Effect of prestrain on tensile properties and ratcheting behaviour of Ti-stabilised interstitial free steel

• Two-stage increase of YS and linear increase of UTS with increase of prestrain.
• Initial compressive ratcheting during cyclic loading with positive mean stress.
• Exponential relationship between N16 and prestrain.
• Bilinear relationship between N16 and YS under prestrained conditions.
• Similar internal stress state at the end of cyclic loading.

Effect of prestrain ranging between 2.5 and 15 percent on tensile properties, and ratcheting behaviour of an interstitial free steel has been studied at two different stress combinations. It is found that while yield strength increases in two distinctly different stages, the increase of tensile strength follows perfect linear relationship with increase in the amount of prestrain. The ratcheting strain accumulation direction during initial stage of asymmetric cyclic loading at constant tensile mean stress depends upon imposed maximum stress and the amount of prestrain. Number of cycles for accumulation of 16.30 pct true ratcheting strain increases with the amount of prestrain following perfect exponential relationships for both the stress combinations; but it increases in a perfectly bilinear manner with tensile yield strength of prestrained specimens. With 16.30 pct accumulated ratcheting strain the amount of back stress is found as 110 MPa irrespective of the amount of prestrain. Marginal variation in post-ratcheting tensile properties as a function of tensile prestrain has been observed.