WrapToR shells: Concept introduction, experimental testing, and design space exploration

This work introduces a novel truss stiffener concept for lightweight structural panels as an alternative to sandwich panels or stringer stiffened panels. The Wrapped Tow Reinforced (WrapToR) truss concept is modified to create stiffened composite panel structures (referred to here as WrapToR Shells). A prototype WrapToR Shell unit cell is manufactured and tested under three-point bending, where it demonstrates high levels of specific stiffness and strength. This experimental result is benchmarked against idealised sandwich panels via a low fidelity comparative analysis, and the study shows that even a best-case sandwich panel of equivalent mass under a representative bending load has an 83% increase in displacement, highlighting the excellent stiffness truss reinforced panels can provide. The design space available to the truss reinforced panels is then explored using finite element analysis and a simple parameter sweep of key truss design variables. A Pareto frontier between the competing objectives of minimising mass and maximising rigidity is shown, and global trends in performance are highlighted. It is observed that increasing the size of the truss profile or longitudinal member has a near linear increase on EI/mass, whereas for increasing shear member angle the inverse is true. For increasing shear member diameter, a less obvious effect on EI/mass is seen, indicating a more complex relationship with the other design variables.