应机械结构强度与振动国家重点实验室邀请，英国拉夫堡大学(Loughborough University of the UK) 赵利果教授来访我院并作学术报告。

报告人：赵利果 教授

时间：2019年9月20日下午16:10

地点：航天航空学院教一楼第二会议室

报告题目：Cyclic Deformation, Fatigue Crack Initiation and Growth in a Nickel-based Single-crystal Superalloy

个人介绍：

Zhao is a Professor in Solid Mechanics (Loughborough University of the UK), with established research in micromechanics-based modelling of deformation, fatigue and failure of advanced materials. He holds a BEng and a PhD in Solid Mechanics, awarded by Xi’an Jiaotong University of China. He has undertaken extensive research on nickel superalloys (for gas turbine baldes and discs), including fracture mechanics, visco-plasticity and crystal-plasticity constitutive modelling, prediction and simulation of crack propagation and fatigue-oxidation damage. Recently, he has extended his research into stent biomechanics, investigating the biomechanical performance of endovascular scaffolds. His research is supported by the EPSRC (Engineering and Physical Science Research Council), the Royal Society, the British Heart Foundation and the Royal Academy of Engineering of the UK. He has been leading four multi-institutional EPSRC projects in this area, and received the award of a prestigious Royal Society-Leverhulme Trust Senior Research Fellowship in 2008. Zhao has more than 10-year postdoctoral research experience, and worked at Cambridge University, Imperial College, Nottingham University and Portsmouth University. He has published over 70 journal papers in Solid and Computational mechanics.

报告摘要：

Cyclic deformation, fatigue crack initiation and short crack growth in a nickel-based single-crystal superalloy have been studied experimentally and numerically. Strain-controlled low-cycle fatigue (LCF) tests were carried out, with a focus on the effects of crystal orientation and temperature. Cyclic hardening/softening was observed during the LCF process, depending on the strain amplitude, crystallographic orientation and temperature. From transmission electron microscope (TEM) analyses, it was found that the processes of g’-precipitate dissolution and dislocation recovery were responsible for cyclic softening. Alignments and pile-ups of dislocations in the g matrix contributed to cyclic hardening. Initiation and growth of short fatigue cracks were also studied by in-situ fatigue experiments within a scanning electron microscope (SEM). Slip-caused crack initiation was identified at room temperature while initiation of a Mode-I crack was observed at 650°C. Slip traces continuously developed ahead of the crack tip once initiated and acted as nuclei for early-stage crack growth. The crack-growth rates were evaluated against stress intensity factor range ΔK, revealing the anomaly of slip-controlled short-crack growth. Furthermore, crystal-plasticity finite-element (CPFE) simulations were carried out to model the stress-strain loops and stress evolution under LCF. The CPFE model was able to predict the slip localisation as well as the direction of slip-trace development, which were correlated well with the behaviours of crack initiation and propagation observed from in-situ SEM.