Silk Sensor Could Speed Development of Composite Materials

A new sensor can help detect damage in composite materials during their development, an advancement that facilitates the design of stronger and better composites.

Researchers have developed a new sensor that can help detect damage in composite materials during their development, an advancement that facilitates the design of stronger and better composites.

Scientists at the National Institute of Standards and Technology (NIST) have developed a way to embed a nanoscale damage-sensing probe made of epoxy and silk into a lightweight composite made of epoxy and silk. The probe—called a mechanophore—is made from a dye, rhodamine spirolactam (RS), that reacts to applied force, changing from a dark state to a light state, they said.

In the experiment, researchers attached a molecule to silk fibers contained inside an epoxy-based composite, then applied more and more force to the material. This stress activated the RS, which caused it to turn fluorescent using detection by a red laser and microscope developed by NIST researchers.

The team, led by NIST researcher Jeffrey Gilman, used this technology to take photos inside the composite, which showed even the tiniest of breaks in the interior of the material where the fiber had fractured.

 

sensor silk
Examples of silk used in experiments to detect damage in composites, shown under black light. Researchers at the National Institute of Standards and Technology (NIST) used a sensor embedded into this material to help detect damage in composite materials during their development, an advancement they said that facilitates the design of stronger and better composites. (Source: Chelsea Davis and Jeremiah Woodcock/NIST)

 

The sensor solves a long-time problem in the development of composites and provides a way forward for designers of these materials to optimize them for various applications, Gilman said.

“There have long been ways to measure the macroscopic properties of composites," he said. "But for decades the challenge has been to determine what was happening inside, at the interface."

That interface—where two materials such as crab shell or bone meet in a composite material—is a critical point in ensuring a material’s durability and ability to withstand damage, with designers favoring interfaces that are both thin and flexible. Historically, however, it’s been difficult to measure the properties of interfaces in composites, Gilman said.

That is, until now, he said. With the development of the sensor, researchers can now, when they attempt a design change, “figure out if the change you made improved the interface of a composite, or weakened it,” Gilman said.

The NIST team published a paper on their work in the journal Advanced Materials Interfaces .

The work has numerous applications for design problems researchers are facing as they ponder better materials for the next generation of everything from fuel-efficient vehicles to stronger bridges, according to the team.

Gilman’s team plans to expand their research to explore how the sensors can be used in various composites, as well as how they can be used to enhance the capability of these composites to withstand extreme cold and heat, he said.
Composites that can perform optimally even with prolonged exposure to water also are in high demand—especially for applications such as bridges and wind turbine blades—so the team also will explore the use of the sensor to achieve better

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