A double-edge-cracked member of 7075-T6 aluminum has dimensions, as defined in Fig. 8.12(b), of b = 28.6 and t = 2.3 mm, and it contains equal initial cracks on each side of length ai = 2.0 mm. Estimate the number of repetitions of the load history shown in Fig. P11.51 necessary to grow the cracks to failure. Materials constants as in Table 11.2 apply, except that the fracture toughness for this thickness is Kc = 78.7 MPa√m.