Progress in fatigue life calculation by implementing life-dependent material parameters in multiaxial fatigue criteria

This paper presents the concept of applying life-dependent material parameters to several multiaxial fatigue criteria. This concept reflects the transformation of damage mechanisms in relation to the applied load level, and also in relation to the varying level of plasticity. The goal of this study is to demonstrate the benefit of introducing life-dependent material parameters into stress-based multiaxial fatigue criteria for predicting the fatigue life of materials. New experimental results of fatigue tests on 2124-T851 aluminium alloy confirm the advantage of the life-dependent concept in life assessment over the concept with fixed weight parameters

THERMO-MECHANICAL FATIGUE ANALYSIS OF A STEAM TURBINE SHAFT

Increasing demands on the flexibility of steam turbines due to the use of renewable energy sources substantially alters the fatigue strength requirements of components of these devices. Rapid start-ups as well as the increased number of the load cycles applied to the turbines must be handled by design methodologies. The goal of the work presented in this paper was to provide a computational framework applicable to the thermo-mechanical fatigue (TMF) prediction of steam turbine shafts. The so-called Damage Operator Approach by Nagode et al. has been implemented to the software codes and applied to fatigue analysis of the thermo-mechanical material response computed numerically by the finite element analysis. Experimental program conducted in order to identify the material thermo-mechanical behavior and to verify numerical simulations is introduced in the paper. Some results of TMF prediction of a sample steam turbine shaft are shown

The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data

The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.Peer reviewe

Coverage of multiaxial fatigue criteria in fatigue limit region

There is a power of methods aimed at calculation of equivalent fatigue limit for arbitrary multiaxial loading. Although there are so many ways of computation, their thorough mutual comparison in a larger scale is missing. The database project presented in this paper comprise of several databases crowned with the FatLim database, which comprise of a huge number of experimental results and of 18 computational method working in the category mentioned before. The great block of data was acquired using in-house fatigue software PragTic, which is offered as a freeware application. The FatLim database follows its philosophy of a simple and non-paid accessibility. Its query tool written in MySQL and PhP allows to users to evaluate a practical usability of tested methods on load cases, which the users define. All the issues covered within this paper are available on the website www.pragtic.com, structure of which is described here

Multiaxial fatigue strength of common structural steel and the response of some estimation methods

This paper describes the multiaxial fatigue strengths obtained from a series of load-controlled fatigue experiments in the high-cycle fatigue domain. The experiments were carried out on unnotched specimens manufactured from common structural steel CSN 41 1523. Various load combinations were induced, including some rare combinations, e.g. a combination of pressurizing and plane bending. The stress states on the inner surface and also on the outer surface of hollow specimens are therefore evaluated in the subsequent fatigue strength analyses. The goal of the paper is to derive a new solution for estimating multiaxial fatigue strength that will better conform to the described experiments than the Manson-McKnight method, but which will keep its simplicity of calculation. Our final proposal - the MMP criterion - is compared with various versions of the Manson-McKnight method, and also with four multiaxial methods (Dang Van, Liu-Zenner, Crossland and Papuga PCr). The results for the MMP criterion are quite motivating, thanks to the simplicity of the computational algorithm and the quality of the prediction output, which is comparable with the output of the evaluated multiaxial methods. However, the set of experiments described here is not large enough either for more thorough statistical analyses of prediction quality, or for more enhanced improvement of the MMP criterion, which would include e.g. the effect of non-proportional loading.Web of Science104422

Validating the Methods to Process the Stress Path in Multiaxial High-Cycle Fatigue Criteria

The paper discusses one of the key features in the multiaxial fatigue strength evaluation—the procedure in which the stress path is analyzed to provide relevant measures of parameters required by multiaxial criteria. The selection of this procedure affects the complete equivalent stress derived for any multiaxial load combinations. Three major concepts—the minimum circumscribed circle, minimum circumscribed ellipse, and moment of inertia methods—are described. Analytical solutions of their evaluation for multiaxial stress state with components described by harmonic functions are provided. The concepts are validated on available experimental data when included into six different multiaxial fatigue strength criteria. The results show that the moment of inertia results in too conservative results. Differences between both methods of circumscribed entities are much smaller. There are indications however that the minimum circumscribed ellipse solution works better for critical plane criteria and for the criteria based on stress tensor transformation into the Ilyushin deviatoric space. On the other hand, the minimum circumscribed ellipse solution tends to shift integral criteria to the conservative side