Buckling Of Panels Research Articles

Analysis and experimental evaluation framework for buckling and post-buckling of composite stiffened panels

The composite thin-walled stiffened panel exhibits considerable potential for post-buckling bearing capacity. However, due to the limitations in post-buckling analysis and experimental evaluation capabilities, local buckling under limited loads is not permissible for current aircraft composite panels, significantly diminishing the weight reduction effect of composite panels. In this paper, experimental research on composite fuselage curved panels under combined compression and shear loads was conducted with an experimental system. The buckling analysis and failure prediction of composite fuselage curved panels were performed by the finite element method, using the interlaminar failure criterion and an improved Tsai-Wu failure criterion. Meanwhile, interaction formulaes were utilized to predict buckling correlation curves and failure envelopes. The results show that the finite element model with improved criteria and the rapid analysis method based on interaction formulaes exhibit high accuracy, which are available for properties analysis of composite panels. The experimental techniques and analytical methods proposed in this paper can provide a way to evaluate the buckling and post-buckling performance of composite stiffened panels.

Investigation of the Mechanical Properties of Composite Honeycomb Sandwich Panels after Fatigue in Hygrothermal Environments.

Since carbon fibre composite sandwich structures have high specific strength and specific modulus, which can meet the requirements for the development of aircraft technology, more and more extensive attention has been paid to their residual mechanical properties after subjecting them to fatigue loading in hygrothermal environments. In this paper, the compression and shear characteristics of carbon fibre-reinforced epoxy composite honeycomb sandwich wall panels after fatigue in hygrothermal environments are investigated through experiments. The experimental results show that under compressive loading, the load required for the buckling of composite honeycomb sandwich wall panels after fatigue loading in hygrothermal environments decreases by 25.9% and the damage load decreases by 10.5% compared to those at room temperature. Under shear loading, the load required for buckling to occur is reduced by 26.2% and the breaking load by 12.2% compared to those at room temperature.

Experimental and numerical studies on buckling and post-buckling behavior of T-stiffened variable stiffness panels

Currently, experimental research on variable stiffness design mainly focuses on laminates. To ensure adaptability in practical application, it is imperative to conduct a systematic study on stiffened variable stiffness structures, including design, manufacture, experiment, and simulation. Based on the minimum curvature radius and process schemes, two types of T-stiffened panels were designed and manufactured. Uniaxial compression tests have been carried out and the results indicate that the buckling load of variable stiffness specimens is increased by 26.0%, while the failure load is decreased by 19.6%. The influence mechanism of variable stiffness design on the buckling and failure behavior of T-stiffened panels was explicated by numerical analysis. The primary reason for the reduced strength is the significantly increased load bearing ratio of stiffeners. As experimental investigations of stiffened variable stiffness structures are very rare, this study can be considered a reference for future work.

Experiment and Analysis of a Hybrid Composite Post-tension Plate Girder

Steel plate girders have been employed as structural bridge parts since the 19th century. They are typically made up of built-up sections in the shape of I-beams. Web and flange plates withstand shear force and bending moment, respectively. However, plate girders are vulnerable to shear buckling. Shear buckling resistance is increased by adding reinforced vertical stiffeners and, in some cases, longitudinal stiffeners. Nevertheless, these stiffeners are sometimes not enough to prevent extreme shear buckling and only delay the shear buckling of slender web panels. This study investigated a hybrid composite post-tension (HCPt) plate girder by experiment and finite element (FE) analysis. The structural performance of the HCPt plate girder was tested using three specimens: a double-web plate girder, an in-fill concrete double-web plate girder and an in-fill concrete double-web plate girder with prestress. Results showed that the steel web filled with concrete presented preferable strength and behaviour to the hollow steel web because of the concrete in-fill. It had high load capacity, strength and ductility. The concrete in-fill prevented the steel web plate from buckling, and beams generally failed in a ductile manner. Applying prestressing techniques reduced deflection under external loads, increased the load-carrying capacity and enhanced its flexural behaviour by 126% compared to the double web plate girder. The failure mode was changed from web shear buckling in a double web girder to bending in a hybrid composite plate girder, with an improvement of web shear buckling by 88%. The FE analysis result showed excellent consistency with the experimental result.

Analytical and numerical analysis on local and global buckling of sandwich panels with strut-based lattice cores

Additive manufacturing (AM) offers new possibilities to fabricate and design lightweight lattice materials. Due to the superior mechanical properties of these lattice structures, they have the potential to replace honeycombs as cores in sandwich panels. In addition to the advantage of the integral fabrication thanks to AM, additively manufactured lattice core sandwich panels may be also used as heat exchangers, enabling a multifunctional use of the core. To ensure a reliable and safe structure, the mechanical response of lattice core sandwich panels under given load conditions must be predictable. In conventional sandwich panels subjected to compressive loads, the sandwich’s global buckling and the face sheets’ local buckling are the dominant failure modes. In constrast, core strut buckling may be the critical failure mode in lattice core sandwich panels. Therefore, an analytical 2D model to predict the local buckling of lattice core struts is considered in this study. Furthermore, the critical load for global buckling is obtained based on the first-order shear deformation theory. Thus, the transition from local buckling to global buckling depending on the length-to-thickness ratio is captured by the presented model. The comparison with finite element modeling of the sandwich model with truss cores has proved the accuracy of the derived model.

Elastic Critical Buckling Coefficients for Skew Plates of Steel Structures under Biaxial Normal Stress

In steel structures, skew thin steel plates serve as panel zones in structures spanning large spaces (e.g., warehouses and gymnasiums). Considerable research has been conducted on the shear buckling of panels due to seismic loads acting on a structure. Conversely, under snow or wind loads, the panel zone may experience compressive and tensile stresses simultaneously from two directions. Considering the economic preference for thin steel plates, evaluating the elastic critical local buckling stresses in the panel zone under biaxial normal stress may provide essential information to structural engineers. In this study, an elastic buckling analysis based on the energy method is performed to clarify the impact of panel geometry and boundary conditions on the elastic local buckling stresses of skew panel zones. As confirmed from the results, the local buckling stresses calculated using the energy method were consistent with those determined using finite element analysis. The findings indicate that a skew angle of up to 30° marginally affects the elastic buckling stress under uniaxial stress. Consequently, engineer-friendly design formulas were developed based on these findings. Comparisons with previous research demonstrated that the buckling loads reported were generally higher than those determined by finite element analysis. The study also established the correlation of the buckling stresses under biaxial stresses, which implied that the skew angle posed minimal influence on buckling stress for skew plates under biaxial stress. Additionally, a method for evaluating this correlation was presented. Engineers can utilize the provided design equations to more efficiently and accurately calculate buckling loads, facilitating a safer and more economical design of structures with skew plates.

Variable kinematics finite plate elements for the buckling analysis of sandwich composite panels

This paper extends sublaminate-based variable kinematics plate finite elements towards the buckling analysis of composite structures. Robust locking-free 4-node and 8-node interpolations are used to build the finite element matrices in terms of fundamental nuclei, invariant with respect to the employed kinematic model of the composite plate. Geometric nonlinearities are accounted for in the von Kármán sense. The classical linearized stability analysis is mainly conducted for sandwich panels, for which different kinematic assumptions are employed for the skins and the core. Global buckling of the sandwich panel as well as short-wavelength wrinkling of the skins are investigated by referring to a variety of case studies, including homogeneous and laminated skins as well as isotropic and orthotropic cores. Convergence studies are performed to establish the minimum number of elements for the local instabilities to be grasped. The proposed computational framework requires a simple 2D mesh and is capable of providing quasi-3D response patterns. This is as demonstrated by numerous case studies that address the transition from global to local buckling, the onset of wrinkling in flat sandwich panels with anisotropic skins under various loading conditions as well as the local face sheet instability occurring in sandwich panels working in bending. It is concluded that he proposed FEM-based tool is computationally efficient and can be advantageously employed in pre-sizing design phases without resorting to full 3D models.

Seismic behavior of masonry-infilled reinforced concrete frames strengthened using ultra-high performance concrete diagonal strips

An extensive experimental program was undertaken which aimed at investigating the lateral cyclic behavior of non-ductile masonry infilled RC frames strengthened with Ultra-High Performance Concrete precast plates. In response, a series of four ½ scale single-storey, one-bay masonry infilled RC frames were meticulously designed and constructed. Among these, one frame was tested as-build with masonry infill, another was strengthened with 300 mm wide CFRP diagonal sheets, while the remaining two were strengthened with 355 mm wide UHPC diagonal plates. CFRP and UHPC strengthening was applied to one side of the masonry infill and the main test variable was the thickness of the UHPC plates. Based on experimental results, it was found that UHPC-strengthened specimens exhibited approximately twice the peak lateral strength that of the as-built specimen and 1.3 times that of the FRP strengthened specimen. Stiffness analysis indicated that UHPC-strengthened frames possessed an initial stiffness approximately 71% higher than the as-built frames, contributing significantly to their enhanced seismic performance. Nevertheless, it is important to note that UHPC-strengthened specimens also experienced stiffness degradation, although at a slower rate when compared to the as-build and CFRP-strengthened specimens. Moreover, UHPC-strengthened frames dissipated roughly three times more energy than the as-built frame and twice as much as the FRP-strengthened frame. While doubling the UHPC plate thickness from 10 mm to 20 mm led to a significant increase in masonry tensile strength, it also introduced structural asymmetry between the strengthened and unstrengthened sides of the wall. This asymmetry resulted in masonry panel buckling, ultimately leading to the failure of both UHPC-strengthened specimens at the same peak lateral load. In summary, this investigation underscores the promising role of UHPC retrofitting as a highly effective and occupant-friendly strategy for enhancing the seismic performance of masonry infilled RC frames. These findings carry significant implications for enhancing structural safety and resilience in earthquake-prone areas. Furthermore, this study provides a solid basis for further research and practical implementations in the realm of seismic retrofitting, contributing to the advancement of safer and more resilient infrastructure globally.

Free-Vibration, Buckling, and Static Analysis of Sandwich Panels with a Square Honeycomb Core Using a Meshfree Method

Meshless methods are a relatively modern approach that has garnered significant interest in analyzing and investigating complex structural problems thanks to distinctive features such as high accuracy, flexibility, rapid calculation speed, and cost–effectiveness. In the present study, the element-free Galerkin method is employed as a meshless approach, wherein a set of arbitrary nodes is distributed across the problem’s geometry, including its boundaries, to define the problem domain. The Moving Least Squares approximation is also utilized to formulate the shape functions. Given the intricate geometry of the honeycomb core within sandwich panels, the study employs the generalized method to derive the effective mechanical properties of the honeycomb core. Furthermore, to acquire displacement fields and establish relationships for the problem, the classic plate theory and the first-order shear deformation theory are independently applied. These relationships are then formulated using the Galerkin meshless method. Finally, the obtained parameters are evaluated, and the validity of these relationships is confirmed by comparing the results of this study with those presented in existing articles. The outlined procedure has been systematically simulated through a step-by-step MATLAB program. Subsequently, the impact of different boundary conditions, individual layer thicknesses, dimension ratios, and core wall spacing on the panel’s displacement, free-vibration, and buckling behaviors is thoroughly investigated. The obtained results substantiate the efficacy of the utilized methodology, demonstrating a favorable combination of accuracy and convergence rate.

Статична стійкість тришарових панелей із стільниковими заповнювачами, виготовленими адитивними технологіями

This paper presents approaches to and the results of finite-element analysis of static buckling in cylindrical sandwich panels. The core layer of the panels is a polylactide honeycomb core 3D printed using the Fused Deposition Modeling (FDM) additive technology. The two thin face layers are made of carbon fiber reinforced polymer. Such structures are promising for use as structural elements of rockets and drones. For them, the determination of stability under longitudinal and radial loads is an important issue. The global buckling of a cylindrical panel under longitudinal loads and the local buckling of a honeycomb core as a plate structure under radial loads are studied. The geometrically nonlinear deformation of a cylindrical panel under a combination of transverse and radial loads is studied. Seven cylindrical sandwich panels with the radius-to-thickness ratio in the range 5 ? R/h ? 50 and a sandwich plate are considered. The effect of the radius of curvature on the characteristics of local and global buckling is investigated. The problem is solved by the finite element method using the ANSYS software system. The convergence of the finite element model was investigated. For this purpose, a strained state under the action of a longitudinal load was studied. The finite-element mesh parameters were selected to ensure the convergence of the results. Two finite element models, an “exact” one and an “approximate” one, were constructed to investigate global buckling under longitudinal loads. The «exact» model includes a honeycomb core represented by its geometry. In the «approximate» model of the sandwich panel, the honeycomb core is replaced with an equivalent homogenized layer. It was found that for longitudinal loads the modes of the global buckling of the cylindrical sandwich panels and the sandwich plate under study are almost the same. It was shown that the critical loads obtained by the «exact» and the «approximate» model are close. It was found that when a cylindrical panel is deformed under the action of a combination of longitudinal and radial subcritical loads, the calculated results for the «exact» and the «approximate» model are close. Therefore, longitudinal buckling can be considered using the homogenized model, which is much simpler in terms of computations.

Finite element simulation and strength evaluation on innovative and traditional composite shear wall systems

SummaryComposite shear wall (CSW) system, which consists of a steel boundary frame and a steel panel with a reinforced concrete (RC) panel attached to one side of it using bolts, is commonly used in mid‐ to high‐rise buildings. In a CSW system, RC panel functions as out‐of‐plane restraint to prevent overall buckling of steel panel, thereby enhancing system behavior. However, for a traditional CSW system, the RC panel is in direct contact with the steel boundary frame. The RC panel tends to crush under seismic loading, thereby leading to a weak constraint to steel panel buckling. The innovative CSW system, where a gap remained between steel boundary frame and RC panel, demonstrated better cyclic behavior than the traditional CSW system. Current studies aimed to investigate cyclic behavior, parameter effects, and determination of RC panel stiffness of CSW systems. In this paper, detailed FE models were developed for simulating cyclic behavior of both innovative and traditional CSW systems and validated by test results. FE models accurately predicted lateral load‐drift response and failure patterns of both innovative and traditional CSW systems. System failure patterns and load‐carrying mechanism of RC panels were discussed. The effects of major parameters, including steel panel thickness, RC panel thickness, ratio of bolt spacing to steel panel thickness, and gap between frame and RC panel, were examined using the validated models. Simulation results indicated that steel panel thickness contributed to increase the lateral strength and initial stiffness of both innovative and traditional CSW systems. Although RC panel thickness, ratio of bolt spacing to steel panel thickness, and gap between frame and RC panel had negligible effects on system strength and stiffness, they should also be carefully designed to ensure local stability of the steel panel and system ductility. Formulations were proposed for predicting the lateral strength of both innovative and traditional CSW systems. The average difference between calculated and test/simulated lateral strength was less than 3%.

High-speed shock–boundary-layer interaction over deformed surfaces

This paper concerns the interaction of an oblique shock wave with a supersonic turbulent boundary layer over a thin panel surface, leading to shock–boundary layer interaction and panel buckling. We have performed high-order numerical simulations featuring various static two-dimensional surface deformations typically encountered in experiments. The deformation amplitudes we examined were at least half the height of the incoming turbulent boundary layer thickness. The results show that along the panel midspan, where the maximum deformation amplitude is located, the mean and root mean square pressure are affected by about 10%. Cases for which the pressure at the shock–boundary layer interaction was increased relative to the planar case showed to decrease downstream, and vice versa. Despite the weak response to the mean pressure amplitude, the mean pressure surface contour plots reveal that the streamwise, particularly the spanwise distribution, is affected more noticeably. For example, the surface deformation modes are shown to disrupt the spanwise constant mean pressure, forming higher (or lower) values at either the panel's midspan or edges, depending on the mode. Moreover, the surface curvature leads to a characteristic bending of the spanwise distribution, which can be concave or convex depending on the deformation mode. Analysis of the Reynolds stress anisotropy componentality at different heights from the buckled surface reveals a similar spanwise response of the turbulent velocity fluctuations. The results suggest that the deformation rate plays an important role alongside the deformation amplitude in the turbulent layer and shock–boundary layer interaction.

Nonlinear buckling and postbuckling analysis of cylindrical and sinusoid FG-GPLRC panels under axial compressive load

This paper presents and analyzes the nonlinear buckling responses of cylindrical and sinusoid Functionally graded graphene platelet reinforced composite (FG-GPLRC) panels under axial compressive load. The higher-order shear deformation theory is applied to establish the governing equations of structures. The stress function is approximated using the like-Galerkin method, and the Galerkin method is applied to solve the governing equations. The critical buckling loads and postbuckling load-deflection curves are expressed in explicit form. The effects of panel types, geometrical parameters, imperfection, and foundation on the critical buckling loads and postbuckling curves of cylindrical and sinusoid FG-GPLRC panels are discussed. Numerical results also evaluate and compare the buckling responses of cylindrical and sinusoid panels.

Nonlinear buckling and postbuckling analysis of cylindrical and sinusoid FG-GPLRC panels under axial compressive load

This paper presents and analyzes the nonlinear buckling responses of cylindrical and sinusoid Functionally graded graphene platelet reinforced composite (FG-GPLRC) panels under axial compressive load. The higher-order shear deformation theory is applied to establish the governing equations of structures. The stress function is approximated using the like-Galerkin method, and the Galerkin method is applied to solve the governing equations. The critical buckling loads and postbuckling load-deflection curves are expressed in explicit form. The effects of panel types, geometrical parameters, imperfection, and foundation on the critical buckling loads and postbuckling curves of cylindrical and sinusoid FG-GPLRC panels are discussed. Numerical results also evaluate and compare the buckling responses of cylindrical and sinusoid panels.

Failure mechanisms and load paths in a standing seam metal roof under extreme wind loads

In this paper, the failure sequence and load sharing for standing seam metal roofs (SSMR), up to the limit state, were investigated using full-scale experiments. The tested SSMR system had full-scale dimensions and boundary conditions, which provided the opportunity to investigate the performance of SSMR systems under realistic conditions. The results show that there is a linear relationship between the wind pressure and clip reaction under low wind pressure (less than 500 Pa). Load redistribution happens along with the deformation of roof panels with greater load transfer to the ridge and eaves of the roof at higher pressure. Near the corner of the roof, between 27 and 46 % of the applied load is transferred to edges of the eaves and gable end. Away from the roof corner, between 17 and 23 % of the applied load is transferred to eave edge. Global buckling of panels occurs before connection failures and the initial location of global buckling is near the seam and in the middle of two adjacent clips. Two failure modes for the connections, clip slippage and fastener failure, were observed during the tests. However, the failure modes vary with the clip arrangement and boundary conditions.

Dynamic buckling of active sandwich panels

In this work, a laminated sandwich plate model with external piezoelectric layers is extended for buckling and dynamic stability analysis. In-plane harmonic uniformly distributed loads are considered in the dynamic stability problem, and the Mathieu-type equilibrium equations are solved using Bolotin’s method to obtain the regions of dynamic instability. The model is validated to begin with, using available results in the literature for static and dynamic buckling of laminated soft core sandwich panels. Ultimately, the model is used to simulate the behaviour of laminated composite and sandwich plates with piezoelectric patches, controlled using a closed loop law with proportional and derivative gains, for buckling and dynamic stability analysis. This control system is used to postpone buckling, increase fundamental frequencies and reshape the regions of dynamic instability.

Static Aeroelastic Optimization of High-Aspect-Ratio Composite Aircraft Wings via Surrogate Modeling

The race towards cleaner and more efficient commercial aviation demands novel designs featuring improved aerodynamic and structural characteristics, the main pillars that drive aircraft efficiency. Among the many proposed and introduced, the increase in the aspect ratio of the wings enables greater fuel efficiency by reducing induced drag. Nevertheless, such structures are characterised by elevated flexibility, aggravating static and dynamic aeroelastic phenomena. Consequently, the preliminary and conceptual design and optimization stages using high-fidelity numerical tools is rendered extremely intricate and prohibitive in terms of computational cost. Low-fidelity tools, contrastingly, enable computational-burden alleviation. In our approach, a computational framework for the low-fidelity steady-state static aeroelastic optimization of a composite high-aspect-ratio commercial aircraft wing via surrogate modelling is proposed. The methodology starts with the development of the 3D panel method as well of the elements of the surrogate model. The design variables, objective function and constraints which formulate the optimization problem are then provided. Moreover, comparison against rigid aerodynamics indicate the significant load-alleviation capabilities of the present case study. The effect of structural nonlinearities is also explored. The optimization framework is executed and optimal laminates for the structural members are obtained. The optimal structure was deemed critical in panel buckling.

Development and testing of knife-plate connected steel panel dampers

Steel panel dampers (SPDs), consisting of the inelastic panel and elastic connecting segments, have been widely used in steel building structures commonly with brace- or stub-column-type configurations, especially in high seismic regions. The elastic connecting segments of stub-column-type SPDs were usually significantly enlarged to ensure their elasticity under the associated extreme loads of the inelastic panel. With the aim of improving the structural efficiency and ductility capability of SPDs, a novel design, named as knife-plate-connected SPD (KSPD), was proposed in the study. The proposed KSPD consisted of one steel panel and two boundary-columns on the horizontal sides with pinned column ends, which were achieved by knife-plate details, connecting to the framing systems. The designed configuration of KSPDs potentially reduced the aspect ratio of the steel panels for easily achieving shear yielding while remaining the stud-column appearance, and mitigated the deformation amplification of the steel panels usually occurred in conventional stub-column-type SPDs. Five full-scale KSPD specimens with various configurations of the panel stiffeners have been experimentally examined and compared under cyclic loadings including fatigue cycles. The feasibility of the KSPD design was experimentally validated, and the developed KSPDs were verified to achieve stable energy dissipation and significant ductility of approximate ten and cumulative plastic deformation (CPD) value up to 796. For the design purpose of the members, the width-to-thickness limits of the steel panel were established to prevent panel buckling and the sub-panel edge fracture upon the test results, respectively, and a design inequality of the knife plates upon strengths was developed to prevent the fracture of the knife plate. Finally, the design suggestions of the proposed KSPD were summarized upon the experimental results and findings of the study.

Study on thermal buckling of a lattice sandwich panel (2nd Report, Effects of core stiffness and micro-architectures on the buckling temperature)

In this paper, the critical buckling temperature of a lattice sandwich panel was investigated using FE analysis. In the previous study[Sebata, Y., Ushijima, K., Study on thermal buckling temperature of a lattice sandwich panel, Transaction of the JSME (in Japanese), Vol. 88, No. 905 (2022)], a Pyramid-shaped core unit was selected and the effects of unit-cell height and width on the buckling temperature were investigated. In the present study, two kinds of lattice core, BCC and f2BCC were added for investigation, and the effects of the core stiffness and micro-architecture on the buckling temperature were discussed. It was revealed from this study that the constraint of rotational angle at the connection point between the face sheet and the core strands could enhance the local buckling temperature. Also, enlarging the core stiffness could enhance the local buckling temperature. Moreover, the local buckling temperature can be predicted theoretically based on the thick shell theory by considering the effective width of the face sheet for one unit-cell reflected by the cross-sectional area for a strut.

Nonlinear buckling and post-buckling of imperfect FG porous sandwich cylindrical panels subjected to axial loading on elastic foundation

This paper deals with the nonlinear buckling and post-buckling of sandwich cylindrical panels with non-uniform porous core and functionally graded face sheets. The imperfect sandwich cylindrical panels are subjected to axial loading on elastic foundation. Based on the Donnell shell theory, with von Kármán geometrical nonlinearity, the governing equations are derived. The effects of elastic foundation, various panel geometrical characteristics, porosity parameters, and the thickness of the porous core are investigated. The effects of foundation parameters, porosity parameters, the thickness of the porous core, and material parameters are investigated.