고체역학 (Beer) — Transformations of Stress and Strain: Problem 7.156

7.156 The given state of plane stress is known to exist on the surface of a machine component. Knowing that $E = 200 \text{ GPa}$ and $G = 77.2 \text{ GPa}$, determine the direction and magnitude of the three principal strains (a) by determining the corresponding state of strain [use Eq. (2.34) and Eq. (2.29)] and then using Mohr’s circle for strain, (b) by using Mohr’s circle for stress to determine the principal planes and principal stresses and then determining the corresponding strains.