고체역학 (Beer) — Pure Bending: Problem 4.28

4.28 A portion of a square bar is removed by milling, so that its cross section is as shown. The bar is then bent about its horizontal axis by a couple M. Considering the case where \( h = 0.9h_0 \), express the maximum stress in the bar in the form \( \sigma_m = k\sigma_0 \) where \( \sigma_0 \) is the maximum stress that would have occurred if the original square bar had been bent by the same couple M, and determine the value of k.