CMMI-EPSRC: Thermoacoustic Response of Additively Manufactured Metals: A Multi-Scale Study from Grain to Component Scales

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This research project was funded under the NSF Engineering–UKRI Engineering and Physical Sciences Research Council opportunity, NSF 20-510. The grant will support research towards understanding the potential for additive manufacturing (AM) in the production of metallic components subject to extreme thermomechanical excitation. Structures in demanding environments where high temperatures and vibratory loads are combined (e.g., sustained hypersonic flight, space re-entry, exhaust-wash structures, breeder blankets in fusion reactors) often experience fatigue which shortens their lifecycle. It is likely that these types of structures will be produced only in small quantities, making it appropriate to consider additive manufacturing for their construction. Successful design, manufacture and service deployment of such components requires an understanding of the component's progression from its virgin state, through shake-down, towards initiation of detectable non-critical damage, and ultimately to failure. To date, this failure evolution process is fairly well understood for traditional subtractive-manufactured metals. However, there is very limited fundamental understanding of the multi-scale material-structure interactions for failure of AM metals. Because of the unique microstructure of AM metals, their complex thermal history during manufacture, and the presence of significant residual stresses, it is hypothesized that their response under extreme thermoacoustic loading will be significantly different from their traditional counterparts, especially in defect-driven processes such as failure. By understanding the details of this failure process in AM metals under extreme thermoacoustic loading, the results of this study will shed light onto how to better tailor the additive manufacturing approach to produce materials and structures most suitable for operating in such adverse environments.The research will be undertaken jointly by the PI in collaboration with researchers at the University of Liverpool in the United Kingdom, focusing on key aspects that link material-level (micro- and mesoscale) response to the structural-level (macroscale) response. Damage accumulation at the microscale for additively-manufactured metals subjected to cyclic loading and global and local thermal gradients will be quantified using high resolution digital image correlation. At a larger length scale, additively-manufactured plates with geometric reinforcement subjected to thermal buckling during thermo-mechanical excitation will be studied using real-time optical and thermal imaging. A key aspect will be to explore the interaction of the complex thermal processing history of AM metals (including any existing residual stresses) with the transient and coupled thermomechanical loading applied. Finally, the project will identify the fundamental rules governing AM for reliable components subject to high-temperature broadband excitation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.