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.

scholarly journals Thickness Effect Analysis on Fatigue Crack Propagation of 7475 Plate Material under Variable Amplitude Loading

2018 ◽  
Vol 188 ◽  
pp. 02015
Author(s):  
Jakub Šedek ◽  
Roman Růžek
Keyword(s):  
Plastic Zone ◽  
Crack Growth ◽  
Prediction Models ◽  
Model Simulation ◽  
Thickness Effect ◽  
Original Form ◽  
Specimen Thickness ◽  
Constraint Factor ◽  
Variable Amplitude Loading ◽  
Variable Amplitude

In the crack growth prediction models, the effect of variable amplitude loading is taken into account by different ways. One of them the Newman’s model is used very often, but in its original form it is not able to take into account the effect of specimen thickness. The new modification which involves the specimen thickness is presented. The study of variable thickness impact is based on the FE – analysis of M(T) specimen. The variability of constrained factor α was analysed for several load levels and specimen thicknesses. The value of α is governed by the ratio of thickness B versus plastic zone size rp. The effect of overloads on the plastic zone and relevant constraint factor value is analysed as well. During loading, it was found, that the constraint factor value is lower after overloads than when creating monotonic plastic deformation on the same load level in a large part of the cycle. The influence of thickness effect based on different α value after overload was successfully implemented into the strip yield model. Simulation of crack growth taking into account the thickness of the specimen under variable amplitude loading shows similar behaviour like the experimental data.

Fatigue Crack Growth Behavior of TC-128-B Steel Under Variable Amplitude Loading

2007 ◽  
Author(s):  
Daniel B. Garcia ◽  
James H. Feiger ◽  
Peter C. McKeighan ◽  
Joseph W. Cardinal ◽  
David Y. Jeong
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Prediction Models ◽  
Interaction Model ◽  
Crack Growth Behavior ◽  
Growth Data ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Compressive Loads

Railroad tank cars are exposed to a high degree of variable amplitude loading that is comprised of both tensile compressive cycles. In order to consistently and accurately predict this type of loading, material properties, usage, and load interaction models must be used in concert. The objective of this study is to present the methodology necessary to generate tank car specific spectrum crack growth life prediction models. Experimental fatigue crack growth data from this project and previous efforts provided the baseline data necessary to develop NASGRO® models and predict simplified over-load and under-load experiments. The methods were then advanced to predict spectrum crack growth experimental data representative of tank car usage. The results show that significant amounts of compressive loads in the tank car spectra essentially negate the need for a tensile stress based load interaction model. In order to provide consistently conservative prediction, the most basic model must be implemented instead of the more elaborate retardation models.

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.

Modeling and analysis of gear tooth crack growth under variable-amplitude loading

2013 ◽  
Vol 40 (1) ◽  
pp. 105-113 ◽  
Author(s):  
Juliang Yin ◽  
Wenyi Wang ◽  
Zhihong Man ◽  
Suiyang Khoo
Keyword(s):  
Crack Growth ◽  
Gear Tooth ◽  
Variable Amplitude Loading ◽  
Modeling And Analysis ◽  
Variable Amplitude
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