On the distribution and scatter of fatigue lives obtained by integration of crack growth curves: Does initial crack size distribution matter?

2018 ◽  
Vol 191 ◽  
pp. 111-124 ◽  
Author(s):  
M. Ciavarella ◽  
A. Papangelo
Keyword(s):  
Size Distribution ◽  
Crack Growth ◽  
Growth Curves ◽  
Crack Size ◽  
Initial Crack

Numerical Analysis of the Crack Growth in a High Loaded Bolt Connection

2007 ◽  
Vol 348-349 ◽  
pp. 625-628
Author(s):  
Marko Knez ◽  
Srečko Glodež ◽  
Janez Kramberger
Keyword(s):  
Crack Growth ◽  
Crack Size ◽  
Initial Crack ◽  
Structural Elements ◽  
Element Analysis ◽  
Critical Crack ◽  
Critical Crack Length ◽  
Final Failure ◽  
Heavy Loads ◽  
Bolt Connection

The present paper deals with the research on the crack growth in a bolt connection of a lug for crane counter weight bars. Counter weight bars are structural elements that are subjected to very heavy loads and therefore special attention must be paid. The main purpose of this research is to determine the number of the load cycles required for a crack to propagate from initial to critical crack length, when the final failure can be expected to occur. All required material parameters and the experimental results were determined in our previous research. The influence of the initial crack size upon the remaining life of the lug is researched numerically by means of finite element analysis and analytically by use of the corrected analytical model.

A New Model of Stochastic Crack Growth under Random Loading and Reliability Analysis of Fatigue Life

2007 ◽  
Vol 353-358 ◽  
pp. 81-84
Author(s):  
Hong Zhong Huang ◽  
G. Huang ◽  
Qiang Miao ◽  
Dan Ling ◽  
Q. Ma
Keyword(s):  
Reliability Analysis ◽  
Crack Growth ◽  
Critical Size ◽  
Crack Size ◽  
Initial Crack ◽  
Random Loading ◽  
New Model ◽  
First Order ◽  
Moment Approximation ◽  
First Order Second Moment

A new model is proposed for the analysis of fatigue crack growth under random loading. The fatigue rule of crack length is transformed into the monotony function rule based on types of the crack. By performing reliability analysis, the randomness of the stress, the stochastic nature of the crack growth, the fuzziness of the initial crack size and the randomness of the crack critical size are considered. The First-order-second-moment approximation method is used to obtain the solution of the probability density function. An example is given to illustrate feasibility of the proposed method.

Analysis of Crack Growth in a 3D Voronoi Structure: A Model for Fatigue in Low Density Trabecular Bone

2002 ◽  
Vol 124 (5) ◽  
pp. 512-520 ◽  
Author(s):  
A. M. Makiyama ◽  
S. Vajjhala ◽  
L. J. Gibson
Keyword(s):  
Fatigue Life ◽  
Relative Density ◽  
Trabecular Bone ◽  
Crack Growth ◽  
Three Dimensional ◽  
Crack Size ◽  
Initial Crack ◽  
Low Density ◽  
Cycle Fatigue ◽  
Crack Growth Model

Both creep and crack growth contribute to the reduction in modulus associated with fatigue loading in bone. Here we simulate crack growth and subsequent strut failure in fatigue in an open-cell, three-dimensional Voronoi structure which is similar to that of low density, osteoporotic bone. The model indicates that sequential failure of struts leads to a precipitous drop in modulus: the failure of 1% of the struts leads to about a 10% decrease in modulus. A parametric study is performed to assess the influence of normalized stress range, relative density, initial crack size, crack shape and cell geometry on the fatigue life. The fatigue life is most sensitive to the relative density and the initial crack length. The results lead to a quantitative expression for the fatigue life associated with crack growth. Data for the fatigue life of trabecular bone are compared with the crack growth model described in this paper, as well as with a previous model for creep of a three-dimensional Voronoi structure. In our models, creep dominates the fatigue behavior in low cycle fatigue while crack growth dominates in high cycle fatigue, consistent with previous observations on cortical bone. The large scatter in the trabecular bone fatigue data make it impossible to identify a transition between creep dominated fatigue and crack growth dominated fatigue. The parametric study of the crack growth model indicates that variations in relative density among specimens, initial crack size within trabeculae and crack shape could easily produce such variability in the test results.

A Surface Pitting Life Model for Spur Gears: Part II—Failure Probability Prediction

1991 ◽  
Vol 113 (4) ◽  
pp. 719-724 ◽  
Author(s):  
J. W. Blake ◽  
H. S. Cheng
Keyword(s):  
Size Distribution ◽  
Failure Probability ◽  
Spur Gear ◽  
Crack Size ◽  
Initial Crack ◽  
Spur Gears ◽  
Probability Estimates ◽  
Probability Prediction ◽  
Life Model ◽  
Service Behavior

A predictive pitting model for estimating failure probabilities and service lives has been developed. This paper presents the failure probability analysis and a discussion of the model’s application to spur gears. Probability estimates are based on an initial crack size distribution and on possible interaction between cracks and inclusions. Plots of the fraction of components experiencing pitting (percent) versus life show less spread than would be expected. However, trends predicted based on parametric variation are consistent with service behavior. The model is applied by linking the pitting model with a spur gear performance code. Results are compared with AGMA standards.

scholarly journals Comparing a Fracture Mechanics Model to the SN-Curve Approach for Jacket-Supported Offshore Wind Turbines: Challenges and Opportunities for Lifetime Prediction

2016 ◽  
Author(s):  
Lisa Ziegler ◽  
Michael Muskulus
Keyword(s):  
Crack Growth ◽  
Wind Turbines ◽  
Wind Farms ◽  
Crack Size ◽  
Initial Crack ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Mechanics Model ◽  
Lifetime Extension ◽  
Sn Curve

Accurate lifetime predictions are needed for support structures of offshore wind turbines to optimize operation and maintenance and to decide about lifetime extension of aging wind farms. A comparison of a facture mechanics model to the SN-curve approach for jacket supported offshore wind turbines shows that it is attractive for lifetime extension decisions; however major challenges are calibration of material parameters and assumptions for initial crack size. Crack growths on a Y-joint connecting brace and jacket leg was analysed with simulations of structural response to aero- and hydrodynamic loading and Paris’ law for crack propagation. The model was calibrated to yield an identical fatigue life as obtained from the SN-curve analysis. The effect of weather seasonality on crack growth was evaluated with a Markov weather model and Monte Carlo simulations. Results show that crack growth is sensitive to parameter calibration and follows seasonal weather trends.

An Equivalent Creep Crack Growth Model for Probabilistic Life Prediction of Plastic Pipe Materials

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Yuhao Wang ◽  
Tishun Peng ◽  
Ernest Lever ◽  
Yongming Liu
Keyword(s):  
Experimental Data ◽  
Crack Growth ◽  
Growth Model ◽  
Life Prediction ◽  
Creep Crack Growth ◽  
Creep Damage ◽  
Crack Size ◽  
Initial Crack ◽  
Local Geometry ◽  
Crack Growth Model

Abstract Life prediction in energy infrastructure such as gas pipelines is important to maintain the integrity of such systems. This paper explores a life prediction model for polyethylene materials in natural gas distribution pipelines under creep damage. The model uses a power law equation to describe the crack growth rate and an asymptotic solution for the stress intensity factor (SIF) calculation considering local geometry variations. The SIF solution considers the effect of stress concentration introduced by common damages in pipes such as rock impingement and slit. An effective initial crack size model is proposed for the life prediction of plastic pipes considering the intrinsic initial defect. Large loading-induced plastic deformation is included by a correction factor in the crack growth model. The model is calibrated and validated using experimental data on Aldyl-A pipes with different types of damage. Due to the stochastic nature of the crack growth process, uncertainty quantification is performed, and Monte Carlo (MC) simulation is used to estimate the failure probability. The predicted probabilistic life distributions under different loading conditions are compared with the experimental data. Some conclusions and future work are drawn based on the proposed study and experimental validation.

A Probabilistic Environmentally Assisted Cracking Model for Steam Generator Tubes

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Tae Hyun Lee ◽  
Jae Young Yoon ◽  
Hyo On Nam ◽  
Il Soon Hwang
Keyword(s):  
Bayesian Inference ◽  
Stress Distribution ◽  
Size Distribution ◽  
Steam Generator ◽  
Crack Size ◽  
Initial Crack ◽  
Probability Of Detection ◽  
Alloy 600 ◽  
Pressurized Water ◽  
Environmentally Assisted Cracking

A probabilistic environmentally assisted cracking (PEAC) model was developed to describe the propagation of primary water stress corrosion cracking for Alloy 600 in roll-transition region of steam generator (SG), a severe environmentally assisted cracking problem in pressurized water reactors (PWRs). In the PEAC model, crack growth rate (CGR) and probability of failure (POF) were obtained by adopting a Bayesian inference that decreases the uncertainties of unknown parameters and their distributions in theoretical equations. The CGR is mainly dependent on three factors: probability of detection (POD), initial crack size distribution, and stress distribution. The POD, which is a logistic link was updated with Bayesian inference based on SG inspection data. The crack size distribution, which is relative to initiation time expressed by a Weibull function, was also updated with Bayesian inference using POD. The stress distribution caused by mechanical rolling is considered to be a major contributing factor along the SG tube. It based on finite element analysis is deterministic model unlike POD and initial crack distribution. According to this model, the uncertainty of hyperparameters in the CGR which are parameters of a prior distribution was reduced, and the appropriate level of confidence was achieved by utilizing the available data. Moreover, a benchmark study for the SG tube was performed to evaluate reliability of Alloy 600 SG components in nuclear power plants. The POF was estimated from the developed PEAC model and failure criteria by taking into account the effects of inspection and repair of defective tubes. The results from this study are applied to demonstrate risk reduction in PWRs by adopting risk-informed in-service inspection.

Proof-Test-Based Life Prediction of High-Toughness Pressure Vessels

1996 ◽  
Vol 118 (1) ◽  
pp. 86-94 ◽  
Author(s):  
T. L. Panontin ◽  
M. R. Hill
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Life Prediction ◽  
Crack Size ◽  
Initial Crack ◽  
Pressure Vessels ◽  
Operating Pressure ◽  
High Toughness

The paper examines the problems associated with applying proof-test-based life prediction to vessels made of high-toughness metals. Two A106 Gr B pipe specimens containing long, through-wall, circumferential flaws were tested. One failed during hydrostatic testing and the other during tension-tension cycling following a hydrostatic test. Quantitative fractography was used to verify experimentally obtained fatigue crack growth rates and a variety of LEFM and EPFM techniques were used to analyze the experimental results. The results show that: plastic collapse analysis provides accurate predictions of screened (initial) crack size when the flow stress is determined experimentally; LEFM analysis underestimates the crack size screened by the proof test and overpredicts the subsequent fatigue life of the vessel when retardation effects are small (i.e., low proof levels); and, at a high proof-test level 2.4 × operating pressure), the large retardation effect on fatigue crack growth due to the overload overwhelmed the deleterious effect on fatigue life from stable tearing during the proof test and alleviated the problem of screening only long cracks due to the high toughness of the metal.

Fatigue Crack Growth Simulation Using S-Version FEM

2008 ◽  
Author(s):  
Masanori Kikuchi ◽  
Yoshitaka Wada ◽  
Masafumi Takahashi ◽  
Yulong Li
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Problem ◽  
Crack Size ◽  
Initial Crack ◽  
Crack Growth Simulation ◽  
Curved Crack ◽  
Crack Problems ◽  
New Criterion

Fatigue crack growth under mixed mode loading conditions is simulated using S-FEM. By using S-FEM technique, only local mesh should be remeshed and it becomes easy to simulate crack growth. By combining with re-meshing technique, local mesh is re-meshed automatically, and curved crack path is modeled easily. Plural fatigue crack problem is solved by this technique. For two through crack problems, crack coalescence condition is proposed by JSME standard. By simulating this problem by S-FEM, it is shown that thid criterion depends on initial crack size. Then more than 160 cases are simulated by changing several parameters. Results are summarized by normalized form, and new criterion is proposed.

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