Biaxial in-plane yield and failure of paperboard

Paperboard is oftentimes subjected to biaxial in-plane stress and strain states, although very few experimental studies of the biaxial in-plane yield and failure of paperboard have been conducted. A new biaxial testing method to determine the in-plane stress- and strain based yield and failure surface of paperboard was proposed and implemented. The method utilized cruciform specimens containing a reduced-thickness region (prepared by laser engraver) to increase probability of failure in that region, and digital image correlation was utilized to measure strain. The obtained stress-based failure surface was similar to previously reported results in the literature, but the obtained strain based failure surface differed from the one previously reported strain-based failure surface. The obtained yield and failure surfaces had similar shape, providing confidence in both results due to the related deformation and failure mechanisms in paperboard. Furthermore, the overall shape of the stress- and strain-based yield surfaces was unaffected by the definition of the yield point. The obtained strain-based failure surface revealed the forming limits and therefore strengths and limitations of various 3-D forming methods for paperboard.