Bauschinger effect
Encyclopedia
The Bauschinger effect refers to a property of material
s where the material's stress/strain characteristics change as a result of the microscopic stress
distribution of the material. For example, an increase in tensile yield strength occurs at the expense of compressive yield strength.
The Bauschinger effect is named after the German engineer Johann Bauschinger
.
While more tensile cold working increases the tensile yield strength, the local initial compressive yield strength after tensile cold working is actually reduced. The greater the tensile cold working, the lower the compressive yield strength.
The Bauschinger effect is normally associated with conditions where the yield strength of a metal decreases when the direction of strain is changed. It is a general phenomenon found in most polycrystalline metals. The basic mechanism for the Bauschinger effect is related to the dislocation
structure in the cold worked metal. As deformation occurs, the dislocation
s will accumulate at barriers
and produce dislocation pile-up
s and tangles. Based on the cold work structure, two types of mechanisms are generally used to explain the Bauschinger effect.
First, local back stresses may be present in the material, which assist the movement of dislocations in the reverse direction. Thus, the dislocations can move easily in the reverse direction and the yield strength of the metal is lower. The pile-up of dislocations at grain boundaries and Orowan loops around strong precipitates are two main sources of these back stresses.
Second, when the strain direction is reversed, dislocations of the opposite sign can be produced from the same source that produced the slip-causing dislocations in the initial direction. Dislocations with opposite signs can attract and annihilate each other. Since strain hardening is related to an increased dislocation density, reducing the number of dislocations reduces strength.
The net result is that the yield strength for strain in the opposite direction is less than it would be if the strain had continued in the initial direction.
Material
Material is anything made of matter, constituted of one or more substances. Wood, cement, hydrogen, air and water are all examples of materials. Sometimes the term "material" is used more narrowly to refer to substances or components with certain physical properties that are used as inputs to...
s where the material's stress/strain characteristics change as a result of the microscopic stress
Stress (physics)
In continuum mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the body on which internal forces act. These internal forces are a reaction to external forces applied on the body...
distribution of the material. For example, an increase in tensile yield strength occurs at the expense of compressive yield strength.
The Bauschinger effect is named after the German engineer Johann Bauschinger
Johann Bauschinger
Johann Bauschinger was a mathematician, builder, and professor of Engineering Mechanics at Munich Polytechnic from 1868 until his death. The Bauschinger effect in materials science is named after him. He was also the father of astronomer Julius Bauschinger ....
.
While more tensile cold working increases the tensile yield strength, the local initial compressive yield strength after tensile cold working is actually reduced. The greater the tensile cold working, the lower the compressive yield strength.
The Bauschinger effect is normally associated with conditions where the yield strength of a metal decreases when the direction of strain is changed. It is a general phenomenon found in most polycrystalline metals. The basic mechanism for the Bauschinger effect is related to the dislocation
Dislocation
In materials science, a dislocation is a crystallographic defect, or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials...
structure in the cold worked metal. As deformation occurs, the dislocation
Dislocation
In materials science, a dislocation is a crystallographic defect, or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials...
s will accumulate at barriers
and produce dislocation pile-up
Grain boundary strengthening
Grain-boundary strengthening is a method of strengthening materials by changing their average crystallite size...
s and tangles. Based on the cold work structure, two types of mechanisms are generally used to explain the Bauschinger effect.
First, local back stresses may be present in the material, which assist the movement of dislocations in the reverse direction. Thus, the dislocations can move easily in the reverse direction and the yield strength of the metal is lower. The pile-up of dislocations at grain boundaries and Orowan loops around strong precipitates are two main sources of these back stresses.
Second, when the strain direction is reversed, dislocations of the opposite sign can be produced from the same source that produced the slip-causing dislocations in the initial direction. Dislocations with opposite signs can attract and annihilate each other. Since strain hardening is related to an increased dislocation density, reducing the number of dislocations reduces strength.
The net result is that the yield strength for strain in the opposite direction is less than it would be if the strain had continued in the initial direction.
See also
- BacklashBacklash (engineering)In mechanical engineering, backlash, sometimes called lash or play, is clearance between mating components, sometimes described as the amount of lost motion due to clearance or slackness when movement is reversed and contact is re-established...
, a similar extrinsic behavior in large-scale mechanical systems.