Bauschinger

The Bauschinger effect is a material-science phenomenon in which the yield strength of a metal in the reverse direction is reduced after prior plastic deformation in the forward direction. It is named after the German engineer Johann Bauschinger, who described the behaviour in metals in the late 19th century. The effect is particularly noted in metals such as steel and copper and is relevant to processes that involve reversed or cyclic loading.

Mechanism: Plastic deformation creates dislocation structures, such as walls and cells, and residual back stresses that oppose subsequent dislocation glide in the opposite direction. When loading is reversed, these internal stresses lower the stress required to initiate yielding, producing a lower yield point in the reverse direction than in the initial loading. The effect increases with pre-strain and is influenced by temperature and microstructure.

Applications and measurement: The Bauschinger effect informs metal-forming simulations, residual-stress assessment, and fatigue life predictions, because reverse loading conditions can lead to earlier plastic yielding. It is often represented in constitutive models as kinematic hardening with back stresses. The Bauschinger test, in which a specimen is pre-strained in one direction and then loaded in the opposite direction, is used to quantify the effect and to calibrate models.

Related concepts include back stress and kinematic hardening, which are used to model the Bauschinger effect in steel and other metals.