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Ronald C Averill - One of the best experts on this subject based on the ideXlab platform.

  • An improved thermal lamination model for analysis of heat transfer in composite structures
    Journal of Composite Materials, 2002
    Co-Authors: Antonio Pantano, Ronald C Averill
    Abstract:

    A new thermal lamination model and its associated finite element model are presented for analysis of heat transfer in laminated composite structures. The form of the present model closely resembles that of recent zig-zag sublaminate structural laminate theories. The through-thickness distribution of temperature is assumed to vary linearly within each ply, and continuity of transverse flux at ply interfaces is enforced analytically. Thus, the number of computational degrees-offreedom (DOFs) is made independent of the number of plies in the sublaminate. In its present form, the model contains only two computational DOFs in each sublaminate–the temperature at the top and bottom surface of the sublaminate. This model lends itself well to development of convenient and efficient finite element models, as demonstrated herein. Both linear and nonlinear numerical results are presented to demonstrate the effectiveness of the present approach.

  • a three dimensional laminated plate finite element with high order zig zag sublaminate approximations
    International Journal of Computational Engineering Science, 2001
    Co-Authors: Ronald C Averill
    Abstract:

    This paper describes a new laminated composite plate theory and associated finite element model that allow variable through-the-thickness refinement, as needed, to capture higher-order thickness effects and interlaminar stresses in laminated composite and sandwich panels. The theory and finite element model utilize a new zig-zag sublaminate concept, in which each computational layer (or sublaminate) contains several, even many, physical layers. Within each sublaminate, a high-order zig-zag kinematic assumption is employed, providing very high accuracy, even when the entire laminate is modeled using only a single sublaminate. The accuracy and efficienty of the model are thus adaptable, depending upon the number of Sublaminates used. In order to facilitate through-the-thickness refinement, the finite element model is cast in the form of an eight-noded brick-type element, with displacements and rotations as nodal degrees-of-freedom. At interlaminar element boundaries, interlaminar shear traction degrees-of-freedom are also present, so that transverse shear stress continuity can be enforced through the entire thickness of the laminate, irrespective of the thickness discretization chosen. Numerical examples are presented to demonstrate the effectiveness of the current model for the analysis of laminated composite and sandwich panels that are very thick or thin.

  • first order zig zag sublaminate plate theory and finite element model for laminated composite and sandwich panels
    Composite Structures, 2000
    Co-Authors: Ronald C Averill
    Abstract:

    A refined laminated plate theory and three-dimensional finite element based on first-order zig-zag sublaminate approximations has been developed. The in-plane displacement fields in each sublaminate are assumed to be piecewise linear functions and vary in a zig-zag fashion through-the-thickness of the sublaminate. The zig-zag functions are evaluated by enforcing the continuity of transverse shear stresses at layer interfaces. This in-plane displacement field assumption accounts for discrete layer effects without increasing the number of degrees of freedom as the number of layers is increased. The transverse displacement field is assumed to vary linearly through-the-thickness. The transverse normal strain predictions are improved by assuming a constant variation of transverse normal stress in each sublaminate. In the computational model, each finite element represents one sublaminate. The finite element is developed with the topology of an eight-noded brick, allowing the thickness of the plate to be discretized into several elements, or Sublaminates, where each sublaminate can contain more than one physical layer. Each node has five engineering degrees of freedom, three translations and two rotations. Thus, this element can be conveniently implemented into general purpose finite element codes. The element stiffness coefficients are integrated exactly, yet the element exhibits no shear locking due to the use of an interdependent interpolation scheme and consistent shear strain fields. Numerical performance of the current element is investigated for a composite armored vehicle panel and a sandwich panel. These tests demonstrate that the element is very accurate and robust.

  • a 3d zig zag sublaminate model for analysis of thermal stresses in laminated composite and sandwich plates
    Journal of Sandwich Structures and Materials, 2000
    Co-Authors: Antonio Pantano, Ronald C Averill
    Abstract:

    A laminated plate theory and 3D finite element model based on first-order zig-zag sublaminate approximations are presented for thermal stress analysis of composite laminates and sandwich plates. The finite element is developed with the topology of an eight-noded brick, allowing the thickness of the plate to be discretized into several elements, or Sublaminates, where each sublaminate can contain more than one physical layer. The temperature field is first computed by a thermal model, where the through-thickness distribution of temperature is assumed to vary linearly within each ply, and continuity of transverse flux at ply interfaces is enforced analytically. Similarly, the in-plane displacement fields in each sublaminate are assumed to be piecewise linear functions and vary in a zig-zag fashion through the thickness of the sublaminate. The zig-zag functions are evaluated by enforcing the continuity of transverse shear stresses at layer interfaces. The formulation also enforces continuity of the transvers...

  • zigzag sublaminate model for nonlinear analysis of laminated panels
    Journal of Aerospace Engineering, 2000
    Co-Authors: Ronald C Averill
    Abstract:

    A geometrically nonlinear first-order zigzag sublaminate theory and finite-element model are presented that account for moderately large displacements and moderate rotations using a total Lagrangian formulation. The model contains special laminated plate bending kinematics but is cast in the form of a 3D eight-noded brick finite-element topology with five engineering degrees of freedom per node—three translations and two rotations. This permits discretization through the thickness of a laminate to obtain higher accuracy of displacements and stresses when required. The accuracy of the present model is demonstrated by comparing its structural response predictions with results from previous experimental investigations and with numerical tests using a commercial finite-element code.

M Dottavio - One of the best experts on this subject based on the ideXlab platform.

  • the ritz sublaminate generalized unified formulation approach for piezoelectric composite plates
    International Journal of Smart and Nano Materials, 2018
    Co-Authors: M Dottavio, Lorenzo Dozio, Riccardo Vescovini, Olivier Polit
    Abstract:

    This paper extends to composite plates including piezoelectric plies the variable kinematics plate modeling approach called Sublaminate Generalized Unified Formulation (SGUF). Two-dimensional plate equations are obtained upon defining a priori the through-thickness distribution of the displacement field and electric potential. According to SGUF, independent approximations can be adopted for the four components of these generalized displacements: an Equivalent Single Layer (ESL) or Layer-Wise (LW) description over an arbitrary group of plies constituting the composite plate (the sublaminate) and the polynomial order employed in each sublaminate. The solution of the two-dimensional equations is sought in weak form by means of a Ritz method. In this work, boundary functions are used in conjunction with the domain approximation expressed by an orthogonal basis spanned by Legendre polynomials. The proposed computational tool is capable to represent electroded surfaces with equipotentiality conditions. ...

  • benchmark solutions and assessment of variable kinematics models for global and local buckling of sandwich struts
    Composite Structures, 2016
    Co-Authors: M Dottavio, Olivier Polit, Anthony M Waas
    Abstract:

    Abstract This paper investigates the periodic global buckling and wrinkling of sandwich struts subjected to uniaxial loads. An exact elasticity solution is obtained in the plane strain setting for selected benchmark problems and serves as reference for a systematic assessment of several displacement-based sandwich plate models. The Sublaminate Generalized Unified Formulation is used to generate the algebraic two-dimensional governing equations of the variable kinematics models, for which a Navier-type solution is adopted.

  • bending analysis of composite laminated and sandwich structures using sublaminate variable kinematic ritz models
    Composite Structures, 2016
    Co-Authors: M Dottavio, Lorenzo Dozio, Riccardo Vescovini, Olivier Polit
    Abstract:

    Abstract This paper presents a novel numerical tool for the bending analysis of thin and thick composite plates, including monolithic and sandwich structures. The formulation is developed within a displacement-based approach, where the Principle of Virtual Displacements (PVD) and the method of Ritz are adopted to derive the governing equations. The approach relies upon the Sublaminate Generalized Unified Formulation (S-GUF) as underlying kinematic theory describing the behavior across the plate thickness. Main idea of the S-GUF is to group the plies into a number of smaller units called Sublaminates, each of them characterized by an independent, variable-kinematic theory. Continuity conditions between the Sublaminates are enforced in strong form during the assembly procedure of the governing equations. The S-GUF appears particularly useful when theories of different order are needed to approximate the displacement field of different portions of the structure, such as in the case of sandwich panels. A number of test cases from the literature is discussed, and results are validated against exact 3D solutions. The results demonstrate the ability of the approach to obtain accurate results, both in terms of deformed shapes, and intra- and inter-laminar stress distributions. A set of novel results is also presented for future benchmarking purposes.

  • a sublaminate generalized unified formulation for the analysis of composite structures
    Composite Structures, 2016
    Co-Authors: M Dottavio
    Abstract:

    This paper presents a very flexible variable kinematics modeling technique for composite structures. The key point is the subdivision of the multilayered cross-section into numerical Sublaminates, each consisting of one or more physical plies, and the formulation of model assumptions independently in each sublaminate according to the compact index notation known as Generalized Unified Formulation. Reference is made to the classical displacement-based and the mixed RMVT variational frameworks. For each sublaminate, the user may thus freely choose the order of the through-thickness polynomial distribution of each unknown as well as whether the unknown is described in an Equivalent Single Layer (ESL) or Layer-Wise (LW) approach. Sublaminates are always assembled in a Layer-Wise manner. This Sublaminate-GUF (S-GUF) is generally applicable to multilayered structures, but is particularly useful for sandwich panels, in which different models may be used for the thick, soft core and the thin, stiff skins. A Navier-type solution is used for demonstrating the validity of this approach by means of benchmark problems concerning the static response of sandwich plates.

Paolo Sebastiano Valvo - One of the best experts on this subject based on the ideXlab platform.

  • An Elastic Interface Model for the Delamination of Bending-Extension Coupled Laminates
    Applied Sciences, 2019
    Co-Authors: Stefano Bennati, Paolo Fisicaro, Luca Taglialegne, Paolo Sebastiano Valvo
    Abstract:

    The paper addresses the problem of an interfacial crack in a multi-directional laminated beam with possible bending-extension coupling. A crack-tip element is considered as an assemblage of two Sublaminates connected by an elastic-brittle interface of negligible thickness. Each sublaminate is modeled as an extensible, flexible, and shear-deformable laminated beam. The mathematical problem is reduced to a set of two differential equations in the interfacial stresses. Explicit expressions are derived for the internal forces, strain measures, and generalized displacements in the Sublaminates. Then, the energy release rate and its Mode I and Mode II contributions are evaluated. As an example, the model is applied to the analysis of the double cantilever beam test with both symmetric and asymmetric laminated specimens.

  • An elastic-interface model for the mixed-mode bending test under cyclic loads
    Procedia structural integrity, 2016
    Co-Authors: Stefano Bennati, Paolo Fisicaro, Paolo Sebastiano Valvo
    Abstract:

    Abstract We have developed a mechanical model of the mixed-mode bending (MMB) test, whereby the specimen is considered as an assemblage of two identical Sublaminates, modelled as Timoshenko beams. The Sublaminates are partly connected by a linearly elastic–brittle interface, transmitting stresses along both the normal and tangential directions with respect to the interface plane. The model is described by a set of suitable differential equations and boundary conditions. Based on the explicit solution of this problem and following an approach already adopted to model buckling-driven delamination growth in fatigue, we analyse the response of the MMB test specimen under cyclic loads. Exploiting the available analytical solution, we apply a fracture mode-dependent fatigue growth law. As a result, the number of cycles needed for a delamination to extend to a given length can be predicted.

  • an enhanced beam theory model of the mixed mode bending mmb test part i literature review and mechanical model
    Meccanica, 2013
    Co-Authors: Stefano Bennati, Paolo Fisicaro, Paolo Sebastiano Valvo
    Abstract:

    The paper presents a mechanical model of the mixed-mode bending (MMB) test used to assess the mixed-mode interlaminar fracture toughness of composite laminates. The laminated specimen is considered as an assemblage of two Sublaminates partly connected by an elastic–brittle interface. The problem is formulated through a set of 36 differential equations, accompanied by suitable boundary conditions. Solution of the problem is achieved by separately considering the two subproblems related to the symmetric and antisymmetric parts of the loads, which for symmetric specimens correspond to fracture modes I and II, respectively. Explicit expressions are determined for the interfacial stresses, internal forces, and displacements.

  • an enhanced beam theory model of the mixed mode bending mmb test part ii applications and results
    Meccanica, 2013
    Co-Authors: Stefano Bennati, Paolo Fisicaro, Paolo Sebastiano Valvo
    Abstract:

    The paper presents an enhanced beam-theory (EBT) model of the mixed-mode bending (MMB) test, whereby the specimen is considered as an assemblage of two Sublaminates partly connected by an elastic–brittle interface. Analytical expressions for the compliance, energy release rate, and mode mixity are deduced. A compliance calibration strategy enabling numerical or experimental evaluation of the interface elastic constants is also presented. Furthermore, analytical expressions for the crack length correction parameters—analogous to those given by the corrected beam-theory (CBT) model for unidirectional laminated specimens—are furnished for multidirectional laminated specimens, as well. Lastly, an example application to experimental data reduction is presented.

Valvo P.s. - One of the best experts on this subject based on the ideXlab platform.

  • An experimental compliance calibration strategy for estimating the elastic interface constants of delamination test specimens
    Edizioni Libreria Cortina, 2013
    Co-Authors: Bennati S, Valvo P.s.
    Abstract:

    The delamination of composite laminates can be effectively modelled by considering a delaminated laminate as an assemblage of Sublaminates connected by an elastic interlaminar interface. In this context, the question arises on the values to be assigned to the elastic interface constants. In the present study, we show how the elastic interface constants can be estimated through an experimental compliance calibration strategy. The method is based on the analytical solution for the MMB test, derived in a previous study. Here, a nonlinear least squares fitting procedure is applied to obtain the values of the elastic interface constants from the experimental results of DCB and ENF tests. Preliminary experimental tests have been conducted to check the effectiveness of the proposed strategy

  • A mechanical model of the four-point end notched flexure (4ENF) test based on an elastic-brittle interface
    A.S.I. klub ESIS, 2008
    Co-Authors: Bennati S, Taglialegne L, Valvo P.s.
    Abstract:

    The paper introduces a mechanical model of the four-point end notched flexure (4ENF) test used to assess the mode II interlaminar fracture toughness in laminated specimens under stable crack-growth conditions. The model considers the specimen as an assemblage of two Sublaminates, partly bonded together by a deformable interface. Each sublaminate is modelled as an elastic orthotropic beam, while the interface consists of a continuous distribution of normal and tangential linearly elastic-brittle springs. The mechanical behaviour of the system is described by a set of twenty-four differential equations, endowed with suitable boundary conditions. The original problem is split into two sub-problems, considering separately the symmetric and antisymmetric loads. The explicit solution to the problem is deduced for the internal forces and interlaminar stresses. Moreover, the energy release rate and compliance are determined. The predictions of the model are compared to theoretical and experimental results available in the literature

  • Does shear deformability influence the mode II delamination of laminated beams?
    A.S.I. klub ESIS, 2008
    Co-Authors: Valvo P.s.
    Abstract:

    Laminated beams affected by interlaminar cracks can be schematised as assemblages of Sublaminates, modelled according to some appropriate beam theory. Shear deformability is neglected by the Euler-Bernoulli beam theory, but is taken into account at first order by the Timoshenko beam theory and at higher orders by more refined theories. As well, the connection between the Sublaminates can be described by models of growing complexity, ranging from rigid to deformable (elastic or inelastic) interfaces. Consistent with the adopted model, the energy release rate associated to delamination growth can be determined and decomposed into its opening (mode I) and sliding (mode II) contributions. Shear deformability increases the compliance of the structural system and, consequently, may influence the energy release rate. However, the specific influence of shear deformability on the mode II contribution to the energy release rate is not always clear and literature on this point is contradictory. This paper tries to shed light on this controversial issue, by reviewing and critically analysing some of the most relevant studies on this topic. Hence, the circumstances and the ways in which shear deformability may (or may not) influence mode II fracture of delaminated beams should be clarified

  • Enhanced beam models for delamination toughness tests: mixed-mode fracture tests
    Università di Genova, 2008
    Co-Authors: Bennati S, Valvo P.s.
    Abstract:

    The delamination toughness of composite laminates is commonly assessed via tests on beam-shaped specimens. In mixed-mode fracture tests, asymmetry is introduced either in the load conditions (e.g., mixed-mode bending, MMB) or in the specimen’s geometry (e.g., asymmetric double cantilever beam, ADCB). Models based on Timoshenko’s beam theory have been developed for both cases by adding elastic-fragile interfaces connecting the separating Sublaminates. Through an appropriate change of variables, the fracture modes are partitioned and explicit solutions deduced

  • An enhanced beam model of the mixed-mode bending (MMB) test
    Starrylink Editrice, 2007
    Co-Authors: Bennati S, Fisicaro P, Valvo P.s.
    Abstract:

    The paper presents an enhanced model of the mixed-mode bending (MMB) test, commonly used for assessing the mixed-mode interlaminar fracture toughness of composite laminates. The specimen is considered as an assemblage of two identical Sublaminates, partly bonded together by an elastic interface. Each sublaminate is modelled as an orthotropic beam, deformable due to bending, extension and shear. The interface is thought of as a continuous distribution of normal and tangential springs, whose elastic reactions produce transverse and axial loads in the Sublaminates, as well as distributed couples. The mechanical behaviour of the system is described by a set of eighteen differential equations, endowed with suitable boundary conditions. The problem is split into the superposition of two subproblems, where the applied loads are symmetric and antisymmetric with respect to the interface plane, respectively. This approach allows for a simpler analytical solution and leads to a natural separation of the fracture modes within the context of beam theory. Through lengthy yet elementary calculations, a complete explicit solution to the original problem is deduced, in terms of displacements, internal forces and interfacial stresses. In particular, the mode I and II contributions to the energy release rate and the mode mixity ratio are determined

Olivier Polit - One of the best experts on this subject based on the ideXlab platform.

  • the ritz sublaminate generalized unified formulation approach for piezoelectric composite plates
    International Journal of Smart and Nano Materials, 2018
    Co-Authors: M Dottavio, Lorenzo Dozio, Riccardo Vescovini, Olivier Polit
    Abstract:

    This paper extends to composite plates including piezoelectric plies the variable kinematics plate modeling approach called Sublaminate Generalized Unified Formulation (SGUF). Two-dimensional plate equations are obtained upon defining a priori the through-thickness distribution of the displacement field and electric potential. According to SGUF, independent approximations can be adopted for the four components of these generalized displacements: an Equivalent Single Layer (ESL) or Layer-Wise (LW) description over an arbitrary group of plies constituting the composite plate (the sublaminate) and the polynomial order employed in each sublaminate. The solution of the two-dimensional equations is sought in weak form by means of a Ritz method. In this work, boundary functions are used in conjunction with the domain approximation expressed by an orthogonal basis spanned by Legendre polynomials. The proposed computational tool is capable to represent electroded surfaces with equipotentiality conditions. ...

  • benchmark solutions and assessment of variable kinematics models for global and local buckling of sandwich struts
    Composite Structures, 2016
    Co-Authors: M Dottavio, Olivier Polit, Anthony M Waas
    Abstract:

    Abstract This paper investigates the periodic global buckling and wrinkling of sandwich struts subjected to uniaxial loads. An exact elasticity solution is obtained in the plane strain setting for selected benchmark problems and serves as reference for a systematic assessment of several displacement-based sandwich plate models. The Sublaminate Generalized Unified Formulation is used to generate the algebraic two-dimensional governing equations of the variable kinematics models, for which a Navier-type solution is adopted.

  • bending analysis of composite laminated and sandwich structures using sublaminate variable kinematic ritz models
    Composite Structures, 2016
    Co-Authors: M Dottavio, Lorenzo Dozio, Riccardo Vescovini, Olivier Polit
    Abstract:

    Abstract This paper presents a novel numerical tool for the bending analysis of thin and thick composite plates, including monolithic and sandwich structures. The formulation is developed within a displacement-based approach, where the Principle of Virtual Displacements (PVD) and the method of Ritz are adopted to derive the governing equations. The approach relies upon the Sublaminate Generalized Unified Formulation (S-GUF) as underlying kinematic theory describing the behavior across the plate thickness. Main idea of the S-GUF is to group the plies into a number of smaller units called Sublaminates, each of them characterized by an independent, variable-kinematic theory. Continuity conditions between the Sublaminates are enforced in strong form during the assembly procedure of the governing equations. The S-GUF appears particularly useful when theories of different order are needed to approximate the displacement field of different portions of the structure, such as in the case of sandwich panels. A number of test cases from the literature is discussed, and results are validated against exact 3D solutions. The results demonstrate the ability of the approach to obtain accurate results, both in terms of deformed shapes, and intra- and inter-laminar stress distributions. A set of novel results is also presented for future benchmarking purposes.

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