CMMI-EPSRC: Thermoacoustic response of Additively Manufactured metals: A multi-scale study from grain to component scales

The proposal builds on an existing collaboration which has focussed on achieving a multi-scale understanding of the material-structure response to thermoacoustic excitation at up to 750K and 800 Hz using detailed experiments and simulations, in plates and beams of conventionally-manufactured metals, ranging from aluminium to Hastelloy X. Results have shown, at a microscale, a tendency for deformation to concentrate in the larger grains of oligocrystal within the material microstructure at locations disparate from where macroscale homogeneous analysis predicts (Carroll et al., Int. J. Fatigue, 57: 140-150, 2013), demonstrating that non-uniformity in the microstructure can lead to significant and service critical errors in predicting failure.

Further laboratory-scale experiments, using maps of surface deformation measured during broadband thermoacoustic excitation, have confirmed the presence of mode jumping and shifting when non-uniform heating generates thermal buckling (Lopez-Alba et al, J. Sound & Vibration 439:241-250, 2019). With this in mind, the research team scaled these tests to component scale, establishing quantitative validation procedures for coupled models of thermoacoustic excitation of simple components (Berke et al, Exptl. Mech., 56(2):231-243, 2016). In doing so, the team developed two unique pieces of experimental apparatus: in Illinois, for localised heating and modal excitation of coupons; and in Liverpool, to deliver spatially distributed heating at 21kW while simultaneously applying random broadband excitation to small components. Both rigs have real-time, full-field temperature and displacement measurement capability. Lambros and Patterson have correspondingly complementary expertise in multi-scale mechanics of materials under extreme loading (Lambros) and in measurement, simulation and validation of structural responses (Patterson).

It is proposed to exploit these findings, facilities and expertise to understand the potential for additive manufacturing in the production of components subject to extreme thermomechanical excitation in demanding environments. It is likely that this type of structure will be produced in small quantities rendering it appropriate to consider additive manufacturing; however, the extreme conditions of temperature and mechanical loading make it a challenging application for any material. Successful design, manufacture and service deployment of such components requires an understanding of the multi-scale material-structure response to loading and its evolution with a component's progression from its virgin state through shake-down towards initiation of detectable non-critical damage. These responses are understood at a fundamental level for subtractively-manufactured metals; however, there is very limited fundamental understanding of these material-structural interactions for additively-manufactured metals, at either room temperature (Attar et al, IJ Mach. Tools & Manu., 133: 85-102, 2018, Foehring et al, Mat. Sci. Eng. A, 724: 536-546, 2018) or elevated temperatures (Roberts et al, Progress. Add. Manu., 1-8, 2018). It is hypothesized, because of the unique microstructure containing the previously studied larger grains of oligocrystal, the complex thermomechanical history of their manufacture and the presence of significant residual stresses, that the response of additively-manufactured metals under extreme thermoacoustic loading will be significantly different from their subtractively-manufactured counterparts, especially in defect-driven processes such as failure.

This proposal extends the research of Lambros and Patterson by adding the additive manufacturing expertise and facilities provided by Sutcliffe (R&D Director at Renishaw AMPD, RAe Silver Medallist 2018 with over 20 years researching metal additive manufacturing) who has unparalleled access to the latest additive manufacturing technology.

The project team have considered carefully the way in which Impact will be delivered from this work. We have followed EPSRC guidelines and have identified, costed and planned significant Impact generation mechanisms that augment the project and have only minor effect on the generation of urgently required scientific knowledge. In summary, we have divided, as required, our impacts into four objectives identifying in total 1890 hours of people-centric training at UG, PG and staff level and fully 125 individually recorded impact pathways costing an additional £18,500. We will manage and optimise our impact objectives by recruiting a committee to steer our impact activities. This committee will comprise both academics and industrialists and will met bi-annually and will write a yearly impact report to be collated at the end of our work and passed to the UoL School of Engineering impact Lead for inclusion in the next REF submission. The team will take a modern, targeted, connected multi-level approach to disseminating results using all available tools and making publications open access where required.

The project directly develops skills at both UG, PG and staff level in: experimental mechanics, computer science, additive manufacturing, materials science, standards, and international collaboration. Both Illinois and Liverpool have well defined on-job training programmes; for example, at Liverpool, researchers and students have access to Professional Development (PD) in four streams: Personal, Leadership, Research and Teaching. In addition, we will ensure that project staff and students develop broader capabilities, attributes and the mind-set needed to thrive in the multiple careers that early career researchers migrate to. We will also recruit one PhD student with industrial sponsors in year two and lever the intellectual, operational and physical capital generated for the training and development of UG/PG level students by running two (12 in total) UG/PG projects.

To ensure that the scientific knowledge generated is effectively disseminated we will complete a minimum of 32 knowledge dissemination tasks including high-impact journal publications, conferences, invited keynote presentations, periodicals, social media, and non-standard knowledge sharing on dedicated web sites.

Our societal impacts are derived from four sources, the development of fundamental data to inform standards allowing the deployment of AM in highly loaded environments, the creation of strong transatlantic links between excellent research groups, the internationalisation of our Staff/PG/UG cohort and the publication of accessible articles.

Economic impact from fundamental research projects such as this are sometimes difficult to justify as the work can be many steps from a product or service; however this project has at its core a drive to enable the use of an emerging technology in fields of use that are high value and which are globally important. To ensure impact we will engage with our national business facing research centres to garner interest from their client base in the research; for example, the National Centre for Additive Manufacturing at The MTC will be a key pathway and presentations will be held at the MTC helping to establish networks with SMEs and to identify future impact opportunities. The team will also directly approach companies who are active in the application of AM.

Generating long-lasting and significant impact from the research is incredibly important and because of this it must be budgeted correctly both in terms of researcher time and additional costs. The project team have spent time fully costing the additional impact work as described in the Justification of Resources.