Many safety-critical engineering systems require transparent materials with high-impact absorption. Existing composites have increased impact resistance but often fail catastrophically because of poor impact absorption.
Scientists at Polytechnique Montréal (Montreal, Canada) recently proposed a novel solution of new impact-absorbing transparent composites that simulate the mechanisms found in spiderwebs, such as sacrificial bonds and hidden lengths, that greatly enhance energy dissipation. The materials consist of an elastomer matrix and an instability-assisted, 3D-printed, bidirectional fabric of microstructure fibers.
How did the scientists find inspiration in a spiderweb? Spiderwebs evolved to dissipate the tremendous kinetic energy experienced during prey capture. Unlike other biological materials, up to 70% of the energy absorbed by a spiderweb dissipates out of the system. Upon stretching the web, the breaking of hydrogen bonds and uncoiling of protein chains contribute to the extensibility and high energy dissipation. The elastic energy released upon unloading is minimized to avoid the catapulting of objects by the oscillating web after impact, preventing prey from escaping.
To evaluate their composites, the scientists at Polytechnique Montréal used a falling dart impact tester equipped with an electro-resistive force sensor that measured the displacement of four different composite blends. A MotionBLITZ Cube4 GigE CMOS monochrome camera from Mikrotron (SVS-Vistek) captured the dart motion during impact set at a rate of 2230 frames per second and 1280 x 512 pixel resolution. A MATLAB program, written by the scientists, was used to read the dart displacement and obtain a representative contact force-displacement curve for each type of film. The camera also captured the 3D printing of the fabric during its construction.
Composites developed at Polytechnique Montréal were found to reproduce the energy-dissipating mechanisms of a spiderweb. In addition, its optical properties achieved the required transparency in part due to the refractive index engineering that effectively reduced the composite’s haze. Using images from the Mikrotron camera, it was determined that the microstructured sacrificial bonds in the fabrics significantly increased energy dissipation, minimizing the released elastic energy and reducing the rebounding damage. This meant that if the design structure failed, it would fail gracefully rather than catastrophically.
These fiber fabrics open a new avenue for manufacturing transparent energy-absorbing composites for impact protection. Moreover, the concept can be extended to other applications, transparent or not, by replacing the components with engineering materials, such as polyether ether ketone (PEEK) or Kevlar fiber. Adapting this design to high-performance materials could allow potential applications for bulletproof windows or those used in spacecraft.