Running shoes have inspired a new material to protect buildings from impacts. 

A material used in shoes and memory foam pillows is the basis of the design of a new, 3D-printed product that could help protect buildings from collision damage and other high impact forces, equivalent to a car travelling at 60km/hr.

Research engineer Dr Tatheer Zahra from the QUT has used off-the-shelf bioplastic to 3D print geometric shapes that mimic the behaviour of auxetic materials - materials that become thicker perpendicular to the applied force.

“Rather than flattening when stretched or bulging when compressed, auxetic materials expand or contract in all directions at once, which makes them highly energy-absorbent and load resistant,” Dr Zahra said.

“But existing commercial auxetic material is expensive and not locally available, so I designed geometric shapes that achieved the same behaviour.”

Dr Zahra said 3D-printing auxetic geometries could potentially replace steel and fibre reinforced polymer mesh reinforcements in composites, and could also be used as a flexible and widely applicable protective wall render.

She said the energy absorption would be equivalent to a 20mm thick reinforced composite protective render over a full-scale building wall, which could potentially withstand the impact force of a car travelling at 60km/hr.

“At scale, composites embedded with these geometries could theoretically resist high impact or shock energy caused by gas explosions, earthquakes and wind forces, and car collisions,” Dr Zahra said.

“In Australia, there’s an estimated 2000 vehicular crashes each year. Direct building damage cost at 2.5 per cent would put the damage bill at about $38.65M/year for housing.

“Since vehicles also crash into apartments, office building, restaurants and convenience stores, this cost of building damage would probably be higher.

“Loss of life would be the highest cost.”

Dr Zahra said protection for masonry walls is especially important because it is an essential part of most commercial and residential buildings.

“Masonry is a very cheap material that is resilient to noise, heat, and has better fire protection properties compared to wood or steel, but its mortar joints weaken the overall structural strength,” she said.

“If auxetic geometries were embedded into the mortar to make protective composites, they would also be protected from microorganisms and temperatures over 60°C, and should last the design life of the structure.”

Proven at lab scale, Dr Zahra now aims to test the designs on full scale masonry and concrete structures. 

Her latest study is accessible here.