Solution: Based on the von Mises Theory, failure occurs when the von Mises stress equals one half the yield stress. Based on data from the field test the von Mises stress is:

so =

1 2

sx2 sxsy + sy2 + 3ty2

1/2

so =

1 2

162 (16)(8) + 82 + 3(4.5)2

1/2

= 15.9 ksi

Therefore, the yield stress of the material is:

s_y = 2 s_o = 31.8 MPa