Four stress analysis strategies to use the Modified Wöhler Curve Method to perform the fatigue assessment of weldments subjected to constant and variable amplitude multiaxial fatigue loading

2014 ◽  
Vol 67 ◽  
pp. 38-54 ◽  
Author(s):  
Luca Susmel
Keyword(s):  
Stress Analysis ◽  
Fatigue Loading ◽  
Multiaxial Fatigue ◽  
Fatigue Assessment ◽  
Variable Amplitude ◽  
Analysis Strategies ◽  
Curve Method

scholarly journals The elasto-plastic Point Method to estimate fatigue lifetime of notched metallic materials under variable amplitude multiaxial fatigue loading

2019 ◽  
Vol 300 ◽  
pp. 13004
Author(s):  
Namiq Zuhair Faruq ◽  
Luca Susmel
Keyword(s):  
Biaxial Loading ◽  
Fatigue Loading ◽  
Medium Carbon Steel ◽  
Multiaxial Fatigue ◽  
Point Method ◽  
Assessment Procedure ◽  
Fatigue Lifetime ◽  
Fatigue Assessment ◽  
Variable Amplitude ◽  
Strain Components

The present paper deals with the formulation and implementation of a novel fatigue lifetime estimation technique suitable for designing notched components against multiaxial fatigue. This fatigue assessment procedure was devised by combining the Modified Manson-Coffin Curve Method and the Shear Strain-Maximum Variance Method with the elasto-plastic Point Method. The accuracy of the approach being proposed was checked against a large number of experimental results that were generated by testing notched cylindrical samples of medium-carbon steel En8. These tests were run under proportional/non-proportional constant/variable amplitude biaxial loading, with the effect of non-zero mean stresses and different frequencies between the axial and torsional stress/strain components being also investigated. The results from this validation exercise demonstrate that the novel multiaxial fatigue assessment methodology being proposed is highly accurate, with its systematic usage resulting in predictions falling within an error factor of 2. This remarkable level of accuracy is very promising especially in light of the fact that this approach can be applied by directly post-processing the results from elasto-plastic Finite Element (FE) models solved using commercial codes.

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.

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 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.

A Simple and Efficient Reformulation of the Classical Manson–Coffin Curve to Predict Lifetime Under Multiaxial Fatigue Loading—Part II: Notches

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Luca Susmel ◽  
Giovanni Meneghetti ◽  
Bruno Atzori
Keyword(s):  
Notch Root ◽  
Constitutive Relations ◽  
Complex Loading ◽  
Fatigue Loading ◽  
Initiation Site ◽  
Multiaxial Fatigue ◽  
Stress Strain ◽  
Maximum Shear Strain ◽  
Curve Method ◽  
Number Of Cycles

The present study is concerned with the use of the modified Manson–Coffin curve method to estimate the lifetime of notched components subjected to multiaxial cyclic loading. The above criterion postulates that fatigue strength under complex loading paths can efficiently be evaluated in terms of maximum shear strain amplitude, provided that the reference Manson–Coffin curve used to predict the number of cycles to failure is defined by taking into account the actual degree of multiaxiality/nonproportionality of the stress/strain state damaging the assumed crack initiation site. The accuracy and reliability of the above fatigue life estimation technique was checked by considering about 300 experimental results taken from the literature. Such data were generated by testing notched cylindrical samples made of four different metallic materials and subjected to in-phase and out-of-phase biaxial nominal loading. The accuracy of our criterion in taking into account the presence of nonzero mean stresses was also investigated in depth. To calculate the stress/strain quantities needed for the in-field use of the modified Manson–Coffin curve method, notch root stresses and strains were estimated by using not only the well-known analytical tool due to Köttgen et al. (1995, “Pseudo Stress and Pseudo Strain Based Approaches to Multiaxial Notch Analysis,” Fatigue Fract. Eng. Mater. Struct., 18(9), pp. 981–1006) (applied along with the ratchetting plasticity model devised by Jiang and Sehitoglu (1996, “Modelling of Cyclic Ratchetting Plasticity, Part I: Development and Constitutive Relations. Transactions of the ASME,” ASME J. Appl. Mech., 63, pp. 720–725; 1996, “Modelling of Cyclic Ratchetting Plasticity, Part I: Development and Constitutive Relations,” Trans. ASME J. Appl. Mech., 63, pp. 720–725)) but also by taking full advantage of the finite element method to perform some calibration analyses. The systematic use of our approach was seen to result in estimates falling within an error factor of about 3.

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