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The adaptive modification of the mechanical properties of structures has been described as a key to a number of new or
enhanced technologies, ranging from prosthetics to aerospace applications.
Previous work reported the electrostatic tuning of the bending stiffness of simple sandwich structures by modifying the
shear stress transfer parameters at the interface between faces and the compliant core of the sandwich. For this purpose,
the choice of a sandwich structure presented considerable experimental advantages, such as the ability to obtain a large
increase in stiffness by activating just two interfaces between the faces and the core of the beam.
The hypothesis the development of structures with tunable bending stiffness is based on, is that by applying a normal
stress at the interface between two layers of a multi-layer structure it is possible to transfer shear stresses from one layer
to the other by means of adhesion or friction forces. The normal stresses needed to generate adhesion or friction can be
generated by an electrostatic field across a dielectric layer interposed between the layers of a structure. The shear stress
in the cross section of the structure (e.g. a beam) subjected to bending forces is transferred in full, if sufficiently large
normal stresses and an adequate friction coefficient at the interface are given. Considering beams with a homogeneous
cross-section, in which all layers are made of the same material and have the same width, eliminates the need to consider
parameters such as the shear modulus of the material and the shear stiffness of the core, thus making the modelling work
easier and the results more readily understood.
The goal of the present work is to describe a numerical model of a homogeneous multi-layer beam. The model is
validated against analytical solutions for the extreme cases of interaction at the interface (no friction and a high level of
friction allowing for full shear stress transfer). The obtained model is used to better understand the processes taking place
at the interfaces between layers, demonstrate the existence of discrete stiffness states and to find guidance for the selection
of suitable dielectric layers for the generation of the electrostatic normal stresses needed for the shear stress transfer at the
interface.
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