ISMR June 2022 - Page 19


Speed of sound to measure material elasticity

Researchers at the University of Nottingham in the UK 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 to develop new designer alloys with tailored stiffness ,” commented the University of Nottingham .
Dr . Paul Dryburgh , co-lead on the study ( from the Optics and Photonics Research Group at the University of Nottingham ), added : “ 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 . 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 nextgeneration materials with superior properties , making SRAS ++ an essential tool in the development of new materials ,” commented Professor Matt Clark , co-lead on the study from the Optics and Photonics Research Group at the University of Nottingham .
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 ( of the many thousands ) have 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 used .
Laser ultrasound , the science of turning high-energy optical energy into sound , allows ultrasound to be created in an extremely small area ( 200 µ m , approx . the same width as two-three human hairs ). This means the researchers can precisely create sound waves in each of these crystals in the metal one-byone . 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 ten times faster than through air ( at ~ 3000 m / s ).
The findings are reported in a new paper , entitled ‘ Measurement of the single crystal elasticity matrix of polycrystalline materials ’, published in the journal , Acta Materalia . n

Deep drawing research

The “ Deep Drawing with a Thin-Film Inductive Sensor for Monitoring Flange Draw- In ” IGF research project was successfully completed at the end of the 2021 . In this project , the IFUM ( Institute of Forming Technology and Machines , Leibnitz University Hannover ), in cooperation with the Institute for Microproduction Technology ( IMPT ), developed and tested a new type of inductive sensor for measuring the flange pull in deep drawing processes . The sensor system extends monitoring forming processes and offers “ a robust and reliable option for process monitoring ,” according to the IFUM .
As part of the research project , the sensor was first designed using electromagnetic finite element simulations and manufactured by thin-film processes . With the aim of increasing the quality of drawn parts and reducing reject rates , the sensor was then integrated into a forming tool . Integration
Deep-drawn part examples .
into the specially designed tool was done by using special tool inserts . Close-toproduction , deep-drawing tests were used to characterise the sensor and investigate the relevant parameters influencing the sensor signal .
“ It was found that the tool temperature and the sheet material , in particular , have a significant influence on the measured signal . The deep-drawing tests also demonstrated that the sensor system can reliably detect typical defects during deep drawing , such as cracks and wrinkles in the flange area , at the time they occur . Rejects can therefore be identified accurately , quickly and inexpensively based on the sensor signal . In the future , the flange draw-in measurement can be used as an input variable for process control to counteract process fluctuations . This will improve the quality of the drawn part and consequently reduce production costs ,” said the IFUM .
The research project from the Research Association for Steel Application ( Forschungsvereinigung Stahlanwendung e . V ., FOSTA ) was supported by the Federal Ministry of Economic Affairs and Climate Action ( BMWK ) through the German Federation of Industrial Research Associations ( AiF ), as part of the programme for promoting industrial cooperative research ( IGF ) decided by the German Bundestag . n
ISMR June 2022 | sheetmetalplus . com | 19