This research proposal concerns the mechanics of fibered Soft Active Materials (SAM) and wants to exploit their peculiar behavior for new applications whilst reinforcing the theoretical knowledge paramount to their accurate modeling. The applications are concerning fiber reinforced magneto-rheological elastomers (fMRE) and fiber reinforced electro-rheological elastomers (fERE), which are interesting materials, due to their capability of bearing large deformations, controlled by external fields, either electric or magnetic in the present case. The fibers are usually the active part of the composite and are embedded into a highly deformable matrix. Their active behavior can be described within the framework of finite elasticity with remodeling distortions that has already successfully applied to the myocardium tissues by some components of the research group. One of the short-term goals of the project will be the active control of the micro and macro shape-changes of these materials via theoretical and computational modeling.
As long-term objectives, the focus of this project is on two applications: vibration absorbers and dampers with magnetically controllable hysteresis and virtual artificial prototypes of myocardium patches, a sort of precursors of the in-vitro engineered constructs of functional myocardium which are currently under investigation. The applications can be realized by using fMRE and fERE; both the applications require the active control of the micro and macro shape-changes of those materials.
The most ambitious targets of the program are: (a) theoretical and computational modeling of the active control of the strain pattern in fMRE and fERE thin sheets through remodeling theory; (b) exploit the use of fMRE to realize new technologies within the context of vibration absorbers and dampers with magnetically controllable hysteresis; (c) exploit the use of fERE to realize virtual prototypes tuned to replicate the mechanical behavior of myocardium tissue along the cardiac cycle.
All of them will determine a progress beyond the State of the Art, as detailed below and in the next section (tasks of the participants).
Target a.
The key ideas behind our modeling approach to fMRE and fERE are that the fibers are the only active components of the composite and, according to the active stimuli they receive, they would change their state as they were free from the surrounding passive matrix. For instance, in fMRE, the fibers would rotate to align with the external magnetic field, hence the active deformation Fo is locally described by a rotation field; in fEREs, fibers would like to change their lengths, hence the active deformation Fo is locally described by an uniaxial tensor field. In these composites with active fibers, Fo is never compatible and such a lack of compatibility induces elastic strains in the materials, and stresses according to the selected passive material response. The active control of the micro and macro strains occurring due to the lack of compatibility are studied following successive steps described in the next section, based on a new remodeling balance equation.
It is worth noting that a secondary goal in exploiting the target is the identification of the source terms, depending on the magnetic or electric field, in the remodeling balance equation which represent the driving forces of the deformation processes. It is a key challenge, largely studied in the theory of growth [23], and would determine a novel methodological approach in the modeling of fMRE and fERE mechanical behavior.
Target b.
Under large amplitude oscillatory shear, magneto-rheological elastomers have been already used to control the friction force in a sliding rheometer plate by modulating the external magnetic field. This elastomer are commonly produced by dispersing carbonyl iron spherical particles in silicone rubber. However, recent work [20] has shown the feasibility of replacing the spherical filler with short carbon fibers coated with nickle that enlarge the design space for this type of actuators possibly leading to novel applications [21]. In particular, the accurate control of the fiber orientation in the soft matrix by an external magnetic field can have a significant effect on the roughness properties of an elastomeric sheet.
Target c.
The key issues are: (c1) non-invasive data capture on patients and healthy people via 3DSTE; (c2) post-processing of data to get global and local measures of the strain pattern via Modern Shape Analysis (MSA) and Principal Strain Analysis (PSA), respectively (up to now successfully used by some components of the group to study the mechanical behavior of the left heart under physiological and physio-pathological conditions); (c3) use of the inferred global and local strain measures to tune the mechanic behavior of a fERE thin sheet capable to replicate myocardium mechanics, i.e. our virtual synthetic prototype of a cardiac patch of functional myocardium.
We will use a 3DSTE system to get in-vivo data on myocardium tissue; the post-processing analysis of data based on MSA and PSA is developed within a MatLab code with reference to selected small patches of the myocardium, also corresponding to an infarcted area, when interested. Both the studies will be in details described in the next sections. Eventually, an inverse problem will be set to get the appropriate tuning of fERE thin sheets apt to replicate myocardium functionality.
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