From S-N to the Paris law with a new mixed-mode cohesive fatigue model for delamination in composites

•New cohesive fatigue model for delamination initiation and propagation.•Model relies on the relationship between fatigue life and crack propagation rates.•Model parameters are obtained from simplified stress-life curves.•Goodman diagram and Fleck assumption are used in lieu of material data.•Model...

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Bibliographic Details
Published in:Theoretical and applied fracture mechanics 2020-04, Vol.106, p.102499, Article 102499
Main Author: Dávila, C.G.
Format: Article
Language:English
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Summary:•New cohesive fatigue model for delamination initiation and propagation.•Model relies on the relationship between fatigue life and crack propagation rates.•Model parameters are obtained from simplified stress-life curves.•Goodman diagram and Fleck assumption are used in lieu of material data.•Model accounts for R-curve, the stress ratio, mode mixity, and load-type control. The relationship between fatigue life and fatigue crack propagation rate in composites is explored with a new cohesive damage model. The parameters of the model are obtained from idealizations of S-N diagrams used in engineering design. The model assumes that the quasi-static cohesive law that describes tearing is the envelope of the fatigue damage. Fatigue damage within the cohesive envelope accumulates at a rate that satisfies the S-N diagram and Miner’s cumulative fatigue damage rule. The fatigue model was implemented as a UMAT subroutine for Abaqus cohesive elements by adding fatigue damage accumulation within a cohesive model based on the Turon mixed-mode model. The analyses were conducted using a simplified cyclic loading procedure in which the maximum load is applied quasi-statically and load cycling is represented within the constitutive model. The predicted propagation rates of delamination in mode I and mixed mode were compared to experimental results for IM7/8552 graphite/epoxy tape. Several aspects of the results were investigated, including the effects of R-curves, the stress ratio R, and the difference between displacement and force control.
ISSN:0167-8442
1872-7638
DOI:10.1016/j.tafmec.2020.102499