Friday, July 4, 2014

The materials sciences continue to wow

As someone who frittered away much of my youth building flying model airplanes, I have an especially warm spot in my heart for balsa wood.  Strong, light, and ridiculously easy to shape, balsa was the perfect material for modeling.  Unfortunately, it is an exotic species that has become very rare over time.  Model airplane kits that cost $4 in the early 60s now cost $60 (and yes, there are identical kits from that era still for sale) and almost all that cost increase is due to the cost of balsa.

If balsa were not so rare and expensive, it would be the perfect core material for composite construction—especially for demanding applications like the fabrication of wind turbine blades.  If someone were able to fabricate a synthetic balsa, the potential market would be large.

Well, apparently someone HAS figured out how to build a synthetic balsa.  Even more astonishing, this breakthrough has happened at Harvard.  Yes, I know that Harvard is best known as a finishing school for economic criminals but it seems this quintessential Leisure Class institution has corners where useful work is permitted.

Now, I wonder if it is as easy to fabricate a set of model airplane ailerons from fake balsa as it is with the real thing.

Harvard Researchers Are 3-D Printing Fake Balsa Wood For Next-Generation Wind Turbines

ANDY TULLY, JUN. 29, 2014

The ancient Greek mathematician and engineer Heron of Alexandria designed the earliest known wind turbine in the first century AD. For all that’s happened in the ensuing two millennia, his technology hasn’t changed much.

Now, though, a team of Harvard researchers has found a way to update the turbines, which these days are being increasingly used to generate electricity. The blades of the new turbines look like metal, but what you see is merely a sheath over a core of extremely low-tech balsa wood.

The point of using balsa, even today, is that it’s very light yet very stiff, which is ideal for a wind turbine. But although the balsa tree grows quickly, its wood is rare, and like many other trees it’s getting rarer, and therefore more expensive. Fully 95 percent of the wood comes from the forests of Ecuador.

And being a natural product, it’s structure isn’t perfectly geometrical. Variations in its grain can interfere with the ever-increasing need for the blades to operate smoothly and precisely. After all, some turbine blades are more than 80 feet long and have to be virtually maintenance-free to generate electricity without interruption.

In a paper published online in the journal Advanced Materials, the researchers report that they’ve developed cellular composite materials that mimic balsa wood. They are extremely light and extremely stiff and actually appear to be better than balsa for wind turbines.

In fact, the teams from the Harvard School of Engineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically Inspired Engineering say they outperform even the highest-quality polymers and polymer composites now being made by 3-D printers.

The Harvard and Wyss researchers used special fiber-reinforced, epoxy-based resins that, when heated, can be molded only once. Then, for the first time, they ran them through a 3-D extrusion printer. Until now, such printers have been used only for the kinds of resins and plastics that aren’t considered suitable for structural applications.

“By moving into new classes of materials like epoxies, we open up new avenues for using 3-D printing to construct lightweight architectures,” says principal investigator Jennifer A. Lewis, the Hansj√∂rg Wyss Professor of Biologically Inspired Engineering at Harvard SEAS. “Essentially, we are broadening the materials palate for 3D printing.”

Lewis said the key to balsa’s light weight and great strength is that the wood is mostly empty space, and what’s not empty is its rigid cell walls: “We've borrowed this design concept and mimicked it in an engineered composite.”

The report says the 3-D printing process can be used to create many other valuable materials with applications in many fields, including the automotive industry, where strong, light materials can help in the design of vehicles with greater fuel efficiency. One estimate says removing 110 pounds from each of the 1 billion cars on the planet could save $40 billion in fuel costs. more

No comments:

Post a Comment