Effect of strain rate on plastic anisotropy of advanced high strength steel sheets

This paper investigates the effect of strain rate on plastic anisotropy of advanced high strength steel sheets at static and intermediate strain rates. Uniaxial tensile tests were performed at different strain rates to obtain yield stresses and r-values at various loading angles to the reference rolling direction on two advanced high strength steel sheets of TRIP590 and DP780 and a conventional cold-rolled steel sheet of SPCC for comparison. A new method was proposed to measure r  -values at intermediate strain rates with the aid of digital image correlation to investigate the deformation history during tensile tests. Plastic anisotropy of the steels was modeled with Hill48, Yld89 and Yld2000-2d yield functions at strain rates between 0.001s-1 and 100s-1. The performance of the three yield criteria was evaluated by comparisons of theoretically calculated planar distributions of the uniaxial yield stress and the r-value with experimental data. Yld2000-2d yield function was found to accurately describe the in-plane anisotropy of the uniaxial yield stress and the r-value of the advanced high strength steels since it has great flexibility due to a larger number of the mechanical parameters incorporated than that of Hill48 yield function with which the anisotropy of SPCC can be described acceptably. Yld2000-2d yield loci were constructed on the two advanced high strength steel sheets and SPCC in order to investigate the effect of the strain rate on their plastic anisotropy at the given range of strain rates. For the materials that we investigated, it is evident that strain rate has a distinct effect both on the shape and magnitude of the yield surface, and the plastic anisotropy tends to diminish at a higher strain rate.

► We measure r-values at strain rates between 0.001 s−1 and 100 s−1.
► The r-value varies with the strain rate as well as the yield stress ratio.
► We construct yield surfaces based on the Yld2000-2d yield criteria at different strain rates.
► Strain rate has a distinct effect both on the shape and magnitude of the yield surface.
► In general, there exists an overall tendency that the plastic anisotropy attenuates with increasing strain rate.