An investigation into the uncertainties in the crack resistance curves of nodular cast iron

The present study is concerned with a multiscale analysis of the scatter and uncertainty in the ductile crack initiation of pre-cracked nodular cast iron. In a numerical analysis on the microscale using a detailed model of the polydisperse microstructure, a relation between microstructural geometric and topological uncertainty of the microstructure and the material uncertainty on the material level is established. The microstructural model is generated by a numerical algorithm utilizing random number generation based on experimental observations of the microstructural disorder of a reference material. Using finite element models of the microstructure together with material data determined from tensile experiments on the reference material, the initiation and initial propagation of the crack through the random microstructure of the 𝛼-iron matrix with its spherical graphite inclusions is analysed. The results are evaluated statistically for the macroscopic crack resistance curve. The approach is validated against an experimental database of fracture experiments on SE(B) specimens of the reference material. The numerical prediction is found in good agreement with the experimental observation concerning both the mean and scatter band of the results. Subsequently, the approach is employed in parametric studies concerning the basic features of the microstructure, such as inclusion size and density. The findings of the present study may be employed as the basis towards a reliable, high precision probabilistic fracture and toughness assessment of nodular cast iron and structural components made thereof.