Accounting for Natural Crack Growth Shapes During Environmental Cracking

2012 ◽  
Author(s):  
Do-Jun Shim ◽  
Fredrick Brust ◽  
Gery Wilkowski
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Analysis ◽  
Structural Integrity ◽  
Oil And Gas ◽  
Gas Production ◽  
Oil And Gas Production ◽  
Growth Method

Environmental cracking, such as stress-corrosion cracking (SCC), is a significant issue for a variety of industries, such as those dealing with power generation — nuclear, oil and gas production, and pipeline transmission, etc. SCC is particularly of concern in that catastrophic failures can occur even at low applied stress levels (e.g., residual stress produced by welding). Thus, it is critical to evaluate the behavior of SCC for structural integrity assessments. In this paper, three different crack growth methods (i.e., idealized crack growth analysis, crack growth analysis using finite element alternating method; FEAM, and the natural crack growth method) are summarized. These methods all utilize the stress intensity factor for crack growth evaluations. Thus, these methods can be used for assessment of environmental cracking that is based on stress intensity factor. Various examples are shown in this paper to demonstrate the applicability of these methods. Comparisons of results obtained from different methods are also provided in this paper.

Study on Evaluation Accuracy Required for Stress Intensity Factor Solution

2013 ◽  
Author(s):  
Naoki Miura ◽  
Masaki Nagai ◽  
Masaki Shiratori
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Power Plants ◽  
Growth Analysis ◽  
Correction Factors ◽  
Evaluation Accuracy

Stress intensity factor solutions are often used as a dominant fracture mechanics parameter for fatigue crack growth analysis. In ASME Boiler and Pressure Vessel Code Section XI as well as JSME Rules on Fitness-for-Service for Nuclear Power Plants, fatigue crack growth is predicted on the basis of the stress intensity factor range. Stress intensity factor solutions are frequently provided by the correction factors, which are tabulated as the functions of structure and/or crack sizes. In this study, the effect of the variation of the correction factors on the crack growth analysis results was investigated for pipes with surface cracks. The evaluation accuracy required for the correction factors of the stress intensity factor solutions was then examined and recommended from the comparison with the necessary accuracy of the parameters used for the fatigue crack growth analysis.

Application of 3D Fracture Mechanics for Improved Crack Growth Predictions of Gas Turbine Components

2017 ◽  
Author(s):  
Kanwardeep S. Bhachu ◽  
Santosh B. Narasimhachary ◽  
Sachin R. Shinde ◽  
Phillip W. Gravett
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Gas Turbine ◽  
Crack Growth ◽  
Structural Integrity ◽  
Crack Arrest ◽  
3D Crack Growth ◽  
Mechanics Analysis

Fracture mechanics analysis is essential for demonstrating structural integrity of gas turbine components. Usually, analyses based on simpler 2D stress intensity solutions provide reasonable approximations of crack growth. However, in some cases, simpler 2D solutions are too-conservative and does not provide realistic crack growth predictions; often due to its inability to account for actual 3D geometry, and complex thermal-mechanical stress fields. In such cases, 3D fracture mechanics analysis provides extra fidelity to crack growth predictions due to increased accuracy of the stress intensity factor calculations. Improved fidelity often leads to benefits for gas turbine components by reducing design margins, improving engine efficiency, and decreasing life cycle costs. In this paper, the application of 3D fracture mechanics analysis on a gas turbine blade for predicting crack arrest is presented. A comparison of stress intensity factor values from 3D and 2D analysis is also shown. The 3D crack growth analysis was performed by using FRANC3D in conjunction with ANSYS.

Life Estimation of a Spur Gear With a Tooth Cracked at Fillet Region

1998 ◽  
Author(s):  
M. A. Sahir Arıkan ◽  
A. Ismail Tarhan ◽  
O. Selçuk Yahşi
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Cyclic Load ◽  
Growth Analysis ◽  
Spur Gear ◽  
Life Estimation ◽  
Variable Position ◽  
Face Width

Abstract A computer program is developed to find the dynamic tooth load variation, make growth analysis of the crack at tooth fillet region, and determine the life of a spur gear in terms of load cycles. Variable amplitude-variable position cyclic load on the tooth is found by using a model based on torsional vibrations of gears. Stress intensity factor is determined by assuming small, through face width cracks. Paris-Erdogan crack growth rate equation is used for crack growth analysis. Load interaction effects are taken into consideration by using Willenborg retardation model. Stress intensity factor variation is arranged by using range-pair range cycle counting method. Rack cutter tip fillet radius and rack cutter geometry are taken into consideration in tooth modeling and rack cutters standardized by ISO are used for the analysis. Finite element method is used to find tooth stifnesses. Bending deformations of gear bodies and supporting shafts, bearing deformations, torsional deformations of gear bodies, and contact deformations of teeth are included in stiffness calculations.

Research on Simplified Method of Transients Combining and Loading in Fatigue Crack Growth Analysis of Carbon Steel Nuclear Piping

2018 ◽  
Author(s):  
Zhenshun Liu ◽  
Hongdong Zhen
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Carbon Steel ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Analysis ◽  
Analysis Method ◽  
Simplified Analysis

The fatigue crack growth analysis of nuclear piping is a nonlinear calculation process. The loading sequence and combination mode could affect the results. How to consider these effects is unclear. Fatigue crack growth analysis includes a large number of nonlinear iterative calculations, and the calculation speed is slow. This paper selects carbon steel nuclear piping as the research object. Based on the analysis process provided by ASME code XI volume, a simplified analysis method is explored by introducing the reference crack depth a’ and the envelope transient. The simplified analysis method is conservative because it has been proved that the crack growth rate is positively related to the crack size only if the maximum stress intensity factor is greater than 0 and the minimum stress intensity factor is less than 0. The simplified analysis method is proved to be able to significantly improve the calculation speed by comparing the number of iterative calculations in the simplified analysis method and in the conventional analysis method. The results indicate that the simplified analysis method could provide a conservative way of loading and combining the complex transients and could significantly reduce the number of nonlinear iterative calculations in the process of crack fatigue growth analysis for carbon steel nuclear piping when the maximum stress intensity factor greater than 0 and the minimum stress intensity factor is less than 0.

The Effect of Crack Shape Idealisation on Leak-Before-Break Assessment

2016 ◽  
Author(s):  
Renaud Bourga ◽  
Bin Wang ◽  
Philippa Moore ◽  
Yin Jin Janin
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Crack Front ◽  
Structural Integrity ◽  
Crack Opening ◽  
Integrity Assessment ◽  
Crack Shape ◽  
Leak Before Break

Based on detailed 3D finite element (FE) analyses, idealized and non-idealized axial through-wall flaws were evaluated in a cylinder under internal pressure. The key parameters (Stress Intensity Factor, Reference stress, and Crack Opening Area) from widely accepted structural integrity assessment procedures (BS 7910 and API 579-1/ASME FFS-1) were explored and compared between idealized (perpendicular straight-sided flaw) and non-idealized geometry. The effect of crack shape on the evolution of stress intensity factors and crack opening areas along the crack front were also investigated. Non-idealized crack shapes have been modelled assuming a straight crack front with different internal and external crack lengths. The influence of crack shape has been evaluated by varying the crack front location and lengths ratios. The current findings highlight the significance of assessing a more realistic crack shape and should be considered in a leak-before-break (LBB) analysis. A non-idealized crack has a significantly smaller crack opening area than the equivalent idealized through-wall crack. Therefore the leakage rate at this stage of crack growth will be lower than predicted by standard solutions. Stress intensity factor solutions should also take the crack shape variation into account with regards to fatigue crack growth as a surface flaw propagates through-thickness.

Crack Growth in Stainless Steel 304 under Creep-Fatigue Loading

2007 ◽  
Vol 353-358 ◽  
pp. 485-490 ◽  
Author(s):  
Y.M. Baik ◽  
K.S. Kim
Keyword(s):  
Stress Intensity Factor ◽  
Stainless Steel ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Rates ◽  
Static Loading ◽  
Fatigue Loading ◽  
Creep Fatigue ◽  
Crack Growth Rates

Crack growth in compact specimens of type 304 stainless steel is studied at 538oC. Loading conditions include pure fatigue loading, static loading and fatigue loading with hold time. Crack growth rates are correlated with the stress intensity factor. A finite element analysis is performed to understand the crack tip field under creep-fatigue loading. It is found that fatigue loading interrupts stress relaxation around the crack tip and cause stress reinstatement, thereby accelerating crack growth compared with pure static loading. An effort is made to model crack growth rates under combined influence of creep and fatigue loading. The correlation with the stress intensity factor is found better when da/dt is used instead of da/dN. Both the linear summation rule and the dominant damage rule overestimate crack growth rates under creep-fatigue loading. A model is proposed to better correlate crack growth rates under creep-fatigue loading: 1 c f da da da dt dt dt Ψ −Ψ     =         , where Ψ is an exponent determined from damage under pure fatigue loading and pure creep loading. This model correlates crack growth rates for relatively small loads and low stress intensity factors. However, correlation becomes poor as the crack growth rate becomes large under a high level of load.

Slow Crack Growth in Glasses and Ceramics Under Residual and Applied Stresses

1989 ◽  
Vol 111 (1) ◽  
pp. 61-67 ◽  
Author(s):  
F. Erdogan
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Residual Stresses ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Threshold Value ◽  
Crack Arrest ◽  
Growing Crack ◽  
Applied Stresses

The problem of slow crack growth under residual stresses and externally applied loads in plates is considered. Even though the technique developed to treat the problem is quite general, in the solution given it is assumed that the plate contains a surface crack and the residual stresses are compressive near and at the surfaces and tensile in the interior. The crack would start growing subcritically when the stress intensity factor exceeds a threshold value. Initially the crack faces near the plate surface would remain closed. A crack-contact problem would, therefore, have to be solved to calculate the stress intensity factor. Depending on the relative magnitudes of the residual and applied stresses and the threshold and critical stress intensity factors, the subcritically growing crack would either be arrested or become unstable. The problem is solved and examples showing the time to crack arrest or failure are discussed.

Effect of Temperature on Fatigue Crack Growth in CPVC

2003 ◽  
Vol 125 (1) ◽  
pp. 71-77 ◽  
Author(s):  
Muhammad Irfan-ul-Haq ◽  
Nesar Merah
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Effect Of Temperature ◽  
Stress Intensity Factor Range ◽  
Crack Growth Behavior ◽  
Different Temperatures

This study addresses the effect of temperature on fatigue crack growth (FCG) behavior of CPVC. FCG tests were conducted on CPVC SEN tensile specimens in the temperature range −10 to 70°C. These specimens were prepared from 4-in. injection-molded pipe fittings. Crack growth behavior was studied using LEFM concepts. The stress intensity factor was modified to include the crack closure and plastic zone effects. The effective stress intensity factor range ΔKeff gave satisfactory correlation of crack growth rate (da/dN) at all temperatures of interest. The crack growth resistance was found to decrease with temperature increase. The effect of temperature on da/dN was investigated by considering the variation of mechanical properties with temperature. Master curves were developed by normalizing ΔKeff by fracture strain and yield stress. All the da/dN-ΔK curves at different temperatures were collapsed on a single curve. Crazing was found to be the dominant fatigue mechanism, especially at high temperature, while shear yielding was the dominant mechanism at low temperatures.

Mechanisms of Fatigue Crack Growth in WC-Co Cemented Carbides

2005 ◽  
Vol 297-300 ◽  
pp. 1120-1125 ◽  
Author(s):  
Myung Hwan Boo ◽  
Chi Yong Park
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Stress Ratio ◽  
Cemented Carbides ◽  
Stress Intensity Factor Range

In order to study the influence of stress ratio and WC grain size, the characteristics of fatigue crack growth were investigated in WC-Co cemented carbides with two different grain sizes of 3 and 6 µm. Fatigue crack growth tests were carried out over a wide range of fatigue crack growth rates covering the threshold stress intensity factor range DKth. It was found that crack growth rate da/dN against stress intensity factor range DK depended on stress ratio R. The crack growth rate plotted in terms of effective stress intensity factor range DKeff still exhibited the effect of microstructure. Fractographic examination revealed brittle fracture at R=0.1 and ductile fracture at R=0.5 in Co binder phase. The amount of Co phase transformation for stress ratio was closely related to fatigue crack growth characteristics.

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