overall shape of the stress strain curve?

Question

Answer 1

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Look at each option in turn.  It is elastic when it obeys Hooke's law.  That only applies up to 340 units of stress.  A brittle material has a very high stress and a very low strain before it suddenly fails.  A and C are wrong.  So look at B and D.  Only one can be right.  What happens at 340 units?  The material stretches ( increased strain) with no increase in stress.  What is happening?  Clearly we are having plastic deformation.  It will not return to its original size even if the force is reduced.  It is permanently lengthened which must mean that its cross sectional area has reduced.  ie "necking".

Answer 2

The last option is correct