BOOK_CONTENT
From Handbook of Die Design, Second Edition

8-1 STRESS, STRAIN, ELONGATION, COMPRESSION

The process of material forming (i.e., deformation) depends on several laws, closely related to those of physics. First of all, the law of constant volume applies here. No matter how much we shrink or stretch a part, no matter how much we form it, draw it, or compress it, the basic volume we had at the beginning will always be there. True, minor volumnar changes may take place during compressive forming, but these are so minute, so small with regard to the bulk of the part that they can easily be considered irrelevant.

Another rule is pertaining to the distribution of particles in formed material. During changes of material structure, all affected segments will attempt to relocate into areas of least resistance. In other words, the material will always tend to flow where it is not obstructed, or to fill the gaps located nearby, or to conform to shapes exerting pressure upon it.

Rule number three: Every permanent deformation takes place after the changes in the material structure exceeded the maximum elastic limit of that material. However, this is not the final deformation achieved, as, after release of the applied forming pressure, the material makes an attempt to return to its previous location; we say it springs back. The complete amount of deformation is therefore equal to the sum of the elastic segment and the plastic segment of the operation, or


There are two types of deformation that can be observed during any forming...

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