I have calculated a static contact stress of 670 N/mm2 using formula from Mechanical Engineering Design, Shigley, 5th Edition. My problems lies that there is no acceptance criteria. I'm using Grade 5 Structural Steel (yield~355 N/mm2). Previous threads have stated that a 2.5 * yield can be used for pass criteria but i cant this referenced in any code or book. Can anyone provide a reference or justification for 2.5 * yield?