Modelling approach

To investigate the influence of both surface finish and sub-surface porosity a series of 2D models were created. These were based on the concept of a simple test specimen, either containing sub-surface porosity, or having a rough surface, or both. Figure 2 indicates a typical geometry for a test specimen, an enlarged image of the gauge section (the region in which a specimen would be expected to fail under test), the modelled region, and a further enlarged image showing the detailed area of model as will correspond to the geometry construction diagrams in later figures.
In all figures, the rough surface/porous sub-surface is shown vertically on the right, and is intended to be indicative of roughness at the edge of the specimen gauge section. The model assumes 2D plane stress and mirror symmetry. Additionally, on the basis of Saint-Venant principle [71], detailed modelling of the geometry and loading is unnecessary at a sufficient distance from the region of the model of interest. On this basis, the FEA model could be reduced to the form indicated in Figure 2(c).