Uniform Compressive Load Research Articles

Numerical Modeling and Experimental Behavior of Closed-Cell Aluminum Foam Fabricated by the Gas Blowing Method under Compressive Loading.

This paper deals with the experimental and numerical study of closed-cell aluminum-based foam under compressive loading. Experimental samples were produced by the gas blowing method. Foam samples had an average cell size of around 1 mm, with sizes in the range 0.5–5 mm, and foam density of 0.6 g/cm3. Foam samples were subjected to a uniaxial compression test, at a displacement rate of 0.001 mm/s. Load and stress were monitored as the functions of extension and strain, respectively. For numerical modeling, CT scan images of experimental samples were used to create a volume model. Solid 3D quadratic tetrahedron mesh with TETRA 10-node elements was applied, with isotropic material behavior. A nonlinear static test with an elasto-plastic model was used in the numerical simulation, with von Mises criteria, and strain was kept below 10% by the software. Uniform compressive loading was set up over the top sample surface, in the y-axis direction only. Experimental tests showed that a 90 kN load produced complete failure of the sample, and three zones were exhibited: an elastic region, a rather uniform plateau region (around 23 MPa) and a densification region that started around 35 MPa. Yielding, or collapse stress, was achieved around 20 MPa. The densification region and a rapid rise in stress began at around 52% of sample deformation. The numerical model showed both compressive and tensile stresses within the complex stress field, indicating that shear also had a prominent role. Mainly compressive stresses were exhibited in the zones of the larger cells, whereas tensile stresses occurred in zones with an increased number of small cells and thin cell walls.

Dynamic instability of curved variable angle tow composite panel under axial compression

Variable angle tow (VAT) composites have demonstrated better performance in buckling and post-buckling over straight fiber composites based on the mechanics of load redistribution from critical regions to supported edges. In this work, the dynamic instability behavior of a curved VAT composite panel subjected to periodic axial compression load is investigated. The governing energy functional of a curved symmetric VAT panel under external loading is derived using Donnell's shallow shell theory. Later, the discretized equations of motion are derived using the Rayleigh–Ritz method combined with the generalized differential integral quadrature method (GDIQM). Initially, the pre-buckling problem is solved by applying a uniform compression load to compute the stress resultant distribution which is used to evaluate the buckling load of the curved VAT panel. Subsequently, the dynamic/parametric instability region of a curved VAT panel subjected to periodic axial compression load is determined using Bolotin's first-order approximation. Then, the dynamic instability performance is evaluated for a curved VAT panel with linear fiber angle distribution and compared with straight fiber laminates. Finally, the influence of fiber angle orientation, the radius of curvature, aspect ratio and plate boundary conditions on the dynamic instability of VAT panel is presented.

Nonlinear Buckling and Postbuckling of FGM Shear-Deformable Truncated Conical Shells Reinforced by FGM Stiffeners

In this study, the nonlinear buckling of stiffened FGM truncated conical shells resting on an elastic foundation and subjected to a uniform axial compressive load is considered. The shells are reinforced by FGM stringers and rings. Using the analytical approach, FSDT, Galerkin method, geometrical nonlinearity in the von Karman–Donnell sense, and Leknitskii smeared stiffener technique, the governing equations are derived. Closed-form expressions for determining the critical buckling load and for analyzing the postbuckling load–deflection curves are obtained. Finally, the effect of stiffeners, dimensional parameters, semivertex angle, material properties, and foundations on the nonlinear response of FGM truncated conical shells are analyzed and discussed in detail.

On the design, elastic modeling and experimental characterization of novel tensegrity units

Purpose This study aims to focus on a short review on recent results dealing with the mechanical modelling and experimental characterization of a novel class of tensegrity structures, named class θ = 1 tensegrity prisms. The examined structures exhibit six bars connected by two disjoint sets of strings. Design/methodology/approach First, the self-equilibrium problem of tensegrity θ = 1 prisms is numerically investigated for varying values of two aspect parameters and, next, their prestress stability is studied. The mechanical behavior of the examined structures in the large displacements regime under uniform compression loading is also numerically computed through a path-following procedure. Finally, the predicted constitutive response is validated through experimental tests. Findings The presented results highlight that the examined structures exhibit a large number of infinitesimal mechanisms from the freestanding configuration, and reveal that they exhibit tunable elastic response switching from stiffening to softening. Originality/value This multi-faceted elastic response is in agreement with previous literature results on the elastic response of minimal tensegrity prism, and suggests that such units can be usefully used as non-linear springs in next-generation tensegrity metamaterials.

Overall instability performance of concrete-infilled double steel corrugated-plate wall

This paper proposes a new type of composite walls, namely concrete-infilled double steel corrugated-plate walls (CDSCWs). The CDSCW consists of a wall element that is formed by two steel corrugated-plates, where they are interconnected through high-strength bolts, and the spacing between the two steel corrugated-plates is filled with concrete. Additionally, two concrete-infilled steel tubes (CFSTs) are assigned as vertical boundary elements at both sides of the wall element. Not only the corrugated configuration of steel sheets themselves would significantly improve the load-bearing efficiency of CDSCWs, but also the interactions and combined actions among steel corrugated-plates, high-strength bolts and concrete could provide much better load-bearing capacity and seismic performance for CDSCWs. In addition, industrial mass production of the CDSCWs can be achieved by adopting integrated cold-formed steel rolling techniques. Therefore, the CDSCWs are much more suitable for applications in high-rise building structures as shear wall structural systems that carry axial loads and bending moments as well as shear loads. This paper mainly investigates the overall instability performance of I-section CDSCWs under uniform compressions and corresponding design formulae are recommended. Firstly, Finite Element (FE) eigenvalue buckling analyses are carried out to investigate the overall elastic buckling behavior of CDSCWs subjected to vertical compressive loads. The formulae for estimating the elastic buckling loads of CDSCWs and corresponding normalized slenderness ratios λn are obtained based upon the form of Euler's formula. The overall instability performance of CDSCWs under compressions is then studied by FE nonlinear analyses, leading to the overall stability coefficient φ as well as φ-λn curve for their strength design. Moreover, an I-section CDSCW specimen has been designed and tested under uniform compressive load, and its overall instability performance is investigated experimentally. The results obtained from the experiment show an agreement with those obtained from FE numerical analyses, which also verifies the safety and validity of φ-λn curves for the strength design of CDSCWs.

Numerical and experimental analysis of perforated rack members under compression

This paper presents a numerical and experimental study of uprights with rack-type perforated section in cold-formed profiles, subjected to axial compression. 18 tests were performed on uprights with fixed-ends under uniform compression load to obtain the ultimate load applied, along with the measurement of the displacements. A numerical model with material and geometric nonlinearities was calibrated with the experimental tests. Next, a parametric analysis with 64 different numerical models was performed, determining the ultimate loads of the models. These results, when compared to the DSM predictions, showed that the equations of DSM are unreliable to predict the strength of this type of perforated uprights. Therefore, based on the model results, modifications were proposed to the parameters of the DSM distortional mode curve, so that it can predict the strength of the models studied.

Local buckling of thin plate on tensionless elastic foundations under interactive uniaxial compression and shear

ABSTRACT This paper uses a mathematical method to develop an analytical solution to the local buckling behaviour of long rectangular plates resting on tensionless elastic Winkler foundations and under combined uniform longitudinal uniaxial compressive and uniform in-plane shear loads. Fitted formulas are derived for plates with clamped edges and simplified supported edges. Two examples are given to demonstrate the application of the current method: one is a plate on tensionless spring foundations and the other is the contact between the steel sheet and elastic solid foundation. Finite element (FE) analysis is also conducted to validate the analytical results. Good agreement is obtained between the current method and FE analysis.

Effects of different cyclic loading on lightweight self-compacting concrete

Self-compacting concrete (SCC) use is increasing and understanding its behaviour under cyclic loading is therefore important. This research study investigated the behaviour of lightweight SCC under eight different types of compressive cyclic loading. Three loadings were applied to examine pre-peak lightweight SCC behaviour, two loadings were used to examine the post-peak behaviour and three loadings are complete. The total loading in the pre- and post-peak range exposed lightweight SCC to compressive were used to examine both pre- and post-peak stages. 120 standard cylindrical specimens were tested. 90 specimens were exposed to cyclic compressive loading and 30 specimens to uniform compressive loading. The mean compressive strength of the study specimens was 40 MPa and the slump flow was 64 cm. The results showed that increasing the number of loadings reduced the peak strength and increased strain. The reduction in strength and increase in strain depend on the number of pre-peak loadings. The damage caused by cyclic loading, the amount of energy absorbed due to the cracks caused by loading and the amount of energy absorbed by the concrete in hysteresis loops were studied with respect to the type of loading.

Flutter Instability of Cracked Rotating Non-Uniform Beams Subjected to Distributed Follower Force

In this paper, the effect of an open edge crack on the instability of rotating non-uniform beams subjected to uniform distributed tangential compressive load is studied. The local stiffness due to the presence of crack is considered in the global stiffness matrix of the structure using the finite element method. The cracked beam element is modeled as two equal sub-beam elements connected by a massless rotational spring. Based on the fracture mechanics, the strain energy release rate and the stress intensity factors are employed to investigate the stiffness of the rotational spring. Then, the modified shape functions are developed to reflect the crack stiffness in the finite element analysis. To validate the accuracy of the finite element model and results obtained, comparisons have been made between the results obtained and those available in the literature. The effects of several parameters, including the linear and nonlinear thickness variations, angular velocity, crack location and size, on the instability of cracked rotating non-uniform cantilevers are also examined. The results show that the location of crack significantly influences the critical magnitude of the follower force that destabilizes the cantilevers. In addition, geometric non-uniformity reduces the stability of the cracked cantilevers. For the same amount of cantilever mass, different patterns of mass distribution result in different stability diagrams.

Design optimization of stiffened panels using finite element integrated force method

The objective of the present paper is to develop an efficient and accurate design optimization procedure to minimize the mass of the stiffened panels subjected to uniform compression loading, while guarding against the buckling failure. A Finite Element (FE) model based on the Integrated Force Method (IFM) is developed to perform the buckling analysis of stiffened panels. It has been shown that the finite element analysis based on the force methodology is able to predict the critical buckling load accurately and efficiently. The Sequential Quadratic Programming (SQP) is then applied to the established IFM model to minimize the mass of stiffened panels while guarding against buckling failure. An efficient analytical formulation to perform the sensitivity analysis is formulated using the developed finite element force method, and then utilized in the SQP formulation as the gradient information. Illustrated examples have been presented to verify the validities of the proposed methodologies. It has been shown that comparing to the numerical sensitivity analysis, the design optimization using the developed analytical sensitivity formulation is very efficient and accurate.

Analyzing the Edge Cracked Semicircular Disc under Uniform Compressive (ECSD(UD)) Load

In this study, by employing the edge cracked semicircular disc under uniform (ECSD(UC)) and calculating the shape factor, the toughness of brittle materials under uniform compressive load has been quickly evaluated. Samples, on the loading location and the support, under angle β changing from 0 to 10 degrees, with the crack length (a) changing from 1 to 29 mm and the thickness (t) changing from 1 to 30 mm were investigated. By taking into account the simultaneous effect of thickness and crack length, a relationship for the shape factor (F) of the ECSD(UC) was presented.

Numerical Analysis of Kraft Paper Honeycomb subjected to uniform compression loading

The objective of this study is to investigate the crushing strength of Kraft paper honeycomb with different thickness of cell wall and different cell size subjected to compression loading. At first, experimental tests were carried out on Kraft paper honeycomb with 10mm cell size and 0.6mm thickness of paper with different mass density (RO). Then, a finite element model was developed in order to study the effect of cell size and thickness of cell wall on crushing properties of Kraft paper honeycomb. Based on the simulation results, the cell size and thickness of cell wall of Kraft paper honeycomb influence the crushing properties of the honeycomb. Crushing strength increases with decreasing the cell size which for the range of the study, cell size 10mm shows the highest strength. Meanwhile, 0.4mm thickness of cell wall results the higher crushing strength of honeycomb. Also, higher density gives higher crushing strength where in this study is found for 2.236× 106 kg/mm3.

Analytical solution for vibration and buckling of annular sectorial porous plates under in-plane uniform compressive loading

In this article, an analytical solution for free vibration of moderately thick annular sectorial porous plates in the presence of in-plane loading is presented. Because of the in-plane loading, before the vibrational analysis, a buckling analysis is performed. To this end, equations of motion together with the stability equations are derived using Hamilton principle. Both the governing equations of motion and stability are highly coupled differential equations, which are difficult to solve analytically. So, they are decoupled through performing some mathematical operations. The decoupled equations are then solved analytically for annular plates with simply supported boundary conditions on the radial edges and different boundary conditions on the circumferential edges. Natural frequencies and also critical buckling load are obtained and the effects of thickness ratio, radii ratio, porosity, and boundary conditions are studied in detail. Finally, the effect of in-plane loading on the natural frequency of the plate is studied comprehensively. Numerical results show that the natural frequency decreases as the load ratio approaches one and vanishes as it reaches one.

Multiaxial tension/compression asymmetry of Ti/TiN nano laminates: MD investigation

Metal-ceramic multilayers have been reported to show high strength, measurable plasticity, and a high strain-hardening rate when the crystallographic layers are a few nanometers thick. In this work, large-scale molecular dynamics simulations are carried out in order to understand the deformation mechanisms of the Ti/TiN multilayer subjected to multiaxial loading. The yield behavior of the Ti/TiN multilayer is thoroughly explored by constructing the yield surface in the interface plane. The strong dependency of the yielding stresses on the loading direction highlights the anisotropic behavior of the structure. The Ti/TiN multilayer structure shows high strength and ductility under uniform compression loading. However, low strength and ductility are observed under tensile loading, which favors crack initiation and propagation. Unlike typical metal stress-strain curves, metal/ceramic multilayers show two main yield points. Furthermore, the Ti/TiN multilayer structure shows three distinctive peak points for compressive loading normal and parallel to the interface. Different slip planes are activated depending on loading directions. Two main mechanisms are found to control the plasticity of the Ti/TiN multilayer: (1) interface strengthening, in which, when the metal-ceramic multilayers are under compressive loading, the interface acts as a barrier and induces repulsive forces against the slip transmission from the Ti layer into the TiN layer; (2) interface softening, in which, when applying tensile loading on the metal-ceramic multilayer structure, the interfacial misfit dislocations act as sources for the emission of dislocations into the TiN layer or promote slip transmission from the Ti to the TiN layer.

Work principle in inelastic buckling analysis of axially compressed rectangular plates

PurposeThe purpose of this paper is to analyze the inelastic buckling of a rectangular thin flat isotropic plate subjected to uniform uniaxial in-plane compression using a work principle, a deformation plasticity theory and Taylor–Maclaurin series formulation.Design/methodology/approachThe non-loaded longitudinal edges of the rectangular plate are clamped, whereas the loaded edges are simply supported (CSCS). Total work error function is applied to Stowell’s plasticity theory in the derivation of the inelastic buckling equation. Mathematical formulation of the Taylor–Maclaurin series deflection function satisfied the boundary conditions of the CSCS rectangular plate. The critical inelastic load of the plate is then derived by applying variational principles.FindingsValues of the plate buckling coefficient are calculated using various values of moduli ratio for aspect ratios ranging from 0.1 to 1.0, in intervals of 0.1. The accuracy of the proposed technique is validated by comparing the results obtained in the present study with solutions from a previous investigation. The percentage differences in the values of the buckling coefficient ranged from −0.122 to −4.685 per cent.Originality/valueThe results indicate that the work principle approach can be used as an alternative approximate method for analyzing inelastic buckling of rectangular thin flat isotropic plates under uniform in-plane compressive loads.

Experimental study on energy absorption of foam filled kraft paper honeycomb subjected to quasi-static uniform compression loading

A statistical analysis was performed to evaluate the effect of factor and to obtain the optimum configuration of Kraft paper honeycomb. The factors considered in this study include density of paper, thickness of paper and cell size of honeycomb. Based on three level factorial design, two-factor interaction model (2FI) was developed to correlate the factors with specific energy absorption and specific compression strength. From the analysis of variance (ANOVA), the most influential factor on responses and the optimum configuration was identified. After that, Kraft paper honeycomb with optimum configuration is used to fabricate foam-filled paper honeycomb with five different densities of polyurethane foam as filler (31.8, 32.7, 44.5, 45.7, 52 kg/m3). The foam-filled paper honeycomb is subjected to quasi-static compression loading. Failure mechanism of the foam-filled honeycomb was identified, analyzed and compared with the unfilled paper honeycomb. The peak force and energy absorption capability of foam-filled paper honeycomb are increased up to 32% and 30%, respectively, compared to the summation of individual components.

Progressive Failure Analysis of Laminated Composite Plates with Elliptical or Circular Cutout Using Finite Element Method

The progressive failure analysis of symmetrically laminated composite plate [0°/+45°/-45°/90°]2s with circular or elliptical cutout under uniform uniaxial compression loading is carried out using finite element method. Hashin's failure criterion is used to predict the lamina failure. A parametric study has been carried out to study the effect of elliptical / circular cutout orientation, cutout size and plate thickness on the ultimate failure load of laminated composite plate under uni-axial compression loading. It is noticed that elliptical cutout orientation has influence on the strength of the notched composite plates. It is observed that the laminate size of the elliptical/circular cutout and plate thickness has substantial influence on the ultimate failure load of notched composite plates.

Strengthening of Circular RC Column through External Confinement using Ferrocement

Objectives: The present study investigates the effect of confinement using ferrocement as wrapping material on the circular RC columns under concentric loading condition. Methods: Experimental studies were carried out on the confining effect using external confinement technique with one layer and two layers of GI wire mesh under concentrically loaded condition. All columns were tested by uniform concentric compressive load from top with a hydraulic compression testing machine of capacity 1000 KN. Findings: Most of the researches have done on confining effect of either long column or short column (slenderness ratio more than 3). This paper demonstrates the confining effect on short column having slenderness ratio is less than 3, such a column is called pedestal. Pedestal is a form of short column which is used as a base support for steel structure, statue or vase. To protect the column of steel structure from corrosion that is in direct contact of soil, pedestal is provided. During earthquake such a structure can collapse or even cracks can develop. Hence, ferrocement structures are highly ductile and energy dissipating material that can undergoes large deformations without collapsing during earthquakes. Even the deformed structures can be strengthened at very low cost after deformation. Steel jacketing has proved to be an effective measure for strengthening or retrofitting and has been widely used in practice, but the engineering community is currently looking for alternatives. Applications/Improvements: Material like ferrocement is oldest, cost effective method emerges an alternative solution for strengthening of reinforced concrete column. External confinement or encasing of column with ferrocement enhances the strength and ductility of concrete column.

Size scale dependence of compressive instabilities in layered composites in the presence of stress gradients

The compressive strength of unidirectionally or layer-wise reinforced composite materials in direction parallel to their reinforcement is limited by micro-buckling instabilities. Although the inherent compressive strength of a given material micro-structure can easily be determined by assessing its stability under a uniform compressive load, this is often not sufficient for predicting failure initiation within a larger structure. In cases, where the composite material micro-structure is locally subjected to strongly non-uniform loadings, compressive instabilities depend not only on the maximum compressive stress but also on spatial stress or strain gradients, rendering failure initiation size scale dependent. The present work demonstrates and investigates the aforementioned effect through numerical simulations of periodically layered structures with notches and holes under bending and compressive loads, respectively. The presented results emphasize the importance of the reinforcing layer thickness on the load carrying capacity of the investigated structures, at a constant volumetric fraction of the reinforcement. The observed strengthening at higher values of the relative layer thickness is attributed to the bending stiffness of the reinforcing layers.

Nonlinear Buckling of Circular Nano Plates on Elastic Foundation

The following article investigates nonlinear symmetric buckling of moderately thick circular Nano plates with an orthotropic property under uniform radial compressive in-plane mechanical load. Taking into account Eringen nonlocal elasticity theory, principle of virtual work, first order shear deformation plate theory (FSDT) and nonlinear Von-Karman strains, the governing equations are obtained based on displacements. The differential quadrature method (DQM) as a numerical procedure is applied for solving the equations. In this analysis, for solving the stability equations, adjacent equilibrium methodis employed. In nonlinear buckling analyses and for obtaining the buckling load, generally the available nonlinear terms of the stability equation are neglected. However, in this study, for getting the most accurate data, nonlinear terms are considered and the non-dimensional buckling load is compared with the condition of considering or neglecting that of terms and the effect of that of terms are also studied. The accuracy of the present results is validated by comparing the solutions with available studies. The effects of nonlocal parameter, thickness, radiusand elastic foundation are investigated on non-dimensional buckling loads. The results of analyses based on local and non-local theories are compared. From the results, it can be seen that the effect of nonlocal parameter on simply support condition is less than clamped condition. It can be observed that with increasing the radius of the plate, the difference between local and non-local analyses,increases.