Investigations of Roughness Evolution in Uniaxial and Biaxial Stretching of Interstitial Free - IF Steel Sheet

The aim of work is to present experimental results for the evolution of surface roughness and waviness parameters with plastic strains in uniaxial and biaxial stretching tests of Interstitial Free-IF steel thin-sheet. Additionally, investigate the correlation between experimental FLC and Forming Limit Waviness curves of Wt*, FLW, by displaying them on the same Map of Principal Surface Limit Strains, MPLS. Material plasticity parameters and strain hardening law were obtained by tensile tests at 0°, 45° and 90° to RD. Nakazima formability tests were performed using the Marciniak's flat head punch for in-plane stretching. Surface roughness and waviness profile parameters such as the maximum distance peak-valley roughness Rt, arithmetic average waviness Wa, total height peak-valley waviness Wt, maximum valley depth Pv were measured during uniaxial and biaxial tests. Nakazima uniaxial and biaxial samples were deformed in incremental steps to determine the negative and positive quadrants of the MPLS of IF steel. From these data, comparison of experimental and predicted local necking curve, FLC-N, by the strain gradient model, using Barlat's Yld 2000-2d yield function, and experimental FLW were plotted. Parameter Wt* is nearly constant between 2.2 and 3.0 µm. Also, curves of roughness and waviness parameters versus equivalent strains were displayed.