toughness

Mother of pearl – also known as nacre – is a natural material found in certain seashells such as those of oysters and abalone. On the microscopic level, it consists of hexagonal tablets of the hard mineral aragonite glued together by a soft biopolymer. The aragonite gives nacre its strength, and the biopolymer adds flexibility and crack resistance.

Scientists at Princeton University have developed innovative composite materials inspired by nacre by utilizing conventional construction materials like Portland cement paste combined with a limited amount of polymer. The new material consists of alternating layers of cement paste sheets with the highly stretchable polymer polyvinyl siloxane.

The materials were subjected to bending tests to evaluate crack resistance or fracture toughness. Three different versions of the material were tested that used different ways of interposing the polymer layers. The new materials were compared with similar structures composed entirely of cement.

The concrete-only samples were brittle, breaking suddenly and completely upon reaching their failure point. The samples with alternating cement and polymer layers demonstrated increased ductility and resistance to cracking.

By fully mimicking the structure of nacre – using completely separated hexagonal cement tablets – the researchers demonstrated materials with 19 times the ductility and 17 times the fracture toughness of cement while retaining nearly the same strength as solid cement samples.

Engineered materials inspired by nature could eventually help increase the durability of a wide range of brittle ceramic materials, from concrete to porcelain.

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From seashells to cement, nature inspires tougher building material

Photo, posted January 2, 2016, courtesy of Yantra via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

In 2015, UC Riverside materials scientists placed a mottled black beetle in a parking lot and ran it over with a Toyota Camry. Twice. Crushed beneath the wheels of a 3,500-pound sedan, the inch-long insect made it through without a scratch.

For the past five years, a group of scientists have been studying this remarkable bug, which has the splendid name of the diabolical ironclad beetle. Using a combination of advanced microscopy, mechanical testing, and computer simulations, the researchers have figured out the secret of this beetle’s crush resistance.

The beetle’s super-toughness lies in two armorlike structures called elytra that meet in a line, called a suture, running the length of the abdomen. The suture acts like a jigsaw puzzle. It connects various exoskeletal blades – the puzzle pieces – in the abdomen under the elytra. These structural components can act in different ways. The interconnecting blades lock to prevent themselves from pulling out of the suture. The suture and blades delaminate, leading to a graceful deformation rather than catastrophic failure. These strategies dissipate energy to circumvent fracturing.

The researchers found that the diabolical ironclad beetle – just had to say that name again – can take on an applied force of about 150 newtons, a load at least 39,000 times its body weight. (That’s the equivalent of a 150-pound person resisting the crush of about 25 blue whales).

An ongoing challenge for structural engineering is how to join together different materials without limiting their ability to support loads. The strategies evolved in these beetles may be applicable in gas turbines of aircraft, for example, where metals and composite materials are joined together with mechanical fasteners. We can learn things from the toughest beetle of them all.

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Diabolical ironclad beetles inspire tougher joints for engineering applications

Photo, posted April 9, 2017, courtesy of Vahe Martirosyan via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Seashells inspire better concrete

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The Toughest Beetle Of Them All | Earth Wise

In 2015, UC Riverside materials scientists placed a mottled black beetle in a parking lot and ran it over with a Toyota Camry. Twice. Crushed beneath the wheels of a 3,500-pound sedan, the inch-long insect made it through without a scratch.

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