scholarly journals Structural Reliability Prediction Using Acoustic Emission-Based Modeling of Fatigue Crack Growth

2018 ◽  
Vol 8 (8) ◽  
pp. 1225 ◽  
Author(s):  
Azadeh Keshtgar ◽  
Christine Sauerbrunn ◽  
Mohammad Modarres
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Titanium Alloys ◽  
Crack Growth ◽  
Structural Reliability ◽  
Bayesian Regression ◽  
Model Parameters ◽  
Loading Frequency ◽  
Proposed Model ◽  
Crack Growth Model

In this paper, AE signals collected during fatigue crack-growth of aluminum and titanium alloys (Al7075-T6 and Ti-6Al-4V) were analyzed and compared. Both the aluminum and titanium alloys used in this study are prevalent materials in aerospace structures, which prompted this current investigation. The effect of different loading conditions and loading frequencies on a proposed AE-based crack-growth model were studied. The results suggest that the linear model used to relate AE and crack growth is independent of the loading condition and loading frequency. Also, the model initially developed for the aluminum alloy proves to hold true for the titanium alloy while, as expected, the model parameters are material dependent. The model parameters and their distributions were estimated using a Bayesian regression technique. The proposed model was developed and validated based on post processing and Bayesian analysis of experimental data.

A Probabilistic Treatment of Microstructural Effects on Fatigue Crack Growth of Large Cracks

1996 ◽  
Vol 118 (3) ◽  
pp. 379-386 ◽  
Author(s):  
K. S. Chan ◽  
T. Y. Torng
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Yield Stress ◽  
Crack Growth ◽  
Structural Reliability ◽  
Dislocation Cell ◽  
Microstructural Effects ◽  
Dislocation Barrier ◽  
Stress Fatigue ◽  
Crack Growth Model

A probabilistic model has been developed for treating the effects of microstructural variation on the fatigue crack growth response of large cracks in structural alloys. The proposed methodology is based on a microstructure-based fatigue crack growth law that relates the crack growth rate, da/dN, to the dislocation barrier spacing, yield stress, fatigue ductility coefficient, Young’s modulus, and the dislocation cell size or crack jump distance. Probabilistic treatment of these microstructure-dependent variables has led to a fatigue crack growth law that includes explicitly the randomness of the yield stress, fatigue ductility coefficient, and the dislocation barrier spacing in the response equation. Applications of the probabilistic crack growth model to structural reliability analyses for steels and Ti-alloys are illustrated, and the probabilistic sensitivities of individual random variables are evaluated.

An Integrated Prognostics Approach for Pipeline Fatigue Crack Growth Prediction Utilizing Inline Inspection Data

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Mingjiang Xie ◽  
Steven Bott ◽  
Aaron Sutton ◽  
Alex Nemeth ◽  
Zhigang Tian
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Measurement Uncertainty ◽  
Stress Analysis ◽  
Crack Growth ◽  
Integrated Approach ◽  
Model Parameters ◽  
Growth Prediction ◽  
Depth Measurement ◽  
Crack Growth Model

Fatigue cracking is a key type of defect for liquid pipelines, and managing fatigue cracks has been a top priority and a big challenge for liquid pipeline operators. The existing inline inspection (ILI) tools for pipeline defect evaluation have large fatigue crack measurement uncertainties. Furthermore, the current physics-based methods are mainly used for fatigue crack growth prediction, where the same or a small range of fixed model parameters is used for all pipes. They result in uncertainty that is managed through the use of conservative safety factors such as adding depth uncertainty to the measured depth in deciding integrity management and risk mitigation strategies. In this study, an integrated approach is proposed for pipeline fatigue crack growth prediction utilizing ILI data including consideration of crack depth measurement uncertainty. This approach is done by integrating the physical models, including the stress analysis models, the crack growth model governed by the Paris’ law, and the ILI data. With the proposed integrated approach, the finite element (FE) model of a cracked pipe is built and the stress analysis is performed. ILI data are utilized to update the uncertain physical parameters for the individual pipe being considered so that a more accurate fatigue crack growth prediction can be achieved. Time-varying loading conditions are considered in the proposed integrated method by using rainflow counting method. The proposed integrated prognostics approach is compared with the existing physics-based method using examples based on simulated data. Field data provided by a Canadian pipeline operator are also employed for the validation of the proposed method. The examples and case studies in this paper demonstrate the limitations of the existing physics-based method, and the promise of the proposed method for achieving accurate fatigue crack growth prediction as continuous improvement of ILI technologies further reduces ILI measurement uncertainty.

Formulation of a Polynomial Stochastic Fatigue Crack Growth Model

2014 ◽  
Vol 909 ◽  
pp. 467-471 ◽  
Author(s):  
C.C. Ni
Keyword(s):  
Distribution Function ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Model ◽  
Analytical Solutions ◽  
Growth Function ◽  
Crack Size ◽  
Model Parameters ◽  
Crack Growth Model

The study is focused on the formulation of a proposed polynomial stochastic fatigue crack growth model. Assuming the fatigue crack growth rate equal to a deterministic polynomial function in terms of fatigue crack size multiplied by a stationary lognormal random factor accounting for the statistical scatter of the fatigue crack growth, the analytical solutions of fatigue crack growth function and median crack growth function in term of model parameters were derived. Two extreme cases, lognormal random variable and lognormal white noise, of the proposed model were also investigated, and the analytical solutions of the distribution function of the random crack size at any service time and distribution function of random time to reach a specified crack size were obtained.

Characterization of Crack Tip Damage Zone Formation on Alloy 625 During Fatigue Crack Growth at 750°C by Transmission EBSD Method

2017 ◽  
Author(s):  
Yuji Ozawa ◽  
Tatsuya Ishikawa ◽  
Yoichi Takeda
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Power Plants ◽  
Crack Path ◽  
Damage Zone ◽  
Crack Tip ◽  
Loading Frequency ◽  
Zone Formation ◽  
Alloy 625

In order to clarify the mechanism of fatigue crack growth in alloy 625, which is a candidate material for use in advanced ultra supercritical power plants, the crack tip damage zone formation after a crack growth test conducted in high temperature steam was investigated. It was observed that the oxide thickness at the crack tip tended to increase with decreasing cyclic loading frequency. The crack path was a mix of transgranular and intergranular fractures. According to the grain reference orientation deviation (GROD) maps, it was revealed that the density of geometrically necessary dislocations (GNDs) in the matrix along the crack path and ahead of crack tip increased with an increase in the fatigue crack growth rate (FCGR) due to environmental effects. It was observed that (1) mobile dislocations at the crack surface were blocked due to the thick oxide layer, resulting in an increase in the density of GNDs, and (2) an increase in the density of GNDs might induce stress concentration at the crack tip, deformation twinning, and the acceleration of FCGRs.

Evaluation of Fatigue Crack Growth Curves in Existing Codes and a Proposed Modification Based on Experimental Data of Cr-Ni-Mo-V Steel Welded Joints

2016 ◽  
Author(s):  
Yan-Nan Du ◽  
Ming-Liang Zhu ◽  
Fu-Zhen Xuan ◽  
Shan-Tung Tu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Welded Joints ◽  
Growth Curves ◽  
Crack Growth Behavior ◽  
Fatigue Assessment ◽  
Crack Growth Model ◽  
Threshold Regime ◽  
Near Threshold

A comparison of currently available codes for assessment of fatigue crack growth, including ASME (America Society of Mechanical Engineers) SEC. XI, FKM (Forchungskuratorium Maschinenbau) guideline, WES (Japan Welding Engineering Society) 2805, BS7910 and JSME (The Japan Society of Mechanical Engineers), was carried out by paying attention to the suitability of application and the easiness to obtain the parameters, based on fatigue crack growth data of Cr-Ni-Mo-V steel welded joints. Results showed that fatigue crack growth curves provided by the FKM or WES were good choice when few inputs were at hand while the curves in the BS7910, JSME and ASME were recommended for precise estimation. It was indicated that the assessment of welded joints solely by fatigue crack growth behavior at base metal part and the assessment of fatigue crack growth for the aged condition by as-received one both resulted in non-conservativeness, albeit dependent on the range of stress ratios, R. A new bilinear form of fatigue crack growth model independent of R was developed based on transition point occurred in the near-threshold regime. This constituted the bilinear approach to fatigue assessment, and thus contributed to the optimization of fatigue assessment in the near-threshold regime.

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