Brittle Fracture Summary

BRITTLE FRACTURE MECHANISM DOE-HDBK-1017/2-93 Brittle Fracture Summary The important information in this chapter is summarized below. Brittle Fracture Summary Ductile fracture is exhibited when metals can sustain substantial plastic strain or deformation before fracturing. Brittle fracture is exhibited when metals fracture with a relatively small or negligible amount of plastic strain. Nil-Ductility Transition (NDT) temperature is the temperature above which a material is ductile and below which it is brittle. Changes made to decrease NDT include: Use of smaller grain size in metals Small additions of selected alloying elements such as nickel and manganese to low-carbon steels NDT decreases due to smaller grain size and increases due to irradiation Brittle fracture requires three conditions: Flaw such as a crack Stress sufficient to develop a small deformation at the crack tip Temperature at or below NDT Conditions to mitigate crack initiation: Smaller grain size Higher temperature Lower stress levels Factors determining fracture toughness of a metal include: Metal composition Metal temperature Extent of deformations to the crystal structure Metal grain size Metal crystalline form MS-04 Page 6 Rev. 0