Capable composites

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 February 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 said.

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,’ said Drugan.