in stress strain curve of ducktile material why curve decrease after elastic limit?

Question

stress strain curve for duck tile material .belongs to mechanical Eng.

Answer 1

Steel generally exhibits a very linear stress–strain relationship up to a well defined yield point .

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.

Answer 2

Its a result of dislocations within the crystal matrix of the material. Imagine the particles of the material are rows marbles trying to slide over one another. Once a row has gotten over the "hump" of the row beneath it, it can move more easily. This is an analogy of what is happening at a molecular level to the bonds holding the material together of course, but it is a useful way of thinking of it.

Answer 3

You'd have to contact a manufacturer of the relevant material, and ask them for technical specifications.