Modelling damage evolution in composite laminates subjected to low velocity impact

Recent developments on damage modeling and finite element analysis for composite laminates: A review

Progressive damage and nonlinear analysis of 3D four-directional braided composites under unidirectional tension

The relationships between a resistance curve (R-curve), the corresponding fracture process zone length, the shape of the traction-displacement softening law, and the propagation of fracture are examined in the context of the through-the-thickness fracture of composite laminates. A procedure for superposing linear cohesive laws to approximate an experimentally-determined R-curve is proposed. Simple equations are developed for determining the separation of the critical energy release rates and the strengths that define the independent contributions of each linear softening law in the superposition. The proposed procedure is demonstrated for the longitudinal fracture of a fiber-reinforced polymer-matrix composite. It is shown that the R-curve measured with a Compact Tension Specimen test cannot be predicted using a linear softening law, but can be reproduced by superposing two linear softening laws.

A procedure for superposing linear cohesive laws to represent multiple damage mechanisms in the fracture of composites

Finite element analysis of dynamic progressive failure of plastic composite laminates under low velocity impact

This paper presents an anisotropic damage model suitable for predicting failure and post-failure behavior in fiber-reinforced materials. In the model the plane stress formulation is used and the response of the undamaged material is assumed to be linearly elastic. The model is intended to predict behavior of elastic-brittle materials that show no significant plastic deformation before failure. Four different failure modes – fiber tension, fiber compression, matrix tension, and matrix compression – are considered and modeled separately. The onset of damage is predicted using Hashin’s initiation criteria [Hashin Z, Rotem A. A fatigue failure criterion for fiber-reinforced materials. J Compos Mater 1973;7:448; Hashin Z. Failure criteria for unidirectional fiber composites. J Appl Mech 1980;47:329–34] and the progression of damage is controlled by a new damage evolution law, which is easy to implement in a finite element code. The evolution law is based on fracture energy dissipation during the damage process and the increase in damage is controlled by equivalent displacements. The issues related to numerical implementation, such as mesh sensitivity and convergence in the softening regime, are also addressed.

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Progressive damage modeling in fiber-reinforced materials

In the last five decades, continuum damage mechanics has proven to be a valuable tool to study material degradation. Many damage models have been developed that allow an accurate description of damage processes for a wide range of materials. At the same time, much effort has been expended to develop robust algorithms for obtaining numerical solutions to problems with damage. Some of the models have already been implemented in commercial finite element codes and have become a valuable tool in helping engineers predict behavior of engineering structures. In this article, a general framework for modeling damage, based on the theory of irreversible thermodynamics with internal variables, is outlined. Special attention is devoted to issues related to the numerical implementation of material models with damage, such as mesh sensitivity of the solution and convergence difficulties.


Keywords:

continuum damage mechanics;
finite element method;
mesh sensitivity;
viscous regularization;
convergence difficulties

Continuum Damage Mechanics

In this paper we present a new constitutive framework, the Parallel Rheological Framework (PRF), for modeling polymers that has been recently developed by the authors and implemented in the commercial finite element software Abaqus [1]. The framework is based on parallel finite-strain viscoelastic and elastoplastic networks. For each viscoelastic network a multiplicative split of the deformation gradient into elastic and viscous components is assumed. The evolution of the viscous component of the deformation gradient is governed by a flow rule obtained assuming the existence of a creep potential. The flow rule is expressed as a function of stress invariants and internal variables, and different evolution laws for the internal variables are allowed within the framework of the model. Similar to the viscoelastic networks, the deformation gradient in the elastoplastic network is decomposed into elastic and plastic components. The yield surface is defined assuming combined isotropic/kinematic hardening. The yield surface is a function of a scalar internal variable that describes isotropic hardening, and a tensorial internal variable (backstress) that describes the shift of the yield surface in the stress space. The evolution of the scalar variable is governed by associated flow rule, while the evolution of backstresses is determined by the Armstrong-Frederick law [2], which is extended to finite-strain deformations. Finally, stress softening is introduced into an elastoplastic network using a modified version of Ogden and Roxbourgh’s pseudo-elasticity model [3].This paper presents an outline of the framework, including two recent enhancements: a new creep model (the power law model) and combined isotropic/kinematic hardening plasticity model. The framework is then applied to analyze numerically the uniaxial loading/unloading behaviors of filled natural rubber and an EPDM polymer. The results obtained using finite element simulations show very good correlation with experimental data.Copyright © 2014 by ASME

Ireneusz Lapczyk

Papers

Progressive damage modeling in fiber-reinforced materials

Continuum Damage Mechanics

A Viscoelastic-Elastoplastic Finite Strain Framework for Modeling Polymers