scholarly journals Updating the Distributions of Uncertain Parameters Involved in Fatigue Analysis

2020 ◽  
Vol 8 (10) ◽  
pp. 778
Author(s):  
Hadi Khalili ◽  
Selda Oterkus ◽  
Nigel Barltrop ◽  
Ujjwal Bharadwaj
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Probability Distribution ◽  
Fatigue Damage ◽  
Growth Analysis ◽  
Probability Distributions ◽  
Crack Size ◽  
Probability Of Failure ◽  
Uncertain Parameters ◽  
Tubular Joint

Fatigue is an important failure mode in offshore jacket platforms. To evaluate the fatigue damage, these platforms are periodically inspected during their lifetime. Regarding fatigue damage, the information from inspection consists of crack measurement. A Bayesian framework can be used to update the probability distribution of the crack size. The main purpose of this study is to develop a framework to update the probability distributions of all uncertain parameters involved in the fatigue crack growth analysis. This methodology maximizes the benefit of the inspection results by updating several uncertain parameters involved in the fracture mechanics approach. Two sets of cracks are used to obtain the updated distributions for uncertain parameters; prior cracks and simulated reality cracks. By comparing these cracks, the updated distributions for uncertain parameters are obtained. The updated crack size distribution can be used to update the estimation of the probability of failure. To demonstrate the developed framework, a tubular joint in a specific jacket platform is considered and the framework is applied for that joint. The results of the developed methodology indicate that the updated distributions of uncertain parameters shift towards the simulated reality distributions.

scholarly journals Different Bayesian Methods for Updating the Fatigue Crack Size Distribution in a Tubular Joint

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
H. Khalili ◽  
S. Oterkus ◽  
N. Barltrop ◽  
U. Bharadwaj
Keyword(s):  
Numerical Methods ◽  
Probability Distribution ◽  
Size Distribution ◽  
Fatigue Damage ◽  
Crack Size ◽  
Offshore Platforms ◽  
Additional Information ◽  
Joint Reliability ◽  
Service Lifetime ◽  
Tubular Joint

Abstract Offshore platforms are prone to fatigue damage. To evaluate the fatigue damage, these platforms are periodically inspected during the in-service lifetime. Inspection activities provide additional information, which includes detection and measurement of crack size. A Bayesian framework can be used to update the probability distribution of the uncertain parameters such as crack size. After updating the distribution of the crack size, it is possible to improve the estimation of joint reliability. The main purpose of this study is to present different methods of Bayesian inference to update the probability distribution of the crack size using the inspection results and to demonstrate how the results are different. Two different methods are presented: analytical (conjugate) and numerical methods. The advantages and shortcomings of each method are discussed. To compare the results of the analytical and numerical methods, two different situations are considered; updating the crack size distribution for a particular joint and updating the crack size distribution for several joints that have almost the same conditions. Although the proposed methodology can be applied to different kinds of structures, an example of tubular joints in a specific jacket platform is presented to demonstrate the proposed approach and to compare the results of two methods.

Modeling of Fatigue Crack Propagation

2004 ◽  
Vol 126 (1) ◽  
pp. 77-86 ◽  
Author(s):  
Yanyao Jiang ◽  
Miaolin Feng
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Fatigue Crack Propagation ◽  
Fatigue Crack Initiation ◽  
Cyclic Plasticity ◽  
R Ratio

Fatigue crack propagation was modeled by using the cyclic plasticity material properties and fatigue constants for crack initiation. The cyclic elastic-plastic stress-strain field near the crack tip was analyzed using the finite element method with the implementation of a robust cyclic plasticity theory. An incremental multiaxial fatigue criterion was employed to determine the fatigue damage. A straightforward method was developed to determine the fatigue crack growth rate. Crack propagation behavior of a material was obtained without any additional assumptions or fitting. Benchmark Mode I fatigue crack growth experiments were conducted using 1070 steel at room temperature. The approach developed was able to quantitatively capture all the important fatigue crack propagation behaviors including the overload and the R-ratio effects on crack propagation and threshold. The models provide a new perspective for the R-ratio effects. The results support the notion that the fatigue crack initiation and propagation behaviors are governed by the same fatigue damage mechanisms. Crack growth can be treated as a process of continuous crack nucleation.

Fatigue Damage Analysis on Crack Growth and Fatigue Life of Welded Bridge Members with Initial Crack

2006 ◽  
Vol 324-325 ◽  
pp. 251-254 ◽  
Author(s):  
Tai Quan Zhou ◽  
Tommy Hung Tin Chan ◽  
Yuan Hua
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Initial Crack ◽  
Traffic Loading

The behavior of crack growth with a view to fatigue damage accumulation on the tip of cracks is discussed. Fatigue life of welded components with initial crack in bridges under traffic loading is investigated. The study is presented in two parts. Firstly, a new model of fatigue crack growth for welded bridge member under traffic loading is presented. And the calculate method of the stress intensity factor necessary for evaluation of the fatigue life of welded bridge members with cracks is discussed. Based on the concept of continuum damage accumulated on the tip of fatigue cracks, the fatigue damage law suitable for steel bridge member under traffic loading is modified to consider the crack growth. The proposed fatigue crack growth can describe the relationship between the cracking count rate and the effective stress intensity factor. The proposed fatigue crack growth model is then applied to calculate the crack growth and the fatigue life of two types of welded components with fatigue experimental results. The stress intensity factors are modified by the factor of geometric shape for the welded components in order to reflect the influence of the welding type and geometry on the stress intensity factor. The calculated and measured fatigue lives are generally in good agreement, at some of the initial conditions of cracking, for a welded component widely used in steel bridges.

Experiment and Modeling of Fatigue Crack Growth With Altering Loading Direction

2009 ◽  
Author(s):  
Wenfeng Tu ◽  
Xiaogui Wang ◽  
Zengliang Gao
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Growth Behavior ◽  
Cyclic Plasticity ◽  
Crack Growth Behavior ◽  
Loading Direction

The experiments of mixed Mode I-II fatigue crack growth with altering loading direction were conducted with compact specimens made of 16MnR steel. The specimens were tested under three loading steps. When the crack reached a certain length in the first step, the loading direction was switched to a certain angle. Finally, the loading direction was returned to the original orientation. The crack grow direction had a tendency perpendicular to the loading axis. Right after the loading direction was changed, the crack growth rate was retarded. A new approach developed was used to predict the crack growth behavior. The elastic-plastic stress analysis was performed using the finite element method with the implementation of a cyclic plasticity model. Based on the stress-strain response, fatigue damage near the crack tip was determined by a multi-axial fatigue criterion. Both the crack growth rate and cracking direction were obtained according to the maximum fatigue damage distribution on the critical material plane. The predictions for the crack growth behavior including the crack growth rate and crack growth path were in agreement with the experimental data.

Sign in / Sign up

Export Citation Format

Share Document