Explain stress-strain diagram for a wire under continuously increasing load.
1 Answer
Answer :
A graph or diagram of stress and strain is shown as above.
OE Portion is straight line which indicates that stress is proportional to strain. Therefore the wire obeys Hooke’s law upto the point E this point is called elastic limit.
EE’ Portion is curved towards strain axis this shows that increase in strain is more, than increase in stress. In this region stress is not proportional to strain. Between any point E and E’ if all load is removed then some permanent elonganation/ Expansion / increase in length takes place in the wire this is called set. When wire is again loaded, a new straight line SE’ is obtained which obey Hooke’s law. Some portion after the point Y is almost parallel to strain axis this shows that strain increases without increase in stress just like wire flows. This is called plastic flow. The point at which the plastic flow begins is called yield point. During the plastic flow the wire becomes thin and thin. Some weak points called neck are formed in the wire. At weakest point (neck), wire breaks. The maximum stress upto which wire can be loaded or wire can bear is called breaking stress. Point B is breaking point. Before point B the point D is ultimate stress point. It is the max. stress the wire is capable of with standing.