruit/vegetable with exocarp and sarcocarp as a hyperelastic layer-substrate structure subjected to uniaxial compression. A careful analysis on the derived bifurcation condition leads to the finding of a critical thickness ratio which separates the buckling and wrinkling modes, and remarkably, which is independent of the material stiffnesses. More specifically, it is found that if the thickness ratio is smaller than this critical value a fruit/vegetable should be in a buckled shape (under a sufficient stress); if a fruit/vegetable is in a wrinkled shape the thickness ratio is always larger than this critical value. To verify the theoretical prediction, we consider four types of buckled fruits/vegetables and four types of wrinkled fruits/vegetables with three samples in each type. The geometrical parameters for the 24 samples are measured and it is found that indeed all the data fall into the theoretically predicted buckling or wrinkling domains.
Engineering electronic states of periodic and quasiperiodic chains by buckling
Mukherjee, Amrita; Nandy, Atanu; Chakrabarti, Arunava
2017-07-01
The spectrum of spinless, non-interacting electrons on a linear chain that is buckled in a non-uniform, quasiperiodic manner is investigated within a tight binding formalism. We have addressed two specific cases, viz., a perfectly periodic chain wrinkled in a quasiperiodic Fibonacci pattern, and a quasiperiodic Fibonacci chain, where the buckling also takes place in a Fibonacci pattern. The buckling brings distant neighbors in the parent chain to close proximity, which is simulated by a tunnel hopping amplitude. It is seen that, in the perfectly ordered case, increasing the strength of the tunnel hopping (that is, bending the segments more) absolutely continuous density of states is retained towards the edges of the band, while the central portion becomes fragmented and host subbands of narrowing widths containing extended, current carrying states, and multiple isolated bound states formed as a result of the bending. A switching ;on; and ;off; of the electronic transmission can thus be engineered by buckling. On the other hand, in the second example of a quasiperiodic Fibonacci chain, imparting a quasiperiodic buckling is found to generate continuous subband(s) destroying the usual multifractality of the energy spectrum. We present exact results based on a real space renormalization group analysis, that is corroborated by explicit calculation of the two terminal electronic transport.
A strategy to compute plastic post-buckling of structures
International Nuclear Information System (INIS)
Combescure, A.
1983-08-01
The paper gives a general framework to the different strategies used to compute the post-buckling of structures. Two particular strategies are studied in more details and it is shown how they can be applied in the plastic regime. All the methods suppose that the loads F are proportional to a simple parameter lambda; more precisely: eq (1) F = lambda F 0 . The paper shows how these methods can be implemented in a very simple way. In the elastic case we show the application of the method to the calculation of post buckling response of a clamped arch. The method is also applied to a very simple case of two bars which can be calculated analytically. In the plastic range, the method is applied to the post-buckling of an imperfect ring which can be calculated analytically. Another example is the comparison of the comparison of the computed post-buckling of a thin cylinder under axial compression, and of the experimental behavior on the same cylinder. The limitation of these types of strategies are also mentionned and the physical signifiance of calculations in the post-buckling regime are discussed
Research on the Numerical Simulation of Sleeper in the Pipeline Global Buckling Controlling Practice
Directory of Open Access Journals (Sweden)
Liu Wen-Bin
2017-01-01
Full Text Available This paper analyzed the lateral buckling of pipelines located in Western Africa with ABAQUS software. The application of sleepers in practice is explored to guide the pipeline buckling controlling design.
Effect of corrosion on the buckling capacity of tubular members
Øyasæter, F. H.; Aeran, A.; Siriwardane, S. C.; Mikkelsen, O.
2017-12-01
Offshore installations are subjected to harsh marine environment and often have damages from corrosion. Several experimental and numerical studies were performed in the past to estimate buckling capacity of corroded tubular members. However, these studies were either based on limited experimental tests or numerical analyses of few cases resulting in semi-empirical relations. Also, there are no guidelines and recommendations in the currently available design standards. To fulfil this research gap, a new formula is proposed to estimate the residual strength of tubular members considering corrosion and initial geometrical imperfections. The proposed formula is verified with results from finite element analyses performed on several members and for varying corrosion patch parameters. The members are selected to represent the most relevant Eurocode buckling curve for tubular members. It is concluded that corrosion reduces the buckling capacity significantly and the proposed formula can be easily applied by practicing engineers without performing detailed numerical analyses.
Buckling induced by cyclic straining: Analysis of simple models
International Nuclear Information System (INIS)
Devos, J.; Gontier, C.; Hoffmann, A.
1983-01-01
Progressive buckling of a structure may occur under imposed loads below the critical value in cases where progressive distortion due to cyclic straining is possible. This interaction between ratchetting and buckling is usually not taken into account in design rules, such as the ASME rules. This paper presents the complete analysis of two simple cases and gives rules established on this basis. The first model is a modified version of SHANLEY's two bars; it is submitted to a constant axial compressive force F and a variable thermal stress Q. It simulates a compressed clamped-clamped beam subjected to a variable through-thickness thermal gradient. The second model is a refined version of the first taking into account strain-hardening of the deformable sections. One finds that progressive buckling is possible only if the applied force F is greater than SHANLEY's critical load and tangent moduli of the moment-curvature law, respectively. (orig./GL)
Vibrations of post-buckled rods: The singular inextensible limit
Neukirch, Sé bastien; Frelat, Joë l; Goriely, Alain; Maurini, Corrado
2012-01-01
The small-amplitude in-plane vibrations of an elastic rod clamped at both extremities are studied. The rod is modeled as an extensible, shearable, planar Kirchhoff elastic rod under large displacements and rotations, and the vibration frequencies are computed both analytically and numerically as a function of the loading. Of particular interest is the variation of mode frequencies as the load is increased through the buckling threshold. While for some modes there are no qualitative changes in the mode frequencies, other frequencies experience rapid variations after the buckling threshold, the thinner the rod, the more abrupt the variations. Eventually, a mismatch for half of the frequencies at buckling arises between the zero thickness limit of the extensible model and the inextensible model. © 2011 Elsevier Ltd. All rights reserved.
Buckling analysis of SMA bonded sandwich structure – using FEM
Katariya, Pankaj V.; Das, Arijit; Panda, Subrata K.
2018-03-01
Thermal buckling strength of smart sandwich composite structure (bonded with shape memory alloy; SMA) examined numerically via a higher-order finite element model in association with marching technique. The excess geometrical distortion of the structure under the elevated environment modeled through Green’s strain function whereas the material nonlinearity counted with the help of marching method. The system responses are computed numerically by solving the generalized eigenvalue equations via a customized MATLAB code. The comprehensive behaviour of the current finite element solutions (minimum buckling load parameter) is established by solving the adequate number of numerical examples including the given input parameter. The current numerical model is extended further to check the influence of various structural parameter of the sandwich panel on the buckling temperature including the SMA effect and reported in details.
Lower bound buckling loads for design of laminate composite cylinders
Croll, James G. A.; Wang, Hongtao
2017-01-01
Over a period of more than 45 years, an extensive research program has allowed a series of very simple propositions, relating to the safe design of shells experiencing imperfection sensitive buckling, to be recast in the form of a series of lemmas. These are briefly summarized and their practical use is illustrated in relation to the prediction of safe lower bounds to the imperfection sensitive buckling of axially loaded, fiber reinforced polymeric, laminated cylinders. With a fundamental aspect of the approach, sometimes referred to as the reduced stiffness method, being the delineation of the various shell membrane and bending stiffness (or perhaps more appropriately energy) components contributing to the buckling resistance, the method will be shown to also provide a powerful way of making rational design decisions to optimize the use of fiber reinforcement.
Finite element predictions of active buckling control of stiffened panels
Thompson, Danniella M.; Griffin, O. H., Jr.
1993-04-01
Materials systems and structures that can respond 'intelligently' to their environment are currently being proposed and investigated. A series of finite element analyses was performed to investigate the potential for active buckling control of two different stiffened panels by embedded shape memory alloy (SMA) rods. Changes in the predicted buckling load increased with the magnitude of the actuation level for a given structural concept. Increasing the number of actuators for a given concept yielded greater predicted increases in buckling load. Considerable control authority was generated with a small number of actuators, with greater authority demonstrated for those structural concepts where the activated SMA rods could develop greater forces and moments on the structure. Relatively simple and inexpensive analyses were performed with standard finite elements to determine such information, indicating the viability of these types of models for design purposes.
Bifurcations in the optimal elastic foundation for a buckling column
International Nuclear Information System (INIS)
Rayneau-Kirkhope, Daniel; Farr, Robert; Ding, K.; Mao, Yong
2010-01-01
We investigate the buckling under compression of a slender beam with a distributed lateral elastic support, for which there is an associated cost. For a given cost, we study the optimal choice of support to protect against Euler buckling. We show that with only weak lateral support, the optimum distribution is a delta-function at the centre of the beam. When more support is allowed, we find numerically that the optimal distribution undergoes a series of bifurcations. We obtain analytical expressions for the buckling load around the first bifurcation point and corresponding expansions for the optimal position of support. Our theoretical predictions, including the critical exponent of the bifurcation, are confirmed by computer simulations.
Bifurcations in the optimal elastic foundation for a buckling column
Energy Technology Data Exchange (ETDEWEB)
Rayneau-Kirkhope, Daniel, E-mail: ppxdr@nottingham.ac.u [School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD (United Kingdom); Farr, Robert [Unilever R and D, Olivier van Noortlaan 120, AT3133, Vlaardingen (Netherlands); London Institute for Mathematical Sciences, 22 South Audley Street, Mayfair, London (United Kingdom); Ding, K. [Department of Physics, Fudan University, Shanghai, 200433 (China); Mao, Yong [School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD (United Kingdom)
2010-12-01
We investigate the buckling under compression of a slender beam with a distributed lateral elastic support, for which there is an associated cost. For a given cost, we study the optimal choice of support to protect against Euler buckling. We show that with only weak lateral support, the optimum distribution is a delta-function at the centre of the beam. When more support is allowed, we find numerically that the optimal distribution undergoes a series of bifurcations. We obtain analytical expressions for the buckling load around the first bifurcation point and corresponding expansions for the optimal position of support. Our theoretical predictions, including the critical exponent of the bifurcation, are confirmed by computer simulations.
Buckle initiation and delamination of patterned ITO layers on a polymer substrate
Abdallah, Amir; Bouten, P.C.P.; Toonder, den J.M.J.; With, de G.
2011-01-01
Buckle initiation and delamination of patterned ITO layers on a polymer substrate were studied. Various buckle modes have been observed depending on the type of etch defects and the crack patterns. The buckle density was found to be dependent on the number of etch defects, imperfections, applied
Determining the asymptotic buckling for the reference RB reactor lattice
International Nuclear Information System (INIS)
Martinc, R.; Sotic, O.
1969-01-01
Material buckling was measured for reference lattice of the heavy water reflected system with 2% enriched uranium fuel. Experiments were done for cores with lattice pitch values: 8, 8√2, i 16 cm. Each of these cores had heavy water reflector, as well as active reflector - heavy water lattice with natural uranium fuel. The core was reflected by natural uranium lattice in order to approach asymptotic regime in the central zone. Buckling values obtained with the natural uranium lattice as reflector are, as a rule, lower then in case of heavy water reflector [sr
On the buckling behavior of piezoelectric nanobeams: An exact solution
International Nuclear Information System (INIS)
Jandaghian, Ali Akbar; Rahmaini, Omid
2015-01-01
In this paper, thermoelectric-mechanical buckling behavior of the piezoelectric nanobeams is investigated based on the nonlocal theory and Euler-Bernoulli beam theory. The electric potential is assumed linear through the thickness of the nanobeam and the governing equations are derived by Hamilton's principle. The governing equations are solved analytically for different boundary conditions. The effects of the nonlocal parameter, temperature change, and external electric voltage on the critical buckling load of the piezoelectric nanobeams are discussed in detail. This study should be useful for the design of piezoelectric nanodevices.
Buckling Causes Nonlinear Dynamics of Filamentous Viruses Driven through Nanopores.
McMullen, Angus; de Haan, Hendrick W; Tang, Jay X; Stein, Derek
2018-02-16
Measurements and Langevin dynamics simulations of filamentous viruses driven through solid-state nanopores reveal a superlinear rise in the translocation velocity with driving force. The mobility also scales with the length of the virus in a nontrivial way that depends on the force. These dynamics are consequences of the buckling of the leading portion of a virus as it emerges from the nanopore and is put under compressive stress by the viscous forces it encounters. The leading tip of a buckled virus stalls and this reduces the total viscous drag force. We present a scaling theory that connects the solid mechanics to the nonlinear dynamics of polyelectrolytes translocating nanopores.
A review of analysis methods about thermal buckling
International Nuclear Information System (INIS)
Moulin, D.; Combescure, A.; Acker, D.
1987-01-01
This paper highlights the main items emerging from a large bibliographical survey carried out on strain-induced buckling analysis methods applicable in the building of fast neutron reactor structures. The work is centred on the practical analysis methods used in construction codes to account for the strain-buckling of thin and slender structures. Methods proposed in the literature concerning past and present studies are rapidly described. Experimental, theoretical and numerical methods are considered. Methods applicable to design and their degree of validation are indicated
NASTRAN buckling study of a linear induction motor reaction rail
Williams, J. G.
1973-01-01
NASTRAN was used to study problems associated with the installation of a linear induction motor reaction rail test track. Specific problems studied include determination of the critical axial compressive buckling stress and establishment of the lateral stiffness of the reaction rail under combined loads. NASTRAN results were compared with experimentally obtained values and satisfactory agreement was obtained. The reaction rail was found to buckle at an axial compressive stress of 11,400 pounds per square inch. The results of this investigation were used to select procedures for installation of the reaction rail.
Baumgarten, Lorenz; Kierfeld, Jan
2018-05-01
We study the influence of thermal fluctuations on the buckling behavior of thin elastic capsules with spherical rest shape. Above a critical uniform pressure, an elastic capsule becomes mechanically unstable and spontaneously buckles into a shape with an axisymmetric dimple. Thermal fluctuations affect the buckling instability by two mechanisms. On the one hand, thermal fluctuations can renormalize the capsule's elastic properties and its pressure because of anharmonic couplings between normal displacement modes of different wavelengths. This effectively lowers its critical buckling pressure [Košmrlj and Nelson, Phys. Rev. X 7, 011002 (2017), 10.1103/PhysRevX.7.011002]. On the other hand, buckled shapes are energetically favorable already at pressures below the classical buckling pressure. At these pressures, however, buckling requires to overcome an energy barrier, which only vanishes at the critical buckling pressure. In the presence of thermal fluctuations, the capsule can spontaneously overcome an energy barrier of the order of the thermal energy by thermal activation already at pressures below the critical buckling pressure. We revisit parameter renormalization by thermal fluctuations and formulate a buckling criterion based on scale-dependent renormalized parameters to obtain a temperature-dependent critical buckling pressure. Then we quantify the pressure-dependent energy barrier for buckling below the critical buckling pressure using numerical energy minimization and analytical arguments. This allows us to obtain the temperature-dependent critical pressure for buckling by thermal activation over this energy barrier. Remarkably, both parameter renormalization and thermal activation lead to the same parameter dependence of the critical buckling pressure on temperature, capsule radius and thickness, and Young's modulus. Finally, we study the combined effect of parameter renormalization and thermal activation by using renormalized parameters for the energy
Analysis of Lateral Buckling of Bar with Axial Force Accumulation in Truss
Wattanamankong, Nuttapon; Petchsasithon, Arthit; Dhirasedh, Suwat
2017-06-01
This research studies the lateral buckling behavior in truss and lateral buckling coefficient of truss. Lateral buckling analysis of truss is performed by simulating the structural model with both end supports being pinned and roller-supports. The analysis is indirectly conducted using Elastic Theory to evaluate the length of lateral buckling by calculating the determinant of the Matrix [K]. Results from the analysis are marginally different from those obtained from finite element program and are considerably less than those obtained from Eurocode standard. This can be concluded that using elastic theory to evaluate lateral buckling coefficient of truss member will result in more economical section.
Initial post dynamic buckling of a quadratic-cubic column ...
African Journals Online (AJOL)
In this investigation, we determine the dynamic buckling load of an imperfect finite column resting on a mixed quadratic-cubic nonlinear elastic foundation trapped by an explicitly time dependent sinusoidally slowly varying dynamic load .The resultant coefficients are dynamically slowly varying and the formulation contains ...
Buckling behavior of origami unit cell facets under compressive loads
Kshad, Mohamed Ali Emhmed; Naguib, Hani E.
2018-03-01
Origami structures as cores for sandwich structures are designed to withstand the compressive loads and to dissipate compressive energy. The deformation of the origami panels and the unit cell facets are the primary factors behind the compressive energy dissipation in origami structures. During the loading stage, the origami structures deform through the folding and unfolding process of the unit cell facets, and also through the plastic deformation of the facets. This work presents a numerical study of the buckling behavior of different origami unit cell elements under compressive loading. The studied origami configurations were Miura and Ron-Resch-like origami structures. Finite element package was used to model the origami structures. The study investigated the buckling behavior of the unit cell facets of two types of origami structures Miura origami and Ron-Resch-Like origami structures. The simulation was conducted using ANSYS finite element software, in which the model of the unit cell represented by shell elements, and the eigenvalues buckling solver was used to predict the theoretical buckling of the unit cell elements.
Buckling of thin-walled beams under concentrated transverse loading
Menken, C.M.; Erp, van G.M.; Krupta, V.; Drdacky, M.
1991-01-01
The transversely loaded thin-walled beam under a non-uniform bending moment forms an example of the detrimental influence that a local effect may have on the overall behaviour. The local effect is the plate buckling in the region of maximum bending moment. The overall behaviour is the
Buckling of Thin Films in Nano-Scale
Directory of Open Access Journals (Sweden)
Li L.A.
2010-06-01
Full Text Available Investigation of thin film buckling is important for life prediction of MEMS device which are damaged mainly by the delamination and buckling of thin films. In this paper the mechanical and thermal properties of compressed thin film titanium films with 150 nm thickness deposited on an organic glass substrate under mechanical and thermal loads were measured and characterized. In order to simulate the thin films which subjected to compound loads and the buckle modes the external uniaxial compression and thermal loading were subjected to the specimen by the symmetric loading device and the electrical film in this experiment. The temperature of the thin film deposited on substrate was measured using thermoelectric couple. The range of temperature accords with the temperature range of the MEMS. It is found that the size and number of the delamination and buckling of the film are depended upon the pre-fixed mechanical loading and thermal temperature. The thermal transient conduction and thermal stability of the film and substrate was studied with finite element method.
Local buckling failure analysis of high-strength pipelines
Institute of Scientific and Technical Information of China (English)
Yan Li; Jian Shuai; Zhong-Li Jin; Ya-Tong Zhao; Kui Xu
2017-01-01
Pipelines in geological disaster regions typically suffer the risk of local buckling failure because of slender structure and complex load.This paper is meant to reveal the local buckling behavior of buried pipelines with a large diameter and high strength,which are under different conditions,including pure bending and bending combined with internal pressure.Finite element analysis was built according to previous data to study local buckling behavior of pressurized and unpressurized pipes under bending conditions and their differences in local buckling failure modes.In parametric analysis,a series of parameters,including pipe geometrical dimension,pipe material properties and internal pressure,were selected to study their influences on the critical bending moment,critical compressive stress and critical compressive strain of pipes.Especially the hardening exponent of pipe material was introduced to the parameter analysis by using the Ramberg-Osgood constitutive model.Results showed that geometrical dimensions,material and internal pressure can exert similar effects on the critical bending moment and critical compressive stress,which have different,even reverse effects on the critical compressive strain.Based on these analyses,more accurate design models of critical bending moment and critical compressive stress have been proposed for high-strength pipelines under bending conditions,which provide theoretical methods for highstrength pipeline engineering.
Lateral-torsional buckling resistance of cellular beams
Sonck, Delphine; Belis, Jan
The evenly spaced circular web openings in I-section cellular beams have an advantageous effect on the material use if these beams are loaded in strong-axis bending. However, not all aspects of the behaviour of such beams have been studied adequately, such as the lateral–torsional buckling failure.
Buckling analysis for anisotropic laminated plates under combined inplane loads
Viswanathan, A. V.; Tamekuni, M.; Baker, L. L.
1974-01-01
The buckling analysis presented considers rectangular flat or curved general laminates subjected to combined inplane normal and shear loads. Linear theory is used in the analysis. All prebuckling deformations and any initial imperfections are ignored. The analysis method can be readily extended to longitudinally stiffened structures subjected to combined inplane normal and shear loads.
An embeddable optical strain gauge based on a buckled beam.
Du, Yang; Chen, Yizheng; Zhu, Chen; Zhuang, Yiyang; Huang, Jie
2017-11-01
We report, for the first time, a low cost, compact, and novel mechanically designed extrinsic Fabry-Perot interferometer (EFPI)-based optical fiber sensor with a strain amplification mechanism for strain measurement. The fundamental design principle includes a buckled beam with a coated gold layer, mounted on two grips. A Fabry-Perot cavity is produced between the buckled beam and the endface of a single mode fiber (SMF). A ceramic ferrule is applied for supporting and orienting the SMF. The principal sensor elements are packaged and protected by two designed metal shells. The midpoint of the buckled beam will experience a deflection vertically when the beam is subjected to a horizontally/axially compressive displacement. It has been found that the vertical deflection of the beam at midpoint can be 6-17 times larger than the horizontal/axial displacement, which forms the basis of a strain amplification mechanism. The user-configurable buckling beam geometry-based strain amplification mechanism enables the strain sensor to achieve a wide range of strain measurement sensitivities. The designed EFPI was used to monitor shrinkage of a square brick of mortar. The strain was measured during the drying/curing stage. We envision that it could be a good strain sensor to be embedded in civil materials/structures under a harsh environment for a prolonged period of time.
An embeddable optical strain gauge based on a buckled beam
Du, Yang; Chen, Yizheng; Zhu, Chen; Zhuang, Yiyang; Huang, Jie
2017-11-01
We report, for the first time, a low cost, compact, and novel mechanically designed extrinsic Fabry-Perot interferometer (EFPI)-based optical fiber sensor with a strain amplification mechanism for strain measurement. The fundamental design principle includes a buckled beam with a coated gold layer, mounted on two grips. A Fabry-Perot cavity is produced between the buckled beam and the endface of a single mode fiber (SMF). A ceramic ferrule is applied for supporting and orienting the SMF. The principal sensor elements are packaged and protected by two designed metal shells. The midpoint of the buckled beam will experience a deflection vertically when the beam is subjected to a horizontally/axially compressive displacement. It has been found that the vertical deflection of the beam at midpoint can be 6-17 times larger than the horizontal/axial displacement, which forms the basis of a strain amplification mechanism. The user-configurable buckling beam geometry-based strain amplification mechanism enables the strain sensor to achieve a wide range of strain measurement sensitivities. The designed EFPI was used to monitor shrinkage of a square brick of mortar. The strain was measured during the drying/curing stage. We envision that it could be a good strain sensor to be embedded in civil materials/structures under a harsh environment for a prolonged period of time.
Buckling analysis of rectangular composite plates with rectangular ...
Indian Academy of Sciences (India)
In aeronautical, marine and automobile industries the use of composite laminates .... load of fibre-reinforced plastic square panels using finite element method. .... lar cutout i.e d/b = 0.1 and β =0, the reduction in buckling load by increasing c/b ...
Studies of the Buckling of Composite Plates in Compression
DEFF Research Database (Denmark)
Hayman, B.; Berggreen, Christian; Lundsgaard-Larsen, Christian
2011-01-01
As part of the Network of Excellence on Marine Structures (MARSTRUCT), a series of studies has been carried out into the buckling of glass-fibre-reinforced polymer plates with in-plane compression loading. The studies have included fabrication and testing of square, laminated panels with various...
Studies of the buckling of composite plates in compression
DEFF Research Database (Denmark)
Hayman, B.; Berggreen, Christian; Lundsgaard-Larsen, Christian
2009-01-01
As part of the MARSTRUCT Network of Excellence on Marine Structures, a series of studies has been carried out into the buckling of glass fibre reinforced polymer plates with in-plane compression loading. The studies have included fabrication and testing of square, laminated panels with various...
Stretchable transistors with buckled carbon nanotube films as conducting channels
Arnold, Michael S; Xu, Feng
2015-03-24
Thin-film transistors comprising buckled films comprising carbon nanotubes as the conductive channel are provided. Also provided are methods of fabricating the transistors. The transistors, which are highly stretchable and bendable, exhibit stable performance even when operated under high tensile strains.
On the dynamic buckling of a weakly damped nonlinear elastic ...
African Journals Online (AJOL)
In this paper we determine the dynamic buckling load of a strictly nonlinear but weakly damped elastic oscillatory model structure subjected to small perturbations The loading history is explicitly time dependent and varies slowly with time over a natural period of oscillation of the structure. A multiple timing regular ...
Buckling instabilities of subducted lithosphere beneath the transition zone
Ribe, N.M.; Stutzmann, E.; Ren, Y.; Hilst, R.D. van der
2007-01-01
A sheet of viscous fluid poured onto a surface buckles periodically to generate a pile of regular folds. Recent tomographic images beneath subduction zones, together with quantitative fluid mechanical scaling laws, suggest that a similar instability can occur when slabs of subducted oceanic
International Nuclear Information System (INIS)
Mallett, R.H.
1986-12-01
This report documents analytical and experimental results from a survey of the technical literature on buckling of thick-walled cylinders under external pressure. Based upon these results, a load factor is suggested for the design of waste package containers for disposal of high-level radioactive waste in repositories mined in salt formations. The load factor is defined as a ratio of buckling pressure to allowable pressure. Specifically, a load factor which ranges from 1.5 for plastic buckling to 3.0 for elastic buckling is included in a set of proposed buckling design criteria for waste disposal containers. Formulas are given for buckling design under axisymmetric conditions. Guidelines are given for detailed inelastic buckling analyses which are generally required for design of disposal containers
An impact test system design and its applications to dynamic buckling of a spacer grid assembly
Energy Technology Data Exchange (ETDEWEB)
Liu, Sheng, E-mail: liusheng_05@126.com; Fan, Chenguang; Yang, Yiren
2016-11-15
This study is aimed at investigating the dynamic buckling load, dynamic stiffness, damping and buckling characteristics of the spacer grid assembly (SGA). A pendulum impact test system is designed to experiment the buckling of SGAs. Three criterions are discussed and compared to determine the buckling loads of SGAs: B-R criterion, energy criterion and extreme value criterion. Two approaches are applied to calculate the dynamic stiffness of SGAs: One method is natural period method based on the hypothesis of harmonic motion of the pendulum whose period is approximated because of the passivation and tailing of the impact force time history; and the other is energy method based on the conservation of mechanical energy. The equivalent viscous damping is defined as the resultant cause of dissipation and is obtained by the energy principle. The impact force time history loses its approximate symmetry after buckling occurs. The impact force and displacement reach their maxima almost at the same time at pre-buckling states but not post-buckling states. Vertical straps in SGA are found to be transversely shared by horizontal straps at the buckling position. The buckling of SGA results from the lack of strength of complete structure; and the strength of material has no effects on the buckling.
Measurement of material buckling of subcritical assembly CAPITU
International Nuclear Information System (INIS)
Pombo, J.B.S.M.
1976-11-01
Material buckling and cadmium ratio measurements for 5 lattices of the subcritical assembly CAPITU with UO 2 as fuel (French fuel elements) and D 2 O as moderator are reported. Flux shape method from foil activation data has been used. Some developed accessories, experimental procedures and the counting system used are also described. Flux distributions were analysed by least squares fitting method and by a moments method. Final results for material buckling were confronted with theoretical values and with values obtained by pulsed neutron techniques. A summary of the programs used for preliminary processing of counting data and for least squares fitting are included. Although the measurements involved some problems which were not definitively solved, results seem to be reasonably reliable and the methodology well implemented. (Author) [pt
Reversible patterning of spherical shells through constrained buckling
Marthelot, J.; Brun, P.-T.; Jiménez, F. López; Reis, P. M.
2017-07-01
Recent advances in active soft structures envision the large deformations resulting from mechanical instabilities as routes for functional shape morphing. Numerous such examples exist for filamentary and plate systems. However, examples with double-curved shells are rarer, with progress hampered by challenges in fabrication and the complexities involved in analyzing their underlying geometrical nonlinearities. We show that on-demand patterning of hemispherical shells can be achieved through constrained buckling. Their postbuckling response is stabilized by an inner rigid mandrel. Through a combination of experiments, simulations, and scaling analyses, our investigation focuses on the nucleation and evolution of the buckling patterns into a reticulated network of sharp ridges. The geometry of the system, namely, the shell radius and the gap between the shell and the mandrel, is found to be the primary ingredient to set the surface morphology. This prominence of geometry suggests a robust, scalable, and tunable mechanism for reversible shape morphing of elastic shells.
Magneto-electro-elastic buckling analysis of nonlocal curved nanobeams
Ebrahimi, Farzad; Reza Barati, Mohammad
2016-09-01
In this work, a size-dependent curved beam model is developed to take into account the effects of nonlocal stresses on the buckling behavior of curved magneto-electro-elastic FG nanobeams for the first time. The governing differential equations are derived based on the principle of virtual work and Euler-Bernoulli beam theory. The power-law function is employed to describe the spatially graded magneto-electro-elastic properties. By extending the radius of the curved nanobeam to infinity, the results of straight nonlocal FG beams can be rendered. The effects of magnetic potential, electric voltage, opening angle, nonlocal parameter, power-law index and slenderness ratio on buckling loads of curved MEE-FG nanobeams are studied.
Buckling transition and boundary layer in non-Euclidean plates.
Efrati, Efi; Sharon, Eran; Kupferman, Raz
2009-07-01
Non-Euclidean plates are thin elastic bodies having no stress-free configuration, hence exhibiting residual stresses in the absence of external constraints. These bodies are endowed with a three-dimensional reference metric, which may not necessarily be immersible in physical space. Here, based on a recently developed theory for such bodies, we characterize the transition from flat to buckled equilibrium configurations at a critical value of the plate thickness. Depending on the reference metric, the buckling transition may be either continuous or discontinuous. In the infinitely thin plate limit, under the assumption that a limiting configuration exists, we show that the limit is a configuration that minimizes the bending content, among all configurations with zero stretching content (isometric immersions of the midsurface). For small but finite plate thickness, we show the formation of a boundary layer, whose size scales with the square root of the plate thickness and whose shape is determined by a balance between stretching and bending energies.
Buckling of long liquid-filled cylindrical shells
International Nuclear Information System (INIS)
Saal, H.
1982-01-01
The experimental investigation confirms the stresses and displacements which result from a nonlinear analysis of the shell. The linear analysis gives a good approximation for the stresses and deformations which significantly deviate from those according to beam theory. This approximation is to the safe side - (remarkably only for the displacements and circumferential stresses). The application of an equivalent cylinder model to the determination of the buckling load gives rather good agreement with the experimental results. There is only little imperfection sensitivity in this load case as the experiments show. Again the theoretical buckling load which is based on the stresses and displacements from linear shell theory is on the safe side. (orig./RW)
Numerical Analysis Of Buckling Of Von Mises Planar Truss
Directory of Open Access Journals (Sweden)
Kalina Martin
2015-12-01
Full Text Available A computational algorithm of a discrete model of von Mises planar steel truss is presented. The structure deformation is evaluated by seeking the minimal potential energy. The critical force invented by mathematical solution was compared with solution by computer algorithm. Symmetric and asymmetric effects of initial shape of geometric imperfection of axis of struts are used in model. The shapes of buckling of von Mises planar truss of selected vertical displacement of top joint are shown.
Longitudinal Weld Land Buckling in Compression-Loaded Orthogrid Cylinders
Thornburgh, Robert P.; Hilburger, Mark W.
2010-01-01
Large stiffened cylinders used in launch vehicles (LV), such as the Space Shuttle External Tank, are manufactured by welding multiple curved panel sections into complete cylinders. The effects of the axial weld lands between the panel sections on the buckling load were studied, along with the interaction between the acreage stiffener arrangement and the weld land geometry. This document contains the results of the studies.
Calculation of the geometric buckling for reactors of various shapes
Energy Technology Data Exchange (ETDEWEB)
Sjoestrand, N E
1958-05-15
A systematic investigation is made of the eleven coordinate systems in which the reactor equation {nabla}{sup 2}{phi} + B{sup 2}{phi} = 0 is separable. The fundamental solution and geometric buckling are given for those cases where the separated equations lead to known functions. It is especially shown that reactors of prolate and oblate spheroidal shape can be calculated in detail, and the results are given in extensive tables.
Scleral buckling for retinal detachment in patients with retinoblastoma
International Nuclear Information System (INIS)
Buzney, S.M.; Pruett, R.C.; Regan, C.D.; Walton, D.S.; Smith, T.R.
1984-01-01
Three children (two girls and one boy) with bilateral retinoblastoma each developed a presumed rhegmatogenous retinal detachment in one eye. All three eyes had previously received radiation and cryotherapy. In each case the retinal detachment responded promptly to conventional surgical methods via scleral buckling in the area of treated retinoblastoma and presumed retinal break. All three eyes have retained useful vision for follow-up periods of 3.5 to 12 years
Scleral buckling for retinal detachment in patients with retinoblastoma
Energy Technology Data Exchange (ETDEWEB)
Buzney, S.M.; Pruett, R.C.; Regan, C.D.; Walton, D.S.; Smith, T.R.
1984-10-15
Three children (two girls and one boy) with bilateral retinoblastoma each developed a presumed rhegmatogenous retinal detachment in one eye. All three eyes had previously received radiation and cryotherapy. In each case the retinal detachment responded promptly to conventional surgical methods via scleral buckling in the area of treated retinoblastoma and presumed retinal break. All three eyes have retained useful vision for follow-up periods of 3.5 to 12 years.
Outpatient- and inpatient-based buckling surgery: a comparative study
Directory of Open Access Journals (Sweden)
Lee JC
2014-04-01
Full Text Available Jin Cheol Lee,* Yu Cheol Kim*Department of Ophthalmology, Keimyung University School of Medicine, Dongsan Medical Center, Daegu, Korea *Both authors contributed equally to this workPurpose: To evaluate the clinical outcomes of ambulatory buckling surgery, comparing outpatient- with inpatient-based surgery.Methods: The authors performed a retrospective study of 80 consecutive cases of rhegmato genous retinal detachment from January 2009 to December 2011 treated by scleral buckling surgery. Two groups of patients were defined according to inpatient (group 1 or outpatient (group 2 surgery, and a comparison of several parameters between these two groups was performed.Results: Of the 80 subjects in this study, the average age of group 1 (50 patients was 49.7 years, and that of group 2 (30 patients was 47.5 years. There were no statistically significant differences in the average logarithm of the minimum angle of resolution-visual acuity, the condition of the lens, or the presence of retinal lattice degeneration prior to the surgery between the groups. There were no statistically significant differences in the patterns of tear or retinal detachment or in surgical procedure between the groups. Comparing the best-corrected visual acuity after 6 months with that prior to the surgery, the changes in group 1 and group 2 were 0.26 and 0.31, respectively. The functional success rates of group 1 and group 2 after 6 months were 90% and 93%, respectively, and the anatomical success rates of group 1 and group 2 after 6 months were 94% and 96%, respectively, but these were also statistically insignificant.Conclusion: Hospitalization is not essential for buckling surgery in uncomplicated rhegmatogenous retinal detachment surgery.Keywords: ambulatory, scleral buckling, rhegmatogenous retinal detachment
Elastoplastic buckling of quasi axisymmetric shells of revolution
International Nuclear Information System (INIS)
Combescure, A.
1987-01-01
This paper gives the formulation of a finite element which allows the computation of quasi axisymmetric shells of revolution. This element has two nodes and the displacement field is developped in Fourier series. In this paper, an emphasis is put on the elastic and plastic buckling formulation. Two examples are developped in details showing the applicability and the interest of such a finite element. (orig.)
Buckled graphene: A model study based on density functional theory
Khan, Yasser
2010-09-01
We make use of ab initio calculations within density functional theory to investigate the influence of buckling on the electronic structure of single layer graphene. Our systematic study addresses a wide range of bond length and bond angle variations in order to obtain insights into the energy scale associated with the formation of ripples in a graphene sheet. © 2010 Elsevier B.V. All rights reserved.
Dynamic plastic buckling of cylindrical and spherical shells
International Nuclear Information System (INIS)
Jones, N.; Okawa, D.M.
1975-01-01
A theoretical analysis is developed to predict the dynamic plastic buckling of a long, impulsively loaded cylindrical shell in order to examine various features of plastic buckling and to assess the importance of several approximations with previous authors have introduced in dynamic plastic buckling studies. The influence of a time-dependent circumferential membrane force, the sharpness of the peaks in the displacement and velocity amplification functions, the restrictions which are implicit when employing the Prandtl-Reuss equations in this class of problems, and the limitations due to elastic unloading are examined in some detail. A summary of all previously published theoretical investigations known to the authors is undertaken for the dynamic plastic behavior of cylindrical shells and rings which are made from rigid-plastic, rigid-visco-plastic, elastic-plastic and elastic-visco-plastic materials and subjected to initial axisymmetric impulsive velocity fields. The theoretical predictions of the dominant motions, critical mode numbers, and threshold impulses are compared and critically reviewed. An experimental investigation was also undertaken into the dynamic plastic buckling of circular rings subjected to uniformly distributed external impulsive velocities. It appears that no experiments have been reported previously on mild steel cylindrical shells with an axial length (L) less than four times the shell radius (R). The experimental values of the average final radial deflections, critical mode numbers and dimensions of the permanent wrinkles in the mild steel and some aliminium 6,061 T6 specimens are compared with all the previously published theoretical predictions and experimental results on cylindrical shells with various axial lengths. (orig./HP) [de
Buckled graphene: A model study based on density functional theory
Khan, Yasser; Mukaddam, Mohsin Ahmed; Schwingenschlö gl, Udo
2010-01-01
We make use of ab initio calculations within density functional theory to investigate the influence of buckling on the electronic structure of single layer graphene. Our systematic study addresses a wide range of bond length and bond angle variations in order to obtain insights into the energy scale associated with the formation of ripples in a graphene sheet. © 2010 Elsevier B.V. All rights reserved.
Tailored Buckling Microlattices as Reusable Light-Weight Shock Absorbers.
Frenzel, Tobias; Findeisen, Claudio; Kadic, Muamer; Gumbsch, Peter; Wegener, Martin
2016-07-01
Structures and materials absorbing mechanical (shock) energy commonly exploit either viscoelasticity or destructive modifications. Based on a class of uniaxial light-weight geometrically nonlinear mechanical microlattices and using buckling of inner elements, either a sequence of snap-ins followed by irreversible hysteretic - yet repeatable - self-recovery or multistability is achieved, enabling programmable behavior. Proof-of-principle experiments on three-dimensional polymer microstructures are presented. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Mechanics of nanowire/nanotube in-surface buckling on elastomeric substrates
Energy Technology Data Exchange (ETDEWEB)
Xiao, J; Huang, Y [Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208 (United States); Ryu, S Y; Paik, U [Division of Materials Science and Engineering, Hanyang University, 17 Hangdang-dong, Sungdong-gu, Seoul 133-791 (Korea, Republic of); Hwang, K-C [Department of Engineering Mechanics, Tsinghua University, Beijing 100084 (China); Rogers, J A, E-mail: y-huang@northwestern.edu, E-mail: jrogers@uiuc.edu [Department of Materials Science and Engineering, Frederick-Seitz Materials Research Laboratory and Beckman Institute, University of Illinois at Urbana-Champaign, Illinois 61801 (United States)
2010-02-26
A continuum mechanics theory is established for the in-surface buckling of one-dimensional nanomaterials on compliant substrates, such as silicon nanowires on elastomeric substrates observed in experiments. Simple analytical expressions are obtained for the buckling wavelength, amplitude and critical buckling strain in terms of the bending and tension stiffness of the nanomaterial and the substrate elastic properties. The analysis is applied to silicon nanowires, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanotube bundles. For silicon nanowires, the measured buckling wavelength gives Young's modulus to be 140 GPa, which agrees well with the prior experimental studies. It is shown that the energy for in-surface buckling is lower than that for normal (out-of-surface) buckling, and is therefore energetically favorable.
Mechanics of nanowire/nanotube in-surface buckling on elastomeric substrates
International Nuclear Information System (INIS)
Xiao, J; Huang, Y; Ryu, S Y; Paik, U; Hwang, K-C; Rogers, J A
2010-01-01
A continuum mechanics theory is established for the in-surface buckling of one-dimensional nanomaterials on compliant substrates, such as silicon nanowires on elastomeric substrates observed in experiments. Simple analytical expressions are obtained for the buckling wavelength, amplitude and critical buckling strain in terms of the bending and tension stiffness of the nanomaterial and the substrate elastic properties. The analysis is applied to silicon nanowires, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanotube bundles. For silicon nanowires, the measured buckling wavelength gives Young's modulus to be 140 GPa, which agrees well with the prior experimental studies. It is shown that the energy for in-surface buckling is lower than that for normal (out-of-surface) buckling, and is therefore energetically favorable.
Flexural-torsional buckling analysis of angle-bar stiffened plates
Energy Technology Data Exchange (ETDEWEB)
Ahmad, Rahbar Ranji [Amirkabir University of Technology, Tehran (Iran, Islamic Republic of)
2015-09-15
The interaction of flexural-torsional buckling modes is critical for stiffened plates with asymmetric stiffeners. However, this interaction is ignored in all design rules because it is complex to characterize. In the literature, the presence of an attached plate is ignored, and stiffened plate is treated as an ordinary asymmetric beam. In the flexural buckling mode, stiffener and the attached plate buckle together; in the torsional buckling mode, the attached plate cannot freely rotate with stiffener. Basic equations of the flexural-torsional buckling modes are deduced based on hybrid beam concept and a new strain distribution assumption for sideway bending of stiffeners. Elastic buckling stresses of different angle-bar stiffened plates are calculated and compared with those generated by the Finite element method (FEM) and those available in the literature. The present method has better agreements with FEM.
Buckling analysis of a cylindrical shell, under neutron radiation environment
International Nuclear Information System (INIS)
Arani, A. Ghorbanpour; Ahmadi, M.; Ahmadi, A.; Rastgoo, A.; Sepyani, H.A.
2012-01-01
Highlights: ► The work investigates the buckling of a shell in the neutron radiation environment. ► Radiation induced porosity in elastic materials affects the material's properties. ► The data based technique was used to determine the volume fraction porosity. ► The theoretical formulations are presented based on the classical shell theory (CST). ► It was concluded that both T and neutron induced swelling have significant effects. - Abstract: This research investigates the buckling of a cylindrical shell in the neutron radiation environment, subjected to combined static and periodic axial forces. Radiation induced porosity in elastic materials affects the thermal, electrical and mechanical properties of the materials. In this study, the data based technique was used to determine the volume fraction porosity, P, of shell material. A least-squares fit of the Young's module data yielded the estimated Young's modulus. The shell assumed made of iron irradiated in the range of 2–15e−7 dPa/s at 345–650 °C and theoretical formulations are presented based on the classical shell theory (CST). The research deals with the problem theoretically; keeping in mind that one means of generating relevant design data is to investigate prototype structures. A parametric study is followed and the stability of shell is discussed. It is concluded that both temperature and neutron induced swelling have significant effects on the buckling load.
Nonlinear effects of high temperature on buckling of structural elements
International Nuclear Information System (INIS)
Iyengar, N.G.R.
1975-01-01
Structural elements used in nuclear reactors are subjected to high temperatures. Since with increase in temperature there is a gradual fall in the elastic modulus and the stress-strain relationship is nonlinear at these operating load levels, a realistic estimate of the buckling load should include this nonlinearity. In this paper the buckling loads for uniform columns with circular and rectangular cross-sections and different boundary conditions under high temperature environment are estimated. The stress-strain relationship for the material has been assumed to follow inverse Ramberg-Osgood law. In view of the fact that no closed form solutions are possible, approximate methods like perturbation and Galerkin techniques are used. Further, the solution for general value for 'm' is quite involved. Results have been obtained with values for 'm' as 3 and 5. Studies reveal that the influence of material nonlinearity on the buckling load is of the softening type, and it increases with increase in the value of 'm'. The nonlinear effects are more for clamped boundaries than for simply supported boundaries. For the first mode analysis both the methods are powerful. It is, however, felt that for higher modes the Galerkin method might be better in view of its simplicity. This investigation may be considered as a step towards a more general solution
Fabrication and buckling dynamics of nanoneedle AFM probes
Energy Technology Data Exchange (ETDEWEB)
Beard, J D; Gordeev, S N, E-mail: jdb28@bath.ac.uk [Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY (United Kingdom)
2011-04-29
A new method for the fabrication of high-aspect-ratio probes by electron beam induced deposition is described. This technique allows the fabrication of cylindrical 'nanoneedle' structures on the atomic force microscope (AFM) probe tip which can be used for accurate imaging of surfaces with high steep features. Scanning electron microscope (SEM) imaging showed that needles with diameters in the range of 18-100 nm could be obtained by this technique. The needles were shown to undergo buckling deformation under large tip-sample forces. The deformation was observed to recover elastically under vertical deformations of up to {approx} 60% of the needle length, preventing damage to the needle. A technique of stabilizing the needle against buckling by coating it with additional electron beam deposited carbon was also investigated; it was shown that coated needles of 75 nm or greater total diameter did not buckle even under tip-sample forces of {approx} 1.5 {mu}N.
Comparative thermal buckling analysis of functionally graded plate
Directory of Open Access Journals (Sweden)
Čukanović Dragan V.
2017-01-01
Full Text Available A thermal buckling analysis of functionally graded thick rectangular plates accord¬ing to von Karman non-linear theory is presented. The material properties of the functionally graded plate, except for the Poisson’s ratio, were assumed to be graded in the thickness direction, according to a power-law distribution, in terms of the volume fractions of the metal and ceramic constituents. Formulations of equilibrium and stability equations are derived using the high order shear deformation theory based on different types of shape functions. Analytical method for determination of the critical buckling temperature for uniform increase of temperature, linear and non-linear change of temperature across thickness of a plate is developed. Numeri¬cal results were obtained in МATLAB software using combinations of symbolic and numeric values. The paper presents comparative results of critical buckling tempera¬ture for different types of shape functions. The accuracy of the formulation presented is verified by comparing to results available from the literature.
Snap-Through Buckling Problem of Spherical Shell Structure
Directory of Open Access Journals (Sweden)
Sumirin Sumirin
2014-12-01
Full Text Available This paper presents results of a numerical study on the nonlinear behavior of shells undergoing snap-through instability. This research investigates the problem of snap-through buckling of spherical shells applying nonlinear finite element analysis utilizing ANSYS Program. The shell structure was modeled by axisymmetric thin shell of finite elements. Shells undergoing snap-through buckling meet with significant geometric change of their physical configuration, i.e. enduring large deflections during their deformation process. Therefore snap-through buckling of shells basically is a nonlinear problem. Nonlinear numerical operations need to be applied in their analysis. The problem was solved by a scheme of incremental iterative procedures applying Newton-Raphson method in combination with the known line search as well as the arc- length methods. The effects of thickness and depth variation of the shell is taken care of by considering their geometrical parameter l. The results of this study reveal that spherical shell structures subjected to pressure loading experience snap-through instability for values of l≥2.15. A form of ‘turn-back’ of the load-displacement curve took place at load levels prior to the achievement of the critical point. This phenomenon was observed for values of l=5.0 to l=7.0.
Buckling Experiment on Anisotropic Long and Short Cylinders
Directory of Open Access Journals (Sweden)
Atsushi Takano
2016-07-01
Full Text Available A buckling experiment was performed on anisotropic, long and short cylinders with various radius-to-thickness ratios. The 13 cylinders had symmetric and anti-symmetric layups, were between 2 and 6 in terms of the length-to-radius ratio, between 154 and 647 in radius-to-thickness ratio, and made of two kinds of carbon fiber reinforced plastic (CFRP prepreg with high or low fiber modulus. The theoretical buckling loads for the cylinders were calculated from the previously published solution by using linear bifurcation theory considering layup anisotropy and transverse shear deformation and by using deep shell theory to account for the effect of length and compared with the test results. The theoretical buckling loads for the cylinders were calculated from the previously published solution by using linear bifurcation theory considering layup anisotropy and transverse shear deformation and by using deep shell theory to account for the effect of length. The knockdown factor, defined as the ratio of the experimental value to the theoretical value, was found to be between 0.451 and 0.877. The test results indicated that a large length-to-radius ratio reduces the knockdown factor, but the radius-to-thickness ratio and other factors do not affect it.
Li, Yupeng; Kim, Hyung-Ick; Wei, Bingqing; Kang, Junmo; Choi, Jae-Boong; Nam, Jae-Do; Suhr, Jonghwan
2015-08-01
The local buckling behavior of vertically aligned carbon nanotubes (VACNTs) has been investigated and interpreted in the view of a collective nanotube response by taking van der Waals interactions into account. To the best of our knowledge, this is the first report on the case of collective VACNT behavior regarding van der Waals force among nanotubes as a lateral support effect during the buckling process. The local buckling propagation and development of VACNTs were experimentally observed and theoretically analyzed by employing finite element modeling with lateral support from van der Waals interactions among nanotubes. Both experimental and theoretical analyses show that VACNTs buckled in the bottom region with many short waves and almost identical wavelengths, indicating a high mode buckling. Furthermore, the propagation and development mechanism of buckling waves follow the wave damping effect.The local buckling behavior of vertically aligned carbon nanotubes (VACNTs) has been investigated and interpreted in the view of a collective nanotube response by taking van der Waals interactions into account. To the best of our knowledge, this is the first report on the case of collective VACNT behavior regarding van der Waals force among nanotubes as a lateral support effect during the buckling process. The local buckling propagation and development of VACNTs were experimentally observed and theoretically analyzed by employing finite element modeling with lateral support from van der Waals interactions among nanotubes. Both experimental and theoretical analyses show that VACNTs buckled in the bottom region with many short waves and almost identical wavelengths, indicating a high mode buckling. Furthermore, the propagation and development mechanism of buckling waves follow the wave damping effect. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03581c
DEFF Research Database (Denmark)
Sönmez, Ümit; Tutum, Cem Celal
2008-01-01
In this work, a new compliant bistable mechanism design is introduced. The combined use of pseudo-rigid-body model (PRBM) and the Elastica buckling theory is presented for the first time to analyze the new design. This mechanism consists of the large deflecting straight beams, buckling beams...... and the buckling Elastica solution for an original compliant mechanism kinematic analysis. New compliant mechanism designs are presented to highlight where such combined kinematic analysis is required....
Elastic and plastic buckling of shells. The CEASEMT system. Available results. Comparison with tests
International Nuclear Information System (INIS)
Hoffmann, A.; Roche, R.; Jeanpierre, F.; Goldstein, S.
1977-01-01
Specific routines for the analysis of elastic and elastic-plastic buckling have been written in the CEASEMT system of analysis by the finite element method. The basis of formulation are reviewed with emphasis on important points like: the correct and comprehensive formulation of the second order terms, the nonconservative loads. Some computational results are given and a comparison is made with experimental results (Euler type buckling of a long tube, elastic-plastic buckling of torispherical ends) [fr
International Nuclear Information System (INIS)
Syaputra, Marhamni; Wella, Sasfan Arman; Wungu, Triati Dewi Kencana; Purqon, Acep; Suprijadi
2015-01-01
We study the hydrogenation structures possessed by silicene i.e. planar (PL), low buckled (LB) and high buckled (HB). On those structures we found the hydrogenation process occurs with some particular notes. Hydrogen stable position on the silicene surface is determined by its initial configuration. We only considered the fully hydrogenated case with the formula unit (SiH) n for all of these structures. Physical and electronic structure shift after the process are compared with hydrogenated graphene. Moreover, we observed a chemical process in the presence of hydrogen on the PL structure by nudged elastic band (NEB) which illustrates how hydrogen has a significant impact to the force barrier of the PL that changing it from its original structure
Investigation of scleral buckling by CO2 laser
International Nuclear Information System (INIS)
Maswadi, S.
2001-05-01
This thesis investigates the effect of using the infrared wavelength CO 2 laser (10.6μm) as a localised heat source for inducing scleral buckling on eyes. Retinal detachment disease is a major cause of blindness and the scleral buckling is an important technique used in treatment. A radio-frequency excited 10.6λm laser source is used to heat collagen in the sclera above its shrinkage temperature so as to produce a localised indentation and deformation in the human eye (in vitro). Basic measurements of the onset shrinkage temperatures of porcine and human sclera are taken. Optical properties of sclera tissue at 10.6μm are also determined to provide information about the interaction of the CO 2 laser with the sclera. It is found that CO 2 laser radiation is highly absorbed by the scleral water. Optical diffraction technique is investigated to quantify in-plane deformation in the sclera tissue as result of heating by producing grating on porcine and human sclera using the ArF laser (193nm). Photothermal deflection technique is also used to investigate scleral ablation by using the TEA and Ultrapulse CO 2 laser. This technique provides a useful guide to the regime where ablation rather than heat shrinkage of collagen in the sclera will dominate using the Ultrapulse CO 2 laser. A quantitative assessment of buckling using the technique of projection moire interferometry is described which allows a non-contact measurement to be made of the out-of-plane displacement by laser radiation. In-plane surface strain (shrinkage) has also been demonstrated using in-situ optical microscopy of the laser treated eye. The moire method is suitable to obtain information on buckling in real time and to obtain a three-dimensional view of the eye surface as laser treatment proceeds. A theoretical heat flow model is described for predicting the temperature profile produced in the sclera using the Ultrapulse CO 2 laser. For appropriate exposure parameters the CO 2 laser is found to be an
Investigation of scleral buckling by CO{sub 2} laser
Energy Technology Data Exchange (ETDEWEB)
Maswadi, S
2001-05-01
This thesis investigates the effect of using the infrared wavelength CO{sub 2} laser (10.6{mu}m) as a localised heat source for inducing scleral buckling on eyes. Retinal detachment disease is a major cause of blindness and the scleral buckling is an important technique used in treatment. A radio-frequency excited 10.6{lambda}m laser source is used to heat collagen in the sclera above its shrinkage temperature so as to produce a localised indentation and deformation in the human eye (in vitro). Basic measurements of the onset shrinkage temperatures of porcine and human sclera are taken. Optical properties of sclera tissue at 10.6{mu}m are also determined to provide information about the interaction of the CO{sub 2} laser with the sclera. It is found that CO{sub 2} laser radiation is highly absorbed by the scleral water. Optical diffraction technique is investigated to quantify in-plane deformation in the sclera tissue as result of heating by producing grating on porcine and human sclera using the ArF laser (193nm). Photothermal deflection technique is also used to investigate scleral ablation by using the TEA and Ultrapulse CO{sub 2} laser. This technique provides a useful guide to the regime where ablation rather than heat shrinkage of collagen in the sclera will dominate using the Ultrapulse CO{sub 2} laser. A quantitative assessment of buckling using the technique of projection moire interferometry is described which allows a non-contact measurement to be made of the out-of-plane displacement by laser radiation. In-plane surface strain (shrinkage) has also been demonstrated using in-situ optical microscopy of the laser treated eye. The moire method is suitable to obtain information on buckling in real time and to obtain a three-dimensional view of the eye surface as laser treatment proceeds. A theoretical heat flow model is described for predicting the temperature profile produced in the sclera using the Ultrapulse CO{sub 2} laser. For appropriate exposure
Effect of scleral buckle removal on strabismus surgery outcomes after retinal detachment repair
Chang, Jee Ho; Hutchinson, Amy; Zhang, Monica; Lambert, Scott R.
2015-01-01
Background/Aims To investigate the effect of scleral buckle removal on the outcomes of strabismus surgery in patients with a prior history of retinal detachment surgery. Methods We reviewed the medical records of 18 patients who underwent strabismus surgery following a scleral buckling procedure at one institution. We investigated the effect of multiple variables on outcome, including: gender, age, surgeon, number of strabismus surgeries, adjustable suture use, previous pars plana vitrectomy, preoperative best-corrected visual acuity and time of surgery. Outcomes were considered successful if there was ≤ 10 prism diopter (PD) residual horizontal and/or ≤ 4 PD residual vertical deviation. Outcomes were analyzed statistically using Fisher's exact test and Mann-Whitney test. Results Strabismus surgery coupled with scleral buckle removal was associated with a higher rate of success (success with buckle removal, 62.5%; success without buckle removal, 10.0%; p=0.04). There were no significant difference in preoperative findings between the scleral buckle removal and non- removal groups. No retinal redetachments occurred after scleral buckle removal. Conclusion In our series, scleral buckle removal was associated with improved surgical outcome in patients with strabismus following a scleral buckling procedure. PMID:24299332
Ko, William L.; Jackson, Raymond H.
1991-01-01
Combined compressive and shear buckling analysis was conducted on flat rectangular sandwich panels with the consideration of transverse shear effects of the core. The sandwich panel is fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that the square panel has the highest combined load buckling strength, and that the buckling strength decreases sharply with the increases of both temperature and panel aspect ratio. The effect of layup (fiber orientation) on the buckling strength of the panels was studied in detail. The metal matrix composite sandwich panel was much more efficient than the sandwich panel with nonreinforced face sheets and had the same specific weight.
Directory of Open Access Journals (Sweden)
Rubens Camargo Siqueira
2007-03-01
Full Text Available PURPOSE: To compare the surgical results of vitrectomy with and without scleral buckling for rhegmatogenous retinal detachment (RD. METHODS: Fifty-one patients with rhegmatogenous retinal detachment with proliferative vitreoretinopathy (PVR at different stages were submitted to pars plana vitrectomy as the primary surgery, 23 patients (45.09% with scleral buckle (group I and 28 (54.90% without scleral buckle (group II. Visual acuity, anterior segment complications, intraocular pressure, strabismus and retina reattachment rate were evaluated in both groups. RESULTS: The anatomical success and postoperative complications were similar in both groups. Retinal reattachment was achieved in 20 of 23 eyes (87% of group I and in 24 of 28 eyes (85.7% of group II after the initial surgery (p=1.000. Elevated intraocular pressure was noted in 2 eyes (8.7% of group I and 1 eye (3.6% of group II (p=0.583. Corneal abnormalities were seen in 3 eyes (13% of group I and 2 eyes (7.19% of the group II (p=0.647. Visual acuity improved from a preoperative median of 20/200 to a median of 20/100 in group 1 and from 20/400 to 20/100 in group 2; the difference between the two groups was statistically significant (pOBJETIVOS: Comparar os resultados cirúrgicos da vitrectomia com e sem "buckle" escleral para descolamento da retina regmatogênico (DR. MÉTODOS: Cinqüenta e um pacientes com descolamento da retina regmatogênico com proliferação vitreorretiniana (PVR em diferentes estádios foram submetidos a vitrectomia pars plana como cirurgia primária; 23 pacientes (45,09% com buckle escleral (grupo 1 e 28 pacientes (54,90% sem "buckle" escleral (grupo 2. Acuidade visual, complicações do segmento anterior, pressão intra-ocular, estrabismo e razão do redescolamento da retina foram avaliados em ambos os grupos. RESULTADOS: O sucesso anatômico e complicações pós-operatórias foram semelhantes em ambos os grupos. A reaplicação da retina foi obtida em 20 dos 23
Evolution of normal stress and surface roughness in buckled thin films
Palasantzas, G; De Hosson, JTM
2003-01-01
In this work we investigate buckling of compressed elastic thin films, which are bonded onto a viscous layer of finite thickness. It is found that the normal stress exerted by the viscous layer on the elastic film evolves with time showing a minimum at early buckling stages, while it increases at
The Carnegie-Irvine Galaxy Survey. V. Statistical Study of Bars and Buckled Bars
Li, Zhao-Yu; Ho, Luis C.; Barth, Aaron J.
2017-08-01
Simulations have shown that bars are subject to a vertical buckling instability that transforms thin bars into boxy or peanut-shaped structures, but the physical conditions necessary for buckling to occur are not fully understood. We use the large sample of local disk galaxies in the Carnegie-Irvine Galaxy Survey to examine the incidence of bars and buckled bars across the Hubble sequence. Depending on the disk inclination angle (I), a buckled bar reveals itself as either a boxy/peanut-shaped bulge (at high I) or as a barlens structure (at low I). We visually identify bars, boxy/peanut-shaped bulges, and barlenses, and examine the dependence of bar and buckled bar fractions on host galaxy properties, including Hubble type, stellar mass, color, and gas mass fraction. We find that the barred and unbarred disks show similar distributions in these physical parameters. The bar fraction is higher (70%-80%) in late-type disks with low stellar mass (M * 1010.5 M ⊙), and decreases with higher gas mass ratio. These results suggest that bars are more difficult to grow in massive disks that are dynamically hotter than low-mass disks. However, once a bar forms, it can easily buckle in the massive disks, where a deeper potential can sustain the vertical resonant orbits. We also find a probable buckling bar candidate (ESO 506-G004) that could provide further clues to understand the timescale of the buckling process.
Buckling Response of a Large-Scale, Seamless, Orthogrid-Stiffened Metallic Cylinder
Rudd, Michelle Tillotson; Hilburger, Mark W.; Lovejoy, Andrew E.; Lindell, Michael C.; Gardner, Nathaniel W.; Schultz, Marc R.
2018-01-01
Results from the buckling test of a compression-loaded 8-ft-diameter seamless (i.e., without manufacturing joints), orthogrid-stiffened metallic cylinder are presented. This test was used to assess the buckling response and imperfection sensitivity characteristics of a seamless cylinder. In addition, the test article and test served as a technology demonstration to show the application of the flow forming manufacturing process to build more efficient buckling-critical structures by eliminating the welded joints that are traditionally used in the manufacturing of large metallic barrels. Pretest predictions of the cylinder buckling response were obtained using a finite-element model that included measured geometric imperfections. The buckling load predicted using this model was 697,000 lb, and the test article buckled at 743,000 lb (6% higher). After the test, the model was revised to account for measured variations in skin and stiffener geometry, nonuniform loading, and material properties. The revised model predicted a buckling load of 754,000 lb, which is within 1.5% of the tested buckling load. In addition, it was determined that the load carrying capability of the seamless cylinder is approximately 28% greater than a corresponding cylinder with welded joints.
Numerical analysis of magnetoelastic coupled buckling of fusion reactor components
International Nuclear Information System (INIS)
Demachi, K.; Yoshida, Y.; Miya, K.
1994-01-01
For a tokamak fusion reactor, it is one of the most important subjects to establish the structural design in which its components can stand for strong magnetic force induced by plasma disruption. A number of magnetostructural analysis of the fusion reactor components were done recently. However, in these researches the structural behavior was calculated based on the small deformation theory where the nonlinearity was neglected. But it is known that some kinds of structures easily exceed the geometrical nonlinearity. In this paper, the deflection and the magnetoelastic buckling load of fusion reactor components during plasma disruption were calculated
Flexural torsional buckling of uniformly compressed beam-like structures
Ferretti, M.
2018-02-01
A Timoshenko beam model embedded in a 3D space is introduced for buckling analysis of multi-store buildings, made by rigid floors connected by elastic columns. The beam model is developed via a direct approach, and the constitutive law, accounting for prestress forces, is deduced via a suitable homogenization procedure. The bifurcation analysis for the case of uniformly compressed buildings is then addressed, and numerical results concerning the Timoshenko model are compared with 3D finite element analyses. Finally, some conclusions and perspectives are drawn.
Geometric buckling measurements using the pulsed neutron source method
Energy Technology Data Exchange (ETDEWEB)
Sjoestrand, N G; Mednis, J; Nilsson, T
1959-03-15
The geometric buckling of cylindrical reactors with one or both ends rounded has been determined by pulsed source measurements with small polyethylene geometries. The results were in general accord with theoretical calculations. The diffusion parameters of polyethylene were also determined. The diffusion length was 2.12 {+-} 0.03 cm, and for the capture cross section of hydrogen a value of 0.337 {+-} 0.005 barns was found. The effect of control rods was studied using thin cadmium rods in water. Good agreement was found for axial, central rods, whereas the theoretical predictions for the effect of diagonal rods were too high.
Compressive buckling of black phosphorene nanotubes: an atomistic study
Nguyen, Van-Trang; Le, Minh-Quy
2018-04-01
We investigate through molecular dynamics finite element method with Stillinger-Weber potential the uniaxial compression of armchair and zigzag black phosphorene nanotubes. We focus especially on the effects of the tube’s diameter with fixed length-diameter ratio, effects of the tube’s length for a pair of armchair and zigzag tubes of equal diameters, and effects of the tube’s diameter with fixed lengths. Their Young’s modulus, critical compressive stress and critical compressive strain are studied and discussed for these 3 case studies. Compressive buckling was clearly observed in the armchair nanotubes. Local bond breaking near the boundary occurred in the zigzag ones under compression.
Impact of Holes on the Buckling of RHS Steel Column
Directory of Open Access Journals (Sweden)
Najla'a H. AL-Shareef
2018-03-01
Full Text Available This study presented an experimental and theoretical study on the effect of hole on the behavior of rectangular hollow steel columns subjected to axial compression load. Specimens were tested to investigated the ultimate capacity and the load- axial displacement behavior of steel columns. In this paper finite element analysis is done by using general purpose ANSYS 12.0 to investigate the behavior of rectangular hollow steel column with hole. In the experimental work, rectangular hollow steel columns with rounded corners were used in the constriction of the specimens which have dimensions of cross section (50*80mm and height of (250 and 500mm with thickness of (1.25,4 and 6mm with hole ((α*80*80mm when α is equal to (0.2,0.4,0.6 and 0.8. Twenty four columns under compression load were tested in order to investigate the effect of hole on the ultimate load of rectangular hollow steel column. The experimental results indicated that the typical failure mode for all the tested hollow specimen was the local buckling. The tested results indicated that the increasing of hole dimension leads to reduction in ultimate loads of tested column to 75%. The results show the reducing of load by 94.7% due to decreasing the thickness of column while the hole size is constant (0.2*80*80. The buckling load decreases by 84.62% when hole position changes from Lo=0.25L to 0.75L. Holes can be made in the middle of column with dimension up to 0.4 of column's length. The AISC (2005 presents the values closest to the experimental results for the nominal yielding compressive strength. The effect for increasing of slendeness ratio and thickness to area ratio(t/A leading to decreacing the critical stresses and the failure of column with large size of hole and (t/A ratio less than 0.74% was due to lacal buckling while the global buckling failure was abserve for column with small size of hole and (t/A ratio above than 0.74%. The compersion between the experimental
Geometric buckling measurements using the pulsed neutron source method
International Nuclear Information System (INIS)
Sjoestrand, N.G.; Mednis, J.; Nilsson, T.
1959-03-01
The geometric buckling of cylindrical reactors with one or both ends rounded has been determined by pulsed source measurements with small polyethylene geometries. The results were in general accord with theoretical calculations. The diffusion parameters of polyethylene were also determined. The diffusion length was 2.12 ± 0.03 cm, and for the capture cross section of hydrogen a value of 0.337 ± 0.005 barns was found. The effect of control rods was studied using thin cadmium rods in water. Good agreement was found for axial, central rods, whereas the theoretical predictions for the effect of diagonal rods were too high
Buckling of a stiff thin film on an elastic graded compliant substrate
Chen, Zhou; Chen, Weiqiu; Song, Jizhou
2017-12-01
The buckling of a stiff film on a compliant substrate has attracted much attention due to its wide applications such as thin-film metrology, surface patterning and stretchable electronics. An analytical model is established for the buckling of a stiff thin film on a semi-infinite elastic graded compliant substrate subjected to in-plane compression. The critical compressive strain and buckling wavelength for the sinusoidal mode are obtained analytically for the case with the substrate modulus decaying exponentially. The rigorous finite element analysis (FEA) is performed to validate the analytical model and investigate the postbuckling behaviour of the system. The critical buckling strain for the period-doubling mode is obtained numerically. The influences of various material parameters on the results are investigated. These results are helpful to provide physical insights on the buckling of elastic graded substrate-supported thin film.
Thermal buckling behavior of defective CNTs under pre-load: A molecular dynamics study.
Mehralian, Fahimeh; Tadi Beni, Yaghoub; Kiani, Yaser
2017-05-01
Current study is concentrated on the extraordinary properties of defective carbon nanotubes (CNTs). The role of vacancy defects in thermal buckling response of precompressed CNTs is explored via molecular dynamics (MD) simulations. Defective CNTs are initially compressed at a certain ratio of their critical buckling strain and then undergo a uniform temperature rise. Comprehensive study is implemented on both armchair and zigzag CNTs with different vacancy defects including monovacancy, symmetric bivacancy and asymmetric bivacancy. The results reveal that defects have a pronounced impact on the buckling behavior of CNTs; interestingly, defective CNTs under compressive pre-load show higher resistance to thermal buckling than pristine ones. In the following, the buckling response of defective CNTs is shown to be dependent on the vacancy defects, location of defects and chirality. Copyright © 2017 Elsevier Inc. All rights reserved.
Micro-wrinkling and delamination-induced buckling of stretchable electronic structures
International Nuclear Information System (INIS)
Oyewole, O. K.; Yu, D.; Du, J.; Asare, J.; Fashina, A.; Oyewole, D. O.; Anye, V. C.; Zebaze Kana, M. G.
2015-01-01
This paper presents the results of experimental and theoretical/computational micro-wrinkles and buckling on the surfaces of stretchable poly-dimethylsiloxane (PDMS) coated with nano-scale Gold (Au) layers. The wrinkles and buckles are formed by the unloading of pre-stretched PDMS/Au structure after the evaporation of nano-scale Au layers. They are then characterized using atomic force microscopy and scanning electron microscopy. The critical stresses required for wrinkling and buckling are analyzed using analytical models. The possible interfacial cracking that can occur along with film buckling is also studied using finite element simulations of the interfacial crack growth. The implications of the results are discussed for potential applications of micro-wrinkles and micro-buckles in stretchable electronic structures and biomedical devices
Cox, B. S.; Groh, R. M. J.; Avitabile, D.; Pirrera, A.
2018-07-01
The buckling and post-buckling behaviour of slender structures is increasingly being harnessed for smart functionalities. Equally, the post-buckling regime of many traditional engineering structures is not being used for design and may therefore harbour latent load-bearing capacity for further structural efficiency. Both applications can benefit from a robust means of modifying and controlling the post-buckling behaviour for a specific purpose. To this end, we introduce a structural design paradigm termed modal nudging, which can be used to tailor the post-buckling response of slender engineering structures without any significant increase in mass. Modal nudging uses deformation modes of stable post-buckled equilibria to perturb the undeformed baseline geometry of the structure imperceptibly, thereby favouring the seeded post-buckling response over potential alternatives. The benefits of this technique are enhanced control over the post-buckling behaviour, such as modal differentiation for smart structures that use snap-buckling for shape adaptation, or alternatively, increased load-carrying capacity, increased compliance or a shift from imperfection sensitivity to imperfection insensitivity. Although these concepts are, in theory, of general applicability, we concentrate here on planar frame structures analysed using the nonlinear finite element method and numerical continuation procedures. Using these computational techniques, we show that planar frame structures may exhibit isolated regions of stable equilibria in otherwise unstable post-buckling regimes, or indeed stable equilibria entirely disconnected from the natural structural response. In both cases, the load-carrying capacity of these isolated stable equilibria is greater than the natural structural response of the frames. Using the concept of modal nudging it is possible to "nudge" the frames onto these equilibrium paths of greater load-carrying capacity. Due to the scale invariance of modal nudging
The buckling of fuel rods in transportation casks under hypothetical accident conditions
International Nuclear Information System (INIS)
Bjorkman, G.S.
2004-01-01
The buckling analysis of fuel rods during an end drop impact of a spent fuel transportation cask has traditionally been performed to demonstrate the structural integrity of the fuel rod cladding or the integrity of the fuel geometry in criticality evaluations following a cask drop event. The actual calculation of the fuel rod buckling load, however, has been the subject of some controversy, with estimates of the critical buckling load differing by as much as a factor of 5. Typically, in the buckling analysis of a fuel rod, assumptions are made regarding the percentage of fuel mass that is bonded to or participates with the cladding during the buckling process, with estimates ranging from 0 to 100%. The greater the percentage of fuel mass that is assumed to be bonded to the cladding the higher the inertia loads on the cladding, and, therefore, the lower the ''g'' value at which buckling occurs. Current published solutions do not consider displacement compatibility between the fuel and the cladding. By invoking displacement compatibility between the fuel column and the cladding column, this paper presents an exact solution for the buckling of fuel rods under inertia loading. The results show that the critical inertia load magnitude for the buckling of a fuel rod depends on the weight of the cladding and the total weight of the fuel, regardless of the percentage of fuel mass that is assumed to be attached to or participate with the cladding in the buckling process. Therefore, 100% of the fuel always participates in the buckling of a fuel rod under inertia loading
Buckling of Single-Crystal Silicon Nanolines under Indentation
Directory of Open Access Journals (Sweden)
Min K. Kang
2008-01-01
Full Text Available Atomic force microscope-(AFM- based indentation tests were performed to examine mechanical properties of parallel single-crystal silicon nanolines (SiNLs of sub-100-nm line width, fabricated by a process combining electron-beam lithography and anisotropic wet etching. The SiNLs have straight and nearly atomically flat sidewalls, and the cross section is almost perfectly rectangular with uniform width and height along the longitudinal direction. The measured load-displacement curves from the indentation tests show an instability with large displacement bursts at a critical load ranging from 480 μN to 700 μN. This phenomenon is attributed to a transition of the buckling mode of the SiNLs under indentation. Using a set of finite element models with postbuckling analyses, we analyze the indentation-induced buckling modes and investigate the effects of tip location, contact friction, and substrate deformation on the critical load of mode transition. The results demonstrate a unique approach for the study of nanomaterials and patterned nanostructures via a combination of experiments and modeling.
Robust simulation of buckled structures using reduced order modeling
International Nuclear Information System (INIS)
Wiebe, R.; Perez, R.A.; Spottswood, S.M.
2016-01-01
Lightweight metallic structures are a mainstay in aerospace engineering. For these structures, stability, rather than strength, is often the critical limit state in design. For example, buckling of panels and stiffeners may occur during emergency high-g maneuvers, while in supersonic and hypersonic aircraft, it may be induced by thermal stresses. The longstanding solution to such challenges was to increase the sizing of the structural members, which is counter to the ever present need to minimize weight for reasons of efficiency and performance. In this work we present some recent results in the area of reduced order modeling of post- buckled thin beams. A thorough parametric study of the response of a beam to changing harmonic loading parameters, which is useful in exposing complex phenomena and exercising numerical models, is presented. Two error metrics that use but require no time stepping of a (computationally expensive) truth model are also introduced. The error metrics are applied to several interesting forcing parameter cases identified from the parametric study and are shown to yield useful information about the quality of a candidate reduced order model. Parametric studies, especially when considering forcing and structural geometry parameters, coupled environments, and uncertainties would be computationally intractable with finite element models. The goal is to make rapid simulation of complex nonlinear dynamic behavior possible for distributed systems via fast and accurate reduced order models. This ability is crucial in allowing designers to rigorously probe the robustness of their designs to account for variations in loading, structural imperfections, and other uncertainties. (paper)
Robust simulation of buckled structures using reduced order modeling
Wiebe, R.; Perez, R. A.; Spottswood, S. M.
2016-09-01
Lightweight metallic structures are a mainstay in aerospace engineering. For these structures, stability, rather than strength, is often the critical limit state in design. For example, buckling of panels and stiffeners may occur during emergency high-g maneuvers, while in supersonic and hypersonic aircraft, it may be induced by thermal stresses. The longstanding solution to such challenges was to increase the sizing of the structural members, which is counter to the ever present need to minimize weight for reasons of efficiency and performance. In this work we present some recent results in the area of reduced order modeling of post- buckled thin beams. A thorough parametric study of the response of a beam to changing harmonic loading parameters, which is useful in exposing complex phenomena and exercising numerical models, is presented. Two error metrics that use but require no time stepping of a (computationally expensive) truth model are also introduced. The error metrics are applied to several interesting forcing parameter cases identified from the parametric study and are shown to yield useful information about the quality of a candidate reduced order model. Parametric studies, especially when considering forcing and structural geometry parameters, coupled environments, and uncertainties would be computationally intractable with finite element models. The goal is to make rapid simulation of complex nonlinear dynamic behavior possible for distributed systems via fast and accurate reduced order models. This ability is crucial in allowing designers to rigorously probe the robustness of their designs to account for variations in loading, structural imperfections, and other uncertainties.
Buckling behavior analysis of spacer grid by lateral impact load
International Nuclear Information System (INIS)
Yoon, Kyung Ho; Kang, Heung Seok; Kim, Hyung Kyu; Song, Kee Nam
2000-05-01
The spacer grid is one of the main structural components in the fuel assembly, Which supports the fuel rods, guides cooling water, and protects the system from an external impact load, such as earthquakes. Therefore, the mechanical and structural properties of the spacer grids must be extensively examined while designing it. In this report, free fall type shock tests on the several kinds of the specimens of the spacer grids were also carried out in order to compare the results among the candidate grids. A free fall carriage on the specimen accomplishes the test. In addition to this, a finite element method for predicting the critical impact strength of the spacer grids is described. FE method on the buckling behavior of the spacer grids are performed for a various array of sizes of the grids considering that the spacer grid is an assembled structure with thin-walled plates and imposing proper boundary conditions by nonlinear dynamic impact analysis using ABAQUS/explicit code. The simulated results results also similarly predicted the local buckling phenomena and were found to give good correspondence with the shock test results
Nonlinear buckling analyses of a small-radius carbon nanotube
International Nuclear Information System (INIS)
Liu, Ning; Li, Min; Jia, Jiao; Wang, Yong-Gang
2014-01-01
Carbon nanotube (CNT) was first discovered by Sumio Iijima. It has aroused extensive attentions of scholars from all over the world. Over the past two decades, we have acquired a lot of methods to synthesize carbon nanotubes and learn their many incredible mechanical properties such as experimental methods, theoretical analyses, and computer simulations. However, the studies of experiments need lots of financial, material, and labor resources. The calculations will become difficult and time-consuming, and the calculations may be even beyond the realm of possibility when the scale of simulations is large, as for computer simulations. Therefore, it is necessary for us to explore a reasonable continuum model, which can be applied into nano-scale. This paper attempts to develop a mathematical model of a small-radius carbon nanotube based on continuum theory. An Isotropic circular cross-section, Timoshenko beam model is used as a simplified mechanical model for the small-radius carbon nanotube. Theoretical part is mainly based on modified couple stress theory to obtain the numerical solutions of buckling deformation. Meanwhile, the buckling behavior of the small radius carbon nanotube is simulated by Molecular Dynamics method. By comparing with the numerical results based on modified couple stress theory, the dependence of the small-radius carbon nanotube mechanical behaviors on its elasticity constants, small-size effect, geometric nonlinearity, and shear effect is further studied, and an estimation of the small-scale parameter of a CNT (5, 5) is obtained
Buckling of an Elastic Ridge: Competition between Wrinkles and Creases
Lestringant, C.; Maurini, C.; Lazarus, A.; Audoly, B.
2017-04-01
We investigate the elastic buckling of a triangular prism made of a soft elastomer. A face of the prism is bonded to a stiff slab that imposes an average axial compression. We observe two possible buckling modes which are localized along the free ridge. For ridge angles ϕ below a critical value ϕ⋆≈9 0 ° , experiments reveal an extended sinusoidal mode, while for ϕ above ϕ⋆, we observe a series of creases progressively invading the lateral faces starting from the ridge. A numerical linear stability analysis is set up using the finite-element method and correctly predicts the sinusoidal mode for ϕ ≤ϕ⋆, as well as the associated critical strain ɛc(ϕ ). The experimental transition at ϕ⋆ is found to occur when this critical strain ɛc(ϕ ) attains the value ɛc(ϕ⋆)=0.44 corresponding to the threshold of the subcritical surface creasing instability. Previous analyses have focused on elastic crease patterns appearing on planar surfaces, where the role of scale invariance has been emphasized; our analysis of the elastic ridge provides a different perspective, and reveals that scale invariance is not a sufficient condition for localization.
Nonlinear Dynamic Buckling of Damaged Composite Cylindrical Shells
Institute of Scientific and Technical Information of China (English)
WANG Tian-lin; TANG Wen-yong; ZHANG Sheng-kun
2007-01-01
Based on the first order shear deformation theory(FSDT), the nonlinear dynamic equations involving transverse shear deformation and initial geometric imperfections were obtained by Hamilton's philosophy. Geometric deformation of the composite cylindrical shell was treated as the initial geometric imperfection in the dynamic equations, which were solved by the semi-analytical method in this paper. Stiffness reduction was employed for the damaged sub-layer, and the equivalent stiffness matrix was obtained for the delaminated area. By circumferential Fourier series expansions for shell displacements and loads and by using Galerkin technique, the nonlinear partial differential equations were transformed to ordinary differential equations which were finally solved by the finite difference method. The buckling was judged from shell responses by B-R criteria, and critical loads were then determined. The effect of the initial geometric deformation on the dynamic response and buckling of composite cylindrical shell was also discussed, as well as the effects of concomitant delamination and sub-layer matrix damages.
Nonlinear buckling analyses of a small-radius carbon nanotube
Energy Technology Data Exchange (ETDEWEB)
Liu, Ning, E-mail: liuxiao@ase.buaa.edu.cn; Li, Min; Jia, Jiao [School of Aeronautic Science and Engineering, Beihang University, Beijing 100091 (China); Wang, Yong-Gang [Department of Applied Mechanics, China Agricultural University, Beijing 100083 (China)
2014-04-21
Carbon nanotube (CNT) was first discovered by Sumio Iijima. It has aroused extensive attentions of scholars from all over the world. Over the past two decades, we have acquired a lot of methods to synthesize carbon nanotubes and learn their many incredible mechanical properties such as experimental methods, theoretical analyses, and computer simulations. However, the studies of experiments need lots of financial, material, and labor resources. The calculations will become difficult and time-consuming, and the calculations may be even beyond the realm of possibility when the scale of simulations is large, as for computer simulations. Therefore, it is necessary for us to explore a reasonable continuum model, which can be applied into nano-scale. This paper attempts to develop a mathematical model of a small-radius carbon nanotube based on continuum theory. An Isotropic circular cross-section, Timoshenko beam model is used as a simplified mechanical model for the small-radius carbon nanotube. Theoretical part is mainly based on modified couple stress theory to obtain the numerical solutions of buckling deformation. Meanwhile, the buckling behavior of the small radius carbon nanotube is simulated by Molecular Dynamics method. By comparing with the numerical results based on modified couple stress theory, the dependence of the small-radius carbon nanotube mechanical behaviors on its elasticity constants, small-size effect, geometric nonlinearity, and shear effect is further studied, and an estimation of the small-scale parameter of a CNT (5, 5) is obtained.
Crown sealing and buckling instability during water entry of spheres
Marston, J. O.
2016-04-05
We present new observations from an experimental investigation of the classical problem of the crown splash and sealing phenomena observed during the impact of spheres onto quiescent liquid pools. In the experiments, a 6 m tall vacuum chamber was used to provide the required ambient conditions from atmospheric pressure down to of an atmosphere, whilst high-speed videography was exploited to focus primarily on the above-surface crown formation and ensuing dynamics, paying particular attention to the moments just prior to the surface seal. In doing so, we have observed a buckling-type azimuthal instability of the crown. This instability is characterised by vertical striations along the crown, between which thin films form that are more susceptible to the air flow and thus are drawn into the closing cavity, where they atomize to form a fine spray within the cavity. To elucidate to the primary mechanisms and forces at play, we varied the sphere diameter, liquid properties and ambient pressure. Furthermore, a comparison between the entry of room-temperature spheres, where the contact line pins around the equator, and Leidenfrost spheres (i.e. an immersed superheated sphere encompassed by a vapour layer), where there is no contact line, indicates that the buckling instability appears in all crown sealing events, but is intensified by the presence of a pinned contact line. © 2016 Cambridge University Press.
Condenser tube buckling within tube-tubesheet joints
International Nuclear Information System (INIS)
Willertz, L.E.; Kalnins, A.; Updike, D.P.
1991-01-01
The problem of the appearance of protrusions, or bumps, in the interior of roller-expanded tubes within a tubesheet is addressed. Such bumps have been observed in condensers of power plants. A brief history of the reported occurrences of the bumps is given. The hypothesis is advanced that the mechanics of the formation of the bumps is similar to a buckling problem that has 'bifurcation at infinity'. Following this hypothesis, a two-dimensional physical model is developed, and the application of this model to study a three-dimensional bump is proposed. It is proposed in this paper that an initial deviation from the circular shape of the tube required to produce a bump. It is shown that without such a deviation the tubes cannot buckle. An experiment with short tube segments has been performed that verifies some of the features of the observed condenser tube bumps. Exactly what force produced the initial deviation for the observed bumps is still unknown. Available evidence implicates the hydro-laser jet that is used in the cleaning of tubes and tubesheets. A scenario of how a bump could have been produced by the hydro-laser jet is proposed. (author)
Film stresses and electrode buckling in organic solar cells
Brand, Vitali
2012-08-01
We investigate the film stresses that develop in the polymer films and metal electrodes of poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction (BHJ) organic solar cells. A compressive biaxial stress of ∼-36 MPa was measured in PEDOT:PSS while a tensile stress of ∼6 MPa was measured in the BHJ layer. We then analyze the effect of electrode deposition rate on the film stresses in the Al electrode. Compressive stresses of ∼-100 to -145 MPa in the Al electrode lead to a buckling instability resulting in undulating electrode surface topography. The BHJ layer was found to have the lowest cohesion (∼1.5-1.8 J/m 2) among the layers of the solar cell and dependent on the Al electrode deposition rate. The cohesive failure path in the BHJ layer exhibited the same periodicity and orientation of the Al electrode buckling topography. We discuss the implications of the film stresses on damage processes during device fabrication and operation. © 2012 Elsevier B.V. All rights reserved.
Huang, Shicheng; Tan, Likun; Hu, Nan; Grover, Hannah; Chu, Kevin; Chen, Zi
This reserach introduces a new numerical approach of calculating the post-buckling configuration of a thin rod embedded in elastic media. The theoretical base is the governing ODEs describing the balance of forces and moments, the length conservation, and the physics of bending and twisting by Laudau and Lifschitz. The numerical methods applied in the calculation are continuation method and Newton's method of iteration in combination with spectrum method. To the authors' knowledge, it is the first trial of directly applying the L-L theory to numerically studying the phenomenon of rod buckling in elastic medium. This method accounts for nonlinearity of geometry, thus is capable of calculating large deformation. The stability of this method is another advantage achieved by expressing the governing equations in a set of first-order derivative form. The wave length, amplitude, and decay effect all agree with the experiment without any further assumptions. This program can be applied to different occasions with varying stiffness of the elastic medai and rigidity of the rod.
Directory of Open Access Journals (Sweden)
Kołakowski Zbigniew
2016-06-01
Full Text Available A review of papers that investigate the static and dynamic coupled buckling and post-buckling behaviour of thin-walled structures is carried out. The problem of static coupled buckling is sufficiently well-recognized. The analysis of dynamic interactive buckling is limited in practice to columns, single plates and shells. The applications of finite element method (FEM or/and analytical-numerical method (ANM to solve interaction buckling problems are on-going. In Poland, the team of scientists from the Department of Strength of Materials, Lodz University of Technology and co-workers developed the analytical-numerical method. This method allows to determine static buckling stresses, natural frequencies, coefficients of the equation describing the post-buckling equilibrium path and dynamic response of the plate structure subjected to compression load and/or bending moment. Using the dynamic buckling criteria, it is possible to determine the dynamic critical load. They presented a lot of interesting results for problems of the static and dynamic coupled buckling of thin-walled plate structures with complex shapes of cross-sections, including an interaction of component plates. The most important advantage of presented analytical-numerical method is that it enables to describe all buckling modes and the post-buckling behaviours of thin-walled columns made of different materials. Thin isotropic, orthotropic or laminate structures were considered.
Effect of microscale gaseous thermal conduction on the thermal behavior of a buckled microbridge
International Nuclear Information System (INIS)
Wang Jiaqi; Tang Zhenan; Li Jinfeng; Zhang Fengtian
2008-01-01
A microbridge is a basic micro-electro-mechanical systems (MEMS) device and has great potential for application in microsensors and microactuators. The thermal behavior of a microbridge is important for designing a microbridge-based thermal microsensor or microactuator. To study the thermal behavior of a microbridge consisting of Si 3 N 4 and polysilicon with a 2 µm suspended gap between the substrate and the microbridge while the microbridge is heated by an electrical current fed through the polysilicon, a microbridge model is developed to correlate theoretically the input current and the temperature distribution under the buckling conditions, especially considering the effects of the microscale gaseous thermal conduction due to the microbridge buckling. The calculated results show that the buckling of the microbridge changes the microscale gaseous thermal conduction, and thus greatly affects the thermal behavior of the microbridge. We also evaluate the effects of initial buckling on the temperature distribution of the microbridge. The experimental results show that buckling should be taken into account if the buckling is large. Therefore, the variation in gaseous thermal conduction and the suspended gap height caused by the buckling should be considered in the design of such thermomechanical microsensors and microactuators, which requires more accurate thermal behavior
The effect of thermal loads on buckling strength of cylindrical shells
International Nuclear Information System (INIS)
Kawamoto, Y.; Kodama, T.; Matsuura, S.
1993-01-01
Nuclear power plant components must be designed taking account of strong seismic loads in countries with frequent earthquakes like Japan. When designing such thin-walled shell components as a main vessel of a fast breeder reactor (FBR), one should consider the possibility that buckling might occur. In Japan, a series of buckling research has been conducted under contract with the Ministry of International Trade and Industry to develop the aseismic design method for a demonstration FBR. This study has been also done as a part of them. The problem of thermal loads on buckling strength is one of the important problems in the buckling research for FBR because axial temperature gradient is produced in a main vessel and the significant thermal stress is shown. Some studies on the effect of thermal loads on buckling strength were carried out (Brochard, 1987), (Nakamura, 1987), but its effect in the actual vessel has not been evaluated quantitatively. We have already reported the effect of thermal loads on buckling strength of a pool-type reactor vessel. (Kawamoto ,1989) In this paper, we focus on a loop-type reactor vessel and investigate the effect of thermal loads accompanying with axial temperature change near the sodium level. And the reduction of buckling strength due to the thermal loads is quantitatively evaluated
Buckling behavior of fiber reinforced plastic–metal hybrid-composite beam
International Nuclear Information System (INIS)
Eksi, Secil; Kapti, Akin O.; Genel, Kenan
2013-01-01
Highlights: ► We developed a new plastic–metal hybrid-composite tubular beam structure. ► This structure offers innovative design solutions with weight reduction. ► It prevents premature buckling without adding significant weight to the structure. ► The composite interaction gives better mechanical properties to the products. ► Buckling and bending loads of the beam increased 3.2 and 7.6 times, respectively. - Abstract: It is known that the buckling is characterized by a sudden failure of a structural member subjected to high compressive load. In this study, the buckling behavior of the aluminum tubular beam (ATB) was analyzed using finite element (FE) method, and the reinforcing arrangements as well as its combinations were decided for the composite beams based on the FE results. Buckling and bending behaviors of thin-walled ATBs with internal cast polyamide (PA6) and external glass and carbon fiber reinforcement polymers (GFRPs and CFRPs) were investigated systematically. Experimental studies showed that the 219% increase in buckling load and 661% in bending load were obtained with reinforcements. The use of plastics and metal together as a reinforced structure yields better mechanical performance properties such as high resistance to buckling and bending loads, dimensional stability and high energy absorption capacity, including weight reduction. While the thin-walled metallic component provides required strength and stiffness, the plastic component provides the support necessary to prevent premature buckling without adding significant weight to the structure. It is thought that the combination of these materials will offer a promising new focus of attention for designers seeking more appropriate composite beams with high buckling loads beside light weight. The developed plastic–metal hybrid-composite structure is promising especially for critical parts serving as a support member of vehicles for which light weight is a critical design
The Carnegie-Irvine Galaxy Survey. V. Statistical Study of Bars and Buckled Bars
Energy Technology Data Exchange (ETDEWEB)
Li, Zhao-Yu [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Science, 80 Nandan Road, Shanghai 200030 (China); Ho, Luis C. [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Barth, Aaron J., E-mail: lizy@shao.ac.cn [Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA, 92697-4575 (United States)
2017-08-10
Simulations have shown that bars are subject to a vertical buckling instability that transforms thin bars into boxy or peanut-shaped structures, but the physical conditions necessary for buckling to occur are not fully understood. We use the large sample of local disk galaxies in the Carnegie-Irvine Galaxy Survey to examine the incidence of bars and buckled bars across the Hubble sequence. Depending on the disk inclination angle ( i ), a buckled bar reveals itself as either a boxy/peanut-shaped bulge (at high i ) or as a barlens structure (at low i ). We visually identify bars, boxy/peanut-shaped bulges, and barlenses, and examine the dependence of bar and buckled bar fractions on host galaxy properties, including Hubble type, stellar mass, color, and gas mass fraction. We find that the barred and unbarred disks show similar distributions in these physical parameters. The bar fraction is higher (70%–80%) in late-type disks with low stellar mass ( M {sub *} < 10{sup 10.5} M {sub ⊙}) and high gas mass ratio. In contrast, the buckled bar fraction increases to 80% toward massive and early-type disks ( M {sub *} > 10{sup 10.5} M {sub ⊙}), and decreases with higher gas mass ratio. These results suggest that bars are more difficult to grow in massive disks that are dynamically hotter than low-mass disks. However, once a bar forms, it can easily buckle in the massive disks, where a deeper potential can sustain the vertical resonant orbits. We also find a probable buckling bar candidate (ESO 506−G004) that could provide further clues to understand the timescale of the buckling process.
Timoshenko beam model for buckling of piezoelectric nanowires with surface effects
2012-01-01
This paper investigates the buckling behavior of piezoelectric nanowires under distributed transverse loading, within the framework of the Timoshenko beam theory, and in the presence of surface effects. Analytical relations are given for the critical force of axial buckling of nanowires by accounting for the effects of surface elasticity, residual surface tension, and transverse shear deformation. Through an example, it is shown that the critical electric potential of buckling depends on both the surface stresses and piezoelectricity. This study may be helpful in the characterization of the mechanical properties of nanowires and in the calibration of the nanowire-based force sensors. PMID:22453063
International Nuclear Information System (INIS)
Kokubo, K.; Nakagawa, M.; Kawamoto, Y.; Murakami, T.; Matuura, S.; Hagiwara, Y.
1991-01-01
Shaking table tests for small-scale models and pseudo-dynamic buckling tests for moderate-scale models are conducted in order to investigate nonlinear pre- and post-buckling characteristics of fast breeder reactor vessels under the seismic lateral load. Two types of ground acceleration waves are used in the experiments. Nonlinear one-degree-of-freedom numerical simulations are also conducted using the hysteresis rules obtained by the tests. Good agreements are obtained between the experiments and calculations. The design method for vessels based on the estimation of nonlinear buckling behaviors is considered. (author)
Buckling Analysis of Rectangular Plates with Variable Thickness Resting on Elastic Foundation
International Nuclear Information System (INIS)
Viswanathan, K K; Aziz, Z A; Navaneethakrishnan, P V
2015-01-01
Buckling of rectangular plates of variable thickness resting in elastic foundation is analysed using a quintic spline approximation technique. The thickness of the plate varies in the direction of one edge and the variations are assumed to be linear, exponential and sinusoidal. The plate is subjected to in plane load of two opposite edges. The buckling load and the mode shapes of buckling are computed from the eigenvalue problem that arises. Detailed parametric studies are made with different boundary conditions and the results are presented through the diagram and discussed
Buckling Analysis of Single and Multi Delamination In Composite Beam Using Finite Element Method
Simanjorang, Hans Charles; Syamsudin, Hendri; Giri Suada, Muhammad
2018-04-01
Delamination is one type of imperfection in structure which found usually in the composite structure. Delamination may exist due to some factors namely in-service condition where the foreign objects hit the composite structure and creates inner defect and poor manufacturing that causes the initial imperfections. Composite structure is susceptible to the compressive loading. Compressive loading leads the instability phenomenon in the composite structure called buckling. The existence of delamination inside of the structure will cause reduction in buckling strength. This paper will explain the effect of delamination location to the buckling strength. The analysis will use the one-dimensional modelling approach using two- dimensional finite element method.
International Nuclear Information System (INIS)
Combescure, A.
1983-05-01
The buckling of shells subjected to seismic type of loads is not very well known. To study this type of phenomenon, theoretical and experimental investigations on structures consisting of two shells separed by a thin fluid layer , and submitted to a seismic type of load have been performed. The objectives of these investigations are the following: study coupling between buckling modes vibrations modes and buckling, and the effects of this coupling on the level of pressure; study of the appearance on such structures of dynamic instabilities processes; qualification of computer codes of the CEASEMT system; and, qualification or criticism of the methodology used in the design based on a ''static equivalent'' idea
International Nuclear Information System (INIS)
Jagla, E A
2004-01-01
I study the buckling transition under compression of a two-dimensional, hexagonal, regular elastic honeycomb. Under isotropic compression, the system buckles to a configuration consisting of a unit cell containing four of the original hexagons. This buckling pattern preserves the sixfold rotational symmetry of the original lattice but is chiral, and can be described as a combination of three different elemental distortions in directions rotated by 2π/3 from each other. Non-isotropic compression may induce patterns consisting of a single elemental distortion or a superposition of two of them. The numerical results compare very well with the outcome of a Landau theory of second-order phase transitions
Alternative Shape of Suction Caisson to Reduce Risk of Buckling under high Pressure
DEFF Research Database (Denmark)
Madsen, Søren; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo
2013-01-01
Using large suction caissons for offshore wind turbines is an upcoming technology also referred to as bucket foundations. During operation the bucket foundation is loaded by a large overturning moment from the wind turbine and the wave loads. However, during installation the bucket is loaded...... cylindrical monopod foundation made of steel. In this paper, an alternative design/shape of the suction caisson, having a smaller risk of buckling under high pressure is presented. The risk of structural buckling is addressed using numerical methods to determine the buckling pressures of the re...
An epibulbar chocolate cyst: a rare complication of silicone-based scleral buckle.
Venkatesh, Pradeep; Gogia, Varun; Gupta, Shikha; Nayak, Bhagabat
2015-08-03
A patient with a history of vitreoretinal surgery presented with nasal dystopia, diplopia and epibulbar bluish black mass simulating a chocolate cyst in the right eye. After a non-conclusive ocular examination, he underwent CT of the orbit along with volume rendition and three-dimensional reconstruction, which demonstrated intact globe with laterally displaced band-buckle assembly along with peri-scleral buckle element (SBE) soft tissue proliferation. Imaging-assisted exploration of the lesion was performed and retained scleral buckle element (SBE) was removed in toto; thus relieving the patient long-standing dystopia. 2015 BMJ Publishing Group Ltd.
View-Dependent Adaptive Cloth Simulation with Buckling Compensation.
Koh, Woojong; Narain, Rahul; O'Brien, James F
2015-10-01
This paper describes a method for view-dependent cloth simulation using dynamically adaptive mesh refinement and coarsening. Given a prescribed camera motion, the method adjusts the criteria controlling refinement to account for visibility and apparent size in the camera's view. Objectionable dynamic artifacts are avoided by anticipative refinement and smoothed coarsening, while locking in extremely coarsened regions is inhibited by modifying the material model to compensate for unresolved sub-element buckling. This approach preserves the appearance of detailed cloth throughout the animation while avoiding the wasted effort of simulating details that would not be discernible to the viewer. The computational savings realized by this method increase as scene complexity grows. The approach produces a 2× speed-up for a single character and more than 4× for a small group as compared to view-independent adaptive simulations, and respectively 5× and 9× speed-ups as compared to non-adaptive simulations.
Buckling Behavior of Cold-Formed Studs with Thermal Perforations
Directory of Open Access Journals (Sweden)
Garifullin Marsel
2016-01-01
Full Text Available Studies have shown that the optimal structural scheme for low-rise buildings that meets all regulatory requirements is a frame system. In this connection, thin-walled cold-formed steel (CFS profiles seem to be the best material for constructing light steel framed (LSF walls. The framework of LSF walls is usually constructed from CFS C-shaped profiles. To increase the thermal effectiveness of a wall, CFS profiles usually have thermal perforations and thus are called thermoprofiles. However, these openings have a negative impact on bearing capacity of profiles and require accurate evaluation. In this article a relatively new reticular-stretched thermoprofile with diamond-shaped openings is considered. The article deals with the buckling analysis of perforated CFS C-sections subjected to compression.
Helical Root Buckling: A Transient Mechanism for Stiff Interface Penetration
Silverberg, Jesse; Noar, Roslyn; Packer, Michael; Harrison, Maria; Cohen, Itai; Henley, Chris; Gerbode, Sharon
2011-03-01
Tilling in agriculture is commonly used to loosen the topmost layer of soil and promote healthy plant growth. As roots navigate this mechanically heterogeneous environment, they encounter interfaces between the compliant soil and the underlying compacted soil. Inspired by this problem, we used 3D time-lapse imaging of Medicago Truncatula plants to study root growth in two-layered transparent hydrogels. The layers are mechanically distinct; the top layer is more compliant than the bottom. We observe that the roots form a transient helical structure as they attempt to penetrate the bi-layer interface. Interpreting this phenotype as a form of buckling due to root elongation, we measured the helix size as a function of the surrounding gel modulus. Our measurements show that by twisting the root tip during growth, the helical structure recruits the surrounding medium for an enhanced penetration force allowing the plants access to the lower layer of gel.
Simplified vibrocreep buckling analysis of circular cylindrical shells
International Nuclear Information System (INIS)
Simeonova, K.; Hadjikov, L.; Georgiev, K.; Iotov, I.
1981-01-01
The circular cylindrical shells are used as a mathematical model in the investigation of the reactions of the supporting elements in nuclear reactor core, airplane designing etc. The buckling in the process of vibrocreep is one of the possible catastrophes during the exploitation of those elements. The paper presents a simplified investigation of the vibro-creep stability of a shell axially pressed. The main simplification consists of the fact that the average process of vibro-creep is considered stationary. The modified constitutive equations of Maxwell-Gurevitch-Rabinovitch, concerning elasto-viscous and elasto-plastic material is used. The critical time is calculated after two criteria. Theoretical relations between the critical time and the dynamic loading velocity amplitude are obtained. Those relations are compared to relations experimentally proved. (orig.)
Electron transport in NH3/NO2 sensed buckled antimonene
Srivastava, Anurag; Khan, Md. Shahzad; Ahuja, Rajeev
2018-04-01
The structural and electronic properties of buckled antimonene have been analysed using density functional theory based ab-initio approach. Geometrical parameters in terms of bond length and bond angle are found close to the single ruffle mono-layer of rhombohedral antimony. Inter-frontier orbital analyses suggest localization of lone pair electrons at each atomic centre. Phonon dispersion along with high symmetry point of Brillouin zone does not signify any soft mode. With an electronic band gap of 1.8eV, the quasi-2D nano-surface has been further explored for NH3/NO2 molecules sensing and qualities of interaction between NH3/NO2 gas and antimonene scrutinized in terms of electronic charges transfer. A current-voltage characteristic has also been analysed, using Non Equilibrium Green's function (NEGF), for antimonene, in presence of incoming NH3/NO2 molecules.
Electrostatics-Driven Hierarchical Buckling of Charged Flexible Ribbons.
Yao, Zhenwei; Olvera de la Cruz, Monica
2016-04-08
We investigate the rich morphologies of an electrically charged flexible ribbon, which is a prototype for many beltlike structures in biology and nanomaterials. Long-range electrostatic repulsion is found to govern the hierarchical buckling of the ribbon from its initially flat shape to its undulated and out-of-plane twisted conformations. In this process, the screening length is the key controlling parameter, suggesting that a convenient way to manipulate the ribbon morphology is simply to change the salt concentration. We find that these shapes originate from the geometric effect of the electrostatic interaction, which fundamentally changes the metric over the ribbon surface. We also identify the basic modes by which the ribbon reshapes itself in order to lower the energy. The geometric effect of the physical interaction revealed in this Letter has implications for the shape design of extensive ribbonlike materials in nano- and biomaterials.
International Nuclear Information System (INIS)
Jiang, W.; Batra, R.C.
2009-01-01
We use molecular statics simulations with the embedded atom method potential to delineate yielding (material instability) and buckling (structural instability) in gold nanowires deformed axially in compression. It is found that both local (stacking faults) and global instabilities occur when the gold nanowire yields but only global instabilities occur when the nanowire buckles. Furthermore strong surface effects reorient the lattice structure which significantly increases Young's modulus in the axial direction and cause a nanowire of relatively small slenderness ratio (e.g., 14) to buckle. Upon complete unloading of the nanowires, the average axial stress and the total potential energy revert to their values in the reference configuration for the nanowires that buckled but not for the one that yielded.
The elastic buckling of super-graphene and super-square carbon nanotube networks
International Nuclear Information System (INIS)
Li Ying; Qiu Xinming; Yin Yajun; Yang Fan; Fan Qinshan
2010-01-01
The super-graphene (SG) and super-square (SS) carbon nanotube network are built by the straight single-walled carbon nanotubes and corresponding junctions. The elastic buckling behaviors of these carbon nanotube networks under different boundary conditions are explored through the molecular structural mechanics method. The following results are obtained: (a) The critical buckling forces of the SG and SS networks decrease as the side lengths or aspect ratios of the networks increase. The continuum plate theory could give good predictions to the buckling of the SS network but not the SG network with non-uniform buckling modes. (b) The carbon nanotube networks are more stable structures than the graphene structures with less carbon atoms.
Buckling analysis of micro- and nano-rods/tubes based on nonlocal Timoshenko beam theory
International Nuclear Information System (INIS)
Wang, C M; Zhang, Y Y; Ramesh, Sai Sudha; Kitipornchai, S
2006-01-01
This paper is concerned with the elastic buckling analysis of micro- and nano-rods/tubes based on Eringen's nonlocal elasticity theory and the Timoshenko beam theory. In the former theory, the small scale effect is taken into consideration while the effect of transverse shear deformation is accounted for in the latter theory. The governing equations and the boundary conditions are derived using the principle of virtual work. Explicit expressions for the critical buckling loads are derived for axially loaded rods/tubes with various end conditions. These expressions account for a better representation of the buckling behaviour of micro- and nano-rods/tubes where small scale effect and transverse shear deformation effect are significant. By comparing it with the classical beam theories, the sensitivity of the small scale effect on the buckling loads may be observed
So, Hongyun; Pisano, Albert P.
2013-01-01
© 2013, Springer-Verlag Berlin Heidelberg. This paper reports on a novel thermal actuator with sub-micron metallic structures and a buckling arm to operate with low voltages and to generate very large deflections, respectively. A lumped
a model for the determination of the critical buckling load of self
African Journals Online (AJOL)
HP
Considering the widespread use of this type of structure and the critical role it ... proposed by the model for the critical buckling load of self- supporting lattice tower, whose equivalent solid beam- ... stiffness, both material and geometric, [5, 6].
Buckling rules in design codes: state of the art and future developments
Energy Technology Data Exchange (ETDEWEB)
Turbat, A. [FRAMATOME ANP, 69 - Lyon (France); Meziere, Y. [Electricite de France (EDF SEPTEN), 69 - Villeurbanne (France)
2001-07-01
Buckling, which can affect structures like bars, beams and shells when they are submitted to compressive stresses, can lead to unacceptable deformations and ruptures. Consequently, main Design Codes, especially those used in nuclear industry, include rules and analysis methods in order to prevent this phenomenon. In this paper, a review of buckling rules and/or analysis methods existing in ASME, RCC-M, RCC-MR and European Recommendations is performed. Then, these rules and methods are applied to the case of a cylinder filled with water and submitted to a seismic loading and results are compared. In the last part, current developments of methods to analyse creep buckling and dynamic buckling which should come and complete RCC-MR soon are presented. (author)
Buckling analysis for structural sections and stiffened plates reinforced with laminated composites.
Viswanathan, A. V.; Soong, T.-C.; Miller, R. E., Jr.
1972-01-01
A classical buckling analysis is developed for stiffened, flat plates composed of a series of linked flat plate and beam elements. Plates are idealized as multilayered orthotropic elements; structural beads and lips are idealized as beams. The loaded edges of the stiffened plate are simply supported and the conditions at the unloaded edges can be prescribed arbitrarily. The plate and beam elements are matched along their common junctions for displacement continuity and force equilibrium in an exact manner. Offsets between elements are considered in the analysis. Buckling under uniaxial compressive load for plates, sections and stiffened plates is investigated. Buckling loads are found as the lowest of all possible general and local failure modes and the mode shape is used to determine whether buckling is a local or general instability. Numerical correlations with existing analysis and test data for plates, sections and stiffened plates including boron-reinforced structures are discussed. In general, correlations are reasonably good.
Viswanathan, A. V.; Soong, T.; Miller, R. E., Jr.
1971-01-01
A classical buckling analysis is developed for stiffened, flat plates composed of a series of linked plate and beam elements. Plates are idealized as multilayered orthotropic elements. Structural beads and lips are idealized as beams. The loaded edges of the stiffened plate are simply-supported and the conditions at the unloaded edges can be prescribed arbitrarily. The plate and beam elements are matched along their common junctions for displacement continuity and force equilibrium in an exact manner. Offsets between elements are considered in the analysis. Buckling under uniaxial compressive load for plates, sections, and stiffened plates is investigated. Buckling loads are the lowest of all possible general and local failure modes, and the mode shape is used to determine whether buckling is a local or general instability. Numerical correlations with existing analysis and test data for plates, sections, and stiffened plates including boron-reinforced structures are discussed. In general correlations are reasonably good.
Test and Analysis of a Buckling-Critical Large-Scale Sandwich Composite Cylinder
Schultz, Marc R.; Sleight, David W.; Gardner, Nathaniel W.; Rudd, Michelle T.; Hilburger, Mark W.; Palm, Tod E.; Oldfield, Nathan J.
2018-01-01
Structural stability is an important design consideration for launch-vehicle shell structures and it is well known that the buckling response of such shell structures can be very sensitive to small geometric imperfections. As part of an effort to develop new buckling design guidelines for sandwich composite cylindrical shells, an 8-ft-diameter honeycomb-core sandwich composite cylinder was tested under pure axial compression to failure. The results from this test are compared with finite-element-analysis predictions and overall agreement was very good. In particular, the predicted buckling load was within 1% of the test and the character of the response matched well. However, it was found that the agreement could be improved by including composite material nonlinearity in the analysis, and that the predicted buckling initiation site was sensitive to the addition of small bending loads to the primary axial load in analyses.
Axial buckling scrutiny of doubly orthogonal slender nanotubes via nonlocal continuum theory
Energy Technology Data Exchange (ETDEWEB)
Kiani, Keivan [K.N. Toosi University of Technolog, Tehran (Iran, Islamic Republic of)
2015-10-15
Using nonlocal Euler-Bernoulli beam theory, buckling behavior of elastically embedded Doubly orthogonal single-walled carbon nanotubes (DOSWCNTs) is studied. The nonlocal governing equations are obtained. In fact, these are coupled fourth-order integroordinary differential equations which are very difficult to be solved explicitly. As an alternative solution, Galerkin approach in conjunction with assumed mode method is employed, and the axial compressive buckling load of the nanosystem is evaluated. For DOSWCNTs with simply supported tubes, the influences of the slenderness ratio, aspect ratio, intertube free space, small-scale parameter, and properties of the surrounding elastic matrix on the axial buckling load of the nanosystem are addressed. The proposed model could be considered as a pivotal step towards better understanding the buckling behavior of more complex nanosystems such as doubly orthogonal membranes or even jungles of carbon nanotubes.
On modelling of lateral buckling failure in flexible pipe tensile armour layers
DEFF Research Database (Denmark)
Østergaard, Niels Højen; Lyckegaard, Anders; Andreasen, Jens H.
2012-01-01
In the present paper, a mathematical model which is capable of representing the physics of lateral buckling failure in the tensile armour layers of flexible pipes is introduced. Flexible pipes are unbounded composite steel–polymer structures, which are known to be prone to lateral wire buckling...... when exposed to repeated bending cycles and longitudinal compression, which mainly occurs during pipe laying in ultra-deep waters. On the basis of multiple single wire analyses, the mechanical behaviour of both layers of tensile armour wires can be determined. Since failure in one layer destabilises...... the torsional equilibrium which is usually maintained between the layers, lateral wire buckling is often associated with a severe pipe twist. This behaviour is discussed and modelled. Results are compared to a pipe model, in which failure is assumed not to cause twist. The buckling modes of the tensile armour...
Buckling rules in design codes: state of the art and future developments
International Nuclear Information System (INIS)
Turbat, A.; Meziere, Y.
2001-01-01
Buckling, which can affect structures like bars, beams and shells when they are submitted to compressive stresses, can lead to unacceptable deformations and ruptures. Consequently, main Design Codes, especially those used in nuclear industry, include rules and analysis methods in order to prevent this phenomenon. In this paper, a review of buckling rules and/or analysis methods existing in ASME, RCC-M, RCC-MR and European Recommendations is performed. Then, these rules and methods are applied to the case of a cylinder filled with water and submitted to a seismic loading and results are compared. In the last part, current developments of methods to analyse creep buckling and dynamic buckling which should come and complete RCC-MR soon are presented. (author)
Optimization Formulations for the Maximum Nonlinear Buckling Load of Composite Structures
DEFF Research Database (Denmark)
Lindgaard, Esben; Lund, Erik
2011-01-01
This paper focuses on criterion functions for gradient based optimization of the buckling load of laminated composite structures considering different types of buckling behaviour. A local criterion is developed, and is, together with a range of local and global criterion functions from literature......, benchmarked on a number of numerical examples of laminated composite structures for the maximization of the buckling load considering fiber angle design variables. The optimization formulations are based on either linear or geometrically nonlinear analysis and formulated as mathematical programming problems...... solved using gradient based techniques. The developed local criterion is formulated such it captures nonlinear effects upon loading and proves useful for both analysis purposes and as a criterion for use in nonlinear buckling optimization. © 2010 Springer-Verlag....
Experimental tests on buckling of torispherical heads comparison with plastic bifurcation analysis
International Nuclear Information System (INIS)
Roche, R.L.; Autrusson, B.
1984-06-01
Sixteen torispherical heads have been tested under internal pressure. All these heads were made by cold spinning from mild steel plates. Deflections on the axis and in the knuckle region have been recorded. As an practical result of these experiments, buckling pressure is given for each tested head. It is also indicated the maximum pressure reached during the tests, this pressure is very higher than the buckling pressure. It is also seen that buckling pressure is little sensitive to initial geometric imperfections. These experimental buckling pressure are compared with computation results obtained by plastic bifurcation analysis. Five different models of bifurcation matrix have been considered. If tangent matrix is unconservative, the use of tangent modulus (in lieu of YOUNG's modulus) is overconservative. Finally a mixing of tangent normal modulus and secant shearing modulus seems to be a good enough model (not to far from experimental results, and with not to large standard deviation)
Nonlinear mode interaction in equal-leg angle struts susceptible to cellular buckling.
Bai, L; Wang, F; Wadee, M A; Yang, J
2017-11-01
A variational model that describes the interactive buckling of a thin-walled equal-leg angle strut under pure axial compression is presented. A formulation combining the Rayleigh-Ritz method and continuous displacement functions is used to derive a system of differential and integral equilibrium equations for the structural component. Solving the equations using numerical continuation reveals progressive cellular buckling (or snaking) arising from the nonlinear interaction between the weak-axis flexural buckling mode and the strong-axis flexural-torsional buckling mode for the first time-the resulting behaviour being highly unstable. Physical experiments conducted on 10 cold-formed steel specimens are presented and the results show good agreement with the variational model.
Study on Buckling of Stiff Thin Films on Soft Substrates as Functional Materials
Ma, Teng
In engineering, buckling is mechanical instability of walls or columns under compression and usually is a problem that engineers try to prevent. In everyday life buckles (wrinkles) on different substrates are ubiquitous -- from human skin to a rotten apple they are a commonly observed phenomenon. It seems that buckles with macroscopic wavelengths are not technologically useful; over the past decade or so, however, thanks to the widespread availability of soft polymers and silicone materials micro-buckles with wavelengths in submicron to micron scale have received increasing attention because it is useful for generating well-ordered periodic microstructures spontaneously without conventional lithographic techniques. This thesis investigates the buckling behavior of thin stiff films on soft polymeric substrates and explores a variety of applications, ranging from optical gratings, optical masks, energy harvest to energy storage. A laser scanning technique is proposed to detect micro-strain induced by thermomechanical loads and a periodic buckling microstructure is employed as a diffraction grating with broad wavelength tunability, which is spontaneously generated from a metallic thin film on polymer substrates. A mechanical strategy is also presented for quantitatively buckling nanoribbons of piezoelectric material on polymer substrates involving the combined use of lithographically patterning surface adhesion sites and transfer printing technique. The precisely engineered buckling configurations provide a route to energy harvesters with extremely high levels of stretchability. This stiff-thin-film/polymer hybrid structure is further employed into electrochemical field to circumvent the electrochemically-driven stress issue in silicon-anode-based lithium ion batteries. It shows that the initial flat silicon-nanoribbon-anode on a polymer substrate tends to buckle to mitigate the lithiation-induced stress so as to avoid the pulverization of silicon anode. Spontaneously
Belt Buckles-Increasing Awareness of Nickel Exposure in Children: A Case Report.
Goldenberg, Alina; Admani, Shehla; Pelletier, Janice L; Jacob, Sharon E
2015-09-01
Children, especially those with atopic dermatitis, are at risk for nickel sensitization and subsequent dermatitis from metal-containing objects, namely belt buckles. We describe allergic contact dermatitis in 12 children with peri-umbilical nickel dermatitis (with and without generalized involvement) caused by dimethylglyoxime-positive belt buckles. The patients' symptoms resolved with avoidance of the nickel-containing products. Copyright © 2015 by the American Academy of Pediatrics.
Energy Technology Data Exchange (ETDEWEB)
Raisic, N M; Popovic, D D; Takac, S M; Djordjevic, M M [Boris Kidric Institute of Nuclear Sciences, Vinca, Beograd (Yugoslavia)
1960-03-15
The buckling in the bare heavy water natural uranium critical assembly was determined by measuring the thermal neutron flux distribution. The obtained value for the critical buckling at the temperature of 20 deg C is: B{sup 2} = (8.516 {+-} 0.02) m{sup -2}. The above error is a statistical one, obtained from several series of measurements. The possible systematic error was estimated as 0.1 m{sup -2}. (author)
Effect of geometrical imperfection on buckling failure of ITER VVPSS tank
International Nuclear Information System (INIS)
Jha, Saroj Kumar; Gupta, Girish Kumar; Pandey, Manish Kumar; Bhattacharya, Avik; Jogi, Gaurav; Bhardwaj, Anil Kumar
2015-01-01
The 'Vacuum Vessel Pressure Suppression System' (VVPSS) is Part of ITER machine, which is designed to protect the ITER Vacuum Vessel and its connected systems, from an over-pressure situation. It is comprised of a partially evacuated tank of stainless steel approximately 46 meters long and 6 meters in diameter and thickness 30mm. It is to hold approximately 675 tonnes of water at room temperature to condense the steam resulting from the adverse water leakage into the Vacuum Vessel chamber. For any vacuum vessel, geometrical imperfection has significant effect on buckling failure and structural integrity. Major geometrical imperfection in VVPSS tank depends on form tolerances. To study the effect of geometrical imperfection on buckling failure of VVPSS tank, finite element analysis (FEA) has been performed in line with ASME section VIII division 2 part 5, 'design by analysis method'. Linear buckling analysis has been performed to get the buckled shape and displacement. Geometrical imperfection due to form tolerance is incorporated in FEA model of VVPSS tank by scaling the resulted buckled shape by a factor '60'. This buckled shape model is used as input geometry for plastic collapse and buckling failure assessment. Plastic collapse and buckling failure of VVPSS tank has been assessed by using the elastic-plastic analysis method. This analysis has been performed for different values of form tolerance. The results of analysis show that displacement and load proportionality factor (LPF) vary inversely with form tolerance. For higher values of form tolerance LPF reduces significantly with high values of displacement. (author)
International Nuclear Information System (INIS)
Raisic, N.M.; Popovic, D.D.; Takac, S.M.; Djordjevic, M.M.
1960-01-01
The buckling in the bare heavy water natural uranium critical assembly was determined by measuring the thermal neutron flux distribution. The obtained value for the critical buckling at the temperature of 20 deg C is: B 2 = (8.516 ± 0.02) m -2 . The above error is a statistical one, obtained from several series of measurements. The possible systematic error was estimated as 0.1 m -2 . (author)
International Nuclear Information System (INIS)
Mori, N.; Kobayashi, K.
1996-01-01
A two-dimensional neutron diffusion equation is solved for regular polygonal regions by the finite Fourier transformation, and geometrical bucklings are calculated for regular 3-10 polygonal regions. In the case of the regular triangular region, it is found that a simple and rigorous analytic solution is obtained for the geometrical buckling and the distribution of the neutron current along the outer boundary. (author)
International Nuclear Information System (INIS)
Yas, M.H.; Samadi, N.
2012-01-01
This study deals with free vibrations and buckling analysis of nanocomposite Timoshenko beams reinforced by single-walled carbon nanotubes (SWCNTs) resting on an elastic foundation. The SWCNTs are assumed to be aligned and straight with a uniform layout. Four different carbon nanotubes (CNTs) distributions including uniform and three types of functionally graded distributions of CNTs through the thickness are considered. The rule of mixture is used to describe the effective material properties of the nanocomposite beams. The governing equations are derived through using Hamilton's principle and then solved by using the generalized differential quadrature method (GDQM). Natural frequencies and critical buckling load are obtained for nanocomposite beams with different boundary conditions. Effects of several parameters, such as nanotube volume fraction, foundation stiffness parameters, slenderness ratios, CNTs distribution and boundary conditions on both natural frequency and critical buckling load are investigated. The results indicate that the above-mentioned parameters play a very important role on the free vibrations and buckling characteristics of the beam. Highlights: ► Beams with FG-X distribution have highest fundamental frequency. ► Beams with FG-X distribution have highest critical buckling load. ► Using elastic foundation, lead to increase the natural frequency. ► Using elastic foundation, lead to increase the critical buckling load. ► Increasing CNT volume fraction, lead to increase the natural frequency.
Benchmark study of shear buckling of a cylindrical vessel. Part 2
International Nuclear Information System (INIS)
Combescure, A.; Bastien, R.; Carnoy, E.G.; Dostal, M.; Austin, N.M.; Peano, A.; Angeloni, P.
1988-01-01
In Liquid Metal Fast Breeder Reactors (LMFBR) potential shear buckling failures of the primary vessel, induced through seismic excitations, have to be considered. The primary vessel material, typically 316 stainless steel, has a low yield strength at the normal operating temperatures of around 400 0 C to 500 0 C. There characteristics tend to make the structure relatively flexible and subject to potential elasto-plastic shear buckling failure. The use of finite element techniques in buckling analyses is currently becoming more accepted. There are at present many finite element codes available which have the capacibility to solve buckling problems. The objective of the study reported herein was to follow on from the previous code validation exercise and investigate the ability of finite element codes to predict buckling behaviour in another test cylinder [a/h = 83, a/L = 1] where non-linear effects would be more significant and plastic shear buckling could be a failure mode. As before four organisations took part in the code validation exercise. NNC [UK] and ISMES [Italy] used the commercially available general purpose FE code ABAQUS. CEA [France] used INCA and BILBO which are members of the commercially available CASTEM suite of FE program. Novatome [France] used their in-house FE code NOVNL. The joint effort was co-ordinated by NNC with the assistance of the Commission of the European Communities Working on Codes and Standards AG2
Mikulas, Martin M., Jr.; Nemeth, Michael P.; Oremont, Leonard; Jegley, Dawn C.
2011-01-01
Buckling loads for long isotropic and laminated cylinders are calculated based on Euler, Fluegge and Donnell's equations. Results from these methods are presented using simple parameters useful for fundamental design work. Buckling loads for two types of simply supported boundary conditions are calculated using finite element methods for comparison to select cases of the closed form solution. Results indicate that relying on Donnell theory can result in an over-prediction of buckling loads by as much as 40% in isotropic materials.
Buckling of Flat Thin Plates under Combined Loading
Directory of Open Access Journals (Sweden)
Ion DIMA
2015-03-01
Full Text Available This article aims to provide a quick methodology to determine the critical values of the forces applied to the central plane of a flat isotropic plate at which a change to the stable configuration of equilibrium occurs. Considering the variety of shapes, boundary conditions and loading combinations, the article does not intend to make an exhaustive presentation of the plate buckling. As an alternative, there will be presented only the most used configurations such as: rectangular flat thin plates, boundary conditions with simply supported (hinged or clamped (fixed edges, combined loadings with single compression or single shear or combination between them, compression and shear, with or without transverse loading, encountered at wings and control surfaces shell of fin and rudder or stabilizer and elevator. The reserve factor and the critical stresses will be calculated using comparatively two methods, namely the methodology proposed by the present article and ASSIST 6.6.2.0 – AIRBUS France software, a dedicated software to local calculations, for a simply supported plate under combined loading, compression on the both sides and shear.
Helical instability in film blowing process: Analogy to buckling instability
Lee, Joo Sung; Kwon, Ilyoung; Jung, Hyun Wook; Hyun, Jae Chun
2017-12-01
The film blowing process is one of the most important polymer processing operations, widely used for producing bi-axially oriented film products in a single-step process. Among the instabilities observed in this film blowing process, i.e., draw resonance and helical motion occurring on the inflated film bubble, the helical instability is a unique phenomenon portraying the snake-like undulation motion of the bubble, having the period on the order of few seconds. This helical instability in the film blowing process is commonly found at the process conditions of a high blow-up ratio with too low a freezeline position and/or too high extrusion temperature. In this study, employing an analogy to the buckling instability for falling viscous threads, the compressive force caused by the pressure difference between inside and outside of the film bubble is introduced into the simulation model along with the scaling law derived from the force balance between viscous force and centripetal force of the film bubble. The simulation using this model reveals a close agreement with the experimental results of the film blowing process of polyethylene polymers such as low density polyethylene and linear low density polyethylene.
Thermal Behavior of Cylindrical Buckling Restrained Braces at Elevated Temperatures
Directory of Open Access Journals (Sweden)
Elnaz Talebi
2014-01-01
Full Text Available The primary focus of this investigation was to analyze sequentially coupled nonlinear thermal stress, using a three-dimensional model. It was meant to shed light on the behavior of Buckling Restraint Brace (BRB elements with circular cross section, at elevated temperature. Such bracing systems were comprised of a cylindrical steel core encased in a strong concrete-filled steel hollow casing. A debonding agent was rubbed on the core’s surface to avoid shear stress transition to the restraining system. The numerical model was verified by the analytical solutions developed by the other researchers. Performance of BRB system under seismic loading at ambient temperature has been well documented. However, its performance in case of fire has yet to be explored. This study showed that the failure of brace may be attributed to material strength reduction and high compressive forces, both due to temperature rise. Furthermore, limiting temperatures in the linear behavior of steel casing and concrete in BRB element for both numerical and analytical simulations were about 196°C and 225°C, respectively. Finally it is concluded that the performance of BRB at elevated temperatures was the same as that seen at room temperature; that is, the steel core yields prior to the restraining system.
Thermal behavior of cylindrical buckling restrained braces at elevated temperatures.
Talebi, Elnaz; Tahir, Mahmood Md; Zahmatkesh, Farshad; Yasreen, Airil; Mirza, Jahangir
2014-01-01
The primary focus of this investigation was to analyze sequentially coupled nonlinear thermal stress, using a three-dimensional model. It was meant to shed light on the behavior of Buckling Restraint Brace (BRB) elements with circular cross section, at elevated temperature. Such bracing systems were comprised of a cylindrical steel core encased in a strong concrete-filled steel hollow casing. A debonding agent was rubbed on the core's surface to avoid shear stress transition to the restraining system. The numerical model was verified by the analytical solutions developed by the other researchers. Performance of BRB system under seismic loading at ambient temperature has been well documented. However, its performance in case of fire has yet to be explored. This study showed that the failure of brace may be attributed to material strength reduction and high compressive forces, both due to temperature rise. Furthermore, limiting temperatures in the linear behavior of steel casing and concrete in BRB element for both numerical and analytical simulations were about 196°C and 225°C, respectively. Finally it is concluded that the performance of BRB at elevated temperatures was the same as that seen at room temperature; that is, the steel core yields prior to the restraining system.
Segal, N A; Nevitt, M C; Welborn, R D; Nguyen, U-S D T; Niu, J; Lewis, C E; Felson, D T; Frey-Law, L
2015-07-01
Hamstring coactivation during quadriceps activation is necessary to counteract the quadriceps pull on the tibia, but coactivation can be elevated with symptomatic knee osteoarthritis (OA). To guide rehabilitation to attenuate risk for mobility limitations and falls, this study evaluated whether higher antagonistic open kinetic chain hamstring coactivation is associated with knee joint buckling (sudden loss of support) and shifting (a sensation that the knee might give way). At baseline, median hamstring coactivation was assessed during maximal isokinetic knee extensor strength testing and at baseline and 24-month follow-up, knee buckling and shifting was self-reported. Associations between tertiles of co-activation and knee (1) buckling, (2) shifting and (3) either buckling or shifting were assessed using logistic regression, adjusted for age, sex, knee OA and pain. 1826 participants (1089 women) were included. Mean ± SD age was 61.7 ± 7.7 years, BMI was 30.3 ± 5.5 kg/m(2) and 38.2% of knees had OA. There were no consistent statistically significant associations between hamstring coactivation and ipsilateral prevalent or incident buckling or the combination of buckling and shifting. The odds ratios for incident shifting in the highest in comparison with the lowest tertile of coactivation had similar magnitudes in the combined and medial hamstrings, but only reached statistical significance for lateral hamstring coactivation, OR(95%CI) 1.53 (0.99, 2.36). Hamstring coactivation during an open kinetic chain quadriceps exercise was not consistently associated with prevalent or incident self-reported knee buckling or shifting in older adults with or at risk for knee OA. Copyright © 2015. Published by Elsevier Ltd.
Gong, Yinchun; Ai, Zhijiu; Sun, Xu; Fu, Biwei
2016-01-01
Analytical buckling models are important for down-hole operations to ensure the structural integrity of the drill string. A literature survey shows that most published analytical buckling models do not address the effects of inclination angle, boundary conditions or friction. The objective of this paper is to study the effects of boundary conditions, friction and angular inclination on the helical buckling of coiled tubing in an inclined wellbore. In this paper, a new theoretical model is established to describe the buckling behavior of coiled tubing. The buckling equations are derived by applying the principles of virtual work and minimum potential energy. The proper solution for the post-buckling configuration is determined based on geometric and natural boundary conditions. The effects of angular inclination and boundary conditions on the helical buckling of coiled tubing are considered. Many significant conclusions are obtained from this study. When the dimensionless length of the coiled tubing is greater than 40, the effects of the boundary conditions can be ignored. The critical load required for helical buckling increases as the angle of inclination and the friction coefficient increase. The post-buckling behavior of coiled tubing in different configurations and for different axial loads is determined using the proposed analytical method. Practical examples are provided that illustrate the influence of the angular inclination on the axial force. The rate of change of the axial force decreases with increasing angular inclination. Moreover, the total axial friction also decreases with an increasing inclination angle. These results will help researchers to better understand helical buckling in coiled tubing. Using this knowledge, measures can be taken to prevent buckling in coiled tubing during down-hole operations.
International Nuclear Information System (INIS)
Sahmani, S.; Ansari, R.
2011-01-01
Buckling analysis of nanobeams is investigated using nonlocal continuum beam models of the different classical beam theories namely as Euler-Bernoulli beam theory (EBT), Timoshenko beam theory (TBT), and Levinson beam theory (LBT). To this end, Eringen's equations of nonlocal elasticity are incorporated into the classical beam theories for buckling of nanobeams with rectangular cross-section. In contrast to the classical theories, the nonlocal elastic beam models developed here have the capability to predict critical buckling loads that allowing for the inclusion of size effects. The values of critical buckling loads corresponding to four commonly used boundary conditions are obtained using state-space method. The results are presented for different geometric parameters, boundary conditions, and values of nonlocal parameter to show the effects of each of them in detail. Then the results are fitted with those of molecular dynamics simulations through a nonlinear least square fitting procedure to find the appropriate values of nonlocal parameter for the buckling analysis of nanobeams relevant to each type of nonlocal beam model and boundary conditions analysis
Energy Technology Data Exchange (ETDEWEB)
Sahmani, S.; Ansari, R. [University of Guilan, Rasht (Iran, Islamic Republic of)
2011-09-15
Buckling analysis of nanobeams is investigated using nonlocal continuum beam models of the different classical beam theories namely as Euler-Bernoulli beam theory (EBT), Timoshenko beam theory (TBT), and Levinson beam theory (LBT). To this end, Eringen's equations of nonlocal elasticity are incorporated into the classical beam theories for buckling of nanobeams with rectangular cross-section. In contrast to the classical theories, the nonlocal elastic beam models developed here have the capability to predict critical buckling loads that allowing for the inclusion of size effects. The values of critical buckling loads corresponding to four commonly used boundary conditions are obtained using state-space method. The results are presented for different geometric parameters, boundary conditions, and values of nonlocal parameter to show the effects of each of them in detail. Then the results are fitted with those of molecular dynamics simulations through a nonlinear least square fitting procedure to find the appropriate values of nonlocal parameter for the buckling analysis of nanobeams relevant to each type of nonlocal beam model and boundary conditions analysis.
International Nuclear Information System (INIS)
Aillaud, P.; Buland, P.; Combescure, A.; Queval, J.C.; Garuti, G.
1983-08-01
The buckling of shells subjected to seismic type of loads is not very well known. To study this type of phenomenon we have performed theorical and experimental investigations on structures consisting of two shells separed by a thin fluid layer, and submitted to a seismic type of load. The objectives of these investigations are the following: study the coupling between buckling modes and vibrations modes and buckling of the effects of this coupling on the level of the pressure; study of the appearance on such structures of dynamic instabilities processes; qualification of computer codes of the CEASEMT system; and, qualification or criticism of the methodology used in the design based on a ''static equivalent'' idea. The experiments are made on two types of structures: spherical and cylindrical shells. The load applied on the shells consists of a permanent pressure and of a dynamic pressure due to fluid structure interaction. The systeme is put on the vibrating table and excitation is vertical for the hemispherical case, and horizontal for the cylindrical cases. Six models of each type are tested, with sinusoidal excitation at resonance. The tests on the spherical shells are presented and compared with calculations. The correlation is good and the main results is, as predicted by numerical calculation, that if the sum of the permanent and oscillatory pressure is greater than the static buckling load, the shells buckle. This results validates the static methodology. The tests on the cylindrical tanks will be exploited by the end of the year and presented in this paper
Arjmand, T.; Tagani, M. Bagheri; Soleimani, H. Rahimpour
2018-01-01
Bilayer germanene nanoribbons are investigated in different stacks like buckled and flat armchair and buckled zigzag germanene nanoribbons by performing theoretical calculations using the nonequilibrium Greens function method combined with density functional theory. In these bilayer types, the current oscillates with change of interlayer distances or intra-layer overlaps and is dependent on the type of the bilayer. Band gap of AA-stacked of shifted flat bilayer armchair germanene nanoribbon oscillates by change of interlayer distance which is in contrast to buckled bilayer armchair germanene nanoribbon. So, results show the buckling makes system tend to be a semiconductor with wide band gap. Therefore, AA-stacked of shifted flat bilayer armchair germanene nanoribbon has properties between zigzag and armchair edges, the higher current under bias voltages similar to zigzag edge and also oscillations in current like buckled armchair edges. Also, it is found that HOMO-LUMO band gap strongly affects oscillation in currents and their I-V characteristic. This kind of junction improves the switching properties at low voltages around the band gap.
Paimushin, V. N.; Kholmogorov, S. A.; Gazizullin, R. K.
2018-01-01
One-dimensional linearized problems on the possible buckling modes of an internal or peripheral layer of unidirectional multilayer composites with rectilinear fibers under compression in the fiber direction are considered. The investigations are carried out using the known Kirchhoff-Love and Timoshenko models for the layers. The binder, modeled as an elastic foundation, is described by the equations of elasticity theory, which are simplified in accordance to the model of a transversely soft layer and are integrated along the transverse coordinate considering the kinematic coupling relations for a layer and foundation layers. Exact analytical solutions of the problems formulated are found, which are used to calculate a composite made of an HSE 180 REM prepreg based on a unidirectional carbon fiber tape. The possible buckling modes of its internal and peripheral layers are identified. Calculation results are compared with experimental data obtained earlier. It is concluded that, for the composite studied, the flexural buckling of layers in the uniform axial compression of specimens along fibers is impossible — the failure mechanism is delamination with buckling of a fiber bundle according to the pure shear mode. It is realized (due to the low average transverse shear modulus) at the value of the ultimate compression stress equal to the average shear modulus. It is shown that such a shear buckling mode can be identified only on the basis of equations constructed using the Timoshenko shear model to describe the deformation process of layers.
International Nuclear Information System (INIS)
Baker, W.E.; Babock, C.D.; Bennett, J.G.
1983-01-01
Six steel shells having nuclear containment-like features were fabricated and loaded to failure with an offset axial load. The shells of R/t = 500 buckled plastically. Four of the shells had reinforced circular cutouts. These penetrations were sized to cut no ring-stiffener, a single, two- or three-ring stiffeners. Reinforcing and framing around the penetrations were based upon the area-replacement rule of the applicable portion of the American Society for Mechanical Engineers (ASME) Boiler and Pressure Vessel Code and were of a design to stimulate actual practice for nuclear steel containments. Prior to testing, imperfections were measured and strain gages were applied to determine information on load distribution at the ends of the cylinder and strain fields at areas likely to buckle. Buckling loads were determined for an axial load applied with an eccentricity of R/2 where R is the cylinder radius. The results showed that the buckling load and mode for the shell having a penetration that did not cut a ring stiffener were essentially the same as those for the unpenetrated shell. The buckling loads for the penetrated shells in which stiffeners were interrupted were less than that for the unpenetrated shells. Results of all tests are compared to numerical solutions carried out using a nonlinear collapse analysis and to the predictions of ASME Code Case N-284
Beni, Yaghoub Tadi; Zeverdejani, M Karimi; Mehralian, Fahimeh
2017-10-01
Protein microtubules (MTs) are one of the important intercellular components and have a vital role in the stability and strength of the cells. Due to applied external loads, protein microtubules may be involved buckling phenomenon. Due to impact of protein microtubules in cell reactions, it is important to determine their critical buckling load. Considering nature of protein microtubules, various parameters are effective on microtubules buckling. The small size of microtubules and also lack of uniformity of MTs properties in different directions caused the necessity of accuracy in the analysis of these bio-structure. In fact, microtubules must be considered as a size dependent cylinder, which behave as an orthotropic material. Hence, in the present work using first-order shear deformation model (FSDT), the buckling equations of anisotropic MTs are derived based on new modified couple stress theory (NMCST). After solving the stability equations, the influences of various parameters are measured on the MTs critical buckling load. Copyright © 2017 Elsevier Inc. All rights reserved.
Cholesterol-Induced Buckling in Physisorbed Polymer-Tethered Lipid Monolayers
Directory of Open Access Journals (Sweden)
Christoph A. Naumann
2013-04-01
Full Text Available The influence of cholesterol concentration on the formation of buckling structures is studied in a physisorbed polymer-tethered lipid monolayer system using epifluorescence microscopy (EPI and atomic force microscopy (AFM. The monolayer system, built using the Langmuir-Blodgett (LB technique, consists of 3 mol % poly(ethylene glycol (PEG lipopolymers and various concentrations of the phospholipid, 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC, and cholesterol (CHOL. In the absence of CHOL, AFM micrographs show only occasional buckling structures, which is caused by the presence of the lipopolymers in the monolayer. In contrast, a gradual increase of CHOL concentration in the range of 0–40 mol % leads to fascinating film stress relaxation phenomena in the form of enhanced membrane buckling. Buckling structures are moderately deficient in CHOL, but do not cause any notable phospholipid-lipopolymer phase separation. Our experiments demonstrate that membrane buckling in physisorbed polymer-tethered membranes can be controlled through CHOL-mediated adjustment of membrane elastic properties. They further show that CHOL may have a notable impact on molecular confinement in the presence of crowding agents, such as lipopolymers. Our results are significant, because they offer an intriguing prospective on the role of CHOL on the material properties in complex membrane architecture.
International Nuclear Information System (INIS)
Ito, Tomohiro; Morita, Hideyuki; Sugiyama, Akihisa; Kawamoto, Yoji; Sirai, Eiji; Ogo, Hideyasu
2004-01-01
When a thin walled cylindrical liquid storage tank is exposed to a very large seismic base excitation, buckling phenomena may be caused such as bending buckling where diamond buckling pattern or elephant foot bulge pattern will be found at the bottom portion, and shear buckling at the middle portion of the tank. In this study, dynamic buckling tests were performed using scale models of thin cylindrical liquid storage tanks for the nuclear power plants. The input seismic acceleration was increased until the elephant foot bulge occurred and the vibrational behavior before and after buckling was investigated. And the effects of static and dynamic liquid pressure on the bending buckling patterns and the buckling critical force was investigated by fundamental tests using small tank models. (author)
Non-drainage scleral buckling with solid silicone elements
Directory of Open Access Journals (Sweden)
Pukhraj Rishi
2014-01-01
Full Text Available Background: With the increasing number of cataract surgeries, incidence of posterior segment complications including rhegmatogenous retinal detachment (RRD is likely to rise. Scleral buckling (SB surgery is an effective and less expensive option. The primary advantage of non-drainage procedure is avoidance of possible complications associated with trans-choroidal drainage. The aim of present study is to describe the clinical profile of subjects undergoing non-drainage SB surgery with solid silicone elements for RRD and analyze their treatment outcomes. Materials and Methods: This was a retrospective, non-randomized, interventional study at a tertiary care center. Three hundred and six eyes of 298 patients undergoing non-drainage SB surgery with solid silicone elements from year 2000 to 2006 were included. Inclusion criteria were primary RRD, peripheral depressible retinal break, media clarity affording peripheral retinal view and proliferative vitreo-retinopathy (PVR up to grade C2. Uni- and multivariate analyses was done to analyze factors affecting anatomical and visual outcomes. Statistical analysis was performed using SPSS Version 10. Results: Mean follow-up was 303 ± 393.33 days. Primary anatomical success was obtained in 279 (91.2% eyes; primary functional success in 286 (93.5% eyes. PVR (grade B or C, intraocular pressure <10 mm Hg and the inability to find a retinal break were significantly associated with final anatomical failure. Baseline vision ≤3/60 was significantly associated with poor visual recovery. Conclusions: SB surgery is reasonably safe and highly efficacious. Solid silicone elements are effective in non-drainage SB surgery. However, case selection is important.
2011-03-03
... of Army Corporal Frank W. Buckles, the Last Surviving American Veteran of World War I By the... Corporal Frank W. Buckles, the last surviving American veteran of World War I, and in remembrance of the generation of American veterans of World War I, I hereby order, by the authority vested in me by the...
Viswanathan, A. V.; Tamekuni, M.; Tripp, L. L.
1974-01-01
General-purpose program is intended for thermal stress and instability analyses of structures such as axially-stiffened curved panels. Two types of instability analyses can be effected by program: (1) thermal buckling with temperature variation as specified and (2) buckling due to in-plane biaxial loading.
Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson’s Ratio
Dai, Zhaohe; Weng, Chuanxin; Liu, Luqi; Hou, Yuan; Zhao, Xuanliang; Kuang, Jun; Shi, Jidong; Wei, Yueguang; Lou, Jun; Zhang, Zhong
2016-01-01
In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson’s ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on. PMID:27608928
Surface buckling of black phosphorus: Determination, origin, and influence on electronic structure
Dai, Zhongwei; Jin, Wencan; Yu, Jie-Xiang; Grady, Maxwell; Sadowski, Jerzy T.; Kim, Young Duck; Hone, James; Dadap, Jerry I.; Zang, Jiadong; Osgood, Richard M.; Pohl, Karsten
2017-12-01
The surface structure of black phosphorus materials is determined using surface-sensitive dynamical microspot low energy electron diffraction (μ LEED ) analysis using a high spatial resolution low energy electron microscopy (LEEM) system. Samples of (i) crystalline cleaved black phosphorus (BP) at 300 K and (ii) exfoliated few-layer phosphorene (FLP) of about 10 nm thickness which were annealed at 573 K in vacuum were studied. In both samples, a significant surface buckling of 0.22 Å and 0.30 Å, respectively, is measured, which is one order of magnitude larger than previously reported. As direct evidence for large buckling, we observe a set of (for the flat surface forbidden) diffraction spots. Using first-principles calculations, we find that the presence of surface vacancies is responsible for the surface buckling in both BP and FLP, and is related to the intrinsic hole doping of phosphoresce materials previously reported.
Experimental tests on buckling of ellipsoidal vessel heads subjected to internal pressure
International Nuclear Information System (INIS)
Roche, R.L.; Alix, M.
1980-05-01
Tests were performed on 17 ellipsoidal vessel heads of three different materials and different geometries. The results include the following: 1) Accurate definition of the geometry and particularly a direct measurement of the thickness along the meridian. 2) The properties of the material of each head, obtained from test specimens cut from the head itself after the test. 3) The recording of deflection/pressure curves with indication of the pressure at which buckling occurred. These results can be used for validation and qualification of methods for calculating the buckling load when plasticity occurs before buckling. It was possible to develop an empirical equation representing the experimental results obtained with satisfactory accuracy. This equation may be useful in pressure vessel design
Tuning and switching of band gap of the periodically undulated beam by the snap through buckling
Directory of Open Access Journals (Sweden)
Y. Li
2017-05-01
Full Text Available We propose highly tuning and switching band gaps of phononic crystals through the snap through buckling by investigating wave propagation in a designed tractable undulated beam with single material and periodically arched shape. A series of numerical analyses are conducted to offer a thorough understanding of the evolution of the band gaps as a function of the vertical applied load. We find out that the interesting snap through buckling induced by the vertical load can alter the width of the band gap of the undulated beam dramatically, even switch them on and off. Our researches show an effective strategy to tune the band gaps of phononic crystals through the snap through buckling behavior.
Post-Buckling and Ultimate Strength Analysis of Stiffened Composite Panel Base on Progressive Damage
Zhang, Guofan; Sun, Xiasheng; Sun, Zhonglei
Stiffened composite panel is the typical thin wall structure applied in aerospace industry, and its main failure mode is buckling subjected to compressive loading. In this paper, the development of an analysis approach using Finite Element Method on post-buckling behavior of stiffened composite structures under compression was presented. Then, the numerical results of stiffened panel are obtained by FE simulations. A thorough comparison were accomplished by comparing the load carrying capacity and key position strains of the specimen with test. The comparison indicates that the FEM results which adopted developed methodology could meet the demand of engineering application in predicting the post-buckling behavior of intact stiffened structures in aircraft design stage.
Effect of flurbiprofen sodium on pupillary dilatation during scleral buckling surgery
Directory of Open Access Journals (Sweden)
Roysarkar T
1994-01-01
Full Text Available Maintenance of pupillary dilatation is necessary for success of scleral buckling procedures. The efficacy of 0.03% flurbiprofen in preventing intraoperative miosis was evaluated by a prospective randomized, double-masked controlled trial of 60 patients. Thirty patients received 0.03% flurbiprofen 6 times at 15 minute intervals 90 minutes preoperatively in addition to the routine dilation regimen. The treated group had a mean pupillary decrease of 1.88 mm and the control group had a decrease of 1.57 mm (p > 0.05. Flurbiprofen did not affect the pupillary size at any step of the surgery. Factors such as age of the patient, lens status, number of cryo applications, duration of surgery, and the size and extent of buckle were assessed. The use of flurbiprofen did not affect the mean pupillary change for any of these groups. Preoperative use of flurbiprofen does not significantly decrease intraoperative miosis during scleral buckling procedures
Dynamic buckling and nonlinear response of FBR main vessels under earthquake loading
International Nuclear Information System (INIS)
Hagiwara, Yutaka; Kawamoto, Yoji; Nakagawa, Masaki; Akiyama, Hiroshi.
1991-01-01
Pseudo-dynamic tests of cylindrical shells under high temperature were performed in order to study elasto-plastic shear-bending buckling and the nonlinear response of FBR main vessels under earthquake loading. The test results showed a response reduction effect due to pre-buckling plasticity, and a large seismic margin due to post-buckling energy absorption of the cylinders. A simple expression of the response reduction effect was proposed, as a contribution to the safe and effective seismic design of FBRs. Two methods for seismic margin evaluation were also proposed, and it was shown that appropriate seismic margins can be ensured, when the response reduction effect is incorporated into the seismic design. (author)
Non linear fe analysis on the static buckling behavior of the spacer grid structures
International Nuclear Information System (INIS)
Song, K.N.; Yoon, K.H.
2001-01-01
In this study considered is the static buckling behavior of spacer grids in the fuel assembly, which are required to have a sufficient strength against an accident like earthquake. Special attention is given to the finite element modeling of the spot-welding and the constraints between the spacer strips assembled together: it is found that a proper treatment of the constraints is critical for accurate assessment of the buckling behavior including strain localization at the point of spot welding. The buckling strength of the 17 x 17 spacer grid, which is difficult to analyze due to a large number of degrees of freedom, is estimated from analysis for the smaller models 3 x 3, 5 x 5, 7 x 7, and 9 x 9 spacer grids. (authors)
Magnetic field effects on buckling behavior of smart size-dependent graded nanoscale beams
Ebrahimi, Farzad; Reza Barati, Mohammad
2016-07-01
In this article, buckling behavior of nonlocal magneto-electro-elastic functionally graded (MEE-FG) beams is investigated based on a higher-order beam model. Material properties of smart nanobeam are supposed to change continuously throughout the thickness based on the power-law model. Eringen's nonlocal elasticity theory is adopted to capture the small size effects. Nonlocal governing equations of MEE-FG nanobeam are obtained employing Hamilton's principle and they are solved using the Navier solution. Numerical results are presented to indicate the effects of magnetic potential, electric voltage, nonlocal parameter and material composition on buckling behavior of MEE-FG nanobeams. Therefore, the present study makes the first attempt in analyzing the buckling responses of higher-order shear deformable (HOSD) MEE-FG nanobeams.
Viswanathan, A. V.; Tamekuni, M.
1973-01-01
Analytical methods based on linear theory are presented for predicting the thermal stresses in and the buckling of heated structures with arbitrary uniform cross section. The structure is idealized as an assemblage of laminated plate-strip elements, curved and planar, and beam elements. Uniaxially stiffened plates and shells of arbitrary cross section are typical examples. For the buckling analysis the structure or selected elements may be subjected to mechanical loads, in additional to thermal loads, in any desired combination of inplane transverse load and axial compression load. The analysis is also applicable to stiffened structures under inplane loads varying through the cross section, as in stiffened shells under bending. The buckling analysis is general and covers all modes of instability. The analysis has been applied to a limited number of problems and the results are presented. These while showing the validity and the applicability of the method do not reflect its full capability.
Energy Technology Data Exchange (ETDEWEB)
Malekzadeh, P. [Department of Mechanical Engineering, Persian Gulf University, Bushehr 75168 (Iran, Islamic Republic of); Center of Excellence for Computational Mechanics, Shiraz University, Shiraz (Iran, Islamic Republic of)], E-mail: malekzadeh@pgu.ac.ir; Ouji, A. [Department of Civil Engineering, Persian Gulf University, Bushehr 75168 (Iran, Islamic Republic of); Islamic Azad University, Larestan Branch, Larestan (Iran, Islamic Republic of)
2008-11-15
The buckling analysis of annular thick plates with lateral supports such as two-parameter elastic foundations or ring supports is investigated using an elasticity based hybrid numerical method. For this purpose, firstly, the displacement components are perturbed around the pre-buckling state, which is located using the elasticity theory. Then, by decomposing the plate into a set of sub-domain in the form of co-axial annular plates, the buckling equations are discretized through the radial direction using global interpolation functions in conjunction with the principle of virtual work. The resulting differential equations are solved using the differential quadrature method. The method has the capability of modeling the arbitrary boundary conditions either at the inner and outer edges of thin-to-thick plates and with different types of lateral restraints. The fast rate of convergence of the method is demonstrated and comparison studies are carried out to establish its accuracy and versatility for thin-to-thick plates.
Micro-buckling of periodically layered composites in regions of stress concentration
DEFF Research Database (Denmark)
Poulios, Konstantinos; Niordson, Christian Frithiof
2016-01-01
-buckling related failure in regions of stress concentrations. A series of parametric studies show the effect of non-uniform stress distributions due to bending loads and the presence of geometrical features such as notches and holes on the initiation of micro-buckling. The contribution of the bending stiffness...... of the reinforcing layers on the resistance against micro-buckling introduces a dependence on the layer thickness, resulting in size-scale dependent strength limits. Therefore, both the shape and dimensions of the considered geometrical features and the layering thickness of the micro-structure are varied as part...... of the parametric studies. Moreover, the impact of imperfections in the composite micro-structure on the strength of the considered specimens is investigated....
Highly stretchable carbon nanotube transistors enabled by buckled ion gel gate dielectrics
Energy Technology Data Exchange (ETDEWEB)
Wu, Meng-Yin; Chang, Tzu-Hsuan; Ma, Zhenqiang [Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Zhao, Juan [School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054 (China); Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Xu, Feng; Jacobberger, Robert M.; Arnold, Michael S., E-mail: michael.arnold@wisc.edu [Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
2015-08-03
Deformable field-effect transistors (FETs) are expected to facilitate new technologies like stretchable displays, conformal devices, and electronic skins. We previously demonstrated stretchable FETs based on buckled thin films of polyfluorene-wrapped semiconducting single-walled carbon nanotubes as the channel, buckled metal films as electrodes, and unbuckled flexible ion gel films as the dielectric. The FETs were stretchable up to 50% without appreciable degradation in performance before failure of the ion gel film. Here, we show that by buckling the ion gel, the integrity and performance of the nanotube FETs are extended to nearly 90% elongation, limited by the stretchability of the elastomer substrate. The FETs maintain an on/off ratio of >10{sup 4} and a field-effect mobility of 5 cm{sup 2} V{sup −1} s{sup −1} under elongation and demonstrate invariant performance over 1000 stretching cycles.
Highly stretchable carbon nanotube transistors enabled by buckled ion gel gate dielectrics
International Nuclear Information System (INIS)
Wu, Meng-Yin; Chang, Tzu-Hsuan; Ma, Zhenqiang; Zhao, Juan; Xu, Feng; Jacobberger, Robert M.; Arnold, Michael S.
2015-01-01
Deformable field-effect transistors (FETs) are expected to facilitate new technologies like stretchable displays, conformal devices, and electronic skins. We previously demonstrated stretchable FETs based on buckled thin films of polyfluorene-wrapped semiconducting single-walled carbon nanotubes as the channel, buckled metal films as electrodes, and unbuckled flexible ion gel films as the dielectric. The FETs were stretchable up to 50% without appreciable degradation in performance before failure of the ion gel film. Here, we show that by buckling the ion gel, the integrity and performance of the nanotube FETs are extended to nearly 90% elongation, limited by the stretchability of the elastomer substrate. The FETs maintain an on/off ratio of >10 4 and a field-effect mobility of 5 cm 2 V −1 s −1 under elongation and demonstrate invariant performance over 1000 stretching cycles
Effect of load eccentricity on the buckling of thin-walled laminated C-columns
Wysmulski, Pawel; Teter, Andrzej; Debski, Hubert
2018-01-01
The study investigates the behaviour of short, thin-walled laminated C-columns under eccentric compression. The tested columns are simple-supported. The effect of load inaccuracy on the critical and post-critical (local buckling) states is examined. A numerical analysis by the finite element method and experimental tests on a test stand are performed. The samples were produced from a carbon-epoxy prepreg by the autoclave technique. The experimental tests rest on the assumption that compressive loads are 1.5 higher than the theoretical critical force. Numerical modelling is performed using the commercial software package ABAQUS®. The critical load is determined by solving an eigen problem using the Subspace algorithm. The experimental critical loads are determined based on post-buckling paths. The numerical and experimental results show high agreement, thus demonstrating a significant effect of load inaccuracy on the critical load corresponding to the column's local buckling.
Thermoelastic buckling of plates in a cylindrical geometry against an elastic back support
International Nuclear Information System (INIS)
Simmons, L.D.; Wierman, R.W.
1980-01-01
A plate which is fixed at its edges to a strong edge support structure will develop large compressive stresses when heated from ambient temperature more rapidly than the support structure. Determining the response of the plate to this situation requires stability analysis to ascertain whether the plate might buckle, or whether the constrained thermal expansion will lead to compressive stresses exceeding the yield point because it did not buckle. A special case is considered here, both analytically and experimentally, in which the plate is curved slightly into a cylindrical shape and the convex face of the plate is against a supporting surface. This case is more complex because the buckling mode will be a harmonic rather than the fundamental mode which is usually encountered
International Nuclear Information System (INIS)
Baker, W.E.; Bennett, J.G.; Babcock, C.D.
1983-01-01
Six steel shells having nuclear containment-like features were fabricated and loaded to failure with an offset axial load. The shells of R/t = 500 buckled plastically. Four of the shells had reinforced circular cutouts. These penetrations were sized to cut no ring-stiffener, a single, two- or three-ring stiffeners. Reinforcing and framing around the penetrations were based upon the area-replacement rule of the applicable portion of the American Society for Mechanical Engineers (ASME) Boiler and Pressure Vessel Code and were of a design to simulate actual practice for nuclear steel containments. Prior to testing, imperfections were measured and strain gages were applied to determine information on load distribution at the ends of the cylinder and strain fields at areas likely to buckle. Buckling loads were determined for an axial load applied with an eccentricity of R/2 where R is the cylinder radius
Misuse of booster cushions - an observation study of children's performance during buckling up.
Osvalder, Anna-Lisa; Bohman, Katarina
2008-10-01
Booster cushions are effective tools to protect children from injuries in car crashes, but there remains a large amount of misuse. The aim of this study was to assess potential misuse of booster cushions in an observational laboratory study, and to identify whether booster cushion design, age or clothing had any effect. 130 Swedish children from the ages of 4-12 years participated. Each child buckled up on an integrated and on an aftermarket booster cushion in the rear seat. The older children also buckled up with seat belt only. Interviews, observations and body measurements were performed. Time to buckle up and amount of belt slack were registered. Photographs were taken to document misuse. Results showed that 77% failed to perform correct belt routing on the aftermarket cushion, independent of age, although they were familiar with this system. The misuse rate for the integrated cushion was only 4%. No misuse was found for seat belt only. Few children tightened the belt. The belt slack increased when wearing winter jackets. This indicates the importance of adding pretensioners to the rear seat. Sled tests with HIII&TNO 6y dummies were also performed for the most frequent misuse situations found. The main conclusion is that an integrated booster cushion has many advantages compared to an aftermarket cushion regarding both safety and comfort. It is easy and quick to handle, has few possibilities for misuse, has an intuitive design, the buckling up sequence is equal to buckling up with an ordinary seat belt, and younger children can buckle up correctly.
Implementation of Fiber Optic Sensing System on Sandwich Composite Cylinder Buckling Test
Pena, Francisco; Richards, W. Lance; Parker, Allen R.; Piazza, Anthony; Schultz, Marc R.; Rudd, Michelle T.; Gardner, Nathaniel W.; Hilburger, Mark W.
2018-01-01
The National Aeronautics and Space Administration (NASA) Engineering and Safety Center Shell Buckling Knockdown Factor Project is a multicenter project tasked with developing new analysis-based shell buckling design guidelines and design factors (i.e., knockdown factors) through high-fidelity buckling simulations and advanced test technologies. To validate these new buckling knockdown factors for future launch vehicles, the Shell Buckling Knockdown Factor Project is carrying out structural testing on a series of large-scale metallic and composite cylindrical shells at the NASA Marshall Space Flight Center (Marshall Space Flight Center, Alabama). A fiber optic sensor system was used to measure strain on a large-scale sandwich composite cylinder that was tested under multiple axial compressive loads up to more than 850,000 lb, and equivalent bending loads over 22 million in-lb. During the structural testing of the composite cylinder, strain data were collected from optical cables containing distributed fiber Bragg gratings using a custom fiber optic sensor system interrogator developed at the NASA Armstrong Flight Research Center. A total of 16 fiber-optic strands, each containing nearly 1,000 fiber Bragg gratings, measuring strain, were installed on the inner and outer cylinder surfaces to monitor the test article global structural response through high-density real-time and post test strain measurements. The distributed sensing system provided evidence of local epoxy failure at the attachment-ring-to-barrel interface that would not have been detected with conventional instrumentation. Results from the fiber optic sensor system were used to further refine and validate structural models for buckling of the large-scale composite structures. This paper discusses the techniques employed for real-time structural monitoring of the composite cylinder for structural load introduction and distributed bending-strain measurements over a large section of the cylinder by
International Nuclear Information System (INIS)
Zerna, W.; Mungan, I.; Steffen, W.
1980-01-01
The equations of the bending and stability theories for the orthotropic shell are solved using the FEM. A biaxial material law for concrete and a nearly bilinear stress-strain diagram for reinforcing steel were considered. Taking a layered ring element the influence of bending moments together with the membrane forces can be followed under increasing load up to failure of concrete or steel. At each level the bucking factor can be calculated considering the stress dependent buckling stiffness. The method of calculation is applied to a cooling tower shell under dead load acting simultaneously with an axi-symmetric loading to compensate for the wind effect. Due to orthotropy and descending tangent modulus at the ultimate load the buckling load factor drops to the half of the value obtained assuming a linear elastic behaviour. Additional parametric studies demonstrate the effect of some hypothetic cracks of different position and depth of the bifurcation results. The variation of the safety factors against buckling and ultimate load is obtained by changing the shell thickness. For the shell investigated it turns out that the buckling safety is influenced much more than the safety against material failure if the wall thickness is varied. It is recommended to split the buckling analysis of reinforced concrete shells in two parts. For shells of parts of a shell under only slightly disturbed membrane stress state the buckling analysis governs, otherwise the ultimate state considering the geometric and material nonlinearities is decisive to obtain not only the wall thickness but also the amount of reinforced necessary. (orig./HP) [de
Okajima, Kenji; Imai, Junichi; Tanaka, Tadatsugu; Iida, Toshiaki
Damage to piles in the liquefied ground is frequently reported. Buckling by the excess vertical load could be one of the causes of the pile damage, as well as the lateral flow of the ground and the lateral load at the pile head. The buckling mechanism is described as a complicated interaction between the pile deformation by the vertical load and the earth pressure change cased by the pile deformation. In this study, series of static buckling model tests of a pile were carried out in dried sand ground with various thickness of the layer. Finite element analysis was applied to the test results to verify the effectiveness of the elasto-plastic finite element analysis combining the implicit-explicit mixed type dynamic relaxation method with the return mapping method to the pile buckling problems. The test results and the analysis indicated the possibility that the buckling load of a pile decreases greatly where the thickness of the layer increases.
DEFF Research Database (Denmark)
Henrichsen, Søren Randrup; Lindgaard, Esben; Lund, Erik
2015-01-01
Robust design of laminated composite structures is considered in this work. Because laminated composite structures are often thin walled, buckling failure can occur prior to material failure, making it desirable to maximize the buckling load. However, as a structure always contains imperfections...... and “worst” shape imperfection optimizations to design robust composite structures. The approach is demonstrated on an U-profile where the imperfection sensitivity is monitored, and based on the example it can be concluded that robust designs can be obtained....
Hydrogen-Induced Buckling of Pd Films Deposited on Various Substrates
Vlček, Marián
2015-07-01
A Pd-H system is a model system suitable for studying interactions of hydrogen with metals. In the present work, we studied hydrogen-induced buckling of thin Pd films deposited on various substrates with different bonding strengths (sapphire, glimmer) and also the effect of deposition temperature. Lattice expansion and phase transitions were investigated by X-ray diffraction of synchrotron radiation. The influence of the substrate and microstructure of the film on the buckling process and phase transformation to palladium hydride are discussed.
Creep buckling: an experiment, an 'exact' solution and some simple thoughts
International Nuclear Information System (INIS)
Heller, P.; Anderson, R.G.
1986-01-01
The paper presents attempts to analyse and understand a carefully conducted creep buckling experiment. The analysis was conducted using the ABAQUS Finite Element Code coupled to a number of plausible creep laws. The results show good agreement between ABAQUS runs and experimental deflections but it is difficult to reproduce the early loads. A simple model of buckling analysis for n-power creep laws is derived as an aid to understanding the development of the deflections for non-linear creep laws. In particular, the model suggests why deflections develop so rapidly and how the creep deflection development relates to the elastic behaviour. (author)
Stress analysis and torsional buckling analysis of U-shaped bellows
International Nuclear Information System (INIS)
Watanabe, Osamu; Ohtsubo, Hideomi.
1986-01-01
This paper presents analysis of elastic stress and torsional buckling of U-shaped bellows using ring elements. The expansion joint is considered to be composed of the two toroidal sections and inner-connecting annular plates. The general thin shell theory is employed to derive strain-displacement relations of shells and plates, valid for any loadings. Numerical examples under internal pressure or axial loading are described and compared with the results of existing appropriate analysis. The fundamental aspects of torsional buckling, which have not been studied previously, will also be investigated. (author)
Experimental and modelling buckling of wood-based columns under repeated loading
Directory of Open Access Journals (Sweden)
Nafa Z.
2010-06-01
Full Text Available Collapse of timber constructions can appear under the effect of load that exceeds the resistance of a carrying element or under the effect of a geometrical instability like buckling. In addition, loading can be constant or varying for example loads due to wind or earthquakes. The aim of this paper is to study the behaviour and the lifetime of columns in wood or based-wood material such as glulam (GL or laminated veneer lumber (LVL under repeated loading leading to buckling.
A study of the effects of penetration framing on steel containment buckling capacity
International Nuclear Information System (INIS)
Baker, W.E.; Butler, T.A.
1987-05-01
Polycarbonate cylinders modeling steel containment structures were tested to study the effects of different framing designs around large penetrations on the static buckling capacity of containments. Two of the four models had equipment hatch penetrations and two had personnel airlock penetrations. Both types of models were tested with axial and shear loads as framing was incrementally added. Results indicate that, for the models constructed of polycarbonate, buckling is influenced minimally with added framing. Numerical results support the experimental results. Extrapolation of the results to containment constructed under field conditions with prototypic steel materials is discussed and further testing is recommended
Hydrogen-Induced Buckling of Pd Films Deposited on Various Substrates
Vlček, Mariá n; Luká č, František; Vlach, Martin; Prochá zka, Ivan; Wagner, Stefan; Uchida, Helmut; Pundt, Astrid; Gemma, Ryota; Čí žek, Jakub
2015-01-01
A Pd-H system is a model system suitable for studying interactions of hydrogen with metals. In the present work, we studied hydrogen-induced buckling of thin Pd films deposited on various substrates with different bonding strengths (sapphire, glimmer) and also the effect of deposition temperature. Lattice expansion and phase transitions were investigated by X-ray diffraction of synchrotron radiation. The influence of the substrate and microstructure of the film on the buckling process and phase transformation to palladium hydride are discussed.
BUCKL: a program for rapid calculation of x-ray deposition
International Nuclear Information System (INIS)
Cole, R.K. Jr.
1970-07-01
A computer program is described which has the fast execution time of exponential codes but also evaluates the effects of fluorescence and scattering. The program makes use of diffusion calculations with a buckling correction included to approximate the effects of finite transverse geometry. Theory and derivations necessary for the BUCKL code are presented, and the code results are compared with those of earlier codes for a variety of problems. Inputs and outputs of the program are described, and a FORTRAN listing is provided. Shortcomings of the program are discussed and suggestions are provided for possible future improvement. (U.S.)
Energy Technology Data Exchange (ETDEWEB)
MACKEY TC; JOHNSON KI; DEIBLER JE; PILLI SP; RINKER MW; KARRI NK
2007-02-14
This report documents a detailed buckling evaluation of the primary tanks in the Hanford double-shell waste tanks (DSTs), which is part of a comprehensive structural review for the Double-Shell Tank Integrity Project. This work also provides information on tank integrity that specifically responds to concerns raised by the Office of Environment, Safety, and Health (ES&H) Oversight (EH-22) during a review of work performed on the double-shell tank farms and the operation of the aging waste facility (AWF) primary tank ventilation system. The current buckling review focuses on the following tasks: (1) Evaluate the potential for progressive I-bolt failure and the appropriateness of the safety factors that were used for evaluating local and global buckling. The analysis will specifically answer the following questions: (a) Can the EH-22 scenario develop if the vacuum is limited to -6.6-inch water gage (w.g.) by a relief valve? (b) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario can develop? (c) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario cannot develop? (2) Develop influence functions to estimate the axial stresses in the primary tanks for all reasonable combinations of tank loads, based on detailed finite element analysis. The analysis must account for the variation in design details and operating conditions between the different DSTs. The analysis must also address the imperfection sensitivity of the primary tank to buckling. (3) Perform a detailed buckling analysis to determine the maximum allowable differential pressure for each of the DST primary tanks at the current specified limits on waste temperature, height, and specific gravity. Based on the I-bolt loads analysis and the small deformations that are predicted at the unfactored limits on vacuum and axial loads, it is very unlikely that the EH-22 scenario (i.e., progressive I-bolt failure leading to global
Random fields of initial out of straightness leading to column buckling
DEFF Research Database (Denmark)
Kala, Zdeněk; Valeš, Jan; Jönsson, Jeppe
2017-01-01
The elastic load-carrying capacity and buckling trajectory of steel columns under compression with open and hollow cross-sections, whose axis is curved by spatial random fields, are studied in the article. As a result of the spatial curvature of the axis the cross-sections are subjected to compre...
International Nuclear Information System (INIS)
Liang, Xu; Hu, Shuling; Shen, Shengping
2015-01-01
The symmetry breaking of inversion in solid crystals will induce electric polarization in all solid crystals, which is well known as flexoelectricity. At the nanometer scale, due to the large ratio of surface to volume, piezoelectric structures always exhibit distinct mechanical and electrical behaviors compared with their bulk counterparts. In the current work, the effects of surface and flexoelectricity on the buckling and vibration of piezoelectric nanowires is investigated based on a continuum framework and the Euler–Bernoulli beam hypothesis. Analytical solutions of the electric field in the piezoelectric nanobeam subjected to electrical and mechanical loads are obtained with the surface, flexoelectric and nonlocal electric effects. Numeric simulations demonstrate that the Young’s modulus and bending rigidity of PZT and BaTiO 3 (BT) nanowires are enhanced by flexoelectricity. In addition, the critical buckling voltage is calculated with consideration of the effects of surface and flexoelectricity, and it is found that the effects of surface piezoelectricity, flexoelectricity and residual surface stress play significant roles in determining the critical buckling voltage. Results obtained for the first resonance frequency also indicate that the effects of surface and flexoelectricity are more significant at a narrow range of beam thickness. The first resonance frequency of PZT and BT nanowires is also influenced by the residual surface stress and external applied voltage. The current work is expected to provide a fundamental study on the buckling and vibration behaviors of piezoelectric nanobeams, and it might also be helpful in devising piezoelectric nanowire-based nanoelectronics. (paper)
Post-Buckled Precompressed (PBP) piezoelectric actuators for UAV flight control
Vos, R.; Barrett, R.; Krakers, L.; Van Tooren, M.
2006-01-01
This paper presents the use of a new class of flight control actuators employing Post-Buckled Precompressed (PBP) piezoelectric elements in morphing wing Uninhabited Aerial Vehicles (UAVs). The new actuator relieson axial compression to amplify deflections and control forces simultaneously. Two
Asymptotic solution on the dynamic buckling of a column stressed by ...
African Journals Online (AJOL)
This paper analysis the dynamic stability of a dynamically oscillatory system with slowly varying time dependent parameters. It utilizes the concept of multiple times scaling in an asymptotic evaluation of the dynamic buckling load of the imperfect elastic structure under investigation. Unlike most similar investigations to date ...
Relevance of capsid structure in the buckling and maturation of spherical viruses
International Nuclear Information System (INIS)
Aznar, María; Luque, Antoni; Reguera, David
2012-01-01
The shape and mechanical properties of viral capsids play an important role in several biological processes during the virus life cycle. In particular, to become infective, many viruses require a maturation stage where the capsid undergoes a buckling transition, from an initial spherical procapsid into a final icosahedral faceted shell. Here we study, using a minimal physical model, how the capsid shape and the buckling transition depend on the triangulation number T and the icosahedral class P of the virus structure. We find that, for small shells, capsids with P = 1 are most likely to produce polyhedral shapes that minimize their energy and accumulated stress, whereas viruses with P = 3 prefer to remain spherical. For big capsids, all shells are more stable adopting an icosahedral shape, in agreement with continuum elastic theory. Moreover, spherical viruses show a buckling transition to polyhedral shells under expansion, in consonance with virus maturation. The resulting icosahedral shell is mechanically stiffer, tolerates larger expansions and withstands higher internal pressures before failing, which could explain why some dsDNA viruses, which rely on the pressurization of their genetic material to facilitate the infection, undergo a buckling transition. We emphasize that the results are general and could also be applied to non-biological systems. (paper)
Bauer, Christina T; Kroner, Elmar; Fleck, Norman A; Arzt, Eduard
2015-10-23
Nature uses hierarchical fibrillar structures to mediate temporary adhesion to arbitrary substrates. Such structures provide high compliance such that the flat fibril tips can be better positioned with respect to asperities of a wavy rough substrate. We investigated the buckling and adhesion of hierarchically structured adhesives in contact with flat smooth, flat rough and wavy rough substrates. A macroscopic model for the structural adhesive was fabricated by molding polydimethylsiloxane into pillars of diameter in the range of 0.3-4.8 mm, with up to three different hierarchy levels. Both flat-ended and mushroom-shaped hierarchical samples buckled at preloads one quarter that of the single level structures. We explain this behavior by a change in the buckling mode; buckling leads to a loss of contact and diminishes adhesion. Our results indicate that hierarchical structures can have a strong influence on the degree of adhesion on both flat and wavy substrates. Strategies are discussed that achieve highly compliant substrates which adhere to rough substrates.
Buckling tests of sandwich cylindrical shells with and without cut-outs
Bisagni, C.; Davidson, B.D.; Czabaj, M.W.; Ratcliffe, J.G.
2016-01-01
The results of buckling tests performed during the project DESICOS funded by the European Commission in the FP7 Programme are here presented. The tested structures are sandwich cylindrical shells that consist of reduced models of a component of the Ariane 5 launcher: the Dual Launch System. In
A proposal for the calculation of the critical buckling of a PWR or undermoderated lattice
International Nuclear Information System (INIS)
Benoist, P.
1989-01-01
A method improving the calculation of the critical buckling of a PWR or undermorated lattice is proposed. This method takes into account the lattice heterogeneity with more detail than the existing ones; it lies on some approximations. The method requires a relatively small inplementational effort. It could be used in the calculation of fast reactors [fr
Modelling of the stiffness evolution of truss core structures damaged by plastic buckling
Czech Academy of Sciences Publication Activity Database
Šiška, Filip; Stratil, Luděk; Dlouhý, Ivo; Barnett, M.R.
2015-01-01
Roč. 100, AUG (2015), s. 1-11 ISSN 0168-874X R&D Projects: GA MŠk EE2.3.20.0197 Institutional support: RVO:68081723 Keywords : beam theory * plastic buckling * finite element * beam-columns * truss-coredlaminates Subject RIV: JI - Composite Materials Impact factor: 2.175, year: 2015
Advanced control techniques for post-buckled precompressed (PBP) flight control actuators
Groen, M.; Van Schravendijk, M.; Barrett, R.; Vos, R.
2009-01-01
The dynamic response of a new class of flight control actuators that rely on post-buckled recompressed (PBP) piezoelectric elements is investigated. While past research has proven that PBP actuators are capable of generating deflections three times higher than conventional bimorph actuators, this
Post-Buckling Analysis of Curved Honeycomb Sandwich Panels Containing Interfacial Disbonds
Pineda, Evan J.; Bednarcyk, Brett A.; Krivanek, Thomas K.
2016-01-01
A numerical study on the effect of facesheet-core disbonds on the post-buckling response of curved honeycomb sandwich panels is presented herein. This work was conducted as part of the development of a damage tolerance plan for the next-generation Space Launch System heavy lift launch vehicle payload fairing. As such, the study utilized full-scale fairing barrel segments as the structure of interest. The panels were composed of carbon fiber reinforced polymer facesheets and aluminum honeycomb core. The panels were analyzed numerically using the finite element method incorporating geometric nonlinearity. In a predetermined circular region, facesheet and core nodes were detached to simulate a disbond, between the outer mold line facesheet and honeycomb core, induced via low-speed impact. Surface-to-surface contact in the disbonded region was invoked to prevent interpenetration of the facesheet and core elements and obtain realistic stresses in the core. The diameter of this disbonded region was varied and the effect of the size of the disbond on the post-buckling response was observed. Significant changes in the slope of the edge load-deflection response were used to determine the onset of global buckling and corresponding buckling load. Finally, several studies were conducted to determine the sensitivity of the numerical predictions to refinement in the finite element mesh.
Selective buckling via states of self-stress in topological metamaterials.
Paulose, Jayson; Meeussen, Anne S; Vitelli, Vincenzo
2015-06-23
States of self-stress--tensions and compressions of structural elements that result in zero net forces--play an important role in determining the load-bearing ability of structures ranging from bridges to metamaterials with tunable mechanical properties. We exploit a class of recently introduced states of self-stress analogous to topological quantum states to sculpt localized buckling regions in the interior of periodic cellular metamaterials. Although the topological states of self-stress arise in the linear response of an idealized mechanical frame of harmonic springs connected by freely hinged joints, they leave a distinct signature in the nonlinear buckling behavior of a cellular material built out of elastic beams with rigid joints. The salient feature of these localized buckling regions is that they are indistinguishable from their surroundings as far as material parameters or connectivity of their constituent elements are concerned. Furthermore, they are robust against a wide range of structural perturbations. We demonstrate the effectiveness of this topological design through analytical and numerical calculations as well as buckling experiments performed on two- and three-dimensional metamaterials built out of stacked kagome lattices.
On the buckling of hexagonal boron nitride nanoribbons via structural mechanics
Giannopoulos, Georgios I.
2018-03-01
Monolayer hexagonal boron nitride nanoribbons have similar crystal structure as graphene nanoribbons, have excellent mechanical, thermal insulating and dielectric properties and additionally present chemical stability. These allotropes of boron nitride can be used in novel applications, in which graphene is not compatible, to achieve remarkable performance. The purpose of the present work is to provide theoretical estimations regarding the buckling response of hexagonal boron nitride monolayer under compressive axial loadings. For this reason, a structural mechanics method is formulated which employs the exact equilibrium atomistic structure of the specific two-dimensional nanomaterial. In order to represent the interatomic interactions appearing between boron and nitrogen atoms, the Dreiding potential model is adopted which is realized by the use of three-dimensional, two-noded, spring-like finite elements of appropriate stiffness matrices. The critical compressive loads that cause the buckling of hexagonal boron nitride nanoribbons are computed with respect to their size and chirality while some indicative buckled shapes of them are illustrated. Important conclusions arise regarding the effect of the size and chirality on the structural stability of the hexagonal boron nitride monolayers. An analytical buckling formula, which provides good fitting of the numerical outcome, is proposed.
Orogen-transverse tectonic window in the Eastern Himalayan fold belt: A superposed buckling model
Bose, Santanu; Mandal, Nibir; Acharyya, S. K.; Ghosh, Subhajit; Saha, Puspendu
2014-09-01
The Eastern Lesser Himalayan fold-thrust belt is punctuated by a row of orogen-transverse domal tectonic windows. To evaluate their origin, a variety of thrust-stack models have been proposed, assuming that the crustal shortening occurred dominantly by brittle deformations. However, the Rangit Window (RW) in the Darjeeling-Sikkim Himalaya (DSH) shows unequivocal structural imprints of ductile deformations of multiple episodes. Based on new structural maps, coupled with outcrop-scale field observations, we recognize at least four major episodes of folding in the litho-tectonic units of DSH. The last episode has produced regionally orogen-transverse upright folds (F4), the interference of which with the third-generation (F3) orogen-parallel folds has shaped the large-scale structural patterns in DSH. We propose a new genetic model for the RW, invoking the mechanics of superposed buckling in the mechanically stratified litho-tectonic systems. We substantiate this superposed buckling model with results obtained from analogue experiments. The model explains contrasting F3-F4 interferences in the Lesser Himalayan Sequence (LHS). The lower-order (terrain-scale) folds have undergone superposed buckling in Mode 1, producing large-scale domes and basins, whereas the RW occurs as a relatively higher-order dome nested in the first-order Tista Dome. The Gondwana and the Proterozoic rocks within the RW underwent superposed buckling in Modes 3 and 4, leading to Type 2 fold interferences, as evident from their structural patterns.
DEFF Research Database (Denmark)
Lindgaard, Esben; Lund, Erik
2012-01-01
This paper presents a novel FEM-based approach for fiber angle optimal design of laminated composite structures exhibiting complicated nonlinear buckling behavior, thus enabling design of lighter and more cost-effective structures. The approach accounts for the geometrically nonlinear behavior of...
Out-of-plane buckling of roller bent wide flange arches - imperfections and finite element modeling
Spoorenberg, R.C.; Snijder, H.H.; Hoenderkamp, J.C.D.; Beg, D.; Chan, S.L.; Shu, G.P.
2012-01-01
Steel arches are used more and more in contemporary architecture, combining structural efficiency with architectural merits. If lateral supports are absent, these arches are prone to out-of-plane buckling. Arches are often made by cold bending wide flange beams at ambient temperature. This
Directory of Open Access Journals (Sweden)
Yokoyama T
2015-01-01
Full Text Available Toshiyuki Yokoyama, Koki Kanbayashi, Tamaki YamaguchiDepartment of Ophthalmology, Juntendo University Nerima Hospital, Tokyo, JapanPurpose: To assess the treatment of pediatric patients with rhegmatogenous retinal detachment (RRD by scleral buckling with chandelier illumination.Methods: Three eyes were treated in three patients, healthy boys aged 7 years, 12 years, and 11 years, with RRD, macular involvement, and small retinal holes, of which two were preoperatively undetectable. Conventional scleral buckling with cryoretinopexy was performed under the contact lens for vitreous surgery or noncontact wide-angle viewing system using 27-gauge twin chandelier illumination.Results: The only known predisposing factor for retinal detachment was myopia stronger than 3 D with lattice retinal degeneration in two of the three patients. Retinal reattachment was achieved in all cases without intra- or postoperative complications. However, visual recovery was limited in one of the three patients.Conclusion: Scleral buckling with chandelier illumination is effective for pediatric RRD, especially if the retinal hole is difficult to detect preoperatively. However, visual recovery was sometimes limited because of macular involvement due to late diagnosis, which is one of the characteristic features of pediatric RRD.Keywords: pediatric rhegmatogenous retinal detachment, chandelier illumination, scleral buckling
Thornton, W. A.; Majumder, D. K.
1974-01-01
The investigation reported demonstrates that in the case considered perturbation methods can be used in a straightforward manner to obtain reanalysis information. A perturbation formula for the buckling loads of a general shell of revolution is derived. The accuracy of the obtained relations and their range of application is studied with the aid of a specific example involving a particular stiffened shell of revolution.
Buckling Analysis of Bucket Foundations for Wind Turbines in Deep Water
DEFF Research Database (Denmark)
Madsen, Søren; Andersen, Lars; Ibsen, Lars Bo
2011-01-01
Using large suction caissons for offshore wind turbines is an upcoming technology also referred to as bucket foundations. The bucket foundation does not require heavy installation equipment, but since it is constructed as a thin steel shell structure, instability, in form of buckling, becomes...
International Nuclear Information System (INIS)
Mori, H; Waters, T; Saotome, N; Nagamine, T; Sato, Y
2016-01-01
Passive vibration isolators are desired to have both high static stiffness to support large static load and low local stiffness to reduce the displacement transmissibility at frequencies greater than resonance. Utilization of a vertical buckled beam as a spring component is one way to realize such a stiffness characteristic since it exhibits a smaller ratio of local stiffness to static stiffness than that of a linear spring. This paper investigates the behaviour of a vibration isolator using inclined beams as well as vertical ones and examines the effect of beam inclination for the purpose of improving the isolation performance. The experimental system investigated has an isolated mass which is supported by a combination of two types of beams: buckled beams and constraining beams. The buckled beams can be inclined from the vertical by attachment devices, and the constraining beams are employed to prevent off-axis motion of the isolated mass. The results demonstrate that the inclination of the buckled beams reduces the resonance frequency and improves the displacement transmissibility at frequencies greater than resonance. (paper)
Experimental tests on buckling of ellipsoidal vessel heads under internal pressure
International Nuclear Information System (INIS)
Alix, Michel; Roche, Roland.
1979-01-01
Seventeen heads made out of metal sheets -by cold working- were tested. Three different metals were used - carbon steel, austenitic steel, and aluminium alloy. Nominal dimensions were: diameter D 500 mm height H 50 and 100 mm thickness to diameter ratio t/D in the range 0.001-0.005. The heads had a good axisymmetric shape, but that the thickness was varying along the ellipse. Material characteristic of each head was given by a tensile test (strain-stress curve). The obtained results are mainly the pressure deflexion recordings, strain measurements and visual observations of the geometrical changes. For thin heads, buckling is a very fast event and the first folding occurs sudently, with a strong perturbation on the pressure-deflexion curve. For the thickest heads, circular waves are slowly forming. In all of these tests, yielding occured before buckling and it was possible to increase the pressure beyond the first buckling pressure without failure. The experimental results agree very well (+-5% except one head) with the empirical formula Psub(c)=70000.(sigma y+sigma u/2)(t/D)sup(5/3)((D/H) 2 -8)sup(-2/3). The following notations being used: Psub(c): critical buckling pressure; sigma y: yield strength; sigma u: ultimate stress (same unit); t: knuckle thickness; D: mean diameter; H: height (same unit) [fr
Buckling Capacity Curves for Steel Spherical Shells Loaded by the External Pressure
Błażejewski, Paweł; Marcinowski, Jakub
2015-03-01
Assessment of buckling resistance of pressurised spherical cap is not an easy task. There exist two different approaches which allow to achieve this goal. The first approach involves performing advanced numerical analyses in which material and geometrical nonlinearities would be taken into account as well as considering the worst imperfections of the defined amplitude. This kind of analysis is customarily called GMNIA and is carried out by means of the computer software based on FEM. The other, comparatively easier approach, relies on the utilisation of earlier prepared procedures which enable determination of the critical resistance pRcr, the plastic resistance pRpl and buckling parameters a, b, h, l 0 needed to the definition of the standard buckling resistance curve. The determination of the buckling capacity curve for the particular class of spherical caps is the principal goal of this work. The method of determination of the critical pressure and the plastic resistance were described by the authors in [1] whereas the worst imperfection mode for the considered class of spherical shells was found in [2]. The determination of buckling parameters defining the buckling capacity curve for the whole class of shells is more complicated task. For this reason the authors focused their attention on spherical steel caps with the radius to thickness ratio of R/t = 500, the semi angle j = 30o and the boundary condition BC2 (the clamped supporting edge). Taking into account all imperfection forms considered in [2] and different amplitudes expressed by the multiple of the shell thickness, sets of buckling parameters defining the capacity curve were determined. These parameters were determined by the methods proposed by Rotter in [3] and [4] where the method of determination of the exponent h by means of additional parameter k was presented. As a result of the performed analyses the standard capacity curves for all considered imperfection modes and amplitudes 0.5t, 1.0t, 1.5t
Lateral-Torsional Buckling Instability Caused by Individuals Walking on Wood Composite I-Joists
Villasenor Aguilar, Jose Maria
Recent research has shown that a significant number of the falls from elevation occur when laborers are working on unfinished structures. Workers walking on wood I-joists on roofs and floors are prone to fall hazards. Wood I-joists have been replacing dimension lumber for many floor systems and a substantial number of roof systems in light-frame construction. Wood I-joists are designed to resist axial stresses on the flanges and shear stresses on the web while minimizing material used. However, wood I-joists have poor resistance to applied lateral and torsional loads and are susceptible to lateral-torsional buckling instability. Workers walking on unbraced or partially braced wood I-joists can induce axial and lateral forces as well as twist. Experimental testing demonstrated that workers cause lateral-torsional buckling instability in wood I-joists. However, no research was found related to the lateral-torsional buckling instability induced by individuals walking on the wood I-joists. Furthermore, no research was found considering the effects of the supported end conditions and partial bracing in the lateral-torsional buckling instability of wood I-joists. The goal of this research was to derive mathematical models to predict the dynamic lateral-torsional buckling instability of wood composite I-joists loaded by individuals walking considering different supported end conditions and bracing system configurations. The dynamic lateral-torsional buckling instability was analyzed by linearly combining the static lateral-torsional buckling instability with the lateral bending motion of the wood Ijoists. Mathematical models were derived to calculate the static critical loads for the simply supported end condition and four wood I-joist hanger supported end conditions. Additionally, mathematical models were derived to calculate the dynamic maximum lateral displacements and positions of the individual walking on the wood Ijoists for the same five different supported end
Determination of buckling in the IPEN/MB-01 Reactor in cylindrical configuration
Energy Technology Data Exchange (ETDEWEB)
Purgato, Rafael Turrini; Bitelli, Ulysses d' Utra; Aredes, Vitor Ottoni; Silva, Alexandre F. Povoa da; Santos, Diogo Feliciano dos; Mura, Luis Felipe L.; Jerez, Rogerio, E-mail: rtpurgato@ipen.br, E-mail: ubitelli@ipen.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)
2013-07-01
One of the key parameters in reactor physics is the buckling of a reactor core. It is related to important parameters such as reaction rates, nuclear power operation, fuel burning, among others. In a critical reactor, the buckling depends on the geometric and material characteristics of the reactor core. This paper presents the results of experimental buckling in the reactor IPEN/MB-01 nuclear reactor in its cylindrical configuration with 28 fuel rods along its diameter. The IPEN/MB-01 is a zero power reactor designed to operate at a maximum power of 100 watts, it is a versatile nuclear facility which allows the simulation of all the characteristics of a large nuclear power reactor and ideal for this type of measurement. We conducted a mapping of neutron flux inside the reactor and thereby determined the total buckling of the cylindrical configuration. The reactor was operated for an hour. Then, the activation of the fuel rods was measured by gamma spectrometry on a rod scanner HPGe detector. We analyzed the gamma photons of the {sup 239}Np (276,6 keV) for neutron capture and the {sup 143}Ce (293,3 keV) for fission on both {sup 238}U and {sup 235}U, respectively. We analyzed the axial and radial directions. Other measurements were performed using wires and gold foils in the radial and axial directions of the reactor core. The results showed that the cylindrical configuration compared to standard rectangular configuration of the IPEN/MB-01 reactor has a higher neutron economy, since in this configuration there is less leakage of neutrons. The Buckling Total obtained from the three methods was 95.84 ± 2.67 m{sup -2}. (author)
Institute of Scientific and Technical Information of China (English)
PENG Fan; FU YiMing; CHEN YaoJun
2008-01-01
The effect of matrix cracking on the bifurcation creep buckling of viscoelastic laminated circular cylindrical shells is investigated. The viscoelastic behavior of laminas is modeled by Schapery's integral constitutive equation with growing ma-trix cracks. The values of damage variables are correlated to non-dimensional density of matrix cracks relying on the formulas from meso-mechanics approach, and the evolution equation predicting the growth rate of density of matrix cracks is assumed to follow a power type relation with transverse tensile stress. The gov-erning equations for pre-buckling creep deformation and bifurcation buckling of laminated circular cylindrical shells under axial compression are obtained on the basis of the Donnell type shallow shell theory and Karman-Donnell geometrically nonlinear relationship. Corresponding solution strategy is constructed by inte-grating finite-difference technique, trigonometric series expansion method and Taylor's numerical recursive scheme for convolution integration. The bifurcation creep buckling of symmetrically laminated glass-epoxy circular cylindrical shells with matrix creep cracking coupled are examined for various geometrical parame-ters and parameters of damage evolution as well as boundary conditions. The nu-merical results show that matrix creep cracking remarkably shortens the critic time of bifurcation buckling and reduces the durable critic loads, and its effects become weak and finally vanish with the increase of the ratio of radius to thickness in the case of short laminated circular cylindrical shells, also the influence of the matrix creep cracking is mainly dependent on the boundary conditions at two ends for moderately long circular cylindrical shells.
International Nuclear Information System (INIS)
Jung, Yousung; Shao, Yihan; Gordon, Mark S.; Doren, Douglas J.; Head-Gordon, Martin
2003-01-01
We report a spin-unrestricted density functional theory (DFT) solution at the symmetric dimer structure for cluster models of Si(100). With this solution, it is shown that the symmetric structure is a minimum on the DFT potential energy surface, although higher in energy than the buckled structure. In restricted DFT calculations the symmetric structure is a saddle point connecting the two buckled minima. To further assess the effects of electron correlation on the relative energies of symmetric versus buckled dimers on Si(100), multireference second order perturbation theory (MRMP2) calculations are performed on these DFT optimized minima. The symmetric structure is predicted to be lower in energy than the buckled structure via MRMP2, while the reverse order is found by DFT. The implications for recent experimental interpretations are discussed
National Research Council Canada - National Science Library
Chen, P
2000-01-01
...., excursions from one buckled state to the other. First, a large displacements small strains structural dynamic formulation is developed that accounts for the given temperature effects and relies on a higher-order shear modeling...
Directory of Open Access Journals (Sweden)
Spela Stunf
2011-01-01
Full Text Available Pre-existing scleral pathology is an important risk factor for globe rupture during scleral buckling procedures. We report here, the surgical management of an unexpected scleral pathology found at the scleral buckling procedure in a retinal detachment patient. A 77-year-old white female with retinal detachment underwent a scleral buckling procedure. The surgery was converted into a scleral graft procedure, as extreme scleral thinning was found intraoperatively. An alcohol-preserved donor sclera graft was used. The second surgery for definitive retinal alignment was performed two weeks later. The presented case of an unexpected scleral pathology in a retinal detachment patient was managed with a combination of scleral grafting and pars plana vitrectomy, without any major complications. The anatomical outcome was excellent and the scleral rupture was prevented; the visual outcome was satisfactory. A conversion of the scleral buckling procedure into a scleral graft procedure has proved to be safe and effective for unexpected scleral pathology.
Barrett, R.; McMurtry, R.; Vos, R.; Tiso, P.; De Breuker, R.
2005-01-01
This paper describes a new class of flight control actuators using Post-Buckled Precompressed (PBP) piezoelectric elements. These actuators are designed to produce significantly higher deflection and force levels than conventional piezoelectric actuator elements. Classical laminate plate theory
Biaxially stretchable supercapacitors based on the buckled hybrid fiber electrode array
Zhang, Nan; Zhou, Weiya; Zhang, Qiang; Luan, Pingshan; Cai, Le; Yang, Feng; Zhang, Xiao; Fan, Qingxia; Zhou, Wenbin; Xiao, Zhuojian; Gu, Xiaogang; Chen, Huiliang; Li, Kewei; Xiao, Shiqi; Wang, Yanchun; Liu, Huaping; Xie, Sishen
2015-07-01
In order to meet the growing need for smart bionic devices and epidermal electronic systems, biaxial stretchability is essential for energy storage units. Based on porous single-walled carbon nanotube/poly(3,4-ethylenedioxythiophene) (SWCNT/PEDOT) hybrid fiber, we designed and fabricated a biaxially stretchable supercapacitor, which possesses a unique configuration of the parallel buckled hybrid fiber array. Owing to the reticulate SWCNT film and the improved fabrication technique, the hybrid fiber retained its porous architecture both outwardly and inwardly, manifesting a superior capacity of 215 F g-1. H3PO4-polyvinyl alcohol gel with an optimized component ratio was introduced as both binder and stretchable electrolyte, which contributed to the regularity and stability of the buckled fiber array. The buckled structure and the quasi one-dimensional character of the fibers endow the supercapacitor with 100% stretchability along all directions. In addition, the supercapacitor exhibited good transparency, as well as excellent electrochemical properties and stability after being stretched 5000 times.In order to meet the growing need for smart bionic devices and epidermal electronic systems, biaxial stretchability is essential for energy storage units. Based on porous single-walled carbon nanotube/poly(3,4-ethylenedioxythiophene) (SWCNT/PEDOT) hybrid fiber, we designed and fabricated a biaxially stretchable supercapacitor, which possesses a unique configuration of the parallel buckled hybrid fiber array. Owing to the reticulate SWCNT film and the improved fabrication technique, the hybrid fiber retained its porous architecture both outwardly and inwardly, manifesting a superior capacity of 215 F g-1. H3PO4-polyvinyl alcohol gel with an optimized component ratio was introduced as both binder and stretchable electrolyte, which contributed to the regularity and stability of the buckled fiber array. The buckled structure and the quasi one-dimensional character of the
Tran, Phat; Arnett, Avery; Jarvis, Courtney; Mosley, Thomas; Tran, Khien; Hanes, Rob; Webster, Dan; Mitchell, Kelly; Dominguez, Leo; Hamood, Abdul; Reid, Ted W
2017-09-01
Biofilm formation is a problem for solid and sponge-type scleral buckles. This can lead to complications that require removal of the buckle, and result in vision loss due to related ocular morbidity, primarily infection, or recurrent retinal detachment. We investigate the ability of a covalent organo-selenium coating to inhibit biofilm formation on a scleral buckle. Sponge and solid Labtican brand scleral buckles were coated with organo-selenium coupled to a silyation reagent. Staphylococcus aureus biofilm formation was monitored by a standard colony-forming unit assay and the confocal laser scanning microscopy, while Pseudomonas aeruginosa biofilm formation was examined by scanning electron microscopy. Stability studies were done, by soaking in phosphate buffer saline (PBS) at room temperature for 2 months. Toxicity against human corneal epithelial cell was examined by growing the cells in the presence of organo-selenium-coated scleral buckles. The organo-selenium coating inhibited biofilm formation by gram-negative and gram-positive bacteria. The buckle coatings also were shown to be fully active after soaking in PBS for 2 months. The organo-selenium coatings had no effect on the viability of human corneal epithelial cells. Organo-selenium can be used to covalently coat a scleral buckle, which is stable and inhibits biofilm formation for gram-negative and gram-positive bacteria. The organo-selenium buckle coating was stable and nontoxic to cell culture. This technology provides a means to inhibit bacterial attachment to devices attached to the eye, without damage to ocular cells.
International Nuclear Information System (INIS)
Moon, F.C.
1977-05-01
The main results center around experimental buckling results obtained in a 16 coil superconducting torus. This device is a 1 / 75 th model of an early Argonne National Lab experimental power reactor design. The coils in the experimental torus were designed to buckle below the normal transition current level. Up to 130 KA-turns were placed in the torus during these tests. The test results are described
Energy Technology Data Exchange (ETDEWEB)
Liu, J.C. [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); Zhang, Y.Q., E-mail: cyqzhang@zju.edu.cn [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); State Key Laboratory of Mechanical Structural Strength and Vibration, Xi' an Jiaotong University, Xi' an 710049 (China); Fan, L.F. [College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100084 (China)
2017-04-11
The general equation for transverse vibration of double-viscoelastic-FGM-nanoplate system with viscoelastic Pasternak medium in between and each nanoplate subjected to in-plane edge loads is formulated on the basis of the Eringen's nonlocal elastic theory and the Kelvin model. The factors of the structural damping, medium damping, small size effect, loading ratio, and Winkler modulus and shear modulus of the medium are incorporated in the formulation. Based on the Navier's method, the analytical solutions for vibrational frequency and buckling load of the system with simply supported boundary conditions are obtained. The influences of these factors on vibrational frequency and buckling load of the system are discussed. It is demonstrated that the vibrational frequency of the system for the out-of-phase vibration is dependent upon the structural damping, small size effect and viscoelastic Pasternak medium, whereas the vibrational frequency for the in-phase vibration is independent of the viscoelastic Pasternak medium. While the buckling load of the system for the in-phase buckling case has nothing to do with the viscoelastic Pasternak medium, the buckling load for the out-of-phase case is related to the small size effect, loading ratio and Pasternak medium. - Highlights: • Vibration of double-viscoelastic-FGM-nanoplate system under in-plane edge loads is investigated. • Biaxial buckling of the system with simply supported boundary conditions is analyzed. • Explicit expression for the vibrational frequency and buckling load is obtained. • Impacts of viscoelastic Pasternak medium on vibrational frequency and buckling load are discussed. • Influences of structural damping, small size effect and loading ratio are also considered.
An energy harvesting solution based on the post-buckling response of non-prismatic slender beams
Jiao, Pengcheng; Borchani, Wassim; Hasni, Hassene; Alavi, Amir H.; Lajnef, Nizar
2017-04-01
Systems based on post-buckled structural elements have been extensively used in many applications such as actuation, remote sensing and energy harvesting thanks to their efficiency enhancement. The post-buckling snap- through behavior of bilaterally constrained beams has been used to create an efficient energy harvesting mechanism under quasi-static excitations. The conversion mechanism has been used to transform low-rate and low-frequency excitations into high-rate motions. Electric energy can be generated from such high-rate motions using piezoelectric transducers. However, lack of control over the post-buckling behavior severely limits the mechanism's efficiency. This study aims to maximize the levels of the harvestable power by controlling the location of the snapping point along the beam at different buckling transitions. Since the snap-through location cannot be controlled by tuning the geometry properties of a uniform cross-section beam, non-uniform cross sections are examined. An energy-based theoretical model is herein developed to predict the post-buckling response of non-uniform cross-section beams. The total potential energy is minimized under constraints that represent the physical confinement of the beam between the lateral boundaries. Experimentally validated results show that changing the shape and geometry dimensions of non- uniform cross-section beams allows for the accurate control of the snap-through location at different buckling transitions. A 78.59% increase in harvested energy levels is achieved by optimizing the beam's shape.
Jiao, Pengcheng; Borchani, Wassim; Hasni, Hassene; Lajnef, Nizar
2017-08-01
Thanks to their efficiency enhancement systems based on post-buckled structural elements have been extensively used in many applications such as actuation, remote sensing and energy harvesting. The post-buckling snap-through behavior of bilaterally constrained beams has been exploited to create sensing or energy harvesting mechanisms for quasi-static applications. The conversion mechanism has been used to transform low-rate and low-frequency excitations into high-rate motions. Electric energy has been generated from such high-rate motions using piezoelectric transducers. However, lack of control over the post-buckling behavior severely limits the mechanism’s efficiency. This study aims to maximize the levels of harvestable power by controlling the location of snap-throughs along the beam at different buckling transitions. Since the snap-through location cannot be controlled by tuning the geometric properties of a uniform beam, non-uniform cross-sections are examined. An energy-based theoretical model is herein developed to predict the post-buckling response of non-prismatic beams. The total potential energy is minimized under constraints that represent the physical confinement of the beam between the lateral boundaries. The experimentally validated results show that changing the shape and geometric dimensions of non-uniform beams allows for the accurate controlling of the snap-through location at different buckling transitions. A 78.59% improvement in harvested energy levels has been achieved by optimization of beam shape.
Directory of Open Access Journals (Sweden)
A. Farajpour
Full Text Available Carbon nanotubes are a new class of microtubule-stabilizing agents since they interact with protein microtubules in living cells, interfering with cell division and inducing apoptosis. In the present work, a modified beam model is developed to investigate the effect of carbon nanotubes on the buckling of microtubule bundles in living cell. A realistic interaction model is employed using recent experimental data on the carbon nanotube-stabilized microtubules. Small scale and surface effects are taken into account applying the nonlocal strain gradient theory and surface elasticity theory. Pasternak model is used to describe the normal and shearing effects of enclosing filament matrix on the buckling behavior of the system. An exact solution is obtained for the buckling growth rates of the mixed bundle in viscoelastic surrounding cytoplasm. The present results are compared with those reported in the open literature for single microtubules and an excellent agreement is found. Finally, the effects of different parameters such as the size, chirality, position and surface energy of carbon nanotubes on the buckling growth rates of microtubule bundles are studied. It is found that the buckling growth rate may increase or decrease by adding carbon nanotubes, depending on the diameter and chirality of carbon nanotubes. Keywords: Microtubules, Carbon nanotubes, Buckling, Size effects
Research on Buckling State of Prestressed Fiber-Strengthened Steel Pipes
Wang, Ruheng; Lan, Kunchang
2018-01-01
The main restorative methods of damaged oil and gas pipelines include welding reinforcement, fixture reinforcement and fiber material reinforcement. Owing to the severe corrosion problems of pipes in practical use, the research on renovation and consolidation techniques of damaged pipes gains extensive attention by experts and scholars both at home and abroad. The analysis of mechanical behaviors of reinforced pressure pipelines and further studies focusing on “the critical buckling” and intensity of pressure pipeline failure are conducted in this paper, providing theoretical basis to restressed fiber-strengthened steel pipes. Deformation coordination equations and buckling control equations of steel pipes under the effect of prestress is deduced by using Rayleigh Ritz method, which is an approximation method based on potential energy stationary value theory and minimum potential energy principle. According to the deformation of prestressed steel pipes, the deflection differential equation of prestressed steel pipes is established, and the critical value of buckling under prestress is obtained.
Elastic Moduli of Nanoparticle-Polymer Composite Thin Films via Buckling on Elastomeric Substrates
Yuan, Hongyi; Karim, Alamgir; University of Akron Team
2011-03-01
Polymeric thin films find applications in diverse areas such as coatings, barriers and packaging. The dispersion of nanoparticles into the films was proven to be an effective method to generate tunable properties, particularly mechanical strength. However, there are very few methods for mechanical characterization of the composite thin films with high accuracy. In this study, nanometric polystyrene and polyvinyl alcohol films with uniformly dispersed cobalt and Cloisite nanoparticles at varying concentrations were synthesized via flow-coating and then transferred to crosslinked polydimethylsiloxane (PDMS) flexible substrates. The technique of Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM) was employed to determine the elastic moduli of the films, which were calculated from the buckling patterns generated by applying compressive stresses. Results on moduli of films as a function of the concentrations of nanoparticles and the thicknesses of the composite films will be presented. *Corresponding author: alamgir@uakron.edu
The vibrational and buckling behaviors of piezoelectric nanobeams with surface effects
International Nuclear Information System (INIS)
Yan, Z; Jiang, L Y
2011-01-01
In this work, the influence of surface effects, including residual surface stress, surface elasticity and surface piezoelectricity, on the vibrational and buckling behaviors of piezoelectric nanobeams is investigated by using the Euler-Bernoulli beam theory. The surface effects are incorporated by applying the surface piezoelectricity model and the generalized Young-Laplace equations. The results demonstrate that surface effects play a significant role in predicting these behaviors. It is found that the influence of the residual surface stress and the surface piezoelectricity on the resonant frequencies and the critical electric potential for buckling is more prominent than the surface elasticity. The nanobeam boundary conditions are also found to influence the surface effects on these parameters. This study also shows that the resonant frequencies can be tuned by adjusting the applied electrical load. The present study is envisaged to provide useful insights for the design and applications of piezoelectric-beam-based nanodevices.
Buckling of pressure-loaded, long, shear deformable, cylindrical laminated shells
Anastasiadis, John S.; Simitses, George J.
A higher-order shell theory was developed (kinematic relations, constitutive relations, equilibrium equations and boundary conditions), which includes initial geometric imperfections and transverse shear effects for a laminated cylindrical shell under the action of pressure, axial compression and in-plane shear. Through the perturbation technique, buckling equations are derived for the corresponding 'perfect geometry' symmetric laminated configuration. Critical pressures are computed for very long cylinders for several stacking sequences, several radius-to-total-thickness ratios, three lamina materials (boron/epoxy, graphite/epoxy, and Kevlar/epoxy), and three shell theories: classical, first-order shear deformable and higher- (third-)order shear deformable. The results provide valuable information concerning the applicability (accurate prediction of buckling pressures) of the various shell theories.
How tall can gelatin towers be? An introduction to elasticity and buckling
Taberlet, Nicolas; Ferrand, Jérémy; Camus, Élise; Lachaud, Léa; Plihon, Nicolas
2017-12-01
The stability of elastic towers is studied through simple hands-on experiments. Using gelatin-based stackable bricks, one can investigate the maximum height a simple structure can reach before collapsing. We show through experiments and by using the classical linear elastic theory that the main limitation to the height of such towers is the buckling of the elastic structures under their own weight. Moreover, the design and architecture of the towers can be optimized to greatly improve their resistance to self-buckling. To this aim, the maximum height of hollow and tapered towers is investigated. The experimental and theoretical developments presented in this paper can help students grasp the fundamental concepts in elasticity and mechanical stability.
Nemeth, Michael P.
2014-01-01
Nonlinear and bifurcation buckling equations for elastic, stiffened, geometrically perfect, right-circular cylindrical, anisotropic shells subjected to combined loads are presented that are based on Sanders' shell theory. Based on these equations, a three-parameter approximate Rayleigh-Ritz solution and a classical solution to the buckling problem are presented for cylinders with simply supported edges. Extensive comparisons of results obtained from these solutions with published results are also presented for a wide range of cylinder constructions. These comparisons include laminated-composite cylinders with a wide variety of shell-wall orthotropies and anisotropies. Numerous results are also given that show the discrepancies between the results obtained by using Donnell's equations and variants of Sanders' equations. For some cases, nondimensional parameters are identified and "master" curves are presented that facilitate the concise representation of results.
Kinks and antikinks of buckled graphene: A testing ground for the φ4 field model
Yamaletdinov, R. D.; Slipko, V. A.; Pershin, Y. V.
2017-09-01
Kinks and antikinks of the classical φ4 field model are topological solutions connecting its two distinct ground states. Here we establish an analogy between the excitations of a long graphene nanoribbon buckled in the transverse direction and φ4 model results. Using molecular dynamics simulations, we investigated the dynamics of a buckled graphene nanoribbon with a single kink and with a kink-antikink pair. Several features of the φ4 model have been observed including the kink-antikink capture at low energies, kink-antikink reflection at high energies, and a bounce resonance. Our results pave the way towards the experimental observation of a rich variety of φ4 model predictions based on graphene.
Viswanathan, A. V.; Tamekuni, M.
1973-01-01
An exact linear analysis method is presented for predicting buckling of structures with arbitrary uniform cross section. The structure is idealized as an assemblage of laminated plate-strip elements, curved and planar, and beam elements. Element edges normal to the longitudinal axes are assumed to be simply supported. Arbitrary boundary conditions may be specified on any external longitudinal edge of plate-strip elements. The structure or selected elements may be loaded in any desired combination of inplane transverse compression or tension side load and axial compression load. The analysis simultaneously considers all possible modes of instability and is applicable for the buckling of laminated composite structures. Numerical results correlate well with the results of previous analysis methods.
EXACT SOLUTION FOR TEMPERATURE-DEPENDENT BUCKLING ANALYSIS OF FG-CNT-REINFORCED MINDLIN PLATES
Directory of Open Access Journals (Sweden)
Seyed Mohammad Mousavi
2016-03-01
Full Text Available This research deals with the buckling analysis of nanocomposite polymeric temperature-dependent plates reinforced by single-walled carbon nanotubes (SWCNTs. For the carbon-nanotube reinforced composite (CNTRC plate, uniform distribution (UD and three types of functionally graded (FG distribution patterns of SWCNT reinforcements are assumed. The material properties of FG-CNTRC plate are graded in the thickness direction and estimated based on the rule of mixture. The CNTRC is located in a elastic medium which is simulated with temperature-dependent Pasternak medium. Based on orthotropic Mindlin plate theory, the governing equations are derived using Hamilton’s principle and solved by Navier method. The influences of the volume fractions of carbon nanotubes, elastic medium, temperature and distribution type of CNTs are considered on the buckling of the plate. Results indicate that CNT distribution close to top and bottom are more efficient than those distributed nearby the mid-plane for increasing the stiffness of plates.
Utilization of the perturbation method for determination of the buckling heterogenous reactors
International Nuclear Information System (INIS)
Gheorghe, R.
1975-01-01
Evaluation of material buckling for heterogenous nulcear reactors is a key-problem for reactor people. In this direction several methods have been elaborated: bi-group method, heterogenous method and perturbation methods. Out of them, mostly employed is the perturbation method which is also presented in this paper and is applied in some parameter calculations of a new cell type for which fuel is positioned in the marginal area and the moderator is in the centre. It is based on the technique of progressive substitution. Advantages of the method: buckling comes out clearly, high level defects due to differences between O perturbated fluxes and the unperturbated flux Osub(o) can be corrected by an iterative procedure; using a modified bi-group theory, one can clearly describe effects of other parameters
Finite element analysis of BWR fuel channel buckling during a seismic event
International Nuclear Information System (INIS)
Kinoshita, Mika; Iwamoto, Yuji; Ledford, Kevin; Cantonwine, Paul
2014-01-01
This paper documents the predicted response of three BWR fuel channel designs in bending using a typical moment profile for GNF fuel designs. The bending performance of the fuel channel is predicted using ANSYS, a finite element modeling tool. Specifically, linear and non-linear buckling analyses were performed to determine the onset of elastic buckling, which causes a wavy structure on the compression face in bending that might also increase channel – control blade friction, and to determine to onset of channel collapse, which causes permanent deformation and would inhibit control rod insertion. The three channel designs considered in this paper are the 0.080 inch uniform channel, the 0.100 inch uniform channel and the 0.120 inch uniform channel at the beginning of fuel life (BOL) and at the end of fuel life (EOL). (author)
Temperature and boron dependencies of buckling and radial reflector saving for VVER lattices
International Nuclear Information System (INIS)
Alvarez, C.
1990-01-01
The temperature and boron dependencies of buckling and radial reflectors savings are analyzed in this paper on the basis of the results from the calculations ZR-6M critical assembly. These dependencies are related to the physical behavior of temperature and boron reactivity coefficients for the cores of VVER-type critical facilities. As a byproduct, the parameter was also investigated and its dependence on water density was determined
FEM Modelling of Lateral-Torsional Buckling Using Shell and Solid Elements
DEFF Research Database (Denmark)
Valeš, Jan; Stan, Tudor-Cristian
2017-01-01
The paper describes two methods of FEM modelling of I-section beams loaded by bending moments. Series of random realizations with initial imperfections following the first eigenmode of lateral-torsional buckling were created. Two independent FEM software products were used for analyses of resista...... of resistance. At the end the difference and correlation between the results as well as advantages and disadvantages of both methods are discussed....
Vortex-induced buckling of a viscous drop impacting a pool
Li, Erqiang
2017-07-20
We study the intricate buckling patterns which can form when a viscous drop impacts a much lower viscosity miscible pool. The drop enters the pool by its impact inertia, flattens, and sinks by its own weight while stretching into a hemispheric bowl. Upward motion along the outer bottom surface of this bowl produces a vortical boundary layer which separates along its top and rolls up into a vortex ring. The vorticity is therefore produced in a fundamentally different way than for a drop impacting a pool of the same liquid. The vortex ring subsequently advects into the bowl, thereby stretching the drop liquid into ever thinner sheets, reaching the micron level. The rotating motion around the vortex pulls in folds to form multiple windings of double-walled toroidal viscous sheets. The axisymmetric velocity field thereby stretches the drop liquid into progressively finer sheets, which are susceptible to both axial and azimuthal compression-induced buckling. The azimuthal buckling of the sheets tends to occur on the inner side of the vortex ring, while their folds can be stretched and straightened on the outside edge. We characterize the total stretching from high-speed video imaging and use particle image velocimetry to track the formation and evolution of the vortex ring. The total interfacial area between the drop and the pool liquid can grow over 40-fold during the first 50 ms after impact. Increasing pool viscosity shows entrapment of a large bubble on top of the drop, while lowering the drop viscosity produces intricate buckled shapes, appearing at the earliest stage and being promoted by the crater motions. We also present an image collage of the most intriguing and convoluted structures observed. Finally, a simple point-vortex model reproduces some features from the experiments and shows variable stretching along the wrapping sheets.
Ravichandran, Rajeswari; Venugopal, Jayarama Reddy; Mueller, Martina; Sundarrajan, Subramanian; Mukherjee, Shayanti; Pliska, Damian; Wintermantel, Erich; Ramakrishna, Seeram
2013-12-01
Myocardial infarction is caused after impairment of heart wall muscle following an immense cell loss and also when the myocardial tissue is lacking the inherent capacity to regenerate for normal functioning of myocardium. An immediate challenge in cardiac regeneration is to devise a strategy that leads to a reproducible degree of cardiac differentiation. We have speculated that ex vivo pretreatment of adipose-derived stem cells (ADSCs) using 5-azacytidine and a suitable patterned nanofibrous construct could lead to cardiomyogenic differentiation and results in superior biological and functional effects on cardiac regeneration of infarcted myocardium. Polyglycerol sebacate/gelatin fibers were fabricated by core/shell electrospinning with polyglycerol sebacate as the core material and gelatin as the shell material. Patterning of the core/shell fibers to form orthogonal and looped buckled nanostructures was achieved. Results demonstrated that the buckled fibers showing an orthogonal orientation and looped pattern had a Young's modulus of approximately 3.59 ± 1.58 MPa and 2.07 ± 0.44 MPa, respectively, which was comparable to that of native myocardium. The ADSCs cultured on these scaffolds demonstrated greater expression of the cardiac-specific marker proteins actinin, troponin and connexin 43, as well as characteristic multinucleation as shown by immunocytochemical and morphological analysis, indicating complete cardiogenic differentiation of ADSCs. In the natural milieu, cardiomyogenic differentiation probably involves multiple signaling pathways and we have postulated that a buckled structure combination of chemical treatment and environment-driven strategy induces cardiogenic differentiation of ADSCs. The combination of patterned buckled fibrous structures with stem cell biology may prove to be a productive device for myocardial infarction.
Institute of Scientific and Technical Information of China (English)
2008-01-01
The effect of matrix cracking on the bifurcation creep buckling of viscoelastic laminated circular cylindrical shells is investigated.The viscoelastic behavior of laminas is modeled by Schapery’s integral constitutive equation with growing matrix cracks.The values of damage variables are correlated to non-dimensional density of matrix cracks relying on the formulas from mesomechanics approach,and the evolution equation predicting the growth rate of density of matrix cracks is assumed to follow a power type relation with transverse tensile stress.The governing equations for prebuckling creep deformation and bifurcation buckling of laminated circular cylindrical shells under axial compression are obtained on the basis of the Donnell type shallow shell theory and Kármán-Donnell geometrically nonlinear relationship.Corresponding solution strategy is constructed by integrating finite-difference technique,trigonometric series expansion method and Taylor’s numerical recursive scheme for convolution integration.The bifurcation creep buckling of symmetrically laminated glass-epoxy circular cylindrical shells with matrix creep cracking coupled are examined for various geometrical parameters and parameters of damage evolution as well as boundary conditions.The numerical results show that matrix creep cracking remarkably shortens the critic time of bifurcation buckling and reduces the durable critic loads,and its effects become weak and finally vanish with the increase of the ratio of radius to thickness in the case of short laminated circular cylindrical shells,also the influence of the matrix creep cracking is mainly dependent on the boundary conditions at two ends for moderately long circular cylindrical shells.
Yokoyama, Toshiyuki; Kanbayashi, Koki; Yamaguchi, Tamaki
2015-01-01
Toshiyuki Yokoyama, Koki Kanbayashi, Tamaki YamaguchiDepartment of Ophthalmology, Juntendo University Nerima Hospital, Tokyo, JapanPurpose: To assess the treatment of pediatric patients with rhegmatogenous retinal detachment (RRD) by scleral buckling with chandelier illumination.Methods: Three eyes were treated in three patients, healthy boys aged 7 years, 12 years, and 11 years, with RRD, macular involvement, and small retinal holes, of which two were preoperativel...
Extrusion of hydrogel exoplant into upper eyelid 16 years after a scleral buckle procedure
Directory of Open Access Journals (Sweden)
Chirag P Shah
2011-01-01
Full Text Available Sixteen years after scleral buckle surgery with a hydrogel episcleral exoplant, a 43-year-old woman presented with progressive binocular diplopia, ptosis, and an expanding mass in her upper eyelid. She underwent surgical removal of the hydrogel exoplant through an anterior approach. The exoplant proved to be friable, fragmented, and encapsulated in a fibrous tissue; the exoplant was removed in its entirety. Postoperatively, the eyelid mass resolved, while her diplopia and ptosis improved slightly.
Temperature and boron dependencies of buckling and radial reflector savings for VVER lattices
International Nuclear Information System (INIS)
Alvarez, C.
1990-01-01
The temperature and boron dependencies of buckling and radial reflector savings are analyzed in this paper on the basis of the results from the calculations for the ZR-6M critical assembly. These dependencies are related to he physical behaviour of temperature and boron reactivity coefficients for the cores of VVER-type critical facilities. As a byproduct, the dp/dBg 2 parameter was also investigated and its dependence on water density was determined
Çelik, Kayhan; Kurt, Erol; Uzun, Yunus
2017-07-01
In the present study, experimental and theoretical explorations on the buckling features of a wind energy harvester have been performed. The harvester consists of a piezoelectric layer, which has a certain stiffness and voltage conversion rate. A blade rotates on a shaft carrying a magnet and sweeps the tip of the layer causing a serial buckling effect resulting in energy generation. Since the modeling of the buckling under a magnetic strength includes nonlinear terms over displacements, one requires a detailed study on the characteristics of buckling phenomena. It has been proven that the piezoelectric beam having the magnet at its tip can produce regular and chaotic dynamics for different frequencies (i.e. the rotation speed). In addition, there exist a number of quasi-periodic regions on the parameter space. The overall result indicates that the large area of complicated dynamics requires a detailed study in order to stabilize the position and velocity of the layer tip, thereby a much stabilized energy conversion from mechanical to electrical can be obtained. The present survey on the dynamics of the harvester is a new study and is considered as a two-parameter diagram [i.e. the wind speed (frequency) and magnetic strength]. Mainly, single-, double-, triple- and quadruple-type phase space portraits have been observed and the ripples on the maximal and minimal values of the beam velocity have been observed for certain rotation speeds. These results can be used in order to stabilize the harvester in terms of the reduction of total harmonic distortion in the generated waveform.
International Nuclear Information System (INIS)
Li, C.; Ru, C.Q.; Mioduchowski, A.
2006-01-01
Inspired by recent interest in torsion of the central pair microtubules in eukaryotic flagella, a novel thin-walled elastic beam model is suggested to study critical condition under which uniform bending of a flagellum will cause lateral/torsional buckling of the central pair. The model is directed to the central pair itself and the role of all surrounding cross-linkings inside the flagellum is modeled as an equivalent surrounding elastic medium. The model predicts that bending-driven torsion of the central pair does occur when the radius of curvature of the bent flagellum reduces to a moderate critical value typically of tens of microns. In particular, this critical value is almost independent of the flagellum length, and more sensitive to the parameters defining the surrounding elastic medium than the shear modulus of microtubules. The predicted wavelengths of the torsional buckling mode are insensitive to the flagellum length and comparable to some known related experimental data. These results indicate that torsion of the central pair microtubules in flagella is inevitable as a result of bending-driven lateral buckling. This offers an entirely new insight into the ongoing research on the mechanism of the central pair torsion
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Mahdi Izadi
2015-06-01
Full Text Available Vulnerable buildings and their rehabilitation are important problems for earthquake regions. In recent decades the goal of building rehabilitation and strengthening has gained different rehabilitation systems. However, most of these strengthening techniques disturb the occupants, who must vacate the building during renovation. Several retrofitting techniques such as addition masonry infill wall, application of buckling restrained braces and local modification of components has been studied in order to improve the overall seismic performance of such buildings. In response to many of the practical issues and economic considerations, engineers use often convergent unbuckling steel bracing frames as the lateral load resisting system during an earthquake.This kind of bracings increases the hardness and strength of concrete structures.The aim of the present study is the evaluation and comparison of seismic performance and retrofitting of an existing 7-storeys concrete structure with buckling restrained bracings and shear walls by nonlinear static procedure (NSP and accordance with cod-361. The results show that the buckling restrained bracing, decreased drift to acceptable levels and Structure behaves on the life safety of performance level.
The fluid mechanics of scleral buckling surgery for the repair of retinal detachment.
Foster, William Joseph; Dowla, Nadia; Joshi, Saurabh Y; Nikolaou, Michael
2010-01-01
Scleral buckling is a common surgical technique used to treat retinal detachments that involves suturing a radial or circumferential silicone element on the sclera. Although this procedure has been performed since the 1960s, and there is a reasonable experimental model of retinal detachment, there is still debate as to how this surgery facilitates the re-attachment of the retina. Finite element calculations using the COMSOL Multiphysics system are utilized to explain the influence of the scleral buckle on the flow of sub-retinal fluid in a physical model of retinal detachment. We found that, by coupling fluid mechanics with structural mechanics, laminar fluid flow and the Bernoulli effect are necessary for a physically consistent explanation of retinal reattachment. Improved fluid outflow and retinal reattachment are found with low fluid viscosity and rapid eye movements. A simulation of saccadic eye movements was more effective in removing sub-retinal fluid than slower, reading speed, eye movements in removing subretinal fluid. The results of our simulations allow us to explain the physical principles behind scleral buckling surgery and provide insight that can be utilized clinically. In particular, we find that rapid eye movements facilitate more rapid retinal reattachment. This is contradictory to the conventional wisdom of attempting to minimize eye movements.
A piezoelectric energy harvester for broadband rotational excitation using buckled beam
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Zhengqiu Xie
2018-01-01
Full Text Available This paper proposes a rotational energy harvester using a piezoelectric bistable buckled beam to harvest low-speed rotational energy. The proposed harvester consists of a piezoelectric buckled beam with a center magnet, and a rotary magnet pair with opposite magnetic poles mounted on a revolving host. The magnetic plucking is used to harvest the angular kinetic energy of the host. The nonlinear snap-through mechanism is utilized to improve the vibration displacement and output voltage of the piezoelectric layer over a wide rotation frequency range. Theoretical simulation and experimental results show that the proposed energy harvester can yield a stable average output power ranging between 6.91-48.01 μW over a rotation frequency range of 1-14 Hz across a resistance load of 110 kΩ. Furthermore, dual attraction magnets were employed to overcome the suppression phenomenon at higher frequencies, which yields a broadband and flat frequency response over 6-14 Hz with the output power reaching 42.19-65.44 μW, demonstrating the great potential of the bistable buckled beam for wideband rotation motion energy harvesting.
Lai, Changliang; Wang, Junbiao; Liu, Chuang
2014-10-01
Six typical composite grid cylindrical shells are constructed by superimposing three basic types of ribs. Then buckling behavior and structural efficiency of these shells are analyzed under axial compression, pure bending, torsion and transverse bending by finite element (FE) models. The FE models are created by a parametrical FE modeling approach that defines FE models with original natural twisted geometry and orients cross-sections of beam elements exactly. And the approach is parameterized and coded by Patran Command Language (PCL). The demonstrations of FE modeling indicate the program enables efficient generation of FE models and facilitates parametric studies and design of grid shells. Using the program, the effects of helical angles on the buckling behavior of six typical grid cylindrical shells are determined. The results of these studies indicate that the triangle grid and rotated triangle grid cylindrical shell are more efficient than others under axial compression and pure bending, whereas under torsion and transverse bending, the hexagon grid cylindrical shell is most efficient. Additionally, buckling mode shapes are compared and provide an understanding of composite grid cylindrical shells that is useful in preliminary design of such structures.
Upgrading the seismic capacity of existing RC buildings using buckling restrained braces
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Hamdy Abou-Elfath
2017-06-01
Full Text Available Many existing RC buildings do not meet the lateral strength requirements of current seismic codes and are vulnerable to significant damage or collapse in the event of future earthquakes. In the past few decades, buckling-restrained braces have become increasingly popular as a lateral force resisting system because of their capability of improving the strength, the stiffness and the energy absorbing capacity of structures. This study evaluates the seismic upgrading of a 6-story RC-building using single diagonal buckling restrained braces. Seismic evaluation in this study has been carried out by static pushover analysis and time history earthquake analysis. Ten ground motions with different PGA levels are used in the analysis. The mean plus one standard deviation values of the roof-drift ratio, the maximum story drift ratio, the brace ductility factors and the member strain responses are used as the basis for the seismic performance evaluations. The results obtained in this study indicate that strengthening of RC buildings with buckling restrained braces is an efficient technique as it significantly increases the PGA capacity of the RC buildings. The results also indicate the increase in the PGA capacity of the RC building with the increase in the amount of the braces.
Buckling of Nonprismatic Column on Varying Elastic Foundation with Arbitrary Boundary Conditions
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Ahmad A. Ghadban
2017-01-01
Full Text Available Buckling of nonprismatic single columns with arbitrary boundary conditions resting on a nonuniform elastic foundation may be considered as the most generalized treatment of the subject. The buckling differential equation for such columns is extremely difficult to solve analytically. Thus, the authors propose a numerical approach by discretizing the column into a finite number of segments. Each segment has constants E (modulus of elasticity, I (moment of inertia, and β (subgrade stiffness. Next, an exact analytical solution is derived for each prismatic segment resting on uniform elastic foundation. These segments are then assembled in a matrix from which the critical buckling load is obtained. The derived formulation accounts for different end boundary conditions. Validation is performed by benchmarking the present results against analytical solutions found in the literature, showing excellent agreement. After validation, more examples are solved to illustrate the power and flexibility of the proposed method. Overall, the proposed method provides reasonable results, and the examples solved demonstrate the versatility of the developed approach and some of its many possible applications.
Distortional Buckling Analysis of Steel-Concrete Composite Girders in Negative Moment Area
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Zhou Wangbao
2014-01-01
Full Text Available Distortional buckling is one of the most important buckling modes of the steel-concrete composite girder under negative moment. In this study, the equivalent lateral and torsional restraints of the bottom flange of a steel-concrete composite girder under negative moments due to variable axial forces are thoroughly investigated. The results show that there is a coupling effect between the applied forces and the lateral and torsional restraint of the bottom flange. Based on the calculation formula of lateral and torsional restraints, the critical buckling stress of I-steel-concrete composite girders and steel-concrete composite box girders under variable axial force is obtained. The critical bending moment of the steel-concrete composite girders can be further calculated. Compared to the traditional calculation methods of elastic foundation beam, the paper introduces an improved method, which considers coupling effect of the external loads and the foundation spring constraints of the bottom flange. Fifteen examples of the steel-concrete composite girders in different conditions are calculated. The calculation results show a good match between the hand calculation and the ANSYS finite element method, which validated that the analytic calculation method proposed in this paper is practical.
Rad, Maryam Alsadat; Tijjani, Auwal Shehu; Ahmad, Mohd Ridzuan; Auwal, Shehu Muhammad
2016-12-23
This paper proposes a new technique for real-time single cell stiffness measurement using lead zirconate titanate (PZT)-integrated buckling nanoneedles. The PZT and the buckling part of the nanoneedle have been modelled and validated using the ABAQUS software. The two parts are integrated together to function as a single unit. After calibration, the stiffness, Young's modulus, Poisson's ratio and sensitivity of the PZT-integrated buckling nanoneedle have been determined to be 0.7100 N·m -1 , 123.4700 GPa, 0.3000 and 0.0693 V·m·N -1 , respectively. Three Saccharomyces cerevisiae cells have been modelled and validated based on compression tests. The average global stiffness and Young's modulus of the cells are determined to be 10.8867 ± 0.0094 N·m -1 and 110.7033 ± 0.0081 MPa, respectively. The nanoneedle and the cell have been assembled to measure the local stiffness of the single Saccharomyces cerevisiae cells The local stiffness, Young's modulus and PZT output voltage of the three different size Saccharomyces cerevisiae have been determined at different environmental conditions. We investigated that, at low temperature the stiffness value is low to adapt to the change in the environmental condition. As a result, Saccharomyces cerevisiae becomes vulnerable to viral and bacterial attacks. Therefore, the proposed technique will serve as a quick and accurate process to diagnose diseases at early stage in a cell for effective treatment.
Theoretical and experimental investigations of creep buckling on NiCr 22 Co 12 Mo tubes
International Nuclear Information System (INIS)
Ahmed, K.; Breitbach, G.; Over, H.; Schubert, F.; Nickel, H.
1988-08-01
The postulated pressure loss of the secondary circuit is one of the hardest loading conditions for the heat exchanging components in a HTGR plant. It is to proof for the design that the heat exchanging metallic components (heat exchanger or reformer tubes of a PNP plant for instance) do not collapse under such an emergency condition. An external pressure p a stressed tubes or cylindric shells at a pressure loss of a secondary circuit side. This external pressure buckles the tubes in dependence of the fabrication implied out of roundness 0 (fabrication tolerances) by material creep in the high temperature region. This creep buckling ends in a failure (collapse) of the component after a critical time t cr . The aim of the work is the experimental verification of creep buckling behaviour for the heat exchanger components and the comparison with different constitutive equations. With these equations safety factors can be formulated against as well the critical collapse time and pressure as the permissible out of roundness from fabrication. (orig.) [de
A piezoelectric energy harvester for broadband rotational excitation using buckled beam
Xie, Zhengqiu; Kitio Kwuimy, C. A.; Wang, Zhiguo; Huang, Wenbin
2018-01-01
This paper proposes a rotational energy harvester using a piezoelectric bistable buckled beam to harvest low-speed rotational energy. The proposed harvester consists of a piezoelectric buckled beam with a center magnet, and a rotary magnet pair with opposite magnetic poles mounted on a revolving host. The magnetic plucking is used to harvest the angular kinetic energy of the host. The nonlinear snap-through mechanism is utilized to improve the vibration displacement and output voltage of the piezoelectric layer over a wide rotation frequency range. Theoretical simulation and experimental results show that the proposed energy harvester can yield a stable average output power ranging between 6.91-48.01 μW over a rotation frequency range of 1-14 Hz across a resistance load of 110 kΩ. Furthermore, dual attraction magnets were employed to overcome the suppression phenomenon at higher frequencies, which yields a broadband and flat frequency response over 6-14 Hz with the output power reaching 42.19-65.44 μW, demonstrating the great potential of the bistable buckled beam for wideband rotation motion energy harvesting.
Adhesion-governed buckling of thin-film electronics on soft tissues
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Bo Wang
2016-01-01
Full Text Available Stretchable/flexible electronics has attracted great interest and attention due to its potentially broad applications in bio-compatible systems. One class of these ultra-thin electronic systems has found promising and important utilities in bio-integrated monitoring and therapeutic devices. These devices can conform to the surfaces of soft bio-tissues such as the epidermis, the epicardium, and the brain to provide portable healthcare functionalities. Upon contractions of the soft tissues, the electronics undergoes compression and buckles into various modes, depending on the stiffness of the tissue and the strength of the interfacial adhesion. These buckling modes result in different kinds of interfacial delamination and shapes of the deformed electronics, which are very important to the proper functioning of the bio-electronic devices. In this paper, detailed buckling mechanics of these thin-film electronics on elastomeric substrates is studied. The analytical results, validated by experiments, provide a very convenient tool for predicting peak strain in the electronics and the intactness of the interface under various conditions.
An investigation of CO2 laser scleral buckling using moiré interferometry.
Maswadi, Saher M; Dyer, Peter E; Verma, Dinesh; Jalabi, Wadah; Dave, Dinesh
2002-01-01
To demonstrate suitability of moiré interferometry to assess and quantify laser-induced shrinkage of scleral collagen for buckling procedures. Scleral buckling of human cadaver eyes was investigated using a Coherent Ultrapulse CO2 laser. Projection moiré interferometry was employed to determine the out-of plane displacement produced by laser exposure, and in-situ optical microscopy of reference markers on the eye was used to measure in-plane shrinkage. Measurements based on moiré interferometry allow a three dimensional view of shape changes in the eye surface as laser treatment proceeds. Out-of-plane displacement reaches up to 1.5 mm with a single laser spot exposure. In-plane shrinkage reached a maximum of around 30%, which is similar to that reported by Sasoh et al (Ophthalmic Surg Lasers. 1998;29:410) for a Tm:YAG laser. The moiré technique is found to be suitable for quantifying the effects of CO2 laser scleral shrinkage and buckling. This can be further developed to provide a standardized method for experimental investigations of other laser sources for scleral shrinkage.
Forming three-dimensional closed shapes from two-dimensional soft ribbons by controlled buckling
Aoki, Michio; Juang, Jia-Yang
2018-02-01
Conventional manufacturing techniques-moulding, machining and casting-exist to produce three-dimensional (3D) shapes. However, these industrial processes are typically geared for mass production and are not directly applicable to residential settings, where inexpensive and versatile tools are desirable. Moreover, those techniques are, in general, not adequate to process soft elastic materials. Here, we introduce a new concept of forming 3D closed hollow shapes from two-dimensional (2D) elastic ribbons by controlled buckling. We numerically and experimentally characterize how the profile and thickness of the ribbon determine its buckled shape. We find a 2D master profile with which various elliptical 3D shapes can be formed. More complex natural and artificial hollow shapes, such as strawberry, hourglass and wheel, can also be achieved via strategic design and pattern engraving on the ribbons. The nonlinear response of the post-buckling regime is rationalized through finite-element analysis, which shows good quantitative agreement with experiments. This robust fabrication should complement conventional techniques and provide a rich arena for future studies on the mechanics and new applications of elastic hollow structures.
Yokoyama, Toshiyuki; Kanbayashi, Koki; Yamaguchi, Tamaki
2015-01-01
To assess the treatment of pediatric patients with rhegmatogenous retinal detachment (RRD) by scleral buckling with chandelier illumination. Three eyes were treated in three patients, healthy boys aged 7 years, 12 years, and 11 years, with RRD, macular involvement, and small retinal holes, of which two were preoperatively undetectable. Conventional scleral buckling with cryoretinopexy was performed under the contact lens for vitreous surgery or noncontact wide-angle viewing system using 27-gauge twin chandelier illumination. The only known predisposing factor for retinal detachment was myopia stronger than 3 D with lattice retinal degeneration in two of the three patients. Retinal reattachment was achieved in all cases without intra- or postoperative complications. However, visual recovery was limited in one of the three patients. Scleral buckling with chandelier illumination is effective for pediatric RRD, especially if the retinal hole is difficult to detect preoperatively. However, visual recovery was sometimes limited because of macular involvement due to late diagnosis, which is one of the characteristic features of pediatric RRD.
Nemeth, Michael P.
1990-01-01
Results are presented for unidirectional (0, 10)(sub s) and (90,10)(sub s) plates, ((0/90)(sub 5)(sub s)) plates, and for aluminum plates. Results are also presented for ((+/- theta)(sub 6)(sub s)) angle-ply plates for values of theta = 30, 45, and 60 degrees. The results indicate that the change in axial stiffness of a plate at buckling is strongly dependent upon cutout size and plate orthotropy. The presence of a cutout gives rise to an internal load distribution that changes, sometimes dramatically, as a function of cutout size coupled with the plate orthotropy. In the buckled state, the role of orthotropy becomes more significant since bending in addition to membrane orthotropy is present. Most of the plates with cutouts exhibited less postbuckling stiffness than the corresponding plate without a cutout, and the postbuckling stiffness decreased with increasing cutout size. However, some of the highly orthotropic plates with cutouts exhibited more postbuckling stiffness than the corresponding plate without a cutout. These results suggest the possibility of tailoring the cutout size and the stacking sequence of a composite plate to optimize postbuckling stiffness. It was found that plates with large radius cutouts do exhibit some postbuckling strength. The results also indicate that a cutout can influence modal interaction in a plate. Specifically, results are presented that show a plate with a relatively small cutout buckling at a higher load than the corresponding plate without a cutout, due to modal interaction. Other results are presented that indicate the presence of nonlinear prebuckling deformations, due to material nonlinearity, in the angle-ply plates with theta = 45 and 60 degrees. The nonlinear prebuckling deformations are more pronounced in the plates with theta = 45 degrees and become even more pronounced as the cutout size increases. Results are also presented that show how load-path eccentricity due to improper machining of the test specimens
Scleral buckling for retinal detachment in Ibadan, Sub-Saharan Africa: anatomical and visual outcome
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Oluleye TS
2013-05-01
Full Text Available TS Oluleye, OA Ibrahim, BA OlusanyaRetina and Vitreous Unit, Department of Ophthalmology, University College Hospital, Ibadan, NigeriaBackground: Scleral buckle surgery is not a commonly performed surgical procedure in Sub-Saharan Africa due to a paucity of trained vitreo retinal surgeons. The aim of the study was to review sclera buckle procedures with a view to evaluating the anatomical and visual outcomes.Methods: Case records of patients that had scleral buckle surgery at the Retina Unit of the University College Hospital, Ibadan, Nigeria, between 2007 and 2010 were reviewed. Information retrieved included patients' demographics, duration of symptoms, and presenting vision. Other information included site of retinal break, extent of retinal detachment, involvement of the fellow eye, and macular involvement. Postoperative retina reattachment and postoperative visual acuity were also recorded. Proportions and percentages were used to analyze data.Results: Forty five eyes of 42 patients were studied with a male to female ratio of 1.6:1. The mean age was 47.7 years (±17.6 years. The median duration before presentation was 3 months (range: 5 days – 156 months. Subtotal retinal detachment was found in 35 eyes (77.8% while total retinal detachment occurred in ten eyes (22.2%. Thirty four eyes (75.6% had "macular off" detachments. At 6 weeks, there was an improvement in visual acuity in 23 eyes (51.1%, while visual acuity remained the same in nine eyes (20% and was worse in 13 eyes (28.9%. Anatomical attachment was seen in 43 eyes (95.6% on the operation table, in 40 eyes (90.9% at first day postoperatively and in 32 eyes (86.5% at 6 weeks after surgery.Conclusion: Outcome of sclera buckle surgery for rhegmatogenous retinal detachment may be improved in developing countries of Sub Sahara Africa if adequate awareness is created to educate the populace on early presentation.Keywords: retinal detachment, scleral buckle surgery, anatomical and visual
Pneumatic retinopexy versus scleral buckle for repairing simple rhegmatogenous retinal detachments.
Hatef, Elham; Sena, Dayse F; Fallano, Katherine A; Crews, Jonathan; Do, Diana V
2015-05-07
Rhegmatogenous retinal detachment (RRD) is a full-thickness break in the sensory retina, caused by vitreous traction on the retina. While pneumatic retinopexy, scleral buckle, and vitrectomy are the accepted surgical interventions for eyes with RRD, their relative effectiveness has remained controversial. The objectives of this review were to assess the effectiveness and safety of pneumatic retinopexy versus scleral buckle or pneumatic retinopexy versus a combination treatment of scleral buckle and vitrectomy for people with RRD. The secondary objectives were to summarize any data on economic measures and quality of life. We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2014, Issue 12), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to January 2015), EMBASE (January 1980 to January 2015), Latin American and Caribbean Health Sciences Literature Database (LILACS) (January 1982 to January 2015), the ISRCTN registry (www.isrctn.com/editAdvancedSearch), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 13 January 2015. We included all randomized or quasi-randomized controlled trials comparing the effectiveness of pneumatic retinopexy versus scleral buckle (with or without vitrectomy) for eyes with RRD. After screening for eligibility, two review authors independently extracted study characteristics, methods, and outcomes. We followed systematic review standards as set forth by The Cochrane Collaboration. We included two randomized controlled trials (218 eyes of 216 participants) comparing the effectiveness of pneumatic retinopexy versus scleral buckle for eyes with RRD. We identified no studies
Huang, Yonghui; Yang, Zhicheng; Liu, Airong; Fu, Jiyang
2018-05-28
The buckling behavior of functionally graded graphene platelet-reinforced composite (FG-GPLRC) shallow arches with elastic rotational constraints under uniform radial load is investigated in this paper. The nonlinear equilibrium equation of the FG-GPLRC shallow arch with elastic rotational constraints under uniform radial load is established using the Halpin-Tsai micromechanics model and the principle of virtual work, from which the critical buckling load of FG-GPLRC shallow arches with elastic rotational constraints can be obtained. This paper gives special attention to the effect of the GPL distribution pattern, weight fraction, geometric parameters, and the constraint stiffness on the buckling load. The numerical results show that all of the FG-GPLRC shallow arches with elastic rotational constraints have a higher buckling load-carrying capacity compared to the pure epoxy arch, and arches of the distribution pattern X have the highest buckling load among four distribution patterns. When the GPL weight fraction is constant, the thinner and larger GPL can provide the better reinforcing effect to the FG-GPLRC shallow arch. However, when the value of the aspect ratio is greater than 4, the flakiness ratio is greater than 103, and the effect of GPL's dimensions on the buckling load of the FG-GPLRC shallow arch is less significant. In addition, the buckling model of FG-GPLRC shallow arch with elastic rotational constraints is changed as the GPL distribution patterns or the constraint stiffness changes. It is expected that the method and the results that are presented in this paper will be useful as a reference for the stability design of this type of arch in the future.
Energy Technology Data Exchange (ETDEWEB)
Golmakani, M. E.; Far, M. N. Sadraee; Moravej, M. [Dept. of Mechanical Engineering, Mashhad Branch, Islamic Azad University, Mashhad (Iran, Islamic Republic of)
2016-12-15
Using new approach proposed by Dynamic relaxation (DR) method, buckling analysis of moderately thick Functionally graded (FG) cylindrical panels subjected to axial compression is investigated for various boundary conditions. The mechanical properties of FG panel are assumed to vary continuously along the thickness direction by the simple rule of mixture and Mori-Tanaka model. The incremental form of nonlinear formulations are derived based on First-order shear deformation theory (FSDT) and large deflection von Karman equations. The DR method combined with the finite difference discretization technique is employed to solve the incremental form of equilibrium equations. The critical mechanical buckling load is determined based on compressive load-displacement curve by adding the incremental displacements in each load step to the displacements obtained from the previous ones. A detailed parametric study is carried out to investigate the influences of the boundary conditions, rule of mixture, grading index, radius-to-thickness ratio, length-to-radius ratio and panel angle on the mechanical buckling load. The results reveal that with increase of grading index the effect of radius-to-thickness ratio on the buckling load decreases. It is also observed that effect of distribution rules on the buckling load is dependent to the type of boundary conditions.
Energy Technology Data Exchange (ETDEWEB)
Murayama, Y.; Suda, K.; Ichinomiya, T.; Shinbo, H. [Kajima Corp., Tokyo (Japan)
1994-10-31
For RC (reinforced concrete) columns such as towers of long-span cable-stayed bridges or high-rise piers, there is desired development of an analytical method including a method of arranging reinforcing bars for increasing their ductility against strong earthquake motion. For this, it is necessary to investigate their characteristics after their being rendered to maximum load and their final states, and hence there must be newly investigated the properties of a plastic hinge formed on the bottom of the column, particularly determination of the buckling point of reinforcing bars and a hysteresis model after the buckling. In this study, there is developed a direct method of measuring the stress of reinforcing bars embedded in a model specimen which is conventionally difficult to be measured, and there is investigated the stress-strain hysteresis of the bars before and after the buckling thereof. The principle of the method of measuring the stress is such that only a local minimum portion of objective reinforcing bars is rendered to rf quenching, and a distortion gauge is sticked to the center of the quenching. This is based upon a fact that that portion keeps a linear relationship between the stress and the strain even if a host material is yielded. On the basis of an experimental result, a mechanism of buckling of these bars is clarified and a buckling model of the reinforcing bars at the plastic hinge. 6 refs., 15 figs., 2 tabs.
Directory of Open Access Journals (Sweden)
Najeeb ur Rahman
Full Text Available A one-dimensional finite element model for buckling analysis of hybrid piezoelectric beams under electromechanical load is presented in this work. The coupled zigzag theory is used for making the model. The inplane displacement is approximated as a combination of a global third order variation across the thickness with an additional layer wise linear variation. The longitudinal electric field is also taken into account. The deflection field is approximated to account for the transverse normal strain induced by electric fields. Two nodded elements with four mechanical and a variable number of electric degrees of freedom at each node are considered. To meet the convergence requirements for weak integral formulation, cubic Hermite interpolation function is used for deflection and electric potential at the sub-layers and linear interpolation function is used for axial displacement and shear rotation. The expressions for the variationally consistent stiffness matrix and load vector are derived and evaluated in closed form using exact integration. The present 1D-FE formulation of zigzag theory is validated by comparing the results with the analytical solution for simply-supported beam and 2D-FE results obtained using ABAQUS. The finite element model is free of shear locking. The critical buckling parameters are obtained for clamped-free and clamped-clamped hybrid beams. The obtained results are compared with the 2D-FE results to establish the accuracy of the zigzag theory for above boundary conditions. The effect of lamination angle on critical buckling load is also studied.
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Maryam Alsadat Rad
2016-12-01
Full Text Available This paper proposes a new technique for real-time single cell stiffness measurement using lead zirconate titanate (PZT-integrated buckling nanoneedles. The PZT and the buckling part of the nanoneedle have been modelled and validated using the ABAQUS software. The two parts are integrated together to function as a single unit. After calibration, the stiffness, Young’s modulus, Poisson’s ratio and sensitivity of the PZT-integrated buckling nanoneedle have been determined to be 0.7100 N·m−1, 123.4700 GPa, 0.3000 and 0.0693 V·m·N−1, respectively. Three Saccharomyces cerevisiae cells have been modelled and validated based on compression tests. The average global stiffness and Young’s modulus of the cells are determined to be 10.8867 ± 0.0094 N·m−1 and 110.7033 ± 0.0081 MPa, respectively. The nanoneedle and the cell have been assembled to measure the local stiffness of the single Saccharomyces cerevisiae cells The local stiffness, Young’s modulus and PZT output voltage of the three different size Saccharomyces cerevisiae have been determined at different environmental conditions. We investigated that, at low temperature the stiffness value is low to adapt to the change in the environmental condition. As a result, Saccharomyces cerevisiae becomes vulnerable to viral and bacterial attacks. Therefore, the proposed technique will serve as a quick and accurate process to diagnose diseases at early stage in a cell for effective treatment.
Jegley, Dawn C.
1987-01-01
Buckling loads of thick-walled orthotropic and anisotropic simply supported circular cylinders are predicted using a higher-order transverse-shear deformation theory. A comparison of buckling loads predicted by the conventional first-order transverse-shear deformation theory and the higher-order theory show that the additional allowance for transverse shear deformation has a negligible effect on the predicted buckling loads of medium-thick metallic isotropic cylinders. However, the higher-order theory predicts buckling loads which are significantly lower than those predicted by the first-order transverse-shear deformation theory for certain short, thick-walled cylinders which have low through-the-thickness shear moduli. A parametric study of the effects of ply orientation on the buckling load of axially compressed cylinders indicates that laminates containing 45 degree plies are most sensitive to transverse-shear deformation effects. Interaction curves for buckling loads of cylinders subjected to axial compressive and external pressure loadings indicate that buckling loads due to external pressure loadings are as sensitive to transverse-shear deformation effects as buckling loads due to axial compressive loadings. The effects of anisotropy are important over a much wider range of cylinder geometries than the effects of transverse shear deformation.
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Alexandre Achille Grandinetti
2013-04-01
Full Text Available PURPOSE: To evaluate the changes in corneal topography after 20-gauge pars plana vitrectomy associated with scleral buckling for the repair of rhegmatogenous retinal detachment. METHODS: Twenty-five eyes of 25 patients with rhegmatogenous retinal detachment were included in this study. 20-gauge pars plana vitrectomy associated with scleral buckling was performed in all patients. The corneal topography of each was measured before surgery and one week, one month, and three months after surgery by computer-assisted videokeratoscopy. RESULTS: A statistically significant central corneal steepening (average, 0,9 D , p<0,001 was noted one week after surgery. The total corneal astigmatism had a significant increase in the first postoperative month (p=0,007. All these topographic changes persisted for the first month but returned to preoperative values three months after the surgery. CONCLUSION: Pars plana vitrectomy with scleral buckling was found to induce transient changes in corneal topography.
Jaunky, Navin; Knight, Norman F., Jr.; Ambur, Damodar R.
1995-01-01
A smeared stiffener theory for stiffened panels is presented that includes skin-stiffener interaction effects. The neutral surface profile of the skin-stiffener combination is developed analytically using the minimum potential energy principle and statics conditions. The skin-stiffener interaction is accounted for by computing the stiffness due to the stiffener and the skin in the skin-stiffener region about the neutral axis at the stiffener. Buckling load results for axially stiffened, orthogrid, and general grid-stiffened panels are obtained using the smeared stiffness combined with a Rayleigh-Ritz method and are compared with results from detailed finite element analyses.
Dynamic analysis of a buckled asymmetric piezoelectric beam for energy harvesting
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Van Blarigan, Louis, E-mail: louis01@umail.ucsb.edu; Moehlis, Jeff [Department of Mechanical Engineering, University of California, Santa Barbara, California 93106 (United States)
2016-03-15
A model of a buckled beam energy harvester is analyzed to determine the phenomena behind the transition between high and low power output levels. It is shown that the presence of a chaotic attractor is a sufficient condition to predict high power output, though there are relatively small areas where high output is achieved without a chaotic attractor. The chaotic attractor appears as a product of a period doubling cascade or a boundary crisis. Bifurcation diagrams provide insight into the development of the chaotic region as the input power level is varied, as well as the intermixed periodic windows.
Post-buckling capacity of bi-axially loaded rectangular steel plates
DEFF Research Database (Denmark)
Jönsson, Jeppe; Bondum, T. H.
2012-01-01
slenderness and edge displacement ratio are included in the investigations presented. Capacity interaction curves are established in the bi-axial stress domain. It turns out that for certain stress ratios the imperfections dominating the ultimate capacity are not affine to the lowest classical buckling mode...... for biaxial stress. It is of great interest that short wave imperfections of a lower magnitude compared to conventionally used imperfections are seen to lower the capacity of the bi-axially loaded plates. The topic is of major concern in the flange plates of long span bridges with multi box girder...
Effects of chirality and surface stresses on the bending and buckling of chiral nanowires
International Nuclear Information System (INIS)
Wang, Jian-Shan; Shimada, Takahiro; Kitamura, Takayuki; Wang, Gang-Feng
2014-01-01
Due to their superior optical, elastic and electrical properties, chiral nanowires have many applications as sensors, probes, and building blocks of nanoelectromechanical systems. In this paper, we develop a refined Euler–Bernoulli beam model for chiral nanowires with surface effects and material chirality incorporated. This refined model is employed to investigate the bending and buckling of chiral nanowires. It is found that surface effects and material chirality significantly affect the elastic behaviour of chiral nanowires. This study is helpful not only for understanding the size-dependent behaviour of chiral nanowires, but also for characterizing their mechanical properties. (paper)
Analysis of Potential for Titanium Liner Buckling after Proof in a Large Kevlar/Epoxy COPV
Phoenix, S. Leigh; Kezirian, Michael T.
2009-01-01
We analyze the potential for liner buckling in a 40-in Kevlar49/epoxy overwrapped spherical pressure vessel (COPV) due to long, local depressions or valleys in the titanium liner, which appeared after proof testing (autofrettage). We begin by presenting the geometric characteristics of approximately 20 mil (0.02 in.) deep depressions measured by laser profilometry in several vessels. While such depths were more typical, depths of more than 40 mils (0.02 in.) were seen near the equator in one particular vessel. Such depressions are largely the result of overlap of the edges of overwrap bands (with rectangular cross-section prepreg tows) from the first or second wrap patterns particularly where they start and end. We then discuss the physical mechanisms of formation of the depressions during the autofrettage process in terms of uneven void compaction in the overwrap around the tow overlap lines and the resulting 10-fold increase in through-thickness stiffness of the overwrap. We consider the effects of liner plastic yielding mechanisms in the liner on residual bending moments and interface pressures with the overwrap both at the peak proof pressure (approx.6500 psi) and when reducing the pressure to 0 psi. During depressurization the Bauschinger phenomenon becomes very important whereby extensive yielding in tension reduces the magnitude of the yield threshold in compression by 30 to 40%, compared to the virgin annealed state of the liner titanium. In the absence of a depression, the liner is elastically stable in compression even at liner overwrap interface pressures nominally 6 times the approx. 1000 psi interface pressure that exists at 0 psi. Using a model based on a plate-on-an-elastic-foundation, we develop an extensive analysis of the possible destabilizing effects of a frozen-in valley. The analysis treats the modifying effects of the residual bending moments and interface pressures remaining after the proof hold as well as the Bauschinger effect on the
Buckling of Actin-Coated Membranes under Application of a Local Force
International Nuclear Information System (INIS)
Helfer, E.; Harlepp, S.; Bourdieu, L.; Robert, J.; MacKintosh, F. C.; Chatenay, D.
2001-01-01
The mechanical properties of composite membranes obtained by self-assembly of actin filaments with giant fluid vesicles are studied by micromanipulation with optical tweezers. These complexes exhibit typical mechanical features of a solid shell, including a finite in-plane shear elastic modulus (∼10 -6 N /m). A buckling instability is observed when a localized force of the order of 0.5pN is applied perpendicular to the membrane plane. Although predicted for polymerized vesicles, this is the first evidence of such an instability
Numerical Buckling Analysis of Large Suction Caissons for Wind Turbines on Deep Water
DEFF Research Database (Denmark)
Madsen, Søren; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo
2013-01-01
Using large suction caissons for offshore wind turbines is an upcoming cost-effective technology also referred to as bucket foundations. During operation, the monopod bucket foundation is loaded by a large overturning moment from the wind turbine and the wave loads. However, during installation...... the suction caisson is loaded by external pressure (internal suction) due to evacuation of water inside the bucket and vertical forces due to gravity. The risk of structural buckling during installation of large-diameter suction caissons is addressed using numerical methods. Initial imperfect geometries...
Buckling And Postbuckling Of An Imperfect Plate Subjected To The Shear Load
Directory of Open Access Journals (Sweden)
Psotný Martin
2015-12-01
Full Text Available The stability analysis of an imperfect plate subjected to the shear load is presented. To solve this problem, a specialized computer program based on FEM has been created. The nonlinear finite element method equations are derived from the variational principle of minimum of total potential energy. To obtain the nonlinear equilibrium paths, the Newton-Raphson iteration algorithm is used. Corresponding levels of the total potential energy are defined. Special attention is paid to the influence of imperfections on the post-critical buckling mode. Obtained results are compared with those gained using ANSYS system.
International Nuclear Information System (INIS)
Mackey, T.C.; Johnson, K.I.; Deibler, J.E.; Pilli, S.P.; Rinker, M.W.; Karri, N.K.
2007-01-01
This report documents a detailed buckling evaluation of the primary tanks in the Hanford double-shell waste tanks (DSTs), which is part of a comprehensive structural review for the Double-Shell Tank Integrity Project. This work also provides information on tank integrity that specifically responds to concerns raised by the Office of Environment, Safety, and Health (ES and H) Oversight (EH-22) during a review of work performed on the double-shell tank farms and the operation of the aging waste facility (AWF) primary tank ventilation system. The current buckling review focuses on the following tasks: (1) Evaluate the potential for progressive I-bolt failure and the appropriateness of the safety factors that were used for evaluating local and global buckling. The analysis will specifically answer the following questions: (a) Can the EH-22 scenario develop if the vacuum is limited to -6.6-inch water gage (w.g.) by a relief valve? (b) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario can develop? (c) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario cannot develop? (2) Develop influence functions to estimate the axial stresses in the primary tanks for all reasonable combinations of tank loads, based on detailed finite element analysis. The analysis must account for the variation in design details and operating conditions between the different DSTs. The analysis must also address the imperfection sensitivity of the primary tank to buckling. (3) Perform a detailed buckling analysis to determine the maximum allowable differential pressure for each of the DST primary tanks at the current specified limits on waste temperature, height, and specific gravity. Based on the I-bolt loads analysis and the small deformations that are predicted at the unfactored limits on vacuum and axial loads, it is very unlikely that the EH-22 scenario (i.e., progressive I-bolt failure leading to
DEFF Research Database (Denmark)
Henrichsen, Søren Randrup; Lindgaard, Esben; Lund, Erik
2015-01-01
Robust buckling optimal design of laminated composite structures is conducted in this work. Optimal designs are obtained by considering geometric imperfections in the optimization procedure. Discrete Material Optimization is applied to obtain optimal laminate designs. The optimal geometric...... imperfection is represented by the “worst” shape imperfection. The two optimization problems are combined through the recurrence optimization. Hereby the imperfection sensitivity of the considered structures can be studied. The recurrence optimization is demonstrated through a U-profile and a cylindrical panel...... example. The imperfection sensitivity of the optimized structure decreases during the recurrence optimization for both examples, hence robust buckling optimal structures are designed....
Li, Mingyang; Zu, Mei; Yu, Jinshan; Cheng, Haifeng; Li, Qingwen
2017-03-01
A stretchable fiber supercapacitor (SC) based on buckled MnO 2 /oxidized carbon nanotube (CNT) fiber electrode is fabricated by a simple prestraining-then-buckling method. The prepared stretchable fiber SC has a specific volumetric capacitance up to 409.4 F cm -3 , which is 33 times that of the pristine CNT fiber based SC, and shows the outstanding stability and repeatability in performance as a stretchable SC. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
DEFF Research Database (Denmark)
Gaiotti, Marco; Rizzo, Cesare M.; Branner, Kim
2014-01-01
This paper describes the experimental and numerical studies carried out on delaminated fiberglass epoxy resin laminates made-up by different fabrication methods, namely by vacuum infusion and prepreg. While the tested specimens were originally intended for the assessment of buckling behavior...... of composite laminates of wind turbine blades, results were found valuable for the marine industry as well, because similar laminates are used for the hull shell and stiffeners. Systematic calculations were carried out to assess the effects of an embedded delamination on the buckling load, varying the size...
Qi, Yi; Kim, Jihoon; Nguyen, Thanh D; Lisko, Bozhena; Purohit, Prashant K; McAlpine, Michael C
2011-03-09
The development of a method for integrating highly efficient energy conversion materials onto soft, biocompatible substrates could yield breakthroughs in implantable or wearable energy harvesting systems. Of particular interest are devices which can conform to irregular, curved surfaces, and operate in vital environments that may involve both flexing and stretching modes. Previous studies have shown significant advances in the integration of highly efficient piezoelectric nanocrystals on flexible and bendable substrates. Yet, such inorganic nanomaterials are mechanically incompatible with the extreme elasticity of elastomeric substrates. Here, we present a novel strategy for overcoming these limitations, by generating wavy piezoelectric ribbons on silicone rubber. Our results show that the amplitudes in the waves accommodate order-of-magnitude increases in maximum tensile strain without fracture. Further, local probing of the buckled ribbons reveals an enhancement in the piezoelectric effect of up to 70%, thus representing the highest reported piezoelectric response on a stretchable medium. These results allow for the integration of energy conversion devices which operate in stretching mode via reversible deformations in the wavy/buckled ribbons.
Subscale and Full-Scale Testing of Buckling-Critical Launch Vehicle Shell Structures
Hilburger, Mark W.; Haynie, Waddy T.; Lovejoy, Andrew E.; Roberts, Michael G.; Norris, Jeffery P.; Waters, W. Allen; Herring, Helen M.
2012-01-01
New analysis-based shell buckling design factors (aka knockdown factors), along with associated design and analysis technologies, are being developed by NASA for the design of launch vehicle structures. Preliminary design studies indicate that implementation of these new knockdown factors can enable significant reductions in mass and mass-growth in these vehicles and can help mitigate some of NASA s launch vehicle development and performance risks by reducing the reliance on testing, providing high-fidelity estimates of structural performance, reliability, robustness, and enable increased payload capability. However, in order to validate any new analysis-based design data or methods, a series of carefully designed and executed structural tests are required at both the subscale and full-scale level. This paper describes recent buckling test efforts at NASA on two different orthogrid-stiffened metallic cylindrical shell test articles. One of the test articles was an 8-ft-diameter orthogrid-stiffened cylinder and was subjected to an axial compression load. The second test article was a 27.5-ft-diameter Space Shuttle External Tank-derived cylinder and was subjected to combined internal pressure and axial compression.
Comparison of Methods to Predict Lower Bound Buckling Loads of Cylinders Under Axial Compression
Haynie, Waddy T.; Hilburger, Mark W.
2010-01-01
Results from a numerical study of the buckling response of two different orthogrid stiffened circular cylindrical shells with initial imperfections and subjected to axial compression are used to compare three different lower bound buckling load prediction techniques. These lower bound prediction techniques assume different imperfection types and include an imperfection based on a mode shape from an eigenvalue analysis, an imperfection caused by a lateral perturbation load, and an imperfection in the shape of a single stress-free dimple. The STAGS finite element code is used for the analyses. Responses of the cylinders for ranges of imperfection amplitudes are considered, and the effect of each imperfection is compared to the response of a geometrically perfect cylinder. Similar behavior was observed for shells that include a lateral perturbation load and a single dimple imperfection, and the results indicate that the predicted lower bounds are much less conservative than the corresponding results for the cylinders with the mode shape imperfection considered herein. In addition, the lateral perturbation technique and the single dimple imperfection produce response characteristics that are physically meaningful and can be validated via testing.
Size-dependent vibrations of post-buckled functionally graded Mindlin rectangular microplates
Directory of Open Access Journals (Sweden)
R. Ansari
Full Text Available In this paper, the free vibration behavior of post-buckled functionally graded (FG Mindlin rectangular microplates are described based on the modified couple stress theory (MCST. This theory enables the consideration of the size-effect through introducing material length scale parameters. The FG microplates made of a mixture of metal and ceramic are considered whose volume fraction of components is expressed by a power law function. By means of Hamilton's principle, the nonlinear governing equations and associated boundary conditions are derived for FG micro-plates in the postbuckling domain. The governing equations and boundary conditions are then discretized by using the generalized differential quadrature (GDQ method before solving numerically by the pseudo-arclength continuation technique. In the solution procedure, the postbuckling problem of microplates is investigated first. Afterwards, the free vibration of microplates around the buckled configuration is discussed. The effects of dimensionless length scale parameter, material gradient index and aspect ratio on the on the postbuckling path and frequency of FG microplates subject to arbitrary edge supports are thoroughly discussed.
Noor, Ahmed K.; Kim, Yong H.
1995-01-01
The results of a detailed study of the buckling and postbuckling responses of composite panels with central circular cutouts are presented. The panels are subjected to combined edge shear and temperature change. The panels are discretized by using a two-field degenerate solid element with each of the displacement components having a linear variation throughout the thickness of the panel. The fundamental unknowns consist of the average mechanical strains through the thickness and the displacement components. The effects of geometric nonlinearities and laminated anisotropic material behavior are included. The stability boundary, postbuckling response and the hierarchical sensitivity coefficients are evaluated. The hierarchical sensitivity coefficients measure the sensitivity of the buckling and postbuckling responses to variations in the panel stiffnesses, and the material properties of both the individual layers and the constituents (fibers and matrix). Numerical results are presented for composite panels with central circular cutouts subjected to combined edge shear and temperature change, showing the effects of variations in the hole diameter, laminate stacking sequence and fiber orientation, on the stability boundary and postbuckling response and their sensitivity to changes in the various panel parameters.
Energy Technology Data Exchange (ETDEWEB)
Farajpour, A., E-mail: ariobarzan.oderj@gmail.com; Rastgoo, A.; Mohammadi, M.
2017-03-15
Piezoelectric nanomaterials such as zinc oxide (ZnO) are of low toxicity and have many biomedical applications including optical imaging, drug delivery, biosensing and harvesting biomechanical energy using hybrid nanogenerators. In this paper, the vibration, buckling and smart control of microtubules (MTs) embedded in an elastic medium in thermal environment using a piezoelectric nanoshell (PNS) are investigated. The MT and PNS are considered to be coupled by a filament network. The PNS is subjected to thermal loads and an external electric voltage which operates to control the mechanical behavior of the MT. Using the nonlocal continuum mechanics, the governing differential equations are derived. An exact solution is presented for simply supported boundary conditions. The differential quadrature method is also used to solve the governing equations for other boundary conditions. A detailed parametric study is conducted to investigate the effects of the elastic constants of surrounding medium and internal filament matrix, scale coefficient, electric voltage, the radius-to-thickness ratio of PNSs and temperature change on the smart control of MTs. It is found that the applied electric voltage can be used as an effective controlling parameter for the vibration and buckling of MTs.
GoPro HERO 4 Black recording of scleral buckle placement during retinal detachment repair.
Ho, Vincent Y; Shah, Vaishali G; Yates, David M; Shah, Gaurav K
2017-08-01
GoPro and Google Glass technology have previously been used to record procedures in ophthalmology and other medical fields. In this manuscript, GoPro's latest HERO 4 Black edition camera (GoPro Inc, San Mateo, Calif.) will be used to record the placement of a scleral buckle during retinal detachment surgery. GoPro HERO 4 Black edition camera, which records 4K-quality video with a resolution of 3840 (pixels) x 2160 (lines), was mounted on a head strap to record placement of a scleral buckle for a retinal detachment. Excellent video quality was achieved with the 4K SuperView setting. Bluetooth connection with an Apple iPad (Apple Inc, Cupertino, Calif.) provided live streaming and use of the GoPro App. Zoom, horizontal/vertical alignment, exposure, and contrast adjustments were made with postproduction editing on GoPro Studio software. Video recording with the GoPro HERO 4 Black edition camera is an excellent way to document extraocular procedures to improve medical education, self-training, or medicolegal documentation. Copyright © 2017 Canadian Ophthalmological Society. Published by Elsevier Inc. All rights reserved.
Jahangiri, Mehdi
2017-09-01
A hypothesis is proposed in this work to account for the geometry of individual vertically aligned carbon nanotubes (VACNTs) that not only justifies the directionality of their growth, but also explains the origin of the waviness frequently reported for these nanotube forests. Such waviness has fundamental effects on the transport/conduction properties of VACNTs, either through or along them, regarding phenomena such as mass, stress, heat and electricity. Despite the general opinion about randomness of carbon nanotubes (CNTs) tortuosity, we demonstrate here that rules of helical buckling of tubular strings is applicable to VACNTs, based on which a regular 3D helical geometry is proposed for VACNTs, with a 2D sine wave shape side-profile. In this framework, gradual increase of the total free surface energy by growth of CNTs ensues their partial cohesion, driven by van der Waals interactions, to reduce the excess surface energy. On the other hand, their cohesion is accompanied by their deformation and loss of straightness, which in turn, translates to buildup of an elastic strain energy in the system. The balance of the two energies along with the spatial constraints on each CNT at its contact points with neighboring CNTs, is manifested in its helical buckling, that is systematically influenced by nanostructural characteristics of VACNTs, such as their diameter, wall thickness and inter-CNT spacing.
Stability of twisted rods, helices and buckling solutions in three dimensions
Majumdar, Apala; Raisch, Alexander
2014-01-01
© 2014 IOP Publishing Ltd & London Mathematical Society. We study stability problems for equilibria of a naturally straight, inextensible, unshearable Kirchhoff rod allowed to deform in three dimensions (3D), subject to terminal loads. We investigate the stability of the twisted, straight state in 3D for three different boundary-value problems, cast in terms of Dirichlet and Neumann boundary conditions for the Euler angles, with and without isoperimetric constraints. In all cases, we obtain explicit stability estimates in terms of the twist, external load and elastic constants and in the Dirichlet case, we compute bifurcation diagrams for the Euler angles as a function of the external load. In the same vein, we obtain explicit stability estimates for a family of prototypical helical equilibria in 3D and demonstrate that they are stable for a range of tensile and compressive forces. We propose a numerical L2-gradient flow model to study the stability and dynamical evolution (in viscous model situations) of Kirchhoff rod equilibria. In Nizette and Goriely 1999 J. Math. Phys. 40 2830-66, the authors construct a family of localized buckling solutions. We apply our L2-gradient flow model to these localized buckling solutions, demonstrate that they are unstable, study their evolution and the simulations demonstrate rich spatio oral patterns that strongly depend on the boundary conditions and imposed isoperimetric constraints.
Stability of twisted rods, helices and buckling solutions in three dimensions
Majumdar, Apala
2014-11-03
© 2014 IOP Publishing Ltd & London Mathematical Society. We study stability problems for equilibria of a naturally straight, inextensible, unshearable Kirchhoff rod allowed to deform in three dimensions (3D), subject to terminal loads. We investigate the stability of the twisted, straight state in 3D for three different boundary-value problems, cast in terms of Dirichlet and Neumann boundary conditions for the Euler angles, with and without isoperimetric constraints. In all cases, we obtain explicit stability estimates in terms of the twist, external load and elastic constants and in the Dirichlet case, we compute bifurcation diagrams for the Euler angles as a function of the external load. In the same vein, we obtain explicit stability estimates for a family of prototypical helical equilibria in 3D and demonstrate that they are stable for a range of tensile and compressive forces. We propose a numerical L2-gradient flow model to study the stability and dynamical evolution (in viscous model situations) of Kirchhoff rod equilibria. In Nizette and Goriely 1999 J. Math. Phys. 40 2830-66, the authors construct a family of localized buckling solutions. We apply our L2-gradient flow model to these localized buckling solutions, demonstrate that they are unstable, study their evolution and the simulations demonstrate rich spatio oral patterns that strongly depend on the boundary conditions and imposed isoperimetric constraints.
Buckling of thin viscous sheets with inhomogenous viscosity under extensional flows
Srinivasan, Siddarth; Wei, Zhiyan; Mahadevan, L.
2016-11-01
We investigate the dynamics, shape and stability of a thin viscous sheet subjected to an extensional flow under an imposed non-uniform temperature field. Using finite element simulations, we first solve for the stretching flow to determine the pre-buckling sheet thickness and in-plane flow velocities. Next, we use this solution as the base state and solve the linearized partial differential equation governing the out-of-plane deformation of the mid-surface as a function of two dimensionless operating parameters: the normalized stretching ratio α and a dimensionless width of the heating zone β. We show the sheet can become unstable via a buckling instability driven by the development of localized compressive stresses, and determine the global shape and growth rates of the most unstable mode. The growth rate is shown to exhibit a transition from stationary to oscillatory modes in region upstream of the heating zone. Finally, we investigate the effect of surface tension and present an operating diagram that indicates regions of the parameter space that minimizes or entirely suppresses the instability while achieving desired outlet sheet thickness. Therefore, our work is directly relevant to various industrial processes including the glass redraw & float-glass method.
Shaping through buckling in elastic gridshells: from camping tents to architectural roofs
Reis, Pedro
Elastic gridshells comprise an initially planar network of elastic rods that is actuated into a 3D shell-like structure by loading its extremities. This shaping results from elastic buckling and the subsequent geometrically nonlinear deformation of the grid structure. Architectural elastic gridshells first appeared in the 1970's. However, to date, only a limited number of examples have been constructed around the world, primarily due to the challenges involved in their structural design. Yet, elastic gridshells are highly appealing: they can cover wide spans with low self-weight, they allow for aesthetically pleasing shapes and their construction is typically simple and rapid. We study the mechanics of elastic gridshells by combining precision model experiments that explore their scale invariance, together with computer simulations that employ the Discrete Elastic Rods method. Excellent agreement is found between the two. Upon validation, the numerics are then used to systematically explore parameter space and identify general design principles for specific target final shapes. Our findings are rationalized using the theory of discrete Chebyshev nets, together with the group theory for crystals. Higher buckling modes occur for some configurations due to geometric incompatibility at the boundary and result in symmetry breaking. Along with the systematic classification of the various possible modes of deformation, we provide a reduced model that rationalizes form-finding in elastic gridshells. This work was done in collaboration with Changyeob Baek, Khalid Jawed and Andrew Sageman-Furnas. We are grateful to the NSF for funding (CAREER, CMMI-1351449).
Non-linear buckling of an FGM truncated conical shell surrounded by an elastic medium
International Nuclear Information System (INIS)
Sofiyev, A.H.; Kuruoglu, N.
2013-01-01
In this paper, the non-linear buckling of the truncated conical shell made of functionally graded materials (FGMs) surrounded by an elastic medium has been studied using the large deformation theory with von Karman–Donnell-type of kinematic non-linearity. A two-parameter foundation model (Pasternak-type) is used to describe the shell–foundation interaction. The FGM properties are assumed to vary continuously through the thickness direction. The fundamental relations, the modified Donnell type non-linear stability and compatibility equations of the FGM truncated conical shell resting on the Pasternak-type elastic foundation are derived. By using the Superposition and Galerkin methods, the non-linear stability equations for the FGM truncated conical shell is solved. Finally, influences of variations of Winkler foundation stiffness and shear subgrade modulus of the foundation, compositional profiles and shell characteristics on the dimensionless critical non-linear axial load are investigated. The present results are compared with the available data for a special case. -- Highlights: • Nonlinear buckling of FGM conical shell surrounded by elastic medium is studied. • Pasternak foundation model is used to describe the shell–foundation interaction. • Nonlinear basic equations are derived. • Problem is solved by using Superposition and Galerkin methods. • Influences of various parameters on the nonlinear critical load are investigated
A simplified lumped model for the optimization of post-buckled beam architecture wideband generator
Liu, Weiqun; Formosa, Fabien; Badel, Adrien; Hu, Guangdi
2017-11-01
Buckled beams structures are a classical kind of bistable energy harvesters which attract more and more interests because of their capability to scavenge energy over a large frequency band in comparison with linear generator. The usual modeling approach uses the Galerkin mode discretization method with relatively high complexity, while the simplification with a single-mode solution lacks accuracy. It stems on the optimization of the energy potential features to finally define the physical and geometrical parameters. Therefore, in this paper, a simple lumped model is proposed with explicit relationship between the potential shape and parameters to allow efficient design of bistable beams based generator. The accuracy of the approximation model is studied with the effectiveness of application analyzed. Moreover, an important fact, that the bending stiffness has little influence on the potential shape with low buckling level and the sectional area determined, is found. This feature extends the applicable range of the model by utilizing the design of high moment of inertia. Numerical investigations demonstrate that the proposed model is a simple and reliable tool for design. An optimization example of using the proposed model is demonstrated with satisfactory performance.
Mechanical response and buckling of a polymer simulation model of the cell nucleus
Banigan, Edward; Stephens, Andrew; Marko, John
The cell nucleus must robustly resist extra- and intracellular forces to maintain genome architecture. Micromanipulation experiments measuring nuclear mechanical response reveal that the nucleus has two force response regimes: a linear short-extension response due to the chromatin interior and a stiffer long-extension response from lamin A, comprising the intermediate filament protein shell. To explain these results, we developed a quantitative simulation model with realistic parameters for chromatin and the lamina. Our model predicts that crosslinking between chromatin and the lamina is essential for responding to small strains and that changes to the interior topological organization can alter the mechanical response of the whole nucleus. Thus, chromatin polymer elasticity, not osmotic pressure, is the dominant regulator of this force response. Our model reveals a novel buckling transition for polymer shells: as force increases, the shell buckles transverse to the applied force. This transition, which arises from topological constrains in the lamina, can be mitigated by tuning the properties of the chromatin interior. Thus, we find that the genome is a resistive mechanical element that can be tuned by its organization and connectivity to the lamina.
Growth-induced axial buckling of a slender elastic filament embedded in an isotropic elastic matrix
O'Keeffe, Stephen G.
2013-11-01
We investigate the problem of an axially loaded, isotropic, slender cylinder embedded in a soft, isotropic, outer elastic matrix. The cylinder undergoes uniform axial growth, whilst both the cylinder and the surrounding elastic matrix are confined between two rigid plates, so that this growth results in axial compression of the cylinder. We use two different modelling approaches to estimate the critical axial growth (that is, the amount of axial growth the cylinder is able to sustain before it buckles) and buckling wavelength of the cylinder. The first approach treats the filament and surrounding matrix as a single 3-dimensional elastic body undergoing large deformations, whilst the second approach treats the filament as a planar, elastic rod embedded in an infinite elastic foundation. By comparing the results of these two approaches, we obtain an estimate of the foundation modulus parameter, which characterises the strength of the foundation, in terms of the geometric and material properties of the system. © 2013 Elsevier Ltd. All rights reserved.
Design, Analysis, and On-Sun Evaluation of Reflective Strips Under Controlled Buckling
Jaworske, Donald A.; Sechkar, Edward A.; Colozza, Anthony J.
2014-01-01
Solar concentrators are envisioned for use in a variety of space-based applications, including applications involving in situ resource utilization. Identifying solar concentrators that minimize mass and cost are of great interest, especially since launch cost is driven in part by the mass of the payload. Concentrators must also be able to survive the wide temperature excursions on the lunar surface. Identifying smart structures which compensate for changes in concentrator geometry brought about by temperature extremes are of interest. Some applications may benefit from the ability to change the concentrators focal pattern at will. This paper addresses a method of designing a single reflective strip to produce a desired focal pattern through the use of controlled buckling. Small variations in the cross section over the length of the reflective strip influence the distribution of light in the focal region. A finite element method of analysis is utilized here which calculates the curve produced for a given strip cross section and axial load. Varying axial force and strip cross section over the length of the reflective strip provide a means of optimizing ray convergence in the focal region. Careful selection of a tapered cross section yields a reflective strip that approximates a parabola. An array of reflective strips under controlled buckling produces a light weight concentrator and adjustments in the compression of individual strips provide a means of compensating for temperature excursions or changing the focal pattern at will.
Effect of shear connectors on local buckling and composite action in steel concrete composite walls
International Nuclear Information System (INIS)
Zhang, Kai; Varma, Amit H.; Malushte, Sanjeev R.; Gallocher, Stewart
2014-01-01
Steel concrete composite (SC) walls are being used for the third generation nuclear power plants, and also being considered for small modular reactors. SC walls consist of thick concrete walls with exterior steel faceplates serving as reinforcement. These steel faceplates are anchored to the concrete infill using shear connectors, for example, headed steel studs. The steel faceplate thickness (t p ) and yield stress (F y ), and the shear connector spacing (s), stiffness (k s ), and strength (Q n ) determine: (a) the level of composite action between the steel plates and the concrete infill, (b) the development length of steel faceplates, and (c) the local buckling of the steel faceplates. Thus, the shear connectors have a significant influence on the behavior of composite SC walls, and should be designed accordingly. This paper presents the effects of shear connector design on the level of composite action and development length of steel faceplates in SC walls. The maximum steel plate slenderness, i.e., ratio of shear connector spacing-to-plate thickness (s/t p ) ratio to prevent local buckling before yielding is also developed based on the existing experimental database and additional numerical analysis
Effect of shear connectors on local buckling and composite action in steel concrete composite walls
Energy Technology Data Exchange (ETDEWEB)
Zhang, Kai, E-mail: kai-zh@purdue.edu [School of Civil Engineering, Purdue University, West Lafayette, IN (United States); Varma, Amit H., E-mail: ahvarma@purdue.edu [School of Civil Engineering, Purdue University, West Lafayette, IN (United States); Malushte, Sanjeev R., E-mail: smalusht@bechtel.com [Bechtel Power Corporation, Frederick, MD (United States); Gallocher, Stewart, E-mail: stewart.gallocher@steelbricks.com [Modular Walling Systems Ltd., Glasgow (United Kingdom)
2014-04-01
Steel concrete composite (SC) walls are being used for the third generation nuclear power plants, and also being considered for small modular reactors. SC walls consist of thick concrete walls with exterior steel faceplates serving as reinforcement. These steel faceplates are anchored to the concrete infill using shear connectors, for example, headed steel studs. The steel faceplate thickness (t{sub p}) and yield stress (F{sub y}), and the shear connector spacing (s), stiffness (k{sub s}), and strength (Q{sub n}) determine: (a) the level of composite action between the steel plates and the concrete infill, (b) the development length of steel faceplates, and (c) the local buckling of the steel faceplates. Thus, the shear connectors have a significant influence on the behavior of composite SC walls, and should be designed accordingly. This paper presents the effects of shear connector design on the level of composite action and development length of steel faceplates in SC walls. The maximum steel plate slenderness, i.e., ratio of shear connector spacing-to-plate thickness (s/t{sub p}) ratio to prevent local buckling before yielding is also developed based on the existing experimental database and additional numerical analysis.
Yan, Zheng; Zhang, Fan; Wang, Jiechen; Liu, Fei; Guo, Xuelin; Nan, Kewang; Lin, Qing; Gao, Mingye; Xiao, Dongqing; Shi, Yan; Qiu, Yitao; Luan, Haiwen; Kim, Jung Hwan; Wang, Yiqi; Luo, Hongying; Han, Mengdi; Huang, Yonggang; Zhang, Yihui; Rogers, John A
2016-04-25
Origami is a topic of rapidly growing interest in both the scientific and engineering research communities due to its promising potential in a broad range of applications. Previous assembly approaches of origami structures at the micro/nanoscale are constrained by the applicable classes of materials, topologies and/or capability of control over the transformation. Here, we introduce an approach that exploits controlled mechanical buckling for autonomic origami assembly of 3D structures across material classes from soft polymers to brittle inorganic semiconductors, and length scales from nanometers to centimeters. This approach relies on a spatial variation of thickness in the initial 2D structures as an effective strategy to produce engineered folding creases during the compressive buckling process. The elastic nature of the assembly scheme enables active, deterministic control over intermediate states in the 2D to 3D transformation in a continuous and reversible manner. Demonstrations include a broad set of 3D structures formed through unidirectional, bidirectional, and even hierarchical folding, with examples ranging from half cylindrical columns and fish scales, to cubic boxes, pyramids, starfish, paper fans, skew tooth structures, and to amusing system-level examples of soccer balls, model houses, cars, and multi-floor textured buildings.
Contribution of apparently non-operating loadings to the buckling of thin shells and plates
International Nuclear Information System (INIS)
Delaigue, Didier.
1980-02-01
This work includes four parts: in the first part, the Kirchhoff-Love theory of thin shells is described, a theory taken up and developed by Koiter and whose modelling seems to meet the problems of engineers. The second part deals with the buckling of a thin plate subjected to a load along a part of its edge, of which a part or all is seemingly inoperative. In the third part the study is extended to shells of any shape subjected to a conservative loading of the ''dead-loading'' type along part of their edges. On the basis of the results of the previous study, a study is then made on the taking into account of any load applied to the edge of a thin shell. In the fourth part the previous results are applied to the study of the buckling of a thin shell with a circular base subjected along a part of its edge to a normal prestress and to twisting moments linear density [fr
Energy Technology Data Exchange (ETDEWEB)
Purgato, Rafael Turrini
2014-07-01
One of the key parameters in reactor physics is the Buckling of a reactor core. It is related to important parameters such as reaction rates, nuclear power operation, fuel burning, among others. In a critical reactor, the Buckling depends on the geometric and material characteristics of the reactor core. This work presents the results of experimental Buckling in the reactor IPEN/MB-01 nuclear reactor in its cylindrical configuration with 28 fuel rods along its diameter. The IPEN/MB-01 is a zero power reactor designed to operate at a maximum power of 100 watts, it is a versatile nuclear facility which allows the simulation of all the characteristics of a large nuclear power reactor and ideal for this type of measurement. We conducted a mapping of neutron flux inside the reactor and thereby determined the total Buckling of the cylindrical configuration. The reactor was operated for one hour. Then, the activity of the fuel rods was measured by gamma spectrometry on a rod scanner HPGe detector. We analyzed the gamma photons of the {sup 239}Np (276,6 keV) for neutron capture (n,γ) and the {sup 143}Ce (293,3 keV) for fission (n,f) on both {sup 238}U and {sup 235}U, respectively. We analyzed the axial and radial directions. Other measurements were performed using wires and gold foils in the radial and axial directions of the reactor core. The Buckling Total obtained from the three methods by weighted mean is 96,55 ± 7,47 m{sup -2}. The goal is to obtain experimental values of a set of experimental data to allow one direct comparison with values calculated by the codes used in reactor physics CITATION and MCNP. (author)
Williams, Kristine G; Smith, Gillian; Luhmann, Scott J; Mao, Jingnan; Gunn, Joseph D; Luhmann, Janet D
2013-05-01
Buckle fractures are inherently stable and at low risk for displacement. These advantages allow for treatment options that may create confusion for the practitioner. Accepted immobilization methods include circumferential cast, plaster or prefabricated splint, and soft bandaging. Despite mounting evidence for splinting, the questions of pain, preference, satisfaction, and convenience offer a challenge to changing practice. The purposes of this study were (1) to compare cast versus splint for distal radial buckle fractures in terms of parental and patient satisfaction, convenience, and preference and (2) to compare pain reported for cast versus splint. We conducted a prospective randomized trial of a convenience sample of patients 2 through 17 years with a radiologically confirmed distal radial buckle fracture. Subjects were randomly assigned to short-arm cast or prefabricated wrist splint. We assessed satisfaction, convenience, preference, and pain in the emergency department and at days 1, 3, 7, and 21 after immobilization. Ninety-four patients were enrolled. Compared with the cast group, those in the splint group reported higher levels of satisfaction, preference, and convenience on 10-point visual analog scale. Although pain scores were higher for those in the splint group, the difference was not statistically significant. With the exception of pain reported in the emergency department being higher for the splinted group, all other measures, including convenience, satisfaction, and preference, showed a clear trend favoring splints at almost every time period in the study. This study provides additional evidence that splinting is preferable to casting for the treatment of distal radial buckle fractures.
77 FR 41881 - Safety Advisory 2012-03; Buckling-Prone Conditions in Continuous Welded Rail Track
2012-07-16
... awareness of the potential consequences of an unexpected track buckle, particularly considering the... track is located on or near railroad bridges. It also recommends that track owners and railroads review.... CWR can produce peculiar maintenance issues for the railroad industry due to the constant temperature...
Energy Technology Data Exchange (ETDEWEB)
Singhatanadgid, Pairod; Jommalai, Panupan [Chulalongkorn University, Bangkok (Thailand)
2016-05-15
The extended Kantorovich method using multi-term displacement functions is applied to the buckling problem of laminated plates with various boundary conditions. The out-of-plane displacement of the buckled plate is written as a series of products of functions of parameter x and functions of parameter y. With known functions in parameter x or parameter y, a set of governing equations and a set of boundary conditions are obtained after applying the variational principle to the total potential energy of the system. The higher order differential equations are then transformed into a set of first-order differential equations and solved for the buckling load and mode. Since the governing equations are first-order differential equations, solutions can be obtained analytically with the out-of-plane displacement written in the form of an exponential function. The solutions from the proposed technique are verified with solutions from the literature and FEM solutions. The bucking loads correspond very well to other available solutions in most of the comparisons. The buckling modes also compare very well with the finite element solutions. The proposed solution technique transforms higher-order differential equations to first-order differential equations, and they are analytically solved for out-of-plane displacement in the form of an exponential function. Therefore, the proposed solution technique yields a solution which can be considered as an analytical solution.
International Nuclear Information System (INIS)
Combescure, A.
1986-04-01
During the last ten years, the French Research Institute for Nuclear Energy (Commissariat a l'Energie Atomique) achieved many theoretical as well as experimental studies for designing the first large size pool type fast breeder reactor. Many of the sensitive parts of this reactor are thin shells subjected to high temperatures and loads. Special care has been given to buckling, because it often governs design. Most of the thin shells structures of the french breeder reactor are axisymmetric. However, imperfections have to be accounted for. In order to keep the advantage of an axisymmetric analysis (low computational costs), a special element has been implemented and used with considerable success in the recent years. This element (COMU) is described in the first chapter, its main features are: either non axisymmetric imperfection or non axisymmetric load, large displacement, non linear material behaviour, computational costs about ten times cheaper than the equivalent three dimensional analysis. This paper based on a careful comparison between experimental and computational results, obtained with the COMU, will analyse three problems: First: design procedure against buckling of thin shells structures subjected to primary loads; Second: static post buckling; Third: buckling under seismic loads [fr
Toubia, Elias Anis
Sandwich construction is one of the most functional forms of composite structures developed by the composite industry. Due to the increasing demand of web-reinforced core for composite sandwich construction, a research study is needed to investigate the web plate instability under shear, compression, and combined loading. If the web, which is an integral part of the three dimensional web core sandwich structure, happens to be slender with respect to one or two of its spatial dimensions, then buckling phenomena become an issue in that it must be quantified as part of a comprehensive strength model for a fiber reinforced core. In order to understand the thresholds of thickness, web weight, foam type, and whether buckling will occur before material yielding, a thorough investigation needs to be conducted, and buckling design equations need to be developed. Often in conducting a parametric study, a special purpose analysis is preferred over a general purpose analysis code, such as a finite element code, due to the cost and effort usually involved in generating a large number of results. A suitable methodology based on an energy method is presented to solve the stability of symmetrical and specially orthotropic laminated plates on an elastic foundation. Design buckling equations were developed for the web modeled as a laminated plate resting on elastic foundations. The proposed equations allow for parametric studies without limitation regarding foam stiffness, geometric dimensions, or mechanical properties. General behavioral trends of orthotropic and symmetrical anisotropic plates show pronounced contribution of the elastic foundation and fiber orientations on the buckling resistance of the plate. The effects of flexural anisotropy on the buckling behavior of long rectangular plates when subjected to pure shear loading are well represented in the model. The reliability of the buckling equations as a design tool is confirmed by comparison with experimental results
Ebraert, Evert; Van Erps, Jürgen; Beri, Stefano; Watté, Jan; Thienpont, Hugo
2014-05-01
Fibre-to-the-home (FTTH) networks provide an ideal means to reach the goal the European Union has set to provide 50 % of the households with a broadband connection faster than 100 Mb/s. Deployment of FTTH networks, which is still costly today, could be significantly boosted by novel ferrule-less connectors which don't require highly skilled personnel and allow installation in the field. We propose a ferrule-less connector in which two single-mode fibres (SMFs) are aligned and maintain physical contact by ensuring that at least one fibre is in a buckled state. To this end, we design a cavity in which a fibre can buckle in a controlled way. Using finite element analysis simulations to investigate the shape of the formed buckle for various buckling cavity lengths, we show that it can be accurately approximated by a cosine function. In addition, the optical performance of a buckled SMF is investigated by bending loss calculations and simulations. We show a good agreement between the analytical and the simulated bending loss results for a G.652 fibre at a wavelength of 1550 nm. Buckling cavity lengths smaller than 20 mm should be avoided to keep the optical bending loss due to buckling below 0.1 dB. In this case the cavity height should at least be 2 mm to avoid mechanical confinement of the fibre.
International Nuclear Information System (INIS)
Purgato, Rafael Turrini
2014-01-01
One of the key parameters in reactor physics is the Buckling of a reactor core. It is related to important parameters such as reaction rates, nuclear power operation, fuel burning, among others. In a critical reactor, the Buckling depends on the geometric and material characteristics of the reactor core. This work presents the results of experimental Buckling in the reactor IPEN/MB-01 nuclear reactor in its cylindrical configuration with 28 fuel rods along its diameter. The IPEN/MB-01 is a zero power reactor designed to operate at a maximum power of 100 watts, it is a versatile nuclear facility which allows the simulation of all the characteristics of a large nuclear power reactor and ideal for this type of measurement. We conducted a mapping of neutron flux inside the reactor and thereby determined the total Buckling of the cylindrical configuration. The reactor was operated for one hour. Then, the activity of the fuel rods was measured by gamma spectrometry on a rod scanner HPGe detector. We analyzed the gamma photons of the 239 Np (276,6 keV) for neutron capture (n,γ) and the 143 Ce (293,3 keV) for fission (n,f) on both 238 U and 235 U, respectively. We analyzed the axial and radial directions. Other measurements were performed using wires and gold foils in the radial and axial directions of the reactor core. The Buckling Total obtained from the three methods by weighted mean is 96,55 ± 7,47 m -2 . The goal is to obtain experimental values of a set of experimental data to allow one direct comparison with values calculated by the codes used in reactor physics CITATION and MCNP. (author)
Shevyrin, A. A.; Pogosov, A. G.; Budantsev, M. V.; Bakarov, A. K.; Toropov, A. I.; Ishutkin, S. V.; Shesterikov, E. V.; Kozhukhov, A. S.; Kosolobov, S. S.; Gavrilova, T. A.
2012-12-01
Mechanical stresses are investigated in suspended nanowires made on the basis of GaAs/AlGaAs heterostructures. Though there are no intentionally introduced stressor layers in the heterostructure, the nanowires are subject to Euler buckling instability. In the wide nanowires, the out-of-plane buckling is observed at length significantly smaller (3 times) than the theoretically estimated critical value, while in the narrow nanowires, the experimentally measured critical length of the in-plane buckling coincides with the theoretical estimation. The possible reasons for the obtained discrepancy are considered. The observed peculiarities should be taken into account in the fabrication of nanomechanical and nanoelectromechanical systems.
The magneto-elastica: from self-buckling to self-assembly
Vella, D.; du Pontavice, E.; Hall, C. L.; Goriely, A.
2013-01-01
Spherical neodymium-iron-boron magnets are permanent magnets that can be assembled into a variety of structures owing to their high magnetic strength. A one-dimensional chain of these magnets responds to mechanical loadings in a manner reminiscent of an elastic rod. We investigate the macroscopic mechanical properties of assemblies of ferromagnetic spheres by considering chains, rings and chiral cylinders of magnets. Based on energy estimates and simple experiments, we introduce an effective magnetic bending stiffness for a chain of magnets and show that, used in conjunction with classic results for elastic rods, it provides excellent estimates for the buckling and vibration dynamics of magnetic chains. We then use this estimate to understand the dynamic self-assembly of a cylinder from an initially straight chain of magnets.
Xu, Sheng; Yan, Zheng; Jang, Kyung-In; Huang, Wen; Fu, Haoran; Kim, Jeonghyun; Wei, Zijun; Flavin, Matthew; McCracken, Joselle; Wang, Renhan; Badea, Adina; Liu, Yuhao; Xiao, Dongqing; Zhou, Guoyan; Lee, Jungwoo; Chung, Ha Uk; Cheng, Huanyu; Ren, Wen; Banks, Anthony; Li, Xiuling; Paik, Ungyu; Nuzzo, Ralph G; Huang, Yonggang; Zhang, Yihui; Rogers, John A
2015-01-09
Complex three-dimensional (3D) structures in biology (e.g., cytoskeletal webs, neural circuits, and vasculature networks) form naturally to provide essential functions in even the most basic forms of life. Compelling opportunities exist for analogous 3D architectures in human-made devices, but design options are constrained by existing capabilities in materials growth and assembly. We report routes to previously inaccessible classes of 3D constructs in advanced materials, including device-grade silicon. The schemes involve geometric transformation of 2D micro/nanostructures into extended 3D layouts by compressive buckling. Demonstrations include experimental and theoretical studies of more than 40 representative geometries, from single and multiple helices, toroids, and conical spirals to structures that resemble spherical baskets, cuboid cages, starbursts, flowers, scaffolds, fences, and frameworks, each with single- and/or multiple-level configurations. Copyright © 2015, American Association for the Advancement of Science.
Feng, Guo-Hua; Hou, Sheng-You
2015-09-01
This paper presents an ionic polymer metal composite (IPMC)-driven tentacle-like biocompatible flexible actuator with double-section curvature tunability. This actuator, possessing an embedded electrical transmission ability that mimics skeletal muscle nerves in the human body, affords versatile device functions. Novel micromachined copper buckles and grid wires are fabricated and their superiority in electricity delivery and driving the IPMC component with less flexural rigidity is demonstrated. In addition, soft conductive wires realized on a polydimethylsiloxane structure function as electrical signal transmitters. A light-emitting diode integrated with the developed actuator offers directional guiding light ability while the actuator performs a snake-like motion. The electrical conductivity and Young’s modulus of the key actuator components are investigated, and flexural rigidity and dynamic behavior analyses of the actuator under electrical manipulation are elaborated.
Buckle, ruck and tuck: A proposed new model for the response of graphite to neutron irradiation
Energy Technology Data Exchange (ETDEWEB)
Heggie, M.I., E-mail: m.i.heggie@sussex.ac.uk [Chemistry Subject Group, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QJ (United Kingdom); Suarez-Martinez, I. [Nanochemistry Research Institute, Department of Chemistry, Curtin University of Technology, GPO Box U1987, Perth 6845, Western Australia (Australia); Davidson, C.; Haffenden, G. [Chemistry Subject Group, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QJ (United Kingdom)
2011-06-30
The default theory of radiation damage in graphite invokes Frenkel pair formation as the principal cause of physical property changes. We set out its inadequacies and present two new mechanisms that contribute to a better account for changes in dimension and stored energy. Damage depends on the substrate temperature, undergoing a change at approximately 250 deg. C. Below this temperature particle radiation imparts a permanent, nano-buckling to the layers. Above it, layers fold, forming what we describe as a ruck and tuck defect. We present first principles and molecular mechanics calculations of energies and structures to support these claims. Necessarily we extend the dislocation theory of layered materials. We cite good experimental evidence for these features from the literature on radiation damage in graphite.
Liu, Z F; Fang, S; Moura, F A; Ding, J N; Jiang, N; Di, J; Zhang, M; Lepró, X; Galvão, D S; Haines, C S; Yuan, N Y; Yin, S G; Lee, D W; Wang, R; Wang, H Y; Lv, W; Dong, C; Zhang, R C; Chen, M J; Yin, Q; Chong, Y T; Zhang, R; Wang, X; Lima, M D; Ovalle-Robles, R; Qian, D; Lu, H; Baughman, R H
2015-07-24
Superelastic conducting fibers with improved properties and functionalities are needed for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%) sheath-core conducting fibers created by wrapping carbon nanotube sheets oriented in the fiber direction on stretched rubber fiber cores. The resulting structure exhibited distinct short- and long-period sheath buckling that occurred reversibly out of phase in the axial and belt directions, enabling a resistance change of less than 5% for a 1000% stretch. By including other rubber and carbon nanotube sheath layers, we demonstrated strain sensors generating an 860% capacitance change and electrically powered torsional muscles operating reversibly by a coupled tension-to-torsion actuation mechanism. Using theory, we quantitatively explain the complementary effects of an increase in muscle length and a large positive Poisson's ratio on torsional actuation and electronic properties. Copyright © 2015, American Association for the Advancement of Science.
How the antimicrobial peptides destroy bacteria cell membrane: Translocations vs. membrane buckling
Golubovic, Leonardo; Gao, Lianghui; Chen, Licui; Fang, Weihai
2012-02-01
In this study, coarse grained Dissipative Particle Dynamics simulation with implementation of electrostatic interactions is developed in constant pressure and surface tension ensemble to elucidate how the antimicrobial peptide molecules affect bilayer cell membrane structure and kill bacteria. We find that peptides with different chemical-physical properties exhibit different membrane obstructing mechanisms. Peptide molecules can destroy vital functions of the affected bacteria by translocating across their membranes via worm-holes, or by associating with membrane lipids to form hydrophilic cores trapped inside the hydrophobic domain of the membranes. In the latter scenario, the affected membranes are strongly corrugated (buckled) in accord with very recent experimental observations [G. E. Fantner et al., Nat. Nanotech., 5 (2010), pp. 280-285].
International Nuclear Information System (INIS)
Feng, Guo-Hua; Hou, Sheng-You
2015-01-01
This paper presents an ionic polymer metal composite (IPMC)-driven tentacle-like biocompatible flexible actuator with double-section curvature tunability. This actuator, possessing an embedded electrical transmission ability that mimics skeletal muscle nerves in the human body, affords versatile device functions. Novel micromachined copper buckles and grid wires are fabricated and their superiority in electricity delivery and driving the IPMC component with less flexural rigidity is demonstrated. In addition, soft conductive wires realized on a polydimethylsiloxane structure function as electrical signal transmitters. A light-emitting diode integrated with the developed actuator offers directional guiding light ability while the actuator performs a snake-like motion. The electrical conductivity and Young’s modulus of the key actuator components are investigated, and flexural rigidity and dynamic behavior analyses of the actuator under electrical manipulation are elaborated. (paper)
European column buckling curves and finite element modelling including high strength steels
DEFF Research Database (Denmark)
Jönsson, Jeppe; Stan, Tudor-Cristian
2017-01-01
Eurocode allows for finite element modelling of plated steel structures, however the information in the code on how to perform the analysis or what assumptions to make is quite sparse. The present paper investigates the deterministic modelling of flexural column buckling using plane shell elements...... imperfections may be very conservative if considered by finite element analysis as described in the current Eurocode code. A suggestion is given for a slightly modified imperfection formula within the Ayrton-Perry formulation leading to adequate inclusion of modern high grade steels within the original four...... bucking curves. It is also suggested that finite element or frame analysis may be performed with equivalent column bow imperfections extracted directly from the Ayrton-Perry formulation....
Biomechanical ordering and buckling due to microbial growth confined at oil-water interfaces
Juarez, Gabriel; Stocker, Roman
2015-11-01
Bacteria are unicellular organisms that often exist as densely populated, surface-associated communities. Bacteria are also environmental colloids and spontaneously attach and self-assemble at liquid-liquid interfaces. Here, we present results on the growth dynamics of individual rod-shaped bacteria confined to finite oil-water interfaces of varying curvature. Through experiments using microfluidic chambers and time-lapse microscopy, we study the formation of macroscopic structures observed as adsorbed bacteria grow, divide, and self-assemble in a nematic phase due to biomechanical interactions. The continued growth at the interface leads to a jammed monolayer of cells, which then causes the interface to buckle and undergo large deformations including wrinkling and tubulation. These observations highlight the interplay between physical environment, such as confinement and interface curvature, and active biological processes, such as growth, at the scale of individual agents and shape our understanding of macroscale processes such as microbial degradation of oil in the ocean.
Nonlinear features identified by Volterra series for damage detection in a buckled beam
Directory of Open Access Journals (Sweden)
Shiki S. B.
2014-01-01
Full Text Available The present paper proposes a new index for damage detection based on nonlinear features extracted from prediction errors computed by multiple convolutions using the discrete-time Volterra series. A reference Volterra model is identified with data in the healthy condition and used for monitoring the system operating with linear or nonlinear behavior. When the system has some structural change, possibly associated with damage, the index metrics computed could give an alert to separate the linear and nonlinear contributions, besides provide a diagnostic about the structural state. To show the applicability of the method, an experimental test is performed using nonlinear vibration signals measured in a clamped buckled beam subject to different levels of force applied and with simulated damages through discontinuities inserted in the beam surface.
The magneto-elastica: from self-buckling to self-assembly
Vella, D.
2013-12-04
Spherical neodymium-iron-boron magnets are permanent magnets that can be assembled into a variety of structures owing to their high magnetic strength. A one-dimensional chain of these magnets responds to mechanical loadings in a manner reminiscent of an elastic rod. We investigate the macroscopic mechanical properties of assemblies of ferromagnetic spheres by considering chains, rings and chiral cylinders of magnets. Based on energy estimates and simple experiments, we introduce an effective magnetic bending stiffness for a chain of magnets and show that, used in conjunction with classic results for elastic rods, it provides excellent estimates for the buckling and vibration dynamics of magnetic chains. We then use this estimate to understand the dynamic self-assembly of a cylinder from an initially straight chain of magnets.
Haftka, Raphael T.; Cohen, Gerald A.; Mroz, Zenon
1990-01-01
A uniform variational approach to sensitivity analysis of vibration frequencies and bifurcation loads of nonlinear structures is developed. Two methods of calculating the sensitivities of bifurcation buckling loads and vibration frequencies of nonlinear structures, with respect to stiffness and initial strain parameters, are presented. A direct method requires calculation of derivatives of the prebuckling state with respect to these parameters. An adjoint method bypasses the need for these derivatives by using instead the strain field associated with the second-order postbuckling state. An operator notation is used and the derivation is based on the principle of virtual work. The derivative computations are easily implemented in structural analysis programs. This is demonstrated by examples using a general purpose, finite element program and a shell-of-revolution program.
Buckling Transitions and Clock Order of Two-Dimensional Coulomb Crystals
Directory of Open Access Journals (Sweden)
Daniel Podolsky
2016-08-01
Full Text Available Crystals of repulsively interacting ions in planar traps form hexagonal lattices, which undergo a buckling instability towards a multilayer structure as the transverse trap frequency is reduced. Numerical and experimental results indicate that the new structure is composed of three planes, whose separation increases continuously from zero. We study the effects of thermal and quantum fluctuations by mapping this structural instability to the six-state clock model. A prominent implication of this mapping is that at finite temperature, fluctuations split the buckling instability into two thermal transitions, accompanied by the appearance of an intermediate critical phase. This phase is characterized by quasi-long-range order in the spatial tripartite pattern. It is manifested by broadened Bragg peaks at new wave vectors, whose line shape provides a direct measurement of the temperature-dependent exponent η(T characteristic of the power-law correlations in the critical phase. A quantum phase transition is found at the largest value of the critical transverse frequency: Here, the critical intermediate phase shrinks to zero. Moreover, within the ordered phase, we predict a crossover from classical to quantum behavior, signifying the emergence of an additional characteristic scale for clock order. We discuss experimental realizations with trapped ions and polarized dipolar gases, and propose that within accessible technology, such experiments can provide a direct probe of the rich phase diagram of the quantum clock model, not easily observable in condensed matter analogues. Therefore, this work highlights the potential for ionic and dipolar systems to serve as simulators for complex models in statistical mechanics and condensed matter physics.
Vibration of mechanically-assembled 3D microstructures formed by compressive buckling
Wang, Heling; Ning, Xin; Li, Haibo; Luan, Haiwen; Xue, Yeguang; Yu, Xinge; Fan, Zhichao; Li, Luming; Rogers, John A.; Zhang, Yihui; Huang, Yonggang
2018-03-01
Micro-electromechanical systems (MEMS) that rely on structural vibrations have many important applications, ranging from oscillators and actuators, to energy harvesters and vehicles for measurement of mechanical properties. Conventional MEMS, however, mostly utilize two-dimensional (2D) vibrational modes, thereby imposing certain limitations that are not present in 3D designs (e.g., multi-directional energy harvesting). 3D vibrational micro-platforms assembled through the techniques of controlled compressive buckling are promising because of their complex 3D architectures and the ability to tune their vibrational behavior (e.g., natural frequencies and modes) by reversibly changing their dimensions by deforming their soft, elastomeric substrates. A clear understanding of such strain-dependent vibration behavior is essential for their practical applications. Here, we present a study on the linear and nonlinear vibration of such 3D mesostructures through analytical modeling, finite element analysis (FEA) and experiment. An analytical solution is obtained for the vibration mode and linear natural frequency of a buckled ribbon, indicating a mode change as the static deflection amplitude increases. The model also yields a scaling law for linear natural frequency that can be extended to general, complex 3D geometries, as validated by FEA and experiment. In the regime of nonlinear vibration, FEA suggests that an increase of amplitude of external loading represents an effective means to enhance the bandwidth. The results also uncover a reduced nonlinearity of vibration as the static deflection amplitude of the 3D structures increases. The developed analytical model can be used in the development of new 3D vibrational micro-platforms, for example, to enable simultaneous measurement of diverse mechanical properties (density, modulus, viscosity etc.) of thin films and biomaterials.
Buckling Modes of Structural Elements of Off-Axis Fiber-Reinforced Plastics
Paimushin, V. N.; Polyakova, N. V.; Kholmogorov, S. A.; Shishov, M. A.
2018-05-01
The structures of two types of unidirectional fiber-reinforced composites — with an ELUR-P carbon fiber tape, an XT-118 cold-cure binder with an HSE 180 REM prepreg, and a hot-cure binder — were investigated. The diameters of fibers and fiber bundles (threads) of both the types of composites were measured, and their mutual arrangement was examined both in the semifinished products (in the uncured state) and in the finished composites. The defects characteristic of both the types of binder and manufacturing technique were detected in the cured composites. Based on an analysis of the results obtained, linearized problems on the internal multiscale buckling modes of an individual fiber (with and without account of its interaction with the surrounding matrix) or of a fiber bundle are formulated. In the initial atate, these structural elements of the fibrous composites are in a subcritical (unperturbed) state under the action of shear stresses and tension (compression) in the transverse direction. Such an initial stress state is formed in them in tension and compression tests on flat specimens made of off-axis-reinforced composites with straight fibers. To formulate the problems, the equations derived earlier from a consistent variant of geometrically nonlinear equations of elasticity theory by reducing them to the one-dimensional equations of the theory of straight rods on the basis of a refined Timoshenko shear model with account of tensile-compressive strains in the transverse direction are used. It is shown that, in loading test specimens, a continuous rearrangement of composite structure can occur due to the realization and continuous change of internal buckling modes as the wave-formation parameter varies continuously, which apparently explain the decrease revealed in the tangential shear modulus of the fibrous composites with increasing shear strains.
Energy Technology Data Exchange (ETDEWEB)
MACKEY TC; JOHNSON KI; DEIBLER JE; PILLI SP; RINKER MW; KARRI NK
2009-01-14
This report documents a detailed buckling evaluation of the primary tanks in the Hanford double-shell waste tanks (DSTs), which is part of a comprehensive structural review for the Double-Shell Tank Integrity Project. This work also provides information on tank integrity that specifically responds to concerns raised by the Office of Environment, Safety, and Health (ES&H) Oversight (EH-22) during a review of work performed on the double-shell tank farms and the operation of the aging waste facility (AWF) primary tank ventilation system. The current buckling review focuses on the following tasks: (1) Evaluate the potential for progressive anchor bolt failure and the appropriateness of the safety factors that were used for evaluating local and global buckling. The analysis will specifically answer the following questions: (a) Can the EH-22 scenario develop if the vacuum is limited to -6.6-inch water gage (w.g.) by a relief valve? (b) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario can develop? (c) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario cannot develop? (2) Develop influence functions to estimate the axial stresses in the primary tanks for all reasonable combinations of tank loads based on detailed finite element analysis. The analysis must account for the variation in design details and operating conditions between the different DSTs. The analysis must also address the imperfection sensitivity of the primary tank to buckling. (3) Perform a detailed buckling analysis to determine the maximum allowable differential pressure for each of the DST primary tanks at the current specified limits on waste temperature, height, and specific gravity. Based on the concrete anchor bolt loads analysis and the small deformations that are predicted at the unfactored limits on vacuum and axial loads, it is very unlikely that the EH-22 scenario (i.e., progressive anchor bolt
International Nuclear Information System (INIS)
Mackey, T.C.; Johnson, K.I.; Deibler, J.E.; Pilli, S.P.; Rinker, M.W.; Karri, N.K.
2009-01-01
This report documents a detailed buckling evaluation of the primary tanks in the Hanford double-shell waste tanks (DSTs), which is part of a comprehensive structural review for the Double-Shell Tank Integrity Project. This work also provides information on tank integrity that specifically responds to concerns raised by the Office of Environment, Safety, and Health (ES and H) Oversight (EH-22) during a review of work performed on the double-shell tank farms and the operation of the aging waste facility (AWF) primary tank ventilation system. The current buckling review focuses on the following tasks: (1) Evaluate the potential for progressive anchor bolt failure and the appropriateness of the safety factors that were used for evaluating local and global buckling. The analysis will specifically answer the following questions: (a) Can the EH-22 scenario develop if the vacuum is limited to -6.6-inch water gage (w.g.) by a relief valve? (b) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario can develop? (c) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario cannot develop? (2) Develop influence functions to estimate the axial stresses in the primary tanks for all reasonable combinations of tank loads based on detailed finite element analysis. The analysis must account for the variation in design details and operating conditions between the different DSTs. The analysis must also address the imperfection sensitivity of the primary tank to buckling. (3) Perform a detailed buckling analysis to determine the maximum allowable differential pressure for each of the DST primary tanks at the current specified limits on waste temperature, height, and specific gravity. Based on the concrete anchor bolt loads analysis and the small deformations that are predicted at the unfactored limits on vacuum and axial loads, it is very unlikely that the EH-22 scenario (i.e., progressive anchor
International Nuclear Information System (INIS)
Hoffman, E.L.; Ammerman, D.J.
1995-01-01
A series of tests investigating dynamic pulse buckling of a cylindrical shell under axial impact is compared to several 2D and 3D finite element simulations of the event. The purpose of the work is to investigate the performance of various analysis codes and element types on a problem which is applicable to radioactive material transport packages, and ultimately to develop a benchmark problem to qualify finite element analysis codes for the transport package design industry. During the pulse buckling tests, a buckle formed at each end of the cylinder, and one of the two buckles became unstable and collapsed. Numerical simulations of the test were performed using PRONTO, a Sandia developed transient dynamics analysis code, and ABAQUS/Explicit with both shell and continuum elements. The calculations are compared to the tests with respect to deformed shape and impact load history
STAVREV, A.; STEFANOV, D.; SCHILLINGER, D.; RANK, E.
2013-01-01
The uncertainty of geometric imperfections in a series of nominally equal I-beams leads to a variability of corresponding buckling loads. Its analysis requires a stochastic imperfection model, which can be derived either by the simple variation
Gavva, L. M.; Endogur, A. I.
2018-02-01
The mathematical model relations for stress-strain state and for buckling investigation of structurally-anisotropic panels made of composite materials are presented. The mathematical model of stiffening rib being torsioned under one-side contact with the skin is refined. One takes into account the influence of panel production technology: residual thermal stresses and reinforcing fibers preliminary tension. The resolved eight order equation and natural boundary conditions are obtained with variation Lagrange procedure. Exact analytical solutions for edge problems are considered. Computer program package is developed using operating MATLAB environment. The influence of the structure parameters on the level of stresses, displacements, of critical buckling forces for bending and for torsion modes has analyzed.
Hilburger, Mark W.; Lovejoy, Andrew E.; Thornburgh, Robert P.; Rankin, Charles
2012-01-01
NASA s Shell Buckling Knockdown Factor (SBKF) project has the goal of developing new analysis-based shell buckling design factors (knockdown factors) and design and analysis technologies for launch vehicle structures. Preliminary design studies indicate that implementation of these new knockdown factors can enable significant reductions in mass and mass-growth in these vehicles. However, in order to validate any new analysis-based design data or methods, a series of carefully designed and executed structural tests are required at both the subscale and full-scale levels. This paper describes the design and analysis of three different orthogrid-stiffeNed metallic cylindrical-shell test articles. Two of the test articles are 8-ft-diameter, 6-ft-long test articles, and one test article is a 27.5-ft-diameter, 20-ft-long Space Shuttle External Tank-derived test article.
Pre-Test Analysis Predictions for the Shell Buckling Knockdown Factor Checkout Tests - TA01 and TA02
Thornburgh, Robert P.; Hilburger, Mark W.
2011-01-01
This report summarizes the pre-test analysis predictions for the SBKF-P2-CYL-TA01 and SBKF-P2-CYL-TA02 shell buckling tests conducted at the Marshall Space Flight Center (MSFC) in support of the Shell Buckling Knockdown Factor (SBKF) Project, NASA Engineering and Safety Center (NESC) Assessment. The test article (TA) is an 8-foot-diameter aluminum-lithium (Al-Li) orthogrid cylindrical shell with similar design features as that of the proposed Ares-I and Ares-V barrel structures. In support of the testing effort, detailed structural analyses were conducted and the results were used to monitor the behavior of the TA during the testing. A summary of predicted results for each of the five load sequences is presented herein.
Neukirch, Sébastien
2014-02-01
In-plane vibrations of an elastic rod clamped at both extremities are studied. The rod is modeled as an extensible planar Kirchhoff elastic rod under large displacements and rotations. Equilibrium configurations and vibrations around these configurations are computed analytically in the incipient post-buckling regime. Of particular interest is the variation of the first mode frequency as the load is increased through the buckling threshold. The loading type is found to have a crucial importance as the first mode frequency is shown to behave singularly in the zero thickness limit in the case of prescribed axial displacement, whereas a regular behavior is found in the case of prescribed axial load. © 2013 Elsevier Ltd.
International Nuclear Information System (INIS)
Le Dai Dien
2008-01-01
Benchmark experiments for International Reactor Physics Benchmark Experiments (IRPhE) Project carried out at TCA, the temperature effects on reactivity were studied for light water moderated and reflected UO 2 cores with/without soluble poisons. The buckling coefficient method using the measured critical water levels was proposed by Suzaki et al. The temperature dependence of buckling coefficient of reactivity and its variance by the core configurations of the benchmark experiments was investigated using SRAC and MVP calculations. From the calculations by SRAC as well as by MVP it is seen that the K-value can be taken as an average value only for each core with temperature changes which are considered as perturbation parameter. The difference between our calculations and benchmark results which uses constant K-value for all cores proves that the results depend on K-value and it play important role in defining reactivity effect using the water level worth method. (author)
International Nuclear Information System (INIS)
Singh, B.N.; Lal, Achchhe
2010-01-01
This study deals with the stochastic post-buckling and nonlinear free vibration analysis of a laminated composite plate resting on a two parameters Pasternak foundation with Winkler cubic nonlinearity having uncertain system properties. The system properties are modeled as basic random variables. A C 0 nonlinear finite element formulation of the random problem based on higher-order shear deformation theory in the von Karman sense is presented. A direct iterative method in conjunction with a stochastic nonlinear finite element method proposed earlier by the authors is extended to analyze the effect of uncertainty in system properties on the post-buckling and nonlinear free vibration of the composite plates having Winler type of geometric nonlinearity. Mean as well as standard deviation of the responses have been obtained for various combinations of geometric parameters, foundation parameters, stacking sequences and boundary conditions and compared with those available in the literature and Monte Carlo simulation.
Directory of Open Access Journals (Sweden)
Guo Ruijiang
1995-01-01
Full Text Available A finite element based sensitivity analysis procedure is developed for buckling and postbuckling of composite plates. This procedure is based on the direct differentiation approach combined with the reference volume concept. Linear elastic material model and nonlinear geometric relations are used. The sensitivity analysis technique results in a set of linear algebraic equations which are easy to solve. The procedure developed provides the sensitivity derivatives directly from the current load and responses by solving the set of linear equations. Numerical results are presented and are compared with those obtained using finite difference technique. The results show good agreement except at points near critical buckling load where discontinuities occur. The procedure is very efficient computationally.
Directory of Open Access Journals (Sweden)
Chonghui Shao
2016-01-01
Full Text Available The flutter and thermal buckling behavior of laminated composite panels embedded with shape memory alloy (SMA wires are studied in this research. The classical plate theory and nonlinear von-Karman strain-displacement relation are employed to investigate the aeroelastic behavior of the smart laminated panel. The thermodynamic behaviors of SMA wires are simulated based on one-dimensional Brinson SMA model. The aerodynamic pressure on the panel is described by the nonlinear piston theory. Nonlinear governing partial differential equations of motion are derived for the panel via the Hamilton principle. The effects of ply angle of the composite panel, SMA layer location and orientation, SMA wires temperature, volume fraction and prestrain on the buckling, flutter boundary, and amplitude of limit cycle oscillation of the panel are analyzed in detail.
International Nuclear Information System (INIS)
Benoist, P.
1990-06-01
The migration area, which relates the buckling to the multiplication factor, can be calculated by means of the Deniz formula. This formula involves the direct and adjoint angular fluxes. It is shown in this note that it is possible, using the integral form of the transport equation, to establish an equivalent formula in which only angle-integrated quantities appear. This formulation is more suitable for the calculation by the collision probably method [fr
International Nuclear Information System (INIS)
Bung, Hariddh; Alix, Michel; Hoffmann, Alain.
1980-06-01
In this paper, Buckling calculations with the CEASEMT System (INCA) are compared with experimental results obtained on elliptical heads subjected to an internal pressure. Tests were performed with 18 ellipsoidal heads welded on cylinders made of carbon steel A 36-401, stainless steel Z6CN18-09 and aluminium-magnesium alloys (AG3). Experimental data are higher than calculated data, this leads to a good safety factor [fr
Energy Technology Data Exchange (ETDEWEB)
Purgato, Rafael Turrini; Bitelli, Ulysses d' Utra; Aredes, Vitor Ottoni; Silva, Alexandre F. Povoa da; Santos, Diogo Feliciano dos; Lima, Ana Cecilia de Souza, E-mail: ubitelli@ipen.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)
2015-07-01
This work presents the results of experimental Buckling in the IPEN/MB-01 nuclear reactor in its cylindrical configuration with 28 fuel rods along its diameter. The IPEN/MB-01 is a zero power reactor designed to operate at a maximum power of 100 watts. It is a versatile nuclear facility, which allows for the simulation of all the characteristics of a nuclear power reactor making it an ideal test bed for this kind of measurement. A mapping of neutron flux inside the reactor is carried out in order to determine the total Buckling of the cylindrical configuration. The reactor was operated for one hour. Then, the activity of the fuel rods is measured by gamma ray spectrometry using a HPGe solid state detector and a suitable rod scanner. Photon energies of 276.6keV from {sup 239}Np (neutron capture (n,?) nuclear reaction) and 293.3keV from {sup 143}Ce (fission (n,f) nuclear reaction on both {sup 238}U and {sup 235}U) , are respectively along both axial and radial directions. Other measurements are performed using gold wires and foils along radial and axial directions of the reactor core. The three methods above resulted in a weighted average value of 93.18 ± 8.47 m-2 for the Total Buckling of this cylindrical core configuration with 28 control rods along its diameter with 568 fuel rods and only 271 pcm of excess reactivity. (author)
Directory of Open Access Journals (Sweden)
Svetlana RADAVIČIENĖ
2012-12-01
Full Text Available In production of garments, embroidery carries out a variety of functions, one of which is the aesthetic appearance of the product improvement. The resulting defects, are seen as a negative indicator of the product quality. The discrepancy of the embroidered element to the digital design in size is a defect, which is influenced by the embroidery threads, embroidery materials properties and process parameters. The fabric sorrounded by the embroidery threads between adjancent needle penetrations inside of the embroidered element is compressed, buckling. The aim of this paper is to investigate the influence of the properties of embroidery threads on buckling of fabric inside of the embroidered element. For investigations specimens were prepared using different fibre composition, density and linear structure of the embroidery threads. Specimens were cut and photo-captured at the beginning, middle and end of the embroidered element. It was found, that different properties of the embroidery threads affecting on the different behavior of fabric inside of the embroidered element. The results of the investigations showed that the fabric inside of the embroidered element formed larger waves of buckling using the maximum elongation of the feedback exhibiting embroidery thread.DOI: http://dx.doi.org/10.5755/j01.ms.18.4.3100
LENUS (Irish Health Repository)
Gibran, S K
2012-02-03
AIMS: This pilot study uses Optical Coherence Tomography (OCT) imaging to compare the difference in foveal architecture after successful retinal detachment (RD) surgery by scleral buckling or pars plana vitrectomy (PPV). METHODS: Prospective recruitment of patients with macular off RDs. Detachment surgery was undertaken by scleral buckling, external drainage, and air injection (group 1) or by PPV (group 2). Postoperatively patients had clinical examinations and OCT at 1, 3, 6, and 12 months. If abnormalities persisted, a further OCT was obtained at 18 months. RESULTS: Retinal reattachment, including clinical macular reattachment, was achieved in all cases within 24 h postoperatively. In group 1 (n=22), postoperative OCT showed persistent foveal detachment in 63% of cases (n=14) at 1 and 3 months. At 6 and 12 months, 36% (n=8) and 9% (n=2) had a persistent foveal detachment, respectively, and at 18 months, foveal detachment eventually. In group 2 (n=21), postoperative OCT showed an attached fovea in all cases; however, foveal thickening suggesting intraretinal oedema was present in all cases. The oedematous appearance of retina on OCT settled in 1-3 months. No foveal abnormality was seen at 6 and 12 months postoperatively. CONCLUSIONS: A high proportion of patients with successful retinal reattachment surgery by scleral buckling had foveal detachments postoperatively. No cases who had PPV had foveal detachments; however, transient retinal oedema was evident in all cases. The aetiology of these changes is unknown and warrants further investigation, as there is the potential of a long-term effect on vision.
Residual stress mapping by micro X-ray diffraction: Application to the study of thin film buckling
Energy Technology Data Exchange (ETDEWEB)
Goudeau, P.; Villain, P.; Tamura, N.; Celestre, R.S.; Padmore, H.A.
2002-11-06
Thin films deposited by Physical Vapour Deposition techniques on substrates generally exhibit large residual stresses which may be responsible of spontaneous detachment of the film from its substrate and in the case of compressive stresses, thin film buckling. Although these effects are undesirable for future applications, one may take benefit of it for thin film mechanical properties investigation. Since the 80's, a lot of theoretical works have been done to develop mechanical models with the aim to get a better understanding of driven mechanisms giving rise to this phenomenon and thus to propose solutions to avoid such problems. Nevertheless, only a few experimental works have been done on this subject to support these theoretical results and nothing concerning local stress/strain measurement mainly because of the small dimension of the buckling (few tenth mm). This paper deals with the application of micro beam x-ray diffraction available on synchrotron radiation sources for stress/ strain mapping analysis of gold thin film buckling.
Kovačević, Igor; Radosavljević, Aleksandra; Kalezić, Bojan; Potić, Jelena; Damjanović, Goran; Stefanović, Ivan
2012-01-01
The objective of our study was to analyze the presence of persistent submacular fluid after apparently successful scleral buckle surgery for macula-off retinal detachment, using Optical Coherence Tomography (OCT), and to correlate these findings to postoperative visual acuity. Prospective study of consecutive patients hospitalized for macula-off retinal detachment, between February 2008 and April 2010, was carried out at the single referral centre for vitreoretinal surgery in Serbia. Outcomes were evaluated 1, 3, 6 and 12 months postoperatively, using OCT and best corrected visual acuity (BCVA). All 48 patients with macula-off retinal detachment had undergone clinically successful scleral buckle surgery, 3 to 30 days (mean 14.2 ± 6.9) after the onset of symptoms. Reattachment was achieved and one month later, patients were divided in two groups, according to the presence of submacular fluid assessed by OCT group A with detectable residual submacular fluid (40%) and group B without (60%). The mean BCVA one month postoperatively was significantly lower (pmacula-off retinal detachment who had undergone successful scleral buckle surgery could be explained with presence of submacular fluid, diagnosed by OCT. However, final visual outcome was favourable, due to the gradual resorption of submacular fluid in a 12-month-period. PMID:22938546
International Nuclear Information System (INIS)
Itagaki, Masafumi; Miyoshi, Yoshinori; Hirose, Hideyuki
1993-01-01
A procedure is presented for the determination of geometric buckling for regular polygons. A new computation technique, the multiple reciprocity boundary element method (MRBEM), has been applied to solve the one-group neutron diffusion equation. The main difficulty in applying the ordinary boundary element method (BEM) to neutron diffusion problems has been the need to compute a domain integral, resulting from the fission source. The MRBEM has been developed for transforming this type of domain integral into an equivalent boundary integral. The basic idea of the MRBEM is to apply repeatedly the reciprocity theorem (Green's second formula) using a sequence of higher order fundamental solutions. The MRBEM requires discretization of the boundary only rather than of the domain. This advantage is useful for extensive survey analyses of buckling for complex geometries. The results of survey analyses have indicated that the general form of geometric buckling is B g 2 = (a n /R c ) 2 , where R c represents the radius of the circumscribed circle of the regular polygon under consideration. The geometric constant A n depends on the type of regular polygon and takes the value of π for a square and 2.405 for a circle, an extreme case that has an infinite number of sides. Values of a n for a triangle, pentagon, hexagon, and octagon have been calculated as 4.190, 2.281, 2.675, and 2.547, respectively
Directory of Open Access Journals (Sweden)
Tansu Erakgün
2014-03-01
Full Text Available Objectives: The aim of this study was to compare the surgical impact of scleral buckling (SB and pars plana vitrectomy (PPV on the anatomic results and visual recovery in cases of rhegmatogenous retinal detachment with mild vitreous hemorrhage. Materials and Methods: In this study, we included 78 eyes of 78 phakic patients who underwent primary surgery for rhegmatogenous retinal detachment complicated by mild vitreous hemorrhage (38 eyes by SB,40 eyes by PPV;all patients had been followed for longer than 6 months after surgery. The surgical outcome and the rate of complications were retrospectively compared. Mann-Whitney U-test and chi-square test were used for the statistical analysis. Results: The reattachment rate after the first surgery was 78.9% (30/38 in the SB group and 95% (38/40 in the PPV group. The difference between the groups was statistically significant (p=0.035. Unseen retinal breaks in 4 eyes, malpositioned buckle in 2 eyes and insufficient closure of the break in 2 eyes of SB cases, as well as reopening of the original break in 2 eyes of PPV cases were the causes of failure. Visual improvement in the PPV group was significantly better than in the SB group in the third and sixth postoperative months (p<0.001 and p=0.026, respectively. Peroperative and postoperative complications were as follows: in the SB group-subretinal hemorrhage (5.2%, PVR of grade B or worse (10.5%, macular pucker (7.8%, and postoperative cataract (13%; in the PPV groupiatrogenic breaks (10%, lens damage (5%, PVR of grade B or worse (5%,macular pucker (5%, and postoperative cataract (35%. Conclusion: Even though the high incidence of peroperative complications such as iatrogenic breaks or postoperative complications such as cataract formation was the major drawback, the results indicate that PPV performed to alleviate peripheral vitreoretinal tractions and clear vitreous hemorrhage offers better anatomic and functional results than SB in the management of
Bohman, Katarina; Jorlöv, Sofia; Zhou, Shengqi; Zhao, Cloud; Sui, Bo; Ding, Chengkai
2016-10-02
Traffic crashes are one of the leading causes of fatalities among Chinese children. Booster cushion usage in China is low, and there are no studies showing how a population with limited experience handles booster cushions during buckling up. The purpose of this study was to evaluate the handling of and explore the attitudes toward booster cushions among children, parents, and grandparents in Shanghai. An observational study including a convenience sample of 254 children aged 4-12 years was conducted in 2 passenger cars at a shopping center in Shanghai. Parents, grandparents, or the children themselves buckled up the child on 2 types of booster cushions, a 2-stage integrated booster cushion (IBC) and an aftermarket booster cushion (BC). The test participants were observed during buckling up, first without and then with instructions. The test leaders conducted structured interviews. Ninety-eight percent of the uninstructed participants failed to buckle up without identified misuse on the aftermarket booster cushion and 31% of those uninstructed on the integrated booster cushion. The majority of misuse was severe, including placing the belt behind the arm and the lap belt routing above the guiding loops. Instruction reduced misuse to 58% (BC) and 12% (IBC), respectively, and, in particular, severe misuse. Some misuse was related to limited knowledge of how to buckle up on the booster cushion, and some misuse was intentional in order to reduce discomfort. The participants, both children and adults, reported that they preferred the IBC due to good comfort and convenience. Safety was reported as the main reason for adults using booster cushions in general, whereas children reported comfort as the most important motivation. Education is needed to ensure frequent and correct use of booster cushions in China and to raise safety awareness among children and adults. Furthermore, it is important that the booster cushions offer intuitively correct usage to a population with
Thibado, Paul; Kumar, Pradeep; Singh, Surendra
Internet-of-Things (IoT) is projected to become a multi-trillion-dollar market, but most applications cannot afford replacing batteries on such a large scale, driving the need for battery alternatives. We recently discovered that freestanding graphene membranes are in perpetual motion when held at room temperature. Surprisingly, the random up-down motion of the membrane does not follow classical Brownian motion, but instead is super-diffusive at short times and sub-diffusive at long times. Furthermore, the velocity probability distribution function is non-Gaussian and follows the heavy-tailed Cauchy-Lorentz distribution, consistent with Lévy flights. Molecular dynamics simulations reveal that mechanical buckling is spontaneously occurring, and that this is the mechanism responsible for the anomalous movement. Bucking in this system occurs when the local material suddenly flips from concave to convex. The higher kinetic energy associated with this motion is derived from the surrounding thermal waste heat, and it may be converted into an electrical current and used as the active component of small power generators known as ambient vibration energy harvesters. thibado@uark.edu.
Nonlinear Forced Vibration of a Viscoelastic Buckled Beam with 2 : 1 Internal Resonance
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Liu-Yang Xiong
2014-01-01
Full Text Available Nonlinear dynamics of a viscoelastic buckled beam subjected to primary resonance in the presence of internal resonance is investigated for the first time. For appropriate choice of system parameters, the natural frequency of the second mode is approximately twice that of the first providing the condition for 2 : 1 internal resonance. The ordinary differential equations of the two mode shapes are established using the Galerkin method. The problem is replaced by two coupled second-order differential equations with quadratic and cubic nonlinearities. The multiple scales method is applied to derive the modulation-phase equations. Steady-state solutions of the system as well as their stability are examined. The frequency-amplitude curves exhibit the steady-state response in the directly excited and indirectly excited modes due to modal interaction. The double-jump, the saturation phenomenon, and the nonperiodic region phenomena are observed illustrating the influence of internal resonance. The validity range of the analytical approximations is assessed by comparing the analytical approximate results with a numerical solution by the Runge-Kutta method. The unstable regions in the internal resonance are explored via numerical simulations.
International Nuclear Information System (INIS)
Hansen, F.D.
1976-01-01
Quasi-static and creep consolidation tests have been performed in order to determine the compressibility of granulated rock salt when subjected to uniaxial deformations. The purpose of this analysis is to evaluate the force-displacement characteristics of rock salt that may be used as a backfill material around waste canister sleeves. The test set-up involved placing rock salt pellets in a thin-walled steel cylinder and applying a uniaxial load which compressed the salt while allowing no lateral movement. Tests were run at room temperature, 100 and 200 0 C and consolidated to uniaxial stress levels between 1000 and 4000 psi. Axial force, displacement and time were monitored during each test and the relationships have been evaluated. In particular, compressibility of the rock salt is not drastically effected by the temperature differences, nor is there an appreciable difference between the consolidation tests that were allowed to creep and those that were tested quasi-statically. On the basis of experimental data relating volume change to uniaxial stress, the pressure on the waste canister sleeve has been shown to be a nonlinear function of drillhole displacement. For a proposed in situ field test geometry, a 16 inch drillhole and a canister with a 12.75 inch O.D., the pressure necessary to buckle the canister sleeve will develop when the drillhole closes diametrically 0.5 to 0.6 inches. By the nature of this experimental effort, the results obtained are conservative
Adsorption of metal atoms at a buckled graphene grain boundary using model potentials
International Nuclear Information System (INIS)
Helgee, Edit E.; Isacsson, Andreas
2016-01-01
Two model potentials have been evaluated with regard to their ability to model adsorption of single metal atoms on a buckled graphene grain boundary. One of the potentials is a Lennard-Jones potential parametrized for gold and carbon, while the other is a bond-order potential parametrized for the interaction between carbon and platinum. Metals are expected to adsorb more strongly to grain boundaries than to pristine graphene due to their enhanced adsorption at point defects resembling those that constitute the grain boundary. Of the two potentials considered here, only the bond-order potential reproduces this behavior and predicts the energy of the adsorbate to be about 0.8 eV lower at the grain boundary than on pristine graphene. The Lennard-Jones potential predicts no significant difference in energy between adsorbates at the boundary and on pristine graphene. These results indicate that the Lennard-Jones potential is not suitable for studies of metal adsorption on defects in graphene, and that bond-order potentials are preferable
Thermal and Mechanical Buckling and Postbuckling Responses of Selected Curved Composite Panels
Breivik, Nicole L.; Hyer, Michael W.; Starnes, James H., Jr.
1998-01-01
The results of an experimental and numerical study of the buckling and postbuckling responses of selected unstiffened curved composite panels subjected to mechanical end shortening and a uniform temperature increase are presented. The uniform temperature increase induces thermal stresses in the panel when the axial displacement is constrained. An apparatus for testing curved panels at elevated temperature is described, numerical results generated by using a geometrically nonlinear finite element analysis code are presented. Several analytical modeling refinements that provide more accurate representation of the actual experimental conditions, and the relative contribution of each refinement, are discussed. Experimental results and numerical predictions are presented and compared for three loading conditions including mechanical end shortening alone, heating the panels to 250 F followed by mechanical end shortening, and heating the panels to 400 F. Changes in the coefficients of thermal expansion were observed as temperature was increased above 330 F. The effects of these changes on the experimental results are discussed for temperatures up to 400 F.
Dhar, Namrata; Jana, Debnarayan
2018-04-01
Ab initio magnetic and optical properties of group IV elements (carbon (C) and silicon (Si)) decorated free standing (FS) buckled germanene systems have been employed theoretically. Our study elucidates that, decoration of these elements in proper sites with suitable concentrations form dynamically stable configurations. Band structure is modified due to decoration of these atoms in Ge-nanosheet and pristine semi-metallic germanene undergoes to semiconductors with a finite amount of bandgap. Interestingly, this bandgap value meets closely the requirement of gap for field effect transistor (FET) applications. Moreover, significant magnetic moment is induced in non-magnetic germanene for C decorated structure and ground state in anti-ferromagnetic in nature for this structure. Along with magnetic property, optical properties like dielectric functions, optical absorption, electron energy loss spectra (EELS), refractive index and reflectivity of these systems have also been investigated. Maximum number of plasma frequencies appear for Si decorated configuration considering both parallel and perpendicular polarizations. In addition, birefringence characteristics of these configurations have also been studied as it is an important parameter in various applications of optical devices, liquid crystal displays, light modulators etc.
Morphable 3D mesostructures and microelectronic devices by multistable buckling mechanics
Fu, Haoran; Nan, Kewang; Bai, Wubin; Huang, Wen; Bai, Ke; Lu, Luyao; Zhou, Chaoqun; Liu, Yunpeng; Liu, Fei; Wang, Juntong; Han, Mengdi; Yan, Zheng; Luan, Haiwen; Zhang, Yijie; Zhang, Yutong; Zhao, Jianing; Cheng, Xu; Li, Moyang; Lee, Jung Woo; Liu, Yuan; Fang, Daining; Li, Xiuling; Huang, Yonggang; Zhang, Yihui; Rogers, John A.
2018-03-01
Three-dimensional (3D) structures capable of reversible transformations in their geometrical layouts have important applications across a broad range of areas. Most morphable 3D systems rely on concepts inspired by origami/kirigami or techniques of 3D printing with responsive materials. The development of schemes that can simultaneously apply across a wide range of size scales and with classes of advanced materials found in state-of-the-art microsystem technologies remains challenging. Here, we introduce a set of concepts for morphable 3D mesostructures in diverse materials and fully formed planar devices spanning length scales from micrometres to millimetres. The approaches rely on elastomer platforms deformed in different time sequences to elastically alter the 3D geometries of supported mesostructures via nonlinear mechanical buckling. Over 20 examples have been experimentally and theoretically investigated, including mesostructures that can be reshaped between different geometries as well as those that can morph into three or more distinct states. An adaptive radiofrequency circuit and a concealable electromagnetic device provide examples of functionally reconfigurable microelectronic devices.
Buckling as an origin of ordered cuticular patterns in flower petals
Antoniou Kourounioti, Rea L.; Band, Leah R.; Fozard, John A.; Hampstead, Anthony; Lovrics, Anna; Moyroud, Edwige; Vignolini, Silvia; King, John R.; Jensen, Oliver E.; Glover, Beverley J.
2013-01-01
The optical properties of plant surfaces are strongly determined by the shape of epidermal cells and by the patterning of the cuticle on top of the cells. Combinations of particular cell shapes with particular nanoscale structures can generate a wide range of optical effects. Perhaps most notably, the development of ordered ridges of cuticle on top of flat petal cells can produce diffraction-grating-like structures. A diffraction grating is one of a number of mechanisms known to produce ‘structural colours’, which are more intense and pure than chemical colours and can appear iridescent. We explore the concept that mechanical buckling of the cuticle on the petal epidermis might explain the formation of cuticular ridges, using a theoretical model that accounts for the development of compressive stresses in the cuticle arising from competition between anisotropic expansion of epidermal cells and isotropic cuticle production. Model predictions rationalize cuticle patterns, including those with long-range order having the potential to generate iridescence, for a range of different flower species. PMID:23269848
Buckling Instability Causes Inertial Thrust for Spherical Swimmers at All Scales
Djellouli, Adel; Marmottant, Philippe; Djeridi, Henda; Quilliet, Catherine; Coupier, Gwennou
2017-12-01
Microswimmers, and among them aspirant microrobots, generally have to cope with flows where viscous forces are dominant, characterized by a low Reynolds number (Re). This implies constraints on the possible sequences of body motion, which have to be nonreciprocal. Furthermore, the presence of a strong drag limits the range of resulting velocities. Here, we propose a swimming mechanism which uses the buckling instability triggered by pressure waves to propel a spherical, hollow shell. With a macroscopic experimental model, we show that a net displacement is produced at all Re regimes. An optimal displacement caused by nontrivial history effects is reached at intermediate Re. We show that, due to the fast activation induced by the instability, this regime is reachable by microscopic shells. The rapid dynamics would also allow high-frequency excitation with standard traveling ultrasonic waves. Scale considerations predict a swimming velocity of order 1 cm /s for a remote-controlled microrobot, a suitable value for biological applications such as drug delivery.
Buckling behaviour of imperfect ring-stiffened cone-cylinder intersections under internal pressure
International Nuclear Information System (INIS)
Zhao, Y.
2005-01-01
Cone-cylinder intersections are used commonly in pressure vessels and piping. In the case of a cone large end-to-cylinder intersection under internal pressure, the intersection is subject to a large circumferential compressive force. While both the cone and the cylinder may be locally thickened to strengthen the intersection, it is often desirable and convenient to provide an annular plate ring at the cone-to-cylinder joint to supplement local thickening or as an alternative strengthening measure, leading to a ring-stiffened cone-cylinder intersection. Only limited work has been carried out specifically on ring-stiffened cone-cylinder intersections under internal pressure. This paper presents the first experimental study on such intersections. In addition to the presentation of test results including geometric imperfections, failure behaviour and the determination of buckling mode and load based on displacement measurements, results from nonlinear bifurcation analysis using the perfect shape and nonlinear analysis using the measured imperfect shape are presented and compared with the experimental results
Compliant Buckled Foam Actuators and Application in Patient-Specific Direct Cardiac Compression.
Mac Murray, Benjamin C; Futran, Chaim C; Lee, Jeanne; O'Brien, Kevin W; Amiri Moghadam, Amir A; Mosadegh, Bobak; Silberstein, Meredith N; Min, James K; Shepherd, Robert F
2018-02-01
We introduce the use of buckled foam for soft pneumatic actuators. A moderate amount of residual compressive strain within elastomer foam increases the applied force ∼1.4 × or stroke ∼2 × compared with actuators without residual strain. The origin of these improved characteristics is explained analytically. These actuators are applied in a direct cardiac compression (DCC) device design, a type of implanted mechanical circulatory support that avoids direct blood contact, mitigating risks of clot formation and stroke. This article describes a first step toward a pneumatically powered, patient-specific DCC design by employing elastomer foam as the mechanism for cardiac compression. To form the device, a mold of a patient's heart was obtained by 3D printing a digitized X-ray computed tomography or magnetic resonance imaging scan into a solid model. From this model, a soft, robotic foam DCC device was molded. The DCC device is compliant and uses compressed air to inflate foam chambers that in turn apply compression to the exterior of a heart. The device is demonstrated on a porcine heart and is capable of assisting heart pumping at physiologically relevant durations (∼200 ms for systole and ∼400 ms for diastole) and stroke volumes (∼70 mL). Although further development is necessary to produce a fully implantable device, the material and processing insights presented here are essential to the implementation of a foam-based, patient-specific DCC design.
Macular Buckling Surgery for Retinal Detachment Associated with Macular Hole in High Myopia Eye
Directory of Open Access Journals (Sweden)
Kenan Sönmez
2017-12-01
Full Text Available A 68-year-old woman presented to our clinic with a 1-month history of central scotoma and visual loss in her right eye. The best corrected visual acuity (BCVA was hand motion in her right eye. Fundus examination showed myopic chorioretinal degeneration in association with posterior staphyloma and the retina was slightly elevated throughout the macula. Optical coherence tomography (OCT revealed retinal detachment involving the posterior pole with a macular hole and staphyloma. The patient underwent pars plana vitrectomy, internal limiting membrane peeling, macular buckling, and perfluoropropane gas tamponade. At 3-month follow-up, her BCVA was improved to counting fingers at 1 meter and flattened retina with closed macular hole was observed by OCT. Myopic macular hole with retinal detachment associated with posterior staphyloma represent a challenge regarding their management and several surgical techniques have been described. Although satisfactory anatomical improvement is achieved in these eyes after surgery, the visual acuity outcomes may be poorer than expected due to the chorioretinal atrophy at the posterior pole.
So, Hongyun
2013-10-31
© 2013, Springer-Verlag Berlin Heidelberg. This paper reports on a novel thermal actuator with sub-micron metallic structures and a buckling arm to operate with low voltages and to generate very large deflections, respectively. A lumped electrothermal model and analysis were also developed to validate the mechanical design and easily predict the temperature distribution along arms of the sub-micron actuator. The actuator was fabricated via the combination of electron beam lithography to form actuator arms with a minimum feature size of 200 nm and lift-off process to deposit a high aspect ratio nickel structure. Reproducible displacements of up to 1.9 μm at the tip were observed up to 250 mV under confocal microscope. The experimentally measured deflection values and theoretically calculated temperature distribution by the developed model were compared with finite element analysis results and they were in good agreement. This study shows a promising approach to develop more sophisticated nano actuators required larger deflections for manipulation of sub-micron scale objects with low-power consumption.
Akkoyun, I; Pınarcı, E Y; Yesilirmak, N; Yılmaz, G
2014-10-01
Enhanced depth imaging (EDI) optical coherence tomography (OCT) provides high-definition cross-sectional images of the choroid. Information on alterations in choroidal thickness (CT) after scleral buckling surgery (SBS) is rare. The medical charts of 122 patients (122 eyes) who underwent SBS for macula-off rhegmatogenous retinal detachment (RRD) were retrospectively analyzed. Patients with a follow-up ≥ 6 months were included. Postoperative EDI-OCT images concerning CT were evaluated 1 week, 1 month and 6 months postoperatively in 4 groups: group 1 cerclage + cryopexy (n = 39 eyes), group 2 cerclage + cryopexy + sponge (n = 28 eyes), group 3 SBS + subretinal fluid drainage (SRD) (n = 25 eyes) and group 4 SBS + sponge + SRD (n = 30 eyes). Subfoveal CT was compared between the groups and with the non-operated fellow eye. Subfoveal CT in groups 1, 2, 3 and 4 was thicker 1 week postoperatively. There were no significant differences between the groups or when comparing the operated eye with the fellow eye 1 and 6 months postoperatively. There were no differences in subfoveal CT 1 and 6 months after SBS between the eye with macula-off RRD and the fellow eye. The use of a sponge or SRD induced no differences concerning subfoveal CT.
On-line core monitoring system based on buckling corrected modified one group model
International Nuclear Information System (INIS)
Freire, Fernando S.
2011-01-01
Nuclear power reactors require core monitoring during plant operation. To provide safe, clean and reliable core continuously evaluate core conditions. Currently, the reactor core monitoring process is carried out by nuclear code systems that together with data from plant instrumentation, such as, thermocouples, ex-core detectors and fixed or moveable In-core detectors, can easily predict and monitor a variety of plant conditions. Typically, the standard nodal methods can be found on the heart of such nuclear monitoring code systems. However, standard nodal methods require large computer running times when compared with standards course-mesh finite difference schemes. Unfortunately, classic finite-difference models require a fine mesh reactor core representation. To override this unlikely model characteristic we can usually use the classic modified one group model to take some account for the main core neutronic behavior. In this model a course-mesh core representation can be easily evaluated with a crude treatment of thermal neutrons leakage. In this work, an improvement made on classic modified one group model based on a buckling thermal correction was used to obtain a fast, accurate and reliable core monitoring system methodology for future applications, providing a powerful tool for core monitoring process. (author)
Active oil-water interfaces: buckling and deformation of oil drops by bacteria
Juarez, Gabriel; Stocker, Roman
2014-11-01
Bacteria are unicellular organisms that seek nutrients and energy for growth, division, and self-propulsion. Bacteria are also natural colloidal particles that attach and self-assemble at liquid-liquid interfaces. Here, we present experimental results on active oil-water interfaces that spontaneously form when bacteria accumulate or grow on the interface. Using phase-contrast and fluorescence microscopy, we simultaneously observed the dynamics of adsorbed Alcanivorax bacteria and the oil-water interface within microfluidic devices. We find that, by growing and dividing, adsorbed bacteria form a jammed monolayer of cells that encapsulates the entire oil drop. As bacteria continue to grow at the interface, the drop buckles and the interface undergoes strong deformations. The bacteria act to stabilize non-equilibrium shapes of the oil-phase such wrinkling and tubulation. In addition to presenting a natural example of a living interface, these findings shape our understanding of microbial degradation of oil and may have important repercussions on engineering interventions for oil bioremediation.
Onguchi, Tatsuya; Eshita, Tadahiko; Mita, Shinji; Ishida, Susumu; Shinoda, Kei; Kitamura, Shizuaki; Kawashima, Shinichi; Inoue, Makoto; Oguchi, Yoshihisa; Toda, Ikuko; Kato, Naoko
2002-02-01
As laser in situ keratomileusis (LASIK) becomes the treatment of choice in the field of refractive surgery, postoperative rhegmatogenous retinal detachment has also begun to occur. However, since it has not been reported yet here in Japan, we report two cases of retinal detachment following LASIK with suggestions based on our experience. A 34-year-old male(Case 1) and a 26-year-old male(Case 2) suffered from retinal detachment one month and eight months after LASIK, respectively. Contributing retinal breaks were a horseshoe tear in Case 1 and atrophic holes in the lattice degeneration in Case 2. Each patient underwent partial scleral buckling with no intraoperative complication, resulting in successful retinal reattachment. Postoperatively, myopic changes developed and persisted one month in Case 1 and several months in Case 2. Great attention should be paid to the possibility of postoperative myopia after a repair of retinal detachment following LASIK. Thus, we stress the necessity of close cooperation between LASIK surgeons and vitreoretinal surgeons to settle the matter.
International Nuclear Information System (INIS)
Mokem Fokou, I.S.; Nono Dueyou Buckjohn, C.; Siewe Siewe, M.; Tchawoua, C.
2016-01-01
In this paper, a sandwiched buckled beam with axial compressive force under Gaussian white noise is considered as a piezoelectric energy harvester. A stochastic averaging method is proposed to analytically predict the system’s response, the stability and the estimation of system’s reliability. By using the generalized harmonic transformation, the Itô differential equations with respect to the mechanical and electrical amplitude are derived through this technique. From these differential equations, we construct the Fokker–Plank–Kolmogorov equation for the electrical and mechanical subsystem where the solution of each equation in the stationary state is a probability density. The mean first passage time (MFPT) is numerically provided in order to study the attractor stability(stable equilibrium point observed in the effective potential) which give rise to the noise-enhanced stability(NES) phenomenon. The mean square response and voltage are obtained for different white noise intensities and others system parameters. The effects of linear damping and noise intensity on the mean square voltage are investigated. We notice that harvested energy can be enhanced by suitable choice of noise intensity and others system parameters. In additional, by combining the random signal with harmonic excitation, the stochastic resonance(SR) phenomenon is observed via the mean residence time(TMR) which give rise to the large amplitude of vibrations and consequently, an optimization of harvested energy. The agreements between the analytical method and those obtained numerically validate the effectiveness of analytical investigations.
Yue, Qing-Yang; Yang, Yang; Cheng, Zhen-Jia; Guo, Cheng-Shan
2018-06-01
In this work, the light extraction efficiency enhancement of GaN-based thin-film flip-chip (TFFC) light-emitting diodes (LEDs) with high-refractive-index (TiO2) buckling nanostructures was studied using the three-dimensional finite difference time domain method. Compared with 2-D photonic crystals, the buckling structures have the advantages of a random directionality and a broad distribution in periodicity, which can effectively extract the guided light propagating in all azimuthal directions over a wide spectrum. Numerical studies revealed that the light extraction efficiency of buckling-structured LEDs reaches 1.1 times that of triangular lattice photonic crystals. The effects of the buckling structure feature sizes and the thickness of the N-GaN layer on the light extraction efficiency for TFFC LEDs were also investigated systematically. With optimized structural parameters, a significant light extraction enhancement of about 2.6 times was achieved for TiO2 buckling-structured TFFC LEDs compared with planar LEDs.
Jamalpoor, A.; Ahmadi-Savadkoohi, A.; Hosseini-Hashemi, Sh
2016-10-01
This paper deals with the theoretical analysis of free vibration and biaxial buckling of magneto-electro-elastic (MEE) microplate resting on Kelvin-Voigt visco-Pasternak foundation and subjected to initial external electric and magnetic potentials, using modified strain gradient theory (MSGT). Kirchhoff plate model and Hamilton’s principle are employed to extract the governing equations of motion. Governing equations were analytically solved to obtain clear closed-form expression for complex natural frequencies and buckling loads using Navier’s approach. Numerical results are presented to reveal variations of natural frequency and buckling load ratio of MEE microplate against different amounts of the length scale parameter, initial external electric and magnetic potentials, aspect ratio, damping and transverse and shear stiffness parameters of the visco-Pasternak foundation, length to thickness ratio, microplate thickness and higher modes. Numerical results of this study illustrate that by increasing thickness-to-material length scale parameter ratio, both natural frequency and buckling load ratio predicted by MSGT and modified couple stress theory are reduced because the non-dimensional length scale parameter tends to decrease the stiffness of structures and make them more flexible. In addition, results show that initial external electric and initial external magnetic potentials have no considerable influence on the buckling load ratio and frequency of MEE microplate as the microplate thickness increases.
International Nuclear Information System (INIS)
Bushnell, D.
1982-12-01
Under Task 4 the PANDA computer program was modified to permit calculation of critical load interaction curves for buckling of stiffened cylindrical shells with stiffeners running axially or circumferentially or both. Knockdown factors for geometric imperfections and plasticity reduction factors were introduced so that interaction curves can now be calculated for imperfect elastic-plastic shells. The knockdown factors and plasticity reduction factors are computed from a modified form of ASME Code Case N-284. The new version of PANDA was checked by making numerous comparisons with tests on fabricated stiffened cylinders
Post-buckled precompressed (PBP) piezoelectric actuators for UAV flight control
Vos, Roelof; Barrett, Ron; Krakers, Lars; van Tooren, Michel
2006-03-01
This paper presents the use of a new class of flight control actuators employing Post-Buckled Precompressed (PBP) piezoelectric elements in morphing wing Uninhabited Aerial Vehicles (UAVs). The new actuator relies on axial compression to amplify deflections and control forces simultaneously. Two designs employing morphing wing panels based on PBP actuators were conceived. One design employed PBP actuators in a membrane wing panel over the aft 60% of the chord to impose roll control on a 720mm span subscale UAV. This design relied on a change in curvature of the actuators to control the camber of the airfoil. Axial compression of the actuators was ensured by means of rubber bands and increased end rotation levels with almost a factor of two up to +/-13.6° peak-to-peak, with excellent correlation between theory and experiment. Wind tunnel tests quantitatively proved that wing morphing induced roll acceleration levels in excess of 1500 deg/s2. A second design employed PBP actuators in a wing panel with significant thickness, relying on a highly compliant Latex skin to allow for shape deformation and at the same time induce an axial force on the actuators. Bench tests showed that due to the axial compression provided by the skin end rotations were increased with more than a factor of two up to +/-15.8° peak-to-peak up to a break frequency of 34Hz. Compared to conventional electromechanical servoactuaters, the PBP actuators showed a net reduction in flight control system weight, slop and power consumption for minimal part count. Both morphing wing concepts showed that PBP piezoelectric actuators have significant benefits over conventional actuators and can be successfully applied to induce aircraft control.
Fang, Wei; Li, Jiu-Ke; Jin, Xiao-Hong; Dai, Yuan-Min; Li, Yu-Min
2016-01-01
To evaluate predictive factors for postoperative visual function of primary chronic rhegmatgenous retinal detachment (RRD) after sclera buckling (SB). Totally 48 patients (51 eyes) with primary chronic RRD were included in this prospective interventional clinical cases study, which underwent SB alone from June 2008 to December 2014. Age, sex, symptoms duration, detached extension, retinal hole position, size, type, fovea on/off, proliferative vitreoretinopathy (PVR), posterior vitreous detachment (PVD), baseline best corrected visual acuity (BCVA), operative duration, follow up duration, final BCVA were measured. Pearson correlation analysis, Spearman correlation analysis and multivariate linear stepwise regression were used to confirm predictive factors for better final visual acuity. Student's t-test, Wilcoxon two-sample test, Chi-square test and logistic stepwise regression were used to confirm predictive factors for better vision improvement. Baseline BCVA was 0.8313±0.6911 logMAR and final BCVA was 0.4761±0.4956 logMAR. Primary surgical success rate was 92.16% (47/51). Correlation analyses revealed shorter symptoms duration (r=0.3850, P=0.0053), less detached area (r=0.5489, Ppredictive factors were better baseline BCVA [partial R-square (PR(2))=0.5316, Ppredictive factors for better vision improvement were better baseline vision [odds ratio (OR) =50.369, P=0.0041] and longer follow up duration (OR=1.144, P=0.0067). Independent predictive factors for better visual outcome of primary chronic RRD after SB are better baseline BCVA, shorter symptoms duration, shorter operative duration and longer follow up duration, while independent predictive factors for better vision improvement after operation are better baseline vision and longer follow up duration.
Jo, Jaehyuck; Moon, Byung Gil; Lee, Joo Yong
2017-12-01
To report the outcome of scleral buckling using a non-contact wide-angle viewing system with a 25-gauge chandelier endoilluminator. Retrospective analyses of medical records were performed for 17 eyes of 16 patients with primary rhegmatogenous retinal detachment (RRD) without proliferative vitreoretinopathy who had undergone conventional scleral buckling with cryoretinopexy using the combination of a non-contact wide-angle viewing system and chandelier endoillumination. The patients were eight males and five females with a mean age of 26.8 ± 10.2 (range, 11 to 47) years. The mean follow-up period was 7.3 ± 3.1 months. Baseline best-corrected visual acuity was 0.23 ± 0.28 logarithm of the minimum angle of resolution units. Best-corrected visual acuity at the final visit showed improvement (0.20 ± 0.25 logarithm of the minimum angle of resolution units), but the improvement was not statistically significant (p = 0.722). As a surgery-related complication, there was vitreous loss at the end of surgery in one eye. As a postoperative complication, increased intraocular pressure (four cases) and herpes simplex epithelial keratitis (one case) were controlled postoperatively with eye drops. One case of persistent RRD after primary surgery needed additional vitrectomy, and the retina was postoperatively attached. Scleral buckling with chandelier illumination as a surgical technique for RRD has the advantages of relieving the surgeon's neck pain from prolonged use of the indirect ophthalmoscope and sharing the surgical procedure with another surgical team member. In addition, fine retinal breaks that are hard to identify using an indirect ophthalmoscope can be easily found under the microscope by direct endoillumination. © 2017 The Korean Ophthalmological Society
Hilburger, Mark W.; Waters, W. Allen, Jr.; Haynie, Waddy T.; Thornburgh, Robert P
2017-01-01
Results from the testing of cylinder test article SBKF-P2-CYL-TA02 (referred to herein as TA02) are presented. TA02 is an 8-foot-diameter (96-inches), 78.0-inch-long, aluminum-lithium (Al-Li), orthogrid-stiffened cylindrical shell similar to those used in current state-of-the-art launch-vehicle structures and was designed to exhibit global buckling when subjected to combined compression and bending loads. The testing was conducted at the Marshall Space Flight Center (MSFC), February 3-6, 2009, in support of the Shell Buckling Knockdown Factor Project (SBKF). The test was used to verify the performance of a newly constructed buckling test facility at MSFC and to verify the test article design and analysis approach used by the SBKF researchers.
Directory of Open Access Journals (Sweden)
Kukhar Volodymir
2018-01-01
Full Text Available This paper presents the results of experimental studies of load characteristic changes during the upsetting of high billets with the upsetting ratio (height to diameter ratio from 3.0 to 6.0, which is followed by buckling. Such pass is an effective way of preforming the workpiece for production of forgings with a bended axis or dual forming, and belongs to impression-free (dieless operation of bulk forming. Based on the experimental data analysis, an engineering method for calculation of workpiece pre-forming load as a maximum buckling force has been developed. The analysis of the obtained data confirmed the possibility of performing of this pre-forming operation on the main forging equipment, since the load of shaping by buckling does not exceed the load of the dieforging.
Kukhar, Volodymir; Artiukh, Victor; Prysiazhnyi, Andrii; Pustovgar, Andrey
2018-03-01
This paper presents the results of experimental studies of load characteristic changes during the upsetting of high billets with the upsetting ratio (height to diameter ratio) from 3.0 to 6.0, which is followed by buckling. Such pass is an effective way of preforming the workpiece for production of forgings with a bended axis or dual forming, and belongs to impression-free (dieless) operation of bulk forming. Based on the experimental data analysis, an engineering method for calculation of workpiece pre-forming load as a maximum buckling force has been developed. The analysis of the obtained data confirmed the possibility of performing of this pre-forming operation on the main forging equipment, since the load of shaping by buckling does not exceed the load of the dieforging.
Carreno, Armando Arpys Arevalo
2015-10-27
The integration of thermal bimorph actuators and buckled cantilever structures to form an out-of-plane plate with adjustable angular positions is reported. This structure could be used as a platform to build other transducers such as optical micromirrors, scanning antennas, switches or low-frequency oscillators. The electromechanical characterisation has shown that these structures can adjust their angular position by 6° when they are operated using a DC source. The thermal characterisation performed by an infrared camera showed that the heat-affected zone reaches a maximum temperature of 125°C while the rest of the structure remains unaffected by the generated heat.
Lin, Jing; Wang, Lu; Guidoin, Robert; Nutley, Mark; Song, Ge; Zhang, Ze; Du, Jia; Douville, Yvan
2014-03-01
Stent-grafts externally fitted with a Z-shaped stents were compared to devices fitted with ringed stents in an in vitro oscillating fatigue machine at 200 cycles per minute and a pressure of 360 mmHg for scheduled durations of up to 1 week. The devices fitted with Z-stents showed a considerably lower endurance limit to buckling compared to the controls. The contact between the apexes of adjacent Z-stents resulted in significant damage to the textile scaffolds and polyester fibers due to the sharp angle of the Z-stents. The ringed stents did not cause any fraying in the textile scaffolds.
Directory of Open Access Journals (Sweden)
Filip-Vacarescu Norin
2016-03-01
Full Text Available This paper discusses the concept of a hybrid damper made from a combination of two dissipative devices. A passive hysteretic device like steel Buckling Restrained Brace (BRB can be combined with a magneto-rheological (MR Fluid Damper in order to obtain a hybrid dissipative system. This system can work either as a semi-active system, if the control unit is available, or as a passive system, tuned for working according to performance based seismic engineering (PBSE scale of reference parameters (i.e. interstory drift.
Hilburger, Mark W.; Waters, W. Allen, Jr.; Haynie, Waddy T.
2015-01-01
Results from the testing of cylinder test article SBKF-P2-CYLTA01 (referred to herein as TA01) are presented. The testing was conducted at the Marshall Space Flight Center (MSFC), November 19?21, 2008, in support of the Shell Buckling Knockdown Factor (SBKF) Project.i The test was used to verify the performance of a newly constructed buckling test facility at MSFC and to verify the test article design and analysis approach used by the SBKF project researchers. TA01 is an 8-foot-diameter (96-inches), 78.0-inch long, aluminum-lithium (Al-Li), orthogrid-stiffened cylindrical shell similar to those used in current state-of-the-art launch vehicle structures and was designed to exhibit global buckling when subjected to compression loads. Five different load sequences were applied to TA01 during testing and included four sub-critical load sequences, i.e., loading conditions that did not cause buckling or material failure, and one final load sequence to buckling and collapse. The sub-critical load sequences consisted of either uniform axial compression loading or combined axial compression and bending and the final load sequence subjected TA01 to uniform axial compression. Traditional displacement transducers and strain gages were used to monitor the test article response at nearly 300 locations and an advanced digital image correlation system was used to obtain low-speed and high-speed full-field displacement measurements of the outer surface of the test article. Overall, the test facility and test article performed as designed. In particular, the test facility successfully applied all desired load combinations to the test article and was able to test safely into the postbuckling range of loading, and the test article failed by global buckling. In addition, the test results correlated well with initial pretest predictions.
Schaeffner, Maximilian; Platz, Roland
2018-06-01
For slender beam-columns loaded by axial compressive forces, active buckling control provides a possibility to increase the maximum bearable axial load above that of a purely passive structure. In this paper, an approach for gain-scheduled {{\\mathscr{H}}}∞ buckling control of a slender beam-column with circular cross-section subject to time-varying axial loads is investigated experimentally. Piezo-elastic supports with integrated piezoelectric stack actuators at the beam-column ends allow an active stabilization in arbitrary lateral directions. The axial loads on the beam-column influence its lateral dynamic behavior and, eventually, cause the beam-column to buckle. A reduced modal model of the beam-column subject to axial loads including the dynamics of the electrical components is set up and calibrated with experimental data. Particularly, the linear parameter-varying open-loop plant is used to design a model-based gain-scheduled {{\\mathscr{H}}}∞ buckling control that is implemented in an experimental test setup. The beam-column is loaded by ramp- and step-shaped time-varying axial compressive loads that result in a lateral deformation of the beam-column due to imperfections, such as predeformation, eccentric loading or clamping moments. The lateral deformations and the maximum bearable loads of the beam-column are analyzed and compared for the beam-column with and without gain-scheduled {{\\mathscr{H}}}∞ buckling control or, respectively, active and passive configuration. With the proposed gain-scheduled {{\\mathscr{H}}}∞ buckling control it is possible to increase the maximum bearable load of the active beam-column by 19% for ramp-shaped axial loads and to significantly reduce the beam-column deformations for step-shaped axial loads compared to the passive structure.
Rao, Ch. K.; Rao, L. B.
2018-01-01
The problem of the post-buckling response of a simply supported thin-walled beam subjected to an axial compressive load and supported by the Winkler-Pasternak foundation is studied in this paper. The strains are assumed to be small and elastic. The shear deformations and the in-plane cross-sectional deformations are assumed to be negligible. The post-buckling paths of the simply supported beam are determined for different values of the Winkler and Pasternak stiffness parameters. Bifurcation points are found.
Chen, Chunhong; Li, Xuefeng; Jiang, Deng; Wang, Zhe; Wang, Yong
2018-06-19
To realize the asymmetry for the hollow carbonaceous nanostructures remains to be a great challenge, especially when biomass is chosen as the carbon resource via hydrothermal carbonization (HTC). Herein, a simple and straightforward solvent induced buckling strategy is demonstrated for the synthesis of asymmetric spherical and bowllike carbonaceous nanomaterials. The formation of the bowllike morphology was attributed to the buckling of the spherical shells induced by the dissolution of the oligomers. The bowllike particles made by this solvent-driven approach demonstrated a well-controlled morphology and a uniform particle size of ~360 nm. The obtained nanospheres and nanobowls can be loaded with CoS2 nanoparticles to act as novel heterogeneous catalysts for the selective hydrogenation of aromatic nitro compounds. With the bowllike structure in hand, as expected, the CoS2/nanobowls catalyst showed good tolerance to a wide scope of reducible groups and afforded both high activity and selectivity in almost all the tested substrates (14). © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Norouzzadeh, A.; Ansari, R.; Rouhi, H.
2017-05-01
Differential form of Eringen's nonlocal elasticity theory is widely employed to capture the small-scale effects on the behavior of nanostructures. However, paradoxical results are obtained via the differential nonlocal constitutive relations in some cases such as in the vibration and bending analysis of cantilevers, and recourse must be made to the integral (original) form of Eringen's theory. Motivated by this consideration, a novel nonlocal formulation is developed herein based on the original formulation of Eringen's theory to study the buckling behavior of nanobeams. The governing equations are derived according to the Timoshenko beam theory, and are represented in a suitable vector-matrix form which is applicable to the finite-element analysis. In addition, an isogeometric analysis (IGA) is conducted for the solution of buckling problem. Construction of exact geometry using non-uniform rational B-splines and easy implementation of geometry refinement tools are the main advantages of IGA. A comparison study is performed between the predictions of integral and differential nonlocal models for nanobeams under different kinds of end conditions.
De Pascalis, Riccardo
2010-07-22
Euler\\'s celebrated buckling formula gives the critical load N for the buckling of a slender cylindrical column with radius B and length L as N/(π3B2)=(E/4)(B/L)2 where E is Young\\'s modulus. Its derivation relies on the assumptions that linear elasticity applies to this problem, and that the slenderness (B/L) is an infinitesimal quantity. Here we ask the following question: What is the first non-linear correction in the right hand-side of this equation when terms up to (B/L)4 are kept? To answer this question, we specialize the exact solution of incremental non-linear elasticity for the homogeneous compression of a thick compressible cylinder with lubricated ends to the theory of third-order elasticity. In particular, we highlight the way second- and third-order constants-including Poisson\\'s ratio-all appear in the coefficient of (B/L)4. © 2010 Springer Science+Business Media B.V.
Influence of friction on buckling of a drill string in the circular channel of a bore hole
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Valery Gulyayev
2016-10-01
Full Text Available Abstract Enhancement of technology and techniques for drilling deep directed oil and gas bore hole is one of the most important problems of the current petroleum industry. Not infrequently, the drilling of these bore holes is attended by occurrence of extraordinary situations associated with technical accidents. Among these is the Eulerian loss of stability of a drill string in the channel of a curvilinear bore hole. Methods of computer simulation should play a dominant role in prediction of these states. In this paper, a new statement of the problem of critical buckling of the drill strings in 3D curvilinear bore holes is proposed. It is based on combined use of the theory of curvilinear elastic rods, Eulerian theory of stability, theory of channel surfaces, and methods of classical mechanics of systems with nonlinear constraints. It is noted that the stated problem is singularly perturbed and its solutions have the shapes of localized harmonic wavelets. The calculation results showed that the friction effects lead to essential redistribution of internal axial forces, as well as changing the eigenmode shapes and sites of their localization. These features make the buckling phenomena less predictable and raise the role of computer simulation of these effects.
Tripp, L. L.; Tamekuni, M.; Viswanathan, A. V.
1973-01-01
The use of the computer program BUCLASP3 is described. The code is intended for thermal stress and instability analyses of structures such as unidirectionally stiffened panels. There are two types of instability analyses that can be effected by PAINT; (1) thermal buckling, and (2) buckling due to a specified inplane biaxial loading. Any structure that has a constant cross section in one direction, that may be idealized as an assemblage of beam elements and laminated flat and curved plate strip-elements can be analyzed. The two parallel ends of the panel must be simply supported, whereas arbitrary elastic boundary conditions may be imposed along any one or both external longitudinal side. Any variation in the temperature rise (from ambient) through the cross section of a panel is considered in the analyses but it must be assumed that in the longitudinal direction the temperature field is constant. Load distributions for the externally applied inplane biaxial loads are similar in nature to the permissible temperature field.
Energy Technology Data Exchange (ETDEWEB)
Badjian, H.; Setoodeh, A.R., E-mail: setoodeh@sutech.ac.ir
2017-02-15
Synthesizing inorganic nanostructures such as boron nitride nanotubes (BNNTs) have led to immense studies due to their many interesting functional features such as piezoelectricity, high temperature resistance to oxygen, electrical insulation, high thermal conductivity and very long lengths as physical features. In order to utilize the superior properties of pristine and defected carbon nanotubes (CNTs), a hybrid nanotube is proposed in this study by forming BNNTs surface coating on the CNTs. The benefits of such coating on the tensile and buckling behavior of single-walled CNTs (SWCNTs) are illustrated through molecular dynamics (MD) simulations of the resulted nanostructures during the deformation. The AIREBO and Tersoff-Brenner potentials are employed to model the interatomic forces between the carbon and boron nitride atoms, respectively. The effects of chiral indices, aspect ratio, presence of mono-vacancy defects and coating dimension on coated/non-coated CNTs are examined. It is demonstrated that the coated defective CNTs exhibit remarkably enhanced ultimate strength, buckling load capacity and Young's modulus. The proposed coating not only enhances the mechanical properties of the resulted nanostructure, but also conceals it from few external factors impacting the behavior of the CNT such as humidity and high temperature.
Lovejoy, Andrew E.; Hilburger, Mark W.
2010-01-01
The Shell Buckling Knockdown Factor (SBKF) project includes the testing of sub-scale cylinders to validate new shell buckling knockdown factors for use in the design of the Ares-I and Ares-V launch vehicles. Test article cylinders represent various barrel segments of the Ares-I and Ares-V vehicles, and also include checkout test articles. Testing will be conducted at Marshall Space Flight Center (MSFC) for test articles having an eight-foot diameter outer mold line (OML) and having lengths that range from three to ten feet long. Both ends of the test articles will be connected to the test apparatus using attachment rings. Three multiple-piece and one single-piece design for the attachment rings were developed and analyzed. The single-piece design was chosen and will be fabricated from either steel or aluminum (Al) depending on the required safety factors (SF) for test hardware. This report summarizes the design and analysis of these attachment ring concepts.
Farajpour, M. R.; Shahidi, A. R.; Farajpour, A.
2018-03-01
In this study, the buckling behavior of a three-layered composite nanoplate reinforced with shape memory alloy (SMA) nanowires is examined. Whereas the upper and lower layers are reinforced with typical nanowires, SMA nanoscale wires are used to strengthen the middle layer of the system. The composite nanoplate is assumed to be under the action of biaxial compressive loading. A scale-dependent mathematical model is presented with the consideration of size effects within the context of the Eringen’s nonlocal continuum mechanics. Using the one-dimensional Brinson’s theory and the Kirchhoff theory of plates, the governing partial differential equations of SMA nanowire-reinforced hybrid nanoplates are derived. Both lateral and longitudinal deflections are taken into consideration in the theoretical formulation and method of solution. In order to reduce the governing differential equations to their corresponding algebraic equations, a discretization approach based on the differential quadrature method is employed. The critical buckling loads of the hybrid nanosystem with various boundary conditions are obtained with the use of a standard eigenvalue solver. It is found that the stability response of SMA composite nanoplates is strongly sensitive to the small scale effect.
Directory of Open Access Journals (Sweden)
Solazzi L.
2010-06-01
Full Text Available This paper is concerned with the experimental mechanical analysis of a new design of a joint for a main components of a upper deck of a road bridge. These components are subject to the compression state stress induced by the weight and the load acting on the road. Each upper deck of a bridge (positioned on each side of the bridge is composed by four tubular structures that must be joint each together. The joint must to take in to account many aspects, for example that the length of each component is not the same (because, obviously, there is a mechanical tolerance. This phenomena induce different compression stress on each component and so is very important non only the critical buckling load but also the post buckling behaviour of the structure. It is very important that if a single tubular structure reaches the critical load of instability, it still has load capacity . This is to avoid that, in the case where a column reaches the instability, the entire load acting on a column increase the load on the remaining three. For this purpose many different geometrical solutions have been designed (elaborated by fem analyses and successively tested experimentally. This work reports the main experimental results on the best joint solution and how this increase the load capacity and the displacement respect to the solution without this flange.
De Pascalis, Riccardo; Destrade, Michel; Goriely, Alain
2010-01-01
Euler's celebrated buckling formula gives the critical load N for the buckling of a slender cylindrical column with radius B and length L as N/(π3B2)=(E/4)(B/L)2 where E is Young's modulus. Its derivation relies on the assumptions that linear elasticity applies to this problem, and that the slenderness (B/L) is an infinitesimal quantity. Here we ask the following question: What is the first non-linear correction in the right hand-side of this equation when terms up to (B/L)4 are kept? To answer this question, we specialize the exact solution of incremental non-linear elasticity for the homogeneous compression of a thick compressible cylinder with lubricated ends to the theory of third-order elasticity. In particular, we highlight the way second- and third-order constants-including Poisson's ratio-all appear in the coefficient of (B/L)4. © 2010 Springer Science+Business Media B.V.
Schoelz, James K.
Graphene has the ability to provide for a technological revolution. First isolated and characterized in 2004, this material shows promise in the field of flexible electronics. The electronic properties of graphene can be tuned by controlling the shape of the membrane. Of particular interest in this endeavor are the thermal ripples in graphene membranes. Years of theoretical work by such luminaries as Lev Landau, Rudolf Peierls, David Mermin and Herbert Wagner have established that 2D crystals should not be thermodynamically stable. Experimental research on thin films has supported this finding. Yet graphene exists, and freestanding graphene films have been grown on large scales. It turns out that coupling between the bending and stretching phonons can stabilize the graphene in a flat, albeit rippled phase. These ripples have attracted much attention, and recent work has shown how to arrange these ripples in a variety of configurations. In this thesis, I will present work done using a scanning tunneling microscope (STM) to interact with freestanding graphene membranes. First I will present STM images of freestanding graphene and show how these images show signs of distortion under the electrostatic influence of the STM tip. This electrostatic attraction between the STM tip and the graphene sample can be used to pull on the graphene sample. At the same time, by employing Joule heating in order to heat graphene using the tunneling current, and exploiting the negative coefficient of thermal expansion, a repulsive thermal load can be generated. By repeatedly pulling on the graphene using the electrostatic potential, while sequentially increasing the setpoint current we can generate a thermal mirror buckling event. Slowly heating the graphene using the tunneling current, prepares a small convex region of graphene under the tip. By increasing thermal stress, as well as pulling using the out of plane electrostatic force, the graphene suddenly and irreversibly switches the
Supra choroidal buckling in managing myopic vitreoretinal interface disorders: 1-year data.
El Rayes, Ehab N
2014-01-01
To evaluate the efficacy of supra choroidal buckling procedure using a supra choroidal catheter, as a new approach in treating myopic vitreomacular interface disorders specially in difficult cases of myopic traction maculopathy with or without macular hole retinal detachment in posterior staphyloma depending on the concept of indenting the choroid only, from a 1-year data study. A newly developed supra choroidal catheter was used to deliver stabilized, cross-linked, long-acting hyaluronic acid as a filler in the supra choroidal space in the area of the staphyloma forming a choroidal indenting effect. Before the injection, pars plana vitrectomy was performed without internal limiting membrane peeling to avoid the risk of break of the roof of foveal detachment in case of foveoschisis. This indentation was used to treat 11 patients with myopic foveoschisis and 12 patients with myopic macular hole retinal detachment, 5 of whom had failed primary repair by vitrectomy before inclusion in this trial. Clinical and optical coherence tomographic evaluations of these patients were performed over 1-year follow-up. Retinal layer restoration was achieved in all 11 eyes with myopic foveoschisis. This was gradual over a period of 2 to 6 weeks postoperatively. No recurrence over the 12-month follow-up was observed. Visual acuity improved by 1 line or more in 9 eyes (81.8%). Of the 12 eyes, 10 with macular hole detachment (83%) showed closure of the holes in association with the resolution of the detachment; 2 eyes showed resolution of the detachment and flatting of the edge of the holes but with incomplete closure on optical coherence tomography. Eight eyes (66.6%) showed improvement in visual acuity by 1 or more lines with no recurrence of retinal detachment over the 12-month follow-up period. The indentation effect was sufficient over the 12-month follow-up period. The indentation effect achieved by supra choroidal approach can be used as a method of managing myopic foveoschisis
Sluis, van der O.; Abdallah, Amir; Bouten, P.C.P.; Timmermans, P.H.M.; Toonder, den J.M.J.; With, de G.
2011-01-01
Layer buckling and delamination is a common interfacial failure phenomenon in thin film multi-layer structures that are used in flexible display applications. Typically, the substrate is coated on both sides with a hybrid coating, calleda hard coat (HC), which acts as a gas barrier and also
International Nuclear Information System (INIS)
Persson, R.; Andersson, A.J.W.; Wikdahl, C.E.
1966-11-01
Buckling determinations by means of flux mapping were performed in TZ up to 250 deg C on two lattices of Aagesta fuel assemblies in D 2 O and on D 2 O alone. Most of the flux measurements were made with fission counters in pressure thimbles. The perturbations caused by the thimbles were studied experimentally in various ways and compared with two group diffusion-theory calculations. In one of the lattices the effectiveness of a control rod (AglnCd) was also investigated. The results of the diffusion length experiments indicated some systematic error of the order of 0.15 - 0.10/m 2 in the bucklings measured, though the temperature dependence should be well established. The bucklings of the two lattices studied (square pitches 24 and 27 cm) were found to be less sensitive to temperature than theoretical calculations predict, the temperature coefficient being more than 10 per cent smaller. The buckling changes from 20 to 250 deg C were about -2.4 and -1.8/m 2 , respectively, for the two lattices. During part of the experimental period we had, for some unexplained reason, about 30 per cent excess absorption in the heavy water
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Zihao Yang
Full Text Available A microstructure-dependent model for the free vibration and buckling analysis of an orthotropic functionally graded micro-plate was proposed on the basis of a re-modified couple stress theory. The macro- and microscopic anisotropy were simultaneously taken into account by introducing two material length scale parameters. The material attributes were assumed to vary continuously through the thickness direction by a power law. The governing equations and corresponding boundary conditions were derived through Hamilton’s principle. The Navier method was used to calculate the natural frequencies and buckling loads of a simply supported micro-plate. The numerical results indicated that the present model predicts higher natural frequencies and critical buckling loads than the classical model, particular when the geometric size of the micro-plates is comparable to the material length scale parameters, i.e., the scale effect is well represented. The scale effect becomes more noticeable as the material length scale parameters increase, the anisotropy weaken or the power law index increases, and vice versa. Keywords: Free vibration, Buckling, Functionally graded materials, Modified couple stress theory, Scale effect
Energy Technology Data Exchange (ETDEWEB)
Persson, R; Andersson, A J.W.; Wikdahl, C E
1966-11-15
Buckling determinations by means of flux mapping were performed in TZ up to 250 deg C on two lattices of Aagesta fuel assemblies in D{sub 2}O and on D{sub 2}O alone. Most of the flux measurements were made with fission counters in pressure thimbles. The perturbations caused by the thimbles were studied experimentally in various ways and compared with two group diffusion-theory calculations. In one of the lattices the effectiveness of a control rod (AglnCd) was also investigated. The results of the diffusion length experiments indicated some systematic error of the order of 0.15 - 0.10/m{sup 2} in the bucklings measured, though the temperature dependence should be well established. The bucklings of the two lattices studied (square pitches 24 and 27 cm) were found to be less sensitive to temperature than theoretical calculations predict, the temperature coefficient being more than 10 per cent smaller. The buckling changes from 20 to 250 deg C were about -2.4 and -1.8/m{sup 2}, respectively, for the two lattices. During part of the experimental period we had, for some unexplained reason, about 30 per cent excess absorption in the heavy water.