Role of dislocation in plastic deformation
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While some materials are elastic in nature up point of fracture, many engineering
materials like metals and thermo-plastic polymers can undergo substantial permanent
deformation. This characteristic property of materials makes it feasible to shape them.
However, it imposes some limitations on the engineering usefulness of such materials.
Permanent deformation is due to process of shear where particles change their neighbors.
During this process inter-atomic or inter-molecular forces and structure plays important
roles, although the former are much less significant than they are in elastic behavior.
Permanent deformation is broadly two types – plastic deformation and viscous flow.
Plastic deformation involves the relative sliding of atomic planes in organized manner in
crystalline solids, while the viscous flow involves the switching of neighbors with much
more freedom that does not exist in crystalline solids.
It is well known that dislocations can move under applied external stresses. Cumulative
movement of dislocations leads to the gross plastic deformation. At microscopic level,
dislocation motion involves rupture and reformation of inter-atomic bonds. The necessity
of dislocation motion for ease of plastic deformation is well explained by the discrepancy
between theoretical strength and real strength of solids, as explained in chapter-3. It has
been concluded that one-dimensional crystal defects – dislocations – plays an important
role in plastic deformation of crystalline solids. Their importance in plastic deformation
is relevant to their characteristic nature of motion in specific directions (slip-directions)
on specific planes (slip-planes), where edge dislocation move by slip and climb while
screw dislocation can be moved by slip and cross-slip.
The onset of plastic deformation involves start of motion of existing dislocations in real
crystal, while in perfect crystal it can be attributed to generation of dislocations and
materials like metals and thermo-plastic polymers can undergo substantial permanent
deformation. This characteristic property of materials makes it feasible to shape them.
However, it imposes some limitations on the engineering usefulness of such materials.
Permanent deformation is due to process of shear where particles change their neighbors.
During this process inter-atomic or inter-molecular forces and structure plays important
roles, although the former are much less significant than they are in elastic behavior.
Permanent deformation is broadly two types – plastic deformation and viscous flow.
Plastic deformation involves the relative sliding of atomic planes in organized manner in
crystalline solids, while the viscous flow involves the switching of neighbors with much
more freedom that does not exist in crystalline solids.
It is well known that dislocations can move under applied external stresses. Cumulative
movement of dislocations leads to the gross plastic deformation. At microscopic level,
dislocation motion involves rupture and reformation of inter-atomic bonds. The necessity
of dislocation motion for ease of plastic deformation is well explained by the discrepancy
between theoretical strength and real strength of solids, as explained in chapter-3. It has
been concluded that one-dimensional crystal defects – dislocations – plays an important
role in plastic deformation of crystalline solids. Their importance in plastic deformation
is relevant to their characteristic nature of motion in specific directions (slip-directions)
on specific planes (slip-planes), where edge dislocation move by slip and climb while
screw dislocation can be moved by slip and cross-slip.
The onset of plastic deformation involves start of motion of existing dislocations in real
crystal, while in perfect crystal it can be attributed to generation of dislocations and
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