Where 𝜎𝜎 1 and 𝜎𝜎 2 are the principle stresses, with 𝜎𝜎 1 > 𝜎𝜎 2 . The exact values of 𝜎𝜎 1 , 𝜎𝜎 2 , and 𝜃𝜃′ are determined by the eigenvalues and eigenvectors of the initial system for a given value of 𝜎𝜎 � and 𝛽𝛽. This allows for the determination of the local stress intensity factor by superimposing two principle stresses at 90° to one another, permitting equations 2, 3, and 4 to be rewritten: