Cumulative Damage Under Constant Amplitude and Variable Amplitude Loading: Some New Physical Aspects

1987 ◽  
pp. 49-54 ◽  
Author(s):  
K. Middeldorf ◽  
H. Nowack ◽  
A. Fischer ◽  
H. Harig
Keyword(s):  
Cumulative Damage ◽  
Constant Amplitude ◽  
Variable Amplitude Loading ◽  
Variable Amplitude

Development of Fatigue Testing of Full-Scale Girth Welded Pipes Under Variable Amplitude Loading

2011 ◽  
Author(s):  
Yan-Hui Zhang ◽  
Stephen Maddox
Keyword(s):  
Fatigue Limit ◽  
Fatigue Damage ◽  
Fatigue Testing ◽  
Full Scale ◽  
Cumulative Damage ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Testing Procedures ◽  
Fatigue Design ◽  
Damage Rule

In service the great majority of structures and components are subjected to stresses of variable amplitude (VA). The fatigue design of welded joints in such structures is based on fatigue data obtained under constant amplitude loading, used in conjunction with a cumulative damage rule to estimate the damage introduced by cycles of varying magnitude in the service stress history. There are two major concerns with fatigue design of deepwater steel catenary risers (SCRs): the validity of cumulative damage rule and the damaging effect of stresses below the constant amplitude fatigue limit (CAFL). It is known that SCRs can experience very high numbers of low stress cycles due to vortex induced vibration (VIV) with the result that the choice of method for accounting for the fatigue damage due to stresses below the constant amplitude fatigue limit can be highly significant in terms of the estimated fatigue life. These two fundamental issues have been addressed in a recent group sponsored project. By successfully establishing a loading spectrum representative of that experienced by risers and developing the testing procedures for VA loading using the resonance testing rigs, the fatigue performance of full-scale girth welded pipes under VA loading were investigated. These loading spectra had the same peak/maximum stress histograms but different minimum stresses. Many tests lasted over 108 cycles to investigate the fatigue damage of small stresses in these spectra. This paper describes the development of the method by which fatigue testing of full-scale girth welded pipes under VA loading had been successfully performed.

Alternative Fatigue Lifetime Prediction Formulations for Variable-Amplitude Loading

2002 ◽  
Author(s):  
R. P. L. Nijssen ◽  
D. R. V. van Delft ◽  
A. M. van Wingerde
Keyword(s):  
Turbine Rotor ◽  
Rotor Blades ◽  
Lifetime Prediction ◽  
Constant Amplitude ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Amplitude Data ◽  
The Difference ◽  
Rainflow Counting ◽  
Sn Curve

Possible alternative fatigue formulations to predict lifetime under variable-amplitude loading are investigated. Test results of WISPER and WISPERX variable-amplitude tests on a material representative for wind turbine rotor blades are used. All fatigue calculations are performed using Rainflow counting of the WISPER(X) load histories and employing the Miner summation. The formulation of the SN-curve and the constant-life diagram are varied. Commonly, a log-log SN-curve is used in combination with a linear Goodman constant-life relation. However, in previous work, it was found that these formulations overestimate lifetime of specimens subjected to the variable-amplitude WISPER and WISPERX load histories. This previous work suggested that the SN-formulation be changed and also used an alternative constant-life formulation with parallel lines. These formulations and variations on them are investigated. Also, constant-amplitude data for R = 0.1 are included to construct an alternative constant-life diagram. Including R = 0.1 constant-amplitude data in the lifetime predictions for WISPER(X) seems to improve the accuracy of the calculation. The alternative constant-life formulation might remove the non-conservatism from the lifetime prediction and account for the difference in lifetime between WISPER and WISPERX.

Fatigue Life Prediction of Impacted Glass/Epoxy Composites under Variable Amplitude Loading

2004 ◽  
Vol 261-263 ◽  
pp. 1079-1084 ◽  
Author(s):  
Ki Weon Kang ◽  
Jong Kweon Kim
Keyword(s):  
Fatigue Life ◽  
Impact Damage ◽  
Fatigue Behavior ◽  
Equivalent Stress ◽  
Epoxy Composites ◽  
Constant Amplitude ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Amplitude Data ◽  
The Impact

This paper presents the fatigue behavior of plain-weave E-glass/epoxy composites with impact-induced damage under constant and variable amplitude loading. The constant amplitude fatigue life of the impacted composites can be identified through the prediction model, which was proposed on the carbon/epoxy laminates by authors. Also, the models are derived to calculate the equivalent stress of the composites under variable amplitude loading, considering the impact damage. These models allow fatigue data of the unimpacted and impacted composites under variable amplitude loading to be correlated with constant amplitude data of the unimpacted composites.

In-Service Fatigue Performance of SCR Girth Welds Installed by Reeling

2012 ◽  
Author(s):  
Philippe P. Darcis ◽  
Eduardo Aguilar ◽  
Emma Erezuma ◽  
Israel Marines-Garcia ◽  
Eduardo A. Ruiz ◽  
...  
Keyword(s):  
Time History ◽  
Cumulative Damage ◽  
Fatigue Performance ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Failure Initiation ◽  
Service Conditions ◽  
Girth Welds ◽  
Damage Rule ◽  
Loading Spectrum

Interest arises on verifying the SCR girth welds fatigue response to a more representative loading spectrum of the actual in-service conditions and after reel-lay deformation. It is important to determine if the actual riser component’s qualification, without pre-straining and under constant amplitude loading, evidences discrepancies with in-service conditions, in terms of fatigue strength. This situation has motivated the full scale S-N fatigue performance evaluation of SCR girth welds under constant and variable amplitude loading, and after reel-lay simulations. A CMn steel X65 pipe 10.75” outside diameter (OD) and 25.4 mm wall thickness (WT) was chosen for this program. The Welding Procedure developed for girth welds manufacturing involved the use of the Lincoln STT® process for the root pass and the GMAW process for the fill and cap passes. Reeling trials were performed at Stress Engineering Services, Houston, U.S.A.. A dedicated commercial software was used to simulate the variable amplitude loading spectrum, which is representative of a SCR Touch Down Point (TDP) in West of Africa at a water depth of 1,200 m (3937 ft) and a FPSO as production platform. The experimental approach was focused on estimating the damage introduced by reeling and by loading cycles of various magnitudes in the riser service time history. Results of strained and unstrained specimens, tested at constant and variable amplitude, have been compared, and the cumulative damage rule typically used by Riser fatigue designers has been evaluated (i.e. Miner’s linear cumulative damage rule). Systematic fractographic investigations were performed on all the samples after testing to identify their fatigue failure initiation causes.

Application of Actual In-Service Spectrum to SCR Girth Welds

2011 ◽  
Author(s):  
Philippe P. Darcis ◽  
Israel Marines-Garcia ◽  
E. Aguilar ◽  
Eduardo A. Ruiz ◽  
Hector M. Quintanilla
Keyword(s):  
Fatigue Strength ◽  
Oil Recovery ◽  
Experimental Approach ◽  
Cumulative Damage ◽  
System Response ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Wide Range ◽  
Girth Welds ◽  
Damage Rule

Fatigue is normally the limiting design criterion for Steel Catenary Risers (SCRs) and it represents its major engineering challenge. As a consequence, design of this component generally trusts on a very good fatigue resistance. A common practice, widely adopted in oil recovery industry, is to certify that specific welding procedures have proper fatigue strength equal or better than the one adopted in design; such fatigue strength is commonly evaluated under constant amplitude loading. However, SCRs are subjected to complex loading spectrums which are characterized by a wide range of loading amplitudes induced by different sources that include the overall system response of the barge. Therefore, interest arises in verifying the component response to representative loading spectrums of the actual SCR in-service conditions and determining if actual riser components qualification, under constant amplitude loading, presents discrepancies with their resistance under in-service fatigue conditions. This situation has motivated full scale fatigue performance evaluation of SCR girth welds under constant and variable amplitude loading spectrums. The experimental approach was focused on estimating the damage introduced by loading cycles of various magnitudes. Constant and variable amplitude results were compared and the accuracy of Miner’s linear cumulative damage rule has been evaluated. The experimental approach was focused on estimating the damage introduced by loading cycles of various magnitudes. Constant and variable amplitude results have been compared and the accuracy of Miner’s linear cumulative damage rule [1] has been evaluated.

Cumulative Energy of Fatigue Cracking under Variable Amplitude Loading on the Example of C45 Steel

2014 ◽  
Vol 224 ◽  
pp. 51-56
Author(s):  
Bogdan Ligaj
Keyword(s):  
High Cycle Fatigue ◽  
Stress Amplitude ◽  
Fatigue Cracking ◽  
Relative Difference ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Constant Amplitude ◽  
Cumulative Energy ◽  
Variable Amplitude Loading ◽  
Variable Amplitude

The article presents the results of low and high cycle fatigue tests of C45 steel for constant and variable amplitude loading in the stress and energy based approach. Values of the cumulated energy of plastic strain ΣΔWpl for programmed loading (at selected levels of stress amplitude Sa) were found to meet reliability criteria for results obtained in the condition of constant amplitude loading. (R= -1). It was also found that the results obtained in the energy based approach are characterised by a smaller range of relative difference changes (δ(N) = 0,77 to 1,17) than the results obtained in the stress based approach (δ(N) = 0,15 to 1,94). At stress level Sa = 428 MPa, (corresponding to yield point of C45 steel) value δ(N) is similar for the stress based approach and energy based approach.

scholarly journals Fatigue Characteristic of Designed T-Type Specimen under Two-Step Repeating Variable Amplitude Load with Low-Amplitude Load below the Fatigue Limit

2021 ◽  
Vol 9 (2) ◽  
pp. 107
Author(s):  
Jin Gan ◽  
Di Sun ◽  
Hui Deng ◽  
Zhou Wang ◽  
Xiaoli Wang ◽  
...  
Keyword(s):  
Stress Ratio ◽  
Type Specimen ◽  
Fatigue Tests ◽  
Cumulative Damage ◽  
Cyclic Loads ◽  
Constant Amplitude ◽  
Type Specimens ◽  
Variable Amplitude ◽  
Non Linear ◽  
Low Amplitude

In order to investigate the non-linear fatigue cumulative damage of joints in ocean structural parts, one type of low carbon steel Q345D was employed to prepare designed T-type specimens, and a series of fatigue experiments were carried out on the specimens under two-step repeating variable amplitude loading condition. The chosen high cyclic loads were larger than the constant amplitude fatigue limit (CAFL) and the chosen low cyclic loads were below the CAFL. Firstly, the S-N curve of designed T-type specimen was obtained via different constant amplitude fatigue tests. Then, a series of two-step repeating variable load were carried out on designed T-type specimens with the aim of calculating the cumulative damage of specimen under the variable fatigue load. The discussions about non-linear fatigue cumulative damage of designed T-type specimens and the interaction effect between the high and low amplitude loadings on the fatigue life were carried out, and some meaningful conclusions were obtained according to the series of fatigue tests. The results show that fatigue cumulative damage of designed T-type specimens calculated based on Miner’s rule ranges from 0.513 to 1.756. Under the same cycle ratio, the cumulative damage increases with the increase of high cyclic stress, and at the same stress ratio, the cumulative damage increases linearly with the increase of cycle ratio. Based on the non-linear damage evaluation method, it is found that the load interaction effect between high and low stress loads exhibits different damage or strengthening effects with the change of stress ratio and cycle ratio.

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