Abstract
The effects of notch acuity, inclusion content, and strength level on the toughness of a variety of ductile steels have been investigated infully plastic single edge notched bend testpieces. Results for specimens containing fatigue precracks and sharp notches indicate that accurate predictions of a material's resistance to the initiation of fibrous fracture ahead of afatigue crack may be inferred from tests on notched testpieces andfrom a knowledge of the microstructure of the material; an experimental procedure has been proposed whereby this may be achieved for quality control and material evaluation purposes. The spacing of optically visible inclusions is found essentially to define both the unit of ductile crack extension and, for low-strength steels, the limiting lateral dimensions of the high-strain field ahead of the crack tip. As a consequence, the notch-tip ductility isfound to be invariant with the changes in notch acuity for sharp stress concentrators. The effect of increasing the purity and/or strength level is to alter the mechanism offibrous fracture from one involving void growth and coalescence to one of predominantly shear character.
Get full access to this article
View all access options for this article.