Showing papers by "J. N. Reddy published in 1991"

Thermal stresses and deflections of cross-ply laminated plates using refined plate theories

Abstract: Exact analytical solutions of refined plate theories are developed to study the thermal stresses and deflections of cross-ply rectangular plates. The state-space approach in conjunction with the Levy method is used to solve exactly the governing equations of the theories under various boundary conditions. Numerical results of the higher-order theory of Reddy for thermal stresses and deflections are compared with those obtained using the classical and first-order plate theories.

A study of non-linear dynamic equations of higher-order shear deformation plate theories

Abstract: The non-linear dynamic equations of the first-order shear deformation theory and the third-order shear deformation plate theory of Reddy are reformulated into equations describing the interior and edge-zone problems of rectangular plates. Viscous damping terms are also included. It is shown that, for certain boundary conditions, the number of governing equations can be reduced to three, as in the classical plate theory. Two problems related to static large-deflection and dynamic small-deflection of rectangular plates are considered. Numerical results are presented to demonstrate the effects of non-linearity, shear deformation, rotatory inertia, damping and sonic boom type loadings.

Finite-Element Analysis of Adhesive Joints

Abstract: Adhesive bonding is increasingly used to fasten metallic to metallic or metallic to composite structural components together. This is because in many present-day applications, conventional fasteners such as bolts, rivets, welds, etc., are unsuitable, especially if the components are made of polymeric or composite materials. The sonar transducer adhesively bonded acoustical window, the likely necessity of the repair of the composite structural components of carrier-based aircraft, and door inner assembly to outer panel, main body frame joints, trunk lid inner to outer and sealants in an automobile provide examples of such applications. Penetration methods (i.e., drilling holes, etc.) cause high stress concentrations and, in the case of composites, sever the fiber reinforcement which in turn reduces the strength of the joint. On the other hand, bonded joints tend to be damage-tolerant due to the high damping behavior of the adhesive layer and less expensive due to lower fabrication cost. The use of adhesives increases the joint strength, distributes the loads more evenly, and enables alternative jointing methods to be reduced or eliminated. Dissimilar materials (e.g., steel, aluminum, plastics, glass, etc.) can be joined together by bonding even where it is impossible to gain access to either side of the joint, thereby increasing the design flexibility.

A Unified Formulation of Micromechanics Models of Fiber-Reinforced Composites

Abstract: In a micromechanics constitutive model the overall instantaneous properties of fibrous composites are defined by relations between overall stress and strain averages Such averaging techniques are also known as ‘homogenization’ The models may account for fiber, matrix and fiber-matrix interface properties and their interactions (see [1–5]) Various micromechanics approaches are used to calculate overall stress and strain fields using different representative micro-geometries (ie unit cells); see, for example, the self-consistent method of Hill [1], the variational formulation of Hashin [2], the vanishing fiber diameter model of Dvorak and Bahei-El-Din [3], periodic rectangular array of Aboudi [4], and the periodic hexagonal array (PHA) model of Teply and Dvorak [5] Although various models use different representative geometries of the unit cell and different approximations of the displacements and/or stresses to obtain the overall properties, they all share certain common basis The present paper has the objectives of finding the common basis so that the models can be related to each other

Postbuckling response and failure prediction of flat rectangular graphite-epoxy plates loaded in axial compression

Abstract: The objectives of the study are to assess the capability of a first-order shear deformable degenerated shell finite element theory to predict the postbuckling response and failure modes of various graphite-epoxy panels loaded in axial compression. Two panels without holes and one with a hole are studied, and the resulting responses and failure modes correlated well with the experimental results. A progressive damage failure mechanism is applied in the nonlinear analysis, which proved successful in predictions of failure location, mode, and load.

On the modeling of delamination in thick composites

Abstract: The layerwise laminate theory of Reddy (1989) is used to develop a layerwise, two-dimensional, displacement-based, finite element model of laminated composite plates that provides a convenient format for modeling multiple delaminations. The resulting layerwise model is capable of computing interlaminar stresses, free edge effects, and energy release rates with the same accuracy as a conventional 3D finite element model. Although the total degrees of freedom are comparable in both models, the layerwise, two-dimensional format allows faster computation of the element stiffness matrices. Two example problems are provided to illustrate the accuracy of the present model in computing interlaminar stresses and energy release rates for laminates in bending and extension.

A Probabilistic Postbuckling Analysis of Composite Shells

Abstract: A probabilistic finite element analysis procedure for postbuckling analysis of laminated composite shells is developed. The total Lagrangian formulation, employing a degenerated 3-D laminated composite shell finite element with the full Green-Lagrange strains and first-order shear deformable kinematics is used. The first-order second-moment technique for probabilistic finite element analysis of random fields is employed and results are presented in the form of mean and variance of the structural response. Reliability calculations are made by using the first-order reliability method combined with sensitivity derivatives from the finite element analysis. Two examples are solved to illustrate the variability of shell and panel postbuckling problems. In general, the procedure is quite effective in determining the response statistics and reliability for postbuckling behavior of laminated composite shells.