3. Shaping instabilities

As mentioned above, instability phenomena contribute, alongside damage, to determining the ductility of a product (laboratory sample or industrial part). They manifest themselves in various forms, such as diffuse or localized stresses, or shear bands, adiabatic or not. In all cases, they result in the appearance of deformation heterogeneity on a macroscopic scale, which can lead to material failure in the zone concerned.

Among the many mechanical analyses of instability phenomena in forming 7, four simple models will be presented below, the first two concerning uniaxial tensile stress in an axisymmetric sample, the other two concerning stress in biaxial sheet metal drawing.