Page "Stress–strain curve" Paragraph 5

Low carbon steel generally exhibits a very linear stress – strain relationship up to a well defined yield point ( Fig. 2 ).

The linear portion of the curve is the elastic region and the slope is the modulus of elasticity or Young's Modulus.

After the yield point, the curve typically decreases slightly because of dislocations escaping from Cottrell atmospheres.

As deformation continues, the stress increases on account of strain hardening until it reaches the ultimate strength.

Until this point, the cross-sectional area decreases uniformly because of Poisson contractions.

The actual rupture point is in the same vertical line as the visual rupture point.