Fatigue strength of pressed steel sheets under tension and bending loading

Research during the past 10 or 15 years has been looking into the possibilities of increments in fatigue strength following prestraining of steel sheet materials. Almost inevitably, forming operations of steel sheet materials are also associated with sheet thickness reduction which counteracts the fatigue strength increment due to strain hardening. The net result is not necessarily an improvement of the pressed component fatigue strength. The present paper aims at addressing this question further by summarizing strain cotrolled fatigue life data for 2 austenitic stainless steels and 2 high strength low-carbon sheet steels suitable for press forming of vehicle components. The materials were subjected to various degrees of uniaxial prestraining before fatigue testing. The results indicate that there seems to be an optimum sheet thickness reduction where the fatigue strength increment due to strain hardening overweighs the effect of thickness reduction.