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ENABLING OBJECTIVES (Cont.) - h1017v2_34
Figure 1   Basic Fracture Types

Material Science Volume 2 of 2
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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







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