14 June 2019
High cycle fatigue and fatigue crack propagation behaviour in additive manufactured titanium alloys
Presented By Professor Xiang Zhang, Coventry University
- 1.00 - 2.00 pm
- DAV 1.103, Sir David Davies Building
About this event
Comparing to the powder bed fusion additive manufacturing processes (e.g. the selective laser melting, electron beam melting methods), the Wire + Arc Additive Manufacturing (WAAM) can produce much larger metal parts, in metre-scale and at much higher deposition rate. The process also offers lead time reduction and much lower buy-to-fly ratio compared to the traditional method by forging/casting followed by machining. Research is much needed in the area of fatigue and fracture performance for qualification of safety critical components. WAAM Ti-6Al-4V alloy has been tested and modelled at Coventry University over the last five years, focusing on the structural integrity issues. This talk will cover two topics: (1) effect of porosity defects on fatigue crack initiation; (2) fatigue crack propagation; effect of heterogeneous microstructure and process induced residual stresses.
For topic (1), interrupted fatigue-tomography experiments were performed. Traditional notch fatigue method and modern fracture mechanics approach were applied to micrometer scale pores. Test results could not be correlated well by the traditional S-N curves owing to different pore sizes and their locations. Using the fracture mechanics approach, good correlation was found between the fatigue life and the stress intensity factor parameter. A modified Kitagawa-Takahashi failure diagram was established for criticality analysis of porosity defects. For topic (2), compact tension specimens made by different WAAM build strategies and with two crack orientations were tested. Residual stress were evaluated by the contour method. Microstructure and texture characteristics and their influence on the crack growth rate and crack path were investigated. A predictive model based on linear elastic fracture mechanics was developed.
Prof Xiang Zhang studied aeronautical engineering at Northwestern Polytechnical University in China (MSc). Her PhD study at Imperial College London focused on predicting fatigue crack growth life under variable amplitude loading spectra. In her academic career, she has worked for Imperial College for seven years as Research Associate; Cranfield University for 18 years, with Lecturer, Senior Lecturer and Readership appointments; Coventry University as Professor in Structural Integrity since 2015. Professional status: Fellow of the Royal Aeronautical Society; Chartered Engineer. She has actively conducted research in the field of structural integrity and failure analysis of carbon fibre reinforced polymer composites as well as light weight metallic alloys, completed 26 government or industry funded projects. She has published over 170 papers. In 2016, she received the Helmholtz Association’s International Fellowship Award.