Fracture detection problems:: applications and limitations of the energy momentum tensor and related invariants

We show that under certain circumstances\ if displacement measurements are made inside and:or outside a body\ it is possible to use two invariants based on the energy momentum tensor to determine "to some extent# the crack direction and length for cracks in bidimensional problems or the crack direction and area for cracks in three dimensional problems[ This is done for a certain family of non!linear materials with a given toughness which includes linearly elastic materials with quadratic strain energy and power law elastic[ One of the limitations is that the crack must be straight in 1D or planar in 2D