ABSTRACT
The process of finding the principal stresses and principal strains is discussed in Section 7 and 12 of Sec. 2, respectively. The approach described in these sections ultimately leads to the requirement of calculating the cube root of a complex number. The nth-root of a complex number can be determined using “DeMoivre’s theorem,” which is explained in many advanced calculus books. A complete review of this topic is beyond the scope of the present discussion. The explanation given below is a specialization of DeMoivre’s theorem to find the cube root of a complex number.
