Computer analysis of loading data for fatigue evaluation and testing

The use of computer based fatigue analysis in generating S-N curves for spectrum loading is discussed. Programs were written to provide an iterative trade-off exercise to select the optimum combination of design stress, and notch factor to satisfy fatigue life requirements for a variety of materials at the drawing board stage of design. Memory requirements for the software are shown to be small enough (under 20 kb) to allow its implementation on microcomputers and minicomputers. Enhancements for the software are planned that include: modules for running previously determined low-cycle fatigue data as a 'back-ground'; a module for determining a closed-form stress relationship for fatigue damage increment as a function of mean stress, strain amplitude, and mean strain; and a module to computer design stress as a function of notch root radius for a given elastic design stress.