Designing New Types of Cellular Hybrids for Lightweighting Applications

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Given our looming economic and environmental challenges, a key technological issue is to develop new materials that have enhanced performance at a lower ecological footprint - in other words, discovering ways to do more with less. A very rich potential for reaching new regions of material property space comes from the development of hybrids, which combine two or more materials in order to create material property combinations not offered by either material alone. Lightweight cellular hybrids, created by combining material and open space are particularly attractive in order to reduce the energy consumption in the automotive and aerospace sectors. This NSERC Discovery grant is focussed on advanced cellular hybrid materials because the internal architecture of cellular hybrids provides a means for using shape-based design parameters to dramatically alter the effective properties of a material, allowing them to be specifically tailored for structural applications where minimized system mass is a priority. The materials developed in this grant will have enhanced performance and lower environmental impact in order to give a competitive advantage to the Canadian Aerospace and Manufacturing sectors. Aerospace is a strategic sector for Canada, which, according to the Aerospace Industries Association of Canada, provides high-quality employment for over 80000 Canadians and generates total revenues of $23.6 billion (2008). A major challenge for the Aerospace sector is to manufacture structural materials having the best combinations of strength, stiffness, and density. Microtruss cellular materials have fully triangulated architectures making them the most structurally efficient way of having externally applied loads transmitted through a lightweight cellular hybrid. This can make them more than an order of magnitude more efficient than other lightweight cellular materials, such as metallic foams, and enables much better stiffness-to-mass and strength-to-mass ratios. The critical barrier to their widespread application, however, is that optimally efficient microtruss architectures are often impossible to manufacture from high performance materials. We have found a way to circumvent this problem in the previous Discovery Grant. We use additive manufacturing to create an optimally efficient polymeric scaffold, upon which ultrahigh strength nanocrystalline materials are electrodeposited. These materials are currently being developed in partnership with leading Canadian Aerospace and Nanotechnology companies. At the other end of the spectrum, low cost methods to produce lightweight structural materials having minimized environmental impact are also needed for the Manufacturing sector in general and the Automotive sector in particular. Stochastic honeycombs, also invented by the applicant's research group, need only minimal capital equipment to be manufactured: thermoplastic beads are melted between heated plates, which are then pulled to a fixed distance apart and allowed to cool. The frozen-in web structure spontaneously de-bonds from the metal plates, creating a thermoplastic sandwich panel out of a single material with fully integrated core and facesheets. The mechanical properties of polypropylene stochastic honeycombs are comparable to those seen for commercial polypropylene honeycombs and significantly higher than those of conventional polypropylene foams, with the additional advantage that they can be moulded around sharp corners. A spin-off company, FlyTechnologies, has been formed to commercialize these materials and we are currently working with a leading auto parts manufacturer to fabricate them.