In the material sciences, lightweighting means optimizing your design’s geometry and structure so that it uses less material. The aluminum Coca Cola can is an outstanding example of lightweighting. In the late 1970s the Aluminum Company Of America or ALCOA began offering lightweighting services to can manufacturers. They defined lightweighting as designing a can to use the thinnest aluminum that will still meet specs for strength and appearance. By using laboratory trial and error, and later computer algorithms such as finite element methods (FEM) and analysis, ALCOA's materials researchers reduced aluminum sheet thickness in soda cans from .015 inches to today's 0.115, a savings of millions of tons of aluminum annually.Today such scientists are considering tensegrity as one of th
eir lightweighting tools. Autodesk, a leading provider of computer aided design (CAD) sells a product, Inventor, that can apply FEM and other stress analyses to virtual models. The result is good news for tensegrity: Autodesk produced a set of accessible, easy to understand videos about force, stress and ultimately, tensegrity. Some quotes from the video:
So far, we've seen how stress can be the enemy when trying to lightweight. Too much stress, too little materials and you've got problems. But not all stresses are created equal. Sometimes turning compressive stress into tensile stress can help you reduce material use enormously.Buckminster Fuller called the strategy of using tension for structural integrity, "tensegrity. " It's great when using materials whose strength in tension is similar to its strength in compression.Anything that is resisting compressive forces is resisting buckling. Compression can buckle your product long before the strength of the materials fail. The longer and skinnier your parts are, like spokes, the more likely they are to buckle, and the more you can lightweight them by using tension.In the Needle Tower sculpture the rods and the cables are under the exact same amount of stress, but the much lighter cables are under tension, while the rods are in compression. The stress at which a column buckles is inversely related to the square of how slender the column is. So making a column 3x more slender makes it 9x more likely to buckle. By contrast a part under tension does not need to worry about this buckling equation. If it fails, it will fail at the yield strength of the material.
The video makers conflate tensegrity and tensile structures. They claim, for example, that old sailing ship masts and suspension bridges like the Golden Gate Bridge are examples of tensegrity. Even the claim that a bicycle wheel is a tensegrity is debatable, though it is refreshing to hear them discuss pneumatics as a form of tensegrity.
But Jeremy Faludi's detailed discussion of force distribution, and the wonderful animations by Mr. Animation, make their videos a welcome addition to any tensegrity video library. And I like their closing line:
When it comes to lightweighting, stress can be your friend.
Watch them here or follow the links below to the Autodesk site.
Introduction to Lightweighting and Material Reduction
Learn what lightweighting is, and why it’s important for sustainability; when you should lightweight; and other strategies you can use to reduce material use.
Lightweighting 1: Hollow Parts, Reinforcements, and Trusses
: How can you make your designs strong and light by optimizing geometry and structure? Strategies include hollow parts, ribs, posts, corrugation, trusses, and gussets.Lightweighting 2: Lines of Force and Stress Concentrations
: The forces acting on your design can dictate its structure. Learn how you can use geometry like radiused corners to avoid failures from stress concentrations.Lightweighting 3: Tensegrity Structures
: Learn how to use tension instead of compression to maintain structural integrity and reduce material use, and about tensegrity's application on designs from bike wheels to aluminum cans.Links
View the videos here, or download them http://students.autodesk.com/?nd=sustainable_course&course_id=2.
Autodesk Education Community, http://students.autodesk.com/?nd=sustainable_strategy&course_id=2#introductiontolightweightingandmaterialreduction
ALCOA Beverage Can Story and Lightweighting, http://www.psc.edu/science/ALCOA/ALCOA.html
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