‘Necking’ produces unexpected results in composite material manufacture

Researchers at the University of Central Florida (UCF) have applied a technique from polymer manufacturing, called ‘cold drawing’, to product new kinds of materials for nanomanufacturing.

Cold drawing is used to imbue polyester and nylon fibres with high tensile strength and involves pulling the fibre so that its diameter is reduced and the polymer chains are aligned. The technique was never used on composite materials because it wasn’t deemed useful, but the UCF researchers attempted it just to see what would happen, and found an unexpected occurrence.

Ayman Abouraddy, associate professor at UCF, said: “While we thought the core material would snap into two large pieces, instead it broke into many equal-sized pieces.

Though a surprise to Prof Abouraddy, Robert Hoy, a University of South Florida physicist who specialises in the properties of materials like glass and plastic, wasn’t shocked by the UCF professor’s the initial findings. Hoy recognised this behaviour as something familiar to those in polymer manufacturing - a phenomenon called 'necking', which occurs when cold drawing causes non-uniform strain in a material.

“Dr Abouraddy has found a new application of necking,” Hoy said.“Usually you try to prevent necking, but he exploited it to do something potentially groundbreaking.”

This new application for necking could lead to new approaches to manufacturing smart materials. For instance, the amount of mechanical force used to pull the fibre will affect the breakage patterns in a way that will change the physical properties of the material.

The UCF team has shown that this process may also be applicable to multi-layered materials. That could lead to the packaging of hybrid materials with sensing, optical, and mechanical properties that no single material could achieve.

Tom Austin-Morgan

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