On the use of the Theory of Critical Distances to predict static failures in ductile metallic materials containing different geometrical features

This paper summarises an attempt to use the Theory of Critical Distances (TCD) to predict static failures in notched specimens made of a commercial cold-rolled low-carbon steel. Over the last 80 years, such a theory has been successfully employed to predict both static and fatigue failures in notched components, exploring its accuracy and its reliability in different ambits of the structural integrity field. In most of these previous applications, the stress fields in the relevant region close to the notch could be assumed to be linear-elastic without much loss of accuracy. The aim of the present paper is to investigate whether this linear-elastic TCD can also be successful in predicting static failures in notched components when the final breakage is preceded by large-scale plastic deformations. Notched specimens containing different geometrical features were tested under both tensile loading and three-point bending and failures were predicted by post-processing the results of linear-elastic Finite Element Analysis (FEA). The predictions thus obtained were found to be highly accurate, falling within an error interval of about 15%, independent of specimen thickness, notch geometry and applied load type. A similar degree of accuracy was obtained when elasto-plastic stress analysis was used. This result is very interesting, because it supports the idea that the linear-elastic TCD can successfully be used in situations of practical interest, reducing the time and costs of the design process