A novel incremental sheet forming test for evaluating the fracture forming limit under tension-compression loading

This paper focuses on determining the fracture forming limits for incremental sheet forming processes. It introduces a novel experimental test designed to assess the strains at fracture under tension in the second quadrant (tension-compression) of principal strain space. The presentation details the experimental setup, the testing procedure, and the methodology for determining the strain envelope and the strains at fracture along a meridional cross-section of the specimens. A theoretical framework based on volume incompressibility and membrane analysis is provided to explain the underlying mechanics of the test and the location of cracks. The test, demonstrated using aluminum AA7075-O sheets, is a practical and effective approach for identifying strain limits at fracture during incremental sheet forming processes. Furthermore, it extends the determination of the fracture forming limits beyond the typical tension-tension loading scenarios of existing incremental sheet forming tests, enabling analysis in the second quadrant (tension-compression) of principal strain space.