Skip to main content

Multi-scale, Multi-physics MOdelling and COmputation of magneto-sensitive POLYmeric materials

Final Report Summary - MOCOPOLY (Multi-scale, Multi-physics MOdelling and COmputation of magneto-sensitive POLYmeric materials)

Magneto-sensitive elastomers (MSEs) are a new class of materials that change their mechanical behaviour in response to the application of an external magnetic field. These smart materials have received considerable attention in recent years due to their exciting potential uses in engineering applications. Examples include rapid-response, variable stiffness actuators and dampers for mechanical systems with electronic controls, and artificial muscles for use in robotic and biomechanical devices. Typically, these materials are produced by curing a mixture of ferromagnetic particles (1–5µm in size, between 0–30% by volume and usually composed of iron) distributed in a polymeric matrix. Some properties of the final composite can be controlled by changing the conditions under which the material is cured. Ultimately these, amongst other factors, affect both the stiffness properties of the composite and how it responds to a magnetic field.

As a prerequisite for the design of industrial devices using MSEs, numerous challenges related to the fabrication, testing and computer modelling of these materials needed to be addressed. The MOCOPOLY project sought to overcome these challenges, with its dedicated multinational members contributing in excess of 40 peer-reviewed publications to the scientific literature on a variety of topics.

We developed a methodology to reproducibly fabricate MSEs for the purpose of experimental testing. Two devices (namely a rotational rheometer and tensile test machine) were procured specifically for this purpose. Much work was performed to develop experimental protocols that lead to reliable and repeatable results using this equipment. Auxiliary experimental studies using state-of-the-art technology provided an understanding of the internal structure of the MSEs, and provided a deep understanding of the complex structure of the MSE at macro- and microscopic levels.

Inspired by the experimental data extracted for the MSE in both uncured and cured states, we were able to mathematically model the macroscopic deformation characteristics of MSEs at large strains and in the presence of a magnetic field. We used a unique approach to encapsulate the mechanics of the imperfect chain-like structures that are developed by the particles when the material is cured under a magnetic field. We developed a computational framework to simulate the curing process of the magneto-viscoelastic MSEs, under the influence of a magneto-mechanical load. We also developed a unified framework for computational analysis of the MSEs using high performance, open-source software. Some aspects of this framework and derivative works were, in turn, contributed back to the open-source community.

To complement the work at large length scales, micro-structural studies were conducted to determine the influence of the particles within MSEs. We produced a computational model that captured macro- and nano-scale effects and, with this enhancement, we were able to represent characteristics only observed at this length scale. The process of homogenisation allowed us to estimate the effective large-scale properties of a heterogeneous material from the response of the underlying micro-structure. Using computational methods, we extended the already established methods to encompass phenomena only experienced within MSEs, such as the presence and interaction of magnetisable particles. We therefore developed and utilised approaches to perform studies that produced a statistical quantification of uncertainties indicated in experimental data. To complement and validate these studies, we developed a robust method for the identification of microscopic material parameters using macroscopic experiments.

Due to the nature of the fundamental mathematical equations governing magneto-elasticity and the conditions under which we conduct our studies, much of the theory developed for magneto-mechanics can also be directly applied to electro-mechanics, and vice-versa. Through this interdisciplinary overlap we were able to extend our findings to other interesting electro-mechanical smart materials.

During the first half the MOCOPOLY project we made significant progress towards developing a better understanding of MSEs. In the second half of the project we consolidated our efforts and knowledge gained during the first period, and finalised various avenues of research initiated early in the project. The MOCOPOLY team have successfully achieved the results envisioned at the project's inception, and gratefully acknowledge the funding and support from the ERC and Friedrich-Alexander - Universität Erlangen-Nürnberg.