  It is well-known that there exist rigid frameworks whose physical models can
snap between different realizations due to non-destructive elastic deformations
of material. We present a method to measure these snapping capability based on
the total elastic strain energy density of the framework by using the physical
concept of Green-Lagrange strain. As this so-called snappability only depends
on the intrinsic framework geometry, it enables a fair comparison of
pin-jointed body-bar frameworks, thus it can serve engineers as a criterion
within the design process either to avoid snapping phenomena (e.g. truss
structures) or to utilize them (e.g. multistable materials). Moreover, it turns
out that the value obtained from this intrinsic pseudometric also gives the
distance to the closest shaky configuration in the case of isostatic
frameworks. Therefore it is also of use for the kinematics community, which is
highly interested in the computation of these singularity-distances for diverse
mechanical devices. In more detail we study this problem for parallel
manipulators of Stewart-Gough type.
