Most of the stress intensity formulae is applicable are defined for plates(6 mm or more) . Suppose , there is an elliptical crack in a plate , we can define the formulae of the stress intensity factor according to https://www.sciencedirect.com/science/article/pii/0013794479901395. Since it is mentioned as plate, i cant use the formula for sheets (less than 6mm). All such researches have been done on plates , but not much sheets. Are all those formulae applicable to sheets also?