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......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...
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...
International Nuclear Information System (INIS)
The Containment Buckling program at the Los Alamos National Laboratory is aimed at evaluating the adequacy of the current design procedures for free standing steel nuclear containment shells against static and dynamic structural instability. Such buckling behavior will typically produce large displacements in the shell wall that will potentially violate seals around hatches and penetrations, or even produce puncture or tearing of the shell wall resulting in a loss of containment function. The ultimate goal of the program is to provide NRC with a basis for evaluating the associated licensing issues and to recommend appropriate changes and additions to the NRC Review Criteria
The secondary buckling transition: wrinkling of buckled spherical shells
Knoche, Sebastian; Kierfeld, Jan
2014-01-01
We theoretically explain the complete sequence of shapes of deflated spherical shells. Decreasing the volume, the shell remains spherical initially, then undergoes the classical buckling instability, where an axisymmetric dimple appears, and, finally, loses its axisymmetry by wrinkles developing in the vicinity of the dimple edge in a secondary buckling transition. We describe the first axisymmetric buckling transition by numerical integration of the complete set of shape equations and an app...
Buckling of dislocation in graphene
Yao, Yin; Wang, Shaofeng; Bai, Jianhui; Wang, Rui
2016-10-01
The buckling of dislocation in graphene is discussed through the lattice theory of dislocation and elastic theory. The approximate solution of the buckling is obtained based on the inner stress distribution caused by different structure of dislocations and is proved to be suitable by the simulation. The position of the highest buckling is predicted to be at the vertex of the pentagon far away from the heptagon. The buckling is strongly influenced by the internal stress and the distance between the extrusive area and stretching area, as well as the critical stress σc. The SW defect is proved to be unbuckled due to its strong interaction between extrusion and stretching.
The secondary buckling transition: wrinkling of buckled spherical shells.
Knoche, Sebastian; Kierfeld, Jan
2014-07-01
We theoretically explain the complete sequence of shapes of deflated spherical shells. Decreasing the volume, the shell remains spherical initially, then undergoes the classical buckling instability, where an axisymmetric dimple appears, and, finally, loses its axisymmetry by wrinkles developing in the vicinity of the dimple edge in a secondary buckling transition. We describe the first axisymmetric buckling transition by numerical integration of the complete set of shape equations and an approximate analytic model due to Pogorelov. In the buckled shape, both approaches exhibit a locally compressive hoop stress in a region where experiments and simulations show the development of polygonal wrinkles, along the dimple edge. In a simplified model based on the stability equations of shallow shells, a critical value for the compressive hoop stress is derived, for which the compressed circumferential fibres will buckle out of their circular shape in order to release the compression. By applying this wrinkling criterion to the solutions of the axisymmetric models, we can calculate the critical volume for the secondary buckling transition. Using the Pogorelov approach, we also obtain an analytical expression for the critical volume at the secondary buckling transition: The critical volume difference scales linearly with the bending stiffness, whereas the critical volume reduction at the classical axisymmetric buckling transition scales with the square root of the bending stiffness. These results are confirmed by another stability analysis in the framework of Donnel, Mushtari and Vlasov (DMV) shell theory, and by numerical simulations available in the literature. PMID:25039007
Directory of Open Access Journals (Sweden)
Ramazan ÖZÇELİK
2016-06-01
Full Text Available Buckling restrained braces (BRBs have high energy dissipation capacity and equal tension and compression axial load capacity. Therefore, the application of BRBs has gained popularity in seismic regions. The first studies on BRBs started in Japan in 1970 and since then more studies have been undertaken in other earthquake prone countries. Although the BRBs perform well in component and subassembly tests, they do not perform as well in frame tests because of the interaction between beam-column-gusset plate and BRB. In this study, the component and subassembly test of the BRBs and then BRB frame tests available in the literature are summarized.
Buckling of polymerized monomolecular films
Bourdieu, L.; Daillant, J.; Chatenay, D.; Braslau, A.; Colson, D.
1994-03-01
The buckling of a two-dimensional polymer network at the air-water interface has been evidenced by grazing incidence x-ray scattering. A comprehensive description of the inhomogeneous octadecyltrichlorosilane polymerized film was obtained by atomic force microscopy and x-ray scattering measurements. The buckling occurs with a characteristic wavelength ~=10 μm.
Buckling failures in insect exoskeletons.
Parle, Eoin; Herbaj, Simona; Sheils, Fiona; Larmon, Hannah; Taylor, David
2016-02-01
Thin walled tubes are often used for load-bearing structures, in nature and in engineering, because they offer good resistance to bending and torsion at relatively low weight. However, when loaded in bending they are prone to failure by buckling. It is difficult to predict the loading conditions which cause buckling, especially for tubes whose cross sections are not simple shapes. Insights into buckling prevention might be gained by studying this phenomenon in the exoskeletons of insects and other arthropods. We investigated the leg segments (tibiae) of five different insects: the locust (Schistocerca gergaria), American cockroach (Periplaneta americana), death's head cockroach (Blaberus discoidalis), stick insect (Parapachymorpha zomproi) and bumblebee (Bombus terrestris audax). These were tested to failure in cantilever bending and modelled using finite element analysis (FEA). The tibiae of the locust and the cockroaches were found to be approximately circular in shape. Their buckling loads were well predicted by linear elastic FEA, and also by one of the analytical solutions available in the literature for elastic buckling. The legs of the stick insect are also circular in cross section but have several prominent longitudinal ridges. We hypothesised that these ridges might protect the legs against buckling but we found that this was not the case: the loads necessary for elastic buckling were not reached in practice because yield occurred in the material, causing plastic buckling. The legs of bees have a non-circular cross section due to a pollen-carrying feature (the corbicula). We found that this did not significantly affect their resistance to buckling. Our results imply that buckling is the dominant failure mode in the tibia of insects; it likely to be a significant consideration for other arthropods and any organisms with stiff exoskeletons. The interactions displayed here between material properties and cross sectional geometry may provide insights for the
Buckling failures in insect exoskeletons.
Parle, Eoin; Herbaj, Simona; Sheils, Fiona; Larmon, Hannah; Taylor, David
2016-02-01
Thin walled tubes are often used for load-bearing structures, in nature and in engineering, because they offer good resistance to bending and torsion at relatively low weight. However, when loaded in bending they are prone to failure by buckling. It is difficult to predict the loading conditions which cause buckling, especially for tubes whose cross sections are not simple shapes. Insights into buckling prevention might be gained by studying this phenomenon in the exoskeletons of insects and other arthropods. We investigated the leg segments (tibiae) of five different insects: the locust (Schistocerca gergaria), American cockroach (Periplaneta americana), death's head cockroach (Blaberus discoidalis), stick insect (Parapachymorpha zomproi) and bumblebee (Bombus terrestris audax). These were tested to failure in cantilever bending and modelled using finite element analysis (FEA). The tibiae of the locust and the cockroaches were found to be approximately circular in shape. Their buckling loads were well predicted by linear elastic FEA, and also by one of the analytical solutions available in the literature for elastic buckling. The legs of the stick insect are also circular in cross section but have several prominent longitudinal ridges. We hypothesised that these ridges might protect the legs against buckling but we found that this was not the case: the loads necessary for elastic buckling were not reached in practice because yield occurred in the material, causing plastic buckling. The legs of bees have a non-circular cross section due to a pollen-carrying feature (the corbicula). We found that this did not significantly affect their resistance to buckling. Our results imply that buckling is the dominant failure mode in the tibia of insects; it likely to be a significant consideration for other arthropods and any organisms with stiff exoskeletons. The interactions displayed here between material properties and cross sectional geometry may provide insights for the
Buckling Characteristics of Cylindrical Pipes
Institute of Scientific and Technical Information of China (English)
Toshiaki Sakurai
2015-01-01
This paper describes the buckling pattern of the body frame by energy absorbed efficiency of crashworthiness related toresearch of the buckling characteristics of aluminum cylindrical pipes with various diameters formed mechanical tools. Experimentswere performed by the quasi-static test without lubrication between specimen and equipment. According to the change in the radiusversus thickness of the specimen, the buckling phenomena are transformed from folding to bellows and the rate of energy absorptionis understood. In crashworthiness, frames are characterized by the folding among three patterns from the absorbed energy efficiencypoint of view and weight reduction. With the development of new types of transport such as electric vehicles, innovated bodystructure should be designed.
Nonlinear Analysis of Buckling
Directory of Open Access Journals (Sweden)
Psotný Martin
2014-06-01
Full Text Available The stability analysis of slender web loaded in compression was presented. To solve this problem, a specialized computer program based on FEM was created. The nonlinear finite element method equations were derived from the variational principle of minimum of potential energy. To obtain the nonlinear equilibrium paths, the Newton-Raphson iteration algorithm was used. Corresponding levels of the total potential energy were defined. The peculiarities of the effects of the initial imperfections were investigated. Special attention was focused on the influence of imperfections on the post-critical buckling mode. The stable and unstable paths of the nonlinear solution were separated. Obtained results were compared with those gained using ANSYS system.
Tensile buckling of advanced turboprops
Chamis, C. C.; Aiello, R. A.
1982-01-01
Theoretical studies were conducted to determine analytically the tensile buckling of advanced propeller blades (turboprops) in centrifugal fields, as well as the effects of tensile buckling on other types of structural behavior, such as resonant frequencies and flutter. Theoretical studies were also conducted to establish the advantages of using high performance composite turboprops as compared to titanium. Results show that the vibration frequencies are not affected appreciably prior to 80 percent of the tensile speed. Some frequencies approach zero as the tensile buckling speed is approached. Composites provide a substantial advantage over titanium on a buckling speed to weight basis. Vibration modes change as the rotor speed is increased and substantial geometric coupling is present.
Creep buckling analysis of shells
Energy Technology Data Exchange (ETDEWEB)
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.
Containment buckling program. [PWR; BWR
Energy Technology Data Exchange (ETDEWEB)
Anderson, C.A.; Bennett, J.G.
1981-01-01
The Containment Buckling program at the Los Alamos National Laboratory is aimed at evaluating the adequacy of the current design procedures for free standing steel nuclear containment shells against static and dynamic structural instability. Such buckling behavior will typically produce large displacements in the shell wall that will potentially violate seals around hatches and penetrations, or even produce puncture or tearing of the shell wall resulting in a loss of containment function. The ultimate goal of the program is to provide NRC with a basis for evaluating the associated licensing issues and to recommend appropriate changes and additions to the NRC Review Criteria.
Anisotropic surface tension of buckled fluid membrane
Noguchi, Hiroshi
2011-01-01
Solid sheets and fluid membranes exhibit buckling under lateral compression. Here, it is revealed that fluid membranes have anisotropic buckling surface tension contrary to solid sheets. Surprisingly, the surface tension perpendicular to the buckling direction shows stronger dependence than that parallel to it. Our theoretical predictions are supported by numerical simulations of a meshless membrane model. This anisotropic tension can be used to measure the membrane bending rigidity. It is al...
Mechanical Buckling of Arterioles in Collateral Development
Liu, Qin; Han, Hai-Chao
2012-01-01
Collateral arterioles enlarge in both diameter and length, and develop corkscrew-like tortuous patterns during remodeling. Recent studies showed that artery buckling could lead to tortuosity. The objective of this study was to determine arteriole critical buckling pressure and buckling pattern during arteriole remodeling. Arterioles were modeled as elastic cylindrical vessels with an elastic matrix support and underwent axial and radial growth. Our results demonstrated that arteriole critical...
Elastic buckling strength of corroded steel plates
Indian Academy of Sciences (India)
Ahmad Rahbar-Ranji
2013-02-01
Corrosion makes structures more vulnerable to buckling and yielding failures. It is common practice to assume a uniform thickness reduction for general corrosion. To estimate the remaining strength of corroded structures, typically a much higher level of accuracy is required, since the actual corroded structures have irregular surfaces. Elastic buckling of simply supported rectangular corroded plates are studied with one- and both-sided irregular surfaces. Eigenvalue analysis by using ﬁnite element method (FEM) is employed for computing Euler stress. The inﬂuence of various geometric and corrosion characteristics are investigated and it is found that the aspect ratio of the plate, the average thickness diminution, the standard deviation of thickness diminution and the amount of corrosion loss have inﬂuence on the reduction of buckling strength of the corroded plates. Buckling strength of one- and both-sided corroded plates are the same. In plates with low value of aspect ratio, reduction of buckling strength is negligible. Reduction of buckling strength is more prominent in plates with higher aspect ratio. Reduction of buckling strength is very sensitive to the amount of corrosion loss; the higher the amount of corrosion loss, the more reduction of buckling strength. Reduction of buckling strength is less sensitive to the standard deviation of thickness diminution.
Buckling of conical shell with local imperfections
Cooper, P. A.; Dexter, C. B.
1974-01-01
Small geometric imperfections in thin-walled shell structures can cause large reductions in buckling strength. Most imperfections found in structures are neither axisymmetric nor have the shape of buckling modes but rather occur locally. This report presents the results of a study of the effect of local imperfections on the critical buckling load of a specific axially compressed thin-walled conical shell. The buckling calculations were performed by using a two-dimensional shell analysis program referred to as the STAGS (Structural Analysis of General Shells) computer code, which has no axisymmetry restrictions. Results show that the buckling load found from a bifurcation buckling analysis is highly dependent on the circumferential arc length of the imperfection type studied. As the circumferential arc length of the imperfection is increased, a reduction of up to 50 percent of the critical load of the perfect shell can occur. The buckling load of the cone with an axisymmetric imperfections is nearly equal to the buckling load of imperfections which extended 60 deg or more around the circumference, but would give a highly conservative estimate of the buckling load of a shell with an imperfection of a more local nature.
On the analysis of viscoplastic buckling
DEFF Research Database (Denmark)
Mikkelsen, Lars Pilgaard
1993-01-01
For elastic-viscoplastic structures the classical elastic-plastic bifurcation approach to inelastic buckling is not valid. Only an elastic bifurcation point exists in the el~tic-viscoplastic case, and the inelastic buckling behaviour is controlled by a strong sensitivity to small imperfections...
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...... exhibit a large scatter caused by geometrical variations between test specimens. (C) 2007 Elsevier Ltd. All rights reserved....
Review of strain buckling: analysis methods
International Nuclear Information System (INIS)
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
Stochastic behavior of nanoscale dielectric wall buckling
Friedman, Lawrence H.; Levin, Igor; Cook, Robert F.
2016-01-01
The random buckling patterns of nanoscale dielectric walls are analyzed using a nonlinear multi-scale stochastic method that combines experimental measurements with simulations. The dielectric walls, approximately 200 nm tall and 20 nm wide, consist of compliant, low dielectric constant (low-k) fins capped with stiff, compressively stressed TiN lines that provide the driving force for buckling. The deflections of the buckled lines exhibit sinusoidal pseudoperiodicity with amplitude fluctuation and phase decorrelation arising from stochastic variations in wall geometry, properties, and stress state at length scales shorter than the characteristic deflection wavelength of about 1000 nm. The buckling patterns are analyzed and modeled at two length scales: a longer scale (up to 5000 nm) that treats randomness as a longer-scale measurable quantity, and a shorter-scale (down to 20 nm) that treats buckling as a deterministic phenomenon. Statistical simulation is used to join the two length scales. Through this approach, the buckling model is validated and material properties and stress states are inferred. In particular, the stress state of TiN lines in three different systems is determined, along with the elastic moduli of low-k fins and the amplitudes of the small-scale random fluctuations in wall properties—all in the as-processed state. The important case of stochastic effects giving rise to buckling in a deterministically sub-critical buckling state is demonstrated. The nonlinear multiscale stochastic analysis provides guidance for design of low-k structures with acceptable buckling behavior and serves as a template for how randomness that is common to nanoscale phenomena might be measured and analyzed in other contexts. PMID:27330220
Investigations for buckling risks of PFBR vessels
International Nuclear Information System (INIS)
Buckling analysis of reactor assembly components like main vessel, inner vessel, and roof slab support skirt have been carried out for the normal and seismic loadings corresponding to 0.1g SSE. The results have shown that, the above components are meeting the RCC-MR code limits for buckling with a convenient safety margin. In case, the higher level of seismic load of 0.2g SSE needs to be considered, it will call for some design modifications and further analysis of the above components. In the present work, some simplified approaches have been followed to incorporate the effects of seismic loads and imperfections in buckling. (author)
Medial Rectus Dehiscence following Buckling
Directory of Open Access Journals (Sweden)
Simi Zaka-ur-Rab, Manoj Shukla, Faisal Zubair, Akbar Saleem, Mohd. Shahim Sami
2008-01-01
Full Text Available Migration of silicone explants through rectus muscle insertion is a rare complication with very few casesreported. Anterior migration of a solid silicone band may occur if it is tight, placed anterior to the equatoror not properly anchored to the sclera. The band slowly erodes through the tendon of one or more rectimuscles allowing them to reattach spontaneously with scar tissue behind migrating element. The authorsdescribe a rare case of anterior migration of the buckle following encirclage by a 4mm silicone bandresulting in spontaneous disinsertion of medial rectus muscle where muscle disinsertion had not beenperformed peroperatively. This migration occurred in the absence of any predisposing factors. The muscledisinsertion was so gradual that the muscle got reinserted almost to its original insertion as a result ofwhich there was no heterotropia .
Exact buckling load of a restrained RC column
Krauberger, Nana; Saje, Miran; Planinc, Igor; Bratina, Sebastjan
2015-01-01
Theoretical foundation for the buckling load determination in reinforced concrete columns is described and analytical solutions for buckling loads of the Euler-type straight reinforced concrete columns given. The buckling analysis of the limited set of restrained reinforced concrete columns is also included, and some conclusions regarding effects of material non-linearity and restrain stiffhesses on the buckling loads and the buckling lengths are presented. It is shown that the material non-l...
Curved thin shell buckling behaviour
Directory of Open Access Journals (Sweden)
G. Forasassi
2007-08-01
Full Text Available Purpose: The aim of the paper is to evaluate buckling instabilities behaviour of long curved thin shell. Both initially straight and curved tubes are investigated with numerical and experimental assessment methods, in the context of NPP applications with an illustrative example for IRIS LWR integrated Steam Generator (SG tubes.Design/methodology/approach: In this study structural buckling response tube with combination effects of geometric imperfections as well as initially bent shape under external pressure load are investigated using a non linear finite element (MSC.MARC FEM code formulation analysis. Moreover results are presented, extending the findings of previous research activity works, carried out at Pisa University, on thin walled metal specimen.Findings: The experiments were conducted on Inconel 690 test specimen tube. The comparison between numerical and experimental results, for the same geometry and loading conditions, shows a good agreement between the elastic-plastic finite-element predictions and the experimental data.Research limitations/implications: The presented research results may be considered preliminary in the sense that it would be important to enlarge the statistical base of the results themselves, even if they are yet certainly meaningful to highlight the real problem, considering the relatively large variability of the geometrical imperfections and bending instabilities also in high quality production tubes.Originality/value: From the point of view of the practical implication, besides the addressed problem general interest in industrial plant technology, it is worth to stress that straight and curved axis tubes are foreseen specifically in innovative nuclear reactors SG design.
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.
Buckling optimisation of sandwich cylindrical panels
Abouhamzeh, M.; Sadighi, M.
2016-06-01
In this paper, the buckling load optimisation is performed on sandwich cylindrical panels. A finite element program is developed in MATLAB to solve the governing differential equations of the global buckling of the structure. In order to find the optimal solution, the genetic algorithm Toolbox in MATLAB is implemented. Verifications are made for both the buckling finite element code and also the results from the genetic algorithm by comparisons to the results available in literature. Sandwich cylindrical panels are optimised for the buckling strength with isotropic or orthotropic cores with different boundary conditions. Results are presented in terms of stacking sequence of fibers in the face sheets and core to face sheet thickness ratio.
Scleral buckle infection with aspergillus flavus
Directory of Open Access Journals (Sweden)
Bouhaimed Manal
2008-01-01
Full Text Available Purpose: To present a case of scleral buckle infection with Aspergillus flavus in a tertiary eye center in Saudi Arabia. Methods: A retrospective case report of a 28-year-old Saudi male who presented with a six-month history of conjunctival injection and discharge from the left eye which had undergone uncomplicated conventional retinal detachment surgery, at the King Khaled Eye Specialist Hospital in Riyadh, Saudi Arabia, in the form of cryopexy, subretinal fluid drainage and scleral buckle (grooved segmental sponge and circumferential band with sleeve for a macula on retinal detachment four years earlier. A diagnosis of infected extruded scleral buckle was made and the buckle was removed. Results: The infected scleral buckle was removed under local anesthesia with administration of sub-conjunctival irrigation of 50 mg solution of Vancomycin, and sub-conjunctival injection of 25mg of Vancomycin. Post operative microbiological studies revealed infection with silver staining of moderate Aspergillus flavus hyphae. Visual acuity of the left eye improved from 20/200 before surgery to 20/60 in the two years follow-up visit. Conclusion: This case report indicates the importance of considering infection with multiple organisms - including fungal ones - in cases of scleral buckle infections in our population.
A Reduction Factor for Buckling Load of Spherical Cap Shells
Directory of Open Access Journals (Sweden)
P.N. Khakina
2011-12-01
Full Text Available The classical buckling theory usually overestimates the buckling load of shells. In this study, a reduction factor is determined using geometrical parameters so as to reduce the classical buckling load to a more realistic value based on the post-buckling load. It is observed that the buckling load is directly proportional to the thickness and rise and inversely proportional to the span of the spherical cap. Finite element modeling and simulation using ABAQUS was conducted to determine the buckling behavior of a spherical cap shell subjected to different initial geometrical imperfections. The load-deflection curves drawn from the simulation formed a plateau at the post-buckling load. It is observed that as the initial geometrical imperfection is increased, the value of the initial buckling load is almost the same as the value of the post-buckling load on the plateau. The results obtained from different shells were used to derive a formula for the reduction factor.
Creep buckling problems in fast reactor components
International Nuclear Information System (INIS)
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
Optomechanical Cavity with a Buckled Mirror
Yuvaraj, D; Shtempluck, Oleg; Buks, Eyal
2012-01-01
We study an optomechanical cavity, in which a buckled suspended beam serves as a mirror. The mechanical resonance frequency of the beam obtains a minimum value near the buckling temperature. Contrary to the common case, in which self-excited oscillations of the suspended mirror are optically induced by injecting blue detuned laser light, in our case self-excited oscillations are observed with red detuned light. These observations are attributed to a retarded thermal (i.e. bolometric) force acting on the buckled mirror in the inwards direction (i.e. towards to other mirror). With relatively high laser power other interesting effects are observed including period doubling of self-excited oscillations and intermode coupling.
Buckling instability in amorphous carbon films
Zhu, X. D.; Narumi, K.; Naramoto, H.
2007-06-01
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 °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 °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 check tools for plate panel and column structures
Vuorela, Pia
2014-01-01
Buckling is, besides yielding, one of the major causes of failures in structures, and buckling checks are therefore an integral part of strength analyses. Checks can be performed either with methods requiring heavy numerical calculations or with equations based on rules and recommendations from a classification society. Numerical calculations are extremely time-consuming and commercial buckling check programs are expensive. There is therefore a need for buckling check tools based on the recom...
21 CFR 886.3300 - Absorbable implant (scleral buckling method).
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Absorbable implant (scleral buckling method). 886... SERVICES (CONTINUED) MEDICAL DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3300 Absorbable implant (scleral buckling method). (a) Identification. An absorbable implant (scleral buckling method) is a...
Dynamic buckling of actin within filopodia
DEFF Research Database (Denmark)
Leijnse, Natascha; Oddershede, Lene B; Bendix, Pól Martin
2015-01-01
Filopodia are active tubular structures protruding from the cell surface which allow the cell to sense and interact with the surrounding environment through repetitive elongation-retraction cycles. The mechanical behavior of filopodia has been studied by measuring the traction forces exerted on...... external substrates.(1) These studies have revealed that internal actin flow can transduce a force across the cell surface through transmembrane linkers like integrins. In addition to the elongation-retraction behavior filopodia also exhibit a buckling and rotational behavior. Filopodial buckling in...
Triangular buckling patterns of twisted inextensible strips
Korte, A P; van der Heijden, G H M
2010-01-01
When twisting a strip of paper or acetate under high longitudinal tension, one observes, at some critical load, a buckling of the strip into a regular triangular pattern. Very similar triangular facets have recently been observed in solutions to a new set of geometrically-exact equations describing the equilibrium shape of thin inextensible elastic strips. Here we formulate a modified boundary-value problem for these equations and construct post-buckling solutions in good agreement with the observed pattern in twisted strips. We also study the force-extension and moment-twist behaviour of these strips by varying the mode number n of triangular facets.
Buckling Instability of Self-Assembled Colloidal Columns
Swan, James W.; Vasquez, Paula A.; Furst, Eric M.
2014-09-01
Suspended, slender self-assembled domains of magnetically responsive colloids are observed to buckle in microgravity. Upon cessation of the magnetic field that drives their assembly, these columns expand axially and buckle laterally. This phenomenon resembles the buckling of long beams due to thermal expansion; however, linear stability analysis predicts that the colloidal columns are inherently susceptible to buckling because they are freely suspended in a Newtonian fluid. The dominant buckling wavelength increases linearly with column thickness and is quantitatively described using an elastohydrodynamic model and the suspension thermodynamic equation of state.
Buckling modes of elastic thin films on elastic substrates
Mei, Haixia; Huang, Rui; Chung, Jun Young; Stafford, Christopher M.; Yu, Hong-Hui
2007-04-01
Two buckling modes have been observed in thin films: buckle delamination and wrinkling. This letter identifies the conditions for selecting the favored buckling modes for elastic films on elastic substrates. Transition from one buckling mode to another is predicted as the stiffness ratio between the substrate and the film or is predicted for variation of the stiffness ratio between the substrate and the film or variation of theinterfacial defect size. The theoretical results are demonstrated experimentally by observing the coexistence of both buckling modes and mode transition in one film-substrate system.
Crack buckling in soft gels under compression
Institute of Scientific and Technical Information of China (English)
Rong Long; Chung-Yuen Hui
2012-01-01
Recent interest in designing soft gels with high fracture toughness has called for simple and robust methods to test fracture behavior.The conventional method of applying tension to a gel sample suffers from a difficulty of sample gripping.In this paper,we study a possible fracture mechanism of soft gels under uni-axial compression.We show that the surfaces of a pre-existing crack,oriented parallel to the loading axis,can buckle at a critical compressive stress.This buckling instability can open the crack surfaces and create highly concentrated stress fields near the crack tip,which can lead to crack growth.We show that the onset of crack buckling can be deduced by a dimensional argument combined with an analysis to determine the critical compression needed to induce surface instabilities of an elastic half space.The critical compression for buckling was verified for a neoHookean material model using finite element simulations.
Edmondson, S; Frieda, K; Comrie, JE; Onck, PR; Huck, WTS
2006-01-01
Buckle-driven delamination and subsequent collapse of strained thin polymer films upon triggered release from the substrate is exploited to fabricate striking, well-defined ridging patterns (see figure). An analysis of these patterns is presented, including the effects of film thickness and the exte
Buckling analysis of spent fuel basket
International Nuclear Information System (INIS)
The basket for a spent fuel shipping cask is subjected to compressive stresses that may cause global instability of the basket assemblies or local buckling of the individual members. Adopting the common buckling design practice in which the stability capacity of the entire structure is based on the performance of the individual members of the assemblies, the typical spent fuel basket, which is composed of plates and tubular structural members, can be idealized as an assemblage of columns, beam-columns and plates. This report presents the flexural buckling formulas for five load cases that are common in the basket buckling analysis: column under axial loads, column under axial and bending loads, plate under uniaxial loads, plate under biaxial loadings, and plate under biaxial loads and lateral pressure. The acceptance criteria from the ASME Boiler and Pressure Vessel Code are used to determine the adequacy of the basket components. Special acceptance criteria are proposed to address the unique material characteristics of austenitic stainless steel, a material which is frequently used in the basket assemblies
Plastic Buckling of Cylindrical Shells Under Transverse Loading
Institute of Scientific and Technical Information of China (English)
ZHANG Chonghou; LIU Yansheng; Yoshiaki Goto
2008-01-01
Thick cylindrical shells under transverse loading exhibit an elephant foot buckling mode, whereas moderately thick cylindrical shells show a diamond buckling mode. There exists some intermediate geome- try at which the transition between buckling modes can take place. This behavior is significantly influenced by the radius-to-thickness ratio and the material yield strength, rather than the length-to-radius ratio and the axial force. This paper presents a critical value at which the transition of buckling modes occurs as a func- tion of the radius-to-thickness ratio and the material yield strength. The result shows that the circumferential wave number of the diamond buckling mode increases with decreasing wall thickness. The strain concentra- tion is also intensified for the diamond buckling modes compared with the elephant foot buckling modes.
Buckling of foam stabilised composite structures
Rivallant, Samuel; Ferrero, Jean-François; Barrau, Jean-Jacques
2003-01-01
An analytical modelling of the symmetrical wrinkling is proposed : from original assumptions on displacements within the core, and from an energy minimisation method, it is possible to predict critical loads and buckling modes better than traditional models do, and to distinguish the influence of each structure component. Compression tests were carried out on sandwich structures to validate the model. Little curved structures were also tested to estimate the influence of skin curvature on rup...
Voltage-Induced Buckling of Dielectric Films using Fluid Electrodes
Tavakol, Behrouz
2016-01-01
Accurate and integrable control of different flows within microfluidic channels is crucial to further development of lab-on-a-chip and fully integrated adaptable structures. Here we introduce a flexible microactuator that buckles at a high deformation rate and alters the downstream fluid flow. The microactuator consists of a confined, thin, dielectric film that buckles into the microfluidic channel when exposed to voltage supplied through conductive fluid electrodes. We estimate the critical buckling voltage, and characterize the buckled shape of the actuator. Finally, we investigate the effects of frequency, flow rate, and the pressure differences on the behavior of the buckling structure and the resulting fluid flow. These results demonstrate that the voltage--induced buckling of embedded microstructures using fluid electrodes provides a means for high speed attenuation of microfluidic flow.
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.
Dynamic buckling behavior of thin metal film lines from substrate
Wu, Dan; Xie, Huimin; Wang, Heling; Zhang, Jie; Li, Chuanwei
2014-10-01
The dynamic buckling behavior of thin films from substrate is studied in this work. The experimental results show that the buckling morphology of the constantan film lines from the polymer substrate is inconsistent and non-sinusoidal, which is different from the sinusoidal form of the buckling morphology under static loads. The plastic deformation of the film lines results in the non-sinusoidal buckling morphology and residual deformation when unloaded. Finite element modeling results with regard to the plastic dissipation of the constantan film lines reveal that the plastic dissipation suppresses the buckling-driven delaminating under impact loads. This study will give some new perspectives on the buckling behavior of thin film from substrate.
Buckled graphene for efficient energy harvest, storage and conversion
Jiang, Jin-Wu
2016-10-01
Buckling is one of the most common phenomena in atom-thick layered structures like graphene. While the buckling phenomenon usually causes disaster for most nanodevices, we illustrate one positive application of buckled graphene for energy harvest, storage and conversion. More specifically, we perform molecular dynamical simulations to show that buckled graphene can be used to collect wasted mechanical energy and store the energy in the form of internal knotting potential. Through strain engineering, the knotting potential can be converted into useful kinetic (thermal) energy that is highly concentrated at the free edges of buckled graphene. The present study demonstrates potential applications of buckled graphene for converting dispersed wasted mechanical energy into concentrated useful kinetic (thermal) energy.
Buckled graphene for efficient energy harvest, storage and conversion.
Jiang, Jin-Wu
2016-10-01
Buckling is one of the most common phenomena in atom-thick layered structures like graphene. While the buckling phenomenon usually causes disaster for most nanodevices, we illustrate one positive application of buckled graphene for energy harvest, storage and conversion. More specifically, we perform molecular dynamical simulations to show that buckled graphene can be used to collect wasted mechanical energy and store the energy in the form of internal knotting potential. Through strain engineering, the knotting potential can be converted into useful kinetic (thermal) energy that is highly concentrated at the free edges of buckled graphene. The present study demonstrates potential applications of buckled graphene for converting dispersed wasted mechanical energy into concentrated useful kinetic (thermal) energy.
Method for studying the plastic buckling of shells. Testing
International Nuclear Information System (INIS)
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
Anisotropic growth of buckling-driven wrinkles in graphene monolayer
International Nuclear Information System (INIS)
We theoretically and numerically investigate the growth of buckling-driven wrinkles in graphene monolayers. It is found that the growth of buckling-driven wrinkles in a graphene monolayer is remarkably chirality- and size-dependent. In small sizes, the flexural response of a graphene sheet cannot be accurately described by the classical Euler regime, and the non-continuum effect leads to zigzag-along-preferred buckling. With the increase of size, the width/length ratio α of the compressed region plays an important role in the growth of buckling-driven wrinkles. When α < 0.5, the oblique buckling happens in armchair-along compression; when 0.5 < α < 1.0, the effect of edge warp leads to zigzag-along-preferred buckling. When 1.0 < α < 3.0, the potential energy density difference due to chiral bending stiffness leads to armchair-along-preferred buckling. When α > 3.0, the non-continuum effect and chiral bending stiffness can both be neglected, and the buckling in a graphene monolayer is isotropic. The chirality-along-preferred transition of compressed buckling in a graphene monolayer leads to an improved fundamental understanding of the dynamics mechanism of graphene-based nanodevices, especially for the nanodevices with high frequency response. (paper)
GBT pre-buckling and buckling analyses of thin-walled members under axial and transverse loads
Taig, Gerard; Ranzi, Gianluca; Luongo, Angelo
2016-03-01
This paper presents an analytical approach for pre-buckling and buckling analyses of thin-walled members implemented within the framework of the Generalised Beam Theory (GBT). With the proposed GBT cross-sectional analysis, the set of deformation modes used in the analysis is represented by the dynamic modes obtained for an unrestrained frame representing the cross-section. In this manner, it is possible to account for the deformability of the cross-section in both pre-buckling and buckling analyses. Different loading conditions, including both axial and transverse arrangements, are considered in the applications to highlight under which circumstances the use of the GBT deformation modes is required for an adequate representation of the pre-buckling and buckling response. The numerical results have been validated against those determined using a shell element model developed in the finite element software ABAQUS.
On the buckling of an elastic rotating beam
DEFF Research Database (Denmark)
Furta, Stanislaw D.; Kliem, Wolfhard; Pommer, Christian
1997-01-01
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...
Elastic buckling analysis of corroded stiffened plates with irregular surfaces
Indian Academy of Sciences (India)
Ahmad Rahbar-Ranji
2015-02-01
Numerical simulation is used to study the influence of corrosion damage in stiffened plates focusing on elastic buckling strength. Three-dimensional specta are used to simulate geometries of corroded surfaces and finite element method is employed for computing Euler stress of stiffened plates. The influence of corrosion patterns, amount of corrosion loss and roughness of surface are investigated. Ratio of Euler stress of corroded stiffened plate over Euler stress of un-corroded stiffened plate is used to characterize the effects of corrosion on reduction of buckling strength. Results show that reduction of buckling strength is very sensitive to the amount of corrosion loss and roughness of surface, but less sensitive to the location of corroded region. The potential for decrease in buckling strength as a consequence of corrosion is found to depend on the dominant buckling mode. Residual buckling strength is reduced by as much as 12% for the interaction of plate-web-torsional buckling mode, and by 2% for column buckling.
Dynamic buckling of stiffened plates subjected to explosion impact loads
Wang, J.; Guo, J.; Yao, X. L.; Zhang, A. M.
2016-03-01
The dynamic buckling characteristics and criteria of a ship's structural stiffened plate subjected to underwater explosion impact loads are investigated in this study. Using the structural deformations observed in the experiments of underwater explosions against a plated grillage model, the mode shapes of the dynamic buckling were obtained. Through the construction of a computational model of stiffened plates subjected to an underwater explosion shock wave, the impact load was theoretically calculated and transformed into a rectangular pulse. According to the different response patterns of stiffened plates under different impact loads, a dynamic buckling criterion for the stiffened plates subjected to an explosion shock wave was proposed. Additionally, the static buckling phenomenon in the stiffened plates was analysed based on the minimum excess principle. In combination with the dynamic buckling criterion, the effects of various stiffening configurations on the dynamic and static buckling loads are discussed. The calculation results show that when the equivalent rectangular pulse is 2-3 times that of the static buckling load, the responses of the stiffened plates under the original shock load and the equivalent rectangular pulse are virtually identical. The impact load amplitude is the primary influencing factor in the dynamic buckling of stiffened plates subjected to underwater explosive impact loads. The stiffened plate aspect ratio has a substantial influence on the dynamic load factor. The analytical method and results are presented, which can be used to design stiffened optimum hull structures to enhance the dynamic load carrying capacity to withstand underwater shock damage.
Dynamic torsional buckling of multi-walled carbon nanotubes embedded in an elastic medium
Institute of Scientific and Technical Information of China (English)
Chengqi Sun; Kaixin Liu; Guoxing Lu
2008-01-01
In this paper the dynamic torsional buckling of multi-walled carbon nanotubes (MWNTs) embedded in an elastic medium is studied by using a continuum mechan-ics model. By introducing initial imperfections for MWNTs and applying the preferred mode analytical method, a buck-ling condition is derived for the buckling load and associ-ated buckling mode. In particular, explicit expressions are obtained for embedded double-walled carbon nanotubes (DWNTs). Numerical results show that, for both the DWNTs and embedded DWNTs, the buckling form shifts from the lower buckling mode to the higher buckling mode with increasing the buckling load, but the buckling mode is invari-able for a certain domain of the buckling load. It is also indicated that, the surrounding elastic medium generally has effect on the lower buckling mode of DWNTs only when compared with the corresponding one for individual DWNTs.
Electrical characterization of a buckling thermal energy harvester
Trioux, E.; Rufer, L.; Monfray, S.; Skotnicki, T.; Muralt, P.; Basrour, S.
2015-12-01
This paper presents the electrical characterizations of a novel concept for thermal energy harvesting at micro scale. The devices presented here are based on a two-step transduction combining thermo-mechanical and piezoelectric conversion. The piezoelectric layer is directly integrated into a buckling bilayer plate made of aluminium and aluminium nitride. For the first time, we have characterized the structures electrically and we have investigated their output power during the buckling. Firstly, we have used an insulating tip to make the plate buckle in order to have an estimation of the output power due to piezoelectric contribution only, and to eliminate any pyroelectric contribution that might be present during the thermal actuation. Then, we heated up the structure and we collected the output signal with an instrumentation amplifier in order to measure the voltage generated during the buckling. The output power during the mechanical and the thermal buckling is compared in the paper.
Global lateral buckling analysis of idealized subsea pipelines
Institute of Scientific and Technical Information of China (English)
刘润; 刘文彬; 吴新利; 闫澍旺
2014-01-01
In order to avoid the curing effects of paraffin on the transport process and reduce the transport difficulty, usually high temperature and high pressure are used in the transportation of oil and gas. The differences of temperature and pressure cause additional stress along the pipeline, due to the constraint of the foundation soil, the additional stress can not release freely, when the additional stress is large enough to motivate the submarine pipelines buckle. In this work, the energy method is introduced to deduce the analytical solution which is suitable for the global buckling modes of idealized subsea pipeline and analyze the relationship between the critical buckling temperature, buckling length and amplitude under different high-order global lateral buckling modes. To obtain a consistent formulation of the problem, the principles of virtual displacements and the variation calculus for variable matching points are applied. The finite element method based on elasto-plastic theory is used to simulate the lateral global buckling of the pipelines under high temperature and pressure. The factors influencing the lateral buckling of pipelines are further studied. Based upon some actual engineering projects, the finite element results are compared with the analytical ones, and then the influence of thermal stress, the section rigidity of pipeline, the soil properties and the trigging force to the high order lateral buckling are discussed. The method of applying the small trigging force on pipeline is reliable in global buckling numerical analysis. In practice, increasing the section rigidity of a pipeline is an effective measure to improve the ability to resist the global buckling.
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.
Early detection of local buckling in structural members
Ali, Bashir; Sundaresan, Mannur J.; Schulz, Mark J.; Hughes, Derke
2005-05-01
Most structural health monitoring analyses to date have focused on the determination of damage in the form of crack growth in metallic materials or delamination or other types of damage growth in composite materials. However, in many applications, local instability in the form of buckling can be the precursor to more extensive damage and unstable failure of the structure. If buckling could be detected in the very early stages, there is a possibility of taking preventive measures to stabilize and save the structure. Relatively few investigations have addressed this type of damage initiation in structures. Recently, during the structural health monitoring of a wind turbine blade, local buckling was identified as the cause of premature failure. A stress wave propagation technique was used in this test to detect the precursor to the buckling failure in the form of early changes in the local curvature of the blade. These conditions have also been replicated in the laboratory and results are reported in this paper. A composite column was subjected to axial compression to induce various levels of buckling deformation. Two different techniques were used to detect the precursors to buckling in this column. The first identifier is the change in the vibration shapes and natural frequencies of the column. The second is the change in the characteristics of diagnostic Lamb waves during the buckling deformation. Experiments indicate that very small changes in curvature during the initial stages of buckling are detectable using the structural health monitoring techniques. The experimental vibration characteristics of the column with slight initial curvatures compared qualitatively with finite element results. The finite element analysis is used to identify the frequencies that are most sensitive to buckling deformation, and to select suitable locations for the placement of sensors that can detect even small changes in the local curvature.
Pseudo-nonlinear dynamic analysis of buckled pipes
Gültekin Sınır, B.
2013-02-01
In this study, the post-divergence behavior of fluid-conveying pipes supported at both ends is investigated using the nonlinear equations of motion. The governing equation exhibits a cubic nonlinearity arising from mid-plane stretching. Exact solutions for post-buckling configurations of pipes with fixed-fixed, fixed-hinged, and hinged-hinged boundary conditions are investigated. The pipe is stable at its original static equilibrium position until the flow velocity becomes high enough to cause a supercritical pitchfork bifurcation, and the pipe loses stability by static divergence. In the supercritical fluid velocity regime, the equilibrium configuration becomes unstable and bifurcates into multiple equilibrium positions. To investigate the vibrations that occur in the vicinity of a buckled equilibrium position, the pseudo-nonlinear vibration problem around the first buckled configuration is solved precisely using a new solution procedure. By solving the resulting eigenvalue problem, the natural frequencies and the associated mode shapes of the pipe are calculated. The dynamic stability of the post-buckling configurations obtained in this manner is investigated. The first buckled shape is a stable equilibrium position for all boundary conditions. The buckled configurations beyond the first buckling mode are unstable equilibrium positions. The natural frequencies of the lowest vibration modes around each of the first two buckled configurations are presented. Effects of the system parameters on pipe behavior as well as the possibility of a subcritical pitchfork bifurcation are also investigated. The results show that many internal resonances might be activated among the vibration modes around the same or different buckled configurations.
Electromechanical Dynamics Analysis of Buckling Microstructure For Micromirror
Energy Technology Data Exchange (ETDEWEB)
Jia, Jianyuan; Chen, Guimin; Fan, Guobin [Xidian Univ., Jiangxi (China)
2002-11-15
The electromechanical dynamics characteristic and emulation of buckling microstructure for digital micromirror device are studied. The microstructure of digital micromirror device based on buckling theory is designed and its electromechanical dynamics model is established. The hidden functions in the dynamics model are found out by numerical methods such as Runge-Kutta method and Finite Element method. A numerical emulation to the whole motion differential equation has been presented, and a continuous angular displacement curve of micro-reflectmirror is obtained. At last, it is concluded that the buckling microstructure has an advantage of light beam stability.
Experimental validation of CASTEM code for buckling problems
International Nuclear Information System (INIS)
For validating the buckling analysis capability of CASTEM code which is used for the buckling design of Prototype Fast Breeder Reactor (PFBR) vessels, a few experiments have been carried out at Indira Gandhi Centre for Atomic Research (IGCAR)in Kalpakkam. Experiments were conducted on aluminium cylindrical shells under axial compression and stainless steel cylindrical shells under external pressure and transverse shear loading. This paper presents the results of experimental and associated theoretical buckling studies performed using the code INCA. (author). 3 refs., 9 figs., 3 tabs
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......, 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...
Buckling and vibration of a rotating beam†
Nachman, A.
1986-09-01
The equations for the vibration of a rotating beam, such as a helicopter blade, are exhibited. The beam is elastic (in general non-linearly so), the description is geometrically exact, the axis of rotation does not necessarily pass through the beam's clamped end (precession) and cross-sectional shearing is accounted for by using a director theory. Particular attention is paid to the impossibility of vibration (or buckling) confined to a plane making an angle β to the axis of rotation unless β=π/2 (orπ/2 or 0) or rotatory inertia is neglected. For purposed of illustration the analysis is specialized to describe Euler-Bernoulli and Timoshenko beams.
Advances in Shell Buckling: Theory and Experiments
Thompson, J. Michael T.
In a recent feature article in this journal, coauthored by Gert van der Heijden, I described the static-dynamic analogy and its role in understanding the localized post-buckling of shell-like structures, looking exclusively at integrable systems. We showed the true significance of the Maxwell energy criterion load in predicting the sudden onset of "shock sensitivity" to lateral disturbances. The present paper extends the survey to cover nonintegrable systems, such as thin compressed shells. These exhibit spatial chaos, generating a multiplicity of localized paths (and escape routes) with complex snaking and laddering phenomena. The final theoretical contribution shows how these concepts relate to the response and energy barriers of an axially compressed cylindrical shell. After surveying NASA's current shell-testing programme, a new nondestructive technique is proposed to estimate the "shock sensitivity" of a laboratory specimen that is in a compressed metastable state before buckling. A probe is used to measure the nonlinear load-deflection characteristic under a rigidly applied lateral displacement. Sensing the passive resisting force, it can be plotted in real time against the displacement, displaying an equilibrium path along which the force rises to a maximum and then decreases to zero: having reached the free state of the shell that forms a mountain-pass in the potential energy. The area under this graph gives the energy barrier against lateral shocks. The test is repeated at different levels of the overall compression. If a symmetry-breaking bifurcation is encountered on the path, computer simulations show how this can be suppressed by a controlled secondary probe tuned to deliver zero force on the shell.
Scleral buckling biomaterials and implants for retinal detachment surgery.
Baino, Francesco
2010-11-01
Scleral buckling is a widely used surgical procedure that aims at repairing retinal detachments. Many materials and procedural techniques have been variously proposed and tested in an attempt to find the best combination for providing optimal results to the patient. This review highlights the evolution of scleral buckling implants and chronicles the main advances that have been made in such a context. Specifically, the limitations of the materials and implants fallen in disuse, as well as the advantages of currently adopted devices are critically examined and discussed. Future directions for the research are considered, underlining in particular the great potential carried by the development of accurate mathematical models for describing the postoperative evolution of buckled eye. These analytical models, supported by a comprehensive data set provided by advanced techniques of medical investigations, may become useful tools for helping surgeons to choose, and to design if necessary, the best buckling material and configuration to be used in each specific clinical case.
Buckling and failure characteristics of graphite-polyimide shear panels
Shuart, M. J.; Hagaman, J. A.
1983-01-01
The buckling and failure characteristics of unstiffened, blade stiffened, and hat stiffened graphite-polyimide shear panels are described. The picture frame shear test is used to obtain shear stress-strain data at room temperature and at 316 deg C. The experimental results are compared with a linear buckling analysis, and the specimen failure modes are described. The effect of the 316 deg C test temperature on panel behavior are discussed.
Improvement of the axial buckling capability of elliptical cylindrical shells
Paschero, Maurizio
2008-01-01
A rather thorough and novel buckling analysis of an axially-loaded orthotropic circular cylindrical shell is formulated. The analysis assumes prebuckling rotations are negligible and uses a unique re-defining of the orthotropic material properties in terms of a so-called geometric mean isotropic (GMI) material. Closed-form expressions for the buckling stress in terms of cylinder geometry and orthotropic material properties are presented, the particular closed form depending on ...
Buckling Analysis of Woven Glass Epoxy Laminated Composite Plate
M Mohan Kumar
2013-01-01
Buckling behavior of laminated composite plates subjected to in-plane loads is an important consideration in the preliminary design of aircraft components. The sizing of many structural subcomponents of the aircraft structures is often determined by stability constraints. The objective of the current study is to understand the influence of the length-to-thickness ratio, the aspect ratio, the fiber orientation and the cut-out shapes on the buckling load for the glass epoxy laminated composit...
Lateral buckling and axial walking of surface laid subsea pipeline
Obele, Ifenna
2013-01-01
Subsea pipelines are increasingly being required to operate at high temperature and pressure HT/HP. The pipeline installed on the seabed and left exposed have a potential to buckle, walk and change configuration under high temperature and pressure (HT/HP). This could lead to failure of the Pipeline if buckling and walking is not properly controlled or mitigated. The objective of the thesis work is to study and understand the influence of pipeline-soil interaction on the design ...
Local and distortional buckling of perforated steel wall studs
Kesti, Jyrki
2000-01-01
The local and distortional buckling behaviour of flange and web-stiffened compression members was investigated. In particular, the behaviour of web-perforated sections was investigated both numerically and experimentally. Perforation reduces the perpendicular flexural stiffness of the web and thus particularly reduces the distortional buckling strength of the section. The main task of the research was to develop a design method for estimating the compression capacity of a perforated steel wal...
Buckling Analysis of Functionally Graded Plates with Simply Supported Edges
Directory of Open Access Journals (Sweden)
Megueni ABDELKADER
2009-12-01
Full Text Available Thermal buckling analyses of S-FGM are investigated by using first order shear deformation theory. Material properties are varied continuously in the thickness direction according to a sigmoid distribution. The thermal buckling behaviours under uniform, linear and sinusoidal temperature rise across the thickness are analyzed. 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 classic plate theory (CPT.
Wing Panel Design with Novel Skin-Buckling Containment Features
Houston, G; Quinn, D.; Murphy, A; Bron, F.
2016-01-01
The impact of buckling containment features on the stability of thin-gauge fuselage, metallic stiffened panels has previously been demonstrated. With the continuing developments in manufacturing technology, such as welding, extrusion, machining, and additive layer manufacture, understanding the benefits of additional panel design features on heavier applications, such as wing panels, is timely. This compression testing of thick-gauge panels with and without buckling containment features has b...
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)
BUCKLING ANALYSES OF A HEAVY COLUMN CONSIDERATED IN WATER
Directory of Open Access Journals (Sweden)
Yeliz PEKBEY
2008-02-01
Full Text Available In 1744, the critical buckling load with the assumption of uniform cross-section without weight of column were computed by Euler. Whenever an economical solution is required, the weight of column must be considered for solution of buckling analyses. In literature, the critical buckling load and asymptotic behaviour of heavy column in condition of atmosphere have inverstigated for ten different support types. When this literature is examined, it is stated that the differential equations of for four different suppport types in condition of water is similar to condition of atmosphere. However, the differential equations of other four different suppport types in condition of water is different from to condition of atmosphere. And it is stated that the critical buckling load these different suppport types in condition of water is not calculated from condition of atmosphere. The goals of this paper are to develop self weight buckling of column at its top fixed and lower end fixed-roller supported in condition of water. This paper, presents a analytical method for calculating the critical buckling load of the heavy column.
Early detection of local buckling in composite bars
Sundaresan, Mannur J.; Ali, Bashir; Ferguson, Frederick; Schulz, Mark J.
2002-11-01
Most structural health monitoring analyses to date have focused on the determination of damage in the form of crack growth in metallic materials or delamination or other types of damage growth in composite materials. However, in many applications local instability in the form of buckling can be the precursor to more extensive damage and unstable failure of the structure. If buckling could be detected in the very early stages, there is a possibility of taking preventive measures to stabilize and save the structure. Relatively few investigations have addressed this type of damage initiation in structures. Recently, during the structural health monitoring of wind turbine blades, local buckling was identified as the cause of premature failure. Results from this investigation suggested that stress waves could be used for detecting the early signs of change in the local curvature that precedes buckling type of failure in this structure. These conditions have been replicated in the laboratory and detailed investigation on the ability of low frequency vibrations to detect the buckling displacement has been carried out. The experiment was performed on a composite bar. The results clearly show that low frequency vibrations could be used to detect the onset of buckling in which the local deflection is only of the order of 0.25 inches.
Buckling Analysis of Woven Glass Epoxy Laminated Composite Plate
Directory of Open Access Journals (Sweden)
M Mohan Kumar
2013-07-01
Full Text Available Buckling behavior of laminated composite plates subjected to in-plane loads is an important consideration in the preliminary design of aircraft components. The sizing of many structural subcomponents of the aircraft structures is often determined by stability constraints. The objective of the current study is to understand the influence of the length-to-thickness ratio, the aspect ratio, the fiber orientation and the cut-out shapes on the buckling load for the glass epoxy laminated composite plate in clamped-free-clamped-free configuration by FE analysis using MSC.Patran/Nastran. Initially, buckling analysis was carried out on aluminum plates, both; experimentally and numerically; for the two different geometric configurations to predict the critical buckling load and the test results were compared with the FEA predictions, to check the validity of the analysis methodology. The same methodology was further followed for analyzing the buckling behavior of the composite plates. The results shows the effect of orientation of fiber, aspect ratio, cut-out shape and lengthto-thickness ratio on the buckling of the glass epoxy laminated composite plate
Flexural-torsional buckling behavior of aluminum alloy beams
Institute of Scientific and Technical Information of China (English)
Xiaonong GUO; Zhe XIONG; Zuyan SHEN
2015-01-01
This paper presents an investigation on the flexural-torsional buckling behavior of aluminum alloy beams （AAB）. First, based on the tests of 14 aluminum alloy beams under concentrated loads, the failure pattern, load- deformation curves, bearing capacity and flexural-torsional buckling factor are studied. It is found that all the beam specimens collapsed in the flexuml-torsional buckling with excessive deformation pattern. Moreover, the span, loading location and slenderness ratio influence the flexural-torsional buckling capacity of beams significantly. Secondly, besides the experiments, a finite element method （FEM） analysis on the flexural-torsional buckling behavior of AAB is also conducted. The main parameters in the FEM analysis are initial imperfection, material property, cross-section and loading scheme. According to the analytical results, it is indicated that the FEM is reasonable to capture mechanical behavior of AAB. Finally, on the basis of the experimental and analytical results, theoretical formulae to estimate the flexural- torsional buckling capacity of AAB are proposed, which could improve the application of present codes for AAB.
Buckle Driven Delamination in Thin Hard Film Compliant Substrate Systems
Moody, N. R.; Reedy, E. D.; Corona, E.; Adams, D. P.; Kennedy, M. S.; Cordill, M. J.; Bahr, D. F.
2010-06-01
Deformation and fracture of thin films on compliant substrates are key factors constraining the performance of emerging flexible substrate devices. [1-3] These systems often contain layers of thin polymer, ceramic and metallic films and stretchable interconnects where differing properties induce high normal and shear stresses. [4] As long as the films remain bonded to the substrates, they may deform far beyond their freestanding form. Once debonded, substrate constraint disappears leading to film failure. [3] Experimentally it is very difficult to measure properties in these systems at sub-micron and nanoscales. Theoretically it is very difficult to determine the contributions from the films, interfaces, and substrates. As a result our understanding of deformation and fracture behavior in compliant substrate systems is limited. This motivated a study of buckle driven delamination of thin hard tungsten films on pure PMMA substrates. The films were sputter deposited to thicknesses of 100 nm, 200 nm, and 400 nm with a residual compressive stress of 1.7 GPa. An aluminum oxide interlayer was added on several samples to alter interfacial composition. Buckles formed spontaneously on the PMMA substrates following film deposition. On films without the aluminum oxide interlayer, an extensive network of small telephone cord buckles formed following deposition, interspersed with regions of larger telephone cord buckles. (Figure 1) On films with an aluminum oxide interlayer, telephone cord buckles formed creating a uniform widely spaced pattern. Through-substrate optical observations revealed matching buckle patterns along the film-substrate interface indicating that delamination occurred for large and small buckles with and without an interlayer. The coexistence of large and small buckles on the same substrate led to two distinct behaviors as shown in Figure 2 where normalized buckle heights are plotted against normalized film stress. The behaviors deviate significantly from
Buckle Driven Delamination in Thin Hard Film Compliant Substrate Systems
Directory of Open Access Journals (Sweden)
Bahr D.F.
2010-06-01
Full Text Available Deformation and fracture of thin films on compliant substrates are key factors constraining the performance of emerging flexible substrate devices. [1-3] These systems often contain layers of thin polymer, ceramic and metallic films and stretchable interconnects where differing properties induce high normal and shear stresses. [4] As long as the films remain bonded to the substrates, they may deform far beyond their freestanding form. Once debonded, substrate constraint disappears leading to film failure. [3] Experimentally it is very difficult to measure properties in these systems at sub-micron and nanoscales. Theoretically it is very difficult to determine the contributions from the films, interfaces, and substrates. As a result our understanding of deformation and fracture behavior in compliant substrate systems is limited. This motivated a study of buckle driven delamination of thin hard tungsten films on pure PMMA substrates. The films were sputter deposited to thicknesses of 100 nm, 200 nm, and 400 nm with a residual compressive stress of 1.7 GPa. An aluminum oxide interlayer was added on several samples to alter interfacial composition. Buckles formed spontaneously on the PMMA substrates following film deposition. On films without the aluminum oxide interlayer, an extensive network of small telephone cord buckles formed following deposition, interspersed with regions of larger telephone cord buckles. (Figure 1 On films with an aluminum oxide interlayer, telephone cord buckles formed creating a uniform widely spaced pattern. Through-substrate optical observations revealed matching buckle patterns along the film-substrate interface indicating that delamination occurred for large and small buckles with and without an interlayer. The coexistence of large and small buckles on the same substrate led to two distinct behaviors as shown in Figure 2 where normalized buckle heights are plotted against normalized film stress. The behaviors deviate
Institute of Scientific and Technical Information of China (English)
Cheng-Qi Sun; Kai-Xin Liu; You-Shi Hong
2012-01-01
The paper studies the axisymmetric compressive buckling behavior of multi-walled carbon nanotubes (MWNTs) under different boundary conditions based on continuum mechanics model.A buckling condition is derived for determining the critical buckling load and associated buckling mode of MWNTs,and numerical results are worked out for MWNTs with different aspect ratios under fixed and simply supported boundary conditions.It is shown that the critical buckling load of MWNTs is insensitive to boundary conditions,except for nanotubes with smaller radii and very small aspect ratio.The associated buckling modes for different layers of MWNTs are in-phase,and the buckling displacement ratios for different layers are independent of the boundary conditions and the length of MWNTs.Moreover,for simply supported boundary conditions,the critical buckling load is compared with the corresponding one for axial compressive buckling,which indicates that the critical buckling load for axial compressive buckling can be well approximated by the corresponding one for axisymmetric compressive buckling.In particular,for axial compressive buckling of double-walled carbon nanotubes,an analytical expression is given for approximating the critical buckling load.The present investigation may be of some help in further understanding the mechanical properties of MWNTs.
Production TTR modeling and dynamic buckling analysis
Institute of Scientific and Technical Information of China (English)
Hugh Liu; John Wei; Edward Huang
2013-01-01
In a typical tension leg platform (TLP) design,the top tension factor (TTF),measuring the top tension of a top tensioned riser (TTR) relative to its submerged weight in water,is one of the most important design parameters that has to be specified properly.While a very small TTF may lead to excessive vortex induced vibration (ⅤⅣ),clashing issues and possible compression close to seafloor,an unnecessarily high TTF may translate into excessive riser cost and vessel payload,and even has impacts on the TLP sizing and design in general.In the process of a production TTR design,it is found that its outer casing can be subjected to compression in a worst-case scenario with some extreme metocean and hardware conditions.The present paper shows how finite element analysis (FEA) models using beam elements and two different software packages (Flexcom and ABAQUS) are constructed to simulate the TTR properly,and especially the pipe-in-pipe effects.An ABAQUS model with hybrid elements (beam elements globally + shell elements locally) can be used to investigate how the outer casing behaves under compression.It is shown for the specified TTR design,even with its outer casing being under some local compression in the worst-case scenario,dynamic buckling would not occur; therefore the TTR design is adequate.
Buckling of hybrid nanocomposites with embedded graphene and carbon nanotubes
Chandra, Y.; Saavedra Flores, E. I.; Scarpa, F.; Adhikari, S.
2016-09-01
With the aid of atomistic multiscale modelling and analytical approaches, buckling strength has been determined for carbon nanofibres/epoxy composite systems. Various nanofibres configurations considered are single walled carbon nano tube (SWCNT) and single layer graphene sheet (SLGS) and SLGS/SWCNT hybrid systems. Computationally, both eigen-value and non-linear large deformation-based methods have been employed to calculate the buckling strength. The non-linear computational model generated here takes into account of complex features such as debonding between polymer and filler (delamination under compression), nonlinearity in the polymer, strain-based damage criteria for the matrix, contact between fillers and interlocking of distorted filler surfaces with polymer. The effect of bridging nanofibres with an interlinking compound on the buckling strength of nano-composites has also been presented here. Computed enhancement in buckling strength of the polymer system due to nano reinforcement is found to be in the range of experimental and molecular dynamics based results available in open literature. The findings of this work indicate that carbon based nanofillers enhance the buckling strength of host polymers through various local failure mechanisms.
Buckling analysis of partially corroded steel plates with irregular surfaces
Indian Academy of Sciences (India)
Ahmad Rahbar-Ranji
2014-04-01
Corrosion is a long-term, inevitable process, lessens the thickness and load carrying capacity of structures. Old steel structures are more vulnerable to buckling, yielding and fracture due to corrosion. In lieu of a detailed analysis, average thickness assumption is employed for general type of corrosion. However, the estimation of load carrying capacity reduction of corroded structures typically need a much higher level of accuracy, since the actual corroded plates would have irregular surfaces. The objective of this article is to determine the effect of general corrosion on reduction of elastic buckling strength of both-sided partially corroded plates with irregular surfaces. Eigenvalue analysis using finite element method is employed for Euler stress calculation of corroded plates. The effects of different influential parameters are investigated and it is found that, aspect ratio of plate, location of corroded area, standard deviation of thickness diminution and concentration of corrosion have influence on reduction of elastic buckling strength. Reduction of elastic buckling strength is very sensitive to the amount of corrosion loss. The higher the amount of corrosion loss, the more reduction of elastic buckling strength.
Nonlinear Guided Waves in Continuously Welded Rails for Buckling Prediction
Phillips, Robert; Bartoli, Ivan; Coccia, Stefano; Lanza di Scalea, Francesco; Salamone, Salvatore; Nucera, Claudio; Fateh, Mahmood; Carr, Gary
2011-06-01
Most modern railways use Continuous Welded Rail (CWR). A major problem is the almost total absence of expansion joints that can create severe issues such as buckling in hot weather and breakage in cold weather. A related critical parameter is the rail Neutral Temperature (NT), or the temperature at which the net longitudinal force in the rail is zero. In June 2008 the University of California, San Diego (UCSD), under the sponsorship of a Federal Railroad Administration (FRA) Office of Research and Development (R&D) grant, began work to develop a technique for in-situ measurement of NT and detection of incipient buckling in CWR. The method under investigation is based on ultrasonic guided waves, and the ultimate goal is to build and test a prototype that can be used in motion. A large-scale full rail track (70 feet in length) has been constructed at UCSD's Powell Structural Laboratories, the largest laboratories in the country for structural testing, to validate the NT measurement and buckling detection technique under rail heating conditions well controlled in the laboratory. This paper reports on the status of this project, including proof-of-principle results of stress measurement and buckling detection on a steel I-beam, and initial test results from the large-scale rail testbed at the Powell Labs. These results pave the road for the future development of the rail NT/buckling detection prototype.
Column buckling of magnetically affected stocky nanowires carrying electric current
Kiani, Keivan
2015-08-01
Axial load-bearing capacity of current carrying nanowires (CCNWs) acted upon by a longitudinal magnetic field is of high interest. By adopting Gurtin-Murdoch surface elasticity theory, the governing equations of the nanostructure are constructed based on the Timoshenko and higher-order beam models. To solve these equations for critical compressive load, a meshfree approach is exploited and the weak formulations for the proposed models are obtained. The predicted buckling loads are compared with those of assume mode method and a remarkable confirmation is reported. The role of influential factors on buckling load of the nanostructure is carefully addressed and discussed. The obtained results reveal that the surface energy effect becomes important in buckling behavior of slender CCNWs, particularly for high electric currents and magnetic field strengths. For higher electric currents, relative discrepancies between the results of Timoshenko and higher-order beam models increase with a higher rate as the slenderness ratio magnifies. A magnetically affected current-carrying nanowire acted upon by an axial force. Axial buckling of stocky current-carrying nanowires in the presence of a longitudinal magnetic field is of particular interest. Using Timoshenko and higher-order beam theories accounting for surface energy effect, the governing equations are derived and a meshfree methodology is applied to evaluate the buckling load.
Electrical Bending and Mechanical Buckling Instabilities in Electrospinning Jets
Han, Tao; Reneker, Darrell H.
2007-03-01
The electrospinning jet was a continuous fluid flow ejected from the surface of a fluid when the applied electrical force overcomes the surface tension. The jet moved straight away from the tip and then became unstable and bent into coils. This phenomenon is the electrical bending instability [1]. When the distance between the tip and collector was reduced to less than the maximal straight segment length, the electrical bending instability did not occur. The periodic buckling of a fluid jet incident onto a surface is a striking fluid mechanical instability [2]. When axial compressive stress along the jet reached a sufficient value, it produced the fluid mechanics analogue to the buckling of a slender solid column. In the electrospinning, the buckling instability occurred just above the collector where the jet was compressed as it encountered the collector. The buckling frequencies of these jets are in the range of 10^4 to 10^5 Hz. The buckling lengths of these jets are in the range of 10 to 100μm. *Reneker,D.H.; Yarin, A. L.; Fong, H.; Koombhongse, S., Journal of Applied Physics, 87, 4531, 2000 *Tchavdarov B.; Yarin, A. L.; Radev S., Journal of Fluid Mechanics; 253, 593,1993
Periodic buckling patterns of graphene/hexagonal boron nitride heterostructure
International Nuclear Information System (INIS)
Graphene/hexagonal boron nitride (h-BN) heterostructure has showed great potential to improve the performance of a graphene device. A graphene on an h-BN substrate may buckle due to the thermal expansion mismatch between the graphene and h-BN. We used an energy method to investigate the periodic buckling patterns including one-dimensional, square checkerboard, hexagonal, equilateral triangular and herringbone mode in a graphene/h-BN heterostructure under equi-biaxial compression. The total energy, consisting of cohesive energy, graphene membrane energy and graphene bending energy, for each buckling pattern is obtained analytically. At a compression slightly larger than the critical strain, all buckling patterns have the same total energies, which suggests that any buckling pattern may occur. At a compression much larger than the critical strain, the herringbone mode has the lowest total energy by significantly reducing the membrane energy of graphene at the expense of a slight increase of the bending energy of graphene and cohesive energy. These results may serve as guidelines for strain engineering in graphene/h-BN heterostructures. (paper)
Perturbation analysis on post-buckling behavior of pile
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The nonlinear large deflection differential equation, based on the assumption that the subsoil coefficient is the 2nd root of the depth, was established by energy method. The perturbation parameter was introduced to transform the equation to a series of linear differential equations to be solved, and the deflection function according with the boundary condition was considered. Then,the nonlinear higher-order asymptotic solution of post-buckling behavior of a pile was obtained by parameter-substituting. The influencing factors such as bury-depth ratio and stiffness ratio of soil to pile, slenderness ratio on the post-buckling behavior of a pile were analyzed. The results show that the pile is more unstable when the bury-depth ratio and stiffness ratio of soil to pile increase,and although the buckling load increases with the stiffness of soil, the pile may ruin for its brittleness. Thus, in the region where buckling behavior of pile must be taken into account, the high grade concrete is supposed to be applied, and the dynamic buckling behavior of pile needs to be further studied.
NONLINEAR BUCKLING CHARACTERISTIC OF GRADED MULTIWEB STRUCTURE OF HETEROGENEOUS MATERIALS
Institute of Scientific and Technical Information of China (English)
LI Yong; ZHANG Zhi-min
2005-01-01
The graded multiweb structure of heterogeneous anisotropic materials, which makes full use of the continuous, gradual and changing physical mechanical performance of material properties, has a widespread application in aeroplane aerofoil structure and automobile lightweight structure. On the basis of laminate buckling theory,the equivalent rigidity method is adopted to establish the corresponding constitutive relation and the non-linear buckling governing equation for the graded multiweb structure. In finding the solution, the critical load of buckling under different complicated boundary conditions together with combined loads were obtained and testification of the experimental analysis shows that the calculation results can satisfy the requirements of engineering design in a satisfactory way. Results obtained from the research say that: graded materials can reduce the concentrated stress on the interface in an effective way and weaken the effect of initial defect in materials and thereby improve the strength and toughness of materials.
Vibrations of post-buckled rods: The singular inextensible limit
Neukirch, Sébastien
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.
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......, the ordinary finite element method slightly overestimates the buckling load, and with a very few number of elements high rate of convergence to the exact results is observed. If the bending rigidity field is modelled using random fields, stochastic finite element method is utilized. The discretization...... considering safety factors are estimated by means of extensive Monte Carlo simulations. For the case, when the bending rigidity field is taken to be bound from above an below, an integral equation formulation and optimization methods are used to determine conservative bounds for the buckling load...
Bifurcations in the optimal elastic foundation for a buckling column
International Nuclear Information System (INIS)
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
Rayneau-Kirkhope, Daniel; Farr, Robert; Ding, K.; Mao, Yong
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.
Bifurcations in the optimal elastic foundation for a buckling column
Rayneau-Kirkhope, Daniel; 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.
Dynamic buckling of shells: evaluation of various methods
International Nuclear Information System (INIS)
The problem of dynamic stability is substantially more complex than the buckling analysis of a shell subjected to static loads. Even at this date suitable criteria for dynamic buckling of shells, which are both logically sound and practically applicable, are not easily available. Thus, a variety of analyses are available to the user, encompassing various degrees of complexity, and involving a range of simplifying assumptions. The purpose of this paper is to compare and evaluate some of these solutions by applying them to a specific problem. A shallow spherical cap, subjected to an axisymmetric, uniform-pressure, step loading, is used as the structural example. The predictions, by various methods, of the dynamic buckling of this shell into unsymmetric modes, are then investigated and compared. (Auth.)
Buckling of Fiber Reinforced Composite Plates with Nanofiber Reinforced Matrices
Chamis, Christos C.; Murthy, Pappu L. N.
2010-01-01
Anisotropic composite plates were evaluated with nanofiber reinforced matrices (NFRM). The nanofiber reinforcement volumes ratio in the matrix was 0.01. The plate dimensions were 20 by 10 by 1.0 in. (508 by 254 by 25.4 mm). Seven different loading condition cases were evaluated: three for uniaxial loading, three for pairs of combined loading, and one with three combined loadings. The anisotropy arose from the unidirectional plates having been at 30 from the structural axis. The anisotropy had a full 6 by 6 rigidities matrix which were satisfied and solved by a Galerkin buckling algorithm. The buckling results showed that the NFRM plates buckled at about twice those with conventional matrix.
Numerical analysis of linear buckling of wind turbine blade with different trailing bonding models
Zhang, J. D.; Xu, Y.
2013-12-01
The work focus on the linear buckling analysis of wind turbine blade with different trailing bonding models. Based on finite element model, it has been demonstrated that there are some differences for buckling load factor between different models. Several different models are valid for buckling analysis.
Buckling-driven delamination of carbon nanotube forests
Pour Shahid Saeed Abadi, Parisa; Hutchens, Shelby B.; Greer, Julia R.; Cola, Baratunde A.; Graham, Samuel
2013-06-01
We report buckling-driven delamination of carbon nanotube (CNT) forests from their growth substrates when subjected to compression. Macroscale compression experiments reveal local delamination at the CNT forest-substrate interface. Results of microscale flat punch indentations indicate that enhanced CNT interlocking at the top surface of the forest accomplished by application of a metal coating causes delamination of the forest from the growth substrate, a phenomenon not observed in indentation of as-grown CNT forests. We postulate that the post-buckling tensile stresses that develop at the base of the CNT forests serve as the driving force for delamination.
Dynamic Buckling of Column Impacted by a Rigid Body
Institute of Scientific and Technical Information of China (English)
Zhijun Han; Hongwei Ma; Shanyuan Zhang
2004-01-01
The dynamic buckling of an elastic column subjected to axial impact by a rigid body is discussed in accordance with the energy law in this paper. The equation of lateral disturbance used to analysis the problem is developed by taking into account the effect of stress wave. The power series solution of this problem has been obtained by using the power series approach. The buckling criterion of this problem is proposed by analyzing the characteristics of the solution. The relationships between critical velocity and impacting mass as well as critical velocity and critical length are given by using theoretical analysis and numerical computation.
Vibration and local edge buckling of thermally stressed, wedge airfoil cantilever wings.
Bailey, C. D.
1973-01-01
The local edge buckling phenomena that can occur along the heated thin edge of a wedge shape airfoil is calculated. Qualitative comparison (qualitative only because the experimental temperature distribution was not measured) is made to the experimentally observed phenomena. The consequences of the assumption of identical vibration and buckling modes is shown by a comparison of results with and without the assumption of mode identity. Computer plots of the elastic surface as local buckling develops with increasing temperature are shown. The calculated, fully developed local edge buckling is compared to a photograph of a fully developed buckling as observed in the laboratory.
Effect of Topological Defects on Buckling Behavior of Single-walled Carbon Nanotube
Directory of Open Access Journals (Sweden)
Wang Guoxiu
2011-01-01
Full Text Available Abstract Molecular dynamic simulation method has been employed to consider the critical buckling force, pressure, and strain of pristine and defected single-walled carbon nanotube (SWCNT under axial compression. Effects of length, radius, chirality, Stone–Wales (SW defect, and single vacancy (SV defect on buckling behavior of SWCNTs have been studied. Obtained results indicate that axial stability of SWCNT reduces significantly due to topological defects. Critical buckling strain is more susceptible to defects than critical buckling force. Both SW and SV defects decrease the buckling mode of SWCNT. Comparative approach of this study leads to more reliable design of nanostructures.
Functional buckling behavior of silicone rubber shells for biomedical use
van der Houwen, E B; Kuiper, L H; Burgerhof, J G M; van der Laan, B F A M; Verkerke, G J
2013-01-01
BACKGROUND: The use of soft elastic biomaterials in medical devices enables substantial function integration. The consequent increased simplification in design can improve reliability at a lower cost in comparison to traditional (hard) biomaterials. Functional bi-stable buckling is one of the many n
Elastic Buckling of Bionic Cylindrical Shells Based on Bamboo
Institute of Scientific and Technical Information of China (English)
Jian-feng Ma; Wu-yi Chen; Ling Zhao; Da-hai Zhao
2008-01-01
High load-bearing efficiency is one of the advantages of biological structures after the evolution of billions of years.Biomimicking from nature may offer the potential for lightweight design. In the viewpoint of mechanics properties, the culm of bamboo comprises of two types of cells and the number of the vascular bundles takes a gradient of distribution. A three-point bending test was carried out to measure the elastic modulus. Results show that the elastic modulus of bamboo decreases gradually from the periphery towards the centre. Based on the structural characteristics of bamboo, a bionic cylindrical structure was designed to mimic the gradient distribution of vascular bundles and parenchyma cells. The buckling resistance of the bionic structure was compared with that of a traditional shell of equal mass under axial pressure by finite element simulations. Results show that the load-bearing capacity of bionic shell is increased by 124.8%. The buckling mode of bionic structure is global buckling while that of the conventional shell is local buckling.
Buckling of Thin Films in Nano-Scale
Wang, S.; Jia, H. K.; Sun, J.; Ren, X. N.; Li, L. A.
2010-06-01
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.
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.
Use of Buckling Instabilities in Micro Pumps, Valves, and Mixers
Tavakol, Behrouz; Chawan, Aschvin; Holmes, Douglas
2014-03-01
We use the buckling of thin, flexible plates for pumping fluids, controlling the flow rate, and mixing different media within a microfluidic channel. A dielectric elastomeric film with a confined geometry buckles out of the plane when exposed to an electric field. Solid or grease electrodes have traditionally been used as conductive materials to aid in voltage application to both sides of the film. In this work, we use an electrolytic fluid solution as the electrode to enable buckling at relatively low voltages, and to enhance the rate of deformation. We show that this mechanism can be implemented as a microvalve that controls flow rate, or as a micropump that operates over a range of frequencies. A similar mechanism can be used to aid diffusion between two adjacent laminar streams and improve mixing. These low-cost micropumps, microvalves, and micromixers rely on the reversible buckling of thin plates, are easily embeddable in a microfluidic chip, and can potentially be used in variety of applications to accurately control and manipulate fluid flow in a microchannel.
Dynamic buckling of shells: evaluation of various methods
International Nuclear Information System (INIS)
The problem of dynamic stability is substantially more complex than the buckling analysis of a shell subjected to static loads. Suitable criteria for dynamic bulking of shells, which are both logically sound and practically applicable, are not easily available. The purpose of this paper is to compare and evaluate some solutions by applying them to a specific problem. A shallow spherical cap, subjected to an axisymmetric, uniform-pressure, step-loading, is used as the structural example. The predictions, by various methods, of the dynamic buckling of this shell into unsymmetric modes, are then investigated and compared. The approximate methods used by Akkas are compared to the more rigorous and general solutions of the KSHEL, STARS, DYNASOR, and SATANS computer programs, and the various simplifying assumptions utilized are evaluated. Also included in the comparisons, are the predictions of the relatively simple 'dynamic buckling model' approach of Budiansky and Hutchinson. The approaches utilized by the more complex programs are compared in terms of accuracy, idealization complexity, ease of use, and user expertise and experience required for analysis. The comparisons show that the more approximate methods underpredict the dynamic buckling loads for this problem. In addition, some basic assumptions of the simpler solutions are found to be invalid. (Auth.)
Uncertainty modelling of critical column buckling for reinforced concrete buildings
Indian Academy of Sciences (India)
Kasim A Korkmaz; Fuat Demir; Hamide Tekeli
2011-04-01
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 algorithms can be a solution to generate more dependable results. This study investigates the material uncertainties on column design and proposes an uncertainty model for critical column buckling reinforced concrete buildings. Fuzzy logic algorithm was employed in the study. Lower and upper bounds of elastic modulus representing material properties were deﬁned to take uncertainties into account. The results show that uncertainties play an important role in stability analyses and should be considered in the design. The proposed approach is applicable to both future numerical and experimental researches. According to the study results, it is seen that, calculated buckling load values are stayed in lower and upper bounds while the load values are different for same concrete strength values by using different code formula.
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.
Torque-induced buckling behavior in stretched intertwined DNAs
Brahmachari, Sumitabha; Marko, John F.
Two intertwined DNA molecules (a DNA 'braid') is a common occurrence in the cell and is a relevant substrate for the study of topoisomerase and recombination enzymes. Single molecule experiments have observed the signature of a buckling transition in braids under tensile and torsional stress. We present a free energy model for braided DNA to investigate the mechanical properties of these structures. Our model is based on the semi-flexible polymer model for double helix DNA and is in quantitative accord with the experiments. We identify coexistence of a force-extended state with a plectonemically buckled state, which is reminiscent of single supercoiled DNA behavior. However, the absence of an intrinsic twist modulus in braided DNA results in unique mechanical properties such as non-linear torque in the extended state. At the buckling transition, we predict a jump in the braid extension due to the plectoneme end loop which acts as a nucleation barrier. We investigate the effect of salt concentration on the mechanical response of braids, e.g. we find that buckling starts at a lower linking number for lower salt concentration, the opposite of what is seen for single supercoiled DNAs. Also, concentrations less than 20 mM monovalent salt favor formation of multiple plectoneme domains. NSF Grant: DMR-9734178.
Experimental and Numerical Study of Buckling of Vacuum Chambers for Fast-Cycling Synchrotrons
DEFF Research Database (Denmark)
Bräuner, Lars Erik
tendency towards pressure induced buckling due to some combination of excessive out-gassing, fragility, radiation damage, magnetic field distortion,. The analysis for design is complicated because elliptical shell chambers display a complex form of nonlinear snap buckling behavior under the external......The optimal functioning of the long span thin walled elliptical cross section shells used as vacuum chambers for fast-cycling synchrotrons is provided by their buckling capacity. Also it is often necessary to design inter-stiffener panels of elliptical shells used as vacuum chambers to resist any...... pressure. Buckling analysis for shells is further complicated by the observation that geometric imperfections have an important influence on the buckling mode as well as on the buckling load-carrying capacity. Buckling loads are, in general, considerably lower than the lowest critical loads predicted from...
International Nuclear Information System (INIS)
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
Effect of weld reinforcement on axial plastic buckling of welded steel cylindrical shells
Institute of Scientific and Technical Information of China (English)
Chu-lin YU; Zhi-ping CHEN; Ji WANG; Shun-juan YAN; Li-cai YANG
2012-01-01
The effect of weld reinforcement on axial plastic buckling of welded steel cylindrical shells is investigated through experimental and numerical buckling analysis using six welded steel cylindrical shell specimens.The relationship between the amplitude of weld reinforcement and the axial plastic buckling critical load is explored.The effect of the material yield strength and the number of circumferential welds on the axial plastic buckling is studied.Results show that circumferential weld reinforcement represents a severe imperfect form of axially compressed welded steel cylindrical shells and the axial plastic buckling critical load decreases with the increment of the mean amplitude of circumferential weld reinforcement.The material yield strength and the number of circumferential welds are found to have no significant effect on buckling waveforms; however,the axial plastic buckling critical load can be decreased to some extent with the increase of the number of circumferential welds.
Byun, Wanil; Kim, Min Ki; Park, Kook Jin; Kim, Seung Jo; Chung, Minho; Cho, Jin Yeon; Park, Sung-Han
2011-12-01
The supercavitating vehicle is an underwater vehicle that is surrounded almost completely by a supercavity to reduce hydrodynamic drag substantially. Since the cruise speed of the vehicle is much higher than that of conventional submarines, the drag force is huge and a buckling may occur. The buckling phenomenon is analyzed in this study through static and dynamic approaches. Critical buckling load and pressure as well as buckling mode shapes are calculated using static buckling analysis and a stability map is obtained from dynamic buckling analysis. When the finite element method (FEM) is used for the buckling analysis, the solver requires a linear static solver and an eigenvalue solver. In this study, these two solvers are integrated and a consolidated buckling analysis module is constructed. Furthermore, Particle Swarm Optimization (PSO) algorithm is combined in the buckling analysis module to perform a design optimization computation of a simplified supercavitating vehicle. The simplified configuration includes cylindrical shell structure with three stiffeners. The target for the design optimization process is to minimize total weight while maintaining the given structure buckling-free.
ON THE ORIENTATION OF BUCKLING DIRECTION OF ANISOTROPIC ELASTIC PLATE UNDER UNIAXIAL COMPRESSION
Institute of Scientific and Technical Information of China (English)
Zhang Yitong
2001-01-01
The theory of small deformation superimposed on a large deformation of an elastic solid is used to investigate the buckling of anisotropic elastic plate under uniaxial compression. The buckling direction (the direction of buckling wave) is generally not aligned with the compression direction. The equation for determining the buckling direction is obtained. It is found that the out-of-plane buckling of anisotropic elastic plate is possible and both buckling conditions for flexural and extensional modes are presented. As a specific case of buckling of anisotropic elastic plate, the buckling of an orthotropic elastic plate subjected to a compression in a direction that forms an arbitrary angle with an elastic principal axis of the materials is analyzed. It is found that the buckling direction depends on the angle between the compression direction and the principal axis of the materials, the critical compressive force and plate-thickness parameters.In the case that the compression direction is aligned with the principal axis of the materials, the buckling direction will be aligned with the compression one irrespective of critical compressive force and plate-thickness.
Simulating Thin Sheets: Buckling, Wrinkling, Folding and Growth
Vetter, Roman; Stoop, Norbert; Wittel, Falk K.; Herrmann, Hans J.
2014-03-01
Numerical simulations of thin sheets undergoing large deformations are computationally challenging. Depending on the scenario, they may spontaneously buckle, wrinkle, fold, or crumple. Nature's thin tissues often experience significant anisotropic growth, which can act as the driving force for such instabilities. We use a recently developed finite element model to simulate the rich variety of nonlinear responses of Kirchhoff-Love sheets. The model uses subdivision surface shape functions in order to guarantee convergence of the method, and to allow a finite element description of anisotropically growing sheets in the classical Rayleigh-Ritz formalism. We illustrate the great potential in this approach by simulating the inflation of airbags, the buckling of a stretched cylinder, as well as the formation and scaling of wrinkles at free boundaries of growing sheets. Finally, we compare the folding of spatially confined sheets subject to growth and shrinking confinement to find that the two processes are equivalent.
Soft modes near the buckling transition of icosahedral shells
Widom, M.; Lidmar, J.; Nelson, D. R.
2007-01-01
Icosahedral shells undergo a buckling transition as the ratio of Young's modulus to bending stiffness increases. Strong bending stiffness favors smooth, nearly spherical shapes, while weak bending stiffness leads to a sharply faceted icosahedral shape. Based on the phonon spectrum of a simplified mass-and-spring model of the shell, we interpret the transition from smooth to faceted as a soft-mode transition. In contrast to the case of a disclinated planar network where the transition is sharp...
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.
Prebuckling, Buckling, and Postbuckling Response of Segmented Circular Composite Cylinders
Riddick, Jaret Cleveland
2001-01-01
Discussed is a numerical and experimental characterization of the response of small-scale fiber-reinforced composite cylinders constructed to represent a fuselage design whereby the crown and keel consist of one laminate stacking sequence and the two sides consist of another laminate stacking sequence. This construction is referred to as a segmented cylinder. The response to uniform axial endshortening is discussed. Numerical solutions for the nonlinear prebuckling, buckling, and postbuckling...
Buckled graphene: A model study based on density functional theory
Khan, Mohammad A.
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.
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
Buckling of structures with uncertain imperfections - Personal perspective
Elishakoff, Isaac
1998-01-01
The previous review on stochastic buckling of structures was written by Amazigo in 1976. This review summarizes some of the developments which took place in recent two decades. A brief overview is given of the effect on uncertainty in the initial geometric imperfections, elastic moduli, applied forces, and thickness variation. For the benefit of the thinking reader, the review has a critical nature. It should be noted that this manuscript has yet to be completed.
Buckling response of ferritic stainless steel columns at elevated temperatures
Afshan, S; Gardner, L; Baddoo, NR
2013-01-01
This paper presents a numerical study on the buckling behaviour of ferritic stainless steel columns in fire. Finite element models were developed and validated against existing test results to predict the elevated temperature non-linear response of ferritic stainless steel columns. A total of nine austenitic and three ferritic stainless steel column tests were replicated using the finite element analysis package ABAQUS. Parametric studies were performed to investigate the effects of variation...
Scleral buckling for retinal detachment in patients with retinoblastoma
International Nuclear Information System (INIS)
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.
A buckling mechanism for ESCRT-III budding
Lenz, Martin; Joanny, Jean-François
2009-01-01
The ESCRT-III protein complex binds to the membrane of eukaryotic cells, causing it to bud into long tubes. Here we propose that this budding is akin to a buckling instability. We analyze the linear stability of flat ESCRT-III-dressed membranes and account for the formation of long tubes. We study strongly deformed dressed membranes and their bifurcation diagram numerically. Our mechanism is compatible with reasonable in vivo parameter values and we propose an experiment allowing its validation.
Buckling characteristic of multi-laminated composite elliptical cylindrical shells
Kassegne, Samuel Kinde; Chun, Kyoung-Sik
2015-03-01
Fiber-reinforced composite materials continue to experience increased adoption in aerospace, marine, automobile, and civil structures due to their high specific strength, high stiffness, and light weight. This increased use has been accompanied by applications involving non-traditional configurations such as compression members with elliptical cross-sections. To model such shapes, we develop and report an improved generalized shell element called 4EAS-FS through a combination of enhanced assumed strain and the substitute shear strain fields. A flat shell element has been developed by combining a membrane element with drilling degree-of-freedom and a plate bending element. We use the element developed to determine specifically buckling loads and mode shapes of composite laminates with elliptical cross-section including transverse shear deformations. The combined influence of shell geometry and elliptical cross-sectional parameters, fiber angle, and lay-up on the buckling loads of an elliptical cylinder is examined. It is hoped that the critical buckling loads and mode shapes presented here will serve as a benchmark for future investigations.
Thermal buckling analysis of truss-core sandwich plates
Institute of Scientific and Technical Information of China (English)
陈继伟; 刘咏泉; 刘伟; 苏先樾
2013-01-01
Truss-core sandwich plates have received much attention in virtue of the high values of strength-to-weight and stiffness-to-weight as well as the great ability of impulse-resistance recently. It is necessary to study the stability of sandwich panels under the influence of the thermal load. However, the sandwich plates are such complex three-dimensional (3D) systems that direct analytical solutions do not exist, and the finite element method (FEM) cannot represent the relationship between structural parameters and mechanical properties well. In this paper, an equivalent homogeneous continuous plate is idealized by obtaining the effective bending and transverse shear stiffness based on the characteristics of periodically distributed unit cells. The first order shear deformation theory for plates is used to derive the stability equation. The buckling temperature of a simply supported sandwich plate is given and verified by the FEM. The effect of related parameters on mechanical properties is investigated. The geometric parameters of the unit cell are optimized to attain the maximum buckling temperature. It is shown that the optimized sandwich plate can improve the resistance to thermal buckling significantly.
A numerical study of flexural buckling of foliated rock slopes
Adhikary, D. P.; Mühlhaus, H.-B.; Dyskin, A. V.
2001-08-01
The occurrence of foliated rock masses is common in mining environment. Methods employing continuum approximation in describing the deformation of such rock masses possess a clear advantage over methods where each rock layer and each inter-layer interface (joint) is explicitly modelled. In devising such a continuum model it is imperative that moment (couple) stresses and internal rotations associated with the bending of the rock layers be properly incorporated in the model formulation. Such an approach will lead to a Cosserat-type theory. In the present model, the behaviour of the intact rock layer is assumed to be linearly elastic and the joints are assumed to be elastic-perfectly plastic. Condition of slip at the interfaces are determined by a Mohr-Coulomb criterion with tension cut off at zero normal stress. The theory is valid for large deformations. The model is incorporated into the finite element program AFENA and validated against an analytical solution of elementary buckling problems of a layered medium under gravity loading. A design chart suitable for assessing the stability of slopes in foliated rock masses against flexural buckling failure has been developed. The design chart is easy to use and provides a quick estimate of critical loading factors for slopes in foliated rock masses. It is shown that the model based on Euler's buckling theory as proposed by Cavers (Rock Mechanics and Rock Engineering 1981; 14:87-104) substantially overestimates the critical heights for a vertical slope and underestimates the same for sub-vertical slopes.
Analysis modeling for plate buckling load of vibration test
Institute of Scientific and Technical Information of China (English)
SUNG Wen-pei; LIN Cheng-I; SHIH Ming-hsiang; GO Cheer-germ
2005-01-01
In view of the recent technological development, the pursuit of safe high-precision structural designs has been the goal of most structural designers. To bridge the gap between the construction theories and the actual construction techniques, safety factors are adopted for designing the strength loading of structural members. If safety factors are too conservative, the extra building materials necessary will result in high construction cost. Thus, there has been a tendency in the construction field to derive a precise buckling load analysis model of member in order to establish accurate safety factors. A numerical analysis model, using modal analysis to acquire the dynamic function calculated by dynamic parameter to get the buckling load of member, is proposed in this paper. The fixed and simple supports around the circular plate are analyzed by this proposed method. And then, the Monte Carlo method and the normal distribution method are used for random sampling and measuring errors of numerical simulation respectively. The analysis results indicated that this proposed method only needs to apply modal parameters of 7×7 test points to obtain a theoretical value of buckling load. Moreover, the analysis method of inequality-distant test points produces better analysis results than the other methods.
Caught in the Act: Direct Detection of Galactic Bars in the Buckling Phase
Erwin, Peter
2016-01-01
The majority of massive disk galaxies, including our own, have stellar bars with vertically thick inner regions -- so-called "boxy/peanut-shaped" (B/P) bulges. The most commonly suggested mechanism for the formation of B/P bulges is a violent vertical "buckling" instability in the bar, something that has been seen in N-body simulations for over twenty years, but never identified in real galaxies. Here, we present the first direct observational evidence for ongoing buckling in two nearby galaxies (NGC 3227 and NGC 4569), including characteristic asymmetric isophotes and (in NGC 4569) stellar-kinematic asymmetries that match buckling in simulations. This confirms that the buckling instability takes place and produces B/P bulges in real galaxies. A toy model of bar evolution yields a local fraction of buckling bars consistent with observations if the buckling phase lasts ~0.5--1 Gyr, in agreement with simulations.
Buckling of Cracked Laminated Composite Cylindrical Shells Subjected to Combined Loading
Allahbakhsh, Hamidreza; Shariati, Mahmoud
2013-10-01
A series of finite element analysis on the cracked composite cylindrical shells under combined loading is carried out to study the effect of loading condition, crack size and orientation on the buckling behavior of laminated composite cylindrical shells. The interaction buckling curves of cracked laminated composite cylinders subject to different combinations of axial compression, bending, internal pressure and external pressure are obtained, using the finite element method. Results show that the internal pressure increases the critical buckling load of the CFRP cylindrical shells and bending and external pressure decrease it. Numerical analysis show that axial crack has the most detrimental effect on the buckling load of a cylindrical shell and results show that for lower values of the axial compressive load and higher values of the external pressure, the buckling is usually in the global mode and for higher values of axial compressive load and lower levels of external pressure the buckling mode is mostly in the local mode.
Interactive Shear Buckling Of Plate Girder with Corrugated Web (Analytical Solution)
Prof.Dr:S.A.Tohamy; Ass.Prof.Dr:A.B.Saddek; Eng: Asmaa.Y.Hamed
2016-01-01
This paper presents analytical studies the elastic interactive shear buckling stress of corrugated steel web is calculated by all possible failure criteria (steel yielding, local and global buckling stresses), using Minimum Potential Energy Method to determine critical shear stress of local and global buckling of plate girder with corrugated webs. The results are compared with Finite element method (FEM) using ANSYS/V12. It found that the proposed equations are a good agreement with the resul...
Buckling and structural efficiency of sandwich-blade stiffened composite compression panels
Stein, M.; Williams, J. G.
1978-01-01
The minimum mass structural efficiency curve was determined for sandwich blade stiffened composite compression panels subjected to buckling and strength constraints. High structural efficiencies are attainable for this type of construction. A method of analysis is presented for the buckling of panels of this configuration which shows that buckling of such panels is strongly dependent on the through-the-thickness transverse shearing of the stiffener. Experimental results are presented and compared with theory.
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
CRITICAL BUCKLING LOAD ESTIMATION OF THE COMPRESSION RODS USING ARTIFICIAL NEURAL NETWORKS METHOD
BİLGEHAN, Mahmut; PEKGÖKGÖZ, RECEP KADİR
2011-01-01
In this work, the buckling problem of constant rectangular cross-sectional slender prismatic compression members having a nonpropagating open edge crack is investigated by Transfer Matrix and Neural Network methods. Obtained results show that, besides the Transfer Matrix Method whose efficiency on technical problems such as buckling and vibration was seen previously, the Neural Network Method also an efficient and reliable method for determination of buckling load of cracked compression membe...
Thermo-mechanical buckling analysis of FGM plate using generalized plate theory
Sharma, Kanishk; Kumar, Dinesh; Gite, Anil
2016-05-01
This paper investigates the thermo-mechanical buckling behavior of simply-supported FGM plate under the framework of generalized plate theory (GPT), which includes classical plate theory (CPT), first order shear deformation theory (FSDT) and higher order shear deformation theory (HSDT) as special cases. The governing equations for FGM plate under thermal and mechanical loading conditions are derived from the principle of virtual displacements and Navier-type solution is assumed for simply supported boundary condition. The efficiency and applicability of presented methodology is illustrated by considering various examples of thermal and mechanical buckling of FGM plates. The closed form solutions in the form of critical thermal and mechanical buckling loads, predicted by CPT, FSDT and HSDT are compared for different side-to-thickness of FGM plate. Subsequently, the effect of material gradation profile on critical buckling parameters is examined by evaluating the buckling response for a range of power law indexes. The effect of geometrical parameters on mechanical buckling of FGM plate under uni-axial and bi-axial loading conditions are also illustrated by calculating the critical load for various values of slenderness ratios. Furthermore a comparative analysis of critical thermal buckling loads of FGM plate for different temperature profiles is also presented. It is identified that all plate theories predicted approximately same critical buckling loads and critical buckling temperatures for thin FGM plate, however for thick FGM plates, CPT overestimates the critical buckling parameters. Moreover the critical buckling loads and critical buckling temperatures of FGM plate are found to be significantly lower than the corresponding homogenous isotropic ceramic plate (n=0).
Xiao, Yangming; Liu, Qin; Han, Hai-Chao
2016-09-01
Artery buckling alters the fluid shear stress and wall stress in the artery but its temporal effect on vascular wall remodeling is poorly understood. The purpose of this study was to investigate the early effect of artery buckling on endothelial nitric oxide synthase (eNOS) expression and extracellular matrix remodeling. Bilateral porcine carotid arteries were maintained in an ex vivo organ culture system with and without buckling while under the same physiological pressure and flow rate for 3-7 days. Matrix metalloproteinase-2 (MMP-2), MMP-9, fibronectin, elastin, collagen I, III and IV, tissue inhibitor of metalloproteinase-2 (TIMP-2), and eNOS were determined using Western blotting and immunohistochemistry. Our results showed that MMP-2 expression level was significantly higher in buckled arteries than in the controls and higher at the inner curve than at the outer curve of buckled arteries, while collagen IV content showed an opposite trend, suggesting that artery buckling increased MMP-2 expression and collagen IV degradation in a site-specific fashion. However, no differences for MMP-9, fibronectin, elastin, collagen I, III, and TIMP-2 were observed among the outer and inner curve sides of buckled arteries and straight controls. Additionally, eNOS expression was significantly decreased in buckled arteries. These results suggest that artery buckling triggers uneven wall remodeling that could lead to development of tortuous arteries. PMID:26913855
Institute of Scientific and Technical Information of China (English)
王吉; 王肖钧; 王峰; 赵凯
2004-01-01
With finite-element software ANSYS 7.0 and simple thermal-mechanical coupling constitutive relations,the buckling failure of preloaded cylindrical shell irradiated by high power laser beam was studied by numerical simulations. The buckling mode and buckling critical loading were analysed for different preloading conditions. The influence of laser intensity, beam irradiation time, preloading conditions and geometric parameters of cylindrical shell on the buckling mode were discussed. The numerical results show that: ① the buckling deformation of the cylindrical shell was concentrated in the area of laser spot and the radial buckling was the main buckling mode, ② a linear relationship between the buckling eigenvalue and the maximum temperature at the center of laser spot was approached, ③ the buckling failure of cylindrical shell was attributed to the coupling effect of the material softening and the radial deformation in the laser spot, and hence to raise the stiffness of the material would enhance the ability for anti-irradiation of structure substantially.
Buckling patterns of gold thin films on silicon substrates: Formation of superimposed blisters
Colin, J.; Coupeau, C.; Durinck, J.; Grilhé, J.
2009-06-01
Buckling phenomena leading to the formation of superimposed blisters have been experimentally observed with the help of a confocal interferometric microscope onto the surface of gold thin films deposited on silicon substrates. Assuming that residual folding effects resulting from plastic deformation mechanisms take place in the film during its morphological evolution, different probable scenarios for the formation of the observed buckling patterns are elaborated in the framework of the Föppl-von Karman's theory of thin plates. Multi-step buckling with growing interface delamination is considered for the first scenario while a single or multi-step buckling at a given delamination width is assumed for the other ones.
A NASTRAN DMAP alter for linear buckling analysis under dynamic loading
Aiello, Robert A.; Grady, Joseph E.
1989-01-01
A modification to the NASTRAN solution sequence for transient analysis with direct time integration (COSMIC NASTRAN rigid format 9) was developed and incorporated into a DMAP alter. This DMAP alter calculates the buckling stability of a dynamically loaded structure, and is used to predict the onset of structural buckling under stress-wave loading conditions. The modified solution sequence incorporates the linear buckling analysis capability (rigid format 5) of NASTRAN into the existing Transient solution rigid format in such a way as to provide a time dependent eigensolution which is used to assess the buckling stability of the structure as it responds to the impulsive load. As a demonstration of the validity of this modified solution procedure, the dynamic buckling of a prismatic bar subjected to an impulsive longitudinal compression is analyzed and compared to the known theoretical solution. In addition, a dynamic buckling analysis is performed for the analytically less tractable problem of the localized dynamic buckling of an initially flawed composite laminate under transverse impact loading. The addition of this DMAP alter to the transient solution sequence in NASTRAN facilitates the computational prediction of both the time at which the onset of dynamic buckling occurs in an impulsively loaded structure, and the dynamic buckling mode shapes of that structure.
The effect of temperature on the compressive buckling of boron nitride nanotubes
Energy Technology Data Exchange (ETDEWEB)
Shokuhfar, Ali; Ebrahimi-Nejad, Salman [Faculty of Mechanical Engineering, K.N. Toosi University of Technology, 19991-43344 Tehran (Iran, Islamic Republic of); Hosseini-Sadegh, Amin [Faculty of Petroleum Engineering, Petroleum University of Technology, 14539-53153 Tehran (Iran, Islamic Republic of); Zare-Shahabadi, Abolfazl [Department of Mechanical Engineering, Yazd Branch, Islamic Azad University, Yazd (Iran, Islamic Republic of)
2012-07-15
Inspired by the stability at high temperature and the high mechanical strength of boron nitride nanotubes (BNNTs), the effect of temperature on the compressive buckling of BNNTs has been investigated in this paper. Molecular dynamics (MD) simulations of BNNTs subjected to high temperatures (up to 3000 K) were performed and their structures were analyzed by studying their optimized structures at different temperatures through the radial distribution function (RDF). Then, the structural stability and compressive resistance properties of these nanotubes were investigated and the critical buckling loads and critical buckling strains of the nanotubes and their susceptibility to high temperatures were determined. The gradual decrease in the sharpness of the peaks of RDF plots of non-loaded nanotubes implies that at higher temperatures the structure displays greater deviations from that at room temperature. Results of buckling simulations also indicate a general weakening of the nanotubes and lower critical buckling loads and critical buckling strains at increased temperatures. The decrease in the critical buckling load is more significant for the longer nanotube (L {proportional_to} 6 nm) than the shorter one (L {proportional_to} 3 nm). The critical buckling strain experienced a drop of about 35-50% at temperatures higher than 1500 K. A transitional behavior was observed between T = 1000 and 2000 K. Temperature-dependent axial buckling behavior of boron nitride nanotubes. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Experimental Reserch on Buckling of Nano-Thin Film under Alternating Load
Cui, D. Q.; Wang, S. B.; Li, L. A.; Jia, H. K.
In this paper, an experiment focus on thin film buckling under alternating load has been completed. The alternating-loading device based on piezoelectric ceramic which also integrates the force-displacement measure module, has been designed to offer the alternating loading to the metal films deposited on PMMA substrates. The initiation of the straight-side buckling and the cumulative buckling with propagation process are recorded and investigated by using a CCD camera and a optical microscope. It is found that buckling's initiation and propagation are influenced by the frequency, thickness of thin film and number of cycles.
Buckling and Multiple Equilibrium States of Viscoelastic Rectangular Plates
Institute of Scientific and Technical Information of China (English)
无
1999-01-01
On the basis of Karman's theory of thin plates with large deflection, the Boltzmann law on linear viscoelastic materials and the mathematical model of dynamic analysis on viscoelastic thin plates, a set of nonlinear integro-partial-differential equations is first presented by means of a structural function introduced in this paper. Then,by using the Galerkin technique in spatial field and a backward difference scheme in temporal field, the set of nonlinear integro-partial-differential equations reduces to a system of nonlinear algebraic equations. After solving the algebraic equations, the buckling behavior and multiple equilibrium states can be obtained.
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...... thick-nesses and initial geometrical imperfections, material testing, advanced FE modelling studies and finally pa-rametric studies covering a range of slendernesses and imperfection amplitudes. The paper provides an over-view of the studies, which involved several participants in the Network....
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...... thicknesses and initial geometrical imperfections, material testing, advanced finite element modelling studies and finally parametric studies covering a range of slendernesses and imperfection amplitudes. The paper provides an overview of the studies, which involved several participants in the Network....
Estimation of post-buckling fatigue damage for LMFBR reactor vessel under seismic load
Energy Technology Data Exchange (ETDEWEB)
Ogiso, S.; Sasaki, T.; Oooka, Y. [Kawasaki Heavy Industries, Ltd., Tokyo (Japan). Nuclear Systems Div.; Nakamura, H. [Central Research Inst. of Electric Power Industry, Chiba (Japan)
1995-12-31
Estimation of fatigue damage caused by buckling deformation is important to evaluate safety margin in a seismic buckling design criterion for LMFBR reactor vessels, in addition to limiting the buckling strength. An advanced buckling design guideline draft including the seismic margin criterion has been proposed under the sponsorship of MITI to date. An ultimate state in this criterion was defined as the condition that the maximum global displacement {delta}{sub max} reaches a critical displacement {delta}{sub u}. The authors have previously proposed an estimation method of the fatigue damage based on the post buckling fatigue tests 304 s.s. cylinders at room temperature. However, adoption of a modified 316 s.s named 316FR s.s is under development as the material of reactor vessel of the updated design of the Demonstration Fast Breeder Reactor. The buckling tests with 316FR s.s cylinders were performed under high temperature to obtain the skeleton curve of the relation between load and displacement. And the buckling behaviors under the cyclic loading were compared with those of 304 s.s. Objectives of the present study are: to apply the proposed estimation method to a reactor vessel made of 316FR s.s., and clarify the correlation between {delta}{sub max} and fatigue failure; to verify structural soundness of the ultimate state derived from the seismic margin criterion against the fatigue failure due to the buckling deformation. (author). 7 refs., 12 figs., 1 tab.
A Nonlinear Theory of Bending and Buckling of Thin Elastic Shallow Spherical Shells
Kaplan, A; Fung, Y C
1954-01-01
The problem of the finite displacement and buckling, of a shallow spherical dome is investigated both theoretically and experimentally. Experimental results seem to indicate that the classical criterion of buckling is applicable to very shallow spherical domes for which the theoretical calculation was made. A transition to energy criterion for higher domes is also indicated.
Influence of central buckle on suspension bridge dynamic characteristics and driving comfort
Institute of Scientific and Technical Information of China (English)
王达; 邓扬; 刘扬
2015-01-01
The central buckle, which is often used in a suspension bridge, can improve bridges’ performance in the actual operation condition. The influence of the central buckle on natural vibration characteristics and bridge-deck driving comfort of a long-span suspension bridge is studied by using a case study of Siduhe Suspension Bridge in China. Based on the finite element software ANSYS and independently complied program, the influence of the central buckle on the structure force-applied characteristics of a long-span suspension bridge has been explored. The results show that the huge increases of natural frequencies can result in the presence of central buckles because of the increases of bending and torsional rigidities. The central buckle basically makes the stiffening girders and cables within the triangular area covered as a relatively approximate rigid area. Hence, the central buckle can reduce the torsional displacement of the main girder. However, the increases of bending and torsional rigidities have little influence on the impact factor, which is obtained by using vehicle-bridge coupled vibration analysis. This means that the central buckle has little effect on the comfort indices. In addition, it is found that the central buckle can enhance the bridge deck’s driving stability due to the decrease of the torsional displacements of the main girder.
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...
Buckling of composite beams with two enveloped delaminations: Lower and upper bounds
Parlapalli, M.S.R.; Shu, Dongwei; Chai, Gin B.
2008-01-01
Lower and upper bounds of the buckling load of a composite beam with two enveloped delaminations are obtained from newly developed analytical models. The characteristic equation, governing the delamination buckling is derived by using Euler–Bernoulli beam and classical lamination theory, performing
Helical coil buckling mechanism for a stiff nanowire on an elastomeric substrate
Chen, Youlong; Liu, Yilun; Yan, Yuan; Zhu, Yong; Chen, Xi
2016-10-01
When a stiff nanowire is deposited on a compliant soft substrate, it may buckle into a helical coil form when the system is compressed. Using theoretical and finite element method (FEM) analyses, the detailed three-dimensional coil buckling mechanism for a silicon nanowire (SiNW) on a polydimethylsiloxane (PDMS) substrate is studied. A continuum mechanics approach based on the minimization of the strain energy in the SiNW and elastomeric substrate is developed. Due to the helical buckling, the bending strain in SiNW is significantly reduced and the maximum local strain is almost uniformly distributed along SiNW. Based on the theoretical model, the energy landscape for different buckling modes of SiNW on PDMS substrate is given, which shows that both the in-plane and out-of-plane buckling modes have the local minimum potential energy, whereas the helical buckling model has the global minimum potential energy. Furthermore, the helical buckling spacing and amplitudes are deduced, taking into account the influences of the elastic properties and dimensions of SiNWs. These features are verified by systematic FEM simulations and parallel experiments. As the effective compressive strain in elastomeric substrate increases, the buckling profile evolves from a vertical ellipse to a lateral ellipse, and then approaches to a circle when the effective compressive strain is larger than 30%. The study may shed useful insights on the design and optimization of high-performance stretchable electronics and 3D complex nano-structures.
Local Cooling during Welding: Prediction and Control of Residual Stresses and Buckling Distortion
Van der Aa, E.M.
2007-01-01
One of the major problems during welding of thin plate structures is the occurrence of buckling distortion. This type of distortion is caused by the formation of compressive welding stresses; when these stresses exceed a certain critical stress level, the structure will buckle. Most methods for elim
Local buckling of fire-exposed aluminum members: New design model
Maljaars, J.; Soetens, F.; Snijder, H.H.
2010-01-01
Design models for local buckling of fire-exposed aluminum sections are currently lacking. Based on analyses with validated finite-element models, this paper investigates local buckling of extruded sections with stress-strain relationships representative for fire-exposed aluminum alloys. Due to the f
Khang, Dahl-Young; Xiao, Jianliang; Kocabas, Coskun; MacLaren, Scott; Banks, Tony; Jiang, Hanqing; Huang, Yonggang Y; Rogers, John A
2008-01-01
We have studied the scaling of controlled nonlinear buckling processes in materials with dimensions in the molecular range (i.e., approximately 1 nm) through experimental and theoretical studies of buckling in individual single-wall carbon nanotubes on substrates of poly(dimethylsiloxane). The results show not only the ability to create and manipulate patterns of buckling at these molecular scales, but also, that analytical continuum mechanics theory can explain, quantitatively, all measurable aspects of this system. Inverse calculation applied to measurements of diameter-dependent buckling wavelengths yields accurate values of the Young's moduli of individual SWNTs. As an example of the value of this system beyond its use in this type of molecular scale metrology, we implement parallel arrays of buckled SWNTs as a class of mechanically stretchable conductor.
Structural model for the dynamic buckling of a column under constant rate compression
Kuzkin, Vitaly A
2015-01-01
Dynamic buckling behavior of a column (rod, beam) under constant rate compression is considered. The buckling is caused by prescribed motion of column ends toward each other with constant velocity. Simple model with one degree of freedom simulating static and dynamic buckling of a column is derived. In the case of small initial disturbances the model yields simple analytical dependencies between the main parameters of the problem: critical force, compression rate, and initial disturbance. It is shown that the time required for buckling is inversely proportional to cubic root of compression velocity and logarithmically depends on the initial disturbance. Analytical expression for critical buckling force as a function of compression velocity is derived. It is shown that in a range of compression rates typical for laboratory experiments the dependence is accurately approximated by a power law with exponent equal to $2/3$. Theoretical findings are supported by available results of laboratory experiments. Keywords...
Micro-wrinkling and delamination-induced buckling of stretchable electronic structures
International Nuclear Information System (INIS)
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
Micro-wrinkling and delamination-induced buckling of stretchable electronic structures
Energy Technology Data Exchange (ETDEWEB)
Oyewole, O. K. [Department of Theoretical and Applied Physics, African University of Science and Technology, Km 10, Airport Road, Galadimawa, Abuja, Federal Capital Territory (Nigeria); Department of Materials Science and Engineering, Kwara State University, Malete, P.M.B 1530, Ilorin, Kwara State (Nigeria); Yu, D. [Department of Mechanical and Aerospace Engineering, Princeton University, Olden Street, Princeton, New Jersey 08544 (United States); Princeton Institute of Science and Technology of Materials, Princeton University, 70 Prospect Street, Princeton, New Jersey 08544 (United States); Du, J. [Department of Mechanical and Aerospace Engineering, Princeton University, Olden Street, Princeton, New Jersey 08544 (United States); Princeton Institute of Science and Technology of Materials, Princeton University, 70 Prospect Street, Princeton, New Jersey 08544 (United States); Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, 137 Reber Building, University Park, Pennsylvania (United States); Asare, J.; Fashina, A. [Department of Theoretical and Applied Physics, African University of Science and Technology, Km 10, Airport Road, Galadimawa, Abuja, Federal Capital Territory (Nigeria); Oyewole, D. O. [Department of Materials Science and Engineering, African University of Science and Technology, Km 10, Airport Road, Galadimawa, Abuja, Federal Capital Territory (Nigeria); Physics Advanced Laboratory, Sheda Science and Technology Complex, P.M.B 186, Garki, Abuja, Federal Capital Territory (Nigeria); Anye, V. C. [Department of Materials Science and Engineering, African University of Science and Technology, Km 10, Airport Road, Galadimawa, Abuja, Federal Capital Territory (Nigeria); Zebaze Kana, M. G. [Department of Materials Science and Engineering, Kwara State University, Malete, P.M.B 1530, Ilorin, Kwara State (Nigeria); Physics Advanced Laboratory, Sheda Science and Technology Complex, P.M.B 186, Garki, Abuja, Federal Capital Territory (Nigeria); and others
2015-06-21
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.
The effect of delaminations on local buckling in wind turbine blades
DEFF Research Database (Denmark)
Haselbach, Philipp Ulrich; Bitsche, Robert; Branner, Kim
2015-01-01
was setup in Abaqus and cohesive elements were chosen for modelling delamination growth. For initial delaminations with a width of 30–50% of the cap width the study showed that delamination close to the surface started to grow in load ranges of normal operation conditions and led to local buckling modes....... The local buckling caused high strains and stresses in the surrounding of the delamination, which exceeded the material design properties and therefore should be considered as dangerous. Delaminations placed near the mid-surface of the cap did not have a significant effect on the blade response under normal...... operation conditions. In the simulations the static load exceeded the design load by more than 40% before delamination growth or cap buckling occurred. It could be concluded that delamination induced near-surface buckling modes have to be considered critical due to an onset of local sublaminate buckling...
Micro-wrinkling and delamination-induced buckling of stretchable electronic structures
Oyewole, O. K.; Yu, D.; Du, J.; Asare, J.; Oyewole, D. O.; Anye, V. C.; Fashina, A.; Zebaze Kana, M. G.; Soboyejo, W. O.
2015-06-01
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.
Caught in the Act: Direct Detection of Galactic Bars in the Buckling Phase
Erwin, Peter; Debattista, Victor P.
2016-07-01
The majority of massive disk galaxies, including our own, have stellar bars with vertically thick inner region, known as “boxy/peanut-shaped” (B/P) bulges. The most commonly suggested mechanism for the formation of B/P bulges is a violent vertical “buckling” instability in the bar, something that has been seen in N-body simulations for over 20 years, but never identified in real galaxies. Here, we present the first direct observational evidence for ongoing buckling in two nearby galaxies (NGC 3227 and NGC 4569), including characteristic asymmetric isophotes and (in NGC 4569) stellar kinematic asymmetries that match buckling in simulations. This confirms that the buckling instability takes place and produces B/P bulges in real galaxies. A toy model of bar evolution yields a local fraction of buckling bars consistent with observations if the buckling phase lasts ∼0.5–1 Gyr, in agreement with simulations.
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...... are introduced, based on the buckling mode shapes from a linear eigenvalue buckling analysis. Different imperfect geometries are introduced to reveal how sensitive the buckling load is to these imperfections. Including the first 21 mode shapes as imperfect geometries will reduce the buckling pressure compared...
Intrinsic buckling strength of graphene: First-principles density functional theory calculations
Kumar, Sandeep; Hembram, K. P. S. S.; Waghmare, Umesh V.
2010-09-01
How graphene, an atomically thin two-dimensional crystal, explores the third spatial dimension by buckling under compression is not yet understood. Knowledge of graphene’s buckling strength, the load at which it transforms from planar to buckled form, is a key to ensure mechanical stability of graphene-based nanoelectronic and nanocomposite devices. Here, we establish using first-principles theoretical analysis that graphene has an intrinsic rigidity against buckling, and it manifests in a weakly linear component in the dispersion of graphene’s flexural acoustic mode, which is believed to be quadratic. Contrary to the expectation from the elastic plate theory, we predict within continuum analysis that a graphene monolayer of macroscopic size buckles at a nonzero critical compressive strain at T=0K , and demonstrate it numerically from first principles. The origin of this rigidity is traced to the coupling between structural and electronic degrees of freedom arising from curvature-induced overlap between π orbitals in graphene.
Buckling and Vibration of Fiber Reinforced Composite Plates With Nanofiber Reinforced Matrices
Chamis, Christos C.; Murthy, Pappu L. N.
2011-01-01
Anisotropic composite plates were evaluated with nanofiber reinforced matrices (NFRM). The nanofiber reinforcement volumes ratio in the matrix was 0.01. The plate dimensions were 20 by 10 by 1.0 in. (508 by 254 by 25.4 mm). Seven different loading condition cases were evaluated for buckling: three for uniaxial loading, three for pairs of combined loading, and one with three combined loadings. The anisotropy arose from the unidirectional plates having been at 30 from the structural axis. The anisotropy had a full 6 by 6 rigidities matrix which were satisfied and solved by a Galerkin buckling algorithm. For vibration the same conditions were used with the applied cods about a small fraction of the buckling loads. The buckling and vibration results showed that the NFRM plates buckled at about twice those with conventional matrix.
Analytical and experimental vibration and buckling characteristics of a pretensioned stayed column
Belvin, W. K.
1982-01-01
Modal vibration tests to determine lateral modes of vibration of a stayed column and static axial compression tests to determine the column's buckling and postbuckling behavior have been performed. Effects of stay tension levels and vibration-load interaction are presented. Two finite element models are used to analyze the column, a three-dimensional frame using NASTRAN and an equivalent two-dimensional frame using an exact dynamic stiffness matrix. Both analyses correlated well with the linear vibration and buckling experimental data. Results indicate premature buckling of the column due to vibration-load interaction and nonlinear oscillations due to stay slackening. Postbuckling behavior of the column is unusual because of stay slackening and results in a postbuckling restoring force of less than the bifurcation buckling load. Guidelines for design of pretensioned structures are presented which consider buckling, postbuckling and vibration behavior.
International Nuclear Information System (INIS)
Highlights: → We proposed the combination rule of multiple cracks as that of multiple flaws. → We proposed additional safety factor for conventional buckling equations. → The margin for the buckling load of a cylinder with multiple flaws is saved 2.0. - Abstract: The procedures described in based on the p-M (internal pressure ratio and external bending moment ratio) method () were used to predict the plastic initiation condition and the collapse condition for cylinders with a local thin area (LTA) subjected to combined internal pressure and bending moment. The effective wall thickness, t*, for the buckling assessment on a vessel with an LTA was proposed for use instead of wall thickness based on approximation which simply took into account only the effect of section modulus reduction (). The buckling evaluation on a vessel with an LTA was presented by and that was shown to be easily and adequately conducted by applying t* to the well-known Donnell's or Miller's equation. In this paper, the attention was focused on the procedure for assessing the buckling of large D/t vessels with multiple aligned or non-aligned local thin areas. From the comparison with the results of non-linear FEA, a combination rule and a buckling assessment procedure for multiple LTAs (flaws) subjected to external moment are proposed. The interaction-affected area for multiple cracks can be applied as the combination rule to evaluate the buckling of a large diameter vessel with multiple flaws subjected to external moment. From the comparison between the buckling loads of FEA results and the conventional buckling equations using the measured yield stress, an additional safety factor 'ks' is proposed so as to maintain the margin of 1.5. When the specified minimum yield stress is applied to Donnell's or Miller's equations, the margin for the buckling load of a cylinder with multiple flaws is more than 2.08 and 2.29, respectively.
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.
Torsional Buckling and Writhing Dynamics of Elastic Cables and DNA
Energy Technology Data Exchange (ETDEWEB)
Goyal, S; Perkins, N C; Lee, C L
2003-02-14
Marine cables under low tension and torsion on the sea floor can undergo a dynamic buckling process during which torsional strain energy is converted to bending strain energy. The resulting three-dimensional cable geometries can be highly contorted and include loops and tangles. Similar geometries are known to exist for supercoiled DNA and these also arise from the conversion of torsional strain energy to bending strain energy or, kinematically, a conversion of twist to writhe. A dynamic form of Kirchhoff rod theory is presented herein that captures these nonlinear dynamic processes. The resulting theory is discretized using the generalized-method for finite differencing in both space and time. The important kinematics of cross-section rotation are described using an incremental rotation ''vector'' as opposed to traditional Euler angles or Euler parameters. Numerical solutions are presented for an example system of a cable subjected to increasing twist at one end. The solutions show the dynamic evolution of the cable from an initially straight element, through a buckled element in the approximate form of a helix, and through the dynamic collapse of this helix through a looped form.
Euler buckling and nonlinear kinking of double-stranded DNA.
Fields, Alexander P; Meyer, Elisabeth A; Cohen, Adam E
2013-11-01
The bending stiffness of double-stranded DNA (dsDNA) at high curvatures is fundamental to its biological activity, yet this regime has been difficult to probe experimentally, and literature results have not been consistent. We created a 'molecular vise' in which base-pairing interactions generated a compressive force on sub-persistence length segments of dsDNA. Short dsDNA strands (Euler buckling'. We monitored the buckling transition via Förster Resonance Energy Transfer (FRET) between appended fluorophores. For low-to-moderate concentrations of monovalent salt (up to ∼150 mM), our results are in quantitative agreement with the worm-like chain (WLC) model of DNA elasticity, without the need to invoke any 'kinked' states. Greater concentrations of monovalent salts or 1 mM Mg(2+) induced an apparent softening of the dsDNA, which was best accounted for by a kink in the region of highest curvature. We tested the effects of all single-nucleotide mismatches on the DNA bending. Remarkably, the propensity to kink correlated with the thermodynamic destabilization of the mismatched DNA relative the perfectly complementary strand, suggesting that the kinked state is locally melted. The molecular vise is exquisitely sensitive to the sequence-dependent linear and nonlinear elastic properties of dsDNA.
Post Buckling Progressive Failure Analysis of Composite Laminated Stiffened Panels
Anyfantis, Konstantinos N.; Tsouvalis, Nicholas G.
2012-06-01
The present work deals with the numerical prediction of the post buckling progressive and final failure response of stiffened composite panels based on structural nonlinear finite element methods. For this purpose, a progressive failure model (PFM) is developed and applied to predict the behaviour of an experimentally tested blade-stiffened panel found in the literature. Failure initiation and propagation is calculated, owing to the accumulation of the intralaminar failure modes induced in fibre reinforced composite materials. Hashin failure criteria have been employed in order to address the fiber and matrix failure modes in compression and tension. On the other hand, the Tsai-Wu failure criterion has been utilized for addressing shear failure. Failure detection is followed with the introduction of corresponding material degradation rules depending on the individual failure mechanisms. Failure initiation and failure propagation as well as the post buckling ultimate attained load have been numerically evaluated. Final failure behaviour of the simulated stiffened panel is due to sudden global failure, as concluded from comparisons between numerical and experimental results being in good agreement.
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.
Modeling the buckling and delamination of thin films
Jagla, E. A.
2007-02-01
I study numerically the problem of delamination of a thin film elastically attached to a rigid substrate. A nominally flat elastic thin film is modeled using a two-dimensional triangular mesh. Both compression and bending rigidities are included to simulate compression and bending of the film. The film can buckle (i.e., abandon its flat configuration) when enough compressive strain is applied. The buckled configurations of a piece of film with stripe geometry are investigated as a function of the compressive strain. It is found that the stable configuration depends strongly on the applied strain and the Poisson ratio of the film. Next, the film is considered to be attached to a rigid substrate by springs that can break when the detaching force exceeds a threshold value, producing partial delamination of the film. Delamination is induced by a mismatch of the relaxed configurations of film and substrate. The morphology of the delaminated film can be followed and compared with available experimental results as a function of model parameters. “Telephone-cord,” polygonal, and “brainlike” patterns qualitatively similar to experimentally observed configurations are obtained in different parameter regions. The main control parameters that select the different patterns are the strain mismatch between film and substrate and the degree of in-plane relaxation within the unbuckled regions.
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.
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.
Buckling flows - Exploring the origins and structure of turbulence
Bejan, Adrian
1989-11-01
Numerous natural flow phenomena exhibit geometric features that invite an analogy with the classical buckling of solid elastic columns (Euler buckling). The most striking feature of these flows is the deformation of the straight stream into a sinusoidal shape whose wavelength is unique. Only the straightening effect of solid walls or the stabilizing effects of transversal viscous diffusion and density stratification can prevent the stream from exhibiting the sinusoidal deformation. Other turbulent flow features include: the transition to turbulence in all straight and slender flows occurring when the local Reynolds number exceeds 100; the Reynold number range of 100 of the smallest eddy in a turbulent flow; the viscous sublayer with a constant thickness of order 10 appearing in turbulent flow near a straight wall; the Strouhal number for vortex shedding behind a cylinder in a cross-flow, a constant between 0.2 and 0.3; and the Colburn analogy between heat transfer and friction in a turbulent flow near a wall.
Buckling instability of a thin-layer rectilinear Couette flow
Slim, Anja; Mahadevan, L
2011-01-01
We analyse the buckling stability of a thin, viscous sheet when subject to simple shear, providing conditions for the onset of the dominant out-of-plane modes using two models: (i) an asymptotic theory for the dynamics of a viscous plate and (ii) the full Stokes equations. In either case, the plate is stabilised by a combination of viscous resistance, surface tension and buoyancy relative to an underlying denser fluid. In the limit of vanishing thickness, plates buckle at a shear rate $\\gamma/(\\mu d)$ independent of buoyancy, where 2d is the plate thickness, $\\gamma$ is the average surface tension between the upper and lower surfaces and $\\mu$ is the fluid viscosity. For thicker plates stabilised by an equal surface tension at the upper and lower surfaces, at and above onset, the most unstable mode has moderate wavelength, is stationary in the frame of the centre-line, spans the width of the plate with crests and troughs aligned at approximately $45^\\circ$ to the walls and closely resembles elastic shear mode...
Buckling behaviour of PFBR main vessel and its thermal baffles under seismic loadings
International Nuclear Information System (INIS)
The special feature of pool type fast breeder reactor is the usage of very large sized thin shell structures for its reactor vessels. Due to the large diameter to thickness ratio (around 700 to 900), design of these vessels poses challenging structural mechanics problems particularly under seismic loading. An important threat to structural integrity of reactor vessels is the buckling risk during seismic events. The buckling design involves determination of critical buckling load and comparing it with operating load, to ensure that enough safety factors recommended by RCC-MR are available at all loading levels (RCC-MR 1985). The determination of critical buckling load particularly under seismic loading is a complicated task due to dynamic effects, non-axisymmetric nature of loading, material and geometrical nonlinearities, effect of geometric imperfections and boundary conditions and the interaction of different modes of buckling. Based on literature survey and extensive benchmark studies, the above complexities involved in the buckling analysis have been resolved and subsequent analysis is done for the main vessel and its thermal baffle of Prototype Fast Breeder Reactor (PFBR). The integrity of main vessel is very important since it forms an important part of primary containment and also carries around 1250 t of radioactive sodium. The integrity of thermal baffles is not very important during Safe Shutdown Earthquake (SSE) (level D) loading. However, for the operational basis earthquake (OBE) (Level-B loading), thermal baffles should be designed for meeting buckling criteria since either the loss of their integrity or large displacements may affect the cooling passage for the cold sodium flow and in turn, the temperature of main vessel may rise above the creep temperature. While the straight portion of main vessel is subjected to shear and bending mode of buckling, its dished end is subjected to shell mode buckling during seismic events. The dynamic pressure
Basu, Saptarshi; Bansal, Lalit; Miglani, Ankur
2016-06-14
The evaporation of a nanocolloidal sessile droplet exhibits preferential particle assembly, nanoporous shell formation and buckling to form cavities with unique morphological features. Here, we have established many universal trends that explain the buckling dynamics under one umbrella irrespective of hydrophobicity, evaporation mode and particle loading. We provide a regime map explaining the droplet morphology and buckling characteristics for droplet evaporation on various substrates. Specifically, we find that the final droplet volume and the radius of curvature at the buckling onset are universal functions of particle concentration. Furthermore, we establish that post-buckling cavity growth is evaporation driven regardless of the substrate.
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.
Large-Area Buckled MoS2 Films on the Graphene Substrate.
Kim, Seon Joon; Kim, Dae Woo; Lim, Joonwon; Cho, Soo-Yeon; Kim, Sang Ouk; Jung, Hee-Tae
2016-06-01
In this study, a novel buckled structure of edge-oriented MoS2 films is fabricated for the first time by employing monolayer graphene as the substrate for MoS2 film growth. Compared to typical buckling methods, our technique has several advantages: (1) external forces such as heat and mechanical strain are not applied; (2) uniform and controllable buckling over a large area is possible; and (3) films are able to be transferred to a desired substrate. Dual MoS2 orientation was observed in the buckled film where horizontally aligned MoS2 layers of 7 nm thickness were present near the bottom graphene surface and vertically aligned layers dominated the film toward the outer surface, in which the alignment structure was uniform across the entire film. The catalytic ability of the buckled MoS2 films, measured by performing water-splitting tests in acidic environments, shows a reduced onset potential of -0.2 V versus reversible hydrogen electrode (RHE) compared to -0.32 V versus RHE for pristine MoS2, indicating that the rough surface provided a higher catalytic activity. Our work presents a new method to generate a buckled MoS2 structure, which may be extended to the formation of buckled structures in various 2D materials for future applications. PMID:27144288
Large-Area Buckled MoS2 Films on the Graphene Substrate.
Kim, Seon Joon; Kim, Dae Woo; Lim, Joonwon; Cho, Soo-Yeon; Kim, Sang Ouk; Jung, Hee-Tae
2016-06-01
In this study, a novel buckled structure of edge-oriented MoS2 films is fabricated for the first time by employing monolayer graphene as the substrate for MoS2 film growth. Compared to typical buckling methods, our technique has several advantages: (1) external forces such as heat and mechanical strain are not applied; (2) uniform and controllable buckling over a large area is possible; and (3) films are able to be transferred to a desired substrate. Dual MoS2 orientation was observed in the buckled film where horizontally aligned MoS2 layers of 7 nm thickness were present near the bottom graphene surface and vertically aligned layers dominated the film toward the outer surface, in which the alignment structure was uniform across the entire film. The catalytic ability of the buckled MoS2 films, measured by performing water-splitting tests in acidic environments, shows a reduced onset potential of -0.2 V versus reversible hydrogen electrode (RHE) compared to -0.32 V versus RHE for pristine MoS2, indicating that the rough surface provided a higher catalytic activity. Our work presents a new method to generate a buckled MoS2 structure, which may be extended to the formation of buckled structures in various 2D materials for future applications.
Overall Buckling and Wringkling of Debonded Sandwich Beams: Finite Element and Experimental Results
Directory of Open Access Journals (Sweden)
Bambang K. Hadi
2006-05-01
Full Text Available Overall buckling and wrinkling of debonded sandwich beams under compressive loads were analyzed by both finite element and experimental methods. In the finite element method, a quarter and a half models of the specimens were analyzed. It shows that a quarter model is not adequate to analyze buckling of debonded sandwich beams, since it will disregard overall buckling mode that may occur in sandwich beams having compressive loads. At least a half model should be used to analyze buckling of sandwich beams. A finite element program UNA was used extensively to analyze the buckling loads. Experimental buckling of sandwich beams was carried out using a compression testing machine. Two LVDTs were used to measure deflections of the specimen during experimental loading. The loads were measured using load cells available in the machine. Specimens having core thickness of 45 and 75 mm were tested to represent overall and wrinkling modes respectively. The delamination lengths were 20, 60 and 80 mm, which represent 10, 30 and 40% of the beam length. The results show that the differences between experimental and finite element methods were less than 10%. Both overall buckling and wrinkling modes were shown in these specimens.
A map of competing buckling-driven failure modes of substrate-supported thin brittle films
Energy Technology Data Exchange (ETDEWEB)
Jia, Zheng [Department of Mechanical Engineering and Maryland NanoCenter, University of Maryland, College Park, MD 20742 (United States); Peng, Cheng [Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005 (United States); Lou, Jun, E-mail: jlou@rice.edu [Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005 (United States); Li, Teng, E-mail: lit@umd.edu [Department of Mechanical Engineering and Maryland NanoCenter, University of Maryland, College Park, MD 20742 (United States)
2012-08-31
Our in situ experiments of polyimide-supported thin indium tin oxide (ITO) films reveal buckling-driven film cracking in some samples and buckling-driven interfacial delamination in other samples. Although studies of individual buckling-driven failure mode exist, it still remains unclear what governs the competition between these two different failure modes in a given film/substrate structure. Through theoretical analysis and numerical simulations, we delineate a map of competing buckling-driven failure modes of substrate-supported thin brittle films in the parameter space of interfacial adhesion and interfacial imperfection size. Such a map can offer insight on the mechanical durability of functional thin films. For example, interestingly, we show that strongly bonded thin brittle films are more prone to buckling-driven cracking, a more detrimental failure mode for thin brittle ITO transparent conductors widely used in displays and flexible electronics. - Highlights: Black-Right-Pointing-Pointer Map of buckling-driven failure modes of thin brittle films on substrates. Black-Right-Pointing-Pointer We study key parameters that govern buckling-driven failure modes. Black-Right-Pointing-Pointer The map offers insights on optimal design of functional thin films.
Post-buckling analysis of composite beams: A simple intuitive formulation
Indian Academy of Sciences (India)
Jagadish Babu Gunda; G Venkateswara Rao
2013-06-01
Post-buckling analysis of composite beams with axially immovable ends is investigated using an Intuitive formulation. Intuitive formulation uses two parameters namely critical buckling load and axial stretching force developed in the post-buckled domain of composite beam. Geometric nonlinearity of von-Karman type is taken into consideration which accounts for membrane stretching action of the beam. Axial stretching force developed in post-buckled domain of composite beam is evaluated by using an axial governing equation and is expressed either in terms of lateral displacement function as an integrated value, or as a function of both axial and lateral displacement functions at any discrete location of the beam. The available expressions of critical buckling load and derived expressions of axial stretching force developed in the beam are used for obtaining an approximate closed-form expressions for the post-buckling loads of various beam boundary conditions. Numerical accuracy of the proposed analytical closed-form expressions obtained from the intuitive formulation are compared to the available ﬁnite element solutions for symmetric and asymmetric lay-up schemes of laminated composite beam. Effect of central amplitude ratio and lay-up orientation on post-buckling load variation is brieﬂy discussed for various beam boundary conditions considered in this study.
Finite element modeling of coupled global and local buckling of heated pipelines in soft clay
Energy Technology Data Exchange (ETDEWEB)
Cardoso, Carlos de Oliveira; Costa, Alvaro Maia da; Amaral, Claudio dos Santos [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas; Andueza, Alejandro [SERCON Engenharia, Rio de Janeiro, RJ (Brazil)
2003-07-01
This paper presents a new methodology to represent soil-heated pipelines interaction subjected to global-local buckling. The global buckling phenomenon could induce the local buckling of the pipeline wall that occurs due to strain localization in the critical pipeline section. The methodology presented in this paper uses mixed models in the simulation of coupled global-local buckling of heated pipelines considering its interaction with the surrounding soil. The mixed models use shell or 3D solid elements in the region subjected to the maximum bending moment, and 3D beam elements in the rest of the model to represent its thermal feed-in. The soil-pipeline interaction is represented by non-linear spring elements. The methodology using mixed models is used in the analysis of the rupture of PE-2 pipeline located in the Guanabara Bay of Rio de Janeiro, Brazil. The PE-2 pipeline accident occurred due to a lateral buckling caused by temperature gradient, internal pressure and restrictions imposed by the surrounding soil. The global buckling was followed by a plastic strain concentration, which generates a model failure, known as local buckling. (author)
Buckling Analysis of a Honeycomb-Core Composite Cylinder with Initial Geometric Imperfections
Cha, Gene; Schultz, Marc R.
2013-01-01
Thin-walled cylindrical shell structures often have buckling as the critical failure mode, and the buckling of such structures can be very sensitive to small geometric imperfections. The buckling analyses of an 8-ft-diameter, 10-ft-long honeycomb-core composite cylinder loaded in pure axial compression is discussed in this document. Two loading configurations are considered configuration 1 uses simple end conditions, and configuration 2 includes additional structure that may more closely approximate experimental loading conditions. Linear eigenvalue buckling analyses and nonlinear analyses with and without initial geometric imperfections were performed on both configurations. The initial imperfections were introduced in the shell by applying a radial load at the midlength of the cylinder to form a single inward dimple. The critical bifurcation buckling loads are predicted to be 924,190 lb and 924,020 lb for configurations 1 and 2, respectively. Nonlinear critical buckling loads of 918,750 lb and 954,900 lb were predicted for geometrically perfect configurations 1 and 2, respectively. Lower-bound critical buckling loads for configurations 1 and 2 with radial perturbations were found to be 33% and 36% lower, respectively, than the unperturbed critical loads. The inclusion of the load introduction cylinders in configuration 2 increased the maximum bending-boundary-layer rotation up to 11%.
Post-buckling failure in multi-delaminated composite wind turbine blade materials
International Nuclear Information System (INIS)
Highlights: → To study the buckling and post-buckling resistance of multi-delaminated composite structures. → To improve the post-buckling resistance of delaminated composite structures using natural flax yarn. → To investigate the effect of z-pinning on the interlaminar crack propagation in composite materials. → To develop FE techniques to model the buckling process of multi-delaminated composite structures using ANSYS. -- Abstract: This study models the inter-laminar damage due to low velocity impacts on hybrid composite materials typical of those used in wind turbine blade structures. The effect of z-pinning using natural flax yarn on the critical buckling load and post-buckling behaviour of multi-delaminated composite beams was investigated. Laminated composite beams were pinned through their thickness using natural flax yarns to control delamination failure during the post-buckling process. A multiple delamination with a triangular shape was inserted into each of the beams to simulate the damage caused by a low velocity impact e.g. ice, on composite wind turbine blades. For a laminate design of [C90/G90]4, global collapse caused no delamination failure during the post-buckling test while delamination failure occurred for a laminate design of [C0/G0]4. In this case, z-pinning can significantly increase the failure resistance within a composite structure and it can then postpone the failure process. The buckling process of a multi-delaminated composite beam was also simulated by finite element software ANSYS and the results were substantially verified by relevant experimental results.
Indian Academy of Sciences (India)
K Athiannan; R Palaninathan
2004-02-01
This paper presents experimental studies on buckling of cylindrical shell models under axial and transverse shear loads. Tests are carried out using an experimental facility specially designed, fabricated and installed, with provision for in-situ measurement of the initial geometric imperfections. The shell models are made by rolling and seam welding process and hence are expected to have imperfections more or less of a kind similar to that of real shell structures. The present work thus differs from most of the earlier investigations. The measured maximum imperfections $\\delta_{\\text{max}}$ are of the order of $\\pm 3t$ (t = thickness). The buckling loads obtained experimentally are compared with the numerical buckling values obtained through ﬁnite element method (FEM). In the case of axial buckling, the imperfect geometry is obtained in four ways and in the case of transverse shear buckling, the FE modelling of imperfect geometry is done in two ways. The initial geometric imperfections affect the load carrying capacity. The load reduction is considerable in the case of axial compression and is marginal in the case of transverse shear buckling. Comparisons between experimental buckling loads under axial compression, reveal that the extent of imperfection, rather than its maximum value, in a specimen inﬂuences the failure load. Buckling tests under transverse shear are conducted with and without axial constraints. While differences in experimental loads are seen to exist between the two conditions, the numerical values are almost equal. The buckling modes are different, and the experimentally observed and numerically predicted values are in complete disagreement.
Artery buckling analysis using a two-layered wall model with collagen dispersion.
Mottahedi, Mohammad; Han, Hai-Chao
2016-07-01
Artery buckling has been proposed as a possible cause for artery tortuosity associated with various vascular diseases. Since microstructure of arterial wall changes with aging and diseases, it is essential to establish the relationship between microscopic wall structure and artery buckling behavior. The objective of this study was to developed arterial buckling equations to incorporate the two-layered wall structure with dispersed collagen fiber distribution. Seven porcine carotid arteries were tested for buckling to determine their critical buckling pressures at different axial stretch ratios. The mechanical properties of these intact arteries and their intima-media layer were determined via pressurized inflation test. Collagen alignment was measured from histological sections and modeled by a modified von-Mises distribution. Buckling equations were developed accordingly using microstructure-motivated strain energy function. Our results demonstrated that collagen fibers disperse around two mean orientations symmetrically to the circumferential direction (39.02°±3.04°) in the adventitia layer; while aligning closely in the circumferential direction (2.06°±3.88°) in the media layer. The microstructure based two-layered model with collagen fiber dispersion described the buckling behavior of arteries well with the model predicted critical pressures match well with the experimental measurement. Parametric studies showed that with increasing fiber dispersion parameter, the predicted critical buckling pressure increases. These results validate the microstructure-based model equations for artery buckling and set a base for further studies to predict the stability of arteries due to microstructural changes associated with vascular diseases and aging. PMID:27031686
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...
Mechanical behavior of carbon nanotubes in the rippled and buckled phase
Jackman, H.; Krakhmalev, P.; Svensson, K.
2015-02-01
We have studied the mechanical behavior of multi-walled carbon nanotubes for bending strains beyond the onset for rippling and buckling. We found a characteristic drop in the bending stiffness at the rippling and buckling onset and the relative retained stiffness was dependent on the nanotube dimensions and crystallinity. Thin tubes are more prone to buckle, where some lose all of their bending stiffness, while thicker tubes are more prone to ripple and on average retain about 20% of their bending stiffness. In defect rich tubes, the bending stiffness is very low prior to rippling, but these tubes retain up to 70% of their initial bending stiffness.
Approximation of the plastic buckling load as the solution of an eigenvalue problem
Energy Technology Data Exchange (ETDEWEB)
Carnoy, E.G.; Panosyan, G. (Novatome Industries, 92 - Le Plessis-Robinson (France))
1984-04-01
Plastic buckling analysis of thin shell structures is generally performed by employing a Newton's type method within an incremental approach. This process becomes more efficient if a good estimate of the critical buckling load is available. This one can be obtained as the solution of an eigenvalue problem that generalizes the elastic bifurcation analysis. The stability matrix of the eigenvalue problem involves an additional term with respect to the elastic bifurcation problem; that is the material stiffness matrix that accounts for the change of the tangent modulus along the fundamental path. The proposed approach is applied to the elastoplastic buckling of spherical caps under pressure.
Analysis of the LOFT Modular Drag Disc Turbine Transducer (MDTT) spring for compressive buckling
International Nuclear Information System (INIS)
The LOFT Modular Drag Disc Turbine Transducer (MDTT) springs (for range 2, rhoV2 = 4900 lbm/ft-sec2) were analyzed to determine the static rhoV2 load needed to cause a buckling failure. The static load needed to cause elastic buckling was found to be equivalent to a rhoV2 value of 431,000 lbm/ft-sec2 according to classical buckling theory, but could be as low as rhoV2 = 100,000 lbm/ft-sec2 due to uncertain end fixity and other spring imperfections
Directory of Open Access Journals (Sweden)
Zoltán Juhász
2015-01-01
Full Text Available We analyse the buckling process of composite plates with through-the-width delamination and straight crack front applying uniaxial compression. We are focusing on the mixed mode buckling case, where the non-uniform distribution of the in-plane forces controls the occurence of the buckling of the delaminated layers. For the analysis, semi-discrete finite elements will be derived based on the Lèvy-type method. The method of harmonic balance is used for taking into account the force distribution that is generally non uniform in-plane.
Buckling and Delamination of Ti/Cu/Si Thin Film During Annealing
Lin, Qijing; Yang, Shuming; Jing, Weixuan; Li, Changsheng; Wang, Chenying; Jiang, Zhuangde; Jiang, Kely
2014-09-01
In this paper, the formation of buckling and delamination of sandwiched stacking of Ti/Cu/Si thin film are investigated. The crystallization structures, the composition of the Cu/Ti thin films, and the surface morphology are measured during annealing. The results show that the solid-phase reaction between Cu and Ti occurs at the interface. Buckling is initiated in the thin film annealed at 600°C. The volume expansion promotes the buckling and further produces microcracks. With increasing volume expansion, there are cavities formed in the middle layer when the annealing temperature is up to 700°C. Finally, thin film is delaminated from the substrate.
Mechanical buckling of multi-walled carbon nanotubes: The effects of slenderness ratio
Lu, Jian-Ming; Hwang, Chi-Chuang; Kuo, Qu-Yuan; Wang, Yun-Che
2008-03-01
Buckling strengths, in terms of compressive strain, of single-, double- and triple-walled carbon nanotubes (CNTs) are investigated to study the effects of slenderness ratio ( SR) via the molecular dynamics (MD) simulations with the Tersoff potential. Under constant ratio of slenderness, the CNTs with small SR behave like a continuum shell object. For large SR's, multi-walled CNTs exhibit the characteristics of the Euler columns. In addition, smaller nanotubes possess higher buckling-resistance. The buckling strength of multi-walled nanotubes is controlled by the size of their outermost shell.
Periumbilical allergic contact dermatitis: blue jeans or belt buckles?
Byer, Tara T; Morrell, Dean S
2004-01-01
Nickel is the most ubiquitous contact allergen among children and adolescents. Metal blue jeans buttons and belts have been noted to cause nickel dermatitis around the umbilicus. For these children, traditional teaching is strict avoidance of all pants with metal snaps/buttons, particularly blue jeans. In this study we tested 90 pairs of blue jeans and 47 belts for nickel using the dimethylglyoxime spot test. Only 10% of blue jeans tested positive, while 53% of belts tested positive. Furthermore, 10 pairs of nickel-negative blue jeans remained negative after 10 washings. Overall we found no resistance to testing in clothing stores. From these results, we recommend that patients with allergic contact dermatitis secondary to nickel need not strictly avoid blue jeans and metal belt buckles. Rather, families should be encouraged to use the dimethylglyoxime spot test to test these items for nickel prior to purchase.
Buckling failure of the automated planet finder spectrometer determinate spaceframe
Radovan, Matthew V.; Cabak, Gerald F.
2012-09-01
The Ken and Gloria Levy Spectrometer is now operational at a new 2.4 meter telescope on Mt. Hamilton. Together the spectrometer and telescope comprise the Automated Planet Finder (APF), a radial velocity instrument. A catastrophic failure occurred during transit as the instrument was being shipped to the observatory. Several struts buckled in the space frame that supported the echelle grating. This event has caused UCO/Lick to re-evaluate design methodology and how engineering safety factors apply to this type of structure. This paper describes the shipping container design, events during shipment, the failure mechanism, testing and analysis of a remedy, and its implementation. We also suggest design changes to prevent similar failures in the future.
Buckling Imperfection Sensitivity of Axially Compressed Orthotropic Cylinders
Schultz, Marc R.; Nemeth, Michael P.
2010-01-01
Structural stability is a major consideration in the design of lightweight shell structures. However, the theoretical predictions of geometrically perfect structures often considerably over predict the buckling loads of inherently imperfect real structures. It is reasonably well understood how the shell geometry affects the imperfection sensitivity of axially compressed cylindrical shells; however, the effects of shell anisotropy on the imperfection sensitivity is less well understood. In the present paper, the development of an analytical model for assessing the imperfection sensitivity of axially compressed orthotropic cylinders is discussed. Results from the analytical model for four shell designs are compared with those from a general-purpose finite-element code, and good qualitative agreement is found. Reasons for discrepancies are discussed, and potential design implications of this line of research are discussed.
Elastoswellability: Will it bend or will it buckle?
Holmes, Douglas; Pandey, Anupam
2013-03-01
Soft mechanical structures such as biological tissues and gels exhibit motion, instabilities, and large morphological changes when subjected to external stimuli. Swelling is a robust approach for inducing structural change as it occurs naturally in humid environments and can be easily adapted for industrial design. Small volumes of fluid that interact favorably with a material can cause large, dramatic, and geometrically nonlinear deformations including beam bending, plate buckling, and surface wrinkling. In this talk we address an overarching question regarding swelling-induced deformations: will the structural change occur globally, or will it be confined to the material's surface? We introduce a materials and geometry defined transition point that describes a fluid-structure's characteristic ``elastoswellability'' lengthscale. By locally swelling unconstrained slender beams and plates with solvents of varying solubility, we identify a transition between local surface wrinkling and global structural bending.
Buckling-driven Delamination in Layered Spherical Shells
DEFF Research Database (Denmark)
Sørensen, Kim Dalsten; Jensen, Henrik Myhre
2008-01-01
An analysis of buckling-driven delamination of a thin film on a spherical substrate has been carried out. The effects of the substrate having a double curvature compared to previous studies of delamination on cylindrical substrates turn out to be non-trivial: In addition to the effect of the shape...... of the substrate, a new non-dimensional geometrical parameter enters the conditions for steady-state delamination. It is shown that this additional geometrical parameter in most cases of practical relevance has insignificant influence on the fracture mechanical parameters involved for the problem. The consequence...... is that solutions need to be mapped as a function of one rather than two dimensionless parameters. Furthermore, the shape of the substrate has profound influence especially on initiation of delamination growth....
Buckling induced delamination of graphene composites through hybrid molecular modeling
Cranford, Steven W.
2013-01-01
The efficiency of graphene-based composites relies on mechanical stability and cooperativity, whereby separation of layers (i.e., delamination) can severely hinder performance. Here we study buckling induced delamination of mono- and bilayer graphene-based composites, utilizing a hybrid full atomistic and coarse-grained molecular dynamics approach. The coarse-grain model allows exploration of an idealized model material to facilitate parametric variation beyond any particular molecular structure. Through theoretical and simulation analyses, we show a critical delamination condition, where ΔD∝kL4, where ΔD is the change in bending stiffness (eV), k the stiffness of adhesion (eV/Å4), and L the length of the adhered section (Å).
Buckling-driven delamination in layered spherical shells
Sørensen, Kim D.; Jensen, Henrik M.
An analysis of buckling-driven delamination of a layer in a spherical, layered shell has been carried out. The effects of the substrate having a double curvature compared to previous studies of delamination on cylindrical substrates turn out to be non-trivial in the sense that additional to the effect of the shape of the substrate, a new non-dimensional geometrical parameter enters the conditions for steady-state delamination. It is shown that this additional geometrical parameter in most cases of practical relevance has insignificant influence on the fracture mechanical parameters involved for the problem. The consequence is that solutions need to be mapped as a function of one rather than two dimensionless parameters. Furthermore, the shape of the substrate has profound influence especially on initiation of delamination growth.
大展弦比机翼屈曲及后屈曲分析%BUCKLING AND POST-BUCKLING ANALYSIS OF HIGH ASPECT-RATIO WING
Institute of Scientific and Technical Information of China (English)
夏盛来; 何景武; 海尔瀚
2011-01-01
Adopting the FEM( finite element method) ,the buckling and post-buckling analyses are conducted based on the wing structure from some high aspect-ration composite material UAV( unmanned aerial vehicle) . During the analysis,the buckling of the wing structure is analyzed firstly with the help of Patran and Nastran software, aiming to ensure the sectors where the wing structure easily buckles. Then different buckling sectors are analyzed to make sure the detail model that needs the post-buckling analysis,during which the Patran and Marc software are adopted with the arc-length method. Through the post-buckling analysis, the buckling-path in the structure can be found out. The result indicates that the buckling phenomena exist in the wing. The result of the static test on the ground verifies the dependability of the analysis result.%针对某大展弦比复合材料无人机机翼结构,利用有限元素法进行机翼结构的屈曲及后屈曲分析.首先采用MSC.Patran/Nastran软件进行结构屈曲分析,目的是确定机翼结构易发生屈曲的区域；然后对不同区域进行分析,确定需要进行后屈曲分析的细节模型.对细节模型进行后屈曲分析时采用MSC.Patran/Marc软件,分析方法采用弧长法.通过机翼结构的后屈曲分析,可以分析出结构的失稳路径.结果表明,该机翼存在屈曲失稳问题.该机翼的地面静力试验结果验证分析结果的可信性.
Dynamic buckling in a next generation metal coolant nuclear reactor
Directory of Open Access Journals (Sweden)
G. Forasassi
2008-08-01
Full Text Available Purpose: The aim of the paper is to investigate the buckling effects due to the seismic sloshing phenomena interesting for a next generation heavy liquid metal cooled reactor as for example the eXperimental Accelerator Driven System (XADS.Design/methodology/approach: In this study the structural buckling behaviour of a reactor pressure vessel, retaining a rather large amount of liquid and many internal structures, is coupled to the fluid-structure interaction because during a postulated earthquake (e.g. Design Basis Earthquake the primary coolant surrounding the internals may be accelerated with a resulting significant fluid-structure hydrodynamic interaction (known as “sloshing”. Finite element numerical approach is applied because neither linear nor second-order potential theory is directly applicable when steep waves are present and local bulge appear with a marked decrease in strength of structure.Findings: The numerical results are presented and discussed highlighting the importance of the fluid-structure interaction effects in terms of stress intensity and impulsive pressure on the structural dynamic capability. These results allowed to determine the components mostly affected by the loading condition, in order to upgrade the geometrical design, if any, for the considered nuclear power plant (NPP.Research limitations/implications: The presented research results may be considered preliminary; thus it may be useful for a design upgrading of the reactor vessel and for achieving a first evaluation of the real components capacity to bear dynamic loads in particular in the event of a severe earthquake.Originality/value: From the point of view of the practical implication, it is worth to stress that the safety of liquid retaining nuclear structures subjected to a seismic loading is of great importance in regard to the hydrodynamic forces caused by sloshing and impulsive liquid motion determined by the liquid filling levels oscillatory
On Compliance and Buckling Objective Functions in Topology Optimization of Snap-Through Problems
DEFF Research Database (Denmark)
Lindgaard, Esben; Dahl, Jonas
2013-01-01
This paper deals with topology optimization of static geometrically nonlinear structures experiencing snap-through behaviour. Different compliance and buckling criterion functions are studied and applied for topology optimization of a point loaded curved beam problem with the aim of maximizing...... optimized design. A well-known issue in buckling topology optimization is artificial buckling modes in low density regions. The typical remedy applied for linear buckling does not have a natural extension to nonlinear problems, and we propose an alternative approach. Some possible negative implications...... of the analysis method and optimization formulation. We apply a nonlinear path tracing algorithm capable of detecting different types of stability points and an optimization formulation that handles possible mode switching. This is an extension into the topology optimization realm of a method developed, and used...
Structure buckling and non-probabilistic reliability analysis of supercavitating vehicles
Institute of Scientific and Technical Information of China (English)
AN Wei-guang; ZHOU Ling; AN Hai
2009-01-01
To perform structure buckling and reliability analysis on supercavitating vehicles with high velocity in the submarine, supercavitating vehicles were simplified as variable cross section beam firstly. Then structural buckling analysis of supercavitating vehicles with or without engine thrust was conducted, and the structural buckling safety margin equation of supercavitating vehicles was established. The indefinite information was de-scribed by interval set and the structure reliability analysis was performed by using non-probabilistic reliability method. Considering interval variables as random variables which satisfy uniform distribution, the Monte-Carlo method was used to calculate the non-probabilistic failure degree. Numerical examples of supercavitating vehi-cles were presented. Under different ratios of base diameter to cavitator diameter, the change tendency of non-probabilistic failure degree of structural buckling of supereavitating vehicles with or without engine thrust was studied along with the variety of speed.
Predictive analysis of buckling distortion of thin-plate welded structures
Institute of Scientific and Technical Information of China (English)
杨新岐; 霍立兴; 张玉凤; 阎俊霞
2002-01-01
The welding buckling distortions of thin-plated structures were investigated based on finite element methods. An engineering treatment method for predicating the buckling distortion was proposed. The equivalent applied thermal-load was used to simulate the welding residual stress, thus the calculation of complex welding distortion can be transformed into 3D elastic structural applied-load analyses, which can reduce the quantities of calculating work effectively. The validation of the method was verified by comparison of the numerical calculation with experimental results. The prediction of buckling distortion for side-walled structures of passenger train was performed and the calculation was in agreement with measuring results in general. It is shown that the main factors for producing the buckling are the intermittent fillet and plug weld during welding the stiffened beams and columns to the panel.
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
An analysis of buckling/snapping and bending behaviors of magneto-elastic-plastic interaction and coupling for cantilever rectangular soft ferromagnetic plates is presented. Based on the expression of magnetic force from the variational principle of ferromagnetic plates, the buckling and bending theory of thin plates, the Mises yield criterion and the increment theory for plastic deformation, we establish a numerical code to quantitatively simulate the behaviors of the nonlinearly multi-fields coupling problems by the finite element method. Along with the phenomena of buckling/snapping and bending, or the characteristic curve of deflection versus magnitude of applied magnetic fields being numerically displayed, the critical loads of buckling/snapping,and the influences of plastic deformation and the width of plate on these critical loads, the plastic regions expanding with the magnitude of applied magnetic field, as well as the evolvement of deflection configuration of the plate are numerically obtained in a case study.
Buckling analysis of an orthotropic thin shell of revolution using differential quadrature
Energy Technology Data Exchange (ETDEWEB)
Redekop, D. [Department of Mechanical Engineering, University of Ottawa, 161 Louis Pasteur, Ottawa, ON, K1N 6N5 (Canada)]. E-mail: dredekop@tesla.cc.uottawa.ca
2005-08-01
A method is developed to predict the buckling characteristics of an orthotropic shell of revolution of arbitrary meridian subjected to a normal pressure. The solution is given within the context of the linearized Sanders-Budiansky shell buckling theory and makes use of the differential quadrature method. Numerical results for buckling pressures and mode shapes are given for complete toroidal shells. Both completely free shells and shells with circumferential line restraints are covered. The loadings considered consist either of uniform pressure or circumferential bands of constant pressure. It is demonstrated that the differential quadrature method is numerically stable and converges. For isotropic toroidal shells, good agreement is observed with previously published analytical and finite element results. New results for buckling pressures and mode numbers are given for orthotropic shells and for band loaded shells.
Buckling and Delamination Growth Analysis of Composite Laminates Containing Embedded Delaminations
Hosseini-Toudeshky, H.; Hosseini, S.; Mohammadi, B.
2010-04-01
The objective of this work is to study the post buckling behavior of composite laminates, containing embedded delamination, under uniaxial compression loading. For this purpose, delamination initiation and propagation is modeled using the softening behavior of interface elements. The full layer-wise plate theory is also employed for approximating the displacement field of laminates and the interface elements are considered as a numerical layer between any two adjacent layers which delamination is expected to propagate. A finite element program was developed and the geometric non-linearity in the von karman sense is incorporated to the strain/displacement relations, to obtain the buckling behavior. It will be shown that, the buckling load, delamination growth process and buckling mode of the composite plates depends on the size of delamination and stacking sequence of the laminates.
Detailed modelling of delamination buckling of thin films under global tension.
Toth, F; Rammerstorfer, F G; Cordill, M J; Fischer, F D
2013-04-01
Tensile specimens of metal films on compliant substrates are widely used for determining interfacial properties. These properties are identified by the comparison of experimentally observed delamination buckling and a mathematical model which contains the interface properties as parameters. The current two-dimensional models for delamination buckling are not able to capture the complex stress and deformation states arising in the considered uniaxial tension test in a satisfying way. Therefore, three-dimensional models are developed in a multi-scale approach. It is shown that, for the considered uniaxial tension test, the buckling and associated delamination process are initiated and driven by interfacial shear in addition to compressive stresses in the film. The proposed model is able to reproduce all important experimentally observed phenomena, like cracking stress of the film, film strip curvature and formation of triangular buckles. Combined with experimental data, the developed computational model is found to be effective in determining interface strength properties.
External Pressure Forming and Buckling Analysis of Tubular Parts with Ribs
Institute of Scientific and Technical Information of China (English)
Gang LIU; Xuelian YIN; Shijian YUAN
2006-01-01
Buckling and forming processes of tubes with varying slenderness ratio(ratio of length to diameter)under external hydraulic pressure were analyzed with three-dimensional finite element method(FEM)for studying tube external pressure forming(EPF). Buckling pressures for different tube blanks without mandrel were predicted, and an EPF of a carbon steel tube onto a mandrel with six ribs was simulated. Both thickness distribution and buckling pressure from the simulations were found to be in agreement with those from experiments. Buckling pressures are shown to be a function of the slenderness ratio. The tubular part with six ribs produced by EPF has a uniform thickness distribution, whose maximum thinning rate is only 5.9%.
Buckling instability of thin films as a means to control or enhance fluid flow within microchannel
Tavakol, Behrouz; Chawan, Aschvin; Holmes, Douglas
2014-11-01
Here we show that the buckling of thin, flexible plates can be used for pumping fluids, controlling the flow rate, and mixing different media within a microfluidic channel. A confined, dielectric elastomeric film buckles out of the plane when exposed to an electric field. We use an electrolytic fluid solution as the electrode to enable buckling at relatively low voltages, and to enhance the rate of deformation. When embedded in a microfluidic channel, this mechanism can be used as a microvalve that controls the flow rate, or as a micropump that alters the flow rate. A similar mechanism can be used to aid diffusion between two adjacent laminar streams and improve mixing. This novel means for dielectric actuation may improve voltage application, and the buckling microstructures may be used in variety of applications to accurately control and manipulate fluid flow in a microchannel.
Buckling Instability of Dielectric Elastomeric Plates for Soft, Bio-Compatible Microfluidic Pumps
Tavakol, Behrouz; Bozlar, Michael; Froehlicher, Guillaume; Punckt, Christian; Stone, Howard A.; Aksay, Ilhan; Holmes, Douglas
2013-03-01
Dielectric elastomers are well-known for their superior stretchability and permittivity. A fully-clamped thin elastomer will buckle when it is compressed by applying sufficient electric potentials to its sides. When embedded within soft, silicone rubbers, these advanced materials can provide a means for a bio-compatible pumping mechanism that can be used to inject bio-fluids with desired flow rates into microfluidic devices, tissues, and organs of interest. We have incorporated a dielectric film that is sandwiched between two thin, flexible, solid electrodes into a microfluidic device and utilized a voltage-induced out-of-plane buckling instability for pumping of fluids. We experimentally quantify the voltage-induced plate buckling and measure the fluid flow rate when the structure is embedded in a microchannel. Additionally, we offer an analytical prediction that uses plate buckling theory to estimate the flow rate as a function of applied voltage.
Hoang, T M
2016-01-01
We explore how the stability and buckling behavior of a flexible but inextensible loop spanned by a liquid film in a flat circular configuration is influenced by the intrinsic shape of the fiber from which the loop is made.
Experimental and modelling buckling of wood-based columns under repeated loading
Bouras, F.; Chaplain, M.; Nafa, Z.
2010-06-01
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.
Effect of geometrical imperfection on buckling failure of ITER VVPSS tank
International Nuclear Information System (INIS)
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)
Vibration and Buckling of In-Plane Loaded Double-Walled Carbon Nano-Tubes
ECE, Metin AYDOĞDU and Mehmet Cem
2007-01-01
The paper studies vibration and buckling of in-plane loaded double-walled carbon nanotubes. Timoshenko beam theory was used to investigate the vibration and buckling behavior of double-walled and simply supported carbon nanotubes. The influence of in-plane loads on the natural frequencies was determined. The results show that while the natural frequencies decrease with increasing compressive in-plane loads an increase in frequencies is observed for tension type of in-plane loads. T...
Local buckling analysis of biological nanocomposites based on a beam-spring model
Zhiling Bai; Baohua Ji
2015-01-01
Biological materials such as bone, tooth, and nacre are load-bearing nanocomposites composed of mineral and protein. Since the mineral crystals often have slender geometry, the nanocomposites are susceptible to buckle under the compressive load. In this paper, we analyze the local buckling behaviors of the nanocomposite structure of the biological materials using a beam-spring model by which we can consider plenty of mineral crystals and their interaction in our analysis compared with existin...
How Does A Porous Shell Collapse? Delayed Buckling And Guided Folding Of Inhomogeneous Capsules
Datta, Sujit S.; Kim, Shin-Hyun; Paulose, Jayson; Abbaspourrad, Alireza; Nelson, David R; Weitz, David A.
2012-01-01
Colloidal capsules can sustain an external osmotic pressure; however, for a sufficiently large pressure, they will ultimately buckle. This process can be strongly influenced by structural inhomogeneities in the capsule shells. We explore how the time delay before the onset of buckling decreases as the shells are made more inhomogeneous; this behavior can be quantitatively understood by coupling shell theory with Darcy's law. In addition, we show that the shell inhomogeneity can dramatically c...
Design optimization of blade stiffened laminated composite plates for maximum buckling load
Achenbach, Mark R.
1990-01-01
Approved for public release; distribution unlimited. The buckling load of a blade stiffened laminated composite plate having midplane symmetry is maximized for a given total weight. The thickness of the layers and the width and height of the stiffener are taken as the design variables. Buckling analysis is carried out using a finite element method. The optimization problem is solved using commercially available optimization packages. Due to the highly nonlinear nature of the optimality equ...
Serttunc, Metin
1992-01-01
Approved for public release; distribution is unlimited Analyses were performed for static and dynamic buckling of a continuous fiber embedded in a matrix and fiber breakage in order to determine the effects of interfacial debonding on the critical buckling load and the domain of instability. A beam on elastic foundation model was used for this study. The study showed that a local interfacial debonding between a fiber and a surrounding matrix resulted in an increase of the waveleng...
Buckling of Slender Prismatic Columns with a Single Edge Crack under Concentric Vertical Loads
GÜREL, M. Arif
2005-01-01
The investigation of the stability behavior of slender columns with cracks is an important problem and finds applications in structural, mechanical and aerospace engineering. This study investigates the buckling of slender prismatic columns with a single nonpropagating edge crack subjected to concentrated vertical loads. The transfer matrix method and fundamental solutions of intact columns (columns without any cracks) are combined for determining the buckling loads of cracked column...
Analysis of Buckled and Pre-bent Columns Used as Vibration Isolators
Sidbury, Jenny Elizabeth
2003-01-01
Analysis of Buckled and Pre-bent Columns Used as Vibration Isolators By Jenny E. Sidbury Dr. Raymond H. Plaut, Chairman Charles E. Via, Jr. Department of Civil and Environmental Engineering (ABSTRACT) Vibrations resulting from earthquakes, machinery, or unanticipated shocks may be very damaging and costly to structures. To avoid such damage, designers need a structural system that can dissipate the energy caused by these vibrations. Using elastically buckled struts may be a viable means ...
On the structure of Si(100) surface: Importance of higher order correlations for buckled dimer
Back, Seoin; Schmidt, Johan A.; Ji, Hyunjun; Heo, Jiyoung; Shao, Yihan; Jung, Yousung
2013-01-01
We revisit a dangling theoretical question of whether the surface reconstruction of the Si(100) surface would energetically favor the symmetric or buckled dimers on the intrinsic potential energy surfaces at 0 K. This seemingly simple question is still unanswered definitively since all existing density functional based calculations predict the dimers to be buckled, while most wavefunction based correlated treatments prefer the symmetric configurations. Here, we use the doubly hybrid density f...
An Analytical Solution for Lateral Buckling Critical Load Calculation of Leaning-Type Arch Bridge
Directory of Open Access Journals (Sweden)
Ai-rong Liu
2014-01-01
Full Text Available An analytical solution for lateral buckling critical load of leaning-type arch bridge was presented in this paper. New tangential and radial buckling models of the transverse brace between the main and stable arch ribs are established. Based on the Ritz method, the analytical solution for lateral buckling critical load of the leaning-type arch bridge with different central angles of main arch ribs and leaning arch ribs under different boundary conditions is derived for the first time. Comparison between the analytical results and the FEM calculated results shows that the analytical solution presented in this paper is sufficiently accurate. The parametric analysis results show that the lateral buckling critical load of the arch bridge with fixed boundary conditions is about 1.14 to 1.16 times as large as that of the arch bridge with hinged boundary condition. The lateral buckling critical load increases by approximately 31.5% to 41.2% when stable arch ribs are added, and the critical load increases as the inclined angle of stable arch rib increases. The differences in the center angles of the main arch rib and the stable arch rib have little effect on the lateral buckling critical load.
Local buckling analysis of biological nanocomposites based on a beam-spring model
Directory of Open Access Journals (Sweden)
Zhiling Bai
2015-07-01
Full Text Available Biological materials such as bone, tooth, and nacre are load-bearing nanocomposites composed of mineral and protein. Since the mineral crystals often have slender geometry, the nanocomposites are susceptible to buckle under the compressive load. In this paper, we analyze the local buckling behaviors of the nanocomposite structure of the biological materials using a beam-spring model by which we can consider plenty of mineral crystals and their interaction in our analysis compared with existing studies. We show that there is a transition of the buckling behaviors from a local buckling mode to a global one when we continuously increase the aspect ratio of mineral, leading to an increase of the buckling strength which levels off to the strength of the composites reinforced with continuous crystals. We find that the contact condition at the mineral tips has a striking effect on the local buckling mode at small aspect ratio, but the effect diminishes when the aspect ratio is large. Our analyses also show that the staggered arrangement of mineral plays a central role in the stability of the biological nanocomposites.
Directory of Open Access Journals (Sweden)
Caiqi Zhao
2016-06-01
Full Text Available To solve the problem of critical buckling in the structural analysis and design of the new long-span hollow core roof architecture proposed in this paper (referred to as a “honeycomb panel structural system” (HSSS, lateral compression tests and finite element analyses were employed in this study to examine the lateral compressive buckling performance of this new type of honeycomb panel with different length-to-thickness ratios. The results led to two main conclusions: (1 Under the experimental conditions that were used, honeycomb panels with the same planar dimensions but different thicknesses had the same compressive stiffness immediately before buckling, while the lateral compressive buckling load-bearing capacity initially increased rapidly with an increasing honeycomb core thickness and then approached the same limiting value; (2 The compressive stiffnesses of test pieces with the same thickness but different lengths were different, while the maximum lateral compressive buckling loads were very similar. Overall instability failure is prone to occur in long and flexible honeycomb panels. In addition, the errors between the lateral compressive buckling loads from the experiment and the finite element simulations are within 6%, which demonstrates the effectiveness of the nonlinear finite element analysis and provides a theoretical basis for future analysis and design for this new type of spatial structure.
Determination of the critical buckling pressure of blood vessels using the energy approach.
Han, Hai-Chao
2011-03-01
The stability of blood vessels under lumen blood pressure is essential to the maintenance of normal vascular function. Differential buckling equations have been established recently for linear and nonlinear elastic artery models. However, the strain energy in bent buckling and the corresponding energy method have not been investigated for blood vessels under lumen pressure. The purpose of this study was to establish the energy equation for blood vessel buckling under internal pressure. A buckling equation was established to determine the critical pressure based on the potential energy. The critical pressures of blood vessels with small tapering along their axis were estimated using the energy approach. It was demonstrated that the energy approach yields both the same differential equation and critical pressure for cylindrical blood vessel buckling as obtained previously using the adjacent equilibrium approach. Tapering reduced the critical pressure of blood vessels compared to the cylindrical ones. This energy approach provides a useful tool for studying blood vessel buckling and will be useful in dealing with various imperfections of the vessel wall.
Torres, Fernando G; Troncoso, Omar P; Diaz, John; Arce, Diego
2014-11-01
Porcupine quills are natural structures formed by a thin walled conical shell and an inner foam core. Axial compression tests, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) were all used to compare the characteristics and mechanical properties of porcupine quills with and without core. The failure mechanisms that occur during buckling were analyzed by scanning electron microscopy (SEM), and it was found that delamination buckling is mostly responsible for the decrease in the measured buckling stress of the quills with regard to predicted theoretical values. Our analysis also confirmed that the foam core works as an energy dissipater improving the mechanical response of an empty cylindrical shell, retarding the onset of buckling as well as producing a step wise decrease in force after buckling, instead of an instantaneous decrease in force typical for specimens without core. Cell collapse and cell densification in the inner foam core were identified as the key mechanisms that allow for energy absorption during buckling.
Energy Technology Data Exchange (ETDEWEB)
Potoczny, G.A. [School of Metallurgy and Materials, University of Birmingham, Edgbaston, B15 2TT Birmingham (United Kingdom); Bejitual, T.S. [Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, 26506, West Virginia (United States); Abell, J.S. [School of Metallurgy and Materials, University of Birmingham, Edgbaston, B15 2TT Birmingham (United Kingdom); Sierros, K.A. [Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, 26506, West Virginia (United States); Cairns, D.R., E-mail: Darran.Cairns@mail.wvu.edu [Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, 26506, West Virginia (United States); Kukureka, S.N. [School of Metallurgy and Materials, University of Birmingham, Edgbaston, B15 2TT Birmingham (United Kingdom)
2013-01-01
The flexibility and electrical stability of highly conductive and transparent amorphous indium tin oxide (a-ITO) films coated on polyethylene terephthalate and polyethylene naphthalate substrates were investigated by buckling tests with in situ monitoring of the electrical resistance. Monotonic and cyclic loading tests of the ITO/polymer systems were conducted. The results show that monotonic buckling in tension is more critical for electromechanical stability of ITO films than in compression (an increase in electrical resistance was observed at a critical radius of curvature, of ∼ 3 and ∼ 1 mm, respectively for both cases investigated). In contrast, cyclic loading tests show that the compression mode is more critical than the tensile mode which may be a result of the residual stress present in the film structure. Failure of the ITO film was caused by buckling-driven delamination observed using scanning electron microscopy after the tests. The presence of residual stress could mean that buckling-driven delamination is the dominant failure mode for ITO/polymer systems under repeated flexing. In general, comparable electromechanical stability was observed in both cases. Investigating the electromechanical response of such material systems is important for polymer substrate selection and life-time prediction of flexible polyester-based electronic devices. - Highlights: ► Cyclic buckling investigation of flexible electrodes. ► Importance of ITO surface compression mode as opposed to tension. ► Role of ITO residual stresses on controlled buckling investigations.
Directory of Open Access Journals (Sweden)
Tongqing Lu
2014-01-01
Full Text Available In a thin film-substrate system in-plane compressive stress is commonly generated in the film due to thermal mismatch in operation or fabrication process. If the stress exceeds a critical value, part of the film may buckle out of plane along the defective interface. After buckling delamination, the interface crack at the ends may propagate. In the whole process, the compliance of the substrate compared with the film plays an important role. In this work, we study a circular film subject to compressive stress on an infinitely thick substrate. We study the effects of compliance of the substrate by modeling the system as a plate on an elastic foundation. The critical buckling condition is formulated. The asymptotic solutions of post-buckling deformation and the corresponding energy release rate of the interface crack are obtained with perturbation methods. The results show that the more compliant the substrate is, the easier for the film to buckle and easier for the interface crack to propagate after buckling.
Effect of loading pulse duration on dynamic buckling of stiffened panels
Directory of Open Access Journals (Sweden)
Mouhat O.
2014-01-01
Full Text Available Design of stiffened panels requires evaluating their stability under various loading combinations for all possible scenarios regarding material degradation or initial geometric imperfections that could affect them. Both static and dynamic loading conditions are to be investigated for assessing the buckling strength. In this work, dynamic buckling under in-plane uniform axial compression loading having the form of a transient pulse with finite duration is evaluated through nonlinear finite element modelling. A welding induced defect that consists of an initial geometric imperfection modifying the skin plate curvature in the longitudinal direction was incorporated. The Budiansky buckling criterion was employed to predict instability under this dynamic loading. The obtained results have shown that the pulse period yields a drastic effect on the buckling strength. For the considered boundary conditions, half-sine like pulses having periods that are comparable to two times the period of the first mode of natural vibrations of the stiffened plate were found to reduce hugely the buckling strength, with the dynamic buckling load representing almost only half its static value.
Head, D. A.
2006-01-01
Motivated by the buckling of glassy crusts formed on evaporating droplets of polymer and colloid solutions, we numerically model the deformation and buckling of spherical elastic caps controlled by varying the volume between the shell and the substrate. This volume constraint mimics the incompressibility of the unevaporated solvent. Discontinuous buckling is found to occur for sufficiently thin and/or large contact angle shells, and robustly takes the form of a single circular region near the...
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.
Institute of Scientific and Technical Information of China (English)
Su-deok SHON; Seung-jae LEE; Kang-guk LEE
2013-01-01
This study investigated characteristics of bifurcation and critical buckling load by shape imperfection of space truss,which were sensitive to initial conditions.The critical point and buckling load were computed by the analysis of the eigenvalues and determinants of the tangential stiffness matrix.The two-free-nodes example and star dome were selected for the case study in order to examine the nodal buckling and global buckling by the sensitivity to the eigen buckling mode and the analyses of the influence,and characteristics of the parameters as defined by the load ratio of the center node and surrounding node,as well as rise-span ratio were performed.The sensitivity to the imperfection of the initial shape of the two-free-nodes example,which occurs due 1o snapping at the critical point,resulted in bifurcation before the limit point due to the buckling mode,and the buckling load was reduced by the increase in the amount of imperfection.The two sensitive buckling patterns of the numerical model are established by investigating the displaced position of the free nodes,and the asymmetric eigenmode greatly influenced the behavior of the imperfection shape whether it was at limit point or bifurcation.Furthermore,the sensitive mode of the two-free-nodes example was similar to the in-extensional basis mechanism of a simplified model.The star dome,which was used to examine the influence among several nodes,indicated that the influence of nodal buckling was greater than that of global buckling as the rise-span ratio was higher.Besides,global buckling is occurred with reaching bifurcation point as the value of load ratio was higher,and the buckling load level was about 50％-70％ of load level at limit point.
Imperfection sensitivity of pressured buckling of biopolymer spherical shells
Zhang, Lei; Ru, C. Q.
2016-06-01
Imperfection sensitivity is essential for mechanical behavior of biopolymer shells [such as ultrasound contrast agents (UCAs) and spherical viruses] characterized by high geometric heterogeneity. In this work, an imperfection sensitivity analysis is conducted based on a refined shell model recently developed for spherical biopolymer shells of high structural heterogeneity and thickness nonuniformity. The influence of related parameters (including the ratio of radius to average shell thickness, the ratio of transverse shear modulus to in-plane shear modulus, and the ratio of effective bending thickness to average shell thickness) on imperfection sensitivity is examined for pressured buckling. Our results show that the ratio of effective bending thickness to average shell thickness has a major effect on the imperfection sensitivity, while the effect of the ratio of transverse shear modulus to in-plane shear modulus is usually negligible. For example, with physically realistic parameters for typical imperfect spherical biopolymer shells, the present model predicts that actual maximum external pressure could be reduced to as low as 60% of that of a perfect UCA spherical shell or 55%-65% of that of a perfect spherical virus shell, respectively. The moderate imperfection sensitivity of spherical biopolymer shells with physically realistic imperfection is largely attributed to the fact that biopolymer shells are relatively thicker (defined by smaller radius-to-thickness ratio) and therefore practically realistic imperfection amplitude normalized by thickness is very small as compared to that of classical elastic thin shells which have much larger radius-to-thickness ratio.
Kelvin-Helmholtz and Buckling Instabilities for a Viscoelastic Liquid
Keshavarz, Bavand
2012-01-01
In this fluid dynamics video prepared for the APS-DFD Gallery of Fluid Motion we study the Kelvin-Helmholtz instability for both Newtonian and viscoelastic jets. The nonlinear dynamics of the jet motion are slowed down by orders of magnitude using a synchronized strobe effect coupled with precise timing control of perturbation frequencies. Our results show that at high wave-numbers the imposed perturbations initially grow linearly with time and the jet axis remains straight while the Kelvin-Helmholtz wave amplitude grows and rolls up into bags that encapsulate the central jet within themselves. At low wave-numbers (long wave-lengths) the jet axis buckles under the action of viscous stresses and a coupling between the Kelvin-Helmholtz instability and bending of the jet leads to new concertina or chevron modes which grow with time as they move downstream. Addition of viscoelasticity to the jet leads to the pronounced inhibition of the Kelvin-Helmholtz instability as the jet perturbation amplitude grows and larg...
Polymer Thin Film Buckling: Wrinkling and Strain Localizations
Ebata, Yuri; Croll, Andrew B.; Crosby, Alfred J.
2011-03-01
Out of plane deformations of thin films are observed in everyday life, e.g. wrinkled aging human skin or folded fabrics. Recently, these deformations are being pursued for fabricating unique patterned surfaces. In this study, the transition from wrinkling, a low-strain buckling behavior, to localized deformations such as fold and delamination, is investigated for polystyrene films with thickness ranging from 5nm to 180nm. The thin films are attached to a uniaxially strained polydimethysiloxane substrate and the strain is released incrementally to apply increasing compressive strain to the attached film. The wavelength and the amplitude of local out-of-plane deformation are measured as global compression is increased to distinguish between wrinkling, folding, and delamination. The transition from wrinkling to strain localizing events is observed by tracking the statistics of amplitude distribution sampled across a large lateral area. A critical strain map is constructed to denote the strain regimes at which wrinkle, fold, and delamination occur. NSF-DMR 0907219.
Buckling delamination induced microchannel: Flow regulation in microfluidic devices
Kang, Jingtian; Wang, Changguo; Xue, Zhiming; Liu, Mengxiong; Tan, Huifeng
2016-09-01
The buckling delamination induced microchannel is employed to regulate fluid flow as a microvalve which can be utilized in microfluidic devices. This microvalve consists of a soft substrate and a stiff thin film, between which there is a pre-set small imperfection. Two critical strain values, namely, on-off strain and failure strain, have been proposed to determine the working strain interval using analytical predictions. Within this interval, the cross-sectional area of the microchannel can be controlled and predicted by different compressive strains of the film/substrate system. The fluid flow rate within this microchannel can be then estimated by both analytical and numerical simulations and adjusted to satisfy different values by alternating the compressive strain. In addition, a demonstrative experiment has been taken to verify the feasibility of this approach. This flexible microvalve has potential in the application where the use of traditional rigid microvalves is improper in flexible microfluidic devices. The method and approach of this paper can provide a general guide for flow rate control in microfluidic devices.
Buckling of Dielectric Elastomeric Plates for Electrically Active Microfludic Pumps
Holmes, Douglas; Tavakol, Behrouz; Bozlar, Michael; Froehlicher, Guillaume; Stone, Howard; Aksay, Ilhan
2013-11-01
Fluid flow can be directed and controlled by a variety of mechanisms within industrial and biological environments. Advances in microfluidic technology have required innovative ways to control fluid flow on a small scale, and the ability to actively control fluid flow within microfluidic devices is crucial for advancements in nanofluidics, biomedical fluidic devices, and digital microfluidics. In this work, we present a means for microfluidic control via the electrical actuation of thin, flexible valves within microfluidic channels. These structures consist of a dielectric elastomer confined between two compliant electrodes that can be actively and reversibly buckle out of plane to pump fluids from an applied voltage. The out-of-plane deformation can be quantified using two parameters: net change in surface area and the shape of deformation. Change in surface area depends on the voltage, while the deformation shape, which significantly affects the flow rate, is a function of voltage, and the pressure and volume of the chambers on each side of the thin plate. The use of solid electrodes enables a robust and reversible pumping mechanism that will have will enable advancements in rapid microfluidic diagnostics, adaptive materials, and artificial muscles.
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.
Ko, William L.
1995-01-01
Thermal buckling characteristics of hypersonic aircraft sandwich panels of various aspect ratios were investigated. The panel is fastened at its four edges to the substructures under four different edge conditions and is subjected to uniform temperature loading. Minimum potential energy theory and finite element methods were used to calculate the panel buckling temperatures. The two methods gave fairly close buckling temperatures. However, the finite element method gave slightly lower buckling temperatures than those given by the minimum potential energy theory. The reasons for this slight discrepancy in eigensolutions are discussed in detail. In addition, the effect of eigenshifting on the eigenvalue convergence rate is discussed.
Institute of Scientific and Technical Information of China (English)
Zhang Shanyuan; Lei Jianping; Zhao Longmao; Cheng Guoqiang; Lu Guoyun
2000-01-01
This article reports an experimental investigation on the axial impact buckling of thin metallic cylindrical shells fully filled with water. Low velocity impact tests are carried out by DHR-9401 drop hammer rig. The whole process of dynamic buckling is simulated using LS-DYNA computer code. The consistency between experimental observation and numerical simulation is quite satisfactory. The investigation indicates that quite high internal hydrodynamic pressure occurs inside the shell during the impact process. Under the combined action of the high internal pressure and axial compression plastic buckling occurs easily in the thin walled shells and buckling modes take on regular and axisymmetric wrinkles.
Anomalous elastic buckling of layered crystalline materials in the absence of structure slenderness
Ren, Manrui; Liu, Yilun; Zhe Liu, Jefferson; Wang, Lifeng; Zheng, Quanshui
2016-03-01
Layered crystalline materials, such as graphene, boron nitride, tungsten sulfate, phosphorene, etc., have attracted enormous attentions, due to their unique crystal structures and superior mechanical, thermal, and physical properties. Making use of mechanical buckling is a promising route to control their structural morphology and thus tune their physical properties, giving rise to many novel applications. In this paper, we employ molecular dynamics (MD) simulations and theoretical modeling to study the compressive buckling of a column made of layered crystalline materials with the crystal layers parallel to the compressive direction. We find that the mechanical buckling of the layered crystalline materials exhibits two anomalous and counter-intuitive features as approaching the zero slenderness ratio. First, the critical buckling strain εcr has a finite value that is much lower than the material's elastic limit strain. A continuum mechanics model (by homogenizing the layered materials) is proposed for the εcr, which agrees well with the results of MD simulations. We find that the εcr solely depends on elastic constants without any structural dimension, which appears to be an intrinsic material property and thus is defined as intrinsic buckling strain (IBS), εcrIBS , in this paper. Second, below a certain nanoscale length, l0, in the compressive direction (e.g., about 20 nm for graphite), the critical buckling strain εcr shows a size effect, i.e., increasing as the column length L decreases. To account for the size effect, inspired by our recently developed multi-beam shear model (Liu et al., 2011), a bending energy term of individual crystal layer is introduced in our continuum model. The theoretical model of εcr agrees well with the size effects observed in MD simulations. This study could lay a ground for engineering layered crystalline materials in various nano-materials and nano-devices via mechanical buckling.
TRBUCKL - A NASTRAN DMAP ALTER FOR LINEAR BUCKLING ANALYSIS UNDER DYNAMIC LOADING
Aiello, R. A.
1994-01-01
Delaminations near the outer surface of a laminate are susceptible to local buckling and buckling-induced delamination propagation when the laminate is subjected to transverse impact loading. This results in a loss of stiffness and strength. TRBUCKL is an unique dynamic delamination buckling and delamination propagation analysis capability that can be incorporated into the structural analysis program, NASTRAN. This capability will aid engineers in the design of structures incorporating composite laminates. The capability consists of: (1) a modification of the direct time integration solution sequence which provides a new analysis algorithm that can be used to predict delamination buckling in a laminate subjected to dynamic loading; and (2) a new method of modeling the composite laminate using plate bending elements and multipoint constraints. The capability now exists to predict the time at which the onset of dynamic delamination buckling occurs, the dynamic buckling mode shape, and the dynamic delamination strain energy release rate. A procedure file for NASTRAN, TRBUCKL predicts both impact induced buckling in composite laminates with initial delaminations and the strain energy release rate due to extension of the delamination. In addition, the file is useful in calculating the dynamic delamination strain energy release rate for a composite laminate under impact loading. This procedure simplifies the simulation of progressive crack extension. TRBUCKL has been incorporated into COSMIC NASTRAN. TRBUCKL is a DMAP Alter for NASTRAN. It is intended for use only with the COSMIC NASTRAN Direct Transient Analysis (RF 9) solution sequence. The program is available as a listing only. TRBUCKL was developed in 1987.
Mathematical modeling and full-scale shaking table tests for multi-curve buckling restrained braces
Institute of Scientific and Technical Information of China (English)
C. S. Tsai; Yungchang Lin; Wenshin Chen; H. C. Su
2009-01-01
Buckling restrained braces (BRBs) have been widely applied in seismic mitigation since they were introduced in the 1970s. However, traditional BRBs have several disadvantages caused by using a steel tube to envelope the mortar to prevent the core plate from buckling, such as: complex interfaces between the materials used, uncertain precision, and time consumption during the manufacturing processes. In this study, a new device called the multi-curve buckling restrained brace (MC-BRB) is proposed to overcome these disadvantages. The new device consists of a core plate with multiple neck portions assembled to form multiple energy dissipation segments, and the enlarged segment, lateral support elements and constraining elements to prevent the BRB from buckling. The enlarged segment located in the middle of the core plate can be welded to the lateral support and constraining elements to increase buckling resistance and to prevent them from sliding during earthquakes. Component tests and a series of shaking table tests on a full-scale steel structure equipped with MC-BRBs were carried out to investigate the behavior and capability of this new BRB design for seismic mitigation. The experimental results illustrate that the MC-BRB possesses a stable mechanical behavior under cyclic loadings and provides good protection to structures during earthquakes. Also, a mathematical model has been developed to simulate the mechanical characteristics of BRBs.
Directory of Open Access Journals (Sweden)
Kaspars Kalnins
2015-01-01
Full Text Available Nondestructive methods, to calculate the buckling load of imperfection sensitive thin-walled structures, such as large-scale aerospace structures, are one of the most important techniques for the evaluation of new structures and validation of numerical models. The vibration correlation technique (VCT allows determining the buckling load for several types of structures without reaching the instability point, but this technique is still under development for thin-walled plates and shells. This paper presents and discusses an experimental verification of a novel approach using vibration correlation technique for the prediction of realistic buckling loads of unstiffened cylindrical shells loaded under axial compression. Four different test structures were manufactured and loaded up to buckling: two composite laminated cylindrical shells and two stainless steel cylinders. In order to characterize a relationship with the applied load, the first natural frequency of vibration and mode shape is measured during testing using a 3D laser scanner. The proposed vibration correlation technique allows one to predict the experimental buckling load with a very good approximation without actually reaching the instability point. Additional experimental tests and numerical models are currently under development to further validate the proposed approach for composite and metallic conical structures.
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.
Effects of Impact Velocity and Slenderness Ratio on Dynamic Buckling Load for Long Columns
Mimura, K.; Umeda, T.; Yu, M.; Uchida, Y.; Yaka, H.
In this research, the buckling behavior of long columns under dynamic load was investigated both experimentally and numerically, and an effective buckling criterion for dynamic load was derived from the results in terms of the impact velocity and the slenderness ratio. In the experiments, a free fall drop-weight type impact testing machine was employed. The dynamic buckling loads were measured by the load sensing block, and the displacements were measured by a high speed magnetic-resistance device. In the numerical analyses, dynamic FEM code 'MSC-Dytran' was used to simulate the typical experimental results, and the validity and the accuracy of the simulations were checked. The dynamic buckling loads at various impact velocities were then systematically investigated. From both experimental and simulated results, it was found that the dynamic to static buckling load ratios can be successfully described as a square function of the slenderness ratio of the columns, while they can be also described by a power law of the applied impact velocity.
Thermal buckling and natural vibration of the beam with an axial stick-slip-stop boundary
Cui, D. F.; Hu, H. Y.
2014-04-01
As a first attempt to study the dynamics of a heated structure with complicated boundaries, this paper deals with the thermal buckling and the natural vibration of a simply supported slender beam, which is subject to a uniformly distributed heating and has a frictional sliding end within a clearance. This sliding end is initially at a stick status under the friction force, but may be slightly slipping due to the thermal expansion of the beam until the sliding end contacts a stop, i.e., the bound of the clearance. The material properties of the beam are temperature-independent for low temperature, but temperature-dependent for high temperature. For each case, the analytic solutions for the critical buckling temperature and the natural frequencies of the heated beam are derived first. Then, discussions are made to reveal the effects of beam parameters, such as the ratio of beam length to beam thickness, the ratio of clearance to beam length and the temperature-dependent material properties, on the critical buckling temperature and the fundamental natural frequency of the heated beam. The study shows that both friction force and clearance have significant influences on the critical buckling temperature and the fundamental natural frequency of the beam. When the friction force is not very large, the clearance can greatly increase the critical buckling temperature. These conclusions enable one to properly design the stick-slip-stop boundary so as to improve the mechanical performance of the beam in thermal environments.
Atomistic study of the buckling of gold nanowires
Energy Technology Data Exchange (ETDEWEB)
Olsson, Paer A.T., E-mail: par.olsson@mek.lth.se [Division of Mechanics, Lund University, PO Box 118, SE-221 00 Lund (Sweden); Park, Harold S., E-mail: parkhs@bu.edu [Department of Mechanical Engineering, Boston University, Boston, MA 02215 (United States)
2011-06-15
In this work, we present results from atomistic simulations of gold nanowires under axial compression, with a focus on examining the effects of both axial and surface orientation effects on the buckling behavior. This was accomplished by using molecular statics simulations while considering three different crystallographic systems: <1 0 0>/{l_brace}1 0 0{r_brace}, <1 0 0>/{l_brace}1 1 0{r_brace} and <1 1 0>/{l_brace}1 1 0{r_brace}{l_brace}1 0 0{r_brace}, with aspect ratios spanning from 20 to 50 and cross-sectional dimensions ranging from 2.45 to 5.91 nm. The simulations indicate that there is a deviation from the inverse square length dependence of critical forces predicted from traditional linear elastic Bernoulli-Euler and Timoshenko beam theories, where the nature of the deviation from the perfect inverse square length behavior differs for different crystallographic systems. This variation is found to be strongly correlated to either stiffening or increased compliance of the tangential stiffness due to the influence of nonlinear elasticity, which leads to normalized critical forces that decrease with decreasing aspect ratio for the <1 0 0>/{l_brace}1 0 0{r_brace} and <1 0 0>/{l_brace}1 1 0{r_brace} systems, but increase with decreasing aspect ratio for the <1 1 0>/{l_brace}1 1 0{r_brace}{l_brace}1 0 0{r_brace} system. In contrast, it was found that the critical strains are all lower than their bulk counterparts, and that the critical strains decrease with decreasing cross-sectional dimensions; the lower strains may be an effect emanating from the presence of the surfaces, which are all more elastically compliant than the bulk and thus give rise to a more compliant flexural rigidity.
Analysis of polysilicon micro beams buckling with temperature-dependent properties
Shamshirsaz, M; Asgari, M B; Tayefeh, M
2008-01-01
The suspended electrothermal polysilicon micro beams generate displacements and forces by thermal buckling effects. In the previous electro-thermal and thermo-elastic models of suspended polysilicon micro beams, the thermo-mechanical properties of polysilicon have been considered constant over a wide rang of temperature (20- 900 degrees C). In reality, the thermo-mechanical properties of polysilicon depend on temperature and change significantly at high temperatures. This paper describes the development and validation of theoretical and Finite Element Model (FEM) including the temperature dependencies of polysilicon properties such as thermal expansion coefficient and Young's modulus. In the theoretical models, two parts of elastic deflection model and thermal elastic model of micro beams buckling have been established and simulated. Also, temperature dependent buckling of polysilicon micro beam under high temperature has been modeled by Finite Element Analysis (FEA). Analytical results and numerical results ...
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
2016-09-01
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.
Institute of Scientific and Technical Information of China (English)
SHA Feng-huan; ZHAO Long-mao; YANG Gui-tong
2005-01-01
The dynamic response of a double-walled carbon nanotube embedded in elastic medium subjected to periodic disturbing forces is investigated. Investigation of the dynamic buckling of a double-walled carbon nanotube develops continuum model. The effect of the van der Waals forces between two tubes and the surrounding elastic medium for axial dynamic buckling are considered. The buckling model subjected to periodic disturbing forces and the critical axial strain and the critical frequencies are given. It is found that the critical axial strain of the embedded multi-walled carbon nanotube due to the intertube van der Waals forces is lower than that of an embedded single-walled carbon nanotube. The van der Waals forces and the surrounding elastic medium affect region of dynamic instability. The van der Waals forces increase the critical frequencies of a double-walled carbon nanotube. The effect of the surrounding elastic medium for the critical frequencies is small.
Buckling of Laminated Composite Stiffened Panels Subjected to Linearly Varying In-Plane Edge Loading
Mallela, Upendra K.; Upadhyay, Akhil
2014-01-01
The presence of in-plane loading may cause buckling of stiffened panels. An accurate knowledge of critical buckling load and mode shapes is essential for reliable and lightweight structural design. This paper presents parametric studies on simply supported laminated composite blade-stiffened panels subjected to linearly varying in-plane edge/compressive loading. Studies are carried out by changing the panel orthotropy ratio, stiffener depth, pitch length (number of stiffeners), smeared extensional stiffness ratio of stiffener to that of the plate and load distribution parameter. Based on the studies, a few important parameters influencing the buckling behavior are identified and their significance is discussed. Further, the interaction equations for combined loadings are validated by carrying out numerical studies.
Effect of vertical seismic load on shear-bending buckling strength of thin cylindrical shells
International Nuclear Information System (INIS)
The main vessels of Fast Breeder Reactors (FBR) are cylindrical structures containing liquid, and have to be thin-walled in order to withstand severe thermal condition. One of the most critical factors in the design of earthquake-resistant FBRs is the buckling strength of the cylinder part of the reactor vessel. In order to investigate various non-linear response characteristics, including buckling, of thin cylindrical shells under vertical and horizontal seismic motion, pseudo-dynamic experiments and non-linear response simulation analysis is performed. It is confirmed that buckling is caused mainly by horizontal seismic loads, and that vertical seismic loads reduce the lateral load-carrying capacity of cylinders and amplify response displacement for a given horizontal seismic load. To evaluate the amplification of non-linear horizontal responses due to vertical input motions, the authors define a response amplification factor, which is calculated from floor response spectra of seismic waves
DYNAMIC BUCKLING OF ELASTIC-PLASTIC COLUMN IMPACTED BY RIGID BODY
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The dynamic buckling of an elastic-plastic column subjected to an axial impact by a rigid body was discussed by using the energy law. The traveling process of elastic-plastic waves under impact action was analyzed by characteristics method. The equation of lateral disturbance used to analyze the problem was developed by taking into account the effect of elastic-plastic stress wave. The power series solution of this problem has been the power series approach. The buckling criterion of this problem was proposed by analyzing the characteristics of the solution. The relationship among critical velocity and impact mass, critical buckling length, hardening modulus was given by using theoretical analysis and numerical computation.
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
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.
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
Micro-scale delaminating and buckling of thin film on soft substrate
Wu, Dan; Xie, Huimin; Yin, Yajun; Tang, Minjin
2013-03-01
In this paper, a simple process is suggested to estimate the interfacial toughness of the material system ‘aluminum film/soft PDMS substrate’. The specimen, i.e. the aluminum film deposited on the soft polydimethylsiloxane (PDMS) substrate, is subject to a tensile load, and delaminating and buckling of aluminum film are observed in the perpendicular direction to the tensile strain. With the aid of the buckling blisters, the interfacial toughness of the material system is estimated. Large deformation is considered during the buckling of the thin film, and the interfacial toughness is deduced from a fracture theory. Besides, the evolution from one single blister to three blisters and then four blisters is observed in situ under microscope. This simplified method has potential applications to flexible electronics in which interfacial toughness of the metal film/soft substrate must be well controlled.
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.
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....
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
Contractile units in disordered actomyosin bundles arise from F-actin buckling
Lenz, Martin; Gardel, Margaret L; Dinner, Aaron R
2012-01-01
Bundles of filaments and motors are central to contractility in cells. The classic example is striated muscle, where actomyosin contractility is mediated by highly organized sarcomeres which act as fundamental contractile units. However, many contractile bundles in vivo and in vitro lack sarcomeric organization. Here we propose a model for how contractility can arise in actomyosin bundles without sarcomeric organization and validate its predictions with experiments on a reconstituted system. In the model, internal stresses in frustrated arrangements of motors with diverse velocities cause filaments to buckle, leading to overall shortening. We describe the onset of buckling in the presence of stochastic actin-myosin detachment and predict that buckling-induced contraction occurs in an intermediate range of motor densities. We then calculate the size of the "contractile units" associated with this process. Consistent with these results, our reconstituted actomyosin bundles contract at relatively high motor dens...
THE DYNAMIC BUCKLING OF ELASTIC-PLASTIC COLUMN SUBJECTED TO AXIAL IMPACT BY A RIGID BODY
Institute of Scientific and Technical Information of China (English)
Han Zhijun; Wang Jingchao; Cheng Guoqiang; Ma Hongwei; Zhang Shanyuan
2005-01-01
The dynamic buckling of an elastic-plastic column subjected to axial impact by a rigid body has been discussed in this paper. The whole traveling process of elastic-plastic waves under impact action is analyzed with the characteristics method. The regularity of stress changes in both column ends and the first separating time of a rigid body and column are obtained. By using the energy principle and taking into account the propagation and reflection of stress waves the lateral disturbance equation is derived and the power series solution is given. In addition,the critical buckling condition can be obtained from the stability analysis of the solution. By numerical computation and analysis, the relationship among critical velocity and impact mass,hardening modulus, and buckling time is given.
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.
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 a slider. The kinematic analysis of this new mechanism is studied, using nonlinear Elastica buckling beam theory, the PRBM of a large deflecting cantilever beam, the vector loop closure equations, and numerically solving nonlinear algebraic equations. A design method of the bistable mechanism...... in microdimensions is investigated by changing the relative stiffness of the flexible beams. The actuation force versus displacement characteristics of several cases is explored and the full simulation results of one of the cases are presented. This paper demonstrates the united application of the PRBM...
European column buckling curves and finite element modelling including high strength steels
DEFF Research Database (Denmark)
Jönsson, Jeppe; Stan, Tudor-Cristian
2017-01-01
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...... in advanced non-linear finite element analysis (GMNIA) with the goal of being able to reestablish the European buckling curves. A short comprehensive historical review is given on the development of the European buckling curves and the related assumptions made with respect to deterministic modelling of column......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...
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Runyang Suspension Bridge (RSB) with the main span of 1490 m is the longest bridge in China and the third longest one in the world. In this bridge the rigid central buckle is employed for the first time in the mid-span of the suspension bridge in China. For such a super-long-span bridge, the traditional finite element (FE) modeling technique and stress analysis methods obviously cannot satisfy the needs of conducting accurate stress analysis on the central buckle. In this paper, the submodel method is in- troduced and for the first time used in analyzing the stresses of the central buckle. After an accurate FE submodel of the central buckle was specially established according to the analysis results from the whole FE model, the connection technique between the two-scale FE models was realized and the ac- curate stresses of the central buckle under various vehicle load cases were then conducted based on the submodel method. The calculation results were testified to be accurate and reliable by the field measurements, which show the efficiency and reliability of the submodel method on analyzing the mechanical condition of the central buckle of long-span suspension bridges. Finally, the working be- havior and mechanical characteristics of the central buckle of the RSB under vehicle loads were ana- lyzed based on the calculation and measurement results. The results obtained in this paper can provide theoretic references for analyzing and designing the rigid central buckle in long-span suspension bridges in future.
2011-03-03
... thirty- fifth. (Presidential Sig.) [FR Doc. 2011-5032 Filed 3-2-11; 11:15 am] Billing code 3195-W1-P ... Documents#0;#0; ] Proclamation 8632 of February 28, 2011 Death of Army Corporal Frank W. Buckles, the Last... a mark of respect for the memory of Army Corporal Frank W. Buckles, the last surviving...
Buckling and postbuckling analysis of stiffened composite panels in axial compression
Park, Oung
The major objective of this study is to analyze buckling and delamination behavior of composite stiffened panels subjected to axial compression. First, a combined analytical and experimental study of a blade stiffened composite panel subjected to axial compression was conducted. The effects of the differences between a simple model used to design the panel and the actual experimental conditions were examined. It was found that in spite of many simplifying assumptions the design model did reasonably well in that the experimental failure load was only 10% higher than the design load. Several structural analysis programs, including PANDA2, STAGS, and ABAQUS, were used to obtain high fidelity analysis results. The buckling loads from STAGS agreed well with the experimental failure loads. However, substantial differences were found in the out-of-plane displacements of the panel. Efforts were made to identify the source of these differences. Implementing non-uniform load introduction with general contact definition in the STAGS finite element model improved correlation between the measured and predicted out-of-plane deformations. Next, a new method called Crack Tip Force Method (CTFM) is derived for computing point-wise energy release rate along the delamination front in delaminated plates. The CTFM is computationally simple as the G is computed using the forces transmitted at the crack-tip between the top and bottom sub-laminates and the sub-laminate properties. Finally, buckling and postbuckling of a blade-stiffened composite panel under axial compression with a partial skin-stiffener debond are investigated. Two different finite element models, where nodes of the panel skin and the stiffener flange are located on the mid-plane or at the interface between skin and flange, are used. Linear buckling analysis is conducted using both STAGS and ABAQUS. Postbuckling analysis is conducted with STAGS. Comparison between the present results and previous buckling analysis
Directory of Open Access Journals (Sweden)
Alireza Dehghani
2013-01-01
Full Text Available Aim: We aimed to compare peak systolic velocity of central retinal artery (PSV.CRA and peak systolic velocity of ophthalmic artery (PSV.OA between patients with retinal detachment who were treated with segmental scleral bucking and scleral buckling with encircling procedure. Materials and Methods: This study was a descriptive-analytic cross sectional study that was performed in Isfahan university referral centers since April 2010 to April 2011. Of the patients who have undergone scleral buckling surgery, 20 patients belonging to two groups were randomly selected to enroll in the study. Study groups were, patients who have undergone segmental scleral buckling and the other group were patients who have undergone scleral buckling with encircling procedure. Patients were invited to perform color Doppler imaging. PSV-RA and PSV-OA were measured and documented in both operated and unoperated eyes. All of the Doppler′s performed at least three months after ophthalmic surgery. Results: We found significant decrease in PSV.CRA among patients in both groups. In patients who had undergone scleral buckling with encircling procedure PSV.CRA was 11.03 ± 3.04 (cm/sec and 14.83 ± 4.80 in operated and unoperated eye respectively (P = 0.03. In other hand, who treated with segmental scleral buckling these parameters were 11.02 ± 2.48 and 14.45 ± 4.69 (P = 0.03. PSV.OA did not change significantly in each method. The difference between mean PSV.CRA and PSV.OA in operated eye between two study groups was not significant. Conclusion: PSV.CRA reduced significantly in both surgery methods and PSV.OA changes was not significant. However, the mean PSV.CRA and PSV.OA changes did not show statistically significant difference between surgery methods.
Weil, Arlo; Gutiérrez-Alonso, Gabriel; Johnston, Stephen; Pastor Galán, Daniel
2013-04-01
The Paleozoic Variscan orogeny was a large-scale collisional event involving amalgamation of multiple continents and micro-continents. Existing data, suggests oroclinal buckling of an originally near-linear convergent margin during the last stages of Variscan deformation in the late Paleozoic. Closure of the Rheic Ocean resulted in E-W shortening (present-day coordinates) in the Carboniferous, producing a near linear N-S trending, east-verging belt. Subsequent N-S shortening near the Carb-Permian boundary resulted in oroclinal buckling. This late-stage orogenic event remains an enigmatic part of final Pangea amalgamation. The present-day arc curvature of the Variscan has inspired many tectonic models, with little agreement between them. While there is general consensus that two separate phases of deformation occurred, various models consider that curvature was caused by: dextral transpression around a Gondwana indentor; strike-slip wrench tectonics; or a change in tectonic transport direction due to changing stress fields. More recent models explain the curvature as an orocline, with potentially two opposite-facing bends, caused by secondary rotations. Deciphering the kinematic history of curved orogens is difficult, and requires establishment of two deformation phases: an initial compressive phase that forms a relatively linear belt, and a second phase that causes vertical-axis rotation of the orogenic limbs. Historically the most robust technique to accurately quantify vertical axis-rotation in curved orogens is paleomagnetic analysis, but recently other types of data, including fracture, geochemical, petrologic, paleo-current and calcite twin data, have been used to corroborate secondary buckling. A review of existing and new Variscan data from Iberia is presented that argues for secondary buckling of an originally linear orogenic system. Together, these data constrain oroclinal buckling of the Cantabrian Orocline to have occurred in about 10 Ma during the
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.
A comparison of experimental and calculated thin-shell leading-edge buckling due to thermal stresses
Jenkins, Jerald M.
1988-01-01
High-temperature thin-shell leading-edge buckling test data are analyzed using NASA structural analysis (NASTRAN) as a finite element tool for predicting thermal buckling characteristics. Buckling points are predicted for several combinations of edge boundary conditions. The problem of relating the appropriate plate area to the edge stress distribution and the stress gradient is addressed in terms of analysis assumptions. Local plasticity was found to occur on the specimen analyzed, and this tended to simplify the basic problem since it effectively equalized the stress gradient from loaded edge to loaded edge. The initial loading was found to be difficult to select for the buckling analysis because of the transient nature of thermal stress. Multiple initial model loadings are likely required for complicated thermal stress time histories before a pertinent finite element buckling analysis can be achieved. The basic mode shapes determined from experimentation were correctly identified from computation.
A Semi-Analytical Model for Buckling of Stiffened Cylindrical Shells
2013-01-01
Cylindrical shells are common configurations within the technology. The transition from the side to the bottom on a ship has the shape of a fourth of a cylindrical shell. Both ring and stringer stiffeners can be added to the shell for support. Buckling of this type of structure is an important area of interest. The main purpose of this thesis has been to make a semi-analytical model that can describe how a ring stiffened shell and stringer stiffened shell respond during buckling. A va...
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
Molecular dynamics simulations of the buckling of graphyne and its family
International Nuclear Information System (INIS)
Molecular dynamics simulations are employed to study the instability characteristics of graphyne and its family under compressive loads. The effects of nanosheet side length and aspect ratio on the critical compressive force and critical strain are investigated. It is shown that increasing aspect ratio leads to decreasing the critical compressive force. Besides, the effect of atomic structure on the compressive behavior of nanosheets is explored. It is observed that the zigzag graphynes have larger buckling forces than the armchair graphynes with same geometries. Finally, the buckling behavior of different nanosheets from the graphyne family is studied. It is represented that the nanosheets with more acetylene links have smaller critical compressive forces
Optimization of Blade Stiffened Composite Panel under Buckling and Strength Constraints
Todoroki, Akira; Sekishiro, Masato
This paper deals with multiple constraints for dimension and stacking-sequence optimization of a blade-stiffened composite panel. In a previous study, a multiple objective genetic algorithm using a Kriging response surface with a buckling load constraint was the target. The present study focuses on dimension and stacking-sequence optimization with both a buckling load constraint and a fracture constraint. Multiple constraints complicate the process of selecting sampling analyses to improve the Kriging response surface. The proposed method resolves this problem using the most-critical-constraint approach. The new approach is applied to a blade stiffened composite panel and the approach is shown to be efficient.
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.
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.
Shear-Induced Buckling Instability in The Lamellar Phase:a Mechanism for Onions Formation
International Nuclear Information System (INIS)
We present a model of coupling of shear flow to microscopic degrees of freedom in the lyotropic Smectic A (lamellar phase ). This coupling is then shown to produce macroscopic buckling instability analogous to well known undulation instability appearing in thermotropic smectics under dilatation in the direction perpendicular to the layers. The Iyotropic Lamellar phase is experimentally known to become unstable under shear flow. The instability occurs at shear rate γ ∼ 1sec-1and the so called 'onions' (multi lamellar vesicles) are formed. We propose that the instability occurs in two stages. At the first stage, the layers are buckled by shear -induced microscopic tension σ ≅ ηeγd where ηe is an effective viscosity of the system (which can be very large :ηe ≅ 1000ηsolvent) and d is all inter- layer spacing. As the membrane projected area cannot increase (for example, being sandwiched between defects) it has to buckle in the direction perpendicular to itself.There is a critical tension however due to energy cost of compression of layers in the buckled state and of bending and expansion of individual layers. Then one is able to calculate the buckling amplitude Uo and the wavevector k as a function of γ. Denoting K usual smectic bending modulus and B the compressional one, the result is that the transition occurs at σ ≅ T/Dd, where D is the width of a film. For σ - σc >> σc we have k ≅ √(8σ/3dB). At the second stage the buckled structure is deformed by shear (by coupling to Macroscopic degrees of freedom) nad eventually broken, resulting in the formation of onions. We speculate that the buckled state will become unstable when the relaxation time of the buckling structure τc ≅ ηc/Kk2 is shorter than the one needed for shear to deform the structure to a degree that maxima are shifted to the position of neighboring minima. The estimate is γ ≅ Kk2(U0k)-1 which gives γ ∼ d-a with 7/3 < a < 17/7 which is consistent with experimental data a
Harvesting energy from a water flow through ionic polymer metal composites' buckling
Cellini, Filippo; Cha, Youngsu; Porfiri, Maurizio
2014-03-01
This study seeks to investigate the feasibility of energy harvesting from mechanical buckling of ionic polymer metal composites (IPMCs) induced by a steady fluid flow. In particular, we propose a harvesting device composed of a paddle wheel, a slider-crank mechanism, and two IPMCs clamped at both their ends. We test the system in a water tunnel to estimate the effects of the flow speed and the shunting resistance on power harvesting. The classical post-buckling theory of inextensible rods is utilized, in conjunction with a black-box model for IPMC sensing, to interpret experimental results.
Improvement of risk estimate on wind turbine tower buckled by hurricane
Li, Jingwei
2013-01-01
Wind is one of the important reasonable resources. However, wind turbine towers are sure to be threatened by hurricanes. In this paper, method to estimate the number of wind turbine towers that would be buckled by hurricanes is discussed. Monte Carlo simulations show that our method is much better than the previous one. Since in our method, the probability density function of the buckling probability of a single turbine tower in a single hurricane is obtained accurately but not from one approximated expression. The result in this paper may be useful to the design and maintenance of wind farms.
A weighted extended B-spline solver for bending and buckling of stiffened plates
Verschaeve, Joris C G
2015-01-01
The weighted extended B-spline method [Hoellig (2003)] is applied to bending and buckling problems of plates with different shapes and stiffener arrangements. The discrete equations are obtained from the energy contributions of the different components constituting the system by means of the Rayleigh-Ritz approach. The pre-buckling or plane stress is computed by means of Airy's stress function. A boundary data extension algorithm for the weighted extended B-spline method is derived in order to solve for inhomogeneous Dirichlet boundary conditions. A series of benchmark tests is performed touching various aspects influencing the accuracy of the method.
Ansari, R.; Norouzzadeh, A.
2016-10-01
The size-dependent static buckling responses of circular, elliptical and skew nanoplates made of functionally graded materials (FGMs) are investigated in this article based on an isogeometric model. The Eringen nonlocal continuum theory is implemented to capture nonlocal effects. According to the Gurtin-Murdoch surface elasticity theory, surface energy influences are also taken into account by the consideration of two thin surface layers at the top and bottom of nanoplate. The material properties vary in the thickness direction and are evaluated using the Mori-Tanaka homogenization scheme. The governing equations of buckled nanoplate are achieved by the minimum total potential energy principle. To perform the isogeometric analysis as a solution methodology, a novel matrix-vector form of formulation is presented. Numerical examples are given to study the effects of surface stress as well as other important parameters on the critical buckling loads of functionally graded nanoplates. It is found that the buckling configuration of nanoplates at small scales is significantly affected by the surface free energy.
Dynamic buckling of elastic-plastic cylindrical shells and axial stress waves
Institute of Scientific and Technical Information of China (English)
徐新生; 苏先樾; 王仁
1995-01-01
The mechanism for bifurcation of elastic-plastic buckling of the semi-infinite cylindrical shell under impacting axial loads is proposed based on the theory of stress wave. Numerical results on three kinds of end supports and step and impulse loads are given.
Flutter and thermal buckling control for composite laminated panels in supersonic flow
Li, Feng-Ming; Song, Zhi-Guang
2013-10-01
Aerothermoelastic analysis for composite laminated panels in supersonic flow is carried out. The flutter and thermal buckling control for the panels are also investigated. In the modeling for the equation of motion, the influences of in-plane thermal load on the transverse bending deflection are taken into account, and the unsteady aerodynamic pressure in supersonic flow is evaluated by the linear piston theory. The governing equation of the structural system is developed applying the Hamilton's principle. In order to study the influences of aerodynamic pressure on the vibration mode shape of the panel, both the assumed mode method (AMM) and the finite element method (FEM) are used to derive the equation of motion. The proportional feedback control method and the linear quadratic regulator (LQR) are used to design the controller. The aeroelastic stability of the structural system is analyzed using the frequency-domain method. The effects of ply angle of the laminated panel on the critical flutter aerodynamic pressure and the critical buckling temperature change are researched. The flutter and thermal buckling control effects using the proportional feedback control and the LQR are compared. An effective method which can suppress the flutter and thermal buckling simultaneously is proposed.
Post-buckled precompressed (PBP) subsonic micro flight control actuators and surfaces
Barrett, R.; Vos, R.; De Breuker, R.
2007-01-01
This paper describes a new class of flight control actuators using Post-Buckled Precompressed (PBP) piezoelectric elements to provide much improved actuator performance. These PBP actuator elements are modeled using basic large deflection Euler-beam estimations accounting for laminated plate effects
DEFF Research Database (Denmark)
Neves, Miguel M.; Sigmund, Ole; Bendsøe, Martin P.
2002-01-01
The problem of determining highly localized buckling modes in perfectly periodic cellular microstructures of infinite extent is addressed. A double scale asymptotic technique is applied to the linearized stability problem for a periodic structure built from linearly elastic microstructures. The o...
Institute of Scientific and Technical Information of China (English)
2008-01-01
Based on the first order shear deformation theory and classic buckling theory, the paper investigates the creep buckling behavior of viscoelastic laminated plates and laminated circular cylindrical shells. The analysis and elaboration of both instantaneous elastic critic load and durable critic load are emphasized. The buckling load in phase domain is obtained from governing equations by applying Laplace transform, and the instantaneous elastic critic load and durable critic load are determined according to the extreme value theorem for inverse Laplace transform. It is shown that viscoelastic approach and quasi-elastic approach yield identical solutions for these two types of critic load respectively. A transverse disturbance model is developed to give the same mechanics significance of durable critic load as that of elastic critic load. Two types of critic loads of boron/epoxy composite laminated plates and circular cylindrical shells are discussed in detail individually, and the influencing factors to induce creep buckling are revealed by examining the viscoelasticity incorporated in transverse shear deformation and in-plane flexibility.
Active buckling control of beams using piezoelectric actuators and strain gauge sensors
International Nuclear Information System (INIS)
In this paper, a finite element model incorporating active control techniques has been developed to stabilize the first two buckling modes of both a simply supported and a cantilevered beam. The goal is to increase the corresponding beam buckling loads by using piezoelectric actuators along with optimal feedback control. The uniform beams are bonded with two pairs of segmented piezoelectric actuators at the top and bottom. Resistive strain gauges are attached to the centres of the actuators as sensors. Measurements are taken using these, to estimate the system states. The beams are simply supported or cantilevered and subjected to a slowly increasing axial compressive load. Finite element formulations based on the classical Euler–Bernoulli beam theory and linear piezoelectric constitutive equations for the actuators are presented. The associated reduced-order modal equations and the state-space equations are derived for the design of a standard linear quadratic regulator (LQR). The finite element analysis and the active control simulation results are consistent with both theoretical analysis results and experimental data. The designed full state feedback LQR controller is shown to be successful in stabilizing the first two buckling modes of the beams. Also the control simulation shows that the present optimally located segmented actuator pairs along the beam are more effective for buckling control
Selective buckling via states of self-stress in topological metamaterials
Paulose, Jayson; Meeussen, Anne S.; Vitelli, Vincenzo
2015-01-01
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. PMID:26056303
Akkin, C; Erakgun, T
2001-01-01
We have developed a simple technique to verify the final and exact position of the explant on the retinal break before placing the radial or circumferential scleral buckles during the retinal detachment surgery. For this purpose, we used the back end of a dismantled blade holder which is essentially the same size as a sponge. PMID:12678393
Local buckling of aluminium structures exposed to fire. Part 1: Tests
Maljaars, J.; Soetens, F.
2009-01-01
This paper describes an experimental investigation into local buckling of compressed aluminium alloy sections at elevated temperatures. Stress-strain relationships are derived based on uniaxial tensile tests. A special test set-up with a furnace is developed to test slender square hollow sections an
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 desi
Zhen, Wu; Wanji, Chen
2007-05-01
Buckling response of angle-ply laminated composite and sandwich plates are analyzed using the global-local higher order theory with combination of geometric stiffness matrix in this paper. This global-local theory completely fulfills the free surface conditions and the displacement and stress continuity conditions at interfaces. Moreover, the number of unknowns in this theory is independent of the number of layers in the laminate. Based on this global-local theory, a three-noded triangular element satisfying C1 continuity conditions has also been proposed. The bending part of this element is constructed from the concept of DKT element. In order to improve the accuracy of the analysis, a method of modified geometric stiffness matrix has been introduced. Numerical results show that the present theory not only computes accurately the buckling response of general laminated composite plates but also predicts the critical buckling loads of soft-core sandwiches. However, the global higher-order theories as well as first order theories might encounter some difficulties and overestimate the critical buckling loads for soft-core sandwich plates.
Bauer, Christina T; Kroner, Elmar; Fleck, Norman A; Arzt, Eduard
2015-12-01
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.
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
Relevance of capsid structure in the buckling and maturation of spherical viruses
International Nuclear Information System (INIS)
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)
Interaction between cracking, delamination and buckling in brittle elastic thin films
Vellinga, W. P.; Van den Bosch, M.; Geers, M. G. D.
2008-01-01
A discrete lattice based model for the interaction of cracking, delamination and buckling of brittle elastic coatings is presented. The model is unique in its simultaneous incorporation of the coating and of disorder in the interface and material properties, leading to realistic 3D bending (and buck
The effect of interface adhesion on buckling and cracking of hard thin films
Flores-Johnson, E. A.; Shen, L.; Annabattula, R. K.; Onck, P. R.; Shen, Y. G.; Chen, Z.
2014-01-01
The physics behind the strain-released buckling patterns including telephone cords and straight-sided wrinkles with and without cracks, as experimentally observed in sputter-deposited Ti-Si-N thin films on Si substrates, is investigated with model-based simulations by varying the mechanical properti
Wang, Qinghua; Xie, Huimin; Lu, Jian; Chen, Pengwan; Zhang, Qingming
2011-06-15
Measurement of interfacial toughness of a metal film wire and a flexible substrate is a challenging issue for evaluating the interfacial bonding capacity of the film-wire/substrate systems. In this paper, an electricity induced buckling method is proposed to measure the interfacial toughness between a metal film wire and a polymer membrane, which does not use a pre-existing weak interface. This method relies on causing a buckling driven delamination of the metal film wire from the polymer membrane, by inducing a compressive stress due to electrification of the film wire. For a sort of structure formed by a constantan film wire and a polymer membrane, the current density range under which the buckling of the film wire will emerge is obtained from experiments. The average interfacial toughness of one typical sample is measured to be 31.6 J/m(2). According to the buckling topographies under different current densities, the interfacial toughness of the constantan film wire and the polymer substrate is found to vary from 10 J/m(2) to 60 J/m(2).
The Mexican hat effect on the delamination buckling of a compressed thin film
Zhang, Yin; Liu, Yun
2014-12-01
Because of the interaction between film and substrate, the film buckling stress can vary significantly, depending on the delamination geometry, the film and substrate mechanical properties. The Mexican hat effect indicates such interaction. An analytical method is presented, and related dimensional analysis shows that a single dimensionless parameter can effectively evaluate the effect.
A Simple Buckling Analysis Method for Airframe Composite Stiffened Panel by Finite Strip Method
Tanoue, Yoshitsugu
Carbon fiber reinforced plastics (CFRP) have been used in structural components for newly developed aircraft and spacecraft. The main structures of an airframe, such as the fuselage and wings, are essentially composed of stiffened panels. Therefore, in the structural design of airframes, it is important to evaluate the buckling strength of the composite stiffened panels. Widely used finite element method (FEM) can analyzed any stiffened panel shape with various boundary conditions. However, in the early phase of airframe development, many studies are required in structural design prior to carrying out detail drawing. In this phase, performing structural analysis using only FEM may not be very efficient. This paper describes a simple buckling analysis method for composite stiffened panels, which is based on finite strip method. This method can deal with isotropic and anisotropic laminated plates and shells with several boundary conditions. The accuracy of this method was verified by comparing it with theoretical analysis and FEM analysis (NASTRAN). It has been observed that the buckling coefficients calculated via the present method are in agreement with results found by detail analysis methods. Consequently, this method is designed to be an effective calculation tool for the buckling analysis in the early phases of airframe design.
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...
Emission energy, exciton dynamics and lasing properties of buckled CdS nanoribbons.
Wang, Qi; Sun, Liaoxin; Lu, Jian; Ren, Ming-Liang; Zhang, Tianning; Huang, Yan; Zhou, Xiaohao; Sun, Yan; Zhang, Bo; Chen, Changqing; Shen, Xuechu; Agarwal, Ritesh; Lu, Wei
2016-01-01
We report the modulation of emission energy, exciton dynamics and lasing properties in a single buckled CdS nanoribbon (NR) by strain-engineering. Inspired by ordered structure fabrication on elastomeric polymer, we develop a new method to fabricate uniform buckled NRs supported on polydimethylsiloxane (PDMS). Wavy structure, of which compressive and tensile strain periodically varied along the CdS NR, leads to a position-dependent emission energy shift as large as 14 nm in photoluminescence (PL) mapping. Both micro-PL and micro-reflectance reveal the spectral characteristics of broad emission of buckled NR, which can be understood by the discrepancy of strain-induced energy shift of A- and B-exciton of CdS. Furthermore, the dynamics of excitons under tensile strain are also investigated; we find that the B-exciton have much shorter lifetime than that of redshifted A-exciton. In addition, we also present the lasing of buckled CdS NRs, in which the strain-dominated mode selection in multi-mode laser and negligible mode shifts in single-mode laser are clearly observed. Our results show that the strained NRs may serve as new functional optical elements for flexible light emitter or on-chip all-optical devices. PMID:27210303
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.
Buckling Design Studies of Inverted, Oblate Bulkheads for a Propellant Tank
Smeltzer, Stanley S., III; Bowman, Lynn M.
2002-01-01
An investigation of the deformation and buckling characteristics of a composite, oblate bulkhead that has an inverted geometry and is subjected to pressure-only loading is presented for three bulkhead geometries and thicknesses. The effects of a stiffening support ring at the bulkhead to cylinder interface are also evaluated. Buckling analyses conducted using the axisymmetric shell code BOSOR4 are discussed for several bulkhead configurations. These results are analytically verified using results from the Structural Analysis of General Shells (STAGS) code for a selected bulkhead configuration. The buckling characterization of an inverted, oblate bulkhead requires careful attention as small changes in bulkhead parameters can have a significant effect on the critical buckling load. Comparison of BOSOR4 and STAGS results provided a very good correlation between the two analysis methods. In addition, the analysis code BOSOR4 was found to be an efficient sizing tool that is useful during the preliminary design stage of a practical shell structure. Together, these two aspects should give the design engineer confidence in sizing these stability critical structures. Additional characterization is warranted, especially for a composite tank structure, since only one bulkhead configuration was examined closely.
Thermal Buckling and Free Vibration Analysis of Heated Functionally Graded Material Beams
Directory of Open Access Journals (Sweden)
Khalane Sanjay Anandrao
2013-05-01
Full Text Available The effect of temperature dependency of material properties on thermal buckling and free vibration of functionally graded material (FGM beams is studied. The FGM beam is assumed to be at a uniform through thickness temperature, above the ambient temperature. Finite element system of equations based on the first order shear deformation theory is developed. FGM beam with axially immovable ends having the classical boundary conditions is analysed. An exhaustive set of numerical results, in terms of buckling temperatures and frequencies, is presented, considering the temperature independent and temperature dependent material properties. The buckling temperature and fundamental frequency obtained using the temperature independent material properties is higher than that obtained by using the temperature dependent material properties, for all the material distributions, geometrical parameters in terms of length to thickness ratios and the boundary conditions considered. It is also observed that the frequencies of the FGM beam will reduce with the increase in temperature. This observation is applicable for the higher modes of vibration also. The necessity of considering the temperature dependency of material properties in determining thermal buckling and vibration characteristics of FGM beams is clearly demonstrated.Defence Science Journal, 2013, 63(3, pp.315-322, DOI:http://dx.doi.org/10.14429/dsj.63.2370
Verification of The Thermal Buckling Load in Plates Made of Functional Graded Material
Directory of Open Access Journals (Sweden)
Amran Ayob
2010-12-01
Full Text Available In this study, thermal buckling of thin plate made of Functionally Graded Materials (FGM with linearly varying thickness is considered. The material properties are also graded in the thickness direction according to a simple power law distribution in which the properties are stated in terms of the volume fractions of the constituents. All edges of the plate are simply supported. The equilibrium and stability equations of a FGM plate under thermal loads can be derived based on higher order plate theories via variation formulation, and are then used to determine the governing deferential equation of the plate and the pre-buckling forces. The buckling analysis of a FGM plate is conducted by assuming a uniform temperature rise, temperature gradient through the thickness, and linear temperature variation in the thickness. Closed–form solutions are obtained the buckling load defined in a weighted residual approach. In a special case the obtained results are compared with the results of FGM plates with uniform thickness. The influences of the plate thickness variation and the edge ratio on the critical loads are investigated. Different gradient exponent k, different geometries and loading conditions were studied.
Rigorous buckling analysis of size-dependent functionally graded cylindrical nanoshells
Sun, Jiabin; Lim, C. W.; Zhou, Zhenhuan; Xu, Xinsheng; Sun, Wei
2016-06-01
This paper presents new analytical solutions for buckling of carbon nanotubes (CNTs) and functionally graded (FG) cylindrical nanoshells subjected to compressive and thermal loads. The model applies Eringen's nonlocal differential constitutive relation to describe the size-dependence of nanoshells. Based on Reddy's higher-order shear deformation theory, governing equations are established and solved by separating the variables. The analysis first re-examines the classical buckling of single-walled CNTs. Accurate solutions are established, and it is found that the buckling stress decreases drastically when the nonlocal parameter reaches a certain value. For CNTs with constant wall-thickness, the buckling stress eventually decreases with enhanced size effect. By comparing with CNTs molecular dynamic simulations, the obtained nonlocal parameters are much smaller than those proposed previously. Subsequently, FG cylindrical nanoshells are analyzed, and it is concluded that similar behavior that has been observed for CNTs is also valid for FG cylindrical nanoshells. The paper further discusses in detail the effects of different geometric parameters, material distribution, and temperature field.
Shear-lag model of diffusion-induced buckling of core–shell nanowires
Li, Yong; Zhang, Kai; Zheng, Bailin; Yang, Fuqian
2016-07-01
The lithiation and de-lithiation during the electrochemical cycling of lithium–ion batteries (LIBs) can introduce local deformation in the active materials of electrodes, resulting in the evolution of local stress and strain in the active materials. Understanding the structural degradation associated with lithiation-induced deformation in the active materials is one of the important steps towards structural optimization of the active materials used in LIBs. There are various degradation modes, including swelling, cracking, and buckling especially for the nanowires and nanorods used in LIBs. In this work, a shear-lag model and the theory of diffusion-induced stress are used to investigate diffusion-induced buckling of core–shell nanowires during lithiation. The critical load for the onset of the buckling of a nanowire decreases with the increase of the nanowire length. The larger the surface current density, the less the time is to reach the critical load for the onset of the buckling of the nanowire.
Institute of Scientific and Technical Information of China (English)
Zhang Yongcun; Li Xiaobin; Liu Shutian
2016-01-01
Auxetic materials have previously been shown to enhance various performances due to its unusual property of becoming fatter when uniaxially stretched and thinner when uniaxially com-pressed (i.e., the materials exhibit a negative Poisson’s ratio). The current study focuses on assessing the potential of an auxetic material to enhance the buckling capacity of a rectangular plate under uniaxial compression. The in-plane translational restraint along the unloaded edges that was often neglected in open literature is taken into consideration in our buckling model proposed in this study. The closed-form expressions for the critical buckling coefficient of the rectangle are provided and the predicted results agree well with those determined by the finite element method. Further-more, the results indicate that the buckling performance of a rectangular plate under uniaxial com-pression can be significantly improved by replacing the traditional material that has a positive Poisson’s ratio with an auxetic material when there is in-plane translation restraint along the unloaded edges.
On the interaction of thermal buckling and debonding of patched structures
Carabetta, Pamela Marie
The widespread use of patched assemblies in engineering structures creates the need for better fundamental understanding of the failure phenomena of such structures to ensure their safe and effective usage. A structure possessing two substructures, the "patch" and "baseplate", with mismatched coefficients of thermal expansion is studied under thermal loading for two extreme edge conditions. The composite structure is taken as initially flawed, such that partial separation exists at the edges of the patch between the two substructures. Two relevant failure mechanisms are sling-shot buckling and edge debonding (separation). Sling-shot buckling, first observed for perfectly intact structures under thermal loads, occurs when the structure dynamically slings from one equilibrium configuration to another in an opposite sense of deflection at a critical load. It is desired to be able to predict and characterize buckling of the structure, and its coupling with debonding. The geometrically nonlinear problem is formulated via a variational formulation, which allows the boundaries of the domains of the structure to vary in addition to the displacements. The vanishing of the first variation of the potential energy yields governing equilibrium equations, boundary/matching conditions, and transversality conditions. The transversality condition yields a Griffith type delamination criterion. A closed-form solution is obtained after recasting the problem in a mixed formulation. A stability analysis is performed using the second variation of the potential energy functional. The partially debonded structure is seen to possess a "dual nature", where it is structurally different depending on the deflection, due to the existence of the initial flaw. It experiences sling-shot buckling, which, coupled with the structure's duality leads to what we refer to as "Buckle Trapping." It is suggested that, for certain critical temperature fields, the structure oscillates dynamically between
Directory of Open Access Journals (Sweden)
Shrivastava Sachin
2015-01-01
Full Text Available A redesign of canard control-surface of an advanced all-metallic fighter aircraft was carried out by using carbon fibre composite (CFC for ribs and panels. In this study ply-orientations of CFC structure are optimized using a Genetic-Algorithm (GA with an objective function to have minimum failure index (FI according to Tsai-Wu failure criterion. The redesigned CFC structure was sufficiently strong to withstand aerodynamic loads from stress and deflection points of view. Now, in the present work CFC canard structure has been studied for its buckling strength in comparison to existing metallic design. In this study, the existing metallic design was found to be weak in buckling. Upon a detailed investigation, it was revealed that there are reported failures in the vicinity of zones where initial buckling modes are excited as predicted by the finite element based buckling analysis. In view of buckling failures, the redesigned CFC structure is sufficiently reinforced with stringers at specific locations. After providing reinforcements against buckling, the twist and the camber variations of the airfoil are checked and compared with existing structure data. Finally, the modal analysis has been carried out to compare the variation in excitation frequency due to material change. The CFC structure thus redesigned is safe from buckling and aerodynamic aspects as well.
Dynamic and buckling analysis of a thin elastic-plastic square plate in a uniform temperature field
Institute of Scientific and Technical Information of China (English)
Shifu Xiao; Bin Chen
2005-01-01
The nonlinear models of the elastic and elasticlinear strain-hardening square plates with four immovably simply-supported edges are established by employing Hamilton's Variational Principle in a uniform temperature field. The unilateral equilibrium equations satisfied by the plastically buckled equilibria are also established. Dynamics and stability of the elastic and plastic plates are investigated analytically and the buckled equilibria are investigated by employing Galerkin-Ritz's method. The vibration frequencies, the first critical temperature differences of instability or buckling, the elastically buckled equilibria and the extremes depending on the final loading temperature difference of the plastically buckled equillibria of the plate are obtained. The results indicate that the critical buckling value of the plastic plate is lower than its critical instability value and the critical value of its buckled equilibria turning back to the trivial equilibrium are higher than the value. However, three critical values of the elastic plate are equal. The unidirectional snap-through may occur both at the stress-strain boundary of elasticity and plasticity and at the initial stage of unloading of the plastic plate.
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
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.
Generation of buckle folds in Naga fold thrust belt, north-east India
Saha, B.; Dietl, C.
2009-04-01
Naga fold thrust belt (NFTB), India, formed as a result of northward migration of the Indian plate initiated in Eocene and its subsequent collision with the Burmese plate during Oligocene. The NW-SE oriented compression generated a spectrum of structures; among them, we intend to focus on the folds- varying from gentle to tight asymmetric in geometry. Large recumbent folds are often associated with thrusting. Buckle folds forming under shallow crustal conditions are frequently reported from NFTB. Buckle folding occurs mainly within sandstones with intercalated shale layers which are in the study area typical for the Barail, Surma and Tipam Groups. We have tried to explain the controlling factors behind the variation of the buckle fold shapes and their varying wavelengths throughout the fold thrust belt with the aid of analogue (sand box) modelling. It is undoubted that competence contrast along with the layer parallel compressive stress are the major influencing factors in generation of buckle folds. Schmalholz and Podladchikov (1999) and Jeng et al. (2002) have shown that when low strain rate and low temperature are applicable, not only the viscosity contrast, but also the elasticity contrast govern the geometry of the developing buckle folds. Rocks deforming under high temperature and high pressure deform in pure viscous manner, whereas, rocks undergoing less confining stress and less temperature, are subjected to pure elastic deformation. However, they are the end members, and most of the deformations are a combination of these two end members, i.e. of viscoelastic nature. Our models are made up of sieved sand (0.5 mm grain size) and mica layers (1-5 mm) This interlayering imparts a mechanical anisotropy in the model. Mica is not a pure viscous material, rather it displays more elastic behaviour. The mica layers in the model produce bedding parallel slip during shortening through internal reorganization of the individual mica crystals leading to the thickening
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
Thermal post-buckling of slender composite and FGM columns through a simple and novel FE formulation
Indian Academy of Sciences (India)
G VENKATESWARA RAO; K SANJAY ANANDRAO; R K GUPTA
2016-08-01
A simple and novel finite element (FE) formulation is proposed to study the thermal post-buckling of composite and FGM columns with axially immovable ends and operating in severe thermal environment. A linear eigenvalue analysis gives the critical buckling temperature but practically the buckled columns canwithstand additional thermal load beyond critical temperature, which can be obtained using von-Karman geometric nonlinearity, applicable for moderately large deflections. In the present study, the solution of the nonlinear post-buckling problem is obtained by treating it as a linear eigenvalue problem using the concept of effective stiffness. Here, the total degrees of freedom (dof) of the discretized column are reduced and the postbuckling load is obtained without the need for iterative analysis. Comparison of the numerical results obtainedfrom this FE formulation is in very good agreement with those obtained from the earlier FE formulations.
Haxton, Thomas K; Zuckermann, Ronald N; Whitelam, Stephen
2016-01-12
Peptoid polymers form extended two-dimensional nanostructures via an interface-mediated assembly process: the amphiphilic peptoids first adsorb to an air-water interface as a monolayer, then buckle and collapse into free-floating bilayer nanosheets when the interface is compressed. Here, we investigate the molecular mechanism of monolayer buckling by developing a method for incorporating interface fluctuations into an implicit-solvent coarse-grained model. Representing the interface with a triangular mesh controlled by surface tension and surfactant adsorption, we predict the direction of buckling for peptoids with a segregated arrangement of charged side chains and predict that peptoids with with an alternating charge pattern should buckle less easily than peptoids with a segregated charge pattern. PMID:26647143
DEFF Research Database (Denmark)
Bhushan, Karihaloo; Stang, Henrik
2008-01-01
and on the level of the applied stress, it may or may not buckle away from the rest of the laminate. If it buckles, the post-buckling response will depend upon the applied compressive stress level, the thickness of the delaminated ply and the interlaminar critical energy release rate of the composite material...... for the mode mixity present at the delamination front. The pre- and post-buckling response is examined in its simplest form and guidelines provided for assessing whether or not a delamination detected during quality control or inspection poses a threat to the safe operation of the composite laminate.......This paper is concerned with development of a simple procedure to assess the threat posed by interlaminar matrix delaminations to the integrity of composite laminates when they are situated in a compressive stress field. Depending upon the size of the delamination, its location below the surface...
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.
Alexandre Achille Grandinetti; Janaína Dias; Ana Carolina Trautwein; Natasha Iskorostenski; Luciane Moreira; Ana Tereza Ramos Moreira
2013-01-01
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 ...
Wadee, M. Khurram; Lloyd, David J. B.; Bassom, Andrew P.
2016-01-01
A thin flat rectangular plate supported on its edges and subjected to in-plane loading exhibits stable post-buckling behaviour. However, the introduction of a nonlinear (softening) elastic foundation may cause the response to become unstable. Here the post-buckling of such a structure is investigated and several important phenomena are identified, including the transition of patterns from stripes to spots and back again. The interaction between these forms is of importance for understanding t...
Institute of Scientific and Technical Information of China (English)
侯朝胜; 李婧; 龙泉
2003-01-01
The cubic B-splines taken as trial function, the large deflection of a circular plate with arbitrarily variable thickness,as well as the buckling load, have been calculated by the method of point collocation. The support can be elastic. Loads imposed can be polynomial distributed loads, uniformly distributed radial forces or moments along the edge respectively or their combinations. Convergent solutions can still be obtained by this method under the load whose value is in great excess of normal one. Under the action of the uniformly distributed loads, linear solutions of circular plates with linearly or quadratically variable thickness are compared with those obtained by the parameter method. Buckling of a circular plate with identical thickness beyond critical thrust is compared with those obtained by the power series method.
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....... these must be included into the optimization, otherwise the imperfection sensitivity of the structure can be increased through optimization. To minimize the imperfection sensitivity of the structure the so-called Recurrence Optimization is applied. This approach uses a sequence of laminate optimizations...
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.
Evolved Colloidosomes Undergoing Cell-like Autonomous Shape Oscillations with Buckling.
Tamate, Ryota; Ueki, Takeshi; Yoshida, Ryo
2016-04-18
In living systems, there are many autonomous and oscillatory phenomena to sustain life, such as heart contractions and breathing. At the microscopic level, oscillatory shape deformations of cells are often observed in dynamic behaviors during cell migration and morphogenesis. In many cases, oscillatory behaviors of cells are not simplistic but complex with diverse deformations. So far, we have succeeded in developing self-oscillating polymers and gels, but complex oscillatory behaviors mimicking those of living cells have yet to be reproduced. Herein, we report a cell-like hollow sphere composed of self-oscillating microgels, that is, a colloidosome, that exhibits drastic shape oscillation in addition to swelling/deswelling oscillations driven by an oscillatory reaction. The resulting oscillatory profile waveform becomes markedly more complex than a conventional one. Especially for larger colloidosomes, multiple buckling and moving buckling points are observed to be analogous to cells. PMID:26960167
Effect of boundary conditions on piezoelectric buckled beams for vibrational noise harvesting
Cottone, F.; Mattarelli, M.; Vocca, H.; Gammaitoni, L.
2015-11-01
Nonlinear bistable systems have proven to be advantageous for energy harvesting of random and real ambient vibrations. One simple way of implementing a bistable transducer is setting a piezoelectric beam in a post-buckled configuration by axial compression. Besides, hinged or clamped-clamped type of boundary conditions correspond to two different post-buckled shape functions. Here we study, through theoretical analysis and numerical simulations, the efficiency of a hinged and clamped-clamped piezoelectric bridge under band-limited random noise with progressive axial load. Clamped configuration results to harvest 26% more power than hinged around an optimal axial load of 0.05%, while, in the intra-well trapped situation, above 0.1%, the two configurations present no substantial difference. Nevertheless, simulations confirm the advantage of exploiting inter-well oscillations in bistable regime.
Static and dynamic buckling of reconstructions at triple steps on Si(111) surfaces
Energy Technology Data Exchange (ETDEWEB)
Zhachuk, R., E-mail: zhachuk@gmail.com; Teys, S. [Institute of Semiconductor Physics, pr. Lavrentyeva 13, Novosibirsk 630090 (Russian Federation); Coutinho, J. [Department of Physics and I3N, University of Aveiro, Campus Santiago, 3810-193 Aveiro (Portugal); Rayson, M. J. [Department of Chemistry, University of Surrey, Guildford GU2 7XH (United Kingdom); Briddon, P. R. [School of Electrical, Electronic and Computer Engineering, Newcastle University, Newcastle Upon Tyne NE1 7RU (United Kingdom)
2014-10-27
Triple steps on Si(111) surfaces are popular building blocks for bottom-up nanostructure assembly, conferring size uniformity and precise positioning of growing nanostructures. In this work, we employ the Si(7 7 10) regular stepped surface as model system to study the triple steps by scanning tunneling microscopy (STM) and large-scale first-principles calculations. We find a surprising cohabitation of reconstruction elements at the step edge that either buckles statically or dynamically at room temperature. The driving force for the observed sequence of buckling patterns is traced back to Coulomb interactions involving charged adatoms and rest-atoms lying on a mini-terrace. These results reconcile the Si(111) triple step model with the experimental STM data.
A nonlinear model arising in the buckling analysis and its new analytic approximate solution
Energy Technology Data Exchange (ETDEWEB)
Khan, Yasir [Zhejiang Univ., Hangzhou, ZJ (China). Dept. of Mathematics; Al-Hayani, Waleed [Univ. Carlos III de Madrid, Leganes (Spain). Dept. de Matematicas; Mosul Univ. (Iraq). Dept. of Mathematics
2013-05-15
An analytical nonlinear buckling model where the rod is assumed to be an inextensible column and prismatic is studied. The dimensionless parameters reduce the constitutive equation to a nonlinear ordinary differential equation which is solved using the Adomian decomposition method (ADM) through Green's function technique. The nonlinear terms can be easily handled by the use of Adomian polynomials. The ADM technique allows us to obtain an approximate solution in a series form. Results are presented graphically to study the efficiency and accuracy of the method. To the author's knowledge, the current paper represents a new approach to the solution of the buckling of the rod problem. The fact that ADM solves nonlinear problems without using perturbations and small parameters can be judged as a lucid benefit of this technique over the other methods. (orig.)
STACKING SEQUENCE OPTIMIZATION OF LAMINATED COMPOSITE CYLINDER SHELL FOR MAXIMAL BUCKLING LOAD
Institute of Scientific and Technical Information of China (English)
TANG Qian; LIAO Xiaoyun; GAO Zhan
2008-01-01
A new optimization method for the optimization of stacking of composite glass fiber laminates is developed. The fiber orientation and angle of the layers of the cylindrical shells are sought considering the buckling load. The proposed optimization algorithm applies both finite element analysis and the mode-pursuing sampling (MPS)method. The algorithms suggest the optimal stacking sequence for achieving the maximal buckling load. The procedure is implemented by integrating ANSYS and MATLAB. The stacking sequence designing for the symmetric angle-ply three-layered and five-layered composite cylinder shells is presented to illustrate the optimization process, respectively. Compared with the genetic algorithms, the proposed optimization method is much faster and efficient for composite staking sequence plan.
Rigid-Plastic Post-Buckling Analysis of Columns and Quadratic Plates
DEFF Research Database (Denmark)
Jönsson, Jeppe
2008-01-01
of the post-buckling behaviour. The rigid plastic theory of plates, referred to as yield line theory, involves large rigid parts of the plate mutually rotating about yielding hinge lines, however in order to accommodate in plane plastic deformations area “collapse” yield lines have been introduced. The hinge......The objective of this paper is to show the application of a novel approach to the rigid plastic hinge and yield line theory in post-buckling analysis of slender plates and columns. The upper bound theorem of plasticity theory and the associated flow law of plasticity are used to find...... yield lines accommodate differential rotations of rigid parts and the area “collapse” yield lines accommodate local area changes of the rigid parts thereby preserving compatibility of the rigid parts of a plate. The approach will be illustrated for rigid plastic column analysis and for a quadratic plate...
Static and dynamic buckling of reconstructions at triple steps on Si(111) surfaces
Zhachuk, R.; Teys, S.; Coutinho, J.; Rayson, M. J.; Briddon, P. R.
2014-10-01
Triple steps on Si(111) surfaces are popular building blocks for bottom-up nanostructure assembly, conferring size uniformity and precise positioning of growing nanostructures. In this work, we employ the Si(7 7 10) regular stepped surface as model system to study the triple steps by scanning tunneling microscopy (STM) and large-scale first-principles calculations. We find a surprising cohabitation of reconstruction elements at the step edge that either buckles statically or dynamically at room temperature. The driving force for the observed sequence of buckling patterns is traced back to Coulomb interactions involving charged adatoms and rest-atoms lying on a mini-terrace. These results reconcile the Si(111) triple step model with the experimental STM data.
Cherniaev, Aleksandr; Komarov, Valeriy
2015-10-01
Composite drive shafts are extensively used in automotive and aeronautical applications due to lightweight combined with exceptional strength and stiffness. Complexity of the drive shaft design problem associated with the need to determine rational values for multiple parameters characterizing composite material (fiber orientation angles, stacking sequence and ply thicknesses), as well as with the fact that multiple conflicting design constraints should be considered simultaneously. In this paper we approach this problem considering carbon/epoxy drive shaft design as a multistep optimization process. It includes the following steps: 1) determination of fiber orientation angles and laminate stacking sequence based on analysis of loading conditions and analytical expressions predicting buckling load and minimal natural frequency of idealized drive shaft; 2) finding rational ply thicknesses using formal optimization procedure utilizing response surface approximations and gradient-based optimization algorithm; and 3) verification analysis of the optimized configuration with the use of nonlinear buckling analysis to ensure satisfaction of stability constraint.
Buckling test of a 3-meter-diameter corrugated graphite-epoxy ring-stiffened cylinder
Davis, R. C.
1982-01-01
A three m diameter by three m long corrugated cylindrical shell with external stiffening rings was tested to failure by buckling. The corrugation geometry for the graphite epoxy composite cylinder wall was optimized to withstand a compressive load producing an ultimate load intensity of 157.6 kN/m without buckling. The test method used to produce the design load intensity was to mount the specimen as a cantilevered cylinder and apply a pure bending moment to the end. A load introduction problem with the specimen was solved by using the BOSOR 4 shell of revolution computer code to analyze the shell and attached loading fixtures. The cylinder test loading achieved was 101 percent of design ultimate, and the resulting mass per unit of shell wall area was 1.96 kg/sq m.
Secondary Glaucoma Associated with Encircling Scleral Buckle Migration into the Cornea
Directory of Open Access Journals (Sweden)
Şengül Özdek
2016-01-01
Full Text Available Transmuscular migration of the encircling band through rectus muscles and straddling of the cornea has only been reported in a few cases previously in the literature. This rare condition has never been associated with glaucoma. In this report, we aimed to describe a unique case with transmuscular migration of encircling buckle as a probable cause of glaucoma. A 17-year-old female presented with transmuscular migration of buckle and high intraocular pressure (IOP. Limbal/corneal migration of the silicone band was thought to be the main reason for the IOP rise; therefore, scleral band removal was performed. One month after removal, the patient was free of glaucoma medications and IOP was within normal limits. The retina remained attached during all postoperative visits. Transmuscular migration of the encircling band through rectus muscles and straddling of the cornea may act as a trigger for glaucoma.
Experimental analysis of buckling in aircraft skin panels by fibre optic sensors
Güemes, J. A.; Menendez, J. M.; Frövel, M.; Fernandez, I.; Pintado, J. M.
2001-06-01
Three blade-stiffened CFRP panels with co-cured stiffener webs, manufactured by means of an elastomeric mould, have been tested under compressive load. Several Bragg grating sensors have been surface bonded on two of the stiffened panels and have been embedded into the stiffener webs of the third panel. The Bragg grating sensors measured the strain distribution in the stiffener web and in the skin panels. The bucking onset was clearly detected in every case, the post-buckling behaviour can be tracked, but the information is heavily dependent on the right choice of the sensor position and the buckling mode. To calibrate the system, and to evaluate the influence of different curing pressures, and the use of unidirectional or fabric prepreg material, tensile test specimens were made on flat panels. The strain measurements provided by the optical fibre sensors in tensile tests were compared with the strain measurements provided by conventional clamp extensometers.
Numerical analysis of pulse signal restoration by stochastic resonance in a buckled microcavity.
Sun, Heng; Liu, Hongjun; Sun, Qibing; Huang, Nan; Wang, Zhaolu; Han, Jing
2016-04-20
A novel scheme is proposed to restore weak pulse signals immersed in noise by stochastic resonance based on photothermal-effect-induced optical bistability in a buckled dome microcavity. The bistable properties of the dome microcavity are analyzed with different initial detuning wavelengths and effective cavity lengths, and bistable transmission can be obtained for input powers in submilliwatt range. A theoretical model is derived to interpret the nonlinear process of pulse signal recovery through double-well potential theory. The cross-correlation coefficient between output signals and pure input pulses is calculated to quantitatively analyze the influence of noise intensity on stochastic resonance. A cross-correlation gain of 7 is obtained, and the noise-hidden signal can be recovered effectively though the buckled dome microcavity with negligible distortion. The simulation results show the potential of using this structure to restore low-level or noise-hidden pulse signals in all-optical integrated systems. PMID:27140110
Static and dynamic buckling of reconstructions at triple steps on Si(111) surfaces
International Nuclear Information System (INIS)
Triple steps on Si(111) surfaces are popular building blocks for bottom-up nanostructure assembly, conferring size uniformity and precise positioning of growing nanostructures. In this work, we employ the Si(7 7 10) regular stepped surface as model system to study the triple steps by scanning tunneling microscopy (STM) and large-scale first-principles calculations. We find a surprising cohabitation of reconstruction elements at the step edge that either buckles statically or dynamically at room temperature. The driving force for the observed sequence of buckling patterns is traced back to Coulomb interactions involving charged adatoms and rest-atoms lying on a mini-terrace. These results reconcile the Si(111) triple step model with the experimental STM data.
Experimental research on buckling of thin films in nano-scale under mechanical and thermal loading
Wang, S. B.; Jia, H. K.; Ren, X. C.; Li, L. A.
2008-11-01
In this paper, the mechanical and thermal properties of compressed thin film titanium films with 150nm thickness deposited on an organic glass substrate under mechanical and thermal loads were measured and characterized. In order to simulate the thin films in IT which subjected compound loads and to produce the buckle modes, the external uniaxial compression and thermal loading are subjected to the specimen by the symmetric loading device and the electrical resistance 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. The transient conduction and thermal stability of the film and substrate was studied with finite element method.
Optical Evaluation on Delamination Buckling of Composite Laminate with Impact Damage
Directory of Open Access Journals (Sweden)
J. T. Ruan
2014-01-01
Full Text Available The delamination buckling and growth behaviors of a cross-ply composite laminate with damage induced by low velocity impact are investigated optically using three-dimensional digital image correlation (3D-DIC method. For the 3D deformation measurement, the 3D-DIC setup comprised of two CCD cameras was adopted. The rectangle specimen was impacted under the impact energy of 7.0 J using a drop-weight testing machine, and the impact damage was detected by means of X-ray nondestructive evaluation (NDE technique. The 3D deformation field measured with the optical system clearly reveals that the delamination buckling characteristic of the specimen mainly appears local deformation mode under compression after impact test. Moreover, the behavior of delamination growth evaluated by the 3D-DIC optical method reasonably agrees with the NDE observed damage result after compression.
Mullineux, G; Hicks, B J; Berry, C
2012-04-28
Understanding what happens in terms of delamination during buckling of laminate materials is of importance across a range of engineering sectors. Normally concern is that the strength of the material is not significantly impaired. Carton-board is a material with a laminate structure and, in the initial creation of carton nets, the board is creased in order to weaken the structure. This means that when the carton is eventually folded into its three-dimensional form, correct folding occurs along the weakened crease lines. Understanding what happens during creasing and folding is made difficult by the nonlinear nature of the material properties. This paper considers a simplified approach which extends the idea of minimizing internal energy so that the effects of delamination can be handled. This allows a simulation which reproduces the form of buckling-delamination observed in practice and the form of the torque-rotation relation.
Larsen, George K.; Zhao, Yiping
2013-10-01
A fabrication method, based on thin film buckling, is demonstrated to form unique membranes that can be used for applications in optics and biosensing. This method should be applicable to a variety of material systems, which, along with its simplicity and compatibility with different film architectures, allows for widespread implementation.A fabrication method, based on thin film buckling, is demonstrated to form unique membranes that can be used for applications in optics and biosensing. This method should be applicable to a variety of material systems, which, along with its simplicity and compatibility with different film architectures, allows for widespread implementation. Electronic supplementary information (ESI) available: Monolayer characterization and details; morphological parameters of the membranes; diffraction pattern images; rigorous coupled wave analysis; pattern transfer fidelity; experimental details. See DOI: 10.1039/c3nr03933a
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.
Chen, Xiaodong
2012-01-01
In this video, Ray-tracing data visualization technique was used to obtain realistic and detailed flow motions during droplet collision. The differences of collision outcome between Newtonian and non-Newtonian were compared. Various types of droplet collision were presented, including bouncing, coalescence, and stretching separation. Because of the reducing of equivalent viscosity caused by shear stress, the gas film between shear-thinning droplet is thinner than Newtonian liquid. Since thinner gas film promotes coalescence, shear thinning liquid has smaller area of bouncing regime in the diagram of Weber number and impact parameter. During the ligament/thread breakup process of stretching separation, two kinds of instabilities are identified, helical and buckling instabilities. Helical instability is analogous to a viscous rotating liquid jet, while the buckling instability is analogous to electrically charged liquid jets of polymer solutions.
Exploiting Additive Manufacturing Infill in Topology Optimization for Improved Buckling Load
DEFF Research Database (Denmark)
Clausen, Anders; Aage, Niels; Sigmund, Ole
2016-01-01
Additive manufacturing (AM) permits the fabrication of functionally optimized components with high geometrical complexity. The opportunity of using porous infill as an integrated part of the manufacturing process is an example of a unique AM feature. Automated design methods are still incapable...... addresses an important inadequacy of the standard minimum compliance topology optimization approach, in which buckling is rarely accounted for; rather, a satisfactory buckling load is usually assured through a post-processing step that may lead to sub-optimal components. The present work compares...... the standard and coating approaches to topology optimization for the MBB beam benchmark case. The optimized structures are additively manufactured using a filamentary technique. This experimental study validates the numerical model used in the coating approach. Depending on the properties of the infill...
The eigenvalue problem associated with the nonlinear buckling of a shear bending column
Nishimura, Isao
2011-04-01
This paper discusses the eigenvalue problem of a nonlinear differential equation that governs the stability of a shear bending column under extremely large deformation. What is taken into consideration is the geometrical nonlinearity while the material is supposed to be linear. The reason of a superbly stable buckling behavior of a slender rubber bearing is physically explained by pointing out the analogy that is similar to the nonlinear wave propagation expressed in KdV equation. The nonlinear boundary condition and the nonlinear term of the differential equation cancel each other and make the associated eigenvalue rather constant. In other words, as far as the material is supposed to be linear, the column does not buckle no matter how large the deformation is. This theoretical prediction is experimentally verified and successfully applied to a base isolation system of a lightweight structure.
Shojaeian, Milad; Beni, Yaghoub Tadi; Ataei, Hossein
2016-01-01
Electromechanical buckling (EMB) of beam-type nanoelectromechanical systems (NEMSs) is investigated based on modified strain gradient theory. The system is modeled as a clamped-guided nanobeam which is under compressive or tensile axial loads as well as the effect of nonlinear electrostatic and van der Waals symmetric transverse forces. In addition, the beam is considered to be made of axially and transverse functionally graded materials. Here, FGM is Poly-SiGe, of which the general properties change gradually from silicon to germanium based on a simple power-law method. Considering the Euler-Bernoulli beam theory and using the principle of minimum potential energy, the governing equations and corresponding boundary conditions are established. After validation of results, the effects of power law index, variation of size effect parameters, length-thickness ratio and the distance between the two fixed and movable electrodes on the buckling response of the system are discussed.
Flow sensing by buckling monitoring of electrothermally actuated double-clamped micro beams
Kessler, Yoav; Liberzon, Alex
2016-01-01
We report on a flow sensing approach based on deflection monitoring of micro beams buckled by the compressive thermal stress due to electrothermal Joules heating. The air stream convectively cooling the device affects both the critical buckling values of the electric current and the postbuckling deflections of the structure. After calibration, the flow velocity was obtained from the deflections measurements. The quasi-static responses of 2000 microns long, 10 microns wide and 30 microns high single crystal silicon beam transduced using image processing were consistent with the prediction of the reduced order model, which couples thermoelectric, thermofluidic and structural domains. The deflection sensitivity of 1.5 microns/(m/s) and the critical current sensitivity of 0.4 mA/(m/s) were registered in the experiments. Our model and experimental results collectively demonstrate feasibility of the sensing approach and further suggest that simple, robust and potentially downscalable beam-type devices may have use ...
Ye, Hong-Ling; Wang, Wei-Wei; Chen, Ning; Sui, Yun-Kang
2016-08-01
In this paper, a model of topology optimization with linear buckling constraints is established based on an independent and continuous mapping method to minimize the plate/shell structure weight. A composite exponential function (CEF) is selected as filtering functions for element weight, the element stiffness matrix and the element geometric stiffness matrix, which recognize the design variables, and to implement the changing process of design variables from "discrete" to "continuous" and back to "discrete". The buckling constraints are approximated as explicit formulations based on the Taylor expansion and the filtering function. The optimization model is transformed to dual programming and solved by the dual sequence quadratic programming algorithm. Finally, three numerical examples with power function and CEF as filter function are analyzed and discussed to demonstrate the feasibility and efficiency of the proposed method.
Kala, Zdeněk
2013-10-01
The paper deals with the statistical analysis of resistance of a hot-rolled steel IPE beam under major axis bending. The lateral-torsional buckling stability problem of imperfect beam is described. The influence of bending moments and warping torsion on the ultimate limit state of the IPE beam with random imperfections is analyzed. The resistance is calculated by means of the close form solution. The initial geometrical imperfections of the beam are considered as the formatively identical to the first eigen mode of buckling. Changes of mean values of the resistance, of mean values of internal bending moments, of the variance of resistance and of the variance of internal bending moments were studied in dependence on the beam non-dimensional slenderness. The values of non-dimensional slenderness for which the statistical characteristics of internal moments associated with random resistance are maximal were determined.
Some applications of NASTRAN to the buckling of thin cylindrical shells with cutouts
Williams, J. G.; Starnes, J. H., Jr.
1972-01-01
The buckling of isotropic and waffle-stiffened circular cylinders with and without cutouts was studied using NASTRAN's Rigid Format 5 for the case of axial compressive loading. The results obtained for the cylinders without cutouts are compared with available reference solutions. The results for the isotropic cylinders containing a single circular cutout with selected radii are compared with available experimental data. For the waffle-stiffened cyclinder, the effect of two diametrically opposed rectangular cutouts was studied. A DMAP alter sequence was used to permit the necessary application of different prebuckling and buckling boundary conditions. Advantage was taken of available symmetry planes to formulate equivalent NASTRAN model segments which reduced the associated computational cost of performing the analyses. Limitations of the applicability of NASTRAN for the solution of problems with nonlinear characteristics are discussed.
Free vibrations and buckling analysis of laminated plates by oscillatory radial basis functions
Neves, A. M. A.; Ferreira, A. J. M.
2015-12-01
In this paper the free vibrations and buckling analysis of laminated plates is performed using a global meshless method. A refined version of Kant's theorie which accounts for transverse normal stress and through-the-thickness deformation is used. The innovation is the use of oscillatory radial basis functions. Numerical examples are performed and results are presented and compared to available references. Such functions proved to be an alternative to the tradicional nonoscillatory radial basis functions.
Yokoyama, Toshiyuki
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...
Jones, G. W.; Chapman, S. J.; Allwright, D. J.
2008-01-01
The problem of a thin spherical linearly-elastic shell, perfectly bonded to an infinite linearly-elastic medium is considered. A constant axisymmetric stress field is applied at infinity in the matrix, and the displacement and stress fields in the shell and matrix are evaluated by means of harmonic potential functions. In order to examine the stability of this solution, the buckling problem of a shell which experiences this deformation is considered. Using Koiter's nonlinear shallow shell the...
Chen, Licui; Jia, Nana; Gao, Lianghui; Fang, Weihai; Golubovic, Leonardo
2013-04-11
We explore the effects of the peripheral and transmembrane antimicrobial peptides on the lipid bilayer membrane by using the coarse grained Dissipative Particle Dynamics simulations. We study peptide/lipid membrane complexes by considering peptides with various structure, hydrophobicity and peptide/lipid interaction strength. The role of lipid/water interaction is also discussed. We discuss a rich variety of membrane morphological changes induced by peptides, such as pore formation, membrane corrugation and Euler buckling.
Buckling and failure characteristics of compression-loaded stiffened composite panels with a hole
Nagendra, S.; Gurdal, Z.; Haftka, R. T.; Starnes, J. H.
An experimental and analytical study was carried out to investigate the buckling and failure characteristics of stiffened compression-loaded panels with holes and to assess the validity of analytical models used for the design of such panels. Graphite-epoxy panels with four equally spaced blade stiffeners were fabricated with a laminate stacking sequence optimally designed for stiffened panels without holes. Panels with different hole sizes and panels without holes were tested.
Alireza Dehghani; Hassan Razmjoo; Farhad Fazel; Mehdi Karami; Akbar Etesampour; Heshmatolah Ghanbari; Farzan Kianersi; Mohammadreza Akhlaghi; Hamid Fesharaki
2013-01-01
Aim: We aimed to compare peak systolic velocity of central retinal artery (PSV.CRA) and peak systolic velocity of ophthalmic artery (PSV.OA) between patients with retinal detachment who were treated with segmental scleral bucking and scleral buckling with encircling procedure. Materials and Methods: This study was a descriptive-analytic cross sectional study that was performed in Isfahan university referral centers since April 2010 to April 2011. Of the patients who have undergone scleral buc...
International Nuclear Information System (INIS)
The load carrying behaviour of cylindrical thin-walled shell structures under pressure load is strongly dependent on the nature and magnitude of the imperfections invariably caused by various manufacturing processes. The present paper examines instabilities of long homogeneous and isotropic thin elastic tubes, characterized by geometric imperfections like eccentricity or ovality, on the buckling behaviour in conditions for which, at present, a complete theoretical analysis was not found in literature. Moreover, the additional aspect of the influence of the welded joint geometry and position is investigated over a wide range of diameter to thickness ratio, extending the findings of previous works. The problem of buckling for variable load conditions is relevant in the context of NPP applications as, for instance the optimisation of an integrated and innovative LWR Steam Generator (SG) tubes, according to the updated ASME rules. To the purpose, at Pisa University a rather intense research activity is being carried out on the buckling of thin walled metal specimens in the dimensional range suitable for the above mentioned application. Therefore a test equipment (with the necessary data acquisition facility), suitable for carrying out test series on this issue, as well as numerical models implemented on the MARC FEM code, were set up. The experiments were conducted on test specimens with different materials, e.g. A-316 ASTM (with and without seam weld) and Inconel 690 TT, as well as different loading conditions (lateral and hydrostatic external pressure). A validation of numerical evaluations by comparison with test results is also performed. A good agreement has been observed between the experimental data and the elasto-plastic finite element analyses results, highlighting also the different influence of the mentioned imperfections on the buckling loads
Directory of Open Access Journals (Sweden)
Weihai Fang
2013-04-01
Full Text Available We explore the effects of the peripheral and transmembrane antimicrobial peptides on the lipid bilayer membrane by using the coarse grained Dissipative Particle Dynamics simulations. We study peptide/lipid membrane complexes by considering peptides with various structure, hydrophobicity and peptide/lipid interaction strength. The role of lipid/water interaction is also discussed. We discuss a rich variety of membrane morphological changes induced by peptides, such as pore formation, membrane corrugation and Euler buckling.
Energy Technology Data Exchange (ETDEWEB)
Bejitual, T.S.; Morris, N.J.; Cairns, D.R.; Sierros, K.A., E-mail: kostas.sierros@mail.wvu.edu
2013-12-31
There is currently a great interest to design and fabricate novel flexible devices for solar cell, solid-state lighting, biomedical and energy harvesting applications. Such devices require the use of electrode components. Desired electrodes must exhibit structural integrity, low electrical resistivity and, in most cases, high optical transparency in the visible range. Despite growing efforts to replace them, transparent conducting oxide layers deposited on polymer substrates are still enjoying a dominant role as the electrode component. This is because of their excellent combination of electrical and optical properties. However, their performance when they are subjected to externally-applied mechanical stresses is limited. Such performance has been extensively investigated for the case of continuous brittle oxide films on polymer substrates. However, there is relatively little work reported to date on the mechanical behavior of patterned conducting layers on compliant substrates. In this study we report on the mechanical behavior of various patterned indium tin oxide shapes and sizes on polyethylene terephthalate. Micron-sized shapes include squares, circles, and zigzag-based structures. Controlled buckling experiments are performed in-situ using an optical microscope in order to monitor critical strains and potential failure mechanisms. In addition, ITO electrical resistance changes are continuously monitored during deformation. Furthermore, ex-situ characterization of the tested surfaces using scanning electron microscopy is conducted. Higher crack onset values are observed for the smaller size patterns. Also, square-shaped patterns are found to exhibit the lowest crack onset values. SEM observations suggest cracking-driven and buckling-driven delamination during ITO tensile and compressive buckling mode respectively. In both cases, failure is observed to initiate from the pattern edges. - Highlights: • In-situ experimental analysis of various patterned shapes
Buckling of steel and composite steel and concrete columns in case of fire
Correia, Antonio M.; Rodrigues, João Paulo C.
2010-01-01
Bare steel columns are known to have a very low fire resistance. The high thermal conductivity and the sudden decrease of the steel yield stress and Young Modulus in function of the temperature are responsible for this behaviour. The purpose of this study is to compare different modes of failure of building steel columns. The buckling of the columns is strongly influenced by the contact with other elements such as brick walls. Three types of situations were compared: steel columns...
A fracture mechanics model to describe the buckling behavior of lightly rc columns
Porras Soriano, Rocio; Ruiz Carmona, Jacinto; Ruiz Lopez, Gonzalo Francisco; Yu, Chengxiang
2013-01-01
In order to correctly model the behavior of slender columns made of lightly reinforced concrete (RC) sub- jected to buckling load, both tensile fracture and compressive damage should be taken into account. In this work, we propose to consider both failure types as cohesive cracks, governed by a bilinear cohesive law for traction or a linear-decreasing softening equation for compression. Since the columns are lightly reinforced, we assume only one single crack is to propagate at the column cen...
Framework for the Buckling Optimization of Variable-Angle Tow Composite Plates
Wu, Zhangming; Raju, Gangadharan; Weaver, Paul M
2015-01-01
Variable-angle tow describes fibers in a composite lamina that have been steered curvilinearly. In doing so, substantially enlarged freedom for stiffness tailoring of composite laminates is enabled. Variable-angle tow composite structures have been shown to have improved buckling and postbuckling load-carrying capability when compared to straight fiber composites. However, their structural analysis and optimal design is more computationally expensive due to the exponential increase in number ...
ANALYSIS OF THE TOW BUCKLING DEFECT DURING THE COMPLEX SHAPE FORMING OF A FLAX WOVEN FABRIC
Capelle, Emilie; Ouagne, Pierre; Tephany, Christophe; Soulat, Damien; Duriatti, Davy; Hivet, Gilles; Allaoui, Samir
2012-01-01
A flax fibre plain weave fabric has been used to form a complex tetrahedron shape. The global shape has been obtained. Globally, the complex tetrahedron shape was obtained, but tow buckling was observed in specific zones of the shape. The main mechanism at the origin of this defect has been defined. The influence of the fabric architecture has also been discussed and a solution consisting in specifically optimising the architecture of the fabric was proposed and tested with success to prevent...
The design of post-buckled spinal structures for airfoil shape control using optimization methods
Ursache, N.M.; Bressloff, N.W.; Keane, A.J.
2004-01-01
In this paper we examine the use of optimization methods and a variety of shape definition schemes to design spinal structures for the control of deformable shape airfoils. The aim is to find structures that, when suitably loaded, can be used to alter the aerodynamic performance of a cladding that forms the airfoil. Further, by using structures that are acting in the post buckling regime it is possible to obtain significant changes in shape with only modest changes in applied load.
International Nuclear Information System (INIS)
There is currently a great interest to design and fabricate novel flexible devices for solar cell, solid-state lighting, biomedical and energy harvesting applications. Such devices require the use of electrode components. Desired electrodes must exhibit structural integrity, low electrical resistivity and, in most cases, high optical transparency in the visible range. Despite growing efforts to replace them, transparent conducting oxide layers deposited on polymer substrates are still enjoying a dominant role as the electrode component. This is because of their excellent combination of electrical and optical properties. However, their performance when they are subjected to externally-applied mechanical stresses is limited. Such performance has been extensively investigated for the case of continuous brittle oxide films on polymer substrates. However, there is relatively little work reported to date on the mechanical behavior of patterned conducting layers on compliant substrates. In this study we report on the mechanical behavior of various patterned indium tin oxide shapes and sizes on polyethylene terephthalate. Micron-sized shapes include squares, circles, and zigzag-based structures. Controlled buckling experiments are performed in-situ using an optical microscope in order to monitor critical strains and potential failure mechanisms. In addition, ITO electrical resistance changes are continuously monitored during deformation. Furthermore, ex-situ characterization of the tested surfaces using scanning electron microscopy is conducted. Higher crack onset values are observed for the smaller size patterns. Also, square-shaped patterns are found to exhibit the lowest crack onset values. SEM observations suggest cracking-driven and buckling-driven delamination during ITO tensile and compressive buckling mode respectively. In both cases, failure is observed to initiate from the pattern edges. - Highlights: • In-situ experimental analysis of various patterned shapes
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.
Extrusion of hydrogel exoplant into upper eyelid 16 years after a scleral buckle procedure
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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.
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Daniel da Rocha Lucena
2009-04-01
Full Text Available If the ocular media are clear, indirect binocular ophthalmoscopy allows retinal detachment and retinal tear identification and treatment under direct visualization. However, if opacities are present preventing direct fundus examination, ultrasonography becomes the most important tool for evaluating the posterior segment. In addition, ultrasonography can be useful in retinal tear treatment by guiding cryotherapy. In this article we describe a rhegmatogenous retinal detachment treatment technique applied to a patient with corneal opacity. Cryopexy and circumferential and radial buckle positioning were guided by ultrasonography, resulting in retinal attachment during the 6-month follow-up period.Quando os meios oculares são transparentes, oftalmoscopia binocular indireta permite a identificação de descolamento de retina e roturas, bem como seu tratamento sob visibilização direta. Porém, em olhos que apresentam opacidades de meios impedindo o exame oftalmoscópico, a ultrassonografia constitui o exame mais importante do segmento posterior do olho. Além disso, o tratamento de roturas retinianas também pode ser auxiliado pelo uso desse equipamento, orientando a crioterapia. Neste trabalho será apresentada técnica de tratamento de descolamento de retina regmatogênico, no qual a criopexia e o posicionamento dos "buckles" episclerais circunferencial e radial foram guiados pelo ultrassom em paciente com leucoma corneano. O tratamento resultou em aplicação retiniana durante o seguimento em seis meses.
BUCKLING AND POSTBUCKLING OF LAMINATED THIN CYLINDRICAL SHELLS UNDER HYGROTHERMAL ENVIRONMENTS
Institute of Scientific and Technical Information of China (English)
沈惠申
2001-01-01
The influence of hygrothermal effects on the buckling and postbuckling of composite laminated cylindrical shells subjected to axial compression is investigated using a micro-to-macro-mechanical analytical model. The material properties of the composite are affected by the variation of temperature and moisture, and are based on a micromechanical model of a laminate. The governing equations are based on the classical laminated shell theory, and including hygrothermal effects. The nonlinear prebuckling deformations and initial geometric imperfections of the shell were both taken into account. A boundary layer theory of shell buckling was extended to the case of laminated cylindrical shells under hygrothermal environments, and a singular perturbation technique was employed to determine buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling behavior of perfect and imperfect, cross-ply laminated cylindrical shells under different sets of environmental conditiors. The influences played by temperature rise, the degree of moisture concentration, fiber volume fraction, shell geometric parameter, total number of plies, stacking sequences and initial geometric imperfections are studied.
Stam, Samantha; Gardel, Margaret
Viscoelastic networks of biopolymers coordinate the motion of intracellular objects during transport. These networks have nonlinear mechanical properties due to events such as filament buckling or breaking of cross-links. The influence of such nonlinear properties on the time and length scales of transport is not understood. Here, we use in vitro networks of actin and the motor protein myosin II to clarify how intracellular forces regulate active diffusion. We observe two transitions in the mean-squared displacement of cross-linked actin with increasing motor concentration. The first is a sharp transition from initially subdiffusive to diffusive-like motion that requires filament buckling but does not cause net contraction of the network. Further increase of the motor density produces a second transition to network rupture and ballistic actin transport. This corresponds with an increase in the correlation of motion and thus may be caused when forces propagate far enough for global motion. We conclude that filament buckling and overall network contraction require different amounts of force and produce distinct transport properties. These nonlinear transitions may act as mechanical switches that can be turned on to produce observed motion within cells.
Boundaries determine the formation energies of lattice defects in two-dimensional buckled materials
Jain, Sandeep K.; Juričić, Vladimir; Barkema, Gerard T.
2016-07-01
Lattice defects are inevitably present in two-dimensional materials, with direct implications on their physical and chemical properties. We show that the formation energy of a lattice defect in buckled two-dimensional crystals is not uniquely defined as it takes different values for different boundary conditions even in the thermodynamic limit, as opposed to their perfectly planar counterparts. Also, the approach to the thermodynamic limit follows a different scaling: inversely proportional to the logarithm of the system size for buckled materials, rather than the usual power-law approach. In graphene samples of ˜1000 atoms, different boundary conditions can cause differences exceeding 10 eV. Besides presenting numerical evidence in simulations, we show that the universal features in this behavior can be understood with simple bead-spring models. Fundamentally, our findings imply that it is necessary to specify the boundary conditions for the energy of the lattice defects in the buckled two-dimensional crystals to be uniquely defined, and this may explain the lack of agreement in the reported values of formation energies in graphene. We argue that boundary conditions may also have an impact on other physical observables such as the melting temperature.
Prakash, T.; Sundararajan, N.; Ganapathi, M.
2007-01-01
Here, the dynamic thermal buckling behavior of functionally graded spherical caps is studied considering geometric nonlinearity based on von Karman's assumptions. The formulation is based on first-order shear deformation theory and it includes the in-plane and rotary inertia effects. The material properties are graded in the thickness direction according to the power-law distribution in terms of volume fractions of the material constituents. The effective material properties are evaluated using homogenization method. The governing equations obtained using finite element approach are solved employing the Newmark's integration technique coupled with a modified Newton-Raphson iteration scheme. The pressure load corresponding to a sudden jump in the maximum average displacement in the time history of the shell structure is taken as the dynamic buckling load. The present model is validated against the available isotropic case. A detailed numerical study is carried out to highlight the influences of shell geometries, power law index of functional graded material and boundary conditions on the dynamic buckling load of shallow spherical shells.
High-Fidelity Buckling Analysis of Composite Cylinders Using the STAGS Finite Element Code
Hilburger, Mark W.
2014-01-01
Results from previous shell buckling studies are presented that illustrate some of the unique and powerful capabilities in the STAGS finite element analysis code that have made it an indispensable tool in structures research at NASA over the past few decades. In particular, prototypical results from the development and validation of high-fidelity buckling simulations are presented for several unstiffened thin-walled compression-loaded graphite-epoxy cylindrical shells along with a discussion on the specific methods and user-defined subroutines in STAGS that are used to carry out the high-fidelity simulations. These simulations accurately account for the effects of geometric shell-wall imperfections, shell-wall thickness variations, local shell-wall ply-gaps associated with the fabrication process, shell-end geometric imperfections, nonuniform applied end loads, and elastic boundary conditions. The analysis procedure uses a combination of nonlinear quasi-static and transient dynamic solution algorithms to predict the prebuckling and unstable collapse response characteristics of the cylinders. Finally, the use of high-fidelity models in the development of analysis-based shell-buckling knockdown (design) factors is demonstrated.
Buckling Analysis of Functionally Graded Material Plates Using Higher Order Shear Deformation Theory
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B. Sidda Reddy
2013-01-01
Full Text Available The prime aim of the present study is to present analytical formulations and solutions for the buckling analysis of simply supported functionally graded plates (FGPs using higher order shear deformation theory (HSDT without enforcing zero transverse shear stresses on the top and bottom surfaces of the plate. It does not require shear correction factors and transverse shear stresses vary parabolically across the thickness. Material properties of the plate are assumed to vary in the thickness direction according to a power law distribution in terms of the volume fractions of the constituents. The equations of motion and boundary conditions are derived using the principle of virtual work. Solutions are obtained for FGPs in closed-form using Navier’s technique. Comparison studies are performed to verify the validity of the present results from which it can be concluded that the proposed theory is accurate and efficient in predicting the buckling behavior of functionally graded plates. The effect of side-to-thickness ratio, aspect ratio, modulus ratio, the volume fraction exponent, and the loading conditions on the critical buckling load of FGPs is also investigated and discussed.
EXPERIMENTAL INVESTIGATION OF THE PHENOMENON OF BUCKLING FOR STEEL AND ALUMINIUM STRUTS
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Durmuş TÜRKMEN
1995-01-01
Full Text Available The experiment was carried out to investigate the phenomenon of buckling using simple struts. These results were then compared with the theoretical predictions. Three steel struts of different length were used in the experiment; one of them had fix/pinned-end all the others had pin/pin-end joint. The applied load was placed at different eccentricities for each strut. Six aluminium pin-end struts of varying length were also tested. The measured critical load for each strut was compared against the corresponding Euler and Southwell predictions. For a steel strut, it would be expected that buckling would be symmetrical for left and right eccentricities. However, this was not the case due to imperfections in the struts. The struts buckled with half sine-wave and if one end of the strut was fixed the effective length was reduced and the critical load was increased. In the case of the aluminium struts, due to plastic behaviour in the deformation it was much harder to find the critical load. For steel struts both Euler and Southwell predictions were close to initial estimates of critical load.
Salehi-Khojin, Amin; Jalili, Nader
2007-04-01
Unlike widely-used carbon nanotubes, boron nitride nanotubes (BNNTs) have shown to possess stable semiconducting behavior and strong piezoelectricity. Such properties along with their outstanding mechanical properties and thermal conductivity, make BNNTs promising candidate reinforcement materials for a verity of applications especially nanoelectronic and nanophotonic devices. Motivated by these abilities, we aim to study the buckling behavior of BNNT-reinforced piezoelectric polymeric composites when subjected to combined electro-thermo-mechanical loadings. For this, the multi-walled structure of BNNT is considered as elastic media and a set of concentric cylindrical shell with van der Waals interaction between them. Using three-dimensional equilibrium equations, Donnell shell theory is utilized to show that the axially compressive resistance of BNNT varies with applying thermal and electrical loads. The effect of BNNT piezoelectric property on the buckling behavior of the composites is demonstrated. More specifically, it is shown that applying direct and reverse voltages to BNNT changes the buckling loads for any axial and circumferential wavenumbers. Such capability could be uniquely utilized when designing BNNT-reinforced composites.
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R. KANDASAMY
2014-05-01
Full Text Available In this paper, tests on flexural buckling ( Lateral – Torsional of cold-formed steel(CFS lipped Channel beams under restrained boundary conditions are described Two point loading for flexural tests have been established for 3.0m span to obtain uniform bending moment. The section sizes selected for testing are 100x50x10 mm, 100x50x15 mm and 100x50x20 mm with 1.6mm and 2.0mm thickness for the investigation. Carefully designed loading and support systems were used in the tests to apply gravity load through the web of the section and to ensure that simply supported ends were established. The test results are compared in the BS5950:Part 5 and IS code 801-1975. The influence of warping and torsional restraints on flexural capacity is presented. The influence of buckling length for different boundary conditions proposed by Rhodes was considered to calculate critical flexural-torsional buckling moment.
An enriched 1D finite element for the buckling analysis of sandwich beam-columns
Sad Saoud, Kahina; Le Grognec, Philippe
2016-06-01
Sandwich constructions have been widely used during the last few decades in various practical applications, especially thanks to the attractive compromise between a lightweight and high mechanical properties. Nevertheless, despite the advances achieved to date, buckling still remains a major failure mode for sandwich materials which often fatally leads to collapse. Recently, one of the authors derived closed-form analytical solutions for the buckling analysis of sandwich beam-columns under compression or pure bending. These solutions are based on a specific hybrid formulation where the faces are represented by Euler-Bernoulli beams and the core layer is described as a 2D continuous medium. When considering more complex loadings or non-trivial boundary conditions, closed-form solutions are no more available and one must resort to numerical models. Instead of using a 2D computationally expensive model, the present paper aims at developing an original enriched beam finite element. It is based on the previous analytical formulation, insofar as the skin layers are modeled by Timoshenko beams whereas the displacement fields in the core layer are described by means of hyperbolic functions, in accordance with the modal displacement fields obtained analytically. By using this 1D finite element, linearized buckling analyses are performed for various loading cases, whose results are confronted to either analytical or numerical reference solutions, for validation purposes.
Buckling behavior and structural efficiency of open-section stiffened composite compression panels
Williams, J. G.; Stein, M.
1976-01-01
Several experiments with J- and blade-stiffened graphite/epoxy panels were conducted to obtain insight into how well experimental data could be correlated with analysis for the buckling behavior of open-section stiffened composite compression panels. Although some nonlinear behavior was observed during the experiments, adequate correlation with analysis was obtained to justify the use of linear, thin-plate buckling analysis in a minimum-weight design synthesis program for J- and blade-configurations. Results from two design studies using this program are presented. In the first study the minimum weights of Jand blade-configurations for two different material systems (graphite/epoxy and aluminum) are determined subject to buckling and strength constraints for a wide range of the compressive load index. In the second study the minimum weights required for graphite/epoxy blade-stiffened panels to satisfy additional stiffness constraints typical of medium-size commercial aircraft wing structures are determined. Both minimum-weight studies indicate that graphite/epoxy open-section stiffened panels can be designed so that weight savings of 30 to 50% are possible compared with the most efficient aluminum designs.
Vibration and buckling of rotating, pretwisted, preconed beams including Cooriolis effects
Subrahmanyam, K. B.; Kaza, K. R. V.
1985-01-01
The effects of pretwist, precone, setting angle and Coriolis forces on the vibration and buckling behavior of rotating, torsionally rigid, cantilevered beams were studied. The beam is considered to be clamped on the axis of rotation in one case, and off the axis of rotation in the other. Two methods are employed for the solution of the vibration problem: (1) one based upon a finite-difference approach using second order central differences for solution of the equations of motion, and (2) based upon the minimum of the total potential energy functional with a Ritz type of solution procedure making use of complex forms of shape functions for the dependent variables. The individual and collective effects of pretwist, precone, setting angle, thickness ratio and Coriolis forces on the natural frequencies and the buckling boundaries are presented. It is shown that the inclusion of Coriolis effects is necessary for blades of moderate to large thickness ratios while these effects are not so important for small thickness ratio blades. The possibility of buckling due to centrifugal softening terms for large values of precone and rotation is shown.
Experimental Investigation into the Elastic Buckling of a Nuclear Fuel Cladding Tube
International Nuclear Information System (INIS)
Outer diameter of a dual cooled fuel rod needs to be increased considerably from that of a conventional one due to the requirement of a surface area increase as well as the formation of an internal flow passage. As was found previously, the thickness to outer diameter ratio (t/Do) of the conventional PWR fuel rod is mostly 0.058∼0.062. It seemed to be determined from experiences since there was little information about the reason for the t/Do values. Elastic buckling concern would be one of the reasons. Safety factor is more than 3 if a conventional design formula of the elastic buckling was applied. It is almost impossible to apply those values to a dual cooled fuel rod due to a considerably decreased rod-to-rod gap size and the amount of UO2 required for a burnup. So, there is a strong need to investigate the fundamental background of the used formula and its conservatism. In this paper, a classical theory of the stability was revisited and an experiment was conducted. Deduction for the used formula of an elastic buckling is explained. Experimental results are discussed by focusing on the safety margin of the used formula. Finally, the safety factor is considered for the presently determined thickness and diameter of a dual cooled fuel rod
Vibration and buckling of rotating, pretwisted, preconed beams including Coriolis effects
Subrahmanyam, K. B.; Kaza, K. R. V.
1985-01-01
The effects of pretwist, precone, setting angle and Coriolis forces on the vibration and buckling behavior of rotating, torsionally rigid, cantilevered beams were studied. The beam is considered to be clamped on the axis of rotation in one case, and off the axis of rotation in the other. Two methods are employed for the solution of the vibration problem: (1) one based upon a finite-difference approach using second order central differences for solution of the equations of motion, and (2) based upon the minimum of the total potential energy functional with a Ritz type of solution procedure making use of complex forms of shape functions for the dependent variables. The individual and collective effects of pretwist, precone, setting angle, thickness ratio and Coriolis forces on the natural frequencies and the buckling boundaries are presented. It is shown that the inclusion of Coriolis effects is necessary for blades of moderate to large thickness ratios while these effects are not so important for small thickness ratio blades. The possibility of buckling due to centrifugal softening terms for large values of precone and rotation is shown.
Measurement of material buckling in a large heavy water moderated exponential assembly
International Nuclear Information System (INIS)
Exponential measurements of material buckling have been made in a number of Steam Generating Heavy Water lattices, in the large exponential assembly known as SGHW I, at AEE Winfrith. The procedures adopted for the optimum adjustment of neutron source positions, for the analysis of harmonic effects and for the investigation and minimising of random and systematic errors are described in detail in this report. It is believed that these methods are adequate to determine a typical material buckling of 3 m-2 to a statistical accuracy of ± 0.030 m-2 and that the additional contribution from systematic errors is not greater than ± 0.036 m-2. It has been shown that the positions of flux peaks caused by cluster end plates in the axial distributions in these cores are moved vertically by about 2 cm by the interaction with the macroscopic exponential flux distribution. Radial reflector savings have been shown to vary with core composition in a manner which is well predicted by a relatively simple theoretical calculation. This suggests that statistical errors in individual radial buckling determinations in lattices of this type could be reduced from ± 0.016 m-2 to ± 0.005 m-2 by collating radial reflector saving data from similar lattices. (author)
Model Test Based Soil Spring Model and Application in Pipeline Thermal Buckling Analysis
Institute of Scientific and Technical Information of China (English)
GAO Xi-feng; LIU Run; YAN Shu-wang
2011-01-01
The buckling of submarine pipelines may occur due to the action of axial soil frictional force caused by relative movement of soil and pipeline,which is induced by the thermal and internal pressure.The likelihood of occurrence of this buckling phenomenon is largely determined by soil resistance.A series of large-scale model tests were carried out to facilitate the establishment of substantial data base for a variety of burial pipeline relationships.Based on the test data,nonlinear soil spring can be adopted to simulate the soil behavior during the pipeline movement.For uplift resistance,an ideal elasticity plasticity model is recommended in the case of H/D (depth-to-diameter ratio)＞5 and an elasticity softened model is recommended in the case of H/D≤5.The soil resistance along the pipeline axial direction can be simulated by an ideal elasticity plasticity model.The numerical analyzing results show that the capacity of pipeline against thermal buckling decreases with its initial imperfection enlargement and increases with the burial depth enhancement.
International Nuclear Information System (INIS)
The load carrying behaviour of cylindrical thin-walled shell structures under pressure load is strongly dependent on the nature and magnitude of the imperfections invariably caused by various manufacturing processes. The present paper examines instabilities of long homogeneous and isotropic thin elastic tubes, characterized by geometric imperfections like eccentricity or oval shape, on the buckling behaviour in conditions for which, at present, a complete theoretical analysis was not found in literature. Moreover, the additional aspect of the influence of the welded joint geometry and position is investigated over a wide range of diameter to thickness ratio, extending the findings of previous works. The experiments were conducted on test specimens with different materials, e.g. A-316 ASTM (with and without seam weld) and Inconel, as well as different loading conditions (lateral and hydrostatic external pressure). A validation of numerical evaluations by comparison with test results is also performed. A good agreement has been observed between the experimental data and the elasto-plastic finite element analyses results, highlighting also the different influence of the mentioned imperfections on the buckling loads. For all 3 tube families tested, the oval form was found to reduce the collapse pressure quite significantly. The local thickness variation along the longitudinal welding and the interaction between neighbouring imperfections have been shown to be important factors governing buckling
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.
Stability diagram of unilateral buckling patterns of strip-delaminated films.
Parry, G; Cimetière, A; Coupeau, C; Colin, J; Grilhé, J
2006-12-01
Thin films deposited on substrates are usually submitted to large residual compression stresses, causing delamination and buckling of the film into various patterns. The present study is focused on the different equilibria arising on strip-shaped delaminated areas. The three most common types of buckling patterns observed on such strips are known as the straight-sided wrinkles, bubble pattern, and telephone cord blisters. The stability of those equilibria as a function of the two stress components of the loading is investigated. The Föppl-Von Karman model for elastic plates is used for theoretical aspects. The post-critical equilibrium paths of the buckling patterns are investigated numerically by means of the finite-element method. The substrate is assumed to be rigid and the contact to be frictionless. The equilibrium solutions can be classified into families of homologous equilibria allowing the identification of dimensionless parameters for the study of stability. A mapping of the different stable post-critical equilibria is given. It is shown that the straight-sided wrinkles and the bubbles are associated with anisotropy of stresses and/or of elastic properties, whereas the telephone cords are stable at high isotropic stresses. The morphological transitions are experimentally evidenced by in situ atomic force microscopy observations of a nickel 50-nm-thick film under stress.
Theoretical and experimental investigations of creep buckling on NiCr 22 Co 12 Mo tubes
International Nuclear Information System (INIS)
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 pa 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 tcr. 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.)
Localization of duplex thrust-ramps by buckling: analog and numerical modelling
Liu, Shumin; Dixon, John M.
1995-06-01
Duplex structures in natural fold-thrust belts occur over a wide range of geometric scales. Duplex thrust ramps exhibit a regular spacing linearly related to the thickness of strata involved in the duplex. We suggest that buckling instability in layered systems can produce local stress concentrations which localize thrust ramps with regular spacing. This mechanism is demonstrated through analog (centrifuge) and numerical (finite element) modelling. Centrifuge models containing finely-laminated multilayers composed of plasticine and silicone putty (simulating rocks such as limestone and shale) are compressed from one edge; folds propagate from hinterland to foreland. As shortening continues, the lowest competent unit is thrust into a blind duplex structure by breakthrusting. The duplex develops by serial nucleation of faults from hinterland to foreland; the ramp locations are inherited from the initial buckling instability. Finite-element models based on the analog models and their natural prototypes demonstrate that stress concentrations develop in fore-limbs of anticlines within competent stratigraphie units. Models containing thrust discontinuities (at sites of calculated stress concentration) display additional stress concentrations in the forelimbs of unfaulted folds closer to the foreland. The locus of stress concentration thus propagates towards the foreland, consistent with foreland thrust propagation in nature. The location and regular spacing of ramps are inherited from early (possibly even incipient) buckle folds.
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.
Xiong, Liuyang; Tang, Lihua; Ding, Hu; Chen, Liqun; Mace, Brian
2016-04-01
Nonlinear internal resonance mechanism is exploited in piezoelectric vibration energy harvesting (PVEH) for the purpose of broadening the resonance band. Conventional linear energy harvester has narrow operating bandwidth. In this research, a buckled piezoelectric beam structure with preload under transverse excitation is investigated to demonstrate the superiority of internal resonance. The condition for 2:1 internal resonance could be established by truncating the continuum beam with geometrical nonlinearity. Integro-partial-differential equations are derived for governing transverse motion measured from a stable equilibrium position. At specific initial axial compressive force, two modes are coupled through the internal resonance interaction. For weak nonlinear perturbations, multiple scales method is used to explore the amplitude-frequency responses of the buckled beam system under primary resonance with 2:1 internal resonance. Numerical examples demonstrate that the resonance bandwidth is broadened thanks to the coexistence of softening and hardening nonlinear characteristics. Moreover, validity of the approximate analytical method is demonstrated by comparing with simulation. Furthermore, the optimal resistance is discussed with a pure resistive load. This research on the internal resonance of buckled beam provides a basis for structure design and optimization in broadband PVEH.
Equilibrium equations for nonlinear buckling analysis of drill-strings in 3D curved well-bores
Institute of Scientific and Technical Information of China (English)
TAN MeiLan; GAN LiFei
2009-01-01
With the development of drilling technology, the oil/gas well has evolved from its early vertical straight form to the inclined, horizontal, plane curved, or even 3D curved well-bore. Understanding of the buck-ling behavior of a drill-string in a well-bore is crucial for the success of a drilling operation. Therefore, equilibrium equations for analyzing the buckling behavior of a drill-string in a 3D curved well-bore are required. Based on Love's equilibrium equations for a curved and twisted rod in space, s set of equi-librium equations for the nonlinear buckling analysis of a drill-string in a 3D curved well-bore are de-rived by introducing a radial constraint of the well-bore. The proposed formulae can account for the well curvature and tortuosity. Thus, it can be used to analyze the buckling behaviors of a drill-string constrained in a well-bore and subjected to axial compression, torsion at its upper end, and gravity simultaneously. It is worth noting that the existing equations in the literature for a drill-string in a straight and plane curved well-bore with a constant curvature are a special case of the proposed model. Thus, the present model can provide s theoretical basis for the nonlinear buckling analysis of a drill-string constrained in a 3D curved well-bore.
Liu, P. F.; Zheng, J. Y.
2013-12-01
Multiple delamination causes severe degradation of the stiffness and strength of composites. Interactions between multiple delamination, and buckling and postbuckling under compressive loads add the complexity of mechanical properties of composites. In this paper, the buckling, postbuckling and through-the-width multiple delamination of symmetric and unsymmetric composite laminates are studied using 3D FEA, and the virtual crack closure technique with two delamination failure criteria: B-K law and power law is used to predict the delamination growth and to calculate the mixed-mode energy release rate. The compressive load-strain curves, load-central deflection curves and multiple delamination process for eight composite specimens with different initial delamination sizes and their distributions as well as two angle-ply configurations 04//(± θ)6//04 ( θ = 0° and 45°, and "//" denotes the delaminated interface) are comparatively studied. From numerical results, the unsymmetry decreases the local buckling load and initial delamination load, but does not affect the global buckling load compared with the symmetric laminates. Besides, the unsymmetry affects the unstable delamination and buckling behaviors of composite laminates largely when the initial multiple delamination sizes are relatively small.
Investigation on the Geometric Imperfections driven Local Buckling Onset in Composite Conical Shells
Di Pasqua, Maria Francesca; Khakimova, Regina; Castro, Saullo G. P.; Arbelo, Mariano A.; Riccio, Aniello; Raimondo, Antonio; Degenhardt, Richard
2016-08-01
Buckling is a critical failure phenomenon for structures, and represents a threat for thin shells subjected to compressive forces. The global buckling load, for a conical structure, depends on the geometry and material properties of the shell, on the stacking sequence, on the type of applied load and on the initial geometric imperfections. Geometric imperfections, occurring inevitably during manufacturing and assembly of thin-walled composite structures, produce a reduction in the carrying load capability with respect to the design value. This is the reason why investigating these defects is of major concern in order to avoid over-conservative design structures. In this paper, the buckling behavior a conical structure with 45° semi-vertical angle is numerically investigated. The initial imperfections are taken into account by using different strategies. At first, the Single Perturbation Load Approach (SPLA), which accounts for defects in the form of a lateral load, normal to the surface, has been adopted. Then, the actual measured defects have been applied to the structure by using the Real Measured Mid-Surface Imperfections (MSI) approach. Investigations on cylindrical shells using the first strategy have already shown the occurrence of a particular phenomenon called "local snap-through", which represents a preliminary loss of stiffness. In order to better understand this phenomenon for conical shells, both the aforementioned techniques have been used to provide an exhaustive overview of the imperfections sensitiveness in conical composite shells. This study is related to part of the work performed in the frame of the European Union (EU) project DESICOS.
Application of optical 3D measurement on thin film buckling to estimate interfacial toughness
Jia, H. K.; Wang, S. B.; Li, L. A.; Wang, Z. Y.; Goudeau, P.
2014-03-01
The shape-from-focus (SFF) method has been widely studied as a passive depth recovery and 3D reconstruction method for digital images. An important step in SFF is the calculation of the focus level for different points in an image by using a focus measure. In this work, an image entropy-based focus measure is introduced into the SFF method to measure the 3D buckling morphology of an aluminum film on a polymethylmethacrylate (PMMA) substrate at a micro scale. Spontaneous film wrinkles and telephone-cord wrinkles are investigated after the deposition of a 300 nm thick aluminum film onto the PMMA substrate. Spontaneous buckling is driven by the highly compressive stress generated in the Al film during the deposition process. The interfacial toughness between metal films and substrates is an important parameter for the reliability of the film/substrate system. The height profiles of different sections across the telephone-cord wrinkle can be considered a straight-sided model with uniform width and height or a pinned circular model that has a delamination region characterized by a sequence of connected sectors. Furthermore, the telephone-cord geometry of the thin film can be used to calculate interfacial toughness. The instability of the finite element model is introduced to fit the buckling morphology obtained by SFF. The interfacial toughness is determined to be 0.203 J/m2 at a 70.4° phase angle from the straight-sided model and 0.105 J/m2 at 76.9° from the pinned circular model.
Grayscale gel lithography for programmed buckling of non-Euclidean hydrogel plates.
Na, Jun-Hee; Bende, Nakul P; Bae, Jinhye; Santangelo, Christian D; Hayward, Ryan C
2016-06-14
Shape programmable materials capable of morphing from a flat sheet into controlled three dimensional (3D) shapes offer promise in diverse areas including soft robotics, tunable optics, and bio-engineering. We describe a simple method of 'grayscale gel lithography' that relies on a digital micromirror array device (DMD) to control the dose of ultraviolet (UV) light, and therefore the extent of swelling of a photocrosslinkable poly(N-isopropyl acrylamide) (PNIPAm) copolymer film, with micrometer-scale spatial resolution. This approach allows for effectively smooth profiles of swelling to be prescribed, enabling the preparation of buckled 3D shapes with programmed Gaussian curvature. PMID:27169886
DEFF Research Database (Denmark)
Pedersen, Niels Leergaard; Nielsen, A.
2004-01-01
(areas) and shape optimization (joint positions). Topology optimization (removal and introduction of bars) is only considered in the sense that bars of minimum cross-sectional area will have a negligible influence on the performance of the structure. The structures are subjected to multiple load cases...... and the objective of the optimizations is minimum mass with constraints on (possibly multiple) eigenfrequencies, displacements, and stresses. For the case of stress constraints, we deal differently with tensile and compressive stresses, for which we control buckling on the element level. The stress constraints...
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.
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
Energy Technology Data Exchange (ETDEWEB)
MACKEY, T.C.
2006-03-17
This report documents a detailed buckling evaluation of the primary tanks in the Hanford double shell waste tanks. The analysis 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 raise by the Office of Environment, Safety, and Health (ES&H) Oversight (EH-22) during a review (in April and May 2001) of work being performed on the double-shell tank farms, and the operation of the aging waste facility (AWF) primary tank ventilation system.
Zhang, Z.; Challamel, N.; Wang, C. M.
2013-09-01
This paper presents the determination of Eringen's small length scale coefficient e0 for buckling of nonlocal Timoshenko beam from a microstructured beam model. The microstructured beam model is composed of discrete rigid elements (of equal length), which are connected by rotational and shear springs that model the bending and shearing behaviors in a beam. The exact solution of e0 is given for nonlocal Timoshenko beam with small length scale term appearing in the normal stress-strain relation only. It is shown that e0 approaches 1/√12 ≈0.289 which coincides with the one calibrated for nonlocal Euler beams.
Thermal tuning of hollow waveguides fabricated by controlled thin-film buckling.
Epp, E; Ponnampalam, N; McMullin, J N; Decorby, R G
2009-09-28
We describe the thermal tuning of air-core Bragg waveguides, fabricated by controlled formation of delamination buckles within a multilayer stack of chalcogenide glass and polymer. The upper cladding mirror is a flexible membrane comprising high thermal expansion materials, enabling large tuning of the air-core dimensions for small changes in temperature. Measurements on the temperature dependence of feature heights showed good agreement with theoretical predictions. We applied this mechanism to the thermal tuning of modal cutoff conditions in waveguides with a tapered core profile. Due to the omnidirectional nature of the cladding mirrors, these tapers can be viewed as waveguide-coupled, tunable Fabry-Perot filters.
Buckling of Actin-Coated Membranes under Application of a Local Force
Energy Technology Data Exchange (ETDEWEB)
Helfer, E.; Harlepp, S.; Bourdieu, L.; Robert, J.; MacKintosh, F. C.; Chatenay, D.
2001-08-20
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 ({approx}10{sup -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.
Buckling of Actin-Coated Membranes under Application of a Local Force
Helfer, E.; Harlepp, S.; Bourdieu, L.; Robert, J.; Mackintosh, F. C.; Chatenay, D.
2001-08-01
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 0.5 pN is applied perpendicular to the membrane plane. Although predicted for polymerized vesicles, this is the first evidence of such an instability.
NASTRAN static and buckling analysis - comparison with other large-capacity programs
Shah, L. C.
1973-01-01
A square plate with clamped edges under a concentrated load was modeled using NASTRAN and ASKA finite element computer programs. Deflections were computed for various width-to-thickness ratios (b/t) of the plate element, and were compared against the classical theory to determine the b/t limitations. A cylinder with simply supported ends was modeled using NASTRAN and STAGS computer programs for buckling analysis. The models were subjected to a uniform radial pressure loading. Several parameters were changed, and the effects of those variations are presented. Utilizing these data, a model which will produce results comparable to published empirical data can be constructed and processed for a minimized cost.
Dynamic analysis of a buckled asymmetric piezoelectric beam for energy harvesting.
Van Blarigan, Louis; Moehlis, Jeff
2016-03-01
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. PMID:27036185
Directory of Open Access Journals (Sweden)
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.
Indian Academy of Sciences (India)
A Lakshmi Narayana; Krishnamohana Rao; R Vijaya Kumar
2014-06-01
A numerical study is carried out using finite element method, to examine the effects of square and rectangular cutout on the buckling behavior of a sixteen ply quasi-isotropic graphite/epoxy symmetrically laminated rectangular composite plate $[0^\\circ /+45^\\circ /-45^\\circ /90^\\circ ]_{2s}$, subjected to various linearly varying in-plane compressive loads. Further, this paper addresses the effects of size of square/rectangular cutout, orientation of square/rectangular cutout, plate aspect ratio(a/b), plate length/thickness ratio(a/t), boundary conditions on the buckling bahaviour of symmetrically laminated rectangular composite plates subjected to various linearly varying in-plane compressive loading. It is observed that the various linearly varying in-plane loads and boundary conditions have a substantial influence on buckling strength of rectangular composite plate with square/rectangular cutout.
Institute of Scientific and Technical Information of China (English)
Bai Ruixiang; Chen Haoran
2001-01-01
On the basis of the first-order shear deformation plate theory and the zig-zag deformation assumption, an incremental finite element formulation for nonlinear buckling analysis of the composite sandwich plate is deduced and the temperature-dependent thermal and mechanical properties of composite is considered. A finite element method for thermal or thermo-mechanical coupling nonlinear buckling analysis of the composite sandwich plate with an interfacial crack damage between face and core is also developed. Numerical results and discussions concerning some typical examples show that the effects of the variation of the thermal and mechanical properties with temperature, extermal compressive loading, size of the damage zone and piy angle of the faces on the thermal buckling behavior are significant.
Directory of Open Access Journals (Sweden)
Guan Quan
2016-04-01
Full Text Available In this study, an analytical model of the combination of beam-web shear buckling and bottom-flange buckling at elevated temperatures has been introduced. This analytical model is able to track the force-deflection path during post-buckling. A range of 3D finite element models has been created using the ABAQUS software. Comparisons have been carried out between the proposed analytical model, finite element modelling and an existing theoretical model by Dharma (2007. Comparisons indicate that the proposed method is able to provide accurate predictions for Class 1 and Class 2 beams, and performs better than the existing Dharma model, especially for beams with high flange-to-web thickness ratios. A component-based model has been created on the basis of the analytical model, and will in due course be implemented in the software Vulcan for global structural fire analysis.
International Nuclear Information System (INIS)
Progressive collapse is a chain reaction of failures propagating throughout a portion of a structure that is disproportionate to the original local failure. When column members are subjected to unexpected load (compression load), they will buckle it the applied load is greater than the critical load the induces buckling. The post buckling strength of the columns will decrease rapidly, but if there is enough residual strength, the members will absorb the potential energy generated by the impact load to prevent progressive collapse. Thus, it is necessary to identify the relationship of the load deformation of a column member in the progressive collapse of a structure up to final collapse. In this study, we carried out nonlinear FEM analysis and based on deflection theory, we investigated the load deformation relationship of H section steel columns when both ends were fixed
Weil, A. Brandon; Gutiérrez-Alonso, G.; Johnston, S. T.; Pastor-Galán, D.
2013-01-01
The Paleozoic Variscan orogeny was a large-scale collisional event involving amalgamation of multiple continents and micro-continents. Existing data, suggests oroclinal buckling of an originally near-linear convergent margin during the last stages of Variscan deformation in the late Paleozoic. Closure of the Rheic Ocean resulted in E-W shortening (present-day coordinates) in the Carboniferous, producing a near linear N-S trending, east-verging belt. Subsequent N-S shortening near the Carb-Permian boundary resulted in oroclinal buckling. This late-stage orogenic event remains an enigmatic part of final Pangea amalgamation. The present-day arc curvature of the Variscan has inspired many tectonic models, with little agreement between them. While there is general consensus that two separate phases of deformation occurred, various models consider that curvature was caused by: dextral transpression around a Gondwana indentor; strike-slip wrench tectonics; or a change in tectonic transport direction due to changing stress fields. More recent models explain the curvature as an orocline, with potentially two opposite-facing bends, caused by secondary rotations. Deciphering the kinematic history of curved orogens is difficult, and requires establishment of two deformation phases: an initial compressive phase that forms a relatively linear belt, and a second phase that causes vertical-axis rotation of the orogenic limbs. Historically the most robust technique to accurately quantify vertical axis-rotation in curved orogens is paleomagnetic analysis, but recently other types of data, including fracture, geochemical, petrologic, paleo-current and calcite twin data, have been used to corroborate secondary buckling. A review of existing and new Variscan data from Iberia is presented that argues for secondary buckling of an originally linear orogenic system. Together, these data constrain oroclinal buckling of the Cantabrian Orocline to have occurred in about 10 Ma during the
THERMAL POST-BUCKLING OF AN ELASTIC BEAMS SUBJECTED TO A TRANSVERSELY NON-UNIFORM TEMPERATURE RISING
Institute of Scientific and Technical Information of China (English)
李世荣; 程昌钧; 周又和
2003-01-01
Based on the nonlinear geometric theory of axially extensible beams and by usingthe shooting method, the thermal post-buckling responses of an elastic beams, withimmovably simply supported ends and subjected to a transversely non-uniformly distributedtemperature rising, were investigated. Especially, the influences of the transversetemperature change on the thermal post-buckling deformations were examined and thecorresponding characteristic curves were plotted. The numerical results show that theequilibrium paths of the beam are similar to what of an initially deformed beam because ofthe thermal bending moment produced in the beam by the transverse temperature change.
Tuning the Performance of Metallic Auxetic Metamaterials by Using Buckling and Plasticity
Directory of Open Access Journals (Sweden)
Arash Ghaedizadeh
2016-01-01
Full Text Available Metallic auxetic metamaterials are of great potential to be used in many applications because of their superior mechanical performance to elastomer-based auxetic materials. Due to the limited knowledge on this new type of materials under large plastic deformation, the implementation of such materials in practical applications remains elusive. In contrast to the elastomer-based metamaterials, metallic ones possess new features as a result of the nonlinear deformation of their metallic microstructures under large deformation. The loss of auxetic behavior in metallic metamaterials led us to carry out a numerical and experimental study to investigate the mechanism of the observed phenomenon. A general approach was proposed to tune the performance of auxetic metallic metamaterials undergoing large plastic deformation using buckling behavior and the plasticity of base material. Both experiments and finite element simulations were used to verify the effectiveness of the developed approach. By employing this approach, a 2D auxetic metamaterial was derived from a regular square lattice. Then, by altering the initial geometry of microstructure with the desired buckling pattern, the metallic metamaterials exhibit auxetic behavior with tuneable mechanical properties. A systematic parametric study using the validated finite element models was conducted to reveal the novel features of metallic auxetic metamaterials undergoing large plastic deformation. The results of this study provide a useful guideline for the design of 2D metallic auxetic metamaterials for various applications.
Magnetic ordering of the buckled honeycomb lattice antiferromagnet Ba2NiTeO6
Asai, Shinichiro; Soda, Minoru; Kasatani, Kazuhiro; Ono, Toshio; Avdeev, Maxim; Masuda, Takatsugu
2016-01-01
We investigate the magnetic order of the buckled honeycomb lattice antiferromagnet Ba2NiTeO6 and its related antiferromagnet Ba3NiTa2O9 by neutron diffraction measurements. We observe magnetic Bragg peaks below the transition temperatures, and identify propagation vectors for these oxides. A combination of representation analysis and Rietveld refinement leads to a collinear magnetic order for Ba2NiTeO6 and a 120∘ structure for Ba3NiTa2O9 . We find that the spin model of the bilayer triangular lattice is equivalent to that of the two-dimensional buckled honeycomb lattice having magnetic frustration. We discuss the magnetic interactions and single-ion anisotropy of Ni+2 ions for Ba2NiTeO6 in order to clarify the origin of the collinear magnetic structures. Our calculation suggests that the collinear magnetic order of Ba2NiTeO6 is induced by the magnetic frustration and easy-axis anisotropy.
Analysis on Buckling Performance of Submarine Pipelines During Deepwater Pipe-Laying Operation
Institute of Scientific and Technical Information of China (English)
YUAN Lin; GONG Shun-feng; JIN Wei-liang; LI Zhi-gang; ZHAO Dong-yan
2009-01-01
Pipes inevitably encounter high ambient pressure and bending moment during the deepwater pipe-laying process,which can lead to elliptical buckling and even deterioration failure.For the safety of pipe-laying operation,available formalas for the pipe stability are established on the basis of the assumption of uniform deformation along the tube length and symmetrical buckling.This method can predict the nonlinear rcsponse of elliptical collapse of steel circular tubes for different ratios of diameter to thickness (D/t) under pure bending or combined bending and external pressure.In these formulas,the strain-displacement relationship is deduced from the nonlinear ring theory,and the Ramberg-Osgood constitutive model is applied to simulate the inelastic material behavior.Meanwhile,the principle of virtual work is adopted to derive the equilibrium equations.A set of equations is solved by the Newton-Raphson method,and the iterative scheme contains nested iteration for the constitutive relation.In order to check the effectiveness of this theoretical method,illustrative examples are presented in this paper.Besides,the numerical simulation is carried out by use of ANSYS.A comparison of the results shows that the theoretical method can provide reasonable prediction for engineering practice.
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.
Vibration and Buckling Analysis of Moderately Thick Plates using Natural Element Method
Directory of Open Access Journals (Sweden)
Mohammad Etemadi
2015-07-01
Full Text Available Using natural element method (NEM, the buckling and the free vibration behaviors of moderate thick plates is studied here. The basis of NEM is natural neighbors and Voronoi cells concepts. The shape functions of nodes located in the domain is equal to the proportion of common natural neighbors area divided by area that related by each Voronoi cells. First step in analyzing the moderate thick plates is identification boundaries. This is done by nodes scattering on problem domain. Mindlin/Reissner theory is used to express the equations of moderate thick plate. First and second order shape functions obtained from natural element method are used to discretize differential equations. Using numerical integration on whole discrete equations of domain, stiffness, geometry and mass matrices of plate are obtained. Buckling loads and vibration modes are expressed by substituting these matrices in plate equations of motions. Arbitrary shapes of plate are selected for solution. Comparing the results of the current approach with those obtained by other numerical analytical methods, it is shown that natural element method can solve problems with complex areas accurately.
Scleral buckle is good option for treatment of uncomplicated retinal detachment
Directory of Open Access Journals (Sweden)
Iuuki Takasaka
2012-12-01
Full Text Available OBJETIVE: To describe the reattachment rate and visual acuity results of patients with uncomplicated rhegmatogenous retinal detachment who underwent segmental scleral buckle surgery. METHODS: Prospective case series of 100 patients with visual loss or symptoms (floaters and photopsia of less than 30 days' duration scheduled for surgery. No patient had a retinal break greater than 30°, a retinal detachment larger than 2 quadrants or proliferative vitreoretinopathy. RESULTS: The 1-week, 1-month, and 6-month anatomical success rates were 93%, 100%, and 100%, respectively. Seven patients underwent one additional retinal detachment surgery (pars plan vitrectomy after primary failure at 1-week follow-up. The preoperative, 1-month, and 6-month best correct visual acuity were 20/100, 20/80, and 20/50, respectively. The postoperative complications were: eyelid edema in 10% of the patients, transient ocular hypertension in 5%, macular pucker in 3%, transient diplopia in 3%, and hyphema (<0.5mm in 1%. CONCLUSION: In patients with uncomplicated retinal detachment, segmental scleral buckle showed a very good anatomical and functional success, with a few number of major complications.
Lei, Xiao; Narsu, B.; Yun, Guohong; Li, Jiangang; Yao, Haiyan
2016-05-01
Surface effects play a deterministic role in the physical and mechanical properties of nanosized materials and structures. In this paper, we present a self-consistent theoretical scheme for describing the elasticity of nanowires. The natural frequency and the critical compression force of axial buckling are obtained analytically, taking into consideration the influences of lower symmetry, additional elastic parameters, surface reconstruction, surface elasticity, and residual surface stress. Applications of the present theory to elastic systems for the axially oriented Si and Cu nanowires and Ag axially oriented nanowires yield good agreement with experimental data and calculated results. The larger positive value of the new elastic parameter c12α taken into account for Si oriented nanowires drives the curves of natural frequency and critical compression force versus thickness towards the results obtained from density functional theory simulation. Negative surface stress decreases the critical load for axial buckling, thus making the nanowires very easy to bend into various structures. The present study is envisaged to provide useful insights for the design and application of nanowire-based devices.
Lovejoy, Andrew E.; Hilburger, Mark W.; Chunchu, Prasad B.
2010-01-01
A design study was conducted to investigate the effect shell buckling knockdown factor (SBKF), internal pressure and aluminum alloy material selection on the structural weight of stiffened cylindrical shells. Two structural optimization codes were used for the design study to determine the optimum minimum-weight design for a series of design cases, and included an in-house developed genetic algorithm (GA) code and PANDA2. Each design case specified a unique set of geometry, material, knockdown factor combinations and loads. The resulting designs were examined and compared to determine the effects of SBKF, internal pressure and material selection on the acreage design weight and controlling failure mode. This design study shows that use of less conservative SBKF values, including internal pressure, and proper selection of material alloy can result in significant weight savings for stiffened cylinders. In particular, buckling-critical cylinders with integrally machined stiffener construction can benefit from the use of thicker plate material that enables taller stiffeners, even when the stiffness, strength and density properties of these materials appear to be inferior.
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.
Fatigue Crack Propagation in Steel A131 Under Ice Loading of Crushing, Bending and Buckling
Institute of Scientific and Technical Information of China (English)
DUAN Menglan(段梦兰); SONG Lisong(宋立崧); FAN Xiaodong(樊晓东); James C.M.LId; FANG Huacan(方华灿)
2001-01-01
Three types of ice loading, which are most commonly present when ice acts on structures,are chosen and simulated for use of fatigue crack propagation tests on offshore structural steel Al31. The three types of ice categorized in accordance with the failure modes when acting on structures called crushing ice, bending ice, and buckling ice,respectively. This paper presents an experimental investigation on the fatigue crack propagation behavior of widely used high strength steel A 131 for offshore jackets in the loading environment of ice crushing, bending, and buckling. The test results of fatigue crack propagation in steel A 13 l under these simulated ice loading at temperature 292K are presented and analyzed in detail in this paper. The amplitude root mean square stress intensity factor is optimized to be the fundamental parameter of fatigue crack propagation for all types of ice loading histories. The results are also compared with constant amplitude fatigue crack propagation conclusions as in wave load mode, and a joint investigation on the results from ice forces, ice-induced vibrations, and ice-induced fatigue crack propagation is conducted, Conclusions are drawn for reference in structural design and material selection for offshore structures in ice environments.
Maji, Debashis; Das, Debanjan; Wala, Jyoti; Das, Soumen
2015-12-07
Development of flexible sensors/electronics over substrates thicker than 100 μm is of immense importance for its practical feasibility. However, unlike over ultrathin films, large bending stress hinders its flexibility. Here we have employed a novel technique of fabricating sensors over a non-planar ridge topology under pre-stretched condition which not only helps in spontaneous generation of large and uniform parallel buckles upon release, but also acts as stress reduction zones thereby preventing Poisson's ratio induced lateral cracking. Further, we propose a complete lithography compatible process to realize flexible sensors over pre-stretched substrates thicker than 100 μm that are released through dissolution of a water soluble sacrificial layer of polyvinyl alcohol. These buckling assisted flexible sensors demonstrated superior performance along different flexible modalities. Based on the above concept, we also realized a micro thermal flow sensor, conformally wrapped around angiographic catheters to detect flow abnormalities for potential applications in interventional catheterization process.
Saavedra, K.; Allix, O.; Gosselet, P.
2012-08-01
This paper investigates a computational strategy for studying the interactions between multiple through-the-width delaminations and global or local buckling in composite laminates taking into account possible contact between the delaminated surfaces. In order to achieve an accurate prediction of the quasi-static response, a very refined discretization of the structure is required, leading to the resolution of very large and highly nonlinear numerical problems. In this paper, a nonlinear finite element formulation along with a parallel iterative scheme based on a multiscale domain decomposition are used for the computation of 3D mesoscale models. Previous works by the authors already dealt with the simulation of multiscale delamination assuming small perturbations. This paper presents the formulation used to include geometric nonlinearities into this existing multiscale framework and discusses the adaptations that need to be made to the iterative process in order to ensure the rapid convergence and the scalability of the method in the presence of buckling and delamination. These various adaptations are illustrated by simulations involving large numbers of DOFs.
Flow sensing by buckling monitoring of electrothermally actuated double-clamped micro beams
Kessler, Y.; Krylov, S.; Liberzon, A.
2016-08-01
We report on a flow sensing approach based on deflection monitoring of a micro beam buckled by the compressive thermal stress due to electrothermal Joule's heating. The air stream, convectively cooling the device, affects both the critical buckling values of the electric current and the postbuckling deflections of the structure. After calibration, the flow velocity can be obtained from the deflection measurements. The quasi-static responses of 1000 μm and 2000 μm long, 10 μm wide, and 30 μm high single crystal silicon beams were consistent with the prediction of the model, which couples thermoelectric, thermofluidic, and structural domains. The deflection sensitivity of up to 1.5 μm/(m/s) and the critical current sensitivity of up to 0.43 mA/(m/s) were registered in the experiments. Our model and experimental results demonstrate the feasibility of the sensing approach and further suggest that simple, robust, and potentially downscalable beam-type devices may have use in flow velocity and wall shear stress sensors.
Non-linear buckling of an FGM truncated conical shell surrounded by an elastic medium
International Nuclear Information System (INIS)
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
Buckling and its effect on the confined flow of a model capsule suspension
Bryngelson, Spencer; Freund, Jonathan
2015-11-01
The rheology of confined flowing suspensions, such as blood, depend upon the dynamics of the components, which can be particularly rich when they are elastic capsules. Using boundary integral methods, we simulate a two-dimensional model channel through which flows a dense suspension of fluid-filled capsules. A parameter of principal interest is the equilibrium membrane perimeter, which ranges from round capsules to capsules with an elongated dog-bone-like equilibrium shape. It is shown that the minimum effective viscosity occurs for capsules with a biconcave equilibrium shape, similar to that of a red blood cell. The rheological behavior changes significantly over this range; transitions are linked to specific changes in the capsule dynamics. Most noteworthy is an abrupt change in behavior when capsules transition to a dog-bone-like equilibrium shape, which correlates with the onset of capsule buckling. The buckled capsules have a more varied orientation and make significant rotational (rotlet) contributions to the capsule-capsule interactions. Supported under NSF Grant No. CBET 13-36972.
Energy Technology Data Exchange (ETDEWEB)
Barbero, E.J.
1989-01-01
In this study, a computational model for accurate analysis of composite laminates and laminates with including delaminated interfaces is developed. An accurate prediction of stress distributions, including interlaminar stresses, is obtained by using the Generalized Laminate Plate Theory of Reddy in which layer-wise linear approximation of the displacements through the thickness is used. Analytical as well as finite-element solutions of the theory are developed for bending and vibrations of laminated composite plates for the linear theory. Geometrical nonlinearity, including buckling and postbuckling are included and used to perform stress analysis of laminated plates. A general two dimensional theory of laminated cylindrical shells is also developed in this study. Geometrical nonlinearity and transverse compressibility are included. Delaminations between layers of composite plates are modelled by jump discontinuity conditions at the interfaces. The theory includes multiple delaminations through the thickness. Geometric nonlinearity is included to capture layer buckling. The strain energy release rate distribution along the boundary of delaminations is computed by a novel algorithm. The computational models presented herein are accurate for global behavior and particularly appropriate for the study of local effects.
Effect of shear connectors on local buckling and composite action in steel concrete composite walls
International Nuclear Information System (INIS)
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 (tp) and yield stress (Fy), and the shear connector spacing (s), stiffness (ks), and strength (Qn) 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/tp) ratio to prevent local buckling before yielding is also developed based on the existing experimental database and additional numerical analysis
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.
Directory of Open Access Journals (Sweden)
R. A. Jafari-Talookolaei
2011-01-01
Full Text Available The aim of this paper is to present analytical and exact expressions for the frequency and buckling of large amplitude vibration of the symmetrical laminated composite beam (LCB with simple and clamped end conditions. The equations of motion are derived by using Hamilton's principle. The influences of axial force, Poisson effect, shear deformation, and rotary inertia are taken into account in the formulation. First, the geometric nonlinearity based on the von Karman's assumptions is incorporated in the formulation while retaining the linear behavior for the material. Then, the displacement fields used for the analysis are coupled using the equilibrium equations of the composite beam. Substituting this coupled displacement fields in the potential and kinetic energies and using harmonic balance method, we obtain the ordinary differential equation in time domain. Finally, applying first order of homotopy analysis method (HAM, we get the closed form solutions for the natural frequency and deflection of the LCB. A detailed numerical study is carried out to highlight the influences of amplitude of vibration, shear deformation and rotary inertia, slenderness ratios, and layup in the case of laminates on the natural frequency and buckling load.
Gowrishetty, Usha R.; Walsh, Kevin M.; Berfield, Thomas A.
2010-07-01
In this paper we develop vacuum-actuated polyimide bi-stable actuators using buckled diaphragms for applications in the field of MEMS. The fabrication process involves a single mask step and DRIE etch step to fabricate the buckled bi-stable diaphragms. Compressive stresses in a companion thermal oxide layer provide pre-stress in the polyimide mechanical films that initiates diaphragm buckling upon release. Pressure was used to actuate these polyimide diaphragms from their first stable state to their second stable state, resulting in 'zero electrical power' actuation. The buckling height of the polyimide diaphragms is approximately 7.6 µm with an actuation pressure of 41 kPa, which compares favorably with model predictions assuming effective diaphragm properties for a single layer. These polyimide diaphragms can be used as the fundamental building blocks in micro-pumps, micro-valves, switches and optical devices. Because of their bi-stable nature, they can also be used for applications in mechanical memory storage.
International Nuclear Information System (INIS)
In this paper we develop vacuum-actuated polyimide bi-stable actuators using buckled diaphragms for applications in the field of MEMS. The fabrication process involves a single mask step and DRIE etch step to fabricate the buckled bi-stable diaphragms. Compressive stresses in a companion thermal oxide layer provide pre-stress in the polyimide mechanical films that initiates diaphragm buckling upon release. Pressure was used to actuate these polyimide diaphragms from their first stable state to their second stable state, resulting in 'zero electrical power' actuation. The buckling height of the polyimide diaphragms is approximately 7.6 µm with an actuation pressure of 41 kPa, which compares favorably with model predictions assuming effective diaphragm properties for a single layer. These polyimide diaphragms can be used as the fundamental building blocks in micro-pumps, micro-valves, switches and optical devices. Because of their bi-stable nature, they can also be used for applications in mechanical memory storage.
Ganesan, N.; Kadoli, Ravikiran
2004-11-01
Thermoelastic buckling and free vibration analysis of geometrically perfect isotropic hemispherical shells subjected to axisymmetric temperature variation are presented. First order shear deformation theory is used to analyze the moderately thick elastic hemispherical shells. The variations of various field variables are assumed in the circumferential direction and the finite element matrices used in the numerical studies are based on the semi-analytical method. The formulation is validated for thermal buckling strains available in the literature. Thermal buckling temperatures are evaluated for deep shells having a cut-out at the apex. Parameters considered in the study include hemispherical shells with a/ h ratios of 100 and 500 and each with cut-out angle at apex equal to 7°, 30° and 45°. Boundary conditions considered are clamped-clamped and clamped-free. A study on the distribution of the stress resultants due to thermal loading is examined in order to relate their influence on the buckling temperature of the shells with respect to above-stated geometric parameters. The effect of temperature on the free vibration natural frequency of the hemispherical shell is also analyzed.
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.
Computer Simulation of the E.C.C.S. Buckling Curve using a Monte-Carlo Method
Strating, J.; Vos, H.
1973-01-01
The application of a Monte-Carlo simulation procedure to obtain the distribution function of the maximum load of a hinged column with imperfections is discussed. Buckling tests carried out by the E.C.C.S. on IPE 160 sections have been simulated. Information concerning the column variables is obtaine
Equilibrium equations for nonlinear buckling analysis of drill-strings in 3D curved well-bores
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
With the development of drilling technology, the oil/gas well has evolved from its early vertical straight form to the inclined, horizontal, plane curved, or even 3D curved well-bore. Understanding of the buck- ling behavior of a drill-string in a well-bore is crucial for the success of a drilling operation. Therefore, equilibrium equations for analyzing the buckling behavior of a drill-string in a 3D curved well-bore are required. Based on Love’s equilibrium equations for a curved and twisted rod in space, a set of equi- librium equations for the nonlinear buckling analysis of a drill-string in a 3D curved well-bore are de- rived by introducing a radial constraint of the well-bore. The proposed formulae can account for the well curvature and tortuosity. Thus, it can be used to analyze the buckling behaviors of a drill-string constrained in a well-bore and subjected to axial compression, torsion at its upper end, and gravity simultaneously. It is worth noting that the existing equations in the literature for a drill-string in a straight and plane curved well-bore with a constant curvature are a special case of the proposed model. Thus, the present model can provide a theoretical basis for the nonlinear buckling analysis of a drill-string constrained in a 3D curved well-bore.
International Nuclear Information System (INIS)
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 239Np (276,6 keV) for neutron capture (n,γ) and the 143Ce (293,3 keV) for fission (n,f) on both 238U and 235U, 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)
Institute of Scientific and Technical Information of China (English)
WANG Xiao-yu; SHEN Li-ping; HU Rong-rong; XU Wei
2011-01-01
Background After successful scleral buckle and cryotherapy for macular-off retinal detachment (RD),some patients have poor visual acuity without any clinically detected macular change,and the unsatisfactory postoperative visual acuity is difficult to explain.The purpose of this study was to determine the characteristics of subretinal fluid (SRF) after successful scleral buckle surgery for macula-off RD.Methods Twenty-eight eyes from 28 patients were included in this study.The patients underwent scleral buckle surgery combined with cryopexy for macular-off RD.After surgery,all eyes underwent thorough ophthalmologic examinations including slit-lamp biomicroscopy,best-corrected visual acuity (BCVA) test,and binocular indirect ophthalmoscopy.The BCVA prior to the operation,duration of RD,the duration of postoperative retinal reattachment,BCVA when SRF was observed,period required for the SRF to become undetectable,and the BCVA at the final follow-up were included in the clinical data for this study.Optical coherence tomography (OCT) and B-ultrasonography were used to confirm SRF,and fluorescein angiography (FFA) was carried out in several patients.BCVA when SRF was observed and BCVA at the final follow-up were evaluated using a paired ttest.Correlations between BCVA before the operation and duration of RD and BCVA at the final follow-up were analyzed using the Pearson correlation test.The type of SRF under OCT and BCVA at the final follow-up were compared using one-way analysis of variance (ANOVA).Results Postoperative retinal reattachment was achieved in 1.0-7.0 days (average,(2.7±2.1) days).After retinal reattachment,SRF was detected in all eyes by OCT 2 weeks postoperative,while B ultrasonography found no changes.The mean IogMAR BCVA was 0.35±0.27 at the time of the detection of SRF.The period for SRF to become undetectable ranged from 2.0 to 11.0 months (average,(6.3±2.3) months).The time of follow-up ranged from 24.0 to 36.0 months (average,(28.9±3.4) months
Distortional buckling modes of semi-discretized thin-walled columns
DEFF Research Database (Denmark)
Andreassen, Michael Joachim; Jönsson, Jeppe
2012-01-01
in the potential energy and the introduction of the constraints related to beam theory this leads to a modified set of coupled homogeneous differential equations of GBT with initial stress for identification of distortional displacement modes. In this paper we seek instability solutions using these GBT initial...... stress equations for simply supported columns with constrained transverse displacements at the end sections and a constant axial initial stress. Based on the known boundary conditions the reduced order differential equations are solved by using the trigonometric solution functions and solving the related......This paper presents distorting buckling solutions for semi-discretized thin-walled columns using the coupled differential equations of a generalized beam theory (GBT). In two related papers recently published by the authors a novel semi-discretization approach to GBT has been presented. The cross...
BUCKLING ANALYSIS UNDER COMBINED LOADING OF THIN-WALLED PLATE ASSEMBLIES USING BUBBLE FUNCTIONS
Institute of Scientific and Technical Information of China (English)
Gao Xuanneng; Zou Yinsheng; Zhou Xuhong
2000-01-01
Bubble functions are finite element modes that are zero on the boundary of the element but nonzero at the other point. The present paper adds bubble functions to the ordinary Complex Finite Strip Method(CFSM) to calculate the elastic local buckling stress of plates and plate assemblies. The results indi cate that the use of bubble functions greatly improves the convergence of the Finite Strip Method(FSM) in terms of strip subdivision, and leads to much smaller storage required for the structure stiffness and stability matrices. Numerical examples are given, including plates and plate structures subjected to a combination of longitudinal and transverse compression, bending and shear. This study illustrates the power of bubble func tions in solving stability problems of plates and plate structures.
[Scleral necrosis after scleral buckling surgery of the patient with pyoderma gangrenosum].
Kmera-Muszyńska, Maria; Tesla, Piotr; Okruszko, Anna
2009-01-01
Pyoderma gangrenosum (PG) is a rare skin disease caused by immune dysfunction. The systemic diseases are often associated. The aim of the study was to report necrotic scleritis which developed after scleral buckling procedure in the case of the 64 years old patient suffered from primary retinal detachment and idiopathic PG. The retinal reattachment was achieved. The conjunctival wound dehiscence, necrotising scleritis and marginal keratitis as a manifestation of the patergic reaction were diagnosed. The treatment with corticosteroids locally (Dexamethason) and systematically (Prednison and Sulfasalazine), was administrated. The improvement and stabilisation of the local condition of ocular surface were observed. After reduction of systemic drugs, the exacerbation of local inflammation and vitritis was observed. The prolonged therapy was necessary. The risk of wound healing disturbances of an ocular surface with aggravated necrotic reaction must be expected after ocular surgery of the patient with PG. The adequate immunosupressive prolonged treatment with proper collaboration with the dermatologist is necessary.
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.
Hygrothermal effects on free vibration and buckling of laminated composites with cutouts
Natarajan, Sundararajan
2013-01-01
The effect of moisture concentration and the thermal gradient on the free flexural vibration and buckling of laminated composite plates are investigated. The effect of a centrally located cutout on the global response is also studied. The analysis is carried out within the framework of the extended finite element method. A Heaviside function is used to capture the jump in the displacement and an enriched shear flexible 4-noded quadrilateral element is used for the spatial discretization. The formulation takes into account the transverse shear deformation and accounts for the lamina material properties at elevated moisture concentrations and temperature. The influence of the plate geometry, the geometry of the cutout, the moisture concentration, the thermal gradient and the boundary conditions on the free flexural vibration is numerically studied.
Saavedra, Karin; Gosselet, Pierre; 10.1002/nme.4305
2012-01-01
This paper investigates a computational strategy for studying the interactions between multiple through-the-width delaminations and global or local buckling in composite laminates taking into account possible contact between the delaminated surfaces. In order to achieve an accurate prediction of the quasi-static response, a very refined discretization of the structure is required, leading to the resolution of very large and highly nonlinear numerical problems. In this paper, a nonlinear finite element formulation along with a parallel iterative scheme based on a multiscale domain decomposition are used for the computation of 3D mesoscale models. Previous works by the authors already dealt with the simulation of multiscale delamination assuming small perturbations. This paper presents the formulation used to include geometric nonlinearities into this existing multiscale framework and discusses the adaptations that need to be made to the iterative process in order to ensure the rapid convergence and the scalabi...
Akbarov, Surkay
2013-01-01
This book investigates stability loss and buckling delamination problems of the viscoelastic composite materials and structural members made from these materials within the framework of the Three-Dimensional Linearized Theory of Stability (TDLTS). The investigation of stability loss problems is based on the study of an evolution of the initial infinitesimal imperfection in the structure of the material or of the structural members with time (for viscoelastic composites) or with external compressing forces (for elastic composites). This study is made within the scope of the Three-Dimensional Geometrically Non-Linear Theory of the Deformable Solid Body Mechanics. The solution to the corresponding boundary-value problems is presented in the series form in a small parameter which characterizes the degree of the initial imperfection. The boundary form perturbation technique is employed and nonlinear problems for the domains bounded by noncanonical surfaces are reduced to the same nonlinear problem for the correspo...
Dynamic buckling analysis of delaminated composite plates using semi-analytical finite strip method
Ovesy, H. R.; Totounferoush, A.; Ghannadpour, S. A. M.
2015-05-01
The delamination phenomena can become of paramount importance when the design of the composite plates is concerned. In the current study, the effect of through-the-width delamination on dynamic buckling behavior of a composite plate is studied by implementing semi-analytical finite strip method. In this method, the energy and work integrations are computed analytically due to the implementation of trigonometric functions. Moreover, the method can lead to converged results with comparatively small number of degrees of freedom. These features have made the method quite efficient. To account for delamination effects, displacement field is enriched by adding appropriate terms. Also, the penetration of the delamination surfaces is prevented by incorporating an appropriate contact scheme into the time response analysis. Some selected results are validated against those available in the literature.
Hollow Bragg waveguides fabricated by controlled buckling of Si/SiO2 multilayers.
Epp, E; Ponnampalam, N; Newman, W; Drobot, B; McMullin, J N; Meldrum, A F; DeCorby, R G
2010-11-22
We describe integrated air-core waveguides with Bragg reflector claddings, fabricated by controlled delamination and buckling of sputtered Si/SiO2 multilayers. Thin film deposition parameters were tailored to produce a desired amount of compressive stress, and a patterned, embedded fluorocarbon layer was used to define regions of reduced adhesion. Self-assembled air channels formed either spontaneously or upon heating-induced decomposition of the patterned film. Preliminary optical experiments confirmed that light is confined to the air channels by a photonic band-gap guidance mechanism, with loss ~5 dB/cm in the 1550 nm wavelength region. The waveguides employ standard silicon processes and have potential applications in MEMS and lab-on-chip systems.
The dynamic aspects of thermo-elasto-viscoplastic snap-through and creep buckling phenomena
Riff, R.; Simitses, G. J.
1987-01-01
Use of a mathematical model and solution methodology, to examine dynamic buckling and dynamic postbuckling behavior of shallow arches and spherical caps made of a realistic material and undergoing non-isothermal, elasto-viscoplastic deformation was examined. Thus, geometric as well as material type nonlinearities of higher order are included in this analysis. The dynamic stability problem is studied under impulsive loading and suddenly applied loading with loads of constant magnitude and infinite duration. A finite element model was derived directly from the incrementally formulated nonlinear shell equations, by using a tensor-oriented procedure. As an example of the results, the time history of the midspan displacement of a damped shallow circular arch is presented.
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.
Weak Formulation Study For Thermoelastic Buckling Analysis Of Thick Laminated Cylindrical Shells
Directory of Open Access Journals (Sweden)
Kewei Ding
2015-08-01
Full Text Available Weak formulations of mixed state equations of closed laminated cylindrical shells are presented in the Hamilton System. The Hamilton canonical equation of closed cylindrical shell is established. By means of applying the transfer matrix method and taking the advantage of Hamiltonian matrix in the calculation, a unified approach and three-dimensional thermoelastic solutions are obtained for the buckling analysis of closed thick laminated cylindrical shells. All equations of elasticity can be satisfied and all elastic constants can be taken into account. Numerical results are given to compare with those of FEM calculated using SAP5. The principle and method suggested here have clear physical concepts. The equations and boundary conditions proposed in this paper are weakened. The solutions and results given here may serve as a benchmark for other numerical procedures.
Equilibria and vibration of a buckled beam with attached masses or spring-mass systems
Plaut, Raymond H.; Virgin, Lawrence N.
2016-09-01
A buckled beam with immovable pinned ends is considered. Attached to the beam are either one concentrated mass, two concentrated masses, a spring-mass system (that could model a human, robot, or passive vibration absorber), or a horizontal rigid bar with two vertical end springs (a "bounce-pitch" system that could model an animal or a vehicle). In the theoretical analysis, the beam is modeled as an inextensible elastica. Equilibrium configurations are determined first. Then small free vibrations about equilibrium are examined, and the lowest frequencies and corresponding modes are computed. The effects of various parameters are investigated, such as the ratio of the span to the total arc length of the beam, the locations and weights of the attached masses and systems, and the stiffnesses of the springs. For the case of a single attached mass, experiments are conducted and the results are compared to the theoretical ones.
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.
Adsorption-enhanced spin-orbit coupling of buckled honeycomb silicon
Sun, Jia-Tao; Chen, Wei; Sakamoto, Kazuyuki; Feng, Yuan Ping; Wee, Andrew T. S.
2016-09-01
We have studied the electronic structures of quasi-two-dimensional buckled honeycomb silicon (BHS) saturated by atomic hydrogen and fluorine by means of first-principles calculations. The graphene-like hexagonal silicon with chair configurations can be stabilized by atomic hydrogen and fluorine adsorption. Together with a magnetic ground state, large spin-orbit coupling (SOC) of BHS saturated by hydrogen on either side (Semi-H-BHS) indicated by the band splitting of σ bond at Γ point in the Brillouin zone is attributed to the intermixing between the density of states of hydrogen atoms and π bonds of unpassivated Si2 around the Fermi level. The Zeeman spin splitting is most likely caused by the internal electric field induced by asymmetric charge transfer.
Tsiglifis, Kostas; Pelekasis, Nikos A.
2011-01-01
Stability analysis of the radial pulsations of a gas microbubble that is encapsulated by a thin viscoelastic shell and surrounded by an ideal incompressible liquid is carried out. Small axisymmetric disturbances in the microbubble shape are imposed and their long and short term stability is examined depending on the initial bubble radius, the shell properties, and the parameters, i.e., frequency and amplitude, of the external acoustic excitation. Owing to the anisotropy of the membrane that is forming the encapsulating shell, two different types of elastic energy are accounted for, namely, the membrane and bending energy per unit of initial area. They are used to describe the tensions that develop on the shell due to shell stretching and bending, respectively. In addition, two different constitutive laws are used in order to relate the tensions that develop on the membrane as a result of stretching, i.e., the Mooney-Rivlin law describing materials that soften as deformation increases and the Skalak law describing materials that harden as deformation increases. The limit for static buckling is obtained when the external overpressure exerted upon the membrane surpasses a critical value that depends on the membrane bending resistance. The stability equations describing the evolution of axisymmetric disturbances, in the presence of an external acoustic field, reveal that static buckling becomes relevant when the forcing frequency is much smaller than the resonance frequency of the microbubble, corresponding to the case of slow compression. The resonance frequencies for shape oscillations of the microbubble are also obtained as a function of the shell parameters. Floquet analysis shows that parametric instability, similar to the case of an oscillating free bubble, is possible for the case of a pulsating encapsulated microbubble leading to shape oscillations as a result of subharmonic or harmonic resonance. These effects take place for acoustic amplitude values that lie
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
2015-01-01
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.
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].
Flambage vertical des conduites en souillées Vertical Buckling of Buried Pipes
Directory of Open Access Journals (Sweden)
Bournazel C.
2006-11-01
Full Text Available Si l'apparition d'un flambage vertical des conduites rigides enfouies dans une tranchée est un phénomène assez rare, il peut ne pas en être de même pour des conduites flexibles dont les propriétés mécaniques sont de nature différente. Une étude théorique et expérimentale, ayant pour but de proposer une méthode analytique de calcul de l'apparition du flambage et de son évolution sous l'effet de la pression interne, a été réalisée. II apparaît que les conduites flexibles actuelles sont très sensibles à ce phénomène et qu'il serait nécessaire, pour l'éliminer à coup sûr, de réexaminer la structure des flexibles ou d'imaginer des artifices dans la procédure d'ensouillage Whereas the appearance of vertical buckling in rigid pipes buried in a trench is a relatively rare phenomenon, the same cannot be said for flexible pipes which have mechanical properties of a different nature. A theoretical and experimental study has been made with the aim of proposing an analytical method for computing the appearance of buckling and its evolution under the effect of outside pressure. Current flexible pipes appear to be very sensitive to this phenomenon, and to be certain of eliminating it the structure of flexible pipes should be reexamined or stratagems in the burying procedure should be devised.
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
Head, D. A.
2006-10-01
Motivated by observing the buckling of glassy crusts formed on evaporating droplets of polymer and colloid solutions, we numerically model the deformation and buckling of spherical elastic caps controlled by varying the volume between the shell and the substrate. This volume constraint mimics the incompressibility of the unevaporated solvent. Discontinuous buckling is found to occur for sufficiently thin and/or large contact angle shells, and robustly takes the form of a single circular region near the boundary that 'snaps' to an inverted shape, in contrast to the externally pressurized shells case. Scaling theory for shallow shells is shown to approximate well the critical buckling volume, the subsequent enlargement of the inverted region and the contact line force.
International Nuclear Information System (INIS)
It is well known that thin-walled compression members are subject to the effects of local buckling and that due to these local effects the compressive carrying capability of short strut members can be significantly reduced. Finite element simulation is employed in this paper to examine the post-buckled response of thin-walled sections giving due consideration to the influence of geometric imperfections and to elasto-plastic material behaviour. The findings from this work highlight the complete loading history of the compression struts from the onset of elastic local buckling through the nonlinear elastic and elasto-plastic post-buckling phases of behaviour to final collapse and unloading. A detailed account of the growth and redistribution of stresses as well as the influence of yielding and yield propagation throughout loading is given in the paper. The results from the finite element simulations are shown to compare well with independent simulations using the finite strip method of analysis.
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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.
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S. S. Daimi
2014-08-01
Full Text Available Functionally graded materials (FGMs are microscopically inhomogeneous spatial composite materials, typically composed of a ceramic-metal or ceramic-polymer pair of materials. Therefore, it is important to investigate the behaviors of engineering structures such as beams and plates made from FGMs when they are subjected to thermal loads for appropriate design. Therefore, using an improved third order shear deformation theory (TSDT based on more rigorous kinetics of displacements to predict the behaviors of functionally graded plates is expected to be more suitable than using other theories. In this paper, the improved TSDT is used to investigate thermal buckling of functionally graded plates. Temperature dependent material property solutions are adopted to investigate thermal buckling results of functionally graded plates. To obtain the solutions, the Ritz method using polynomial and trigonometric functions for defining admissible displacements and rotations is applied to solve the governing equations.
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Ruijiang Guo
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.
Gruttmann, F.; Pham, V. D.
2008-02-01
The delamination process of thin films on rigid substrates is investigated. Such systems are typically subject to high residual compression and modest adhesion causing them to buckling driven blisters. In certain cases buckles with the shape of telephone cords are observed. A finite element model for quasi-static delamination growth is developed. Applying a Reissner-Mindlin shell kinematic for the film allows C 0- continuous shape functions. The traction vector at the film-substrate interface is obtained from the derivative of a cohesive free energy. Incorporation of loading and unloading conditions is considered for the irreversible process. The equilibrium state is computed iteratively in dependence of the compressive residual stresses. The computed telephone cord delaminations are stable asymmetric configurations whereas the symmetric configurations are unstable.
High-finesse cavities fabricated by buckling self-assembly of a-Si/SiO2 multilayers.
Allen, T W; Silverstone, J; Ponnampalam, N; Olsen, T; Meldrum, A; DeCorby, R G
2011-09-26
Arrays of half-symmetric Fabry-Perot micro-cavities were fabricated by controlled formation of circular delamination buckles within a-Si/SiO(2) multilayers. Cavity height scales approximately linearly with diameter, in reasonable agreement with predictions based on elastic buckling theory. The measured finesse (F > 10(3)) and quality factors (Q > 10(4) in the 1550 nm range) are close to reflectance limited predictions, indicating that the cavities have low roughness and few defects. Degenerate Hermite-Gaussian and Laguerre-Gaussian modes were observed, suggesting a high degree of cylindrical symmetry. Given their silicon-based fabrication, these cavities hold promise as building blocks for integrated optical sensing systems.
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...... and through thickness position of the delamination. Different finite element modeling strategies were considered and validated against the experimental results. The one applying the 9 nodes MITC shell elements was found matching the experimental data despite failure modes were different for the two...
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Houari M.S.A.
2014-04-01
Full Text Available In this work, the size-dependent buckling behavior of functionally graded (FG nanobeams is investigated on the basis of the nonlocal continuum model. The material properties of FG nanobeams are assumed to vary through the thickness according to the power law. In addition, Poisson’s ratio is assumed constant in the current model. The nanobeams is modelled according to the new first order shear beam theory with small deformation and the equilibrium equations are derived using the Hamilton’s principle. The Naviertype solution is developed for simply-supported boundary conditions, and exact formulas are proposed for the buckling load. The effects of nonlocal parameter, aspect ratio, various material compositions on the stability responses of the FG nanobeams are discussed.
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.
S Natarajan; Chakraborty, S.; M. Ganapathi; Subramaniam, M
2013-01-01
In this paper, the effect of local defects, viz., cracks and cutouts on the buckling behaviour of functionally graded material plates subjected to mechanical and thermal load is numerically studied. The internal discontinuities, viz., cracks and cutouts are represented independent of the mesh within the framework of the extended finite element method and an enriched shear flexible 4-noded quadrilateral element is used for the spatial discretization. The properties are assumed to vary only in ...
Guo Ruijiang; Chattopadhyay Aditi
1995-01-01
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 loa...
Filip-Vacarescu Norin; Vulcu Cristian; Dubina Dan
2016-01-01
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 paramet...
Visible-range hollow waveguides by guided buckling of Ta2O5/SiO2 multilayers.
Melnyk, A; Potts, C A; Allen, T W; DeCorby, R G
2016-05-01
Hollow waveguides operating near 550 nm wavelength were fabricated by guided formation of delamination buckles within Ta2O5/SiO2 multilayers. The fabrication process employed a pair of sequentially deposited 10-period Bragg mirrors separated by a patterned, low-adhesion fluorocarbon layer. Propagation loss as low as a few dB/cm was measured, consistent with theoretical predictions.
Skrinar, Matjaž
2012-01-01
This paper brings new insights into the implementation of a simplified computational model in the prediction of buckling load Pcr for slender beam-type structures with a transverse crack. From among several approaches discussed, two of them produced applicable results exhibiting considerably good agreement with those values from more precise and complex computational models. In the first approach, the critical load value is obtained from numerical solutions of analytically expressed character...
Krishnan, Swaminathan
2009-01-01
Analyzing tall braced frame buildings with thousands of degrees of freedom in three dimensions subject to strong earthquake ground motion requires an efficient brace element that can capture the overall features of its elastic and inelastic response under axial cyclic loading without unduly heavy discretization. This report details the theory of a modified elastofiber (MEF) element developed to model braces and buckling-sensitive slender columns in such structures. The MEF element...
Barrett, R.; McMurtry, R.; De 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 (CLPT) models are shown to work very well in capturing the behavior of the free, unloaded elements. A new high transverse deflection model which employs nonlinear structural relations is shown to succe...
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...
Bansal, Lalit; Miglani, Ankur; Basu, Saptarshi
2016-04-01
In this work, we have established the evaporation-liquid flow coupling mechanism by which sessile nanofluid droplets on a hydrophobic substrate evaporate and agglomerate to form unique morphological features under controlled external heating. It is well understood that evaporation coupled with internal liquid flow controls particle transport in a spatiotemporal sense. Flow characteristics inside the heated droplet are investigated and found to be driven by the buoyancy effects. Velocity magnitudes are observed to increase by an order at higher temperatures with similar looking flow profiles. The recirculating flow induced particle transport coupled with collision of particles and shear interaction between them leads to the formation of dome shaped viscoelastic shells of different dimensions depending on the surface temperature. These shells undergo sol-gel transition and subsequently undergo buckling instability leading to the formation of daughter cavities. With an increase in the surface temperature, droplets exhibit buckling from multiple sites over a larger sector in the top half of the droplet. Irrespective of the initial nanoparticle concentration and substrate temperature, growth of a daughter cavity (subsequent to buckling) inside the droplet is found to be controlled by the solvent evaporation rate from the droplet periphery and is shown to exhibit a universal trend.
Roche, Matthieu; Akkaya, Oyku M.; Kellay, Hamid; Stone, Howard A.
2010-11-01
We studied the behavior of density-matched cornstarch solutions during and after pinch-off from a needle. We observed an exponential slowing down in the thinning dynamics of the bridge connecting the droplet to the needle during which the bridge adopts a cylindrical shape. At this stage, the flow is mainly extensional allowing us to explore the behavior of starch solutions at extension rates greater than 10 s-1. The bridge continues to thin and then destabilizes leading to break-up in multiple parts. These parts retract on themselves and buckle. We show that this buckling behavior can be understood as a consequence of a liquid-to-solid transition of starch solutions during thinning. Using microscopy, we demonstrate that the neck is inhomogeneous during the last stages of pinch-off: the thinner sections of the neck are fluid while the thicker regions are jammed. We explain buckling by showing that the bridge deforms around its fluid sections, making this system analogous to a chain of solid links connected by fluid bridges.
Frehner, Marcel; Schmid, Timothy
2016-06-01
Parasitic folds are typical structures in geological multilayer folds; they are characterized by a small wavelength and are situated within folds with larger wavelength. Parasitic folds exhibit a characteristic asymmetry (or vergence) reflecting their structural relationship to the larger-scale fold. Here we investigate if a pre-existing geometrical asymmetry (e.g., from sedimentary structures or folds from a previous tectonic event) can be inherited during buckle folding to form parasitic folds with wrong vergence. We conduct 2D finite-element simulations of multilayer folding using Newtonian materials. The applied model setup comprises a thin layer exhibiting the pre-existing geometrical asymmetry sandwiched between two thicker layers, all intercalated with a lower-viscosity matrix and subjected to layer-parallel shortening. When the two outer thick layers buckle and amplify, two processes work against the asymmetry: layer-perpendicular flattening between the two thick layers and the rotational component of flexural flow folding. Both processes promote de-amplification and unfolding of the pre-existing asymmetry. We discuss how the efficiency of de-amplification is controlled by the larger-scale fold amplification and conclude that pre-existing asymmetries that are open and/or exhibit low amplitude are prone to de-amplification and may disappear during buckling of the multilayer system. Large-amplitude and/or tight to isoclinal folds may be inherited and develop type 3 fold interference patterns.
Institute of Scientific and Technical Information of China (English)
Blake M. Andrews; Junho Song; Larry A. Fahnestock
2009-01-01
Buckling-restrained braces (BRBs) have recently become popular in the United :States for use as primary members of seismic lateral-force-resisting systems. A BRB is a steel brace that does not buckle in compression but instead yields in both tension and compression. Although design guidelines for BRB applications have been developed, systematic procedures for assessing performance and quantifying reliability are still needed. This paper presents an analytical framework for assessing buckling-restrained braced frame (BRBF) reliability when subjected to seismic loads. This framework efficiently quantifies the risk of BRB failure due to low-cycle fatigue fracture of the BRB core. The procedure includes a series of components that: (1) quantify BRB demand in terms of BRB core deformation histories generated through stochastic dynamic analyses; (2) quantify the limit-state of a BRB in terms of its remaining cumulative plastic ductility capacity based on an experimental database; and (3) evaluate the probability of BRB failure, given the quantified demand and capacity, through structural reliability analyses. Parametric studies were conducted to investigate the effects of the seismic load, and characteristics of the BRB and BRBF on the probability of brace failure. In addition, fragility curves (i.e., conditional probabilities of brace failure given ground shaking intensity parameters) were created by the proposed framework. While the framework presented in this paper is applied to the assessment of BRBFs, the modular nature of the framework components allows for application to other structural components and systems.
Zhu, W.; Zhou, Y. C.; Guo, J. W.; Yang, L.; Lu, C.
2015-01-01
A compression-induced buckling delamination test is employed to quantitatively characterize the interfacial adhesion of Ni thin film on steel substrate. It is shown that buckles initiate from edge flaws and surface morphologies exhibit symmetric, half-penny shapes. Taking the elastoplasticity of film and substrate into account, a three-dimensional finite element model for an edge flaw with the finite size is established to simulate the evolution of energy release rates and phase angles in the process of interfacial buckling-driven delamination. The results show that delamination propagates along both the straight side and curved front. The mode II delamination plays a dominant role in the process with a straight side whilst the curved front experiences almost the pure mode I. Based on the results of finite element analysis, a numerical model is developed to evaluate the interfacial energy release rate, which is in the range of 250-315 J/m2 with the corresponding phase angle from -41° to -66°. These results are in agreement with the available values determined by other testing methods, which confirms the effectiveness of the numerical model.
Kurguzov, V. D.; Demeshkin, A. G.
2016-05-01
The paper describes the processes of elastic deformation of thin films under mechanical loading. The film is modeled longitudinally by a compressed plate arranged on an elastic foundation. A computer model of the buckling of the narrow thin plate with a delamination portion located on an elastic foundation is constructed. This paper also touches upon the supercritical behavior of the plate-substrate system. The experiments on the axial compression of a metal strip adhered to a rubber plate are performed, and 2 to 7 buckling modes are obtained therein. The critical loads and buckling modes obtained in the numerical calculations are compared with the experimental data. It is shown that there is the possibility of progressive delamination of the metal plate from the foundation if the critical load is exceeded. It is found that the use of the proposed approach, which, in contrast to other approaches, accounts for the elastic deformation of the substrate, causes the dependence between the critical bending stress and the stiffness of the foundation.
Birman, Victor; Byrd, Larry W.
2008-02-01
The interest to functionally graded materials (FGM) and structures has been generated by their potential advantages, including enhanced thermal properties, reduced or eliminated delamination concerns, a potential for an improved stress distribution, etc. Various aspects of the processing, design, micromechanics and analysis of FGM have been outlined in a number of reviews, mentioned here are [1-3]. In particular, functionally graded panels may be advantageous compared to their conventional counterparts in numerous applications. However, a typical FGM panel is asymmetric about its middle plane resulting in lower buckling loads and fundamental frequencies as well as higher stresses and deformations than the counterpart with a symmetric distribution of the same constituents. The reduced stiffness of FGM panels can be compensated by reinforcing them with stringers. For example, metallic stringers at the metal-rich surface of a FGM ceramic-metal panel may provide an efficient solution enabling a designer to increase both buckling loads as well as natural frequencies. The list of studies on optimization of FGM is extensive as could be anticipated for such tailored structural elements. For example, recent papers by Batra and his collaborators present optimization of the natural frequencies of a FGM plate through material grading [4] and through the graded fiber orientation [5]. The present paper is concerned with an optimum design of the system of stringers for a specified FGM panel. The task is to design the lightest system of stringers enabling the panel to achieve prescribed buckling loads or fundamental frequency.
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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
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Kováč Michal
2015-03-01
Full Text Available Thin-walled centrically compressed members with non-symmetrical or mono-symmetrical cross-sections can buckle in a torsional-flexural buckling mode. Vlasov developed a system of governing differential equations of the stability of such member cases. Solving these coupled equations in an analytic way is only possible in simple cases. Therefore, Goľdenvejzer introduced an approximate method for the solution of this system to calculate the critical axial force of torsional-flexural buckling. Moreover, this can also be used in cases of members with various boundary conditions in bending and torsion. This approximate method for the calculation of critical force has been adopted into norms. Nowadays, we can also solve governing differential equations by numerical methods, such as the finite element method (FEM. Therefore, in this paper, the results of the approximate method and the FEM were compared to each other, while considering the FEM as a reference method. This comparison shows any discrepancies of the approximate method. Attention was also paid to when and why discrepancies occur. The approximate method can be used in practice by considering some simplifications, which ensure safe results.