Viscoelastic mechanics of a bistable composite cylindrical structure.

Bistable composite cylindrical structures have been developed over the last four decades, and show great potential for shape morphing applications, especially in aerospace. Their bistabilities are known to be induced by unsymmetric composite layups, while the governing factors on shape geometries and viscoelastic mechanics remain an enigma. Here, we investigated the intricate relationship between structural geometry and stable mechanics of a bistable unsymmetric composite cylindrical structure. A polylactic acid (PLA)‐based carbon composite laminate was prepared through 3D printing, which released design freedom on structural fiber volume fraction that could be controlled by modulating hatch spacing between the composite yarns. This strategic adjustment allowed the regulation of grid density, hence the in‐plane stress level, which dominates the bistable geometries. The cylindrical composite samples were produced with hatch spacing changed from 1.25 to 5 mm, corresponding to a fiber volume fraction ranged from 24.2% to 6.6%, where the structural curvature was also changed by up to 50% difference and gradually became viscoelastic dependent. It is found that the internal stress difference in thickness direction dominates the structural bistability, and there is a threshold value on the stress difference magnitude to essentially maintain the bistable configurations. These findings are expected to facilitate reversed structural design and manufacturing of the bistable cylindrical shells with tailorable stability, and promote their viscoelastic‐based large shape morphing fatigue life predictions. Highlights: Bistable composite cylindrical shells were produced with various grid density.A theoretical model was established to predict the time‐dependent bistability.Stress difference in thickness direction dominates the structural curvature.Stress contour reveals the viscoelastic‐dependent bistable mechanics. [ABSTRACT FROM AUTHOR]