Nelly Point

A delamination model for laminated composites

The delamination problem of laminated composite plates is considered. The Fremonds adhesion approach is developed and adapted to the delamination problem considered. A consistent thermodynamical formulation for the damage model is presented and the governing equations are carried out. The relation between the proposed approach and the fracture mechanics theory is emphasized. Furthermore, a regularized model is developed. A numerical procedure based on the finite element method and on the elastic predictor-damage corrector method is proposed. Numerical results carried out for beams are compared with the analytical solutions. Finally, the problem of drilling a composite laminate is investigated.

Endochronic theory, non-linear kinematic hardening rule and generalized plasticity: a new interpretation based on generalized normality assumption

A simple way to define the flow rules of plasticity models is the assumption of generalized normality associated with a suitable pseudo-potential function. This approach, however, is not usually employed to formulate endochronic theory and non-linear kinematic (NLK) hardening rules as well as generalized plasticity models. In this paper, generalized normality is used to give a new formulation of these classes of models. As a result, a suited pseudo-potential is introduced for endochronic models and a non-standard description of NLK hardening and generalized plasticity models is also provided. This new formulation allows for an effective investigation of the relationships between these three classes of plasticity models.

Mathematical properties of a delamination model

In this paper, some mathematical properties of a delamination model are studied. The laminate is schematized as two plates connected by a very special interface material. An interface constitutive model, based on the adhesion theory is introduced. The proposed model is governed by a functional which is neither smooth nor convex. The fundamental properties of this nonsmooth model are presented. Then, a regularized interface model is constructed. The existence of a solution for the delamination problem obtained adopting the regularized interface model is proved. It is shown that this solution converges to a solution of the nonsmooth initial delamination problem when the regularization parameters tend to 0. The lack of convexity of the functional governing both the nonsmooth and the regularized problems makes this proof not straightforward.

A Plasticity Model and Hysteresis Cycles

Physical considerations on the micromechanisms involved in plasticity phenomenon are used to derive a four parameters plasticity model. The choice of the more appropriate set of parameters is important for this highly non linear model. Once these parameters, characteristic of the material, are identified, the response to any series of loading and unloading is easily computed. An uniaxial tensile test or experimental hysteresis cycles permit to identify the parameters through a nonlinear least square method. The study of experimental hysteresis cycles for important loads permits an easy evaluation of these characteristics parameters.

Application of the orthogonality principle to the endochronic and Mróz models of plasticity

A new description of the endochronic and the Mroz model is discussed. It is based on the definition of a suitable pseudo-potential and the use of the generalized normality assumption. The key-point of this formulation is the dependence of the pseudo-potentials on state variables.

A Generalization of the Endochronic Theory of Plasticity Based on the Introduction of Several Intrinsic Times

In this note, a generalization of the endochronic theory of plasticity is proposed. The basic idea is the introduction of several distinct intrinsic times instead of the unique one characterizing the standard theory. It follows that endochronic models without elastic domain and multi-layer plasticity models, presenting multi-linear hysteresis loops, can be described by means of a common theoretical framework. Moreover, a new model can be defined, able to produce, for uniaxial loading, closed hysteresis loops for small amplitudes and open loops for larger amplitudes.

A Non-linear Hardening Model Based on Two Coupled Internal Hardening Variables: Formulation and Implementation

An elasto-plasticity model with coupled hardening variables of strain type is presented. In the theoretical framework of generalized associativity, the formulation of this model is based on the introduction of two hardening variables with a coupled evolution. Even if the corresponding hardening rules are linear, the stress-strain hardening evolution is non-linear. The numerical implementation by a standard return mapping algorithm is discussed and some numerical simulations of cyclic behaviour in the univariate case are presented.

A Delamination Model

A delamination model for laminated composites is proposed. A damage variable takes into account the degradation of the adhesive properties of the interfaces. It is described by a nonsmooth, nonconvex functional [1].

A Delamination Model. Mathematical Properties

In this paper some mathematical properties of a delamination model are studied. The laminate is schematized as two plates connected by a very special interface material. An interface constitutive model, based on the adhesion theory is introduced. The proposed model is governed by a functional which is neither smooth nor convex. The fundamental properties of this nonsmooth model are presented. Then a regularized interface model is constructed. The existence of a solution for the delamination problem obtained adopting the regularized interface model is proved. It is shown that this solution convergences to a solution of the nonsmooth initial delamination problem when the regularization parameters tend to 0. The lack of convexity of the functionals governing both the nonsmooth and the regularized problems makes this proof not straightforward.