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This study experimentally investigated the effects of nanoparticle reinforcement on the buckling behavior of composite materials. Different sizes of carboxylic acid functionalized multi-walled carbon nanotubes were used as nanoparticles. E-glass fiber-reinforced composite materials with polymer matrix in the [0°/90°/0°/90°]s cross-ply array with and without carbon nanotube reinforcement were produced by hand lay-up and vacuum bagging. Three types of carbon nanotubes in different sizes and proportions of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by weight were added to the epoxy resin. For the buckling test, the samples with two clamped and two free sides were attached to the universal testing machine to apply a uniaxial compressive load. As a result of the experiments, it was found that the addition of carbon nanotube in certain proportions increases the critical buckling load of composite materials. The highest increase in the critical buckling load (26.10% increase) was achieved with a carbon nanotube reinforcement of 0.2% by weight, having an outer diameter of 10–20 nm, internal diameter of 5–10 nm, and length of 0.5–2 mm. As the carbon nanotube sizes added to the epoxy resin decreased, the buckling strength increased. [ABSTRACT FROM AUTHOR]

High injection pressure resin transfer moulding is a variant of resin transfer moulding in which the preform is compressed in a tool and resin is injected into the mould under very high pressure. The high injection pressure (>20 bar) introduces possible fibre washout that translates into manufacturing defects or causes inconsistencies in processing and leads to scatter in mechanical properties of composite parts. A model is presented which quantifies and provides insight into the influence of process variables such as clamping force and injection pressure on fibre washout distance (the one-dimensional model assumes a rigid preform). A generalised one-dimensional stress model for fibre washout is presented for regions that are impregnated with the resin and the regions that are dry. The model shows fibre washout to be significant at the beginning of the injection process. The model allows one to further refine the injection strategy by adjusting injection pressure to account for washout in high injection pressure resin transfer moulding. [ABSTRACT FROM AUTHOR]

In this work, biaxial buckling analysis of sandwich plates with symmetric composite laminated core and two functionally graded nanocomposite face sheets is carried out by a new improved high-order theory. The nanocomposite face sheets are carbon nanotube (CNT)-reinforced nanocomposites and the material properties of the nanocomposites plates are graded along the thickness and are estimated though the Mori–Tanaka approach. CNTs are assumed randomly oriented and aggregated into some clusters. The same third order theory is used for modeling of core and the faces sheets. The theory has third and second orders of z for in-plane and normal displacements, respectively. The principle of minimum potential energy is used to derive the equations of motion and boundary conditions. Analytical solution for static analysis of simply supported sandwich plates under biaxial in-plane compressive loads is presented using Navier’s solution. The effects of CNT volume fraction, CNT aggregation states, CNT distribution, biaxial loads ratio, and geometric dimensions of sandwich plate are investigated on the overall buckling of functionally graded carbon nanotube-reinforced nanocomposite sandwich plates. [ABSTRACT FROM AUTHOR]

Hybrid lattice cores for sandwich structures containing both solid struts and polymer foam are a recent option available to designers. These cores benefit from a synergistic effect in which the foam supports the slender struts against buckling in addition to carrying a portion of the applied loads directly. This work will optimize these hybrid cores to minimize unit cell density given compressive and shear strength constraints for a variety of unit cell configurations. An analytical model is developed for prediction of failure using the assumption that the foam is an elastic foundation that supports the struts; however, the unit cells are found to be optimal when no polymer foam is used. With the problem thereby simplified, analytical optimization solutions are derived and studied extensively, revealing qualitative insights about efficient lattice core designs. Optimal strut inclination angle, failure mode, and configuration are plotted against loading, which show that, for the large majority of strength constraints, the lowest unit cell density is achieved with tetrahedral cores whose struts fail in compressive yielding. [ABSTRACT FROM AUTHOR]

CCF300/5228A aero composite stiffened panels achieved absorbing saturation in hygrothermal condition (70℃ distilled water), whose absorbing process followed the Fick law. Many debonding and gaps of matrix to fibers could be observed after hygrothermal exposure by scanning electron microscope (SEM). Compressive experiments were conducted on unaged and aged composite stiffened panels. Failure modes of the two types of specimens are quite similar with several major ways, including the debonding and fracture of stiffeners together with the splitting and ripping of panel. Buckling patterns for both types of specimens are similar and characterized by buckling of panels between stiffeners and buckling of the middle two stiffeners. However, the bending direction of buckling mid-panel for aged specimens is opposite to that of the unaged at same position panel, which shows that hygrothermal condition influences the bending direction of buckling mid-panels seriously. There still exists a post-buckling process for aged specimens under axial compression, whose average buckling load and failure load decrease by 3.1% and 22.2% respectively, comparing to that of unaged specimens. [ABSTRACT FROM AUTHOR]

Advanced grid stiffened composite cylindrical shell is widely adopted in advanced structures due to its exceptional mechanical properties. Buckling is a main failure mode of advanced grid stiffened structures in engineering, which calls for increasing attention. In this paper, the buckling response of advanced grid stiffened structure is investigated by three different means including equivalent stiffness model, finite element model and a hybrid model (H-model) that combines equivalent stiffness model with finite element model. Buckling experiment is carried out on an advanced grid stiffened structure to validate the efficiency of different modeling methods. Based on the comparison, the characteristics of different methods are independently evaluated. It is arguable that, by considering the defects of material, finite element model is a suitable numerical tool for the buckling analysis of advanced grid stiffened structures. [ABSTRACT FROM PUBLISHER]

This article is concerned with the numerical modelling and analysis of the mechanical behaviour of composite pipes used for offshore oil and gas applications. Specifically, the bending of the reinforced thermoplastic pipes during the reeling process of reel-lay installation is modelled using non-linear finite-element procedures. In particular, the possible buckling of the reeled composite pipes has been investigated. Composite pipes reinforced with one angle-ply and two angle-ply layers are considered and the effects of different diameter-to-thickness ratios and different angle-ply combinations on the mechanical behaviour of these pipes have been studied. [ABSTRACT FROM AUTHOR]

The solution of the buckling problem for a rectangular composite sandwich plate with two parallel simply supported edges and another two edges clamped (SSCC) is presented in the paper. The plate is composed of two identical composite facings and orthotropic core, and subjected to in-plane uniform compressive load applied to the simply supported edges. Buckling equations are derived based on the first-order shear deformation theory. The problem is solved using the Levy and Galerkin methods. The analytical formula for the critical load has been obtained and verified using finite-element analysis. The design analyses have been performed for the sandwich panels subject to constraints imposed on the value of buckling load. [ABSTRACT FROM AUTHOR]

In this study, the buckling and compressive failure of adhesively-bonded stepped-lap joints (with/without composite patches) composed of pultruded glass fiber-reinforced polymer composite laminates was investigated experimentally and numerically. Two-component epoxy adhesive was used for bonding purposes. Composite patches were woven glass-epoxy layer. They were added onto the conventional stepped-lap joints so that additional load transfer paths were created and localized stress concentrations near joint edge were reduced. The axial compression tests were performed and the results revealed that the buckling and failure load of new stepped lap composite joints with composite patches were significantly higher than the conventional stepped lap joints. The influence of the overlap length was evaluated. For both types of joints, a small increase was observed in failure loads by increase of the overlap length. Numerical results showed a very good agreement with experimental results. [ABSTRACT FROM AUTHOR]

In this article, a new three-dimensional finite element modeling approach with less computing time and space is introduced to study the buckling behavior of sandwich panels, containing a face–core debond. The finite element model presented in this study relates the motion of the face sheets to the core through constraint equations utilizing the concept of slave and master nodes, thus representing a more realistic model of the sandwich panel. The composite face sheets are modeled with shell elements, and the core is modeled using the 3D structural solid elements capable of taking transverse flexibility into consideration. In order to model the debond, the constraints between the nodes of the face sheet and the core are removed and replaced with contact elements in the debonded region to avoid interpenetration. The model is validated through comparison with experimental results reported in the literature. The validated model is then used to study the effects of the size, shape, aspect ratio of the debond, as well as fiber orientation of the face sheets and the influence of core stiffness on the buckling load of the panel subject to different boundary conditions on the top and bottom face sheets of the panel. [ABSTRACT FROM AUTHOR]

The in-plane load-bearing capacity of marine composite plates is an area that has received little attention, in contrast to the significantly larger buckling and post-buckling studies available on aeronautical composites. The aim of this study is to investigate experimentally the strength to failure of large woven composite panels and correlate the results with finite element analyses. The tests performed were able to demonstrate the well-known sensitivity of the panels to boundary conditions and panel imperfection size, which is also reflected in a parametric study carried out in Abaqus/Standard. Two-dimensional stress-based failure criteria were implemented via a user-defined field (USDFLD) subroutine to detect matrix and fiber damage, which allows progressive damage to be modeled. A modification of Hashin’s failure criteria proved to be the most effective in capturing both the size and location of the damage and obtain a good approximation of the load—displacement history and surface strains. [ABSTRACT FROM AUTHOR]

This study has been designed to experimentally assess the changes of buckling loads of the E-glass fiber/epoxy composite laminates impacted at different impact energy levels. With the experiments conducted, the effects of the geometry parameters such as the ratio of impact point to the length of buckling (G = y/L) have been examined. According to the results of the experiments made, when the ratio of impact position is 0.2, buckling behaviors of the impacted specimens made at the energy levels of and under 10 J have been determined to be almost the same as the buckling behaviors of the non-impacted specimens. Generally, it has been found out that buckling behaviors of the impacted specimens made at the energies under such levels of energy as 15 J increase with the impact point ratio, and when the ratio is 0.2, buckling behaviors have been observed to be maximum. [ABSTRACT FROM AUTHOR]

Explicit expressions are developed for the buckling analyses of rectangular (long) plates: for 'linearly varying axial load' the known results for hinged supports are corrected and new results are presented for built-in and constrained edges; for 'shear load' new results are presented for constrained edges; for 'uniform compression' new results are presented when the longitudinal edges are rotationally constrained by stiffeners. The results are based on the Rayleigh-Ritz method. [ABSTRACT FROM AUTHOR]

Cut-outs are often found in composite structures. These are provided with structural components for ventilation and sometimes to lighten the structure. This article addresses the effects of a cut-out on the buckling behavior of rectangular plates made of polymer matrix composites. While the loaded edges are modeled in simply supported boundary conditions, the unloaded edges are taken as free. Finite element analysis is also performed to predict the effects of cut-outs on the buckling behavior of these plates. Several key findings and behavioral characteristics are discussed. These findings include the effects of cut-out size, cut-out orientation, and corner fillet radius conditions. Some overall important findings of these studies are that the critical buckling loads are not changed by increasing cut-out orientation angle and hole corner fillet radius. The maximum variation was obtained as 5.91% by increasing the hole orientation angle in the buckling loads. [ABSTRACT FROM AUTHOR]

The influence of square cut-out upon the buckling stability of multilayered, steel woven fiber-reinforced polypropylene thermoplastic matrix composite plates are studied by using numerical and experimental methods. The laminated plates ([0°]3) under uniform pressure are formed by stacking three composite layers bonded symmetrically. The FE and experimental results are presented for various fiber orientation angles and plate boundary conditions. The critical buckling loads are more affected by square holes under clamped edge boundary conditions than by the simple supported edge case. The biggest decreases in the critical buckling loads are observed between 0° and 15° fiber orientations. [ABSTRACT FROM AUTHOR]

In this study, vibration and buckling of axially functionally graded simply supported beams is analyzed by using the semi-inverse method. Euler-Bernoulli beam theory was used in the analysis. By using a pre-specified frequency and buckling loads, variation of the Young's modulus in the axial direction is obtained in terms of the axial coordinate. It is found that the Young's modulus changes exponentially between the edges of the beam for the vibration and buckling problem. [ABSTRACT FROM AUTHOR]

The buckling of laminated metal-matrix composite (MMC) plates with a central square cutout were analyzed under compressive biaxial loading using the finite element approach. The MMC plates displayed some interesting buckling patterns and initial buckling shapes when subjected to different combination of hole sizes and boundary conditions. In the case of anti-symmetric, free-free boundary conditions, the MMC plates with central square cutout resist higher buckling loads as the hole size increased. Two laminated stacking sequences [90/0/0/90]2 and [45/-45/-45/45]2 were used in this study. For the same hole size, plate aspect ratio, and boundary conditions, the results showed that the critical buckling behavior of the plates were primarily influenced by the edge boundary conditions rather than by the laminated stacking sequences. The overall critical buckling analysis indicated that plates with clamped boundary conditions will take higher compressive loads than that of simply supported boundary conditions by a ratio of 2 to 1. [ABSTRACT FROM AUTHOR]

A cone calorimeter is modified to study the effect of simultaneous high heat flux surface heating and compressive loading on the failure time of fiberglass-reinforced vinyl-ester matrix polymeric composites. Compressive loading of test samples during heat exposure is achieved by using a specially designed mechanical loading fixture that mounted directly below a radiant cone heater. Using specimens with a heated length of 74 and 100mm, the effect of surface heat fluxes from 25 to 75 kW/m² and compressive loads from 3.5 to 10.5 MPa on failure time and failure mode is examined. For an intermediate heat flux level of 50 kW/m², the time-to-failure of the composite varied from 404s at 3.5MPa to 131s at 10.5MPa. All test conditions cause catastrophic failure instability, even at compressive stresses as low as 3.5 MPa. Measurement of the axial and transverse displacements of specimens shows the existence of a thermal bending moment during the combined thermal and mechanical loading. In addition to experimental results for the relationship between heat flux, compressive load and failure-time, details of the experimental procedure, including the modifications made to the cone calorimeter to allow simultaneous mechanical loading are discussed. [ABSTRACT FROM AUTHOR]

In the present study, unified shear deformation theory which was proposed by Soldatos, K.P. and Tımarcı, T. (1993). A Unified Formulation of Laminated Composite, Shear Deformable Five-degrees-of-freedom Cylindrical Shells on the Basis of a Unified Shear Deformable Shell Theory, Compos. Struct., 25(1-4): 165-171 is used to analyze simply supported symmetric cross-ply rectangular plates for deflections, stresses, natural frequencies, and buckling loads. This theory enables the selection of different in-plane displacement components to represent shear deformation. Exponential shear deformation theory, which is proposed by Karama et al., 40(6) (2003). Mechanical Behavior of Laminated Composite Beam by New Multi-layered Laminated Composite Structures Model with Transverse Shear Stress Continuity, Int J Solids Struct., 40: 1525-1546, is used for the first time to analyze the problem considered. Results which are found by exponential theory are compared with those obtained by using the parabolic shear deformation theory of Reddy, J.N., 51(4) (1984). A Simple Higher-order Theory for Laminated Composite Plates, J Appl Mech., 51: 745-752, the trigonometric shear deformation theory of Touratier, M., 29(8) (1991). An Efficient Standard Plate Theory, Int. Jnl. Engng. Sci., 29(8): 901-916, the hyperbolic shear deformation theory of Soldatos, K.P., 94(3-4) (1992). A Transverse Shear Deformation Theory for Homogeneous Monoclinic Plates, Acta Mech., 94: 1995-220 and with the available three-dimensional elasticity solutions. The study shows that while the transverse displacement and the stresses are best predicted by the exponential shear deformation theory, the parabolic shear deformation and the hyperbolic shear deformation theories yield more accurate predictions for the natural frequencies and the buckling loads. [ABSTRACT FROM AUTHOR]

The buckling of composite laminates subjected to in-plane partial edge compression is studied using a refined plate theory. In this theory, transverse shear stresses are continuous at the layer interfaces along with stress-free conditions at the top and bottom surfaces of the plate. It is quite interesting to note that the plate model having all these refined features requires unknowns only at the reference plane. However, this theory demands CI continuity of transverse displacement at the element edges, which is difficult to accommodate in any existing finite element. The present study is made by a new triangular element developed for the purpose. [ABSTRACT FROM AUTHOR]

In this study, buckling analysis of laminated composite circular plates having circular holes and subjected to uniform radial load is investigated by using the finite element method. The effects of hole sizes, location of the holes, thickness variations and boundary conditions on the critical buckling load, and the buckling mode shapes of the composite plates are determined. Eight node isoparametric shell elements with 24 degrees of freedom are used during the investigation. [ABSTRACT FROM AUTHOR]

This paper contributes newly developed closed-form buckling solutions for generic one-edge-free problems common to partially disbonded composite structures. These solutions are shown to be accurate by comparison with experimentally measured buckling loads which are also reported in this paper. The buckling of partially disbonded regions in adhesive joints is a safety concern due to the potential for ensuing buckling-driven disbond growth. In order to design structures to be tolerant to these flaws, closed-form expressions that predict buckling load have been developed based on a one-edge-free buckling model. Comparison of the closed-form predictions with the finite element results verifies the accuracy of the solutions. Validation of these analyses was achieved by comparison with the experimentally determined buckling loads. These were measured to fall within a range of predicted values, as defined by the choice of boundary condition opposite the disbonded flange-free-edge: either clamped or simply-supported. Assumption of either boundary condition provides upper- and lower-bound predictions of buckling in partially disbonded joint flange configurations. [ABSTRACT FROM AUTHOR]

In this study, thermal buckling behaviors of the composite square plates consisting of antisymmetric four laminates with angle crack are examined. Finite element method is used for the solution. First critical buckling loads of an orthotropic plate without crack subjected to unidirectional compression are found. Constraint conditions have been taken two edge clamped and the other edges are free. The thickness of plate is 2 mm (each layer has 0.5 mm thickness). Thermal buckling behaviors of this plate are examined and critical temperatures are determined. Values have been given in the graphs and discussions are presented in the conclusion. [ABSTRACT FROM AUTHOR]

Experimental determination of the flexural and torsional properties of pultruded FRP profiles, based on full section and coupon tests, is described. Results for a range of I-profiles indicates that transverse shear moduli, determined from full section three point bending tests, are influenced significantly by localised deformation at the supports. Closed form solutions for the influence of shear deformation on global flexural, torsional and lateral buckling of pultruded FRP profiles have been developed. Parametric studies for a range of I-profiles indicate that shear deformation can reduce flexural and torsional buckling loads by up to 10%. For wide flange I-profiles pre-buckling displacements can increase lateral buckling moments by more than 20% while the influence of shear deformation is relatively minor. [ABSTRACT FROM AUTHOR]