A mechanistic approach to the Kitagawa–Takahashi diagram using a multiaxial probabilistic framework

Despite the disruptive benefits of Additive Manufacturing (AM), the application of this technology for safety-critical structural parts in aerospace is still far from being achieved and standardised. The necessity to comply with very strict reliability requirements is hindering this final step because of the large scatter and low reproducibility always associated with AM, especially in terms of fatigue strength. In this regard, manufacturing defects are the most important and complex issue, but several other sources of variability have an effect as well. The AM community and the main aerospace industries involved are starting to agree that damage-tolerant approaches are necessary and that probabilistic methods are best-suited to obtain reliable but not over-constrained assessments. To address this issue, the authors have developed Pro-FACE, a fully-probabilistic software that aims to robustly assess the fatigue strength and critical locations of complex components in the presence of defects. This paper presents the underlying concept, its implementation and early validation, and a simple application to a space component. The analytical formulation makes this tool ideal to evaluate very low failure probabilities with limited time and effort, which can provide valuable information to significantly improve part design and qualification.

Section: Model For Fatigue Strengthmentioning

confidence: 99%

A new FE post-processor for probabilistic fatigue assessment in the presence of defects and its application to AM parts

Romano

Miccoli

Beretta

2019

“…This type of diagrams could be very useful for the design of heat treated components with variable hardness. It should be noted that in this work only tensile and shear loads have been investigated, however it is possible to generalise the approach for combined tension-torsion loads using a expression for the stress intensity factor that is suitable for more complex loads [25].…”

Section: Application Using the Papadopoulos And Lefm Criteria Combinamentioning

confidence: 99%

“…Pessard et al [25,26] in order to model the effect of the heat treatment and the presence of defects on the fatigue behaviour of the 22MnB5 steel. The principal hypothesis of this criterion is that two different fatigue damage mechanisms coexist (i.e.…”

Section: A Probabilistic Multiaxial Fatigue Criterion and A Kitagawa mentioning

confidence: 99%

The effect of quenching and defects size on the HCF behaviour of Boron steel

Pessard

Abrivard

Morel

et al. 2014

Self Cite

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. AbstractThis work investigates the effect of natural and artificial surface defects and quenching on the fatigue strength of a Boron Steel (22MnB5). A vast experimental campaign has been undertaken to study the high cycle fatigue behaviour and more specifically the fatigue damage mechanisms observed in quenched and untreated materials, under different loading conditions and with differents artificial defects sizes (from 25µm to 370 µm radius). In order to test the sheet metal in shear an original test apparatus is used. The critical defect size is determined to be 100±50µm. This critical size does not appear to depend on the loading type or the microstructure of the material (i.e. ferritic-perlitic or martensitic). However, for large defects, the quenched material is more sensitive to the defect size than the untreated material. For a defect size range of 100µm to 300µm the slope of the Kitagawa-Takahashi diagram is approximately -1/3 and -1/6 for the quenched and untreated materials respectively. A probabilistic approach that leads naturally to a probabilistic Kitagawa type diagram is developed. This methodology can be used to explain the relationship between the influence of the heat treatment and the defect size on the fatigue behaviour of this steel.

“…Naderi et al [26] investigated the effects of finite element types and sizes, initial flaws and material property variations on the fatigue life scatter of metals, and predicted the plastically induced fatigue damage for four types of metals. Pessard et al [51] developed a probabilistic multiaxial modelling framework to describe the Kitagawa-Takahashi diagram by combining two fatigue damage mechanisms, which is based on the weakest link hypothesis. Recent research in [38] demonstrated that current safe-life design methods [12]- [14], [52], [53] introduced a series of partial safety factors to empirically or semi-empirically consider the variability in applied stress and material behavior.…”

Section: Introductionmentioning

confidence: 99%

Probabilistic framework for multiaxial LCF assessment under material variability

Zhu

Foletti

Beretta

2017

149

Abstract:The influence of material variability upon the multiaxial LCF assessment of engineering components is missing for a comprehensive description. In this paper, a probabilistic framework is established for multiaxial LCF assessment of notched components by using the Chaboche plasticity model and Fatemi-Socie criterion. Simulations from experimental results of two steels reveal that the scatter in fatigue lives can be well described by quantifying the variability of four material parameters . A procedure for choosing the safety factor for fatigue design has been derived by using first order approximation.