고체역학 (Beer) — Pure Bending: Problem 4.88

4.87 and 4.88 For the beam indicated, a couple of moment equal to the full plastic moment $M_p$ is applied and then removed. Using a yield strength of 240 MPa, determine the residual stress at $y = 45\text{ mm}$. 4.88 Beam of Prob. 4.74. (The cross section from Fig. P4.74 has an outer width of 60 mm, outer height of 90 mm, and a central rectangular hole of 30 mm by 30 mm).