In the process of bend to the crack arise up on the stretched (protuberant) surface to the standard. The moment of destruction is fixed after the origin of cracks, that visible with a naked eye. It is possible to consider that deformation of metal on a surface to the standard, that bends flows droningly. It allows enough exactly for curvature of circular net, that is inflicted on a surface to the standard, to define the degree of deformation of change in the place of destruction:
where a1 and b1 - length and width of cell to and after deformation to destruction;
a0 and b0 - also, to deformation.
In the same place above all normal tensions are evened:
Then the index of the tense state which deformation to destruction was at will be:
where
If by a bend it is not succeeded to lead to some plastic materials to destruction, standards preliminary can be added to the small stretch to the origin of signs of loss of equilibrium and origin to the neck. No the monotony of deformation in this case will be small (at a bend that part is considered to the standard only, which stretches) and it can to attention adopt not her.