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M. Springer, A. Turon, H. E. Pettermann:
"A Cyclic Cohesive Zone Model Accounting for Changes in the Fatigue Crack Growth Rate Caused by Variable Amplitude Loading and Pre-damaged Interfaces";
Vortrag: 19th International ASTM/ESIS Symposium on Fatigue and Fracture Mechanics (42nd National Symposium on Fatigue and Fracture Mechanics), Denver, Colorado, USA; 15.05.2019 - 17.05.2019; in: "Proceedings of the 19th International ASTM/ESIS Symposium on Fatigue and Fracture Mechanics (42nd National Symposium on Fatigue and Fracture Mechanics)", (2019), S. 1 - 6.

Laminated composites under cyclic loading conditions may be subjected to fatigue driven delamination which compromises the structural integrity and decreases the load carrying capability of the material compound. Cyclic Cohesive Zone Models (CCZM), based on traction-separation laws, are commonly used within the framework of the Finite Element Method to assess this failure mechanism.
CCZMs can be categorized into hysteresis loop damage models and envelop load damage models. Models from the first category are often derived in a thermodynamically consistent way and utilize a cycle-by-cycle simulation strategy. The calibration of these models is typically based on fitting parameters, which can be a challenging and computational extensive task. In contrast, models of the second category are commonly based on phenomenological approaches where experimentally determined parameters can be directly used for the model calibration. However, the utilization of an envelope load curve to model the cyclic load spectrum is usually limited to constant amplitude loading conditions.
In the present work, a CCZM is presented which is based on physically interpretable interface parameters and uses a cycle-by-cycle simulation strategy which allows for variable amplitude loading conditions. A non-local evaluation of structural parameters during the simulation is used in combination with a Paris´ law to accurately predict the rates of spatial advance of the fracture process zone and the delamination. Furthermore, mixed-mode loading conditions are accounted for and a cycle jump technique is introduced to reduce the computational time.
The CCZM is implemented into APDL v16.2 (ANSYS Inc., Canonsburg, PA, USA) and is demonstrated by simulating End-Notch-Flexure tests under varying fatigue loading conditions. In addition, different types of specimen preparations are considered in the simulations and the effects of pre-damaged and undamaged interfaces, caused by the manufacturing process of the pre-crack, on the initial fatigue crack growth rate are shown.