,actually I have already seen this video by 'The efficient Engineer' and I was referring to his words where he says the ductile materials always fail in max shear direction while the brittle does so in the direction of max principal stresses. If you recall my comment where I mentioned that the picture you upload maybe is showing so because of the loading condition applied, I was referring to this video where he shows the failure of the ductile and brittle material under torsion.nPlease see what this guy says at and after 8:45.nn