Experimental and analytical necking studies of anisotropic sheet metals

Two approaches are detailed for the determination of forming limit diagrams (FLDs). The first one is experimental: a correlation technique has been developed for the displacement field measurement on a sheet. The second approach is theoretical: a necking criterion based on the load-instability and plane strain localisation assumption is proposed. It includes the possibility to introduce the modified Gurson–Tvergaard damage model taking account the Hill’s or others anisotropic yield surfaces and the influence of triaxial stress state in the neck. The criterion is written in an intrinsic form and is as well applicable to linear strain paths as well as to non-linear strain paths. Finally, the FLDs for an aluminium alloy, a mild steel and a titanium alloy obtained by experimental and theoretical ways are compared.