BRITTLE FRACTURE MECHANISM
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
Lower stress levels
Factors determining fracture toughness of a metal include:
Extent of deformations to the crystal structure
Metal grain size
Metal crystalline form