Definition of Bauschinger Effect

Bauschinger Effect:

The Bauschinger effect (BE) can be observed during tension-compression conditions and is

associated with a decrease of the yield stress when the loading direction is reversed (Fig. 1). Such

behaviour may have different origins: for instance, if due to residual macroscopic stresses, it is

not a true Bauschinger effect. Macroscopic residual stresses may result from heat treatment or

from cold work during manufacture.

Two other causes exist. One of them, the principal cause, is related to the dislocation

structure in the work-hardened metal. As deformation occurs, the dislocations accumulate at

barriers (precipitates, grain boundaries) and form dislocation pile-ups and tangles. Two types of

mechanisms are used to explain BE. First, local back stresses, which oppose the applied stress on

the slip plane, are produced by dislocations pile-ups on slip planes at barriers (pile-up of

dislocations at grain boundaries and Orowan loops around strong precipitates). Back stresses

assist the movement of dislocations in the reverse direction due to their favourable orientation to

the stress axis. Thus, the dislocations can move easily in the reverse direction and the yield

strength of the metal is lowered. Secondly, when the slip direction is reversed, dislocations of

opposite sign may be created at the same source that produced the slip-causing dislocations in the

initial direction. Since dislocations of opposite sign attract and annihilate each other, the net

effect is a further softening of the lattice.

The other cause, known as “composite effect”, is due to zones of different yield

strength inside the material, on a microscopic scale. This case is sometimes referred to as a

pseudo-Bauschinger effect. The Masing or generalized Saint-Venant model describes this

behaviour. Figure 2 shows a rheological model for two phases differing by their flow stress.

Figure shows the resulting behaviour:

Stress-strain curve demonstrating a Bauschinger effect. After load inversion, plastic

deformation sets in at a lower stress (in absolute values) in compression than during the previous

load cycle (stress at the reversal point).

Figure Rheological model of the Masing or generalized Saint-Venant model, for two phases