13th International Conference on Fracture June 16–21, 2013, Beijing, China 9 Figure 9. The traction vs. damage evolution curves for ΔKavg=83.1MPa m1/2 and ΔKavg=104.8MPa m1/2. Figure 10. Comparison between the numerical simulation and the experimental data. 5. Concluding remarks In the present paper a cohesive zone model in conjunction with monotonic damage and cyclic fatigue damage was investigated based on experimental tests, to create a unified fatigue crack growth model for both elastic and elastic-plastic fatigue crack growth. In simulations the initial cohesive strength and the corresponding displacement jump are defined based on the true stress-strain relationship so that the cohesive zone does not affect the compliance of the specimen before damage initiation. The penetration of the crack surface under compression is prevented using the contact formulation. The first results confirm that the present cohesive zone model coupled with monotonic and cyclic damage evolution is suitable to describe fracture and fatigue crack growth of stainless steel 304 with severe plastic deformations. In addition, the present computations reveal that the damage evolution in the low stress level and the material compression process could not be properly described need further improvement. More extensive studies on the cohesive model and the damage evolution equation may provide further understanding of ductile fatigue damage under more complex loading conditions.
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