A line defect in a crystal structure. Its Burgers vector measures the closure failure of a circuit around the line. Motion can produce permanent plasticity without simultaneously breaking every bond across a whole plane.
A curved dislocation can be approximated as a line with tension of order . The coefficient depends on elastic constants, character and logarithmic length scales. The simple estimate gives a pinning bypass stress for a semicircular segment of free span .
A dislocation whose Burgers vector is not a full translation of the perfect crystal, so its glide can leave a planar stacking fault. Vector conservation and the actual slip plane constrain reactions and dissociation.
A sessile partial junction associated with intersecting stacking faults. A typical FCC resultant has vector . Its Burgers vector and junction line can define a plane outside the ordinary glide family.
An FCC partial dislocation with Burgers vector lying in a close-packed plane. Two suitable Shockley vectors can sum to an FCC perfect vector .
A perfect vector can separate into two in-plane Shockley partials bounding a stacking-fault ribbon. The sum of squared Burgers magnitudes falls from to , reducing the simplest elastic line-energy estimate, while stacking-fault area costs energy.
An order-preserving total dislocation in an ordered crystal, often dissociated into smaller dislocations separated by an antiphase boundary. Two matching dislocations can restore order in the gamma prime phase.
A dislocation that accommodates some lattice mismatch at an interface. An initially coherent epitaxial layer or island can instead store elastic deformation; introducing a misfit dislocation trades some strain energy for the defect's formation energy. A projected image must be indexed before a particular spacing discrepancy is assigned to misfit strain.
Motion of an edge component perpendicular to its glide plane by absorbing or emitting point defects. Unlike conservative dislocation glide, it changes the extra-plane content locally and is coupled to defect transport. Irradiation can drive climb by creating nonequilibrium vacancies and self-interstitials.
Total dislocation line length per material volume, with units . Circular loops with common radius and number density contribute .
A closed dislocation line. Vacancy or interstitial clustering can form a platelet bounded by a loop; its Burgers vector, habit plane and possible stacking fault specify its crystallographic character.
A line segment formed by interaction of dislocations from different slip planes. A junction can impede further dislocation glide. Energetic favourability alone does not establish whether the resulting segment is mobile on a particular plane.
A junction produced when suitable partial dislocations on intersecting FCC slip planes react to form a low-energy sessile stair-rod segment. It obstructs further slip and can promote work hardening. Frank energetic favorability alone is not a complete calculation of junction geometry or mobility.
The energy criterion associated with Frederick Charles Frank states that, for dislocations of comparable length with approximately common line-energy factors, a reaction conserving Burgers vector is energetically favourable when the displayed inequality holds. The rule is an energy estimate, not a proof that the geometry or kinetic barriers permit the reaction. Edge/screw character, elastic anisotropy and changed lengths refine it.
Conservative motion within a plane containing both the dislocation line and its Burgers vector. For a nonscrew line their cross product determines the plane normal; a screw line can belong to more than one such plane.
A lattice-friction stress for dislocation glide, associated with Rudolf Peierls and Frank Nabarro. A simple model gives , where is core width and the Burgers vector magnitude. Spreading slip over many atomic rows reduces the periodic energy barrier; narrower cores are harder to move in this model.
A crystallographic plane together with an allowed dislocation glide direction in that plane. Geometry alone does not determine its activation stress.
Plastic flow involving more than one active slip system. Interactions between dislocations on intersecting systems can give substantially faster work hardening than easy single slip.
Dislocation glide in a hexagonal crystal on its basal plane, ordinarily along a close-packed basal direction in the family. Direction indices must be converted using the actual hexagonal metric, including the ratio .
For uniaxial stress , projection onto a slip-plane normal and a slip direction gives the displayed shear stress. The angles and are measured from the tensile axis to that normal and direction respectively.
The ratio connecting a macroscopic tensile flow stress to a reference critical resolved shear stress in a specified polycrystal model. Texture, slip families and compatibility assumptions matter. An order-three factor is a conventional estimate for randomly oriented cubic grains, distinct from the factor two for a perfectly oriented single slip system.
The ideal activation criterion compares resolved shear stress with a critical resolved shear stress. Non-glide stresses, notably in some body-centred cubic crystals, can modify this ideal criterion.
In an ideal single-slip tensile test neglecting elastic stretch, the specimen end-to-end vector expressed in crystal coordinates changes as , with unit slip direction and slip-plane normal . It moves towards the slip direction along a great circle. The perpendicular component is unchanged, so . Secondary slip changes this kinematics; equal Schmid factors determine onset only if the systems have equal current critical stresses.
The orientation factor converting the magnitude of uniaxial stress to resolved shear stress. It lies between zero and because the slip-plane normal and slip direction are perpendicular.
For line tangent , a screw dislocation has Burgers vector parallel to , an edge dislocation has it perpendicular, and a mixed dislocation has both components.
Motion of a screw segment from one allowed glide plane to another containing the same Burgers vector.
The lattice translation represented by closure failure of a circuit around a dislocation, with a consistent circuit convention. It is a vector, so dislocation reactions conserve its direction as well as its magnitude.
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Dislocation can refer to different concepts depending on the context. Here are a few interpretations: 1. **Medical Context**: In medicine, a dislocation refers to the displacement of a bone from its normal joint position. This can occur due to trauma, injury, or even certain medical conditions. Common examples include shoulder dislocations or finger dislocations. Symptoms often include severe pain, swelling, and an inability to move the affected joint.