A steel beam with a rectangular cross$-$sectional area has a height $h=40mm$ and breadth $b=18$

$mm.$ It has a through thickness crack of length $a=5mm$ as shown in the figure. The fracture

toughness of the plate material is $K_{IC}=80$MPa$\sqrt[\phantom{2}]{m}.$ The beam is subjected to combined tensile and

bending loading. If the bending moment applied to the beam is $M=300Nm,$ determine the maximum

tensile force $F$ which can be applied to the beam before brittle fracture occurs.