The Stress Dead Zones in the formulation of the Line Spring Model

The stress distribution in flat plates containing cracks and subjected to a uniform remote membrane or bending stress field shows that some zones refer to a high stress concentration compared with nominal values; while conversely, some other zones have almost negligible stresses, as a result of the redistribution of internal forces. Those zones, with a small or residual stress field, can be ignored in the model of the numerical simulation, as in such zones the material does not practically contribute to the structure stiffness. The removal of such Stress “Dead” Zones (SDZ), usually close to the crack mating faces, translates into a useful simplification in the structure shape model. This modified geometry supports the implementation of simple analytical algorithms in the evaluation of stiffness factors necessary for the computation of the associate stress-intensity factor (SIF) along the crack line. The accuracy of such models depends mainly on a precise delimitation of the SDZ at crack vicinity in the structural member. To ensure such precision, Digital Image Correlation was used to achieve reliable results for the SDZ delimitation areas.