Performance of Variable Stiffness Structures Under Compressive Force

With currently available materials, designers of lightweight deployable and adaptable
spacecraft are forced to make a choice. Because most available materials have fixed mechanical
properties, designers can either optimize their structures for flexibility and the ability to change
shape, or they can prioritize their ability to withstand high loads. To combat this problem and
pave the way for future space technologies, materials are being developed with variable
mechanical properties. These materials allow for on-demand control of properties like bending
stiffness, enabling structures to continually adapt to their environments. As part of this effort, the
Stanford Reconfigurable & Active Structures Lab has been developing variable stiffness hinges
made of fiber reinforced polymer and silicone dry adhesive layers. These hinges can switch
between a bonded (stiff) and debonded (soft) state on command. And, when they are integrated
into a larger structure, the hinges will enable the structure to also switch between states. Having
multiple hinges in the same structure will yield even more distinct stiffness states. The goal of
this project is twofold. First, to better understand and characterize the behavior of the hinges by
creating software that can analyze their shape and their performance during experimental testing. Second, to integrate multiple hinges into different structures in order to determine the best configuration for controlling the hinges and yielding different stiffness states. To meet the first goal, MATLAB code was developed that could track the shape of a hinge throughout a testing
video. A new test setup process was also developed to yield videos that were most compatible
with the software. The MATLAB analysis revealed several differences in performance between
the experimental and simulated hinges, suggesting that further work needs to be done on building more consistent and resilient hinges and on improving the simulation model. To meet the second goal, many different geometries were explored and several different structures were tested under compressive force on a universal testing machine. Different problems with each of these structures manifested during testing, and in the end, only a structure containing a single hinge showed promising results. The primary conclusion is that these hinges do not perform reliably under compressive force and that a different approach to hinge integration is needed in the future.