Post-forming monotonic and cyclic behavior in a HSLA steel sheet after large deformations by in-plane compression

• In-plane compression is used to simulate deep drawing deformations in a HSLA steel.
• As-prestrained monotonic and cyclic flow stresses are measured in tension and compression.
• Monotonic and cyclic flow stresses show anisotropy and tension/compression asymmetry.
• Two cyclic stress strain curves are defined to reflect the hysteresis loops asymmetry.
• A portion of the strength increase produced by prestraining is retained after cycling.

The effects of large prestrains (18–40%), produced by in-plane compression, on the asymmetry and the anisotropy of the stress response and on the fatigue life are investigated under fully reversed axial strain for a 345 MPa yield strength V–N high strength low alloy steel sheet. After prestraining, the hysteresis loops are asymmetric and the stress response is anisotropic, i.e., the response differs in directions parallel and perpendicular to that of the compressive prestrain. To understand the cyclic flow stress asymmetry, monotonic tension and compression tests were conducted in these two directions after prestraining. It is shown that the loop asymmetry is related to the Bauschinger effect after prestraining. Two cyclic stress strain curves, one corresponding to the tension side of the hysteresis loops and the other to the compression side, are defined to accurately describe the post-prestraining behavior. The amount of strengthening gained by prestraining is partially retained after cycling. Prestraining increases the fatigue life at low strain amplitudes but decreases it at high strain amplitudes.