Laser ultrasound tests space rock stiffness

Described in Scripta Materialia, the method was developed and patented in-house at Nottingham. It uses a laser ultrasound technique known as spatially resolved acoustic spectroscopy (SRAS++) to non-invasively test meteorites and other space objects. The technique was used to examine fragments of the Gibeon meteorite, composed of an iron-nickel alloy and significant amounts of cobalt and phosphorus, which was discovered in Namibia in the 19^th century. 

The relative scarcity and scientific value of these types of space materials means that alternative, destructive testing methods are not appropriate. Additionally, many meteorites are made of crystalline materials that are formed under extraterrestrial conditions not achievable on Earth, meaning samples for destructive testing cannot be replicated. 

“These materials have evolved in unique conditions over millions of years to form these amazing structures and patterns,” explained lead author Wenqi Li, from the University’s Optics and Photonics research group.

“These conditions cannot be reproduced on Earth and meteorites have amazing large-scale microstructure and phase mixtures which gives mechanical and elastic properties that are quite different to the man-made iron-nickel alloys we can produce on Earth.”

As well as information on the formation and evolution of planetary bodies, SRAS++ testing can provide insights into alloys for aerospace and industrial applications, and further our understanding of the potential for meteorites to act as a resource for extraterrestrial manufacturing.

“The SRAS++ machine uses lasers to make and detect acoustic waves that travel on the surface of the material, this means that we do not need to touch the sample and do not damage the sample in anyway,” said Associate Professor Richard Smith. “This is really important for samples where there is limited supply.

“There are no published values to directly compare the results of this study, as non-destructive measurements of the single crystal elasticity on granular material has not previously been possible. So, we compared our results with theoretical values for man-made iron-nickel alloys. We also calculated the bulk properties from our single crystal elasticity measurements and compared them to published measurements on the Gibeon meteorite and they also agree well.”