A Novel Diagonal-Cruciform Test Specimen to Evaluate Sheet Formability

This paper investigates the application of the recently proposed diagonal-cruciform test specimen to evaluate the formability of C11000 copper sheets. The specimen features a two-dimensional reticular structure with triangular interconnected arms that meet at a central point, aimed at enabling biaxial tension when subjected to uniaxial loading in conventional testing machines. The specimen also features a thickness reduction in the form of spherical cups at the center to ensure damage accumulation. Experimental strain loading paths were captured using digital image correlation (DIC) and analyzed with an in-house computer software to determine and plot the onsets of necking and fracture in principal strain space. Results validate the specimen's ability to induce stable biaxial strain paths in C11000 copper sheets under friction-independent conditions and without requiring complex multi-axial testing apparatuses. The overall work confirms the versatility of the diagonal-cruciform design to evaluate the formability of the C11000 copper sheets and provides insights into its applicability across other sheet materials with appropriate modifications to the inner and outer arm angles.