Measuring the elasticity of a material, or the material’s capacity to return to its original shape once the deforming force that’s applied to it is released is important in the field of materials science. That importance certainly appears to not be lost on researchers from the University of Nottingham (UoN), who found a way to tackle the elasticity problem visually.
Choosing the right material for your application or technology is paramount, as its properties will dictate both the use and the limitations of your final product. Thus, engineers make it a priority to examine the materials they have for their properties—including elasticity.
However, methods to test and quantify these properties have their limits. Most methods leave permanent damage and are destructive in nature, while others simply don’t apply to materials with properties in the extremes. There is then a certain need for a non-invasive approach to examining material properties—and UoN researchers may have found just that using lasers and ultrasound.
To be precise, UoN researchers found a way to measure and visualize the speed of sound across the surface of a material; this, they say, can help give scientists a visual representation of the material’s microscopic elasticity—a technique called spatially-resolved acoustic spectroscopy++ (SRAS++). Their novel methodology was published as a study in the journal Acta Materialia.
“Many materials […] are made up of small crystals. The shape and stiffness of these crystals are essential to the material’s performance. This means that if we tried to pull on the material, as we would a spring, the stretchiness depends on the size, shape, and orientation of each of these hundreds, thousands or even millions of crystals,” said study co-lead Paul Dryburgh from the institution’s Optics and Photonics Research Group.
Dryburgh continued in the UoN press release: “This complex behaviour makes it impossible to determine the inherent microscopic stiffness. This has been an issue for over 100 years, as we’ve lacked an adequate means to measure this property.”
To get around this, Dryburgh and the team employed the use of laser ultrasound, which allowed the conversion of optical energy into sound. This allowed the team to create ultrasound in extremely small areas not much larger than the width of three human hairs.
By shooting a pulse of laser light onto a material, the device creates a sound wave that travels along the surface of the material in question. A detector tracks this sound wave as it propagates through the material surface, which can reveal the orientation of single crystals within the material, as well as its elasticity.
“The development of SRAS++ is a notable breakthrough because it provides the first method to measure the elasticity matrix without knowing the distribution of crystals in the material,” said study co-lead Professor Matt Clark who’s also from the Optics and Photonics Research Group. “SRAS doesn’t require exacting preparation of a single crystal; it is fast (thousands of measurements can be made every second) and offers unparalleled measurement accuracy. The speed of the technique is such that we estimate that we could repeat all the historical elasticity measurements of the past 100 years within the next six months.”
Future work with SRAS++ has the team hoping that it will lead to tailor-made engineering materials with specifically-designed stiffness; these said materials may find use in applications such as in aerospace and in prosthetic applications.
References
- Dryburgh, P., Li, W., Pieris, D., Fuentes-Domínguez, R., Patel, R., Smith, R. J., & Clark, M. (2022). Measurement of the single crystal elasticity matrix of polycrystalline materials. Acta Materialia, 225, 117551. https://doi.org/10.1016/j.actamat.2021.117551
- Lavars, N. (2022, February 16). World-first way to measure material elasticity uses laser ultrasound. New Atlas. https://newatlas.com/materials/world-first-measure-material-elasticity-lasers-sound/
- Lowry, E. (2022, February 11). World-first: Speed of sound used to measure elasticity of materials. University o Nottingham. https://www.nottingham.ac.uk/news/world-first-speed-of-sound-used-to-measure-elasticity-of-materials
