The stress raisers effects on the materials mechanical characteristics, analyzed by local microhardness measurements

There have been few studies on the effects of stress raisers on the parts that are plastically deformed, at least into a certain extent of their volume. Such a situation may arrive near a stress raiser, when the peak stress value rises over the material yield stress limit. Some tensile tests are described in the paper, on flat aluminum specimens, with and without the presence of a stress raiser on their surface, namely a through frontal hole, at the center of their calibrated region. Some of the mechanical characteristics (yield limit, elongation at break, Young's modulus) were affected by the stress raiser presence, but its ductile behavior and tensile strength were not. The effective values of stress and strain concentration coefficients were calculated using the Neuber's rule, but the results may be considered as overestimated. The plastic strain enlargement in the specimen volume was also evaluated by measuring the Vickers microhardness values in the stress raiser vicinity. The tests results were shown that the plastic deformation is more pronounced for the measuring points that are closer to the hole's edge; that fact was confirmed by the specimens appearance, after the material failure. A hardness values ratio is finally proposed as an evaluation of the effective stress concentration coefficient.