The elasticity of materials can now be measured at a microscopic scale by tracking the speed of sound across individual crystals. The spatially resolved acoustic spectroscopy (SRAS++) technique developed at the University of Nottingham, U.K., could be of value in the development of next-generation materials, with potential applications in aerospace engineering and medical implants.

SRAS++ uses high-frequency ultrasound to produce microscopic resolution images of the microstructure and maps the elasticity matrix, or the relationship between stresses and strains in the material. By precisely measuring the speed of sound across the surface of microscopic crystals that compose metal alloys and other materials, their orientation and the material elasticity can be revealed.

Along with the stiffness of the material, the elasticity matrix also provides insight into many important material properties that are hard to measure directly, such as how the material responds to changes in temperature. SRAS++ can provide a crucial tool for new material development as its rapid measurement of the elasticity matrix can guide the discovery of new materials with superior properties.

An experimental laser ultrasound device was engineered to generate high-frequency waves in a 200 micrometers footprint. The laser shoots a high-energy pulse of light at the sample material, which creates a sound wave that travels along its surface and is tracked with a built-in detector to reveal the orientation of single crystals, along with their elasticity. As reported in Acta Materialia, accuracy was validated during tests with pure nickel, titanium and a nickel-CMSX-4 single crystal alloy.

"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 Professor Matt Clark who co-led the research. "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."