On the multiaxial fatigue assessment of complex three-dimensional stress concentrators

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. b s t r a c tThis paper assesses and quantifies the detrimental effects of complex tri-dimensional notches subjected to uniaxial and multiaxial fatigue loading. A number of experimental results taken from the technical literature and generated by testing specimens containing complex geometrical features were reanalysed using a critical distance/plane method. The investigated notched samples were tested under uniaxial and multiaxial constant amplitude load histories, considering also the effects of non-zero mean stresses as well as non-proportional loading. The common feature of the considered notched geometries was that the position of the critical location changed as the degree of multiaxiality of the applied loading varied. The relevant linear-elastic stress fields in the vicinity of the crack initiation points were calculated by the Finite Element method and subsequently post-processed using the Modified Wöhler Curve Method in conjunction with the Theory of Critical Distances (the latter theory being applied in the form of the Point Method). This validation exercise confirms the accuracy and reliability of our multiaxial fatigue life assessment technique, which can be efficiently used in situations of practical interest by directly postprocessing the relevant linear-elastic stress fields calculated with commercial Finite Element software packages.

Assessing the integrity of steel structural components with stress raisers using the Theory of Critical Distances

“…Generally, for notched specimens with standard stress raisers, since the crack initiation location is in known a priori unambiguously, the focus path can be assumed to emanate from the crack initiation point and is parallel to the direction experiencing the maximum stress gradient. However, it was reported in a recent investigation [18] that, for notched components characterized by complex 3D geometries, the…”

“…On the contrary, real engineering components often contain complex geometrical features, where the location of the crack initiation is not always obvious, especially in the presence of complex multiaxial loading. It was demonstrated in a recent research conducted by Louks et al [18] that the TCD used in conjunction with Modified Wöhler Curve Method (MWCM) is capable of giving a high-level accuracy in estimating the fatigue strength of a number of components containing complex/3D geometrical notches subjected to a complex multiaxial fatigue load history, where, however, the common feature of these investigated specimens was that the crack was observed to initiate at the stress raiser apices.…”

“…Generally, for notched specimens with standard stress raisers, since the crack initiation location is in known a priori unambiguously, the focus path can be assumed to emanate from the crack initiation point and is parallel to the direction experiencing the maximum stress gradient. However, it was reported in a recent investigation [18] that, for notched components characterized by complex 3D geometries, theposition of the potential crack initiation location would change depending on the degree of multiaxiality and non-proportionality of the loading path being applied. In this scenario, when using the TCD, static strength has to be estimated by choosing several potential focus paths to find the one which experiences the maximum extent of damage.…”

A generalised approach to rapid finite element design of notched materials against static loading using the Theory of Critical Distances

“…Accordingly, in the presence of threedimensional stress concentrators the simplified formulation of the TCD proposed in the present paper has to be applied by considering the maximum sub-surface stress determined either according to the maximum principal stress criterion (for brittle/quasi-brittle materials) or in terms of von Mises' equivalent stress (for ductile materials). In this context, it is worth observing that, recently, this numerical stress analysis technique applied along with the rigorous formulation of the PM was seen to be successful in estimating both static [46] and high-cycle multiaxial fatigue strength [47] of three-dimensional stress raisers.…”

Multiaxial fatigue assessment of friction stir welded tubular joints of Al 6082-T6

“…By performing a systematic validation exercise based on a large amount of experimental data, it has been demonstrated that the MWCM applied along with the PM can successfully estimate the fatigue strength of notched components subjected to multiaxial fatigue loading, under both constant [68][69][70][71][72] and variable amplitude [73][74][75] multiaxial load histories. The MWCM used in conjunction with the PM has also been observed to be capable of accurately estimating the fatigue lifetime of conventional welded aluminium joints [56,59,64].…”