  The opening profile of the cracks produced in the Double Cleavage Drilled
Compression (DCDC) specimens for brittle materials is investigated. The study
is achieved by combining Finite Element simulations of a DCDC linear elastic
medium with experimental measurements by crack opening interferometry on pure
silica glass samples. We show that the shape of the crack can be described by a
simple expression as a function of the geometrical parameters of the sample and
the external loading conditions. This result can be used to measure accurately
in real time relevant quantities during DCDC experiments, such as the crack
length or the stress intensity factor applied to the specimen.
