The Bauschinger effect

The basics of mechanical engineering starts from the stress strain diagram in which we basically do tension test i.e., the specimen is under tensile force and we study the strain until the specimen is fractured.On the basis of specific strain points like elastic point,yield point,fracture point the corresponding stresses are noted.

But what if after this you reverse the load?
Are they going to show the same yield point and show some symmetric diagram?
Noo!!

Here the yield point in compression is actually reduced.

Figure 1.

The reduction in yield point is only after it goes through the tension.

If the specimen is not prestressed i.e., you apply load from zero to reverse direction then it will follow its predicted symmetric behaviour.

This loss in yield strength after reversal of load from an yielded point is called Bauschinger effect.
This phenomena is also called strain softening or work softening.
Exhibits in all metal and alloys,in different
extents.Even possible in torsion too.

Figure 2

 Similarly if you take the compression test and then reverse the load to tension then a decreased yield point during tension is produced.  As shown above.

 The loop you will get will be like some hysterisis curve of your 12th class magnetic losses chapter.

Do they help in study of design of fatigue loading?
Most probably No!!

Fatigue occurs at very less load than what we use as failure point in static load and other governing factors like if you want to design it for finite life or infinite life etc.So,most probably this small reduction in yielding isn't that substantial to consider for design.