The stiffest porous lightweight materials ever
by Staff Writers
Zurich, Switzerland (SPX) Dec 17, 2018
3D printing and other additive production techniques make it possible to manufacture materials with internal structures of previously unimaginable complexity. This is interesting for lightweight construction, too, as it enables the development of materials that have the highest possible share of interior voids (to make the materials as light as possible) but are simultaneously as robust as possible. Achieving this requires that the internal structures be intelligently organised for maximum efficiency.
A research team from ETH Zurich and MIT led by Dirk Mohr, Professor of Computational Modeling of Materials in Manufacturing, has developed and fabricated material architectures that are equally strong in all three dimensions, and that are simultaneously extremely stiff.
It is possible to determine mathematically just how stiff materials with internal voids can theoretically become; Mohr's structures have been shown to come extremely close to this theoretical maximum stiffness. Put another way, it's practically impossible to develop other material structures that are stiffer for the given weight.
Plates replacing trusses
"The truss principle is very old; it has long been used for half-timbered houses, steel bridges and steel towers, such as the Eiffel Tower. We can see through truss lattices, so they are often perceived as ideal lightweight structures," says Professor Mohr.
"However, using computer calculations, theory and experimental measurements, we have now established a new family of plate-lattice structures that are up to three times stiffer than truss-lattices of the same weight and volume." And it is not just the stiffness (resistance to elastic deformation) of these structures that approaches theoretical maximum values: their strength (resistance to irreversible deformation) does, too.
The ETH researchers initially developed these lattices on the computer, calculating their properties in the process. Then they produced them at the micrometre scale from plastic through 3D printing. Mohr emphasises, however, that the advantages of this design are universally applicable - for all constituent materials and also on all length scales, from the very small (nanometre-sized) to the very large.
Ahead of their time
Lightweight construction, the current cost of which limits its practical use to aircraft manufacturing and space applications, could then also be used for a wide array of applications in which weight plays a role." In addition to making structures lighter, the numerous voids also reduce the amount of raw materials needed, and thus also the material costs.
There's no limit to the potential applications, Mohr says. Medical implants, laptop casings and ultralight vehicle structures are just three of many possible examples. "When the time is right, as soon as lightweight materials are being manufactured on a large scale," Mohr says, "these periodic plate lattices will be the design of choice."
Nanoglue can make composites several times tougher during dynamic loading
Troy NY (SPX) Dec 13, 2018
In a discovery that could pave the way for new materials and applications, materials scientists at Rensselaer Polytechnic Institute have found that oscillating loads at certain frequencies can lead to several-fold increases in the strength of composites with an interface that is modified by a molecular layer of "nanoglue." A newly published article in Nature Communications reports the unexpected discovery of the effects of loading frequency on the fracture energy of a multilayer composite involvin ... read more
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