Non‐local line method for notched elements with use of effective length calculated in an elasto‐plastic condition

Abstract

The paper presents a non‐local line method used to the fatigue life calculation of notched elements. The presented method is based on the concept of an effective length which determines the size of the equivalent fatigue zone. Effective values of normal stress calculated in the critical plane with a weight function were applied when determining the equivalent fatigue zone. Simulation studies were performed for two types of steel and two types of loading. Five different series of tests and simulations were used. Experimental studies were carried out for 40 HM‐T and EA4T steels. These materials are used in railway industry, including the manufacturing of coupling bars. The notched test specimens contained notches with a tip radius of 0.2, 0.5, 0.8 and 1 mm. Stress calculations were performed using the finite element method by adopting cyclic material properties described by the model of a multi‐linear hardening. Non‐local calculations were performed in a defined critical plane for normal stress distribution and a weight function. As a result, the function of variation of the effective length depending on the loading level and geometry of the notch has been determined.

A numerical investigation of the high cycle fatigue sensitivity to microstructure and defect

“…The critical distance is often determined by the effective crack length l 0 introduced by El Haddad or an empirically derived value. Successful applications were reported [37,38] on the homogeneous models. It is expected that the critical zone has some connections with the microstructure.…”

Evaluation of component‐similar rotor steel specimens with a local probabilistic approach for LCF

“…However, there are publications showing that notches are improving the LCF fatigue lives of specimens, e.g., for conventionally cast or even directionally solidified Ni-base superalloys 13,41,42 and steels. 13,31,[43][44][45] Interestingly, Haibach and Matschke et al 31 observed improvements in LCF lives, but HCF strength reductions at notched steel specimens. Furthermore, Eriksson et al 41,46 noted that the LCF notch support at high loads changed to notch weakening at lower load amplitudes for the Nibase alloy IN-718.…”

“…Sometimes, this was not even indicated, or no comparison with a smooth specimen Wöhler curve was provided, which makes it hard to judge whether a notch improves or decreases the fatigue life. However, there are publications showing that notches are improving the LCF fatigue lives of specimens, e.g., for conventionally cast or even directionally solidified Ni‐base superalloys and steels . Interestingly, Haibach and Matschke et al observed improvements in LCF lives, but HCF strength reductions at notched steel specimens.…”