In some steels,is it possible the cleavage fracture happens after large amount of elongation in the uniaxial tension test of intact sample?
Some localized plastic deformation can occur during crack initiation and growth. Your question pertains to large-scale deformation which really blunts the crack tip. In those cases most of the fracture occur by void formation and by tearing of the inter-void material. Question - how you really observed such cleavage after large plastic deformation, in order to ask this question?
Hou Wang - No. cleavage is alternate to flow not sequential. cleavage dissipates the concentrated energy at the crack tip and therefore no further cleavage occurs. However in some cases as H-embrittlement, some localized slip occurs but that get arrested by back stress of the dislocations and cleavage may take over. We have analyzed this problem recently using discrete dislocation modeling.
Hou Wang - your question is about fracture end - Deformation in steels at low temperatures occurs by dislocation process. In there is no pre-existing crack, then fracture has to occur by first initiating a crack and then propagating the initiated crack. Initiation occurs at slip concentration at obstacles - either grain boundaries or in the case of steels carbides. Fracture or crack initiation occurs there - From then on we are concerned about the propagation of the initiated crack, In principle it can propagate by cleavage mode or by deformation induced void formation and coalescence mode. Since you say it is extensive deformation, I would say it is by deformation induced void formation and their coalescence and not by cleavage. In some steels, temper embrittlement can occur. look up in Google to know more about it - then you can not have extensive deformation as you mentioned.
Tearing is to severe plastic deformation. Quasi-cleavage is not for extensive deformations. Quasi-cleavage is supposed to occur when say H enhances one side plasticity - called HELP mechanisms and on the other brittle crack extension by cleavage. We have analyzed this problem recently using discrete dislocations and just submitted for publication and it is under review. Once published it will be posted.
Dear Kuntimaddi:
Is tearing that after severe plastic deformation ,then reduced crosssection can't bear load anymore that atom bonds break directly. tearing seems often accompany ductile or Quasi-cleavage .
Quasi-cleavage mechnism is not clear for me . how it happen and what's the difference between Quasi-cleavage and brittle-ductile fracture?
look forward to read your paper.
The cross section can be between voids not necessarily specimen cross section. Cleavage and deformation are not compatible. HELP mechanisms operate under H - environment - look up under google you can find review paper by Prof R. Gangloff of U. of Virginia. You may also get a better idea about cleavage vs deformation.
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