Exemplary builders from the sea floor

Filigree lattice structures with astonishing features: The skeletons of the glass sponges could inspire architects and technicians to build optimized structures, researchers report. The special arrangement of the struts gives the biomaterial enormous stability without additional material expenditure, experiments show. The system of glass sponges is thus clearly superior to known techniques. For example, it could enable taller buildings, longer bridges and lighter spacecraft to be built, say the scientists.

When we think of sponges, we have something soft in mind. But this does not apply to the so-called glass sponges: their strength gives them a rigid skeleton made of a silicate material that is similar to our glass fibers. The filigree piston structures of the so-called watering can sponge (Euplectella aspergillum) have been the focus of research for some time. The scientists are interested in how the fragile-looking structures can withstand the mechanical stresses in the deep sea. The investigations uncovered an interesting parallel to human construction technology: the bio-glass fibers are arranged in patterns that resemble lattice structures that are used to ensure stability and lightness at the same time.

Previous system not yet exhausted

These lattice structures, characterized by diagonal struts, are used in various metal constructions. The system was developed in the early 1800s by civil engineer Ithiel Town for the production of stable bridges from lightweight and cheap materials. “He established this simple and inexpensive method of stabilizing square lattice structures, which is still used today,” says Matheus Fernandes of Harvard University in Cambridge. He and his colleagues have now investigated the question of whether the special structural arrangement of the skeletal structures of the glass sponges could further optimize the previous concept. Above all: Are there ways of saving material while maintaining the same strength?

As the researchers report, the design of the sponge glass skeletons has a characteristic feature: there is a double set of diagonal struts that are connected to the square grid below. The system is arranged in such a way that a small diamond forms alternately in a square of the checkerboard-like surface, which is missing in the next field. As part of the study, the researchers modeled the features of this system through computer simulations. They also carried out stress tests with models of the glass sponge design produced using the 3D printing process, as well as with comparison objects that have lattice geometries previously used in technology.

Increased stability – without additional material expenditure

As the team reports, Nature’s patent, which is millions of years old, clearly outperformed all technical versions. “We found that the diagonal reinforcement strategy of the sponges ensures the highest load capacity for a given amount of material,” says Fernandes. In other words: The concept achieves a higher strength-to-weight ratio than any lattice structure used previously. Specifically, the investigations showed that the paired diagonal arrangement of the struts can increase the overall structural strength by more than 20 percent without the need to add additional material.

As the scientists explain, there is now enormous potential: “Our research shows that the knowledge gained from the investigation of sponge skeleton systems can be used to build structures that are geometrically optimized to avoid deformations, which has enormous effects has improved material use in modern infrastructure applications, ”says co-author Katia Bertoldi. Her colleague Fernandes adds: “By intelligently rearranging existing material within structures, stronger and more resilient structures can be built”.

In addition to applications in architecture, there is also potential for building structures for the aerospace industry, says co-author James Weaver: “In this and many other areas, the strength-to-weight ratio of a structure is of crucial importance. This biologically inspired arrangement could become a model for the design of lighter, more stable structures for a wide range of applications, ”the scientist is convinced.

Source: John A. Paulson School Of Engineering And Applied Sciences, Article: Nature Materials, doi: 10.1038 / s41563-020-0798-1

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