  We present a theoretical and experimental study of the fragmentation of
closed thin shells made of a disordered brittle material. Experiments were
performed on brown and white hen egg-shells under two different loading
conditions: impact with a hard wall and explosion by a combustible mixture both
give rise to power law fragment size distributions. A three-dimensional
discrete element model of shells is worked out. Based on simulations of the
model we give evidence that power law fragment mass distributions arise due to
an underlying phase transition which proved to be abrupt for explosion and
continuous for impact. We demonstrate that the fragmentation of closed shells
defines a new universality class of fragmentation phenomena.
