Light Weight Structures Follow Instructions from Nature


The picture on the left shows a lightweight structure made of polyamide inspired by bionic principles. The picture on the right shows its detailed simulation on the computer (credit: Fraunhofer IWM).

In nature a large  number of examples of lightweight and yet strong and resilient objects can be found. Just think about bones and teeth or straw or bamboo. The combination of lightweight with excellent mechanical properties is due to the intelligent design of the internal structure evolution has come up with. Hence,  it seems appealing to transfer these ideas to the production of lighter and durable plastic products.

This is why researchers from two Fraunhofer Institutes the ones for Mechanics of Materials IWM and for Environmental, Safety and Energy Technology UMSICHT collaborate on a project entitled “Bionic Manufacturing”. This project intends to mimic nature and, hence, to develop products that are lightweight but strong and economic in their use of materials.

As a first step in the whole process the involved researchers aim on identifying the best internal structures for the manufactured components. “The finished component must not weigh more than necessary and yet still be able to perform its mechanical function reliably”, as stated by Dr. Jaeger from the IWM. In addition, the approach is aimed on providing a high degree of creative freedom allowing the design of not solely goods with the anticipated lightweight and mechanical characteristics, but also goods with high aesthetic value. Even if these objects should break due to excessive loading, the breaking shall follow a benign path, hence, collapsing smoothly in localized areas avoiding the shattering into sharp splinters.

The design process of the bionic inspired goods is based on virtual prototyping followed by the manufacturing of a prototype and real-world testing. Hence, the researchers construct a virtual model of the envisioned workpiece which is filled out its contours with almost identical, cube-shaped, elementary cells. Then the model is analyzed by numerical means. If these reveal that the grid structure does not fulfill the requirements the cell walls (trabecular microstructures) are refined accordingly. This may involve to make them thicker if they are too weak or thinner if they need to be more pliable or aligning them with the force lines along which the load is distributed. As known from virtual prototyping such an approach many different shapes to be designed around an inner cell structure that can then be evaluated and optimized using the simulation tool. To complement the simulations, the researchers carry out tests on real-world components to verify the structure’s mechanical properties.

The Fraunhofer UMSICHT institute takes care of the technical implementation of the bionic design principles. The respective researcher rely on additive manufacturing techniques, in particular laser sintering of polymer materials. This technique fabricates the designed workpiece by depositing layers of a fine polyamide polymer which then is fused together in the desired configuration using a focused laser beam. The researchers consider it as the ideal method for creating complex internal structures and, at a later stage, components with a distributed pattern of material properties.
Dr. Jaeger reports that so far the method has worked well every time they have used it to design any type of workpiece based on two-dimensional templates that can be pulled into the desired shape using the computer simulation. The same applies to components with a relatively regular shape. Despite their light weight, all of these components are very strong and resilient and capable of absorbing even substantial shocks. According to the scientists, they have potential applications wherever there is a need for products that combine a high level of mechanical stability and aesthetic appearance with low weight.

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