Anti-symmetric Lay-up Research Articles

Thermal buckling load optimization of laminated composite plates

In this study, the applicability of the Modified Feasible Direction (MFD) method on the thermal buckling optimization of laminated plates subjected to uniformly distributed temperature load is investigated. The objective function is to maximize the critical temperature capacity of laminated plates and the fiber orientation is considered as design variable. The first-order shear deformation theory is used in the mathematical formulation. For this purpose, a program based on FORTRAN is used for the optimization of laminated plates. Finally, the effect of aspect ratio, antisymmetric lay-up, boundary condition, material anisotropy, ratio of coefficients of thermal expansion, and hybrid laminates on the results is investigated and the results are compared.

Frequency optimization of laminated composite angle-ply plates with circular hole

The fundamental frequencies of simply supported symmetrically laminated composite angle-ply plates with central circular holes with a given material system are maximized with respect to fibre orientations. The first-order shear deformation (FSDT) theory is used for finite element analysis. Modified feasible direction (MFD) method is used for the optimization routine. Also, the optimum fibre orientations are obtained using golden section (GS) method to compare with MFD method. Finally, the significant effects of different number of layers, boundary conditions, plate aspect ratios, hole diameter-to-width ratio, material anisotropy and antisymmetric lay-up on the results are demonstrated.

LATERAL DYNAMIC STABILITY ANALYSIS OF A CANTILEVER LAMINATED COMPOSITE BEAM WITH AN ELASTIC SUPPORT

In this paper, static and dynamic stabilities of a cantilever laminated composite beam, having a linear translation spring as elastic support whose position is changeable from the free end to midspan of the beam, subjected to periodic vertical end loading, are examined. The beam is assumed to be an Euler beam and the finite element model used can accommodate symmetric and antisymmetric lay-ups. Solutions referred to as combination resonance are investigated for the dynamic stability analysis. The effects of length-to-thickness ratio, the variation of cross-section in one direction, orientation angle, static and dynamic load parameters, stiffness and position of the elastic support on stability are examined.

Residual Strength after Low Velocity Impact in Carbon-Epoxy Laminates

The aim of present work is to study the influence of low energy impacts on residual strength of carbon-epoxy laminates. Experimental tests were performed on [0,90,0,90]2s and [0,90]8 laminates using a drop weight-testing machine. The influence of the laminate stacking sequence is analysed under 1.5 J, 2 J, 2.5 J and 3 J impact energies, corresponding to a 0.91 ms-1, 1.05 ms-1, 1.18 ms-1 and 1.29 ms-1 of impact velocity, respectively. The impacted plates were inspected by CScan to evaluate the size, shape and position of the delaminations through the thickness of the plate. The same plates were inspected by C-Scan before the impact, to evaluate the eventual presence of defects produced during the manufacturing process. The residual flexural strength showed that the [0,90,0,90]2s laminates have better performance than the [0,90]8 ones. The explanation is related with the lower flexural stiffness of the antisymmetric lay-up relatively to the symmetric one.

Closed-form analysis of thin-walled composite I-beams considering non-classical effects

In this work, a closed-form analysis of thin-walled open profile composite beams such as I-beam has been performed. The analysis includes the effects of elastic couplings, shell wall thickness, transverse shear deformation, torsion warping, and constrained warping. A mixed beam approach based on Reissner’s semi-complementary energy functional is used to derive the beam force–displacement relations. A closed-form solution for the static response of both symmetric and anti-symmetric layup beams with transverse shear couplings is derived. The beams considered have the boundary condition of one end fixed and the other end warping restrained and are subjected to unit bending or torque load at the beam tip. The shear flow distribution related with the applied forces and moments along the contour of the beam is also identified. The static results of composite I-beams have been validated against those of detailed two-dimensional finite element analysis. The effects of warping restraint and transverse shear deformation on the static behavior of open-section composite beams are investigated in the analysis.

Anisotropic effects in the compression buckling of laminated composite cylindrical shells

This paper addresses two aspects of buckling relevant to design. The first describes the preliminary experimental results that validate the presence of a newly reported spiral buckling mode; whilst the second concerned the effects of extension/twist anisotropy on the buckling loads of cylindrical shells under compression. The influence of designing laminates with antisymmetric lay-ups in comparison with a symmetrical lay-up is also investigated. Antisymmetric quasi-isotropic laminates, based on 0, 90 and ±45° angles produces greater buckling loads than the equivalent symmetric lay-up. Whilst all anisotropic coupling effects appear to lower the buckling loads, a laminate that is 48 plies thick is necessary to eliminate them in thin-walled shells. Such a laminate is at least 6 mm thick. Many designs require thinner laminates, and in so doing, mitigate the need for guidelines on efficient anisotropic lay-ups. Neglecting the effect of prebuckling deformation, it is found that extension/twist coupling is less deleterious than flexural/twist coupling in this respect. Therefore, antisymmetric laminates appear preferable for initial buckling of quasi-isotropic laminates.

Compression tests on anti-symmetric two-ply GFRP cylinders

Abstract This article deals with the experimental buckling behaviour of glass fibre-reinforced plastic (GFRP) cylinders under concentric and eccentric compression. The laminates are of type ‘Rovimat 1200’ consisting of woven glass-fibre roving within a polyester resin matrix. Two-ply cylinders, for which the nominal radius-to-thickness ratio is about 108, with anti-symmetric lay-up of different orientation and overlapping procedure, are examined. In particular, the comparative response of cross-ply and angle-ply configurations is investigated and discussed. The results of experiments on eight models are presented including thickness and imperfection mapping, load and strain measurements as well as salient observations regarding the behaviour of each model. Systematic and automated data acquisition techniques using a laser scanning system and computer-controlled loading procedures were used in order to provide the experimental measurements in a form that can be readily used for further analytical and design studies. The results demonstrate the significant influence of laminate orientation and loading eccentricity on the buckling strength of anti-symmetric cross-ply and angle-ply GFRP cylinders.

Some studies on buckling of laminated composite thin walled box beams

Buckling of laminated composite thin walled rectangular box beam configurations has been studied. The increasing use of composite materials in the construction of aeronautical and civil engineering structures has generated a special interest in the analysis of elastic stability of laminated composite structure subjected to inplane loadings. The effect of number of layers, lay-up sequence and fibre angle on the buckling load is studied for symmetric and anti-symmetric lay-ups.

Higher-order shear deformation theory for thin-walled composite beams

A higher-order shear deformation theory for the static and dynamic analysis of thin-walled composite beams of arbitrary lay-ups and cross sections is presented. The method is applicable to beams of open as well as closed cross sections. The formulation includes Euler-Bernoulli and Timoshenko theories as subsets. The bendingand torsion-related warping functions are derived in closed form. The method is validated by comparison with experimental and analytical results for static deflections of composite beams with symmetric and antisymmetric lay-ups. Comparison with experimental results for the vibration of beams exhibiting bending torsion coupling shows that the present method gives better correlations. The significance of the higher-order theory is brought out by validating the results of the analyses against results from other theoretical methods. The results show the importance of the lay-up sequence on the shear lag in thin-walled composite beams.

Thin-walled composite beams under bending, torsional, and extensional loads

Symmetric and antisymmetric layup graphite-epoxy composite beams with thin-walled rectangular cross sections are fabricated using an autoclave molding technique and tested under bending, torsional, and extensional loads. The bending slope and elastic twist at a station are measured using an optical system, and the results correlated with predicted values from a simple beam analysis as well as a refined finite element analysis. A symmetric ply layup results in bending-twist coupling whereas an antisymmetric layup causes extension-twist coupling. Simple analytical results with plane-stress assumption agree better with measured data as well as finite element predictions than with plane-strain assumption. For symmetric layup beams, the bending-induced twist and torsion-induced bending slope are predicted satisfactorily using simple analytical solution. Correlations with measured data, however, are generally improved using a finite element solution. For antisymmetric beams, axial force-induced twist is predicted satisfactorily by both methods.

The Effects of Moisture Induced Swelling Upon the Shapes of Anti-Symmetric Cross-Ply Laminates

This paper presents an investigation of the effects of moisture-induced swelling upon the out-of-plane warping of general anti-symmetric cross-ply composite laminates. The analy sis assumes linear elastic material behavior and includes non-linear geometric effects. Ap proximate solutions are obtained by assuming kinematically admissible expressions for the mid-plane displacements in terms of several generalized coordinates which are subse quently found by requiring a minimal value for the total potential energy of the laminate. It is shown that any specific anti-symmetric cross-ply lay-up will assume either a unique "saddle" shape or one of two possible approximately cylindrical shapes depending upon the in-plane dimensions of the laminate and the amount and distribution of moisture within the laminate.