The prediction of defects arising in material forming processes and the evaluation of the straining effects in manufactured products are the main objectives of the theoretical and applied research in this field, with obvious economic implications. The results of these investigations are basic elements in optimisation of the material process sequences, product microstructure, mechanical properties and surface finish, tooling geometry and materials, friction, process equipment, etc.

In the past, defects in material working have tended to draw little attention from researchers. Efforts were devoted mostly to ideal materials and material characteristics, and to simplified processes which are easier to solve successfully. Tentative methods have been proposed to explain some defects arising in metal products by using slip-line field theory, upper- and lover-bound techniques of limit analysis. But, as is known, the limit analysis of plasticity theory is one alternative to the absence of precise solutions. On the other hand no prediction of defects can be provided by such methods.

Significant advances were made in the past two decades by introducing a new approach based on mathematical damage models, new bifurcation and instabilities theories in to defect analysis and formability characterisation. In addition, computer techniques based essentially on finite element methods have permitted simulation of plastic flow for more complex constitutive relations, replacing the trial-and error methods which are still commonly used in some material forming industries.

The series of conferences devoted to predictive methods of material processing defects initiated by the author in 1987, has drawn attention to these new...