Stefan Müller

Max Planck Institute for Mathematics in the Science

**ABSTRACT**: A fundamental problem in elasticity is to
derive theories for lower dimensional objects such as plates, shells
or rods from the fully nonlinear three dimensional theory. The usual
approach is to make certain assumptions on the three dimensional
solutions and then to deduce a lower dimensional theory by formal or
rigorous asymptotical analysis. These has lead to large variety of
theories, which are sometimes not mutually compatible.

Since the early 90's a new, mathematically rigorous, approach has emerged, which is based on the variational principle and the associated notion of convergence. Le Dret and Raoult have used convergence to derive a theory for elastic membranes (these have only stretching stiffness, but no bending stiffness and cannot resist compression). In these lectures I will report on ongoing work with G. Friesecke (Munich/ Warwick) and R.D. James (Minnesota) to derive a full hierarchy of limiting theories, which are distinguished by the scaling of the elastic energy as a function of thickness. In particular I will discuss the derivation of Kirchhoff's plate theory (which captures bending) and the much debated von Kármán theory.

A key mathematical ingredient is a quantitative
rigidity estimate which generalizes results
of F. John for deformations with small nonlinear strain.
A classical result says that any Lipschitz map
from a (bounded) connected set in to (we
are interested in ) whose derivative is
an element of a.e. has in fact constant derivative.
The quantative rigidity estimate says that this can be
extended to a linear estimate in . More precisely
for every and every Lipschitz domain we have

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