Papers by Keyword: Theory of Critical Distances

Abstract: This paper explores the initial potential of theory of critical distance (TCD) which offers essential fatigue failure prediction in engineering components. The intention is to find the most appropriate TCD approach for a case of multiple stress concentration features in future research. The TCD is based on critical distance from notch root and represents the extension of linear elastic fracture mechanics (LEFM) principles. The approach is allowing possibilities for fatigue limit prediction based on localized stress concentration, which are characterized by high stress gradients. Using the finite element analysis (FEA) results and some data from literature, TCD applications is illustrated by a case study on engineering components in different geometrical notch radius. Further applications of TCD to various kinds of engineering problems are discussed.

Abstract: The present paper is concerned with the use of the Theory of Critical Distances (TCD), applied in the form of the Point Method (PM), to estimate the range of the threshold value of the stress intensity factor, Kth, as well as the plane strain fracture toughness, KIc. In more detail, by reanalysing a large amount of experimental data taken from the literature, it is proved that Kth can successfully be evaluated through the plain fatigue limit and another fatigue limit generated by testing samples containing a known geometrical feature, whereas KIc is suggested here as being estimated by using experimental results generated by testing samples weakened by notches of different sharpness. The validation exercise summarised in the present paper fully confirms that the TCD is not only a reliable method suitable for performing the static and fatigue assessment of real components, but also an efficient experimental strategy capable of accurately estimating the classical Linear Elastic Fracture Mechanics (LEFM) material properties.

Abstract: This paper reports on the use of the Modified Wöhler Curve Method (MWCM) applied along with the Theory of Critical Distances (TCD) to estimate fatigue lifetime of steel welded joints subjected to both uniaxial and multiaxial cyclic loading. In a recent work [1] we have proved that the above engineering method is highly accurate when calibrated by using standard fatigue curves characterised by a probability of survival equal to 50%. In order to better check its accuracy and reliability, in the present study our approach is systematically applied to a large amount of experimental data by calibrating it using standard fatigue curves having a probability of survival equal to 97.7%. This exercise allowed us to prove that the in-field application of such an engineering procedure results in estimates which fully comply, from a statistical point of view, with Eurocode 3’s recommendations. This result strongly supports the idea that our approach can safely be employed to perform the fatigue assessment of real mechanical assemblies, with the advantage over other existing methods that fatigue lifetime under any kind of fatigue loading can be estimated by simply post-processing linear-elastic Finite Element Models.