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A critical aircraft structural component, shown in the Figure, has an embedded circular crack with radius 'a'. The part has dimensions of b = 25 mm and t = 50 mm. Historical data shows that when the component was subjected to cyclic loading between (-160 MPa and 180 MPa), an initial crack radius of a = 2 mm gave a life of 609,980 cycles, where the life ended due to brittle fracture at af = 11.5 mm. It is proposed to use this component under a new loading condition, where the applied load P is fluctuating between Pmin = -800 kN and Pmax= 1000 kN. Assume that LEFM and the Paris equation is applicable in this problem and Paris equation parameters are: m = 3.9, c = 5.11 x 10-13 m/cycle (MPam) 2b S 2t A. Determine the fracture toughness of the material of the component? B. What is the largest initial crack radius, a,, that can be permitted if the part must withstand the same number of cycles (609,980 cycles) under new loading condition? C. Comment on the practicality of detecting the initial crack radius, ai, that you have determined in B.