If the surface energy of a magnesium oxide - nickel oxide (mgo-nio) solid solution is 1.13 j/m2 and its elastic modulus is 196 gpa, what is the maximum length of an internal elliptical flaw, in mm, if the ceramic part must survive an applied tensile stress of 39 mpa normal to this elliptical flaw ?

be careful !

make sure you reference the flaw geometry figures that explain how the length of a flaw type (internal / external) correlates to the value of a.

answer format: x. xx

unit: mm