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Wire Arc Additive Manufacturing (WAAM) is a Direct Energy Deposition additive manufacturing process that uses well-established welding technology. It consists of a sequential deposition of weld passes and layers to form bases of engineering components later machined to the final shape. The WAAM process is characterised by high heat input, high deposition rate, high surface roughness and the anisotropy of material properties. The high heat input leads to significant development of distortion and residual stresses, which can negatively affect the performance of the final component. At the same time, the high input can lead to the development of a highly textured microstructure. Hence, significant effort is underway to address the development of residual stresses, distortion, or anisotropy in the mechanical properties, which depend on the crystallographic texture. It is, however, impractical, and expensive to test all manufactured components. Therefore, developing validated numerical models is vital to obtain the required information. In this project, the WAAM process has been employed to manufacture multipass, multilayer walls made using 316LSi stainless steel consumable on a 316L substrate at the University of Wollongong. An array of thermocouples on the substrate has been employed to monitor the transient temperature field during the WAAM manufacturing of test specimens. The thermocouple readings are then used to calibrate the thermal model, which will later be used in a phasefield model predicting resulting weld-like microstructure and in a thermo-mechanical model predicting resulting distortion and residual stresses. A microstructural analysis and the assessment of the welding-induced residual stresses support the numerical modelling work by providing means of model validation. [ABSTRACT FROM AUTHOR]

Carbon-based materials, such as graphite and carbon/carbon (C/C) composites, are utilised in various hightemperature applications. For instance, pure graphite is extensively employed in nuclear reactors as a neutron moderator, while C/C composites are predominantly used in specialised high-value applications, such as the nose cone and wing leading edges of NASA's space shuttle. Understanding the mechanical and fracture behaviour of these materials is paramount in ensuring the overall safety of the high-temperature engineering system. In this study, nuclear-grade graphite and needle-punched C/C composite were tested using the splitting tensile strength test, which indirectly evaluated their tensile behaviour. Finite element simulations were then performed to gain insights into both tested materials' elastoplastic and fracture behaviour. The experimental results showed that graphite and C/C composites exhibited an initial linear elastic behaviour in tension, followed by a plastic regime until the maximum load was reached. After the peak load, the graphite specimen failed in a brittle fashion. In contrast, for the C/C composite, the needle fibre bundles enabled different energy-absorbing failure mechanisms, including delamination and matrix cracking and a globalised deformation. The FE models could predict the tension mechanical behaviours and the damage onset of the specimens. The findings herein encourage further investigations using FE simulations to predict the mechanical behaviour of C/C composites and graphite for extreme environment applications. [ABSTRACT FROM AUTHOR]