Introduction to linear and nonlinear programming

Composites science and technology

http://parallel.bas.bg/~ppopov/publications/journal/popov.MECMAT.2006.pdf

Shape memory alloys, Part II: Modeling of polycrystals

A new method to combine interface damage and friction in a cohesive-zone model is proposed. Starting from the mesomechanical assumption, typically made in a damage-mechanics approach, whereby a representative elementary area of the interface can be additively decomposed into an undamaged and a fully damaged part, the main idea consists of assuming that friction occurs only on the fully damaged part. The gradual increase of the friction effect is then a natural outcome of the gradual increase of the interface damage from the initial undamaged state to the complete decohesion. Suitable kinematic and static hypotheses are made in order to develop the interface model whereas no special assumptions are required on the damage evolution equations and on the friction law. Here, the Crisfield's interface model is used for the damage evolution and a simple Coulomb friction relationship is adopted. Numerical and analytical results for two types of constitutive problem show the effectiveness of the model to capture all the main features of the combined effect of interface damage and friction. A finite-step interface law has then been derived and implemented in a finite-element code via interface elements. The results of the simulations made for a fibre push-out test and a masonry wall loaded in compression and shear are then presented and compared with available experimental results. They show the effectiveness of the proposed model to predict the failure mechanisms and the overall structural response for the analysed problems. Copyright © 2006 John Wiley & Sons, Ltd.

Combining interface damage and friction in a cohesive-zone model

A review of constitutive models and modeling techniques for shape memory alloys

http://www-2.unipv.it/compmech/publications/2003_2.pdf

Modelling of SMA materials: Training and two way memory effects

A plastic nonlocal damage model

Continuum damage models describe the changes of material stiffness and strength, caused by the evolution of defects, in the framework of continuum mechanics. In many materials, a fast evolution of defects leads to stress–strain laws with softening, which creates serious mathematical and numerical problems. To regularize the model behaviour, various generalized continuum theories have been proposed. Integral-type non-local damage models are often based on weighted spatial averaging of a strain-like quantity. This paper explores an alternative formulation with averaging of the displacement field. Damage is assumed to be driven by the symmetric gradient of the non-local displacements. It is demonstrated that an exact equivalence between strain and displacement averaging can be achieved only in an unbounded medium. Around physical boundaries of the analysed body, both formulations differ and the non-local displacement model generates spurious damage in the boundary layers. The paper shows that this undesirable effect can be suppressed by an appropriate adjustment of the non-local weight function. Alternatively, an implicit gradient formulation could be used. Issues of algorithmic implementation, computational efficiency and smoothness of the resolved stress fields are discussed. Copyright © 2005 John Wiley & Sons, Ltd.

Non‐local damage model based on displacement averaging

Multiscale damage contact-friction model for periodic masonry walls

A simple shape-memory-alloy (SMA) model to simulate the superelastic behavior as well as the shape memory effect is proposed. It considers only the transformations from austenite to single-variant martensite and from single-variant martensite to austenite, taking into account the ine uence of the temperature in the constitutive relationship. The proposed SMA constitutive model is employed in a novel layerwise beam theory to develop new SMA beam e nite element models with suitable interpolation of the e eld variables involved. The e nite element models developed herein account for the time evolution SMA constitutive equations. In particular, the developed e nite elements treat the SMA material as reinforcement of elastic beams. Several applications are presented to assess the validity of the constitutive model and the proposed numerical procedure.

Sonia Marfia

Papers

Modelling of SMA materials: Training and two way memory effects

A plastic nonlocal damage model

Non‐local damage model based on displacement averaging

Multiscale damage contact-friction model for periodic masonry walls

Superelastic and Shape Memory Effects in Laminated Shape-Memory-Alloy Beams