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Ocean thermal energy conversion (OTEC) is a floating platform that generates electricity from seawater heat. The cold water pipe (CWP) used in OTEC has a length of 1,000 m and a diameter of 10 m, making it susceptible to bending loads from ocean currents. To find suitable geometry and material for the CWP, the finite element method was used to model the real-world geometry. In the D/t variation, lower ratios (increased thickness) result in higher critical moments, maximum stress, strain, and displacement. D/t 50 was chosen for the CWP. In the L/D variation, the critical moment’s impact on L/D ratio was minimal, while reducing L/D (shorter pipe) increased strain, and larger L/D geometries had higher displacements. L/D 10 was selected as it balanced critical moments and reduced the number of stiffeners needed. For diameter size variation, larger diameters increased critical moment and strain, but smaller diameters (larger L/D ratios) also showed high strain due to necking at two points. A diameter of 12 m was chosen for its exceptionally high critical moment. Steel was selected as the suitable material due to its higher critical moment and maximum stress, despite its higher weight and lower maximum strain than composites. Capital shape imperfections had a minimal effect on the CWP’s structure as they were localized.

In order to address the impact of the perforated parameters on the mechanical properties of the plate, the ultimate strength of hyper-ellipse flanged-perforated plates under uniaxial compression stress is numerically investigated in this article. The four edges of the flanged-perforated plate are only supported in the out-of-plane direction while the plate is exposed to uniaxial compressive loads. The impact of the cutout size, flange height, cutout position, rotation angle, and cutout form on the ultimate bearing capacity of the perforated plate with varied thicknesses is investigated and compared through a series of elasto-plastic buckling analyses using the ANSYS software. The structure’s stress and deformation analysis is then used to explain the results of the ultimate strength test. The flange efficiently raises the maximum bearing strength of the structure with cutouts. For the limit strength of thick plate, the cutout size, elliptical shape, cutout rotation angle, and cutout position have considerably more of an impact than they do on the maximum bearing capacity of thin plate. The findings can assist the structural layout of this sort of perforated plate, and the right cutout parameters should be chosen in accordance with the various performance specifications.

In this paper, Variational Iteration Method (VIM) is applied for finding buckling loads of a tilted buckled column with varying flexural rigidity, which is an important engineering problem in structural analysis and design considerations. In the cases where determination of exact solutions of tilt-buckling problems may not be possible, usage of this new technique will give researchers a powerful tool for determining them. This study shows the efficiency of the method and accuracy of the resulting analytic approximate solution for the problem. [ABSTRACT FROM AUTHOR]

The present paper is aimed to study the buckling and postbuckling response of functionally graded carbon nanotube (FG-CNT)- magnesium (Mg) nanocomposite plate with interphase effect. Interphase zone is characterized by employing a cohesive zone model for its elastic modulus and thickness. An equivalent solid fiber (ESF) of CNT and interphase is modeled and dispersed into the matrix material by utilizing random sequential adsorption (RSA) technique. The effective elastic properties of the nanocomposite are computed by finite element method (FEM) based numerical homogenization technique. The obtained elastic properties of nanocomposite are utilized to investigate the buckling and post-buckling behaviour of different functionally graded (i.e., FG) nanocomposite plates modeled by varying the volume fraction of CNT/ESF along thickness direction, under in-plane compressive loads. The non-linear formulation is based on first-order shear deformation theory and von Karman's assumptions. It is found that considering the interphase between CNT and Mg matrix would result in decrease in buckling load and postbuckling strength of FG-CNT-reinforced nanocomposite plate as compared to nanocomposite without interphase. It is also reported that the higher volume fraction of CNTs near top and bottom surfaces than the middle portion of nanocomposite plate provide better resistance to buckling and postbuckling. [ABSTRACT FROM AUTHOR]

Elastic buckling is an instability phenomenon that can occur if a slender and thin plate is subjected to axial compression. An important characteristic of the buckling is that the instability may occur at a stress level that is substantially lower than the material yield strength. Besides, the presence of holes in structural plate elements is common. However these perforations cause a redistribution in plate membrane stresses, significantly altering their stability. In this paper the Bejan's Constructal Design was employed to optimize the geometry of simply supported, rectangular, thin perforated plates subjected to the elastic buckling. Three different centered hole shapes were considered: elliptical, rectangular and diamond. The objective function was to maximize the critical buckling load. The degree of freedom H/L (ratio between width and length of the plate) was kept constant, while H/L (ratio between the characteristic dimensions of the holes) was optimized for several hole volume fractions ( ϕ). A numerical model employing the Lanczos method and based on the finite element method was used. The results showed that, for lower values of ϕ the optimum geometry is the diamond hole. For intermediate and higher values of ϕ, the elliptical and rectangular hole, respectively, led to the best performance. [ABSTRACT FROM AUTHOR]

In this paper, a new perturbation method namely, Homotopy Perturbation Method (HPM), is applied to buckling of non-uniform columns problem, which is an important engineering problem, because of the fact that determining the buckling loads are important steps in structural analysis and design applications. Columns are primary structural forms and there are numerous studies related to this subject. Application of this new method (HPM) will give researchers a new and powerful tool for solving buckling problems for which finding an exact analytical solution may not be possible. An important point of this technique is, in contrast to traditional perturbation methods, that this new technique does not require a small parameter in an equation to be solved. In this method, according to the homotopy technique, a homotopy with an imbedding parameter p ∊ [0,1] is constructed and imbedding parameter is considered as an expanding parameter. The paper shows the efficiency of the method and accuracy of the obtained analytic approximate solution for the problem. [ABSTRACT FROM AUTHOR]

Based on the continuum assumption, an equivalent vibration analysis is performed for lattice sandwich beam. The natural frequencies of the pyramidal core sandwich beam from theoretical prediction are compared with corresponding finite element results. For simply-supported sandwich plates with the tetrahedral and pyramidal cores, the modal analysis and buckling analysis are performed by FEM, and the influences of microscopic geometrical parameters on natural frequency and buckling are also investigated. [ABSTRACT FROM AUTHOR]

The dynamic buckling of a nano-wire of crystal copper is studied including the effects of stress wave, with help of molecular dynamics simulation and buckling theory of continuum mechanics. In the molecular dynamics simulation, the embedded atom potential given by Doyama et al. is used to describe the interatomic interactions, and the dynamic buckling of the nano-wire of crystal copper under axial step load is simulated. For comparison, the nano-wire is modeled as an elastic rod subject to the axial step load, and is analyzed on the basis of buckling theory. The molecular dynamics simulation gives a slightly higher critical load than the buckling theory. Furthermore, the buckling theory predicts that the stress wave has a remarkable effect on the dynamic buckling of nano-wires of crystal copper. [ABSTRACT FROM AUTHOR]

The approach of molecular dynamics simulation is one of the most promising methods for investigating the mechanical behavior of nanostructures, such as nanorods and nanowires, which are used to design nano-devices. The mechanical behavior of a copper nanorod subjected to axial compressive force is simulated using the embedded atom method (EAM). The results obtained show that the mechanical behavior in nanoscale is very different from that in macrosclae. This is due to size and surface effects. It has been found that when the external axial force is below certain critical value, the nanorod contracts in length. However, when the force reaches the critical value, the rod exhibits transverse bending, which is known as buckling. After reaching the critical value, the nanorod is able to withstand further increase in external loading and remains stable, which is so called post-buckling. When the external loading is too big, the nanorod collapses. [ABSTRACT FROM AUTHOR]

This paper applies the variational iteration method for finding buckling loads and mode shapes of a heavy column. The study shows efficiency of the method and accuracy of the obtained analytic approximate solution. [ABSTRACT FROM AUTHOR]

In this paper, stability analysis of continuously restrained Euler columns of variable flexural stiffness is conducted by using homotopy perturbation method (HPM). The restraint considered in this study is an elastic foundation model in engineering practice and it is of great interest to foundation engineers. Critical buckling loads are investigated considering different end conditions. Obtaining analytical solutions for these types of problems was very difficult, now the condition is changed. The study proves that HPM is a very efficient and promising approach to the elastic stability analysis of specified problems. [ABSTRACT FROM AUTHOR]

This article discusses the experimental testing of tapered castellated beams (TCBs) under mid-span concentrated load. These beams are created by cutting the webs of standard I-sections in a particular zigzag pattern and rejoining the two parts by placing variable expansion plates between web posts and welding them together. Generally, the depth of the mid-span will be increased. A standard I-section (IPE140) was selected as a parent beam to fabricate three TCB specimens and one prismatic castellated beam. The experimental results showed that the ultimate load capacity of the TCBs could be increased up to 140% of the ultimate load capacity of the parent section. Fabricating a TCB is an effective way of increasing the allowable load of a long-span member while remaining within International Building Code-defined deflection limits. The experimental results showed that the allowable load at deflection (L/360) increased up to 183% of the allowable load for the control specimen at the same deflection. Finally, the experimental results showed that web-post buckling and joint-weld rupture failure modes occurred in TCBs due to the formation of high shear forces that tried to twist the web posts.

Through reduction of thickness value in nanostructures, the features of surface elasticity become more prominent due to having a high surface-to-volume ratio. The main aim of this research work was to examine the surface residual stress effect on the three-dimensional nonlinear stability characteristics of geometrically perfect and imperfect cylindrical shells at nanoscale under axial compression. To do so, an unconventional three-dimensional shell model was established via combination of the three-dimensional shell formulations and the Gurtin–Murdoch theory of elasticity. The silicon material is selected as a case study, which is the most utilized material in the design of micro-electromechanically systems. Then, the moving Kriging meshfree approach was applied to take numerically into account the surface free energy effects and the initial geometrical imperfection in the three-dimensional nonlinear stability curves. Accordingly, the considered cylindrical shell domain was discretized via a set of nodes together using the quadratic polynomial type of basis shape functions and an appropriate correlation function. It was found that the surface stress effects lead to an increase the critical axial buckling load of a perfect silicon nanoshell about 82.4%82.4 \% for the shell thickness of 2nm2{\rm{nm}}, about 32.4%32.4 \% for the shell thickness of 5nm5{\rm{nm}}, about 15.8%15.8 \% for the shell thickness of 10nm10{\rm{nm}}, and about 7.5%7.5 \% for the shell thickness of 20nm20{\rm{nm}}. These enhancements in the value of the critical axial buckling load for a geometrically imperfect silicon nanoshell become about 92.9%92.9 \% for the shell thickness of 2nm2{\rm{nm}}, about 36.5%36.5 \% for the shell thickness of 5nm5{\rm{nm}}, about 17.7%17.7 \% for the shell thickness of 10nm10{\rm{nm}}, and about 8.8%8.8 \% for the shell thickness of 20nm20{\rm{nm}}.

Free-edge gridshells represent the majority of built gridshells. Indeed, the gridshell reference geometry usually needs to be trimmed in order to provide building access or to insert the gridshell within an existing building, giving rise to one or more elastic boundaries. Despite the current design practice, so far a very limited number of scientific studies has been devoted to investigate the influence of elastic boundaries on the overall structural behaviour of gridshells. This paper focuses on the effects of the orientation of the boundary structure with respect to the grid direction. This is done by studying the buckling behaviour of an ideal single-layer steel gridshell, for different grid layout (quadrangular, hybrid, triangular) and orientation. The results of the parametric study demonstrate that the sensitivity of free-edge single-layer gridshells to the free-edge orientation strongly depends on the grid pattern. In particular, isotropic gridshells have shown an almost negligible influence of the free-edge orientation in terms of buckling load, in opposition to orthotropic gridshells. Moreover, the change in free-edge orientation induces significant variations of the global structural stiffness for all the layouts, resulting in possibly unacceptable displacements in service conditions.

Axisymmetric buckling analysis is presented for moderately thick laminated shallow conical caps under transverse load Buckling under uniformly distributed step loads is considered Marguerre-type, first order shear deformation shallow shell theory in terms of transverse deflection w, the rotation ψ of the normal to the midsurface and the stress fiinction Φ is used. The governing equations are solved by the orthogonal point collocation method in the space domain and Newmark-β method in the time domain. Conical caps having clamped and simple supports with movable and immovable edge conditions are analysed. Dynamic buckling loads are also predicted using a static analysis yielding quite accurate results. Typical numerical results are presented illustrating the effect of various parameters. The dependence of the effect of the shear deformation on the thickness parameter, boundary conditions and ratio of Young's moduli is investigated. [ABSTRACT FROM AUTHOR]

Large deformation behavior and post-buckling modes of single-walled carbon nanotubes are studied numerically by using traditional continuum shell theory and eigenvalue buckling methodology with elasticity parameters obtained by atomistic methods incorporated. Comparison with molecular mechanics and an atomistic-based continuum membrane method shows that the continuum shell theory is convenient and efficient in predicting the post-buckling behavior of the nanotubes subjected to axial compression, torsion and bend loads, providing that the elasticity parameters of the tube are obtained from atomistic theoiy. Higher-order buckling modes, which are difficult to be obtained by molecular mechanics, have analyzed as well. [ABSTRACT FROM AUTHOR]

This study aims to investigate the behavior of concrete slabs acting compositely with symmetrical and asymmetrical castellated beams. Stud connectors are used to connect the concrete slab and steel section. The use of castellated steel beams to build up composite steel-concrete beams is now common practice in building construction. Five simply supported composite beams were examined under two-point loading. Two specimens built up from standard steel beams were used as control specimens and three specimens were built up from castellated steel beams. One of these specimens was built up using a castellated steel beam with an asymmetrical cross-section fabricated from two different standard sections (IPE120/HEA120). The concrete slab of all composite specimens had the same dimensions and properties. The experimental results showed that strength and rigidity were considerably greater for composite castellated steel beams compared to composite beams built up from the parent sections. The ultimate load capacity of a composite castellated beam fabricated from an IPE120 section was 46% greater than that of a composite beam built up using the parent beam, and the ultimate load capacity of a composite castellated beam fabricated from a wide-flanged HEA120 section resulted in an increase of 21% over the parent beam control specimen. The ultimate load capacity of the composite specimen built up using the asymmetrical castellated beam (IPE120/HEA120) achieved increases of 69% and 12%, respectively, compared to the control specimens built up from standard sections.

In the field of logistics, containers are indispensable for shipments of large quantities of goods, particularly for exports and imports distributed by land, sea, or air. Therefore, a container must be able to withstand external loads so that goods can safely reach their destination. In this study, seven different models of container skins were developed: general honeycomb, cross honeycomb, square honeycomb, corrugated wall, flat, flat with a single stiffener, and flat with a cross stiffener. Testing was performed using the finite element method. In the static simulation, the best results were obtained by the model with corrugated walls. As the main element and the content of the sandwich panel structure, the core plays a role in increasing the ability of the structure to absorb force, thereby increasing the strength of the material. In the thermal simulation, the best results were obtained by the general honeycomb walls. Vibration simulations also showed that the square honeycomb design was better at absorbing vibration than the other models. Finally, the corrugated model had the best critical load value in the buckling simulation.

This paper presents a computer simulation for a thermal turnout stability arising from continuous welded rail. The analytical model takes into account the followings: 1) nonlinear relationships between all displacements and the resistances; 2) track misalignment; and 3) the variable track geometry during buckling. The simulation shows that the maximum values of axial forces are in the stock rails in the part near the tongue heel. It exceeded by 1.75 times a value of a straight continuous welded rail, but the turnout itself was not in danger of buckling. [ABSTRACT FROM AUTHOR]

Structural analysis is an intricate subject when nonlinearities occur. They make the structural behavior complex and may have important consequences in the design choice as well. Especially for lattice domes, as snap-through phenomena and local Eulerian instabilities generally affect the structural response, linear analysis is not enough. In this paper, a semi-analytical formulation is used in order to study the geometrically nonlinear behavior of lattice domes subject to vertical loads. The formulation is derived from the equilibrium equations written in the deformed configuration, considering large displacements and taking also into account local buckling conditions. The resulted system of equations, being strongly nonlinear, has been solved by means of a numerical procedure, based on a mixed load-displacement control scheme, leading to the evaluation of the complete equilibrium path. The influence of geometrical parameters on the critical load multiplier and shape of the load-displacement curve is also discussed. In particular, a complex equilibrium path for a sixteen-member five-node lattice structure is analyzed, which is characterized by several branches which can generate ‘snapping’ conditions.

Variable stiffness design (VSD) has been paid more attention for its capability of further exploiting the potential of fiber-reinforced composite in composite structure design. VSD under different mechanical property indexes is reviewed in this paper. The review mostly focuses on strength, buckling, frequency, and other more common mechanical indices. Subsequently, the usage of VSD method for several years is briefly summarized. Some successful tests about variable stiffness composite parts are introduced and the experiment results are also addressed. The article summarizes the research situation from both perspectives based on a number of papers about the VSD of composite materials in recent years and provides theoretical reference and basic knowledge to new researchers. [ABSTRACT FROM AUTHOR]

The buckling of rotationally restrained microbars embedded in an elastic matrix is studied within the framework of strain gradient elasticity theory. The elastic matrix is modeled in this study as Winkler’s one-parameter elastic matrix. Fourier sine series with a Fourier coefficient is used for describing the deflection of the microbar. An eigenvalue problem is obtained for buckling modes with the aid of implementing Stokes’ transformation to force boundary conditions. This mathematical model bridges the gap between rigid and the restrained boundary conditions. The influences of rotational restraints, small scale parameter and surrounding elastic matrix on the critical buckling load are discussed and compared with those available in the literature. It is concluded from analytical results that the critical buckling load of microbar is dependent upon rotational restraints, surrounding elastic matrix and the material scale parameter. Similarly, the dependencies of the critical buckling load on material scale parameter, surrounding elastic medium and rotational restraints are significant.

The new serious consideration to masonry and non-metallic structures evidenced their direct prospective to be, even in the present days, advanced architectural and engineering solutions. In the present paper, a form finding for a cement based tessellated pierced vault is studied. The multi-body rope approach (MRA) was used to define compression-only vault optimal shapes. Successively, the thrust network analysis (TNA) was implemented by Rhino-vault for a further validation of the shape and the definition of different tessellation meshes of the surfaces, according to different hole pattern configuration. Different piercing percentage of the vaults were considered and compared for the best solution identification. In addition, the geometrical solutions were analyzed by means of global stability analysis, taking into account the different positions of the holes. Furthermore, 3D printing with a Fuse Deposition Modeling (FDM) technique in polylactide (PLA) material (completely eco-friendly) is used for the construction of the formworks of the cement based blocks (dowels) useful for the assembly of a vault scaled prototype. The prototype of the vault, characterized by a certain piercing percentage was subjected to different loading conditions and monitored by a non-contact device based on the Digital Image Correlation (DIC) technique. The 3D-DIC was performed to recognize the structural behavior during the loading process of the model (prototype). DIC measurements were used to recognize in advance the critical condition of the vault under loading and the displacement measurements were correlated to the different loading phases up to the collapse condition.

An approach for estimating critical buckling strain of pipe subjected plastic bending is established in the present paper. A rigid - perfectly plastic material model and cross section ovalization of pipe during bending are employed for the approach. The energy rates of the ovalised pipe bending and the cross section ovalising are proposed firstly. Furthermore, these energy rates are combined to perform the buckling analysis of pipe bending, an estimation formula of critical buckling strain for pipe subjected plastic bending is proposed. The predicting result of the new critical buckling strain formula is compared with the available experimental data, it shows that the formula is valid. [ABSTRACT FROM AUTHOR]

Venus and the Ocean Worlds are emerging areas of interest for space exploration, as they can potentially host, or have hosted, conditions compatible with life. Landers and probes for in-situ exploration, however, must deal with very high external pressure, due to the environmental conditions, often resulting in thick and heavy structures. Robust, reinforced shell structures can provide a lightweight solution for the primary structure. In this frame, the isogrid layout is already a standard in aerospace, especially for flat panels or cylindrical shells. In this paper, isogrid-stiffened hemispherical shells, or “geodesic domes”, are described, focusing on the case of a concept of a Venus lander. Early design methods for both plain and geodesic domes subjected to external pressure are presented, providing design equations. Additive Manufacturing is identified as the key technology for fabricating metallic geodesic domes, due to the complexity of the internal features. Moreover, it allows to fabricate ports and integrated thermostructural systems in the same process, potentially resulting in improved performance or cost and schedule savings.

Plenty of research articles are available on the static deformation analysis of laminated straight beams using refined shear deformation theories. However, research on the deformation of laminated curved beams with simply supported boundary conditions is limited and needs more attention nowadays. With this objective, the present study deals with the static analysis of laminated composite and sandwich beams curved in elevation using a new quasi-3D polynomial type beam theory. The theory considers the effects of both transverse shear and normal strains, i.e. thickness stretching effects. In the present theory, axial displacement has expanded up to the fifth-order polynomial in terms of thickness coordinates to effectively account for the effects of curvature and deformations. The present theory satisfies the zero traction boundary condition on the top and bottom surfaces of the beam. Governing differential equations and associated boundary conditions are established by using the Principal of virtual work. Navier's solution technique is used to obtain displacements and stresses for simply supported beams curved in elevation and subjected to uniformly distributed load. The present results can be benefited to the upcoming researchers. [ABSTRACT FROM AUTHOR]

This paper describes the behaviour of axially loaded long and eccentrically loaded short thin-walled steel channels, strengthened with transversely bonded carbon fibre reinforced polymer (CFRP) sheets. Seven long members, each 1400 mm long, and seven short members, each 750mmlong, were tested. The main parameters were the number of CFRP plies (one or two) and the clear spacing between the CFRP strips (50, 100 or 150 mm). The effect of CFRP sheet layer and clear spacing was studied. All the ultimate load capacity of the reinforced members was improved in different extent. A maximum strength gain of 9.13% was achieved for long members with two CFRP layers and 50 mm spacing of CFRP strips. The experimental results show that the global buckling happens to all the long specimens. For short members, the maximum strength gain of 12.1% was achieved with two CFRP layers and 50 mm spacing of CFRP strips. With the exception of the most heavily reinforced (2 plies at 50 and 100 mm), local buckling was observed prior to global buckling for short members, which was completely opposite of the control specimens. Meanwhile, when the clear spacing of CFRP strips is greater than theweb height of steel channel, the transversely bonded CFRP does not have a significant improvement in buckling load capacity of the short- and long-channel components. While the clear spacing is less than the web height, the more number of CFRP layer, the more enhancement of buckling load capacity.

Flexible polyimide probes, used for neuronal signal acquisition, are thought to reduce signal deteriorating gliosis, improving the quality of recordings in brain machine interfacing applications. These probes suffer from the disadvantage that they cannot penetrate brain tissue on their own, owing to their limited stiffness and low buckling forces. A microfluidic device as an external micro-drive which aids in the insertion of flexible polyimide neural probes in 0.6% Agarose gel is presented here.

The in-plane shear strengths (IPSS) of copy paper, filter paper, and sack paper were obtained from an asymmetric four-point bending (AFPB) test. Rectangular tabs of medium-density fibreboard (MDF) were bonded to the paper specimen. The length of the clearance between the tabs was varied, and the influence of the clearance on the IPSS value was investigated. The IPSS obtained from the AFPB test was compared with that obtained from a 35° off-axis tension (OAT) test, which was proposed in a previous study. The IPSS values obtained from the AFPB tests on the copy paper and sack paper were significantly lower than those obtained from the 35° OAT tests because of the localised buckling caused by the negative principal stress. In contrast, the IPSS values obtained from the AFPB and OAT tests on the filter paper were in agreement when the clearance length was >5 mm because the buckling effect was excluded. [ABSTRACT FROM AUTHOR]