consider the stress-strain curve for an ideal elastic-plastic strain hardening metal as shown in the figure. The metal was loaded in uniaxial

Q. Consider the stress-strain curve for an ideal elastic-plastic strain hardening metal as shown in the figure. The metal was loaded in uniaxial tension starting from O. Upon loading, the stress-strain curve passes through initial yield point at P, and then strain hardens to point Q, where the loading was stopped. From point Q, the specimen was unloaded to point R, where the stress is zero. If the same specimen is reloaded in tension from point R, the value of stress at which the material yields again is_____MPa.

Sol:

Initial loading upto Y.P. and then unloading to zero load results in cold working of the material. As a result, Y.S. increases on immediate next reloading. Since it is ideal elastic-plastic, material Y.S. on reloading of the specimen remains at 210 MPa.