BRITTLE FRACTURE MECHANISM

Brittle Fracture DOE-HDBK-1017/2-93 BRITTLE FRACTURE MECHANISM BRITTLE FRACTURE MECHANISM Personnel need to understand brittle fracture. This type of fracture occurs under specific conditions without warning and can cause major damage to plant materials. EO 1.1 DEFINE the following terms: a. Ductile fracture c. Nil-ductility Transition b. Brittle fracture (NDT) Temperature EO 1.2 DESCRIBE the two changes made to reactor pressure vessels to decrease NDT. EO 1.3 STATE the effect grain size and irradiation have on a material's NDT. EO 1.4 LIST the three conditions necessary for brittle fracture to occur. EO 1.5 STATE the three conditions that tend to mitigate crack initiation. EO 1.6 LIST the five factors that determine the fracture toughness of a material. EO 1.7 Given a stress-temperature diagram, IDENTIFY the following points: a. NDT (with no flaw) c. Fracture transition elastic point b. NDT (with flaw) d. Fracture transition plastic point Brittle Fracture Mechanism Metals can fail by ductile or brittle fracture. Metals that can sustain substantial plastic strain or deformation before fracturing exhibit ductile fracture. Usually a large part of the plastic flow is concentrated near the fracture faces. Metals that fracture with a relatively small or negligible amount of plastic strain exhibit brittle fracture. Cracks propagate rapidly. Brittle failure results from cleavage (splitting along definite planes). Ductile fracture is better than brittle fracture, because ductile fracture occurs over a period of time, where as brittle fracture is fast, and can occur (with flaws) at lower stress levels than a ductile fracture. Figure 1 shows the basic types of fracture. Rev. 0 Page 1 MS-04