Ever J. Barbero

Modeling of delamination in composite laminates using a layer-wise plate theory

Abstract The layer-wise laminate theory of Reddy is extended to account for multiple delaminations between layers, and the associated computational model is developed. Delaminations between layers of composite plates are modeled by jump discontinuity conditions at the interfaces. Geometric nonlinearity is included to capture layer buckling. The strain energy release rate distribution along the boundary of delaminations is computed by a novel algorithm. The computational model presented is validated through several numerical examples.

Formulas for the stiffness of composites with periodic microstructure

Abstract In this paper, the mechanical behavior of composite materials with periodic microstructure is analysed. The corresponding elastic problem is solved by using the Fourier series technique and assuming the homogenization eigenstrain to be piecewise constant. Then, the coefficients of the overall stiffness tensor of the composite material are expressed analytically in terms of the elastic properties of the constituents (fibers and matrix) and as a function of nine triple series which take into account the geometry of the inclusions. In the case of composite materials reinforced by long fibers, simple formulas for evaluating these series are proposed. Close-form expressions for the elastic moduli of the fiber reinforced composite with periodic microstructure and for the equivalent transversely isotropic material are obtained. Finally, several comparisons with experimental results are presented.

Analysis and design of pultruded FRP shapes under bending

Abstract A comprehensive approach for the analysis and design of pultruded FRP beams in bending is presented. It is shown that the material architecture of pultruded FRP shapes can be efficiently modeled as a layered system. Based on the information provided by the material producers, a detailed procedure is presented for the computation of fiber volume fraction (V f ) of the constituents, including fiber bundles or rovings, continuous strand mats, and cross-ply and angle-ply fabrics. Using the computed V f s, the ply stiffnesses are evaluated from selected micromechanics models. The wall or panel laminate engineering constants can be computed from the ply stiffnesses and macromechanics, and it is shown that the predictions correlate well with coupon test results. The bending response of various H and box sections is studied experimentally and analytically. The mechanics of laminated beams (MLB) model used in this study can accurately predict displacements and strains, and it can be used in engineering design and manufacturing optimization of cross-sectional shapes and lay-up configurations. The experimental results agree closely with the MLB predictions and finite element verifications.

On the Mechanics of Thin-Walled Laminated Composite Beams

A formal engineering approach of the mechanics of thin-walled laminated beams based on kinematic assumptions consistent with Timoshenko beam theory is pre sented. Thin-walled composite beams with open or closed cross section subjected to bend ing and axial load are considered. A variational formulation is employed to obtain a com prehensive description of the structural response. Beam stiffness coefficients, which account for the cross section geometry and for the material anisotropy, are obtained. An explicit expression for the static shear correction factor of thin-walled composite beams is derived from energy equivalence. A numerical example involving a laminated I-beam is used to demonstrate the capability of the model for predicting displacements and ply stresses.

General two-dimensional theory of laminated cylindrical shells

The theory accounts for a desired degree of approximation of the displacements through the thickness, thus accounting for any discontinuities in their derivatives at the interface of laminae. Geometric nonlinearity in the sense of the von Karman strains is also included. Navier-type solutions of the linear theory are presented for simply supported boundary conditions

Continuum Damage-healing Mechanics with Application to Self-healing Composites

The general behavior of self-healing materials is modeled including both irreversible and healing processes. A constitutive model, based on a continuum thermodynamic framework, is proposed to predict the general response of self-healing materials. The self-healing materials’ response produces a reduction in size of microcracks and voids, opposite to damage. The constitutive model, developed in the mesoscale, is based on the proposed Continuum Damage-Healing Mechanics (CDHM) cast in a consistent thermodynamic framework that automatically satisfies the thermodynamic restrictions. The degradation and healing evolution variables are obtained introducing proper dissipation potentials, which are motivated by physically based assumptions. An efficient three-step operator slip algorithm, including healing variables, is discussed in order to accurately integrate the coupled elastoplastic-damage-healing constitutive equations. Material parameters are identified by means of simple and effective analytical procedures. Results are shown in order to demonstrate the numerical modeling of healing behavior for damaged polymer-matrix composites. Healed and not healed cases are discussed in order to show the model capability and to describe the main governing characteristics concerning the evolution of healed systems.

An Inelastic Damage Model for Fiber Reinforced Laminates

A new modelfor damage behavior of polymer matrix composite laminates is presented. The model is developed for an individual lamina, and then assembled to describe the nonlinear behavior of the laminate. The model predicts the inelastic effects as reduction of stiffness and increments of damage and unrecoverable deformation. The modelis defined using Continuous Damage Mechanics coupled with Classical Thermodynamic Theory. Unrecoverable deformations and Damage are coupled by the concept of effective stress. New expressions of damage and unrecoverable deformation domains are presented so that the number of model parameters is small. Furthermore, model parameters are obtained from existing test data for unidirectional laminae, supplemented by cyclic shear stress strain data. Comparison with lamina and laminate test data are presented to demonstrate the ability of the model to predict the observed behavior.

A phenomenological design equation for FRP columns with interaction between local and global buckling

Abstract A design equation for fiber reinforced plastic columns is presented in this paper, based on the interaction between local (flange) and global (Euler) buckling observed during testing of the FRP columns included in this investigation. An existing interaction equation is adapted to account for the modes of failure observed in columns made of fiber reinforced composite materials. Experimental data generated during this investigation are presented and used to validate the interaction equation and to obtain the interaction constant. A slenderness ratio is proposed and used to present a plot of buckling for all sections and column lengths (short, long, and intermediate). An expression for the optimum column length to be used in the experimental determination of the interaction constant is proposed.

Local buckling experiments on FRP columns

Abstract In this paper, local flange-buckling of thin-walled pultruded FRP columns is investigated. Experimental data are presented and correlated with theoretical predictions. Good agreement between theoretical and experimental results is found. Possible explanations for slight deviations in the experimental data are advanced. The experimental and data reduction procedures used to obtain the local buckling loads are presented. A new data reduction technique using Southwells method is developed to interpret local buckling test data. The usefulness of the data reduction technique is demonstrated for various column sections and experimental conditions.

Euler buckling of thin-walled composite columns

Abstract Pultruded composite structural members with open or closed thin-walled sections are being extensively used as columns for structural applications where buckling is the main consideration in the design. In this paper, global buckling is investigated and critical loads are experimentally determined for various fiber reinforced composite I-beams of long column length. Southwells method is used to determine the critical buckling load about strong and weak axes. The experimentally determined buckling load is compared with theoretical predictions. A number of observations about testing methodology and data reduction techniques are presented.