Formulae For Safe Design Against Fatigue Failures

Through this paper, two vital formulae called Nori Fatigue Formulae are presented for calculation of maximum allowable fatigue stress (MAFS) to eliminate the usage of code-sensitive safety margin or safety factor along with other factored values in the mechanical design engineering work ranging from a safety-pin to spacecraft. The first formula gives the maximum allowable fatigue stress in tension, and the second formula gives the maximum allowable fatigue stress in shear. These formulae are developed through deployment of all the basic mechanical properties of steel like: ultimate tensile strength, yield strength, elongation and reduction of area that are commonly obtained from the engineering stress-strain curve resulting from the standard tensile test. Thus the vast amount of data, on elongation and reduction of area, currently available with the world is put to effective use for calculation of maximum allowable fatigue stress. As a result, application of Nori Fatigue Formulae does not call for generation of additional data that often calls for huge investment of time and money. Work in this direction, hitherto unavailable, is found essential since different international design codes, standards and handbooks have been adopting different design philosophies and different design factors at different times for arriving at the maximum allowable fatigue stress of a given steel in the given condition for the given application.