Jacopo Ciambella

On the ABAQUS FEA model of finite viscoelasticity

Abstract Predictions of the QLV (Quasi-Linear Viscoelastic) constitutive law are compared with those of the ABAQUS viscoelastic model for two simple motions in order to highlight, in particular, their very different dissipation rates and certain shortcomings of the ABAQUS model.

Damage evolution and debonding in hybrid laminates with a cohesive interfacial law

The hybridisation of fibres reinforced laminates, i.e., the combined use of two or more families of fibres, is an effective technique to achieve a pseudo-ductile response and overcome the inherent brittleness which limits the wider use of composite materials. In this paper, a one-dimensional analytical model for unidirectional hybrid laminates is derived. The model considers two elastic–brittle layers bonded together by a cohesive elasto–plastic–brittle interface. This formulation is applied to the study of the debonding and fracture of laminates under uniaxial loading and the results compared to experiments available from the open literature. This study shows that the proposed model provides a close fit to the experimental data and it is able to match accurately the crack patterns seen in the experiments. The model predicts four different failure mechanisms and is able to discriminate among them according to the geometrical and mechanical properties of the layers.

Nonlinear elasticity of auxetic open cell foams modeled as continuum solids

Structure evolution during deformation of isotropic auxetic foams is investigated by simple compression experiments. It is shown that the main feature observed in the experimental data can be accurately described by an isotropic hyperelastic model with an Ogden-type strain energy function. The model can be easily implemented in a finite element code and, hence, can be used to simulate foams undergoing complex structural deformations.

A continuum hyperelastic model for auxetic materials

We propose a simple mathematical model to describe isotropic auxetic materials in the framework of the classical theory of nonlinear elasticity. The model is derived from the Blatz–Ko constitutive equation for compressible foams and makes use of a non-monotonic Poisson function. An application to the modelling of auxetic foams is considered and it is shown that the material behaviour is adequately described with only three constitutive parameters.

Orientation effects in short fibre-reinforced elastomers

The large strain behaviour of a short fibre-reinforced composite is studied through numerical simulations. The reinforcing fibres yield the macroscopic response transversely isotropic which is indeed the case of many reinforcements currently used in composites: short carbon fibres, cellulose whiskers, carbon nanotubes. As a result of the analysis, it is shown that the reorientation of the fibres that takes place at large strain has a significant effect on the overall material response by changing the axis of isotropy. This behaviour can be adequately described by using a transversely isotropic model whose strain energy function depends on three invariants: two isotropic and one representing the stretch along the direction of the fibres. To assess its capabilities, the model is compared to the results of experiments carried out by the authors on nickel-coated chopped carbon fibres in a vulcanised natural rubber matrix for which the fibre orientation is achieved by controlling an external magnetic field prior to curing. Possible applications include micro-sized propulsion devices and actuators.Copyright

Damage detection with auxiliary subsystem

Among Non-Destructive Evaluation, vibration-based methods respond to the current ten- dency which is to integrate into the structure identication and monitoring systems; to this aim transducers and sensors are embedded with the mechanical system and driven by suitably designed electronic controllers. The major limit of this and the other indirect identication techniques based on frequency response measurements turns out to be the small sensitivity to local variations of mechanical characteristics: it re ects on a uncertainty on the identied parameters, since it implies a small curvature of any reasonable identication functional build on these quantities. An enlightening example for the application of the proposed technique is given through a beam- like structure coupled to a network of piezoelectric patches. Although the forces exerted by the piezoelectric transducers are not large, the choice of such a kind of actuators/sensors implies the remarkable advantage of dealing with highly sensitive and easily tunable devices.