In-plane Axial Compression Research Articles

Effect of the micro-structure on the compressive failure behavior of three-dimensional orthogonal woven composites

The failure behavior of three-dimensional orthogonal woven composites (3DOWCs) under in-plane axial compression has been experimentally and numerically investigated. The micro-structure at the intersecting points of the fabric reinforcement, which is induced by the tow force in the weaving process, is introduced. The strength and the induced damage along the warp and weft directions were investigated. The micro-structure of the 3DOWC including the details of the tow waviness and resin distribution was accurately obtained through a multiscale modeling approach. Resin cracking and the local stress concentration were captured by the numerical models, and they showed good correlations with the experimental results. The fiber undulation in the region of the tow intersection concentrated stress, which led to fiber fracture in the compression process. The main load-carrying tow, namely, the warp and weft tow along each direction, had different forms of undulation, which should be the reason for the decreasing compression-carrying capacity of the 3DOWC. With increasing Z-binder tow force, the level of fiber straightness decreased and the failure mode transformed from macroscopic brooming type to fiber microbucking. The inclination angle of the through-thickness fracture path suggested that fracture was induced by the shear failure in the load-carrying tows.

Mechanical properties and energy absorption of 3D printed square hierarchical honeycombs under in-plane axial compression

Hierarchical structural design was considered as a promising approach to improve the performance of regular cellular materials. In this study, square hierarchical honeycombs (SHHs) were fabricated by employing a commercial 3D printer, and their in-plane mechanical properties and energy absorption were investigated. The SHHs were constructed by replacing each solid cell wall of a regular square honeycomb (RSH) with different numbers of smaller square substructures. In-plane quasi-static compressive tests were conducted on SHHs, and the effect of substructure number on the deformation mode, mechanical properties and energy absorption performance were studied. The results revealed that the cells of SHHs and RSH collapsed layer-by-layer along the loading direction, while more localized bands and damage were found for SHHs. Enhanced compressive strength, specific energy absorption and crush force efficiency were found for SHHs when compared with RSH of equal mass. Moreover, the reason for the enhancement and the effect of substructure number on the enhancement were also explored. In addition, analytical expressions for the Young's modulus and compressive strength of SHHs were developed, and the results from experiments and simulations were employed to verify the analytical results. This study elucidates the effect of structural hierarchy on the mechanical properties and energy absorption performance of regular cellular materials.

Empirical formula for predicting ultimate strength of stiffened panel of ship structure under combined longitudinal compression and lateral loads

The influence of lateral pressure and stiffener type on the collapse behaviours of steel stiffened panels are investigated in the FE (finite element) analysis. Based on the numerical results, the empirical expressions are derived for the ultimate strength assessment of stiffened panels under combined in-plane axial compression and different levels of lateral pressure. The regression formulae only include the plate slenderness ratio and column (stiffener) slenderness ratio. Hence, to consider the influence of stiffener type, the databases of sample points are separately grouped for various cross sections in the regression process. At the same time, for the convenient of utilizing the regression model, the coefficients are expressed as water head in meters. To investigate the approximating accuracy of regression model, the statistical measurement analyses are conducted by comparing with FE analysis, simplified analytical method and experiments.

Linear buckling analysis of welded girder webs with variable thickness

Steel girder web panels have been subjected in recent decades, to a number of experimental and numerical studies but the mechanisms that regulate the behaviour of the panels composed by two subpanels with different thickness were not deeply studied. Furthermore specific design rules regarding the estimation of the buckling coefficient for panels with variable thickness are not included in the codes even if this is a common situation particularly for steel bridge girders with beams having significant height. In this framework,this work aims to investigate buckling behaviour of steel beams with webs composed of panels with different thicknesses subjected to both in-plane axial compression and bending moment and gives some simplified equations for the estimation of the buckling coefficient.

Empirical formulations for estimation of ultimate strength of continuous stiffened aluminium plates under combined in-plane compression and lateral pressure

The present research was undertaken based on the results obtained by the same authors in a sensitivity study on the buckling and ultimate strength of continuous stiffened aluminium plates. Empirical expressions are developed for predicting ultimate compressive strength of welded stiffened aluminium plates used in marine applications under combined in-plane axial compression and different levels of lateral pressure. Existing data of the ultimate compressive strength for stiffened aluminium plates numerically obtained by the authors through the previously performed sensitivity analysis are used for deriving formulations that are expressed as functions of two parameters, namely the plate slenderness ratio and the column (stiffener) slenderness ratio. Regression analysis is used in order to derive the empirical formulations. The formulae implicitly include effects of the weld on initial imperfections, and the heat-affected zone.

Y-stiffened panel multi-objective optimization using genetic algorithm

The aim of this paper is to design an optimum Y-stiffener plate combination using multi-objective optimization with real-coded genetic algorithms under the action of uniaxial compressive loads, because the most important loads applied on stiffened plates in ship hull is longitudinal in-plane axial compression arising for instance due to longitudinal bending because the cargo is not distributed equally in holds or due to grounding, stranding or collision. Five of the Y-stiffened panel dimensions were selected to be the independent design variables of the optimization problem. The objective functions are the ultimate buckling load and the volume per unit area of the Y-stiffener plate combination. Nonlinear finite element analysis was used to calculate the ultimate buckling load of 3 5 different sets of the design variables, with certain range for each of the design variables. The effects of independent design variables on the ultimate buckling load and the volume per unit area for Y-stiffener plate combination were studied and discussed. A new surrogate function to predict the ultimate buckling load of Y-stiffener plate combination is created and validated using the values of the ultimate buckling loads calculated using nonlinear finite element analysis. The proposed surrogate function is valid only in the specific ranges of the design variables. The Pareto optimal sets were calculated using multi-objective optimization with real-coded genetic algorithms and the optimum set of the independent design variables which is associated with the optimal geometric dimensions of the Y-stiffened panel was selected as the set which has the maximum ultimate buckling load to volume per unit area ratio. The optimum set was tested and validated using sensitivity analysis technique.

Ultimate Strength and Ductility Characteristics of Intermittently Welded Stiffened Plates Under In-Plane Axial Compression

The ultimate strength and ductility characteristics of the intermittently welded stiffened plates under the action of in-plane axial compression are investigated in this paper. A series of detailed numerical analyses of longitudinally stiffened steel plates subjected to in-plane compressive load is performed using the ADINA commercial finite element code. Complete equilibrium paths are traced up to collapse for a nonlinear elastic-plastic response of stiffened plates. Analyzed stiffened plates are imperfect and their aspect ratio, plate slenderness, and column slenderness are changed in a systematic manner. Different types of stiffener are chosen for stiffened plate models. Three different stiffener-to-plate welding procedures are considered: continuous, chain intermittent, and staggered intermittent fillet welding.

Buckling of centerline-stiffened plates subjected to uniaxial eccentric compression

A solution for the elastic buckling of flat rectangular plates with centerline boundary conditions subjected to non-uniform in-plane axial compression is presented. The loaded edges are simply supported, the non-loaded edges are free, and the centerline is simply supported with a variable rotational stiffness. The Galerkin method is used to establish an eigenvalue problem and a series solution for plate buckling coefficients is obtained by using combined trigonometric and polynomial functions that satisfy the boundary conditions. It is demonstrated that the formulation approaches the classical solution of a plate with a clamped edge as the variable rotational stiffness is increased. The variation of buckling coefficient with aspect ratio is presented for various stress gradient ratios. The coupling between plate aspect ratio, centerline rotational stiffness, and gradient of applied compressive stress is illustrated and discussed. The solution is applicable to stiffened plates and I-shaped beams that are subjected to biaxial bending or combined flexure and torsion, and is important to estimate the reduction in elastic buckling capacity due to stress gradient.

Creep Buckling of a Wedge-Shaped Floating Ice Plate

The paper is concerned with the problem of creep buckling of a floating ice plate pressing against a rigid, vertical-walled, engineering structure of a finite length. The plate is modelled as a truncated wedge of a semi-infinite length and constant thickness, resting on a liquid base and subjected to transverse bending due to the elastic reaction of the base and in-plane axial compression due to wind and water drag forces. The ice is treated as a viscous material, with the viscosity varying with the depth of the ice cover. The results of numerical calculations, carried out by the finite-element method, show the evolution of creep buckles in the plate, and also illustrate the behaviour of the ice cover at different levels of the in-plane axial loading, at different temperatures across the ice, and for different geometries of the wedge-shaped plate.

Structural efficiency study of graphite-epoxy aircraft rib structures

The present study focuses on the structural efficiencies of optimally designed composite wing rib panel configurations. The configurations studied include a tailored corrugated panel, a corrugated panel with a constant-thickness continuous laminate, and a hat-stiffened panel. Also included in the study are a blade-stiffened panel and a flat unstiffened plate which are used as baseline configurations for comparison. Thicknesses of different plies with preselected ply orientations in the different sections of the panels and detailed cross-sectional dimensions are used as sizing variables. The constraints considered include those associated with material strength, buckling, and geometric limits. The loads considered for this study are based on a typical loading of an inboard wing rib fuel cell closeout panel for a large transport aircraft and include in-plane axial compression Nx, shear Nxy, and out-of-plane pressure P. Structural efficiencies and cross-sectional geometries of different configurations are compared for a wide range of combined loads. Transition of the optimal cross-sectional geometry from one panel configuration to another is demonstrated as the loading is varied. The sensitivities of optimized designs to large changes in some of the geometric parameters are also studied.