Toward the use of small size bulge tests: Numerical and experimental study at small bulge diameter to sheet thickness ratios

•The use of small diameter bulge specimens down to 50 mm is possible.•New estimates of curvature radii and bending strain from 3D-DIC are proposed.•Outer and inner radii differs by about twice the thickness at the apex.•A direct identification of the behavior is proposed, for any hardening type.