Materials scientists have developed a novel composite material that successfully merges two seemingly opposing characteristics: rigidity and a high capacity for damping.
Everyday experiences, such as the hum of a compressor, the rattling of an air conditioning unit, or the clattering of a railway carriage can create vibrations that annoy passengers. While these vibrations can be irritating, they may also cause damage over time to materials and machinery, ultimately shortening their lifespan. Additionally, the noise produced can pose risks to human health and overall well-being.
To address the issues of vibrations and noise, engineers often turn to damping materials like foams, rubber, and mechanical components, including springs or shock absorbers. However, incorporating these materials can lead to increased bulk, weight, and cost in many applications. Furthermore, retrofitting existing designs with damping elements does not always yield effective results.
This demand underscores the need for materials that are stiff, capable of bearing loads, and proficient in internal damping. Achieving a material that embodies all these qualities is challenging, as stiffness and damping often contradict each other.
Researchers at ETH have crafted a material that integrates these seemingly incompatible traits. Ioanna Tsimouri, in her doctoral research, with guidance from professors Andrei Gusev and Walter Caseri from the Department of Materials, has pioneered a new composite material. This new material consists of layers of rigid substances interconnected by ultra-thin rubber-like layers made from a crosslinked polydimethylsiloxane (PDMS) mixture.
The initial prototypes utilized silicon and glass plates measuring 0.2 to 0.3 mm thick, bonded with rubber-like layers just a few hundred nanometers thick. Testing confirmed that these new composite materials possessed the desired properties envisioned by the researchers.
The invention was patented earlier this summer and has now been published in the journal Composites Part B: Engineering.
Derived from Theory
Working alongside materials physicist Gusev, the team initially employed computer models to determine the optimal thickness of the adhesive rubber-like layers necessary to achieve high levels of both stiffness and damping in the composite material.
Their calculations indicated that the thickness of the layers must align with a specific ratio to produce the intended properties. The findings suggested that the damping polymer layers should constitute less than 1 percent of the total material volume, while the stiff layers of glass or silicon should make up at least 99 percent. “If the polymer layer is too thin, its damping effect is minimal. Conversely, if it is too thick, the overall material becomes insufficiently stiff,” Tsimouri explains.
Laboratory Implementation
Next, she and Caseri conducted experimental validations of their calculations by producing multiple variants of the composite material in the lab.
For the rigid components, Tsimouri selected smartphone-grade glass. The polymer was created through a mix of available PDMS-based polymers, which include chemically reactive sites. When a catalyst is introduced, these sites fuse, creating a polymer network, a rubbery substance that secures the stiff panels like a two-component adhesive.
With the help of UK associate Peter Hine, the researchers assessed the frequency- and temperature-dependent mechanical properties of the laminate materials through a three-point bending test. She also employed a straightforward yet effective practical test: dropping the laminate plates from a height of 25 centimeters onto a table and comparing their acoustic and mechanical damping to that of a glass plate of the same size.
The laminate exhibited outstanding damping qualities, along with notable stability. It made a softer impact on the table and showed no bouncing, unlike the pure glass, which crashed noisily and flipped over. “This test demonstrated that the laminate effectively dampens vibrations and noise,” Tsimouri remarks.
The researchers assert that this laminate could have a wide range of applications, from window glass and machinery housings to automotive components. It may also be valuable in aerospace and sensor technologies, where demand for advanced damping materials is particularly high. “The global market for damping materials is substantial,” the researchers note.
Moreover, the laminate’s polymer is resistant to temperature fluctuations, maintaining its damping effectiveness across a broad temperature spectrum. It only loses its damping properties and turns glassy when temperatures drop below minus 125 degrees Celsius.
Ultimately, this laminate could also be an environmentally friendly option that conserves resources, as glass and silicon are easily recyclable. When melted, the tiny polymer residues break down into glass, leaving recycling processes unaffected.
Caseri believes that this technology is scalable. “Manufacturers with the right equipment can produce laminate panels measuring several square meters. The production method is relatively simple.”
