A constitutive model for anisotropic damage in fiber-composites

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

A continuum damage model for composite laminates: Part I - Constitutive model

Analysis of cracked laminates: a variational approach

A three-dimensional finite element model is developed to predict damage progression and strength of mechanically fastened joints in carbon fibre-reinforced plastics that fail in the bearing, tension and shear-out modes. The model is based on a three-dimensional finite element model, on a three-dimensional failure criterion and on a constitutive equation that takes into account the effects of damage on the material elastic properties. This is accomplished using internal state variables that are functions of the type of damage. This formulation is used together with a global failure criterion to predict the ultimate strength of the joint. Experimental results concerning damage progression, joint stiffness and strength are obtained and compared with the predictions. A good agreement between experimental results and numerical predictions is obtained.

A progressive Damage Model for Mechanically Fastened Joints in Composite Laminates

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Stiffness changes in unidirectional composites caused by crack systems

Overall stiffnesses and compliances, thermal expansion coefficients, and stress and strain averages are evaluated for a fibrous composite lamina which contains a given density of open transverse cracks and is subjected to uniform mechanical loads and thermal changes. The evaluation procedure is based on the self-consistent method and is similar, in principle, to that used in finding elastic constants of unidirectional com posites.

Analysis of Progressive Matrix Cracking in Composite Laminates I. Thermoelastic Properties of a Ply with Cracks

A procedure is developed for determining the dynamic response of an elastic- half-space to the rigid body motion of an irregularly shaped foundation. The method is to subdivide the foundation into rectanglar subregions and calculate the response for an equivalent circular subregion having a constant load. The load magnitude of the circular region is the same as for the rectangular region. Compliances are computed for foundation shapes that could be compared with the results of others. Accuracy and time for computation for these comparison examples were reasonably good.

Mehdi S. Hejazi

Papers

Stiffness changes in unidirectional composites caused by crack systems

Analysis of Progressive Matrix Cracking in Composite Laminates I. Thermoelastic Properties of a Ply with Cracks

Dynamic Response of Foundations with Arbitrary Geometries