Answer:
0.39 nM
Explanation:
The critical crack tip radius from the equation
attached below
for fracture to occur the бm will have to reach the fracture strength of material
i.e. бm = E/10
from equation 2 attached below
St = ( 400 * a * бo^2 ) / E^2 ------ 3
Given : a = 2*10^-3 mm , бo = 275 MPa, E = 393 * 10^3 MPa ( gotten from table)
Input given values into equation 3
St = 3.9 * 10^-7 ≈ 0.39 nM