Notch toughness is the ability that a material possesses to absorb energy in the presence of a flaw. As mentioned previously, in the presence of a flaw, such as a notch or crack, a material will likely exhibit a lower level of toughness. When a flaw is present in a material, loading induces a triaxial tension stress state adjacent to the flaw. The material develops plastic strains as the yield stress is exceeded in the region near the crack tip. However, the amount of plastic deformation is restricted by the surrounding material, which remains elastic. When a material is prevented from deforming plastically, it fails in a brittle manner.
Stress concentration around the notch causes plastic deformation to occur in this area. The decrease in area caused by the notch increases the stress to a value above the yield stress for the material, while the rest of the specimen may still be at a stress below the yield stress. This plastic hinge which develops at the notch reduces the total amount of plastic deformation in the test specimen.
flaw