Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Theory stretches the limits of composite materials

02.02.2007
In an advance that could lead to composite materials with virtually limitless performance capabilities, a University of Wisconsin-Madison scientist has dispelled a 50-year-old theoretical notion that composite materials must be made only of "stable" individual materials to be stable overall.

Writing in the Feb. 2 issue of the journal Physical Review Letters, Engineering Physics Professor Walter Drugan proves that a composite material can be stable overall even if it contains a material having a negative stiffness, or one unstable by itself-as long as it is contained within another material that is sufficiently stable. "It's saying you're allowed to use a much wider range of properties for one of the two materials," he says.

Comprising everything from golf clubs and bicycle frames to bridge beams and airplane wings, composite materials - or materials made by combining multiple distinct materials - deliver advantages over conventional materials including high stiffness, strength, lightness, hardness, fracture resistance or economy. "The idea is that you have one material with some great properties, but it also has some disadvantages, so you combine it with another material to try to ameliorate the disadvantages and get the best of both," says Drugan.

Until now, materials engineers adhered to proven mathematical limits on composite performance, he says. "For example, if you give me two materials and one has one stiffness and the other has another stiffness, there are rigorous mathematical bounds that show that with these two materials, you cannot make a material that has a stiffness greater than this upper bound," says Drugan. "However, all these theoretical limits are based on the assumption that every material in the composite has a positive stiffness-in other words, that every material is stable by itself."

When slightly disturbed, stable materials, like those with positive stiffness, return easily to their original state. A slightly compressed spring, for example, bounces back after the compression force is removed. Unstable materials, like those with negative stiffness, quickly collapse or undergo a large, rapid deformation at the slightest perturbation. In an example from the structures field, if a vertical column supports a load that becomes too great, even a slight disturbance can cause the column to buckle.

The idea of incorporating a material with negative stiffness into a composite designed to be highly stiff originated with UW-Madison Wisconsin Distinguished Professor of Engineering Physics Roderic Lakes, says Drugan. Some six years ago, Lakes noticed that, in the mathematical formulas that predict how a composite will perform based on its component material properties, employing a material with a suitably chosen negative stiffness theoretically would yield an infinitely stiff composite.

Lakes took his ideas into the lab, where he created such a composite by embedding a material that behaved like one with negative stiffness in a matrix of a material with positive stiffness-somewhat like the shell of a golf ball surrounds its core. Through dynamic experiments, conducted under oscillatory loading, he showed that the composite stiffness was greater than the mathematical bounds indicated it could be, given the combination of materials.

Since Lakes' experiments were dynamic, and since dynamics often has a stabilizing effect, it remained unknown whether such material response could be obtained in the static loading case, which is practically important since many structural components are designed to support static loads.

Lakes and Drugan, who have had a continuing research collaboration on this topic, published a 2002 paper in the Journal of the Mechanics and Physics of Solids in which they showed that if a composite material containing a negative-stiffness phase could be stable, and if they tuned the negative stiffness the right way, the predicted composite property could be infinite stiffness for a broad range of composite materials.

Then Drugan set out to prove theoretically that such a material can be stable under static loading. "In general this is a very challenging problem, but I finally found a clean way to analyze it," he says.

Drugan hopes his proof will awaken materials engineers to a new, broad range of possibilities for making composite materials.

"If you're going to make a composite material from two different materials, you think about all the possible properties that each of the individual materials can have in order to obtain an outstanding overall performance," he says. "If you're suddenly able to greatly expand the range of properties that one of these materials can have, then you have a much wider range of possibilities for the overall composite. And that's what this research does. It says, 'You don't need to limit yourself to two stable materials anymore.'"

Walter Drugan | EurekAlert!
Further information:
http://www.wisc.edu

More articles from Materials Sciences:

nachricht Barely scratching the surface: A new way to make robust membranes
13.12.2018 | DOE/Argonne National Laboratory

nachricht Topological material switched off and on for the first time
11.12.2018 | ARC Centre of Excellence in Future Low-Energy Electronics Technologies

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Data use draining your battery? Tiny device to speed up memory while also saving power

The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.

Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...

Im Focus: An energy-efficient way to stay warm: Sew high-tech heating patches to your clothes

Personal patches could reduce energy waste in buildings, Rutgers-led study says

What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...

Im Focus: Lethal combination: Drug cocktail turns off the juice to cancer cells

A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.

The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...

Im Focus: New Foldable Drone Flies through Narrow Holes in Rescue Missions

A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.

Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...

Im Focus: Topological material switched off and on for the first time

Key advance for future topological transistors

Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

ICTM Conference 2019: Digitization emerges as an engineering trend for turbomachinery construction

12.12.2018 | Event News

New Plastics Economy Investor Forum - Meeting Point for Innovations

10.12.2018 | Event News

EGU 2019 meeting: Media registration now open

06.12.2018 | Event News

 
Latest News

Data use draining your battery? Tiny device to speed up memory while also saving power

14.12.2018 | Power and Electrical Engineering

Tangled magnetic fields power cosmic particle accelerators

14.12.2018 | Physics and Astronomy

In search of missing worlds, Hubble finds a fast evaporating exoplanet

14.12.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>