Solid Mechanic & Metal Forming Laboratory

Small-scale and multi-axial testing of sheet metals, particularly of lightweight aluminum and magnesium alloys are becoming important as these materials exhibit forming behavior sensitive to their unique microstructural features and strain paths. As an alternative to large-scale standard tests, in this project we introduce a novel biaxial tensile test apparatus utilizing miniature cruciform samples. The compact and portable apparatus includes a custom-built optical microscope and high-resolution digital image correlation (DIC) equipment for in-plane and in-situ strain measurements at the microstructure scale.

With our cruciform test setup, it is now possible to test the samples until their fracture limit without the formation of local necking and premature fracture. The predetermined strain path stays constant until the fracture. This way the local necking is eliminated and the actual material behavior is observed under large strains. In the literature, most of the micro-scale strain maps are limited to the small strains. Our surface preparation technique and imaging setup, however, allow the strain maps to be plotted under the large strains. Therefore, we are able to capture the strain localizations to the microstructural features and the defects originating from the strain localizations.