Question 4: For the stress tensor given in question (2), i.e.,
$ \underline{\underline{\tau}}^x = \begin{bmatrix} -70 & 30 & -20 \\ 30 & 40 & -5 \\ -20 & -5 & 30 \end{bmatrix} MPa $
determine the principle stresses and principle directions (Find the base vectors of $x^* - fr$). Please use MATLAB in your computations.
Question 2: Consider a point Q in 3D body. The stress state $\underline{\underline{\tau}}$ referring to $x - fr$ frame at point Q is given by
$ \underline{\underline{\tau}}^x = \begin{bmatrix} -70 & 30 & -20 \\ 30 & 40 & -5 \\ -20 & -5 & 30 \end{bmatrix} MPa $