Abstract
This paper provides an analytical formula for the theoretical stress concentration factor in a common type of excavation repair for large forgings and castings. Mechanical components obtained with these processes are often subjected to superficial defects. As the rejection of such pieces is out of question, given the relevant size and costs associated with them, usual industrial practice consists in the removal of the defect and a portion of the surrounding material through milling processes. The authors have selected a reference geometry of the excavation to be left on the mechanical pieces, which can be easily controllable in practice by three operating parameters. Then, the domain of existence of such a repair was investigated on a sequence of discrete points, by means of FEA, obtaining for each, the values of the stress concentration factor Kt. Finally, through polynomial regression, the Kt functions have been accurately approximated by a sixth degree polynomial formulation, which, given a triplet of dimensional geometric parameters, is able to compute the stress concentration factor Kt, with an error that never exceeds 8%.
Highlights
Large mechanical components obtained by forging or casting can often be affected by different types of superficial defects
At the end of this research, we can conclude that the analytical expressions provide a suitable of the stress concentration factor forthat this geometry under the three Atapproximation the end of this research, we can conclude the analytical expressions p most common load case scenarios
We can assert that a gap in the technical a suitable approximation of the stress concentration factor for this geometry und literature of the sector has been filled, as this type of excavation, obtained by means of a three most common load case scenarios
Summary
Large mechanical components obtained by forging or casting can often be affected by different types of superficial defects. The most common are bubbles and cracks [1], which, depending on their shape and size, may lead to relevant stress concentration, compromising the long-term life of the part To overcome this issue, one of the most common industrial practices consists of the simple technique of removing the defects and a portion of the surrounding material, through manual milling operations, made with a conventional disc cutter or with a ball nose cutter. The time-consuming welding operations may have a negative impact on final delivery times In all such cases, the remedy of sole milling does not bring the defective part to its ideal shape, since a small portion of the material is still removed from its surface, but leaves an imperfection of a more controlled shape. A practical solution of engineering interest is the identification of a theoretical stress concentration factor Kt , defined as the following ratio: conditions of the Creative Commons
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