Modellazione fenomenologica di espansi polimerici smart aventi comportamento magneto-meccanico controllato dal campo magnetico

Responsabili di progetto

Luigi Sorrentino, Pavel Krejci

Accordo

REPUBBLICA CECA - CAS (ex AVCR) - Czech Academy of Sciences

Bando

CNR-CAS (ex AVCR) 2016-2018

Dipartimento

Scienze chimiche e tecnologie dei materiali

Area tematica

Scienze chimiche e tecnologie dei materiali

Stato del progetto

Nuovo

Proposta di ricerca

This proposal is aimed at the phenomenological modeling of a new class of smart materials: composite foams, lightweight and multifunctional, with magneto-mechanical properties and macroscopic behavior that can be controlled by a suitable applied magnetic field (MAPs). The growing success of multifunctional (smart) materials is due to their potential of opening new fields of applications thanks to new uncovered properties. Nevertheless, even in standard applications, smart materials are able to simplify standard designs and increase the performances (for example, piezoelectric materials employed for actuation and sensing). On the other hand, the search for new smart materials is aiming at cheaper and more environmentally friendly materials and applications.
Smart magnetic foams are made by embedding magnetic particles, micrometric or nanometric in size, spread into the polymeric matrix during the foaming process. In presence of a suitable magnetic field, particles align themselves along magnetic field lines leading to an anisotropic structural reinforcement. So, the magnetic field can be used as a further parameter, together with temperature and pressure, to reach the desired properties of the foam. For example, a fibrous aggregation of particles along the force lines of a uniform magnetic field can easily be obtained. The consequent structural behavior is anisotropic, reinforced along the alignment direction. Moreover, the constitutive relationship exhibits a magneto-mechanical coupling. This further functionality makes the smart foam a sort of "active" one where the mechanical quantities can be contactlessly controlled by an applied magnetic field. Apart from obvious actuation purposes, other interesting features can be foreseen:
- They can be lightweight (depending on the porosity induced during the foaming process);
- They allow a high throughput cycle, because the production process (batch or injection moulding, with the presence of suitable electromagnets, designed and controlled with ad-hoc procedures) is easily transferable to the industry;
- They can be made out of polymeric matrices with low environmental impact;
- Their magneto-mechanical properties can be individually designed for a large class of specific purposes in terms of both magnetic particles distribution and foam morphology.
Phenomenological modeling of smart magnetic foams is in its infancy. There are many scientific works [such as Sorrentino et al., Polym Test, 2007, 26, 878-885] that estimate the mechanical properties of foams, treated as biphasic materials consisting of a solid porous matrix filled with gas (air). The mathematical models are based on continuum mechanics equations with different constitutive relations for the two phases. The foam is often represented through a homogenization process. For magnetic foams, theoretical works are available on either modeling (for example: M R Jolly et al, Smart Mater. Struct., 1996) or experimental characterization (for example: Bednarek, J of magn. and magn. mat., 2006) of solid magnetorheological materials but very few investigations relate to validation of experimental data (for example: Zhoug & Jiang, Smart Mater. Struct., 2004; D. Ivaneyko et al, Macromol. Symp. 338, 96-107, 2014).
A mathematical model for magnetic foams must follow general physical principles and reflect the experimental evidence in order to be capable of predictions based on numerical simulations. Electromagnetic field theory, continuum mechanics, and classical thermodynamics will be combined with empirical multi-field constitutive relations to form a model which will have to be experimentally verified. As in other magneto-mechanical systems, multidimensional hysteresis effects have to be taken into account in order to evaluate the energetic efficiency of the control processes.
The modeling will start with the aim to correlate the 4 available macroscopic quantities (stress, strain, magnetic field, magnetization) in the 0D setting. The relationship is non-linear and anisotropic with hysteresis memory effects. The constitutive model has to admit a Gibbs energy compatible with the thermodynamic principles and accounting for magneto-mechanical coupling. The customization of the model and identification of the nonlinearities will be done by comparison with experimental measurements on the smart magnetic foam, already available from the Italian partner CNR. Furthermore, a 3D magneto-mechanical model will be developed. The mechanical characteristic will be obtained by using homogenization techniques and empirical laws, with the goal to derive a full system of balance equations (Maxwell's equations, momentum balance, energy balance) for the magnetic foam. The whole model will be implemented in a FEM code with the aim to correlate simulation parameters (geometry, shape and type of magnetic particles, their distribution, mechanical characteristics of the foam) with experiments, in order to reach a predictive model. The results will help to control the foaming process in order to synthesize magnetic foams that meet design specifications.
The gained knowledge will help to develop products applicable in different industrial activities as, for example, in the automotive or aerospace industry (systems with controlled stiffness), or in the reinforcement of lightweight composites (replacement of honeycomb structures in sandwich structures). In addition, their multifunctionality can be exploited in microfluidics (peristaltic micropumps with magnetic control in the biomedicine) or for vibration damping. The teams involved in this research proposal have complementary skills, and have already collaborated on smart materials and devices development (Davino et al, Smart Mater. Struct. 22 095009, 2013; Sorrentino et al. J Appl Polym Sci, 2011, 119, 1239-1247). This is a good viaticum to reach the aims of the project, which is to make a step forward in the knowledge of smart materials based on polymeric foams.

Obiettivi della ricerca

The aim of the collaboration is to identify the relationship between the characteristics of the raw elements (polymeric foam and magnetic particles) and the magneto-mechanical performance of the magnetic foam. The main goal is a reliable phenomenological model that provides, as output, parameters needed to obtain optimal performance in both "passive" applications (structural reinforcement and gradient properties) and "active" modes (actuation and control through magnetic field) of lightweight porous structures reinforced with aligned magnetic particles. In particular, the average distribution, size and shape of particles, their magnetic characteristics, and mechanical properties of the foam will be considered as processing parameters. About the latter, well established criteria of homogenization will be adopted in order to derive simple constitutive relationships for low computational requirements. The developed 0D constitutive model will be phenomenological, while a FEM model will be based on the magnetic and mechanical balance laws. The development and validation of the model will be performed by comparing predictions with results provided by the experimental characterization of MAPs.

Ultimo aggiornamento: 03/05/2024