  The stress field at the tip of a crack of a thin plate of elastic material
that is broken due to a mode III shear tearing has a universal form with a
non-universal amplitude, known as the stress intensity factor, which depends on
the crack length and the boundary conditions. We present in this paper exact
analytic results for this stress intensity factor, thus enriching the small
number of exact results that can be obtained within Linear Elastic Fracture
Mechanics (LEFM).
