  In the present paper, the simplest model of strain-gradient elasticity will
be considered, that is the isotropy in a bidimensional space. Paralleling the
definition of the classic elastic moduli, our aim is to introduce second-order
isotropic moduli having a mechanical interpretation. A general construction
process of these moduli will be proposed. As a result it appears that many sets
can be defined, each of them constituted of 4 moduli: 3 associated with 2
distinct mechanisms and the last one coupling these mechanisms. We hope that
these moduli (and the construction process) will be useful for forthcoming
investigations on strain-gradient elasticity.
