Bauschinger effect

  • alternate bending
  • alternating loading
  • Bauschinger effect
  • Bauschinger modulus
  • Bauschinger parameter
  • Bauschinger strain
  • hysteresis
  • primary loading
  • secondary loading
  • softening

The Bauschinger effect is a special case of forming behavior among metals. It is defined as a change of material parameters due to a reversal of loading direction between two consecutive loads (e.g. tension/compression). Because of the Bauschinger effect, loading against the initial loading direction results in a distinctly lower beginning of flow (stretching limit, elongation limit). Alternating tension-compression loads result accordingly in a shift of the flow limit. The reasons are to be found in a change of the material's microstructure. Factors affecting the magnitude of the Bauschinger effect include the material, its alloying elements (particularly carbon), the number of load cycles, and the dimensions of external deformation (actual strains). 


A bend is the strain produced in long and endless bodies by external forces, resulting in internal bending moments over their cross sections. The original straightness or curvature of the bodies is changed either elastically or plastically as the result. The internal bending moments arising in every cross section as a reaction to these external bending moments lead to tensile and compressive forces, resulting in an equilibrium of forces and moments.

Bodies subjected to bending are shortened on the one side by compressive stresses while on the other side they are lengthened by tensile forces. There is a (practically Iinear) continuous transition from tensile stress to compressive stress over the cross section, with a neutral fiber that is neither stretched nor compressed and therefore stress-free.

The diagram opposite shows a wire cross section with an applied external bending moment and the resultant strain and stress characteristic.

Bending roll

  • active-bending roll
  • bending roll
  • wrap

A bendlng roll is a rotating roll (pulley) on which the product to be straightened is plastically deformed during a partial or complete wrap. The important point is that the product should only be bent in the direction of its initial curvature. In other words: the initial curvature, the bend and the final curvature should all lie in one plane. A change of plane along this course of curvature and bending during the straightening process will cause helicities (twisting of the product to be straightened).

Subjecting the curvature to several changes of plane has a particularly negative effect. It leads not only to curvature fluctuations, which are very difficult to eliminate, but also to extremely disadvantageous right/left helicities.

The magnitude of plastic deformation suffered by the product to be straightened depends e.g. on its material parameters and on the diameter of the bending roll.