Composites have excellent strength characteristics, are lightweight, and are increasingly being used in space applications. However, they are highly inflexible and require hinged joints when used as deployable structures. This is a challenge for CubeSats/SmallSats, as the hinges and actuation mechanisms get very small and require multiple custom precision parts. A method of impregnating carbon fibers with a silicone matrix has been developed, which makes the composite flexible. This also makes it self-deploying, as the strain energy in the fibers will cause it to straighten. Unfortunately, a purely flexible beam does not have the required rigidity to maintain dimensions accuracy, as it can sag.
To solve this problem, Ultra-FLASH (Ultra-Flexible Adjustable Stiffness Hinge) material (manufactured by L’Garde) was developed by sandwiching a short, flexible, composite beam between two rigid beams, creating a self-deploying hinge. This provides a beam with overall better rigidity, while also allowing it to bend in specific areas. However, this does not completely solve the problem, as the beam is still not rigid in the small, flexible section. This means the two rigid epoxy rods will not necessarily be colinear with each other, which can become a problem when a structure made of such beams experiences a load, as it may significantly deform.
It would be ideal to make the silicone portion rigid after deployment, as this would make the structure more robust. This can be accomplished using a spring-loaded locking mechanism, which would consist of a cylinder that slides into place to make the beam rigid. When the flexible composite hinge is bent, the cylinder would only be covering the rigid portion of the beam. After the beam self-deploys, a spring would push the cylinder forward, across the flexible portion of the beam. The cylinder creates a rigid bridge between the two rigid beam sections, thus making the entire beam stiff after deployment.
There are two ways to implement such an idea. One is to have a spring-loaded cylinder inside the beam (blue bar in Figure 1). In this case, the beam has a hole running through its center. The spring-loaded cylinder is held back by the flexible, bent portion of the hole. When the beam straightens, the rod is pushed through the center hole, connecting the two rigid portions and locking the beams. A second method is to have the cylinder around the beam (Figure 2). Once again, the flexible portion of the rod holds back the spring-loaded cylinder. When the hinge self-deploys, the cylinder springs forward, spanning the gap between the two beams.