Alternative fatigue lifetime prediction formulations for variable-amplitude loading

2002 ◽  
Author(s):  
R. Nijssen ◽  
D. van Delft ◽  
A. van Wingerde
Keyword(s):  
Lifetime Prediction ◽  
Fatigue Lifetime ◽  
Variable Amplitude Loading ◽  
Variable Amplitude

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.

Alternative Fatigue Lifetime Prediction Formulations for Variable-Amplitude Loading

2002 ◽  
Vol 124 (4) ◽  
pp. 396-403 ◽  
Author(s):  
R. P. L. Nijssen ◽  
D. R. V. van Delft ◽  
A. M. van Wingerde
Keyword(s):  
Wind Turbine ◽  
Turbine Rotor ◽  
Lifetime Prediction ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Amplitude Data ◽  
Goodman Diagram ◽  
Rainflow Counting ◽  
Wind Turbine Rotor ◽  
Sn Curve

Accurate prediction of lifetime is an increasingly important issue for wind turbine rotor blade materials. Coupon tests with the variable-amplitude standard loading sequences for wind turbines known as WISPER and WISPERX have indicated that the coupon lifetime can be overestimated by one or two orders of magnitude using conventional lifetime prediction formulations. In the actual design, this might be compensated for by conservative design factors covering other aspects such as environmental conditions. These conventional lifetime prediction formulations use Rainflow counting of the load history, a log-log SN-curve (stress- or strain amplitude versus cycles to failure) for R = −1, a linear Goodman diagram as a constant-life diagram, and Miner summation. In this work, possible alternative fatigue formulations to improve lifetime prediction under variable-amplitude loading are investigated. Results of WISPER and WISPERX variable-amplitude tests on a material representative of wind turbine rotor blades are used. Only alternatives for the SN-curve and the constant-life diagram are investigated; Rainflow counting and Miner summation are used in all predictions discussed here. None of the investigated SN-curves unites an apparent correlation of constant-amplitude data with an accurate and/or conservative lifetime prediction, when including them in a classical linear Goodman diagram. However, the lin-log- and log-log SN-curves do yield better predictions in combination with an alternative constant-life diagram.

scholarly journals A comparison of fatigue lifetime prediction models applied to variable amplitude loading

2017 ◽  
Vol 8 (1) ◽  
pp. 8
Author(s):  
Tom Nottebaere ◽  
Nahuel Micone ◽  
Wim De Waele
Keyword(s):  
Crack Growth ◽  
Prediction Models ◽  
Weighted Average ◽  
Offshore Structures ◽  
Cumulative Damage ◽  
Lifetime Prediction ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Yield Zone ◽  
Damage Models

The loads imposed on, amongst others, offshore structures can vary considerably with time. Lifetime prediction methodologies need to consider possible acceleration and retardation of the crack growth rate due to load sequences. Models based on a linear accumulation of damage will have a limited accuracy and are not considered as a sufficiently valuable asset in lifetime prediction of structures subjected to variable amplitude loading. This necessitates more complex nonlinear damage evolution models that can be applied in a so-called cycle-by-cycle analysis. In this paper, a comparison is made between three cumulative damage models (Miner, modified Miner and weighted average) and two yield zone models (Wheeler and Willenborg). Experimental data of fatigue crack growth in offshore steel specimens subjected to sequential loading is used as basis of the comparison. The modified Miner model is the most promising of the cumulative damage models but the determination of the parameter α requires laboratory tests. Evaluation of the effects of variation in the model input parameters on estimated lifetime reveals a large influence for the Miner and weighted average approaches.

Application of the Strip Yield Model to Crack Growth Predictions for Structural Steel

2010 ◽  
Vol 57 (1) ◽  
pp. 1-20
Author(s):  
Małgorzata Skorupa ◽  
Tomasz Machniewicz
Keyword(s):  
Structural Steel ◽  
Crack Growth ◽  
Model Calibration ◽  
Load History ◽  
Yield Model ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Constraint Factors ◽  
Strip Yield Model ◽  
Closure Mechanism

Application of the Strip Yield Model to Crack Growth Predictions for Structural SteelA strip yield model implementation by the present authors is applied to predict fatigue crack growth observed in structural steel specimens under various constant and variable amplitude loading conditions. Attention is paid to the model calibration using the constraint factors in view of the dependence of both the crack closure mechanism and the material stress-strain response on the load history. Prediction capabilities of the model are considered in the context of the incompatibility between the crack growth resistance for constant and variable amplitude loading.

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