Composite laminated cruciform design for multiaxial testing of metals

The development of a proper cruciform design for multiaxial mechanical testing of sheet metal has been a subject of intense study. Cruciform samples, unlike other sample shapes, allow for both proportional and non-proportional load paths to be tested, and can thus mimic complex stress states experienced during cold-forming processes. However, the amount of plastic deformation in the test section is limited due to the development of stress concentrations in the arms. In this work, a novel, bottom-up approach is proposed to reduce these stress concentrations by reinforcing the arms with a mechanically dissimilar material. As a proof of concept, Aluminum cruciforms were reinforced with polyethylene terephthalate (PET) to create a composite lamellar structure. The cruciforms were deformed under uniaxial and equibiaxial load paths to demonstrate that the reinforcement material effectively reduces stress concentrations in the arms, resulting in increased deformation in the test section. Abaqus finite element analysis is compared to the digital image correlation (DIC) measurements from the mechanical tests.