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The buckling curves, which enable the prediction of buckling resistance of steel structural elements, are physically connected with their type of cross-section, initial out-of-straightness, and the magnitude of residual stresses due to the different manufacturing technologies. It is known that hot-dip galvanisation changes and relives residual stresses, but so far the current design provisions do not take directly into account the impact of hot-dip galvanising on the reduction of residual stresses, and thus the reduction the generalised imperfection in the Ayrton-Perry model. The paper presents the difference between the relative buckling resistance of steel angles with residual stresses resulting from hot rolling and the same elements in which the magnitude of residual stresses was decreased by the hot-dip galvanising process. Carried out tests and geometrically and materially non-linear analyses with imperfections (GMNIA) have shown that angles with residual stresses reduced by heat treatment caused by hot-dip galvanising have higher buckling resistance compared to those with residual stresses after hot rolling. This increase ranges from 2 to 7%. The analyses carried out confirmed that the predicted reduction factors  exhibit values closer to the buckling curve ‘a’, but these values do not reach the ‘a0’ curve recommended by the EN 50341-1 standard.

Purpose: To investigate the efficacy, safety, and indications for additional pneumatic retinopexy (PR) in patients with persistent retinal detachment after scleral buckling., Methods: This retrospective study included patients who underwent additional PR after scleral buckling for primary rhegmatogenous retinal detachment (n = 78). We defined "inadequate buckle" as retinal detachment persistence because of low buckle height despite accurate buckle placement and "buckle misplacement" as an uncovered tear because of incorrect buckle placement., Results: The anatomical success rate after additional PR was 52.6%. Development of proliferative vitreoretinopathy Grade B (hazard ratio, 5.73; P < 0.001) and inferior retinal tears (hazard ratio, 2.12; P = 0.040) were significant risk factors for anatomical failure. The most common cause of anatomical failure was proliferative vitreoretinopathy (19 of 37; 51.4%), and epiretinal membrane formation was a common complication after additional PR (22 of 78; 28.2%). The anatomical success rate with additional PR was significantly higher in the inadequate buckle group than in the misplacement group (8 of 9 [88.9%] vs. 1228 [42.9%]; P = 0.023)., Conclusion: Development of proliferative vitreoretinopathy Grade B and inferior retinal tears were significantly associated with anatomical failure after additional PR. Additional PR may benefit patients with superior retinal tears or low buckle height and those without proliferative vitreoretinopathy.

To compare the efficacy of scleral buckling with adjuvant pneumatic retinopexy (SB with PR) and scleral buckling (SB) alone for primary rhegmatogenous retinal detachment (RRD). This retrospective and comparative study included patients who underwent SB with PR (n = 88) or SB alone (n = 161) for primary RRD. The primary anatomical success rate for SB with PR was 81.8%, whereas that for SB alone was 80.7% (P = 0.836). Among patients who achieved primary anatomical success, those in the SB with PR group showed postoperative epiretinal membrane (ERM) formation more frequently than those in the SB alone group (11 of 72 [15.3%] vs. 6 of 130 [4.6%]) (P = 0.009). The mean time to subretinal fluid absorption was not significantly different between the SB with PR and SB alone groups (11.2 ± 6.2 vs. 11.4 ± 5.8 months, P = 0.881). In the SB with PR group, retinal detachment involving ≥ three quadrants was a significant risk factor for surgical failure (hazard ratio, 3.04; P = 0.041). Adjuvant pneumatic retinopexy does not provide additional benefit in improving the surgical outcomes of SB for primary RRD repair., (© 2024. The Author(s).)

In this study, the post‐buckling damage behavior of cylindrical composite tubes was examined experimentally. The samples were reinforced with glass, carbon, and kevlar fibers to obtain glass‐reinforced fiber polymer (GRFP), carbon‐reinforced fiber polymer (CRFP), and Kevlar‐reinforced fiber polymer (KRFP) cylindrical tubes. The samples were produced using 4 stacking layers with filament winding technology. In producing all composite tubes, the outer diameter was kept constant at 17 mm, and two inner diameters of 12 and 13 mm, two wall thicknesses, 5 winding angles, and two lengths were used as parameters. The load was applied to the samples until completely damaged, and the maximum post‐buckling load values obtained were measured on the testing device. The effect of different reinforcement materials, winding angle, wall thickness, and length on the load‐carrying capacity was analyzed and it was understood that they had a significant effect. It was observed that the load‐carrying capacity of GFRP samples was the highest compared to the others, followed by CFRP and KFRP samples, respectively. In all samples, it was observed that a 0.5 mm wall thickness increase increased the load‐carrying capacity, while a 50 mm length increase decreased it. The energy absorption (EA) values of GFRP, CFRP, and KFRP samples were 46.99, 25.22, and 15.48 Joules, respectively. It was understood that the energy absorption of GFRP samples was 1.86 times better than CFRP and 3 times better than KFRP. Highlights: The samples were produced using the fiber winding method, which is one of the most common production methods in the manufacture of tubes.Three different polymer reinforcement materials were used in the production of the samples.The effects of polymer reinforcement material, winding angle, length, and wall thickness on the maximum post‐buckling load were investigated.Wall thickness was found to have a significant effect on the maximum post‐buckling load.It was observed that GFRP samples had the highest energy absorption feature. [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear post-buckling analysis of imperfect two-dimensional quasicrystal cylindrical shells is performed. The nonlinear governing equations are established by considering initial geometric imperfection, higher-order shear deformation theory and phonon-phason fields coupling effect. The load-shortening curves and buckling modes are obtained by the Galerkin's method. Numerical results are compared with the existing results and excellent agreements are obtained. Effects of geometrical parameters, initial imperfection and phonon-phason fields coupling effect on the critical load and imperfection sensitivity of two-dimensional quasicrystal cylindrical shells are discussed in detail. [ABSTRACT FROM AUTHOR]

Purpose: To introduce a surgical technique for temporary scleral buckling of noncomplex rhegmatogenous retinal detachment using a combination of nonabsorbable and absorbable sutures that would induce minimal permanent refractive changes., Methods: Twenty consecutive patients (20 eyes) with noncomplex rhegmatogenous retinal detachment were prospectively included. Scleral buckling was performed in all eligible subjects, and encircling buckling was added when necessary. The silicone elements were fixed on the sclera with 5-0 nonabsorbable sutures and tightened to form a ridge with 6-0 absorbable sutures. Best-corrected visual acuity, scleral ridge status, axial length, spherical diopter, and cylinder diopter were collected., Results: All patients achieved primary retinal reattachment with significant improvement of best-corrected visual acuity after surgery. Scleral ridge was obvious and in situ at the 1-month follow-up but diminished at the 3-month follow-up. At the 1-month follow-up, axial length increased from 24.78 mm ± 2.14 mm preoperatively to 25.22 mm ± 2.11 mm, and cylinder diopter increased from -1.99 ± 1.03 to -2.95 ± 1.55 (both P < 0.001). At the 3-month follow-up, axial length, spherical diopter, and cylinder diopter decreased significantly compared with the values at the 1-month follow-up (all P < 0.05). No obvious complications were observed during the whole follow-up. Patients who underwent additional encircling buckling exhibited greater changes in axial length and cylinder diopter at the 1-month follow-up (both P < 0.001)., Conclusion: The modified technique of scleral buckling with/without encircling buckling using both nonabsorbable and absorbable sutures offers a safe and effective option to repair noncomplex rhegmatogenous retinal detachment, which would offer an adequate temporary scleral buckling effect and induce minimal permanent refractive changes., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the Opthalmic Communications Society, Inc.)

The present study develops a new finite element (FE) formulation for the lateral torsional buckling (LTB) analyses of steel beams exteriorly bonded with orthotropic fiber-reinforced polymer (FRP) layers. The formulation considers shear deformations, partial material interaction, local and global warping deformations, and orthotropic FRP properties. The buckling responses of multispan FRP-bonded steel beams predicted by the present solutions are excellently validated against experiment and numerical solutions. As observed, the FRP strengthening is highly effective for the LTB resistance of steel beams. However, the LTB responses are strongly dependent on the orthotropic properties and strengthening lengths of FRP layers. The effects of shear deformations, span ratios, and loading conditions on the LTB responses are also quantified in the present study.

Abstract Automated fiber placement (AFP) enables the efficient and precise fabrication of complex-shaped aerospace composite structures with lightweight and high-performance properties. However, due to the excessive compression on the inner edge of the tow placed along the curved trajectory, the resulting defects represented by buckling and wrinkles in spatial tow steering can induce poor manufacturing accuracy and quality degradation of products. In this paper, a theoretical model of tow buckling based on the first-order shear deformation laminate theory, linear elastic adhesion interface and Hertz compaction contact theory is proposed to analyze the formation mechanism of the wrinkles and predict the formation of defects by solving the critical radius of the trajectory, and finite element analysis involving the cohesive zone modeling (CZM) is innovated to simulate the local buckling state of the steered tow in AFP. Additionally, numerical parametric studies and experimental results indicate that mechanical properties and geometric parameters of the prepreg, the curvature of the placement trajectory and critical process parameters have a significant impact on buckling formation, and optimization of process parameters can achieve effective suppression of placement defects. This research proposes a theoretical modeling method for tow buckling, and conducts in-depth research on defect formation and suppression methods based on finite element simulation and placement experiments.

Abstract To improve the energy dissipation and self-resetting ability of bridge structures under strong earthquakes, a new buckling-restrained SMA bar-based friction damper (SFD) is proposed. The damper is composed of buckling-restrained super-elastic SMA bars, friction pads, and a steel frame. The buckling-restrained SMA bars provide self-reset capability, while the friction pads provide additional energy dissipation capacity. Firstly, the configuration, working mechanism, and restoring force model of the SMA bar-based friction damper are introduced. Secondly, a specimen of the damper is made, and the pseudo-static test is carried out. Finally, the experimental results are analyzed based on the Abaqus finite element model. The results indicate that the damper has better self-resetting ability and energy dissipation capacity.

Introduction/purpose: The aim of this study is to examine the buckling and free vibration behavior of laminated composite plates reinforced with carbon nanotubes when various sources of uncertainty are taken into account with 1 the main focus being the existence of porosity. Methods: A porous laminated plate model is developed using a high order shear deformation theory. Different configurations of functionally graded aligned single-walled carbon nanotubes throughout the thickness of each layer are being investigated. The effective properties of materials are evaluated through the extended rule of mixture while considering an upper bound for the effect of porosity. The governing equations are derived and solved using the virtual work principle and Navier's approach. The validity of the current formulation is confirmed by comparing the results with the existing data from literature sources. The impact of numerous parameters such as porosity, carbon nanotube volume fraction, reinforcement distribution types, lamination scheme, and the number of layers on the buckling and free vibration responses is investigated in detail. Results: A key finding of this study is the significant reduction in buckling resistance of laminated FG-CNTRC plates due to porosity, contrasting with the minor impact on the free vibration response. Conclusion: The results of this paper emphasize the critical role of porosity in structural integrity and provide novel insights into the behaviour of advanced composite materials.

This research studies the first part of the failure of a compression member structure due to buckling. This unstable equilibrium collapse, exposes brittle failure which occurs suddenly and therefore should be avoided wherever possible. Unavoidable geometric imperfections due to structural fabrication, will weaken the structure against buckling. The behavior of bar under compression will be closely examined by taking a set of geometric imperfection data synthesized from previously available from the measurement of conical shells. Therefore, the two-dimensional surface imperfection is converted into several one-dimensional imperfection with some probability properties. In order to obtain a comparison tool for different type of imperfections, Fourier analysis is used to convert the imperfection into coefficients of trigonometric function. By examining the coefficients, geometric imperfection patterns introduced by a certain fabrication process are able to be identified. The study successfully demonstrates the applicability of Fourier analysis in representing inherent geometric imperfections as an initial step for conducting probabilistic buckling analysis. Fourier analysis has shown its capability to simultaneously characterize imperfections in two crucial parameters - the magnitude and configuration of the imperfection.

The research focuses on examining the impact of technological defects, specifically "dry-spot" and "wrinkles," on the mechanical behavior and buckling resistance of structural composites. The investigation of the buckling phenomenon was carried out through a compression test on a thin plate fabricated from carbon-fiber-reinforced polymer (CFRP) laminate. This test was performed using a specialized fixture designed in accordance with ASTM 3410 standard. For the analysis, the study employed a three-dimensional digital optical system, Vic-3D, in conjunction with the AMSY-6 acoustic emission system. The research showcases findings from acoustic emission signals that verify the shear-based mechanism of buckling in plates constructed from CFRP featuring "dry-spot" type defects. In the case of "wrinkles" defects, it was observed that transverse shear transpires at the stress concentration points created by the "excess" layers.

In this paper, the static behavior, instability and buckling in porous micro plates under electrostatic field are investigated based on the modified couple stress theory and with regard to modeling, determining equations and solution methods. The plate is considered to be porous and the porosity distribution is considered to be non-uniform. The equations are obtained considering the distributed support load. By using the definition of dimensionless parameters such as load, voltage and length scale, the equations of motion become dimensionless. It can be seen that in the special case, by removing the dimensionless non-classical parameters, the equation of the classical plate under the electrostatic field is obtained. Galerkin mode summation and numerical methods are utilized to solve the static deformation equation and assess the pull-in instability voltages and buckling loads. Convergence analysis is done and the number of approximation functions and elements required for both methods are calculated and the compatibility of the results obtained from the two methods is examined. In the results section, the difference between classical and non-classical theories is examined and the effect of dimensionless parameters of length scale and porosity ratio on maximum displacement, pull-in instability voltages and buckling load is studied. The results show that the use of modified stress couple theory leads to a very large stiffness prediction compared to classical theory. This result highlights the necessity of using the modified couple stress couple theory for the micro-scale. It is observed that the length scale parameter plays the role of stiffening. The change of porosity ratios also shows that as this ratio increases, the displacement increases and the stable areas decrease. Variations in this ratio lead to uniform changes in buckling load and pull-in instability voltage, and linear relationships are obtained to calculate buckling load and pull-in instability voltage versus porosity ratio. Also, in small values of support load, it is shown that the relationship between the instability voltage and the compressive load of the support is linear, but in the buckling range, this relationship is not linear.

This study investigates the influence of temperature variations on the buckling properties of thin-walled omega-profiles fabricated from carbon-epoxy composite materials. Utilizing a MTS testing machine, compression tests were conducted on these profiles at temperatures ranging from -20°C to 80°C, in 20°C increments. The primary objective was to assess how temperature fluctuations impact the buckling load and load-bearing capacity of these composite profiles under axial compression. The experimental setup allowed for precise measurement of load-displacement and load-deflection characteristics, and the critical load at which buckling initiation occurred. Observations revealed that the buckling resistance of the profiles exhibited a complex dependence on temperature. At lower temperatures, the composite material demonstrated enhanced stiffness and strength, marginally increasing buckling resistance. Conversely, at elevated temperatures, a noticeable degradation in mechanical properties was observed, leading to a reduced buckling load and altered failure modes. To complement the experimental findings, a comprehensive finite element (FE) analysis was conducted for sample in room temperature. The FE model, developed to replicate the experimental conditions closely, employed an eigenvalue-based approach to predict the buckling initiation and progression accurately. The presented results are the results of only preliminary tests and they will be expand about more samples number as well as to determine material properties for various temperatures.

The collapsible tubular mast (CTM) can be compactly folded for transport and deployed in orbit to serve as a key structural element. Once deployed, the CTM is vulnerable to buckling under axial load and bending moments, compromising its load-bearing capacity. The intricate relationship between the CTM's cross-section and its buckling behavior poses a significant challenge for designers. This is due to the ultra-thin nature of the CTM, which gives rise to highly localized buckling modes rather than global ones. To overcome this challenge, we developed surrogate models using a neural network (NN) trained with data from finite element analysis (FEA). These NN-based surrogate models provide high computational accuracy in predicting nonlinear buckling loads under axial force and bending moments around the two principal axes of the CTM's cross-section, achieving R 2 values of 0.9906 , 0.9987 , and 0.9628 , respectively. These models also significantly improve computational efficiency, reducing prediction time to a fraction of a second compared to several minutes with FEA. Furthermore, the NN-based surrogate models enable the usage of the non-dominated sorting genetic algorithm (NSGA-II) for multi-objective optimization (MOO) of the CTMs. These models can be integrated in the NSGA-II algorithm to evaluate the objective function of existing and new individuals until a set of 1000 non-dominated solutions, i.e., cross-sectional configurations optimizing buckling performance, is identified. The proposed approach enables the design of ultra-thin CTMs with optimized stability and structural integrity by promoting design decisions based on the quantitative information provided by the NN-based surrogate models. [ABSTRACT FROM AUTHOR]

Two main goals are pursued in the present work. First, the global buckling of axially loaded sandwich beams with composite face sheets and aluminum honeycomb cores under humid environments is investigated. An analytical solution with high accuracy is developed based on piecewise low-order shear deformation theory (PLSDT) to estimate the critical buckling loads. A parametric study is carried out to examine the influence of geometric parameters on the buckling loads of simply supported and clamped sandwich beams under different wet conditions. The obtained results indicate that humidity plays a significant role in the buckling behavior of honeycomb sandwich beams. As the second purpose of the present work, the weight minimization of sandwich beams is studied. The optimization variables include the face sheet thickness, core thickness, honeycomb cell size and honeycomb cell wall thickness. Moreover, different failure modes, including global buckling, face sheet dimpling, face sheet wrinkling, core shear instability, and face sheet failure are considered as design constraints. Imperialist competitive algorithm (ICA), a powerful socio-politically motivated global search strategy, is applied to handle the constrained optimization problem. The optimization results show that the presence of humidity in the environment significantly changes the optimal design of sandwich beams and makes them heavier. Furthermore, it is observed that by increasing the length of the structure, the optimal design is more affected by humidity. Moreover, it is found that ICA is a very powerful optimization tool both in obtaining the best values of geometric parameters and in reducing the computational cost. [ABSTRACT FROM AUTHOR]

The buckling behavior of tubular string is critical for safe oil and gas resource development. In practical engineering, the buckling of tubular string can appear in different development phases, such as casing putting into wellbore, BHA drilling rock, pipeline buckling, etc. Therefore, in this paper, the buckling behavior and buckling evolution of the tubular string are explored considering friction in horizontal wells. By applying the principles of static equilibrium and beam-string theory, an established theoretical model is utilized to examine the buckling behavior of tubular string. The critical load for sinusoidal buckling is determined by using both the series and trial function methods, and a comparison is made between the results obtained from these two techniques. In addition, perturbation analysis is used to obtain the angular displacement's configuration function in the helical buckling post-buckling state. To validate the model's effectiveness, a comprehensive analysis of the numerical results is performed, considering both sinusoidal and helical buckling scenarios. The research findings demonstrate that both the series method and the trial function method can effectively analyze sinusoidal buckling with high accuracy. The presence of friction significantly impedes the buckling behavior of the tubular string. Moreover, friction's influence causes a gradual decline in the efficiency of transmitting axial forces along the wellbore axis. [ABSTRACT FROM AUTHOR]