A probabilistic approach to predict the very high‐cycle fatigue behaviour of spheroidal graphite cast iron structures

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. shown that two different coexisting fatigue damage mechanisms occur in this materials, depending on the presence of different microstructural heterogeneities (i.e. micro-shrinkage pores, Si particles, Ferich intermetallic phases, DAS of the Al-matrix, etc.). In order to take into account both of these damage mechanisms, a probabilistic approach using the weakest link concept is introduced to model the competition between the two mechanisms. This approach leads naturally to a probabilistic Kitagawa type diagram, which explains the relationship between the fatigue behaviour of the material and the different casting processes or post-treatments (e.g. gravity casting and HIP).It is shown that the sensitivity to the different loading modes (i.e. uniaxial with and without mean stress, torsion and equibiaxial tension) depends on the microstructural heterogeneities responsible for crack initiation. For a porosity-free alloy, the predictions are very good for combined tension-torsion loading modes. When pores are present and control the fatigue strength, the predictions are very satisfactory for the uniaxial loads with different R-ratios and slightly conservative for multiaxial loads (i.e. torsion and equibiaxial tension). Never-the-less, they are much better than the predictions of theHighlights ► High cycle fatigue modelling of AlSi7Cu05Mg03 for complex loading conditions. ► Modelling of two coexisting fatigue damage mechanisms. ► A probabilistic approach is proposed to model the competition between these mechanisms. ► The approach leads naturally to a probabilistic Kitagawa type diagram.

Section: Crack Initiation Modellingmentioning

confidence: 99%

A probabilistic model for the high cycle fatigue behaviour of cast aluminium alloys subject to complex loads

Koutiri

Bellett

Morel

et al. 2013

“…Another way to model the fatigue limit scatter is to use the WL-integral, [7,8]. The integration can be performed over the specimen surface area [1,4,9,11,12] or as a volumetric entity [1,3,4,9,13,14].…”

Section: Introductionmentioning

confidence: 99%

An investigation of the location of fatigue initiation – Deterministic and probabilistic aspects

Karlén

Olsson

2014

Fatigue limit tests where there are two competing fatigue failure locations, two notches of different size, are performed in this paper. The normal distribution is used for describing the experimental outcome, where the largest occurring stress value or the gradient adjusted stress is used as a stress measure. Another model for describing the experimental outcome is the Weakest Link (WL)-integral where the integration is performed over the specimen surface area or the specimen volume. The longitudinal positions of the estimated fatigue failure sites are measured and investigated as well. Neither the normal distribution (point stress and gradient adjusted point stress), nor the WL-integral can explain the experimental outcome from the competing notch tests. They all predict the same trend, but not the same trend as in the experiments. When looking at the estimated longitudinal location of fatigue failure it can be seen that it differs considerably from experiment to experiment. If the stress is evaluated at the estimated fatigue failure location, it is seen that the local stress is much lower than the maximal stress. The load cases where there should be an equal amount of failures in both notches according to the different models do not agree with the experimental findings. It is concluded that stress based continuum models can not describe the experimental outcome when there are competing fatigue failure sites (notches) present.

“…According to Hild [4] and Chantier [5], the fatigue strength of cast parts is generally reduced by the presence of initial casting flaws that are more or less randomly distributed within the material. Under cyclic loading conditions, microcracks propagate from these initial flaws.…”

Section: Introductionmentioning

confidence: 99%

“…A usual statistical approach (i.e. the weakest link concept, already used by Bomas [3], Hild [4], Chantier [5] and Flacelière [6]) is hereafter combined with the deterministic volumetric energy-based criterion proposed in Refs. [1,2].…”

Section: Introductionmentioning

confidence: 99%

Estimation of the fatigue strength distribution in high-cycle multiaxial fatigue taking into account the stress–strain gradient effect

Delahay

Palin‐Luc

2006

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. AbstractBased on the weakest link concept, a probabilistic approach in high-cycle multiaxial fatigue is developed to predict, for a given number of cycles, the probability distribution of the fatigue strength for metallic structural components. EMAS: Stockholm; 2002, p. 283-90]. Whatever the stress state and the loading type are, the corresponding fatigue strength probability distribution can be deduced from three usual experimental fatigue limits. The scale effect is also predicted. Experimental probability distributions and theoretical predictions of the fatigue strength of smooth specimens are in good agreement for the five materials investigated: the 30NiCrMo16 and 35CrMo4 quenched and tempered steels, the C20 annealed steel, the EN-GJS800-2 nodular cast iron and the Ti-6Al-4V titanium alloy.