Designing Foldable Composite Structures on the Micrometre Scale

High performance applications requiring high specific strength and stiffness are taking advantage of thin-ply composite materials. Additionally, these materials can enable novel functionalities beyond the classical application in lightweight structures. We show that thin fiber reinforced composite structures can be utilized to create stiff self-expandable structures that can be packaged into tight volumes and expand to more than twice their packaged size. We extend the capabilities of foldable and expandable structures to lower scales, demonstrating that continuous cylindrical composite shells can be designed and manufactured to have the potential to act as cardiovascular implants. The design of expandable cylindrical structures made from fiber reinforced composites, however, faces a number of challenges including large strain flexural behaviour, material and manufacturing imperfections in the micrometre regime as well as structural anisotropy. To find the stiffest layup that can be packaged into a given catheter size, we combine large deformation experimental procedures, microscopic structural analysis and non-linear finite element analysis and investigate the complex relation between packaging scheme, structural anisotropy and the consideration of unavoidable manufacturing induced imperfections. Results can lead to a predictable design of a continuous composite shell at the scale of an aortic stent, that can adapt its diameter by more than 2.5 times and is stiff enough to expand inside a confined environment like a human artery.