고체역학 (Beer) — Pure Bending: Problem 4.92

4.92 A beam of the cross section shown is made of a steel that is assumed to be elastoplastic with $E = 29 \times 10^6$ psi and $\sigma_Y = 42$ ksi. A bending couple is applied to the beam about the $z$ axis, causing plastic zones 2 in. thick to develop at the top and bottom of the beam. After the couple has been removed, determine (a) the residual stress at $y = 2$ in., (b) the points where the residual stress is zero, (c) the radius of curvature corresponding to the permanent deformation of the beam.