Sandwich Columns Research Articles

Innovative Sandwich Columns Including Steel, Carbon Fiber–Reinforced Polymer, and Timber under Axial Compression

Innovative Sandwich Columns Including Steel, Carbon Fiber–Reinforced Polymer, and Timber under Axial Compression

Enhanced Photoluminescence Intensity of Quantum Dot Films With the Sandwich Column Array Structure by Uniform Electrical Induction

Quantum dots (QDs) are ideal color-conversion materials for display fields. Preparation of micro-nanostructures is a mainstream method for obtaining a high photoluminescence (PL) intensity. Electrical induction, a method of preparing micro-nanostructures, was introduced to obtain QD films with high PL performance by preparing a sandwich column array structure (SCAS). By changing the spacer thickness, a series of SCAS-QD films were fabricated, after optimizing the voltage. The SCAS-QD layers with a 25- μm spacer obtained the maximum PL enhancement of green light intensity: up to 42.8%. The enhancement was caused by the microcavity trapping and light extraction effects. The former could increase the utilization factor of blue light and the latter could increase the emission probability of green light. This is a simple, high-efficient, and low-cost method for preparing QD films with high PL performance without increasing the QD concentration.

Composite honeycomb sandwich columns under in-plane compression: Optimal geometrical design and three-dimensional failure mechanism maps

In this paper, three-dimensional failure mechanism maps are developed to investigate the in-plane compressive characteristics of all-composite honeycomb sandwich columns and optimize their load-weight efficiency. Analytical models are derived based on five possible failure modes, including shear macro-buckling, intracellular dimpling, face wrinkling, face fracture and debonding. The dominant failure mode can be determined by three dimensionless geometrical parameters, i.e., the length-height ratio of the sandwich column, the height ratio of face and core, and the relative density of honeycomb core. A series of three-dimensional failure mechanism maps are constructed based on the fiber orientations in the face sheet and honeycomb core. It is observed that failure mode transforms with dimensionless geometrical parameters in a spatial region. A typical three-dimensional failure mechanism map is experimentally validated. Sectional views in different directions are used to locate the boundaries of failure modes. All-composite honeycomb sandwich columns are designed and fabricated using the tailor-folding method. In-plane compressive experiments are carried out to verify the analytical models and three-dimensional failure mechanism map. The experimental results agree well with analytical predictions. Optimal geometrical design is performed to obtain the geometrical relations of honeycomb sandwich columns with the highest load-weight efficiency under in-plane compression. The novelty of this work lies in broadening the failure mechanism map to spatial region and optimal geometrical design.

Crushing responses and optimization of novel sandwich columns

The paper proposes a design method of the sandwich column with the corrugated sinusoidal core and develops the triangular corrugated sandwich column (TCSC), quadrangular corrugated sandwich column (QCSC) and hexagonal corrugated sandwich column (HCSC). The experimental tests of the TCSC and QCSC with A = 8 and N = 1 are conducted to estimate the crushing responses and the reliability of the numerical model of the sandwich column. The crushing responses are numerically investigated of the TCSC, QCSC and HCSC with different geometrical characteristics and the same mass under the axial impacting load. The results show that the energy absorption of the sandwich column is significantly affected by the geometric parameters A and N of the sinusoidal core tube, and the sandwich design has the large advantage of the energy absorption over corresponding members. Furthermore, the theoretical model of the mean crushing force is derived using the simplified super folding element theory, and the comparisons on experimental result and the finite element analysis demonstrate high prediction accuracy of the theoretical model. Lastly, a numerical optimization is proposed by combining orthogonal experimental design and discrete optimization to obtain the optimal crashworthiness of the sandwich column. Optimization results show that the discrete optimization method can be fast convergence and obtain the optimal design parameters. The energy absorption of the optimal sandwich column is about 10% higher than the initial design. Furthermore, the HCSC has the highest specific energy absorption under the same mass and design constraints.

Axial Low-Velocity Impact of Sandwich Columns With Aluminum Face-Sheets and Hexagonal Honeycomb Core

Abstract The dynamic behavior of sandwich columns with aluminum face-sheets and hexagonal honeycomb core under axial low-velocity impact is investigated experimentally and theoretically. In the impact tests, two typical competing cases of deformation, i.e., core shear-curling (CS-Cu) and local denting-plastic hinge (LD-PH), were observed following the first-order or higher-order global buckling. The deformation process, permanent deformation, cushioning property, energy dissipation efficiency, and factors affecting the competition of CS-Cu and LD-PH were compared and discussed in detail. It is found that, if CS-Cu occurs instead of LD-PH, an axially impacted sandwich column may perform better in both cushioning and efficiently dissipating residual energy. The theoretical analysis is carried out by extending the existing quasi-static global buckling theory of sandwich columns. A good agreement between the oscillatory plateau on the measured force–time curve and the predicted critical plastic global buckling load is found for the strain rate-insensitive face-sheet material.

Crushing behaviors of the thin-walled sandwich column under axial load

Thin-walled columns have been widely used in the protective structure due to their excellent energy absorption capacity and lightweight property. The paper proposes a new design method of the sandwich column composed of a double circular column and a core column to enhance the structural crushing performance under the axial crushing load. The quasi-static crushing test is conducted to investigate the collapse process of the AA6061-O aluminum alloy sandwich column. The good agreement between the experimental test and numerical analysis validates the accuracy of the finite element model of the sandwich column. Then, the numerical investigations of the sandwich column and corresponding members are performed under the dynamic impacting load. The results show that the interaction effect of the sandwich column and corresponding members can significantly improve the energy absorption of the sandwich column. Furthermore, the effects of the geometrical characteristics of the sandwich column are further investigated on the crashworthiness. The results show that the peak height A and number N of the peak of the core column have an important influence on the energy absorption and distribution of the collapse mode. Moreover, the sandwich column with A = 4 mm and N = 14 has the greatest energy absorption capacity. In addition, the wall thickness distribution of the sandwich column plays an important role in energy absorption during the crushing process. Therefore, the results of this paper provide a new method to design the thin-walled structures with high energy absorption.

Axial behavior of full‐scale sandwich columns with different compressive strengths

AbstractIn this study, a total of six full‐scale sandwich columns were fabricated, and experiments on their load transfer performance were conducted. The effects of steel fiber reinforcement and the ratio of the column width to the slab thickness on the effective compressive strength were theoretically analyzed, and briefly compared the test results of full‐ and reduced‐scale specimens. The current design codes do not take into account the ratio of the column width to the slab thickness when estimating the effective compressive strengths of slabs and columns with different compressive strengths. The test results conducted in this study, however, showed that the effective compressive strength tended to decrease with increasing slab thickness. In addition, the specimen reinforced with steel fibers in the column region exhibited a higher effective compressive strength than the specimen with steel fibers in the slab region.

Global/local analytical and numerical free vibration analysis of sandwich columns

Sandwich structures are increasingly applied in many industrial fields of application, due to their lightweight combined with favorable mechanical properties. Despite this, such structures are subject to specific failure modes, such as buckling or vibratory resonance. In both cases, due to the presence of thin and stiff skins, global but also local modes may be of great interest when dimensioning such composite structures, which makes it impossible to use classical models. In this paper, the free vibration problem of classical sandwich columns (with homogeneous core materials) is investigated, using special kinematic models, so as to deal with both global and local eigenmodes in an effective and precise way. First, the problem is addressed analytically, where the two faces are represented by Euler-Bernoulli beams and the core material is considered as a 2D continuous solid, in small strain elasticity. Then, an enriched 1D finite element formulation is developed, so as to handle efficiently more general configurations encountered in practice. The homogeneous core layer is here described using hyperbolic functions, in accordance with the modal displacement fields obtained analytically. The present analytical and numerical solutions (natural frequencies and vibration modes) are contrasted against each other and compared to 2D reference numerical results.

Buckling and crushing behavior of foam-core hybrid composite sandwich columns under quasi-static edgewise compression

Buckling and crushing behavior of foam-core hybrid composite sandwich columns under edgewise compressive load is dealt in this study. Composite laminates with different stacking sequence configurations made of glass and Dyneema-woven fabrics and AL 2024-T3 sheets were used in combination of polyvinyl chloride foam core to manufacture the specimens. Effects of face sheet thickness and stacking sequence configuration, slenderness ratio, boundary conditions, and sandwich reinforcement with through-thickness resin pins on the buckling and crushing behavior of the specimens were investigated. The results revealed that using the resin pins changes the unstable Euler buckling mode to a more stable progressive end-crushing and significantly increases the buckling load, specific buckling load, and energy absorption capability, which are highly favorable. Also, the results showed that in the specimens with fiber metal laminates, the major failure modes are face sheet-core debonding and face sheet delamination. However, based on the results, specimen with hybrid face sheets made from Dyneema fabrics and aluminum plates has the highest buckling load as well as the highest specific buckling load. Also, a specific fixture was designed to laterally clamp the sandwich column which causes a reduction in the probability of specimen end-crushing and significantly increases the buckling load.

Dynamic In‐Plane Compression of Asymmetric Metal Corrugated Sandwich Columns

Dynamic in‐plane compression of asymmetric metal corrugated sandwich columns is conducted analytically and numerically. The initial collapse modes of the asymmetric sandwich columns are observed and identified, i.e., elastic face wrinkling, plastic face wrinkling, macro plastic buckling, and macro elastic buckling. The collapse mechanism maps are conducted for asymmetric metal corrugated sandwich columns under the dynamic in‐plane compression. The analytical collapse mechanism map captures numerical results compressed at velocity V = 1 m s−1 reasonably. It is shown that velocity has a significant effect on the deformation mode of asymmetric metal corrugated sandwich columns under the dynamic in‐plane compression. The ratio of the thickness of top and bottom face sheets has the effect on the dominant deformation modes of the metal corrugated sandwich columns to some extent and has an insignificant effect on the collapse loads of metal corrugated sandwich columns.

The edgewise compressive behavior and failure mechanism of the composite Y-frame core sandwich column

A novel fabrication method was developed to fabricate the composite Y-frame core sandwich columns by hot-press molding method. The Y-frame core sandwich columns with different relative densities were obtained by hot-press molding method. The edgewise compressive tests were conducted. From the edgewise compressive tests, the mechanical behavior of the Y-frame core sandwich columns was recorded and analyzed. The effects of relative density on the failure modes, failure load and load-displacement curves were investigated. The dominant failure modes of the Y-frame core sandwich columns were macro buckling. The analytical prediction on the failure load of the Y-frame core sandwich column was presented, which was based on the macro buckling. The failure loads of the Y-frame core sandwich column at different relative densities were predicted with proposed method and compared with the experimental results.

Stability and free vibration analysis of tapered sandwich columns with functionally graded core and flexible connections

In this study, the buckling and free vibration behavior of tapered functionally graded material (FGM) sandwich columns is explored. The connections are considered to be semi-rigid. The core material is functionally graded along the beam depth according to the simple power law form. Euler–Bernoulli beam theory and the Ritz method will be employed to derive the governing equations. Legendre polynomials are chosen as auxiliary functions. After reducing the order of Euler’s buckling equation, an Emden–Fowler differential equation will be obtained. To reach a closed-form solution, the flexural rigidity of the column will be approximated with an exponential function by enforcing least-squares method. Non-dimensional natural frequencies and critical buckling loads will be presented for various cross-sectional types. The effects of FGM power, taper ratio, and spring rigidities on the critical buckling loads, and natural frequencies will be also investigated. Numerical results for various boundary conditions and configurations reveal the high accuracy of authors’ scheme.

Prediction of Corner Columns’ Load Capacity Using Composite Material Analogy

There are numerous reasons for which concrete has become the most widely used construction material in buildings, one of them being its availability in different types, such as fiber-reinforced, lightweight, high strength, conventional and self-compacting concrete. This advantage is specially realized in high-rise building construction, where common construction practice is to use concretes of different types or strength classes in slabs and columns. Columns in such structures are generally made from concrete which is higher in compressive strength than the one used in floors or slabs. This raises issue of selection of concrete strength that should be used for estimating column capacity. Current paper tries to address this issue by testing nine (09) sandwich column specimens under axial loading. The floor concrete portion of the sandwich column was made of normal strength concrete, whereas column portions from comparatively higher strength concrete. Test results show that aspect ratio (h/b) influences the effective concrete strength of such columns. A previously adopted methodology of composite material analogy with some modifications has been found to predict well the capacity of columns where variation in floor and concrete strength is significant.

Nondeterministic optimization of tapered sandwich column for crashworthiness

Foam-filled thin-walled structures signify a class of a promising energy absorber for improving the crashworthiness and safety of vehicles. Although the conventional deterministic optimization has been extensively applied to crashworthiness design of foam-filled thin-walled structures, the optimal solution could become infeasible when uncertainties of design variables and noise factors present in real world. To address this issue, a reliability based design optimization (RBDO) is adopted to consider the uncertainties of design variables and noise factors in crashworthiness optimization for the foam-filled bitubal tapered structure in this paper. Moreover, to comprehensively investigate the differences between deterministic and reliability based design optimization, single objective and multiple objective RBDO are established by integrating Kriging approximation with Monte Carlo Simulation (MCS). Since the optimal results of deterministic design usually converge at the constraint boundary, the solutions of RBDO often need to compromise some objective performance to satisfy the predetermined reliability levels. Furthermore, a comparative study on different Pareto fronts yielded from the deterministic optimization and RBDO under different reliability levels is conducted here. Besides, a grey relational analysis is carried out to determine the most satisfactory solution from the Pareto-set. The results demonstrate that the optimized foam-filled bitubal tapered columns are capable to considerably improve capacity of energy absorption with an increased reliability, potentially being a structural configuration for energy absorber.

Post-buckling analysis of elastoplastic sandwich columns by means of an enriched 1D finite element model

An advantageous 1D finite element model is designed in the present paper so as to analyze in an efficient way the post-buckling behavior of sandwich beams, known to be commonly responsible for the final collapse of such structures. An enriched beam formulation is defined, where the relatively thin skin layers are modeled as Timoshenko–Reissner beams, as they may undergo large rotations at advanced post-buckled stages. As for the homogeneous core layer, its complex behavior is represented by specific kinematics involving hyperbolic functions. The numerical model is developed within a total Lagrangian formulation framework, considering purely elastic behavior for the skins and an elastoplastic core material. The 1D finite element program incorporates effective incremental control techniques, namely arc-length methods and branch-switching procedures, in order to cope with limit and bifurcation points due to material and geometric non-linearities. A series of incremental calculations is performed in the case of axially compressed columns, exhibiting both global and local buckling modes depending on the geometric and material features. Secondary bifurcations, giving rise to unstable post-buckled solutions, are encountered in most cases due to the operating modal interaction phenomena. The results are compared with reference numerical computations achieved using a 2D finite element customized program.

Dynamic failure of a sandwich structure subjected to an in-plane axial impact

Dynamic response of sandwich structures subjected to in-plane axial impact loading is investigated experimentally and numerically. A comprehensive set of impact test results on sandwich panels with various configurations is presented. Experimental observation is made using high-speed cameras to closely examine the detailed temporal responses of the sandwich columns before the collapse of the entire structures. It is found that the failure mode is significantly affected by the core thickness. Finite-element based simulation is also performed to have a better understanding of the failure mechanism. Discrete cohesive zone model (DCZM) is utilized to model delamination failure at the interface between the skins and core. The interfacial failure is driven by dynamic buckling of the skin, competing against the bonding strength at the interface.

Buckling analysis of a reinforced sandwich column using the Bloch wave theory

This paper deals with sandwich structures whose core layer is made of a homogeneous foam periodically strengthened by orthogonal reinforcements. Beside traditional sandwiches which generally display satisfactory specific flexural properties but fatally insubstantial stiffnesses in the through-thickness direction, 3D reinforced sandwich materials provide optimal out-of-plane mechanical properties. Despite this, buckling remains one of the major failure modes of such structures and, compared to the case of traditional sandwiches, both global and local buckling phenomena are more complicated in presence of transverse reinforcements. Indeed, in most cases, the modal deformed shapes involve simultaneously the skins and the reinforcements in an intricate way. The main feature of these buckling modes is periodicity, but the typical wave length appears to be generally different from the characteristic length between reinforcements. However, it is possible to investigate such periodic modes on a simple unit cell by using the so-called Bloch wave theory. In this work, an efficient procedure is defined so as to deal with the buckling behavior of a sandwich column with periodic orthogonal reinforcements. First, a numerical method is implemented in the framework of the commercial software Abaqus. The evaluation of the critical strains is performed on a unit cell: an initial average compressive strain is enforced, then natural frequencies are computed and the critical strains are deduced by extrapolation of the previous eigenvalues. A Python program is developed so as to automate these successive calculation steps and a Fortran program is also needed (within Abaqus) in order to cope with the two real and imaginary problems to be solved due to the Bloch-periodic conditions. Furthermore, an exact analytical solution of this problem is obtained in the particular case of a reinforced sandwich with no foam core (for simplicity purposes). The analytical and numerical solutions obtained with a unit cell model are finally compared to the results of numerical computations performed on a complete beam with an arbitrary number of cells, for validation purposes. The critical strains/displacements are found to be in very good agreement and the buckling modes rebuilt from the real and imaginary components of the unit cell modal solutions perfectly coincide with the buckling modes of the complete beam obtained through a linearized buckling analysis.

Numerical Studies on Buckling and Post-Buckling of Composite Sandwich Columns with Face/Core Debond under Axial Compression

Numerical studies of buckling failure and debond propagation were carried out on composite sandwich columns with face/core debond. Nonlinear simulations with cohesive elements were carried out by Abaqus 6.14 to predict the buckling modes and debond propagation in sandwich composite columns. For specimens with embedded circular face/core debond, the debond propagated in the interface along the direction which was perpendicular to the compression direction until the through-the-width debond was formed. After that, the face/core debond propagated along the compression direction just as these specimens with through -the-width rectangle debond. Comparisons of the experimental and simulated ultimate loads associated with failure modes showed a good agreement. The maximum error of ultimate load was 10.61%, which proved that the model was capable of predicting accurate buckling loads and post-buckling behaviors.

Experimental Studies of Composite Sandwich Columns with Face/Core Debond under Axial Compression

Experimental studies of buckling failure and debond propagation were carried out on composite sandwich columns with face/core debond. The edgewise compression tests were conducted on two type specimens. Namely, one containin throughthe-width rectangle face/core debond, and the other with embedded circular interfacial debond. High-speed photography technology has been used to record the debond propagating paths. Two main failure modes of collapse were recorded in the tests: core shear buckling and mixed buckling.

Optimization of the Sandwich Column with the Truss Core Which is Subjected to the Compressive Loading

Abstract The sandwich structures have multifold advantages with respect to other types of structures. Besides the architectural possibilities due to their appearance, those structures can carry the same or even higher loads than some other similar structures. Optimization of the sandwich columns with the truss core, subjected to the compressive axial load, is presented in this paper. The two types of optimization were performed: the three-parameter and the four-parameter optimization - the so called full optimization. The optimization of the column geometry (face thickness, core member height and core member diameter and core height) was performed, from the aspect of the minimal weight of the structure in terms of the load index. It was performed for four types of restrictions imposed by the corresponding column failure modes: column buckling, truss macro-buckling, local buckling of the face and face wrinkling. The tree-parameter optimization resulted in somewhat larger weight of the column than the full, four-parameter optimization.