Problem $7\mathrm{.}11$

Problem Statement: Strains are measured on the surface of a part made from the titanium alloy Ti$-6$Al$-4$V $($solution treated and aged$)$ of Table $14\mathrm{.}1,$ as follows: ${}_{}=3800{10}^{-6},{}_{yy}=160{10}^{-6},$ and ${}_{xy}=720{10}^{-6}.$ Assume that no yielding has occurred, and also that no loading is applied directly to the surface, so that ${}_{zz}={}_{yz}={}_{xz}=0.$ What is the safety factor against yielding?