Papers by Author: Paolo Livieri

Abstract: In the field of cast metals, fatigue strength assessment necessarily deals with the strength reduction caused by randomly distributed small-sized defects. When components are taken into account, stress raisers due to component geometry are possible crack initiation sites as well as defects. For the investigation of the overall performance, an appropriate model considering notch sensitivity of parent material and defect behavior shall be used. Unfortunately, several mechanical models of material sensitivity to notches and defects require the knowledge of the un-defected material strength, which is not obtainable in this case. In this contribution, experimental fatigue tests have been carried out on plane and notched specimens, considering small size notches as well. An appropriate analysis of the generated results allowed the evaluation of the material behavior and its notch sensitivity according to critical distances theories. The obtained results have been confirmed also direct inspection of broken samples.

Abstract: This paper attempts to critically review some numerical methods for fatigue strength assessment of welded joints by means of stress analysis tools (usually FE models). In particular, it focuses on the significance of geometrical model, by distinguishing beams from shells and solids, more than distinguishing among nominal, structural and notch stress type. In addition, basing on continuous mechanics theories, a distinction between “local” and “non-local” stress approaches is proposed. Finally the advantages of notch stress approaches are showed by commenting also problems connected to multiaxiality and three-dimensionality of stress states.

Abstract: This paper proposes a method for evaluation of the Stress Intensity Factors (SIFs) of embedded cracks lying along the bisector of the welded toe angle. The SIFs are calculated on the basis of the JV parameter (extension of the J-integral to a sharp V-notch) for a path radius equal to the crack extension without modelling the crack. The numerical calculations in the paper show the stability of the proposed method also with course meshes.