Probabilistic damage tolerant assessment of cracked structures under size effect

Abstract

Aero-engine turbine disks and other hot-end components, as the core parts of major equipment, are strategic focal points for the sustainable development of future industries. Their structural integrity and safety reliability are crucial foundations for guaranteeing the long-term service of hot-end structures. In this study, focusing on cracked structures of the FGH96 turbine disk, the simulated specimens and round-bar specimens of different sizes with an artificial defect were designed. Combining in-situ and direct current potential drop (DCPD) technologies, the study on fatigue crack initiation and propagation tests at 600˚C was conducted on the materials and structures of turbine disks, specifically including crack growth behavior, failure mechanisms, and probabilistic life models. First, the initial fatigue crack was pre-produced and the crack growth rate was monitored using the DCPD technique, while the critical crack size at fracture was measured using optical microscopy. Subsequently, the uncertainty quantification study was performed on the initial and critical crack sizes. Considering the evolution of crack size, a novel failure assessment diagram was proposed to evaluate the critical crack size, then, developing a damage tolerance assessment diagram. Fracture morphology and failure assessment diagram results indicated that the crack tip was in a plastic state, leading to the inapplicability of traditional elastic crack growth models. Therefore, a residual life prediction framework accounting for crack tip plasticity was proposed. Additionally, it was found that the stress intensity factor of the specimen at fracture was related to geometric dimensions. Finally, integrating initial crack size, critical crack size, and geometric dimensions, a probabilistic life prediction model based on the weakest link theory was proposed. This work introduces a novel approach to probabilistic damage tolerance assessment for components with defects, providing significant engineering insights.

Shun-Peng Zhu

Professor

Ph.D, Professor, Doctoral Supervisor, PIF Fellow of Politecnico di Milano, Italy since April 2016 and research associate at University of Maryland, United States from 2010 to 2011. His research which has been published in scholarly journals and edited volumes, over 100 peer-reviewed book chapters, journals and proceedings papers, explores the aspects: Fatigue assessment; Probabilistic Physics of Failure modeling; reliability and risk analysis; Multi-physics damage modeling and life prediction under uncertainty; Multi-scale uncertainty quantification and propagation; Bayesian inference and Fuzzy sets; Probability-based life prediction/design for engineering components/materials. Dr. Zhu also studies advanced numerical methods for uncertainty quantification in engineering. He received the Award of Merit of European Structural Integrity Society (ESIS)-TC12 in 2019, Most Cited Chinese Researchers (Elsevier) in the field of Safety, Risk, Reliability and Quality since 2018, 2nd prize of the National Defense Science and Technology Progress Award of Ministry of Industry and Information Technology of China in 2014, Polimi International Fellowship in 2015, Hiwin Doctoral Dissertation Award in 2012, Best Paper Awards of several international conferences and Elsevier Outstanding Reviewer Status. He serves as guest editor, editorial board member of several international journals and Springer book series, Organizing Committee Co-Chair of the International Conference on Quality, Reliability, Risk, Maintenance, and Safety Engineering (QR2MSE 2013), TPC Member of ICMR 2015, ICMFM XIX 2018-2020 and IRAS 2019.