Effect of cyclic stress on Mechanical properties of Steels

Abstract

Studies have been made of the effect of cyclic stress in flexure on static mechanical properties of three types of structural steel. The effects of over-stress (stress-cycle beyond fatigue limit) with different values of the ratio: applied cycles/cycles to fracture have been determined in relation to the general nature of the true-stress/true-stress/true-strain curve and the convectional mechanical properties by subsequent tensile tests. A small degree of work-hardening was noticed in two steels tested, but no appreciable change was detected in a third, softer steel. Such changes as occurred appeared to reach their maximum after a relatively small number of cycles and then the properties remain almost unchanged. This was true whether the cycles were of under-stress or over-stress. No evidence of crack formation was generally revealed in the tensile tests even when the number of fatigue cycles was as high as 75% of the anticipated number of cycles to fracture. The results have been discussed in relation to the theory of the mechanism of fatigue failure. They indicate little chance of mechanical tests revealing impending fatigue failure in engineering components.