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The application of fracture mechanics approach to residual stresses evaluation is reviewed and extended
to a general plane problem. The method is related to the progressive cutting techinique where the cut is
so thin to be considered as a crack and a Linear Elastic Fracture Mechanics approach is then applied.
When a crack-like cut is produced in a plane body affected by residual stresses, stresses rearrange and
the resulting strain relaxation is measured. The relationship between released residual stresses and
measured relaxed strains is discussed for a general position of the strain-gage. Moreover a general
condition is assumed where the crack is supposed to be straight but not necessarily perpendicular to the
surface or lying in a plane of symmetry; thus residual stress released on the crack-faces has both normal
and shear components. In this condition Mode I and Mode II Loadings are produced and also their
interaction has to be taken into account. The influence functions for the strain-gages are obtained by the
application of the Weight Functions Method.