Environment

  • Issue 117 / May - June 2017



    Technology Inspired by Wheat Stems

    Sam Plat

    Human beings have made significant developments in technology. Better designs are emerging by the day.¬† The dizzying speed of development hasn’t just brought serious technological progress, but serious competition ‚Äď which has, in turn, begat even more progress. Old, inefficient models are being replaced by high efficiency, energy-saving designs. ¬†

    As part of these new developments, humans are discovering inspiration in the works of art hidden in nature.  Although Biomimetics has recently emerged as a scientific discipline, many researchers are already switching over to it.  Biomimetics is the study of the design available with all its grandeur in nature and searching for ideal solutions to human problems. These solutions are then used to develop new technologies.  Basically, it aims to make progress in technology by imitating the perfection of nature.

    Many examples of what has been transferred from living things to technology, in fields as diverse as robotics, optics, new materials, vehicle technology, and so on, are now all around us.¬† Yet, all engineering designs face a basic challenge: “ensuring the highest endurance with the least amount of material.” Spending less on materials will reduce overall costs, in both the long and short term. Lightweight materials mean saving money on energy over the lifetime of a project.

    Thankfully, as Biomimeticians have discovered, nature is designed to be efficient.

    Research into wheat stems has shown that they have remarkable characteristics when it comes to strength. Most of us have seen wheat fields waving in a wind strong enough to topple trees.  Despite carrying a relatively heavy ear of grain and being supported by a delicate stem structure, the wheat is able to withstand strong winds. It rarely breaks. 

    This kind of strength could be an asset in building skyscrapers. While the ratio of the height of a wheat stalk to the base diameter is 500, the tallest building in the world, the 828-meter-high Burj Khalifa, has a height to width ratio of only 5.  Wheat stems may hold the key to taller, stronger, more efficient buildings.

    What are the physical and geometric reasons underlying the strength of wheat stems? Can these features be imitated to inspire new designs? Not only is the material used for great stability, but the geometric features and distribution of those materials have an important effect, too. The cross-sectional area of a characteristic wheat stem is shown in Figure 2.

    When the cross-sectional area of the plant is examined, the following characteristics are seen: 1) The cross-sectional area is circular, cylindrical, and empty.  2) The filled wall section is similar to a honeycomb.  3) The density of the material increases gradually from the center to the outside, while the honeycombs formed by the hexagonal cells are shrinking in size. 4) The density of the material in the outermost periphery has increased greatly and the honeycomb structure has disappeared.  5) There are areas where the material is heavily piled up in the form of small circles near the outer wall. 

    When studying this design, an engineer will note a few things: 1) The hollow cylindrical structures increase the cross-sectional inertia and increase the flexural resistance.  2) The honeycomb structure is important for ensuring maximum durability using minimal material. Mathematicians have proved that a honeycomb structure can enable us to divide an area into small equal pieces with the shortest length of line. Just as in beehives, this structure exhibits the most efficient use of materials possible. 3) The increase in material density from the inner radius to the outer radius is intended to increase the cross-sectional inertia of the field in the cylinder and this increases flexural resistance.  4) It is also important, in terms of flexural resistance, that the material density at the outer wall rises to the highest level.  5) The circular small areas near the outer wall are similar to iron bars placed in cement. They increase the stiffness of the stem against bending.  In fact, engineers have designed more robust bars, inspired by the geometry of the wheat stem (Figure 3).

    In Figure 3, the dashed curve represents the actual measurements of the wheat stem and the parabolic continuous line represents the approximate curve calculated in accordance with the actual measurements. As can be seen in the figure, there is a slight decrease in material density in the inner wall.  Then the density of the material making up the outer wall increases nearly 100%. The slight increase in the material inside the inner wall can be considered a kind of reinforcement to prevent damage to this small inner area. Based on this material density range, a new material for steel rods can be produced using a porous but simpler structure.

    In Figure 4, we see a cross section of cylindrical rods that are filled, hollow, and inspired by wheat stems. According to the loading analyses done with the computer-based ANSYS program, it is observed that the newly designed rod had the lowest minimum stress and lowest maximum stress (Figure 5). This shows that in the new design, the stiffness decreases and the durability increases.

    While studying nature, it is important to remember that nothing is pointless. Natural structures have been perfectly calibrated, and the scholars who know how to read them can create incredible works of art. A good analysis of nature’s perfection will enrich our minds and open the door to new inventions that will make our lives easier.


    Reference

    Strength of Wheat and Barley stems and Design of New Beam/Columns, Mathematical and Computational Applications, 15 (1), 1-13, 2010.

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