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Hygrothermal effects on free vibration of woven fiber glass/epoxy laminated composite cylindrical shallow shells are investigated both numerically and experimentally. In the present finite element analysis a composite doubly curved shell model based on first order shear deformation theory (FSDT) is used for free vibration of cylindrical shell panels in hygrothermal environment. B&K FFT analyzer is used to determine the natural frequencies of vibration experimentally by conducting non-destructive testing. The effects of curvature ratios, lamination sequences and boundary conditions on natural frequencies of vibration under hygrothermal loading are investigated. The frequency of vibration decreases with increase of temperature and moisture. [ABSTRACT FROM AUTHOR]

The present study deals with the finite element analysis of parametric instability characteristics of delaminated bidirectional Glass/Epoxy composite panels exposed to hygrothermal field with harmonic in-plane loading based on first order shear deformation theory. An 8-noded isoparametric finite element model was developed which takes account of the influences of area delamination and hygrothermal environment for predicting dynamic instability regions of composite flat panels. Validation of numerical results from finite element analysis was done with those available from previous researches. The influences of various parameters like static load factor, area of delamination, temperature, moisture, fiber orientations, boundary conditions and stacking sequence on the dynamic instability regions of bidirectional Glass/Epoxy flat panels were investigated. Significant effects of these parameters on the dynamic stability characteristics of composite plates were observed and discussed. [ABSTRACT FROM AUTHOR]

Abstract: The present study deals with the effects of moist environment on the natural frequencies of vibration of Glass/Epoxy woven fibre composite doubly curved panels with strip delamination using the finite element method (FEM). For modelling the delamination, multipoint constraint algorithm is incorporated in the analysis. The effects of boundary condition, delamination size and shape of panels on natural frequencies of vibration are investigated in the moisture content range. The frequencies of vibration reduce with increase of moisture in delaminated curved panels. The reductions of frequencies are more prominent for higher degree of moisture concentrations and significantly affected by boundary conditions. [Copyright &y& Elsevier]

Abstract: Free vibration response of laminated composite shells with delamination is presented using the finite element method based on first order shear deformation theory. The shell theory used is the extension of dynamic, shear deformable theory according to the Sanders'' first approximation for doubly curved shells, which can be reduced to Love''s and Donnell''s theories by means of tracers. An eight-noded C 0 continuity, isoparametric quadrilateral element with five degrees of freedom per node is used in the formulation. For modeling the delamination, multipoint constraint algorithm is incorporated in the finite element code. The natural frequencies of the delaminated cylindrical (CYL), spherical (SPH) and hyperbolic paraboloid (HYP) shells are determined by using the above mentioned shell theories, namely Sanders'', Love''s, and Donnell''s. The validity of the present approach is established by comparing the authors'' results with those available in the literature. Additional studies on free vibration response of CYL, SPH and HYP shells are conducted to assess the effects of delamination size and number of layers considering all three shell theories. It is shown that shell theories according to Sanders and Love always predict practically identical frequencies. Donnell''s theory gives reliable results only for shallow shells. Moreover, the natural frequency is found to be very sensitive to delamination size and number of layers in the shell. [Copyright &y& Elsevier]

• A formulation for vibration of composite beam with cracks is presented. • A program is developed in MATLAB environment based on finite element method. • Natural frequencies of vibration are obtained experimentally and numerically. • Effect of boundary, location and depth of cracks on the frequencies is analyzed. Composite beams are increasingly used in aerospace, automobile, and other applications. Crack is the most common defect in structures during its service life. The cracked composite beams are subjected to dynamic loads and the vibration of the cracked beams is of technical significance to the structural integrity of systems. The objective of the present investigation is to demonstrate the vibration characteristics of a laminated composite beam (LCB) with multiple transverse cracks. Finite element method (FEM) is used for the frequency-based crack analysis in this study. A computer program is developed in MATLAB environment for numerical analysis. First-order shear deformation theory (FSDT) is adopted for the finite element analysis. Natural frequencies of vibration are computed through the eigenvalue solver. Composite specimens are fabricated using hand lay-up technique and are tested for its material constants under tensile test. Experiments are conducted using woven roving Glass/Epoxy laminated beam samples with pre-defined cracks. The obtained test results from the experimental work using FFT analyzer are validated with the numerical results obtained through MATLAB. The effects of natural frequencies with respect to the various boundary conditions, crack depth and locations are investigated to support in real applications. A fine agreement is accomplished between the numerical and test results. Both the studies showed that natural frequencies in the LCB are significantly influenced by the location and size of the cracks. The results show that natural frequencies are decreased with cracks and an increase in fiber orientation. [ABSTRACT FROM AUTHOR]

The stochastic dynamic stability analysis of laminated composite curved panels under non-uniform partial edge loading is studied using finite element analysis. The system input parameters are randomized to ascertain the stochastic first buckling load and zone of resonance. Considering the effects of transverse shear deformation and rotary inertia, first order shear deformation theory is used to model the composite doubly curved shells. The stochasticity is introduced in Love's and Donnell's theory considering dynamic and shear deformable theory according to the Sander's first approximation by tracers for doubly curved laminated shells. The moving least square method is employed as a surrogate of the actual finite element model to reduce the computational cost. The results are compared with those available in the literature. Statistical results are presented to show the effects of radius of curvatures, material properties, fibre parameters, and non-uniform load parameters on the stability boundaries. [ABSTRACT FROM AUTHOR]

The present computational study investigates on stochastic natural frequency analyses of laminated composite curved panels with cutout based on support vector regression (SVR) model. The SVR based uncertainty quantification (UQ) algorithm in conjunction with Latin hypercube sampling is developed to achieve computational efficiency. The convergence of the present algorithm for laminated composite curved panels with cutout is validated with original finite element (FE) analysis along with traditional Monte Carlo simulation (MCS). The variations of input parameters (both individual and combined cases) are studied to portray their relative effect on the output quantity of interest. The performance of the SVR based uncertainty quantification is found to be satisfactory in the domain of input variables in dealing low and high dimensional spaces. The layer-wise variability of geometric and material properties are included considering the effect of twist angle, cutout sizes and geometries (such as cylindrical, spherical, hyperbolic paraboloid and plate). The sensitivities of input parameters in terms of coefficient of variation are enumerated to project the relative importance of different random inputs on natural frequencies. Subsequently, the noise induced effects on SVR based computational algorithm are presented to map the inevitable variability in practical field of applications. [ABSTRACT FROM AUTHOR]