Showing papers by "J. N. Reddy published in 1993"
TL;DR: In this paper, a layerwise, two-dimensional, displacement-based, finite element model of laminated composite plates is proposed to compute interlaminar stresses and other localized effects with the same level of accuracy as conventional 3D finite element models.
Abstract: The layerwise laminate theory of Reddy (1987) is used to develop a layerwise, two-dimensional, displacement-based, finite element model of laminated composite plates that assumes a piecewise continuous distribution of the tranverse strains through the laminate thickness. The resulting layerwise finite element model is capable of computing interlaminar stresses and other localized effects with the same level of accuracy as a conventional 3D finite element model. Although the total number of degrees of freedom are comparable in both models, the layerwise model maintains a 2D-type data structure that provides several advantages over a conventional 3D finite element model, e.g. simplified input data, ease of mesh alteration, and faster element stiffness matrix formulation. Two sample problems are provided to illustrate the accuracy of the present model in computing interlaminar stresses for laminates in bending and extension.
451 citations
TL;DR: In this article, a review of equivalent single-layer and layerwise laminate theories is presented and their computational models are discussed, where the layerwise theory advanced by the author is reviewed and a variable displacement finite element model and the mesh superposition techniques are described.
317 citations
TL;DR: In this article, the results obtained from this theory are compared with those obtained from a full-fledged three-dimensional elasticity analysis and various equivalent single-layer theories that are available, such as the classical laminated plate theory (CLPT), the first-order shear deformation laminated plates theory (FSDPT), and the third-order Shear Deformation Plate theory (THSDPT).
Abstract: Reddy's layerwise theory is used. The results obtained from this theory are compared with those obtained from a full-fledged three-dimensional elasticity analysis and various equivalent single-layer theories that are available. These include the classical laminated plate theory (CLPT), the first-order shear deformation laminated plate theory (FSDPT), and the third-order shear deformation plate theory (THSDPT). The elasticity equations are solved by utilizing the state space variables and the transfer matrix
230 citations
19 Apr 1993
77 citations
TL;DR: In this paper, a 3D progressive failure algorithm is developed, where the layerwise laminate theory (LWLT) of Reddy is used for kinematic description, and a parametric study is conducted to investigate the effect of out-ofplane material properties, 3D stiffness reduction methods, and boundary conditions on the failure loads and strains of a composite laminate under axial extension.
Abstract: A three-dimensional (3D) progressive failure algorithm is developed, where the layerwise laminate theory (LWLT) of Reddy is used for kinematic description. The finite element model based on the layerwise theory predicts both inplane and interlaminar stresses with the same accuracy as that of a conventional 3D finite element model and provides a convenient format for modeling the 3D stress fields in composite laminates. A parametric study is conducted to investigate the effect of out-of-plane material properties, 3D stiffness reduction methods, and boundary conditions on the failure loads and strains of a composite laminate under axial extension. The results indicate that different parameters have a different degree of influence on the failure loads and strains. The predictive ability of various phenomenological failure criteria is evaluated in the light of experimental results available in the literature, and the predictions of the LWLT are compared with those of the first-order shear deformation theory. It is concluded that a 3D stress analysis is necessary to predict accurately the failure behavior of composite laminates.
71 citations
TL;DR: In this paper, a theory for laminated composite shells and a finite element model based on this theory are presented, which accounts for an accurate description of the shear deformation and the stretching of transverse normals to the middle surface.
55 citations
TL;DR: In this article, a concentric cylinder model was used to analyze the stress state in a continuously reinforced coated fiber composite subjected to transverse loading and incorporated this analysis into the analysis.
Abstract: In this article we utilize a concentric cylinder model to analyze the stress state in a continuously reinforced coated fiber composite subjected to transverse loading. We incorporate this analysis ...
55 citations
TL;DR: In this paper, an analytical solution for buckling loads of composite cylindrical shells with axial and circumferential stiffeners is presented using a layerwise shell theory, which accounts for displacement variations through the thickness of the shell.
51 citations
TL;DR: In this article, a probabilistic finite element analysis procedure for laminated composite shells is developed, where the first-order second-moment technique is employed to calculate the mean and variance of the structural response.
Abstract: A probabilistic finite element analysis procedure for laminated composite shells is developed. A total Lagrangian finite element formulation, employing a degenerated three-dimensional laminated composite shell 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. Both ply-level and micromechanics-level random variables are incorporated, the latter by means of the Aboudi micromechanics model. Two sample problems are solved to verify the accuracy of the procedures developed and to quantify the variability of certain material type/structure combinations. In general, the procedure is quite effective in determining the response statistics and reliability for linear and geometric nonlinear behavior of laminated composite shells.
47 citations
TL;DR: In this article, a finite element method based on the Eulerian velocity correction method has been used to analyse the laminar natural convection in an annular cavity and the effect of the radius of curvature on the heat transfer coefficient was investigated.
Abstract: A finite element method based on the Eulerian velocity correction method has been used to analyse the laminar natural convection in an annular cavity. Unsteady, incompressible, axisymmetric Navier‐Stokes equations have been made use of. Different radius ratios of the annular cavity have been considered to investigate the effect of the radius of curvature on the heat transfer coefficient.
14 citations
01 Aug 1993-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, a finite element model for the solidification of molten metals and alloys in cylindrical molds is developed using the energy equation in terms of temperature and enthalpy.
Abstract: A finite element model for the solidification of molten metals and alloys in cylindrical molds is developed using the energy equation in terms of temperature and enthalpy. TheNewton-Raphson technique was used to solve the resulting nonlinear algebraic equations. A computer program is developed to calculate the enthalpy, temperature, and fraction solid per the classical Lever rule, Scheile equation, and Brody-Flemings models. Cooling curves are calculated for pure metal (aluminum), two eutectic alloys (Al-33.2 pct Cu and Al-12.6 pct Si), and three hypoeutectic alloys (Al-2.2 pct Cu, Al-4.5 pct Cu and Al-7 pct Si) and are compared with the experimental curves.
08 Sep 1993
TL;DR: In this paper, a cylindrical truss element actuator is developed which may be used for damping vibrations of truss type structures and the effects of a piezoelectric patch have been investigated.
Abstract: An elasticity solution is presented for the static equilibrium equations of an axisymmetriccomposite cylinder under loadings due to surface mounted or embedded piezoelectric laminae.Both uniform and non—uniform distributions of the piezoelectric effect are studied and results areverified using a finite element analysis based on axisymmetric 2—D elasticity theory equations. Acylindrical truss element actuator is developed which may be used for damping vibrations of truss type structures. Finally, the effects of a piezoelectric patch have been investigated. The axial forces generated at the fixed ends of a cylinder are found to be proportional to the length of thepatch. 1. INTRODUCTION One of the most recent advancements in the field of piezoelectricity is the discovery of thepiezoelectric effect in a polymer based material called polyvinylidene fluoride (PVDF)' . Compared to other materials, PVDF is flexible, rugged, available in thin sheets and easily manufactured inlarge quantities and at a low cost2. For these reasons, PVDF is currently being studied for useas distributed sensors/actuators in flexible structures. However, before piezoelectric materials canbe successfully used for control, the mechanical interaction between them and the structure beingcontrolled must be well understood.In this paper, two analytical tools are used to study the effects of embedded PVDF laminae inan axisymmetric composite cylinder. An elasticity solution is presented for the static equilibriumequations and verified using the finite element method. These tools are used to develop a cylindrical
01 Jan 1993
TL;DR: In this paper, the authors investigated the nonlinear response of laminated composite structures subjected to thermal loads using a refined theory and an associated finite element model for geometrically nonlinear analysis of shell structures and found that critical buckling temperatures are strongly dependent upon whether or not the transverse normal deformations are restrained along the boundaries of the panels.
Abstract: The nonlinear response of laminated composite structures subjected to thermal loads is investigated. Analysis is performed using a refined theory and an associated finite element model for geometrically nonlinear analysis of laminated composite shell structures. The model is based on a third-order displacement field which accounts for both transverse shear and transverse normal deformations. Numerical studies of simply-supported plates and cylindrical panels indicate that when the panels are free to expand or contract in the transverse direction, the predicted critical buckling temperatures do not depend significantly upon whether or not transverse normal deformations are explicitly accounted for in the analysis model. However, the critical buckling temperatures are strongly dependent upon whether or not the transverse normal deformations are restrained along the boundaries of the panels.
01 Feb 1993
TL;DR: In this paper, a probabilistic finite element analysis procedure for laminated composite shells has been developed and results are presented in the form of mean and variance of the structural response.
Abstract: A probabilistic finite element analysis procedure for laminated composite shells has been developed. A total Lagrangian finite element formulation, employing a degenerated 3-D laminated composite shell with the full Green-Lagrange strains and first-order shear deformable kinematics, forms the modeling foundation. 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. The effects of material nonlinearity are included through the use of a rate-independent anisotropic plasticity formulation with the macroscopic point of view. Both ply-level and micromechanics-level random variables can be selected, the latter by means of the Aboudi micromechanics model. A number of sample problems are solved to verify the accuracy of the procedures developed and to quantify the variability of certain material type/structure combinations. Experimental data is compared in many cases, and the Monte Carlo simulation method is used to check the probabilistic results. In general, the procedure is quite effective in modeling the mean and variance response of the linear and nonlinear behavior of laminated composite shells.
Journal Article•
TL;DR: The ability of two types of Conjugate Gradient like iterative solvers to resolve large-scale phenomena as a function of mesh density and convergence tolerance limit is investigated and an empirical relationship between the element size, the penalty parameter, and the convergence tolerance is presented.
Abstract: The ability of two types of Conjugate Gradient like iterative solvers (GMRES and ORTHOMIN) to resolve large-scale phenomena as a function of mesh density and convergence tolerance limit is investigated. The flow of an incompressible fluid inside a sudden expansion channel is analyzed using three meshes of 400, 1600 and 6400 bilinear elements. The iterative solvers utilize the element-by- element data structure of the finite element technique to store and maintain the data at the element level. Both the mesh density and the penalty parameter are found to influence the choice of the convergence tolerance limit needed to obtain accurate results. An empirical relationship between the element size, the penalty parameter, and the convergence tolerance is presented. This relationship can be used to predict the proper choice of the convergence tolerance for a given penalty parameter and element size.
TL;DR: In this paper, an overview of the primitive variable finite element models of viscous, incompressible fluids in three-dimensional enclosures, with emphasis on penalty finite elements models, is presented.
08 Sep 1993
TL;DR: In this article, two global/local finite element modeling procedures are integrated to permit the analysis of localized three-dimensional affects in laminated composite plates with bonded or embedded actuators.
Abstract: Two global/local finite element modeling procedures are integrated to permit the analysis of localized three-dimensional affects in laminated composite plates with bonded or embedded actuators. The first technique concerns the use of variable kinematic finite elements which are elements that contain several different types of assumed displacement fields. By choosing appropriate terms from the composite displacement field, an entire array of elements with different levels of kinematic complexity can be formed. The different elements can be conveniently connected together in a single domain for global/local analysis. The second technique concerns the use of finite element mesh superposition in which an independent overlay mesh is superimposed on a global mesh to provide localized refinement for regions of interest regardless of the original global mesh topology. Integration of these two ideas yields a very robust, economical analysis tool for global/local analysis of composite laminates.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
01 Sep 1993
TL;DR: In this article, the development of probabilistic methods for micromechanics-based constitutive and failure models, and application of the Probabilistic methodology in the evaluation of various composite materials and simulation of expected uncertainties in unidirectional fiber composite properties, and influence of the uncertainties in composite properties on the structural response were discussed.
Abstract: The three-year program of research had the following technical objectives: the development of probabilistic methods for micromechanics-based constitutive and failure models, application of the probabilistic methodology in the evaluation of various composite materials and simulation of expected uncertainties in unidirectional fiber composite properties, and influence of the uncertainties in composite properties on the structural response The first year of research was devoted to the development of probabilistic methodology for micromechanics models The second year of research focused on the evaluation of the Chamis-Hopkins constitutive model and Aboudi constitutive model using the methodology developed in the first year of research The third year of research was devoted to the development of probabilistic finite element analysis procedures for laminated composite plate and shell structures