(Nanowerk Spotlight) All mechanical systems exhibit vibrational resonances, where energy transmission through the structure spikes at certain natural frequencies. This resonance effect stems from the mass and stiffness properties of the system. At these resonant frequencies, even small vibrational inputs can get amplified into large oscillatory motions. For example, pushing a child on a swing at the natural frequency leads to huge oscillations from minimal effort.
In mechanical engineering applications, these resonances can be disastrous, often producing intolerable noise and vibration, or even catastrophic failure in sensitive equipment. Limiting amplification at resonance frequencies is therefore paramount for mitigating these damaging effects across fields ranging from aerospace to acoustics.
Traditional vibration damping solutions often involve a complex trade-off between damping performance, mass, and stiffness. These solutions typically rely on complex mechanical structures or electrical systems, which can add mass or reduce stiffness, making them unsuitable for many applications. The buckling metamaterials overcome these limitations by using buckling instabilities to achieve high damping performance without the need for added mass or loss in stiffness.
Researchers have developed a new class of mechanical metamaterials that leverage buckling instabilities to achieve extreme vibration damping, according to a groundbreaking recent study published in Advanced Materials (“Buckling Metamaterials for Extreme Vibration Damping”). These “buckling metamaterials” could enable lightweight structures that dampen vibrations more effectively than existing materials and transform a wide range of technologies where controlling vibrations is critical.
The new metamaterials take a completely different approach, using buckling instabilities of their primary load-bearing components to induce nonlinear behavior that damps vibrations. “We demonstrate that freestanding load-carrying metamaterials undergoing buckling instabilities can set hard limits on vibration transmission, saturating acceleration at a maximum value regardless of input,” explained lead author David Dykstra from the University of Amsterdam.
Damping vibrations with buckling. A) A mass (M) spring damper system, with base excitation (blue) can show a large amplified response (orange) around resonance. B) When the spring is a slender beam, which can buckle when subjected to a sufficient compressive load from the base excitation, the amplified response may be lower. C,D) The deformation of a holar sample with mass mounted on top when subjected to a base excitation from the bottom around the eigenfrequency. C) Base excitation acceleration of 0.26G at 33.8 Hz; D) cbase excitation acceleration of 0.89G at 33.0 Hz. The ellipticity of the holes, Ω, is tracked with red and blue ellipses (see “Image Analysis” in the Experimental Section, color bar). E,F) Base excitations (blue) of 0.26G (E) and 0.89G (F) induce output accelerations (orange) of 4.3G (E) and 5.7G (F), respectively. (Reprinted with permission by Wiley-VCH Verlag)
The researchers first illustrated the concept using a polymeric metamaterial with a pattern of circular holes, which buckles under compression at higher vibration amplitudes. The buckling nonlinearity causes a plateau in the force transmitted regardless of vibration input amplitude. It also introduces damping that further suppresses vibration transmission in both compression and tension. This means that these materials can effectively control vibrations even when they are being pulled apart, a significant advancement in the field of vibration damping.
The team showed this mechanism efficiently damps vibrations in elastomeric metamaterials across a range of controlled and random input vibrations. But elastomers have inherently low stiffness, making them impractical for many applications.
So the researchers went on to develop a metallic buckling metamaterial using an intricate lattice of curved steel sheets. The thin-walled design allows elastic buckling without permanent deformation. Under vibration, the structure exhibits snap-through buckling events that dissipate energy.
The steel metamaterial displayed a damping coefficient around 23 times higher than conventional lightweight metals. According to co-author Corentin Coulais, “This shows that buckling metamaterials can be used to surpass the Ashby limits of loss coefficient versus specific modulus.”
The study demonstrates the concept works for both soft and stiff materials. In addition to the experimental work, the researchers developed a simple numerical model to predict the response of buckling-based vibration damping. This model is a valuable tool for future design and optimization of these materials, paving the way for more efficient and effective damping systems.
The potential applications of buckling metamaterials are vast and transformative. In the aerospace industry, for example, these materials could enable lighter, more vibration-resistant aircraft structures. Thinner, damped wings or cabins would improve fuel efficiency, passenger comfort, and safety by averting structural failures.
For makers of high-precision scientific instruments like electron microscopes, the materials could eliminate interfering vibrations that undermine image accuracy without compromising stiffness. Their high-damping lightweight structures could also stabilize equipment in dynamic environments like self-driving cars.
In addition, the automotive sector could employ buckling metamaterials to quiet cabins and improve ride quality without adding weight. The materials’ elastic stability means they could withstand repeated vibration cycles without fatigue. Their thin-walled architecture could enable more compact damping components.
The findings will also help optimize designs of wind turbines and bridges. Damping tower and deck vibrations avoids material fatigue and resonance issues that curtail service lives. Civil engineers can now create more resilient infrastructure with longer operational lifetimes.
And manufacturers of industrial machines and robotic arms could integrate the metamaterials to reduce oscillations that hamper precision and quality. Eliminating vibrations will boost productivity in automated factories.
The potential extends to fields like acoustics and MEMS as well. By expanding practical means to control resonances, buckling metamaterials provide a flexible platform to stabilize and enhance performance across nearly any vibration-sensitive application.
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