Dislocation-free zone model of fracture comparison with experiments

Journal Article · Sun Aug 01 04:00:00 EDT 1982 · J. Appl. Phys.; (United States)

DOI:https://doi.org/10.1063/1.331448· OSTI ID:5043515

Ohr, S M; Chang, S

The dislocation-free zone (DFZ) model of fracture has been extended to study the relationship between the stress intensity factor, extent of plastic deformation, and crack tip geometry of an elastic-plastic crack as a function of applied stress. The results show that the stress intensity factor K decreases from the elastic value at first slowly, then goes rapidly to zero as the number of dislocations in the plastic zone increases. The crack with a zero stress intensity factor has its crack tip stress field completely relaxed by plastic deformation and hence is called a plastic crack. Between the elastic and plastic cracks, a wide range of elastic-plastic cracks having both a stress singularity and a plastic zone are possible. These elastic-plastic cracks with a DFZ are predicted if there is a critical stress intensity factor K/sub g/ required for the generation of dislocations at the crack tip. The expression for K/sub g/ is obtained from the crack tip dislocation nucleation model of Rice and Thomson. In most metals, the magnitude of K/sub g/ is less than the critical stress intensity factor for brittle fracture K/sub c/. The values of K are determined from electron microscope fracture experiments for various metals and they are found to be in good agreement with the K/sub g/ predicted from the model. It is concluded that for most ductile and semibrittle metals, the mechanism of dislocation generation is more important than the fracture surface energy in determining the stress intensity factor at the crack tip.

• Research Organization: Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
• DOE Contract Number: W-7405-ENG-26
• OSTI ID: 5043515
• Journal Information: J. Appl. Phys.; (United States), Journal Name: J. Appl. Phys.; (United States) Vol. 53:8; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DEFORMATION
DISLOCATIONS
ELECTRON MICROSCOPY
ELEMENTS
FAILURES
FRACTURES
GEOMETRY
LINE DEFECTS
MATHEMATICAL MODELS
MATHEMATICS
MECHANICAL PROPERTIES
METALS
MICROSCOPY
PLASTICITY
STRESSES