Question 6 Mohr's modified shear stress theory is applicable to brittle materials. What assumption is made in this failure theory that is absent in others? (4 marks) a) b) A solid steel shaft transmits 4 kW when rotating at 1500 rev/min. There is also an axial thrust acting on the shaft which produces a compressive stress of two-thirds the magnitude of the shear stress due to torsion. Determine the minimum required diameter of the shaft if the maximum allowable direct stress is 150 MPa and the shear strain energy theory of failure (von Mises) is applicable for this steel. (16 marks)