Speed of sound used to measure elasticity of materials

Date:
February 15, 2022
Source:
University of Nottingham
Summary:
Researchers have devised a revolutionary new technique for
measuring the microscopic elasticity of materials. Known as SRAS,
the technology works by measuring the speed of sound across the
material's surface.



FULL STORY ========================================================================== Researchers at the University of Nottingham have devised a revolutionary
new technique for measuring the microscopic elasticity of materials for
the first time. Known as SRAS, the technology works by measuring the
speed of sound across the material's surface.


==========================================================================
The Engineering and Physical Sciences Research Council (EPSRC)-funded innovation uses high-frequency ultrasound to produce microscopic
resolution images of the microstructure and maps the relationship between stresses and strains in the material (the elasticity matrix). These
crystals are normally invisible to the naked eye, but by precisely
measuring the speed of sound across the surface of these crystals, their orientation and the inherent elasticity of the material can be revealed.

This technology is already starting to be used in fields such as
aerospace to understand the performance of new materials and manufacturing processes. In the future, this will launch a new field of research as
the technique is used as a completely new way to evaluate materials for improving safety in systems such as jet engine turbine blades or develop
new designer alloys with tailored stiffness. For example, in medical
implants, it is vital to match the stiffness of prosthetic devices to
the properties of the human body to ensure harmonious operation.

Paul Dryburgh, co-lead on the study -- from the Optics and Photonics
Research Group at the University of Nottingham -- said, "Many materials
(such as metals) 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. 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." "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," explains co-author, Professor Matt Clark -- 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." There is a great push for new lighter and stronger
materials to deliver more efficient systems. However, finding a new
material with the desired properties has been described as a needle
in a haystack problem. 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. This means the rapid measurement
of the elasticity matrix can be used as a 'road map' to finding the next-generation materials with superior properties, making SRAS++ an
essential tool in the development of new materials.

Previously, the only way to measure the elasticity matrix was to cut
up the component or attempt to grow a single crystal of the material,
a process that cannot be done for many materials, such as the titanium
alloys used in modern jet engines. Estimates are that less than 200
materials have (of the many thousands) had their elasticity measured. The result is that the elasticity of most industrial materials is unknown,
meaning there is significant (and in some cases, potentially hazardous) uncertainty in the actual performance of the material put to use.

Laser ultrasound, the science of turning high-energy optical energy
into sound, allows ultrasound to be created in an extremely small area
(200 mym, approx.

the same width as 2-3 human hairs). This means the researchers can
precisely create sound waves in each of these crystals in the metal
one by one; by then measuring the speed of sound across each crystal,
they can tell the shape of the crystals and the elasticity matrix of
the material at a microscopic scale.

Sound travels across the surface of metals 10 times faster than through
air (at ~3000 m/s).

========================================================================== Story Source: Materials provided by University_of_Nottingham. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Paul Dryburgh, Wenqi Li, Don Pieris, Rafael Fuentes-Domi'nguez,
Rikesh
Patel, Richard J. Smith, Matt Clark. Measurement of the single
crystal elasticity matrix of polycrystalline materials. Acta
Materialia, 2022; 225: 117551 DOI: 10.1016/j.actamat.2021.117551 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220215092516.htm

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