Alireza Golahmar is an Industrial PhD student at Technical University of Denmark, DTU, Department of Civil and Mechanical Engineering. His PhD project aims at developing new computational tools that can predict the service life of offshore wind turbine support structures. The project is a collaboration between DTU and Imperial College London, and it is sponsored by Vattenfall Offshore Wind and Innovation Fund Denmark.
Abstract
Phase field fracture modelling has emerged as a promising variational approach to capture complex cracking conditions, such as nucleation from multiple sites or the coalescence of numerous defects, in arbitrary geometries and dimensions [1]. The method builds upon Griffith’s thermodynamics framework and has recently been extended to fatigue damage [2], showing that features such as stress-fatigue life (S-N) curves or fatigue crack growth rate curves can be predicted without any prior assumptions. However, most structural failures often occur due to the synergistic effects of fatigue damage and environment. One of the most important environmental effects is what is generally referred to as hydrogen embrittlement [3]. Hydrogen is ubiquitous and it significantly reduces the ductility, strength, toughness, and fatigue crack growth resistance of metallic materials.
In this work, we present the first multi-physics phase field-based model for hydrogen-assisted fatigue. The modelling framework builds upon the success of a recent phase field fracture formulation for hydrogen assisted cracking under static loads [4]. The model is first used to gain fundamental insight and provide a mechanistic rationale for the trends observed in the fatigue experiments. The comparison with experiments reveals that the model can accurately predict fatigue lives and endurance limits, as well as naturally capture the influence of the stress concentration factor and the load ratio. In addition, the model is employed to capture hydrogenassisted fatigue damage in case studies of particular technological interest. We show that the modelling framework presented can be used to predict the impact of the environment on fatigue crack growth rate curves and S-N curves, enabling optimising design and maintenance through Virtual Testing, as well as planning efficient and targeted experimental campaigns.
References
[1] B. Bourdin, G. A. Francfort, and J.-J. Marigo, “The Variational Approach to Fracture,” J. Elast., vol. 91, no. 1–3, pp. 5–148, Apr. 2008.
[2] P. Carrara, M. Ambati, R. Alessi, and L. De Lorenzis, “A framework to model the fatigue behavior of brittle materials based on a variational phase-field approach,” Comput. Methods Appl. Mech. Eng., vol. 361, p. 112731, 2020.
[3] R. P. Gangloff, “Hydrogen-assisted Cracking,” in Comprehensive Structural Integrity Vol. 6, I. Milne, R. O. Ritchie, and B. Karihaloo, Eds. New York, NY: Elsevier Science, 2003, pp. 31–101.
[4] E. Martínez-Pañeda, A. Golahmar, and C. F. Niordson, “A phase field formulation for hydrogen assisted cracking,” Comput. Methods Appl. Mech. Eng., 2018.
Session
| Room | Date | Hour | Subject |
|---|---|---|---|
| Room 8 | Wednesday 29th November | 12:15-12:45 | Alireza Golahmar S10-1 Fatigue under severe environmental conditions 26 - Phase field modelling of fatigue in hydrogen environments |
