By Arya Shahrostambeik, Laboratory Scientist (M.ScE)
Viscoelastic Properties of Materials
Have you ever wondered why some materials stretch like a rubber band while others flow like honey? The secret lies in their viscoelastic properties. This blog will provide you with insights to the characterization viscoelastic properties and what makes materials behave the way they do.
What is Viscoelasticity?
Viscoelasticity is a unique property of materials that exhibit both viscous and elastic characteristics. To put it simply, viscous materials, like honey, resist flow and take time to deform. Elastic materials, like rubber bands, can stretch and return to their original shape. Viscoelastic materials combine these two behaviors, allowing them to both stretch and flow depending on the conditions.
Common Examples
Imagine you have a piece of slime. When you pull it slowly, it stretches out like a rubber band (elastic behavior). But if you pull it quickly, it might snap or break, behaving more like a thick liquid (viscous behavior). In general, elastic materials tend to return to their original shape after a deformation is applied, while viscous materials resist deformation, and if a deformation is made, they do not go back to their original shape. This dual nature is what makes viscoelastic materials so interesting and useful in various applications.
The Importance of Viscoelasticity
Viscoelastic materials are everywhere around us. They are used in car tires, shoe soles, medical devices, and even in food products like gelatin. Understanding their viscoelastic properties helps engineers and scientists design materials that can withstand different types of forces and stresses.
For example, car tires need to be both flexible and durable to provide a smooth ride and ensure safety. Shoe soles must absorb impact while providing comfort. Medical devices, such as prosthetics, need to mimic the natural movement of the human body. All these applications rely on the unique viscoelastic properties of materials.
The Science Behind Viscoelasticity
At a molecular level, viscoelastic materials consist of long polymer chains that can move and slide past each other. When a force is applied, these chains can stretch and align in the direction of the force, giving the material its elastic properties. However, because the chains can also move past each other, the material can flow and deform over time, which gives it its viscous properties.
How Do We Measure Viscoelasticity?
One way to measure the viscoelastic properties of a material is through a test called Dynamic Mechanical Analysis (DMA). In this test, a sample of the material is subjected to a sinusoidal (wave-like) force or displacement, and the resulting response is measured. By analyzing the phase difference (phase angle) between the applied force or displacement and the resulting feedback, scientists can determine the material’s storage modulus (a measure of its elastic behavior) and loss modulus (a measure of its viscous behavior or how material can disperse the energy though its matrix).
Viscoelasticity Saves You from Getting Injured by a Cast Saw!
Have you ever wondered why a cast saw, which can easily cut through a hard cast, doesn’t cut through your skin? It is due to the unique design and operation of the cast saw. Unlike traditional saws that spin or move continuously, a cast saw’s blade oscillates back and forth in very short, rapid motions. This oscillating motion allows the saw to cut through rigid materials like plaster or fiberglass but not viscoelastic materials.
The cast saw blade moves a very small distance, about three thumbnail-thicknesses. This short distance is enough to break the rigid material of the cast but not enough to cut through the flexible and elastic skin. Unlike rigid materials that cannot dissipate energy effectively, the skin can stretch and move, absorbing the blade’s motion without damage. This is why medical professionals can safely use cast saws to remove casts from patients without worrying about any damage.
Conclusion
Viscoelastic materials are fascinating because they combine the properties of both solids and liquids. Their unique behavior allows them to be used in a wide range of applications, from everyday items like shoes and tires to advanced technologies in medicine and engineering. Understanding the viscoelastic properties of materials helps scientists and engineers create products that are both durable and flexible but capable of withstanding various forces and stresses.
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About the Author
Arya Shahrostambeik is a Laboratory Scientist at C-Therm Technologies specializing in the Metravib product line. Having completed his Masters Degree in Chemical Engineering at the University of New Brunswick, Arya has extensive experience in the area of DMA and other materials characterization techniques.