Comments on fatigue crack growth models

1987 ◽  
Vol 18 (1) ◽  
pp. 57-60 ◽  
Author(s):  
Martin Newby
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Models

Effective Modeling of Fatigue Crack Growth in Pipelines

2012 ◽  
Author(s):  
Steven J. Polasik ◽  
Carl E. Jaske
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Growth Models ◽  
Critical Parameters ◽  
Operating Pressure ◽  
Mechanics Model ◽  
Key Variables

Pipeline operators must rely on fatigue crack growth models to evaluate the effects of operating pressure acting on flaws within the longitudinal seam to set re-assessment intervals. In most cases, many of the critical parameters in these models are unknown and must be assumed. As such, estimated remaining lives can be overly conservative, potentially leading to unrealistic and short reassessment intervals. This paper describes the fatigue crack growth methodology utilized by Det Norske Veritas (USA), Inc. (DNV), which is based on established fracture mechanics principles. DNV uses the fracture mechanics model in CorLAS™ to calculate stress intensity factors using the elastic portion of the J-integral for either an elliptically or rectangularly shaped surface crack profile. Various correction factors are used to account for key variables, such as strain hardening rate and bulging. The validity of the stress intensity factor calculations utilized and the effect of modifying some key parameters are discussed and demonstrated against available data from the published literature.

Evaluations of some Stochastic Fatigue Crack Growth Models through Experimental Verification

2018 ◽  
Vol 928 ◽  
pp. 221-228
Author(s):  
Chih Chung Ni
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Growth Models ◽  
Random Factor ◽  
Normal Probability ◽  
Log Normal

The study is focused on the comparisons among three stochastic fatigue crack growth models through evaluations of experimental data. The first model assumed that the coefficient and exponent parameters of Paris-Erdogan law are mutually dependent normal random variables. The second model assumed that the fatigue crack growth rate equals to the deterministic Paris-Erdogan law multiplied by a stationary log-normal random factor while the third model proposed by the author was assumed that the fatigue crack growth rate equals to a deterministic polynomial in terms of fatigue crack size multiplied by a stationary log-normal random factor. Compact-tension specimens cut from a 2024-T351 aluminum-alloy plate were used for fatigue crack growth experiments under constant loads performed on thirty specimens. The normal probability paper for the first model was investigated to show the validity of the normal random parameter, and the log-normal probability papers for the second and third models were also investigated to show the validity of log-normal assumption of the random factors. The investigations on the probability of crack exceedance and distribution of random time of the three models were also made, and the comparisons of the results for all models were made as well.

Simulation and Experimental Analysis of Fatigue Crack Growth under Cyclic Loading

2011 ◽  
Vol 462-463 ◽  
pp. 501-505
Author(s):  
S.M. Beden ◽  
Shahrum Abdullah ◽  
Ahmad Kamal Ariffin ◽  
N.A. Al-Asady
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Growth Models ◽  
Rate Data ◽  
Structural Elements ◽  
Structural Element

The problem of crack growth is a major issue in the prediction and maintenance of engineering structural elements. Prediction of expected life of a structural element due to constant (static) and alternating loading (fatigue) is of major concern to the designers. Prediction of remaining life of the structural elements influences the decisions of maintenance engineers (checking intervals, corrections, and replacements).The fatigue crack growth rate, which determine the fatigue life of the components after crack initiation need to be experimentally and theoretically investigated. In this study, fatigue crack growth tests were conducted under constant amplitude loading at a stress ratio of 0.1, using three-point bend (TPB) specimens of ASTM A533 steel material. For the simulation part of this study, three fatigue crack growth models, i.e. the Paris, modified Forman and Austen were examined. None of the models has a fit for the fatigue crack growth rate data in a similar behaviour compared to others. The modified Forman model provided a closer fit than the Paris model with respect to the experimental results. However, the Austen model provided the best fit to the fatigue crack growth rate data as compared with the other two models. Therefore, this model is suggested for use in critical applications.

Observing Load Sequence Effects on Simulated and Experimental Fatigue Crack Growth Occurrence

2011 ◽  
Vol 462-463 ◽  
pp. 489-494 ◽  
Author(s):  
S.M. Beden ◽  
Shahrum Abdullah ◽  
Ahmad Kamal Ariffin ◽  
Nawar A. Kadhim
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Test Data ◽  
Growth Models ◽  
Load Cycle ◽  
Engineering Structures ◽  
Variable Amplitude Loading ◽  
Variable Amplitude

Load cycle interactions can have a significant effect in fatigue crack growth (FCG) under variable amplitude loading. Studying of FCG and fatigue life calculation under spectrum loading is important for the reliable life prediction of engineering structures. Many models have been proposed, but yet no universal model exists. In this paper, a fatigue life predicted under various load spectra, using three different fatigue crack growth models namely, the Austen, modified Forman and NASGRO models. These models are validated with fatigue crack growth test data under various amplitude loadings. This application is performed with aids of three-point bend specimens of ASTM A533 steel material. The results clearly show the load sequences effect and the predicted results agree with some discrepancies between the different models as well as with the test data. Thus, neglecting the effect of cycle interaction in fatigue calculations under variable amplitude loading can lead to invalid life predictions.

Evaluations of Stochastic Fatigue Crack Growth Models through Experimental Data

2016 ◽  
Vol 878 ◽  
pp. 132-136
Author(s):  
C.C. Ni
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Models ◽  
Compact Tension ◽  
Random Factor ◽  
Alloy Plate ◽  
Deterministic Function ◽  
Log Normal

The study is focused on the comparisons between a polynomial and power-law stochastic fatigue crack growth models through evaluations of experimental data. Both models were assumed that the fatigue crack growth rate equals to a deterministic function in terms of fatigue crack size multiplied by a stationary log-normal random factor. Compact-tension specimens cut from a 2024-T351 aluminum-alloy plate were used for fatigue crack growth experiments under random loads performed on twenty-five specimens. The log-normal probability papers for both models were investigated to show the validity of the log-normal assumption of the random factor . The investigations on the probability of crack exceedance and distribution of random time of the two models were also made, and the comparisons of the results for both models were made as well.

Probabilistic Fatigue Crack Growth Analysis for Life Prediction of Automotive Components

2013 ◽  
Author(s):  
Mahboubeh Yazdanipour ◽  
Mohammad Pourgol-Mohammad ◽  
Naghd-Ali Choupani ◽  
Mojtaba Yazdani
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Probabilistic Models ◽  
Growth Models ◽  
Fatigue Loading ◽  
Deterministic Models ◽  
Propagation Of Uncertainty ◽  
Automotive Parts ◽  
Crack Growth Model

This research focuses on investigating the probabilistic fatigue crack growth models on W319 aluminum alloy which has vast applications in automotive parts products. The aim of this study is to determine the crack growth rate probabilistically and quantification of uncertainty of probabilistic models on estimation of damages (crack length) versus life (number of cycles) under fatigue loading in automotive parts. The models used in this paper include Walker and Forman correlations. The deterministic forms of these models are verified with AFGROW code and validated experimentally with fatigue data of W319 aluminum. After verifying the accuracy of deterministic models, the models are treated probabilistically by considering the models’ parameters stochastic. Monte Carlo simulation is devised to investigate the models under stochastic conditions by drawing samples from these random variables. Finally the propagation of uncertainty is quantified by calculating standard deviations of crack lengths through propagation of the uncertainties via cycles. The results are useful for selecting a proper probabilistic fatigue crack growth model in specific applications and can be used in future studies in automotive industry to obtain more accurate and reliable conclusions.

scholarly journals Fatigue Growth Models for Multiple Long Cracks in Plates under Cyclic Tension Based on ΔKI, ΔJ-Integral and ΔCTOD Parameter

2011 ◽  
Vol 488-489 ◽  
pp. 525-528 ◽  
Author(s):  
Željko Božić ◽  
Siegfried Schmauder ◽  
Marijo Mlikota
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Steel Plate ◽  
Growth Models ◽  
Fatigue Tests ◽  
Collinear Cracks ◽  
Cyclic Tension ◽  
Multiple Site Damage

This paper presents the implementation of fatigue crack growth power law equations based on ΔK,ΔJ-integral andΔCTODfracture mechanics parameters determined in an FE analysis, to plates with multiple site damage (MSD). Results of fatigue tests with constant amplitude tensile loading carried out on mild steel plate specimens damaged with a single central crack and with three collinear cracks are presented. A relatively larger plastic zone occurred in the crack tip region at higher fatigue crack growth rate (FCGR), from 10-7to 10-6m/cycle. The crack growth models based on the elastic-plastic fracture mechanics (EPFM) parameters describe better fatigue crack growth in this range as compared to the liner elastic models.

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