Influence of hard and soft inclusions inside a ferritic matrix

In the case of an interior fracture mode in fatigue, material impurities play a fundamental role in the generation and the propagation of cracks. In general, the presence of hard or soft inclusions, voids, materials imperfections, etc., alter the local stress state in the matrix generating the accumulation of plastic deformations which lead to the crack formation. In terms of inclusions, high strength steels are often characterized by the presence of aluminum oxides Al2O3 or Manganese sulfide MnS. The experimental works reported by several authors pointed out that the critical location for the crack nucleation is, often, at the edge of the inclusion and it subsequently propagates on a plane orthogonal to the loading direction. In a previous work, the authors investigated the stress distribution around a spherical inclusion inside a ferritic matrix, pointing out the role of the material anisotropy and the different crystallographic orientation of the matrix. However, the investigations dealt with simple loading conditions and linear elasticity. The present paper aims to extend the field of investigations to the elasto-plastic domain, focusing the attention on the role of the crystallographic orientation and comparing the results with the previous study.