Within the Institute of Structural Materials (ISM) labs, universal test machines are used to assess the properties (strength, toughness, hardness…etc.) of materials under various stress conditions and monitor the ways in which damage mechanisms influence the life of a specimen or component.
Here we’re going to look at equipment used in the research into composite materials for gas turbine propulsion systems: Mistras®/Physical Acoustics Corp® 4-channel acoustic emission monitoring system upgrade.
This updated bit of kit is used for Rolls-Royce/Innovate UK funded projects investigating damage progression in ceramic matrix composite (CMC) materials. Acoustic emission (AE) is the term given to transient elastic waves arising due to cracking or other rapid stress redistribution in material (think of a tree creaking or twig gradually snapping). The AE system ‘listens’ for these events, then uses various signal processing techniques to determine the nature of each event and condition of the material under investigation.
By upgrading our system, through the recent IMPACT equipment fund, we are now able to monitor smaller specimens, increase the frequency range of our data capture, and – most importantly – pinpoint the location of events occurring within a 2D plane enclosed by the sensor array. This provides a clearer picture of precisely where damage initiates and accumulates within a specimen or component and informs the development of the CMC material. Additionally, the new sensors can work as a second stand-alone system which has now doubled the capacity for normal testing.
Ceramic matrix composite (CMC) materials are an attractive material for certain components in next-generation high-performance gas turbine aircraft engines, as it offers lower density (i.e. weight reduction) and improved corrosion resistance compared to traditional metal alloy counterparts. Furthermore, advantageous thermal properties potentially mean that internal cooling systems currently required for metallic engine components are no longer necessary. There is a significant fuel efficiency increase to be gained by the inclusion of CMC components.
The nature of damage evolution in CMCs is still a subject of intense investigation. The complex service conditions – involving static and cyclic mechanical/thermal stresses and chemical corrosion – require a wide range of lab-based testing regimes to thoroughly understand the material’s behaviour before it can be adopted. Our AE system is routinely employed during CMC testing, including temperatures exceeding 1000°C, and the results are an important part of the ISM’s publication output and Rolls-Royce’s material development.
Visit the Institute of Structural Materials (ISM) site.
