Research on Structural Integrity of Welded Joints Containing Crack-like Defects
Guiyi Wu1*, C Seow2, H Coules2
1 Centre of Excellence for Advanced Materials, Dongguan, 523808, China
2 University of Bristol, Bristol, BS8 1TR, United Kingdom
EXTENDED ABSTRACT: Welded joints are likely to have crack-like defects due to the influence of welding process or service environment. Such defects have potential threats to structural safety so research has been carried out to develop structural integrity assessment methods for welded structures. However, with the development of additive manufacturing, the applicability of the existing methods to additively manufactured components is a challenge. Wire and arc additive manufacturing (WAAM) has the advantages of rapid prototyping, free design, high efficiency and less material waste so it is promising in the production of large and complex metallic structures. Nickel-based super-alloys IN625 and IN718 are ideal materials for WAAM because of high material cost, good weldability and wide application. However, crack-like defects could be induced during WAAM with inappropriate deposition conditions. In addition, WAAM process will produce large temperature gradient in the manufacturing direction, which induces epitaxial grain growth and leads to anisotropy of microstructure and material properties. These make the safety assessment of WAAM components more challenging. In this paper, the crack-like defects of WAAM components were analyzed using metallurgical examination techniques and characterized using non-destructive inspection methods. It is found that the occurrence of crack-like defects was related to the deposition path. The in-situ tests of CT specimens were carried out using neutron diffraction combined with DIC to study the fracture behavior of WAAM components with defects. A crystal plasticity finite element model was developed to predict the stress-strain field in front of the crack tip, which showed good agreement with experimental results. It is found that the fracture of WAAM specimens with defects is a mixture of unstable and stable crack extension and the apparent fracture toughness showed anisotropy which can be attributed to the microstructure and the interaction between fatigue-induced crack and pre-existing defects.
Guiyi Wu has completed his PhD from University of Bristol in 2014. He used to be the principal engineer and ECA software manager at TWI, UK before his current role of Dean Assistant and Director of Structural Integrity Research Centre at CEAM, Dongguan, China. His main research interests lie in fracture and fatigue mechanisms and assessment methodology as well as additive manufacturing. He has completed more than 30 research and industry projects and published more than 20 peer-reviewed papers.