Effects of fiber non-linearity and matrix type on the realization of foldable structures

摘要

High strain composite (HSC) shells made from carbon fiber (CF) reinforced polymers can enable considerable mass savings in deplorable space structures. Minimizing the packaged volume while maintaining structural stiffness, is a key challenge in the design of HSC structures and requires accurate prediction of a structure's behavior during folding. A major unknown in the design of such structures is the non-linear material behavior and its effects on the stress distribution in composite laminates. This paper addresses this challenge by experimentally quantifying and modelling non-linear material behavior in unidirectional CF-Polyether ether ketone (PEEK) composites and extending the investigations to laminate level by means of an extended laminate theory. It was found that fiber non-linearity has a positive effect on laminate's flexibility, especially in cross-ply laminates. Here, neutral axis shift delays the formation of high strains on the tensile side and can mitigate critical transverse tensile stresses in off-axis plies. The susceptibility of a lamina to transverse cracking, however, limits design choices and flexibility. This highlights the importance of a suitable matrix system for these composites, which offers sufficient transverse strength to cope with off-axis stresses. The findings are put into context of foldable structures by considering the design and manufacturing of a lenticular boom structure.