$2.)$ A $40mm$ thick high strength steel plate is to be used for fabrication of an oil tanker$.$ The tanker will be used in conditions where the temperatures may reach $-40C.$ After construction, the tanker is tested by a non$-$destructive method that will reveal any cracks longer than $2mm.$ Calculate the maximum stress that may be applied to the plate without causing brittle fracture. The properties of the material at $-40C$ are: $n=0\mathrm{.}3$;${}_{\text{U}\text{T}\text{S}}=1600$MPa;$E=250$GPa;$g_s=4\frac{J}{m^2}$;$g_p=3000\frac{J}{m^2}.$A factor of safety of $1\mathrm{.}5$ is required. Assume plane strain.