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We examine numerically the uniaxially compressed stability of triaxially woven fabric (TWF) composites employing a proposed geometrically nonlinear finite composite plate element model with volume segmentation ABD constitutive relation, taking advantage of greatly reduced degrees of freedom. From satisfactory agreement with results from literature, numerous boundary conditions are explored for various aspect ratios in the buckling analysis. High dependencies of post-buckling patterns on plate aspect ratios are observed, from which a computationally time-saving characteristic equations have been defined before the occurrence of post-buckling state for practical convenience, best described on the basis of logarithmic critical buckling load and stiffness factor. These buckling characteristics have a direct general correlation to TWF’s aspect ratios and boundary rigidities. [ABSTRACT FROM AUTHOR]

The influence of periodical imperfections on the buckling load value of shallow elastic closed conical shells undergoing external pressure was investigated by numerical analysis. Results are compared with experimental data. It is established that initial imperfections significantly influence the buckling pressure value only for large imperfection amplitude (an order of magnitude more than the shell thickness). The existence is established of the effect of a ‘static resonance’. [ABSTRACT FROM AUTHOR]

This paper presents a new higher-order shear deformation theory for static, buckling and free vibration analysis of functionally graded sandwich beams. In this theory, the axial displacement accounts for a third-order and inverse trigonometric distribution, and the transverse shear stress satisfies the traction-free boundary conditions on the top and bottom surfaces of the beams. Governing equations of motion are derived from the Hamilton’s principle for sandwich beams with homogeneous hardcore and softcore. Navier-type solution for simply-supported beams is developed to solve the problem. Numerical results are obtained to investigate effects of the power-law index, span-to-height ratio and thickness ratio of layers on the displacements, stresses, critical buckling load and frequencies. [ABSTRACT FROM AUTHOR]

Stacking sequence design is indispensable to make efficient use of the material properties of laminated composite materials. These laminated composites are usually fabricated from unidirectional plies of given thickness with fiber orientations limited to a small set of angles (e.g., 0°, +45°, –45°, and 90°). This leads to a combinatorial optimisation problem, which is rather complex to solve. In this paper, a new multi-population-based harmony search algorithm with dynamic interaction of populations, hybridised with a customised neighborhood algorithm to solve the layup sequence design problem of laminate composite plate is presented. Numerical experiments have been carried out by first considering the buckling and failure load optimisation of a laminate composite plate and later studies have been carried out using hybrid laminate plates for maximisation of buckling load and fundamental frequency with varied levels of hybridisation and for various plate aspect ratios. Numerical studies carried out in this paper clearly indicate that proposed dynamic hybrid adaptive harmony search algorithm is an effective combinatorial optimisation tool for stacking sequence optimisation of laminate composite structures and the computational performance is found to be superior when compared to other popular implementations of harmony search algorithm. [ABSTRACT FROM PUBLISHER]

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]

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]

This paper deals with the failure of compression-loaded sandwich panels with an implanted circular face/core debond. Uniform compression tests were conducted on intact sandwich panels with three different types of core material (H130, H250 and PMI) and on similar panels with circular face/core debonds having three different diameters. The strains and out-of-plane displacements of the panel surface were monitored using the digital image correlation technique. Mixed mode bending tests were conducted to determine the fracture toughness of the face/core interface of the panels. Finite element analysis and linear elastic fracture mechanics were employed to determine the critical buckling load and compression strength of the panels. Modeling approaches and failure criteria are discussed. Numerically determined crack propagation loads in most of the cases show a fair agreement with experimental results, but in a few cases up to 45% deviation is seen between numerical and experimental results. This can be ascribed to several factors such as the large scatter in the measured interface fracture toughness, differing crack tip details and crack growth mechanisms between the panels and the mixed mode bending specimens. Tentative strength reduction curves are presented, but uncertainty concerning the intact strengths of the materials used needs to be removed before these can be utilized with confidence. [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]

A novel approach to the optimization of flexible columns against buckling is presented. The problem of determining the shape of the column that has possibly the largest critical buckling load of columns of a given length and volume is solved for composite materials. The objective of this study was to develop and design an optimized composite column against buckling. Determining what shape of column has the largest possible buckling load of composite column of a given length and volume was considered. Clamped-clamped supported column is an important limit case because it caused debate in many publications. Moreover, in this study, the optimization problem of the clamped-clamped column under buckling load, which was previously dealt with by Tadjbakhsh and Keller [5], Olhoff and Rasmussen [6] and Masur [7] is reinvestigated. It is also proved that the solutions of Tadjbakhsh and Keller, Olhoff and Rasmussen and Masur are not optimum for columns with clamped ends. The present model formulation considers columns for which crush is taken into account in the formulation of the column optimization problem, allowing for bimodal optimum solution. This leads to the necessity for both stability and crush criterion formulation of the optimization problem. The new proposed optimum model solution has been verified with numerical analysis using ANSYS and experimental data for columns with clamped-clamped ends. It was shown that the new proposed model was given the optimum solution for the clamped-clamped case. Detailed results are presented and discussed for clamped-clamped columns having circular cross-sectional configuration. As a result of this study, it was shown that results obtained in previous studies of variation optimum cross-sectional area for columns under compressive forces clamped-clamped ends were erroneous. The corrected optimum form was obtained and results checked by numerical calculations and experimental tests of composite columns. [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]

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]