Effect of defects on the fatigue crack initiation strength of ferrite-pearlitic nodular cast iron test specimens and componentsTuesday (26.05.2020) 15:10 - 15:30
The study investigates the defect influenced fatigue on the example of complex industrial components. The phenomenon is analysed through fatigue testing and fracture surface analysis complemented with simulations based on the Finite Element (FE) Method and the evaluation of the local cyclic stress state with the Defect Stress Gradient Approach [1,2].
With the comparison of computation with experimental results for artificial and natural defects at specimen and component scales, conclusions are drawn with scientific and practical consequences.
The Defect Stress Gradient approach is applied to evaluate the local stress state computed by elasto-plastic and linear elastic FE-calculations or estimated by the simplified technique proposed in . The calculation based on the elastoplastic stress-state with the simulation of the load cycles and consideration of the cyclic nonlinear kinematic hardening behaviour leads to a precise assessment of the fatigue strength of test specimens and components with artificial defects having various shapes.
Utilizing a simplified estimation for the stress concentration factors leads to a directly expressable allowable defect size, which can be plotted as an FE-result field and used effectively for the quality control process of safety critical castings.
 M. Vincent, C. Nadot-Martin, Y. Nadot, and A. Dragon, “Fatigue from defect under multiaxial loading: Defect Stress Gradient (DSG) approach using ellipsoidal Equivalent Inclusion Method,” Int. J. Fatigue, vol. 59, pp. 176–187, 2014.
 M. Groza, Y. Nadot, and K. Varadi, “Defect size map for nodular cast iron components with ellipsoidal surface defects based on the defect stress gradient approach,” Int. J. Fatigue, vol. 112, no. February, pp. 206–215, 2018.