A circular rod with $0\mathrm{.}5$ in diameter is used to actuate the aerodynamic brake of a fighter jet. It is subjected to a cyclic stress of constant amplitude $(0-{}_{\text{m}\text{a}\text{x}}),$ that happens once per flight, during landing. One of these rods failed after a few months of use. One of the unknowns for this actuator is the level of stress it really holds, due to uncertainties of the maximum drag offered by the aerodynamic brake. After SEM topography analysis, an image of the fracture surface could be obtained and it is shown in Fig. $1.$ This image was taken at a distance of $c=0\mathrm{.}150$ in from the crack origin, as illustrated in Fig. $1,$ what represents the crack length at that point, as depicted in Fig. $2.$ The strut is made of AA $2024-$T$351,$ and failed after $730$ flights. With the available data, determine:

a$)$ The maximum stress acting on the rod.

b$)$ The critical crack size.

c$)$ Determine if final failure was due to ductile $($net$-$section$)$ or brittle