WAAM is a technique which uses a welding arc to build up metallic 3D parts in successive layers. Due to the nature of the WAAM process, parts produced may have significantly different material properties to parts machined from wrought material, and their structural integrity may not be fairly assessed using existing guidelines such as BS7910 and R6. In order to bring WAAM into industry, new structural integrity assessment rules will have to be developed to enable engineers to predict the integrity of WAAM parts efficiently and accurately. The development of such rules will require extensive experimental evidence and validation using numerical models.
This research project will involve gathering said experimental evidence, for example, study of phase transformation, material properties and residual stress measurement. Residual stress and phase characterisation will be carried out using neutron and synchrotron diffraction at central facilities. In terms of measuring residual stresses left behind by the WAAM process, non-destructive techniques such as neutron and synchrotron diffraction will be used and supplemented by destructive techniques such as block cutting and deep-hole drilling. The non-uniform texture of WAAM-deposited material deep inside metallic specimens will also be characterised using neutron diffraction techniques.
Residual stress measurements will be taken for a range of shapes and dimensions. From observed trends and patterns in the residual stress distributions of these specimens, factors that influence stresses in WAAM components can be determined. The data will also be used to formulate upper-bound residual stress profiles for WAAM components, which can be used to conduct fracture mechanics analysis to understand the failure mode of the component under different applied loads.
Throughout this work, the fracture properties of WAAM material will be characterised considering the effects of microstructure, residual stress and macro-scale anisotropy. A link between microstructure and macro-scale fracture behaviour will be established. Using the new knowledge in conjunction with existing characterisation data, a quantitative structural integrity assessment method for WAAM components will be developed.