고체역학 (Beer) — Pure Bending: Problem 4.66

4.66 The allowable stress used in the design of a steel bar is 80 MPa. Determine the largest couple M that can be applied to the bar (a) if the bar is designed with grooves having semicircular portions of radius r = 15 mm, as shown in Fig. a, (b) if the bar is redesigned by removing the material to the left and right of the dashed lines as shown in Fig. b.