A rectangular beam made of ABS plastic is b = 20 mm deep and t = 10 mm thick. As shown in Figure 4, a bending moment M is applied, and a through-thickness edge crack may be present. For a safety factor against brittle fracture of 2.5 in stress, what is the largest crack length a that can be allowed if: (a) M = 10 N-m, and (b) M = 3.0 N- m? Finally, (c) also considering fully plastic yielding, what is the controlling safety factor for case (a) and for case (b)? Use Kic = 3.0 MPam and oo = 42 MPa. CO B b M h Figure 4