Tuning bifurcation loads in bistable composites with tunable stiffness mechanisms

Bistable composites are energy efficient morphing mechanisms. These mechanisms are typically controlled by: 1) active control i.e. using motors, hydraulics/ pneumatic/ piezoelectric actuators and piezo-microfiber composite materials resulting in higher energy requirements or 2) passive control i.e. designing the bistable composite to achieve a particular shape at certain loads or reinforcing the composite to alter the bifurcation loads. These methods require either complex manufacturing of bistable composites or result in high energy requirements. This research proposes a novel approach of targeted adjustment of load distribution in an indeterminate structure, composed of a bistable composite and a tunable stiffness mechanism (TSM) to tune bifurcation loads. A multilayer glass fiber composite with asymmetric layup and an initial curvature is fabricated, and a TSM is integrated. A finite element (FE) model with a bistable composite arc and a TSM is developed; the stiffness range of the TSM is designed through an arc's failure analyses to ensure safe load distribution. Experimental validation shows that the bifurcation load of the composite can be controlled and increased by approximately 70% by tuning the stiffness of the TSM. The novel semi-active morphing mechanism is suitable for various morphing applications, energy harvesters and switching mechanisms.