Materials scientists at the ETH-Zurich (Swiss Federal Institute of Technology-Zurich) have developed a technique for creating an entirely new family of composites based on mimicking the way an abalone shell's structure aligns strong, stiff elements within a softer matrix.
The ETH-Zurich research team appears to have solved an essential problem of creating composites by discovering how to build materials that use reinforcing elements within 3D architectures, in a manner similar to those used by biological systems. Examples of such 3D reinforcing strategies are found in abalone shells, as well as in teeth, bone, and plant stems.
Previously, in order to combine different material properties from different classes of materials -- such as simultaneously light and flexible, as well as stiff and strong -- composite manufacturers have had to create materials that are flat. To achieve combinations of different properties, the strong and stiff ceramic or polymer fibers must be correctly oriented and placed within a softer, lighter polymer material, such as an epoxy glue. If the fibers are not correctly oriented, they don't strengthen the softer material.
Since manufacturers have not been able to control the fibers' orientation, composites have been formed by stiff fibers woven into a thin fabric that is permeated with a softer, lighter polymer resin, and stacked in layers. The resulting material is stiff and strong in the plane of the fabric, but not in other directions, making them susceptible to delamination between layers. By contrast, the strong elements in an abalone shell's structure are strong in all three directions because they are oriented to all three directions.
Although the materials commonly used in industrial composites are non-magnetic, the ETH-Zurich team discovered a technique that causes a magnetic response by attaching an extremely small amount of magnetic nanoparticles on the surface of the stiff elements. This works as long as those elements are of a certain size in the micrometer range, which is within the same range of sizes that is of interest to composite manufacturers.
Previously, composite materials could be strong in the plane of the fabric, i.e., two directions. What's different here is that it can be strong in all three directions. This implies, although the researchers don't quite say so, that the material does not have to be made in flat layers, but is a true 3D matrix structure. That implies that it could actually be strong in more than three directions. But as naperlou points out, abalone shells can break, too. Although much of that has to do with their brittleness, i.e., a quality of the material, not just how it is constructed.
Charles, I am just taking a guess here, but that is the implication. There could always be certain types of stresses that cause problems. Even abalone shells are not indestructible.
Thanks, Dave, for some interesting insight into similar techniques. I came across at least three other different research projects by different people looking to capitalize on the structure of nacre (mother-of-pearl), although not this one.
Re commercialization, all we know is that it's apparently in process. The ease, cost, and success of commercialization of any technique depend on several factors not limited to the technique itself.
Effectively arranging reinforcements in three dimensions is the key to making tough composites. Coating reinforcements with superparamagnetic nanoparticles and using magnetic fields to align them is an interesting approach. Once the reinforcement is coated with these nanoparticles, it's amazing how little magnetic field is actually required to align them -- just an order of magnitude greater than the earth's natural magnetic field, and two orders of magnitude less than a common refrigerator magnet. This ultrahigh magnetic response may have other useful applications outside of composites.
At last year's Materials Science and Technology conference, Dr. Robert Ritchie gave a fascinating presentation about another method to make composites with a three-dimensional structure. He freezes water under carefully controlled conditions to create three-dimensional templates. The water is then replaced with a polymer matrix. This might prove to be more cost-effective than the technique described in this article, but only time will tell -- all of these technologies are still pretty far from commercialization.
Another great example of biomimickry, where design engineers take a page from nature to figure out tough design problems. Any sense, Ann, how practical this 3D architecture technique is to commercialize? After all, it's one thing to borrow from mother nature in terms of theoretical design, quite another to actually make it viable for productive us
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