Taking Full Advantage of Nominal Stresses to Design Notched Components against Variable Amplitude Multiaxial Fatigue

2011 ◽  
Vol 488-489 ◽  
pp. 747-750 ◽  
Author(s):  
Luca Susmel ◽  
David Taylor
Keyword(s):  
Experimental Investigation ◽  
Shear Stress ◽  
Fatigue Damage ◽  
Fatigue Loading ◽  
Multiaxial Fatigue ◽  
Critical Plane ◽  
Variable Amplitude ◽  
Maximum Variance ◽  
Curve Method ◽  
Notched Components

The present paper is concerned with the use of the Modified Wöhler Curve Method (MWCM), applied in terms of nominal stresses, to estimate lifetime of notched components subjected to variable amplitude multiaxial fatigue loading. The MWCM is applied by defining the critical plane through that direction experiencing the maximum variance of the resolved shear stress: since the shear stress resolved along the above direction is a monodimensional quantity, fatigue cycles are directly counted by the classical Rain-Flow method. The performed validation exercise, based on an extensive experimental investigation, seems to strongly support the idea that the MWCM applied along with the classical nominal stress based approach is capable of accurately estimating fatigue damage also in notched components subjected to variable amplitude multiaxial load histories.

scholarly journals A Multiaxial Notch Fatigue Methodology to Estimate In-Service Lifetime of Corroded Cast Iron Water Pipes

2013 ◽  
Vol 577-578 ◽  
pp. 125-128
Author(s):  
W. Brevis ◽  
Luca Susmel ◽  
J.B. Boxall
Keyword(s):  
Cast Iron ◽  
Fatigue Damage ◽  
Fatigue Loading ◽  
Multiaxial Fatigue ◽  
Variable Amplitude ◽  
Water Pipes ◽  
Service Lifetime ◽  
Curve Method ◽  
Over Time

The present paper summarises an attempt of using the so-called Modified Wöhler Curve Method (MWCM) to estimate fatigue damage in pitted cast iron water pipes subjected to in-service variable amplitude multiaxial fatigue loading. In this setting, pits are treated as hemispherical/hyperbolic notches whose depth increases over time due to conventional corrosion processes taking places in buried cast-iron pipes. The validity of such an approach is proven by showing, through a case study, that, under particular circumstances, the combined effect of corrosion and fatigue can remarkably shorten the in-service lifetime of cast-iron pipes as observed in the case study.

scholarly journals A universal, damage-criterion-independent cycle counting method for multiaxial and variable amplitude fatigue

2019 ◽  
Vol 300 ◽  
pp. 17004
Author(s):  
K.G. F. Janssens
Keyword(s):  
Fatigue Damage ◽  
Fatigue Loading ◽  
Multiaxial Fatigue ◽  
Mean Stress ◽  
Counting Method ◽  
Damage Criterion ◽  
Variable Amplitude ◽  
Counting Procedure ◽  
Counting Methods ◽  
Set Up

None of the procedures for cycle-counting defined in the ASTM document with designation E1049-85 (Reapproved 2017) [1] are generally applicable to non-proportional, multi-axial Fatigue. In addition, as the concepts of amplitude and mean stress are defined per cycle, their values are dependent (or co-define) the cycle counting method. This poses an obvious problem to the analysis of non-proportional, multi-axial fatigue damage, as lifetime is, not in all but in many cases, an amplitude and mean stress dependent material property. Most of the newer cycle counting methods developed till date are at least inspired by the works of Wang & Brown [2] and of Bannantine & Socie [3], both of which are themselves still frequently used. Being built inspired by counting methods developed for uniaxial cycling, all of the approaches to date known to this author are limited in a way that is very well phrased by Anes et al [4], whom, on page 79 of their article, write that (quote): The damage criterion is the base stone to set up random fatigue. The damage parameter must capture the fatigue damage behavior to allow set up a cycle counting method and an accumulation model. Challenging this statement, a new cycle counting procedure is presented that is completely independent of the damage criterion, and universally works from the simplest uniaxial experiment, to the most complex, variable amplitude and frequency, non-proportional multiaxial fatigue loading. The definition of this new cycle counting concept is surprisingly simple. Despite of its simplicity, the new cycle counting procedure has different advantages when compared to the procedures known to date. Its standalone definition, allows it to be combined with any damage criterion. It does not require periodicity of the loading cycle, and can therefore be straightforwardly used to analyze variable frequency and amplitude, multiaxial fatigue loading.

Life Prediction Techniques for Variable Amplitude Multiaxial Fatigue—Part 1: Theories

1996 ◽  
Vol 118 (3) ◽  
pp. 367-370 ◽  
Author(s):  
C. H. Wang ◽  
M. W. Brown
Keyword(s):  
Fatigue Damage ◽  
Life Prediction ◽  
Local Strain ◽  
Multiaxial Fatigue ◽  
Critical Plane ◽  
Random Loading ◽  
Variable Amplitude ◽  
Fatigue Damage Accumulation ◽  
Prediction Techniques ◽  
Searching Method

Fatigue life prediction under multiaxis random loading is an extremely complex and intractable topic; only a few methods have been proposed in the literature. In addition, experimental results under multiaxis random loading are also scarce. In part one of this two-part paper, a multiaxial non-proportional cycle counting method and fatigue damage calculation procedure are proposed, which is compared with one published damage-searching method. Both theories are based on critical plane concepts, one being an extension of the local strain approach for uniaxial variable amplitude loading and the other employing a new counting algorithm for multiaxis random loading. In principle, these two methods can be considered as bounding solutions for fatigue damage accumulation under multiaxis random loading.

Multiaxial fatigue assessment for outer cylinder of landing gear by critical plane method

2021 ◽  
pp. 095441002110260
Author(s):  
Yingyu Wang ◽  
Xiaofan Zhang ◽  
Xingliang Dong ◽  
Weixing Yao
Keyword(s):  
Outer Cylinder ◽  
Fatigue Loading ◽  
Landing Gear ◽  
Multiaxial Fatigue ◽  
Critical Plane ◽  
Proportional Loading ◽  
Fatigue Lifetime ◽  
Plane Method ◽  
Multiaxial Stress State ◽  
Maximum Variance

The in-service loadings on the landing gear are usually complex and from different directions, which lead to the fatigue critical locations in the landing gear structure mostly in multiaxial stress state. A methodology based on the critical plane method was proposed for estimating the fatigue lifetime of outer cylinder of the main landing gear undergoing variable amplitude (VA) multiaxial proportional loading. The orientation of the critical plane was determined by the so-called maximum variance method. The Bannantine–Socie’s cycle counting method and Miner’s linear rule were applied with Zhang–Yao’s criterion in this research. The calculated results on the fatigue lifetime of the outer cylinder were compared with the experimental data. The results indicate that the methodology proposed in this article is a sound method for fatigue life prediction of engineering components bearing complex VA multiaxial fatigue loading.

Estimating Lifetime of Notched Components Subjected to Variable Amplitude Fatigue Loading According to the Elastoplastic Theory of Critical Distances

2015 ◽  
Vol 137 (1) ◽  
Author(s):  
Luca Susmel ◽  
David Taylor
Keyword(s):  
Fatigue Damage ◽  
Critical Length ◽  
Fatigue Loading ◽  
Loading Path ◽  
Stress Strain ◽  
Variable Amplitude ◽  
Elastoplastic Stress ◽  
Starting Point ◽  
Geometrical Features ◽  
Notched Components

The present paper is concerned with the use of the elastoplastic theory of critical distances (TCD) to perform the fatigue assessment of notched components subjected to in-service variable amplitude (VA) fatigue loading. The elastoplastic TCD takes as its starting point the assumption that the detrimental effect of stress/strain concentrators of any kind can efficiently be taken into account by directly postprocessing the entire elastoplastic stress/strain field in the vicinity of the notch apex. Thanks to its specific features, the TCD can be formalized in different ways by simply changing size and geometrical features of the domain used to calculate the required effective stress. The so-called point method (PM) is the simplest form in which this theory can be applied. This formalization of the TCD postulates that the elastoplastic stress/strain state to be used to estimate fatigue damage has to be determined at a given distance from the tip of the notch being assessed. According to the TCD's philosophy, such a distance is treated as a fatigue property. Therefore, given the material, this critical length does not change as either the features of the assessed stress/strain concentrator or the profile of the investigated loading path vary. In the present study, the above design strategy is attempted to be used to estimate lifetime of notched component subjected to VA loading, the required critical distance being determined under constant amplitude (CA) loading. The accuracy and reliability of the devised approach were checked by using a number of experimental results generated by testing, under both concave upward and concave downward spectra, notched samples containing geometrical features having a different sharpness. Such a validation exercise allowed us to prove that the elastoplastic TCD, used in the form of the PM, is highly accurate in estimating fatigue damage also in notched components subjected to in-service VA loading.

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