Comparison of Peak Stress-Based and Flaw Tolerance-Based Fatigue Analysis of a Cylinder With Variable Stress Concentrations

2014 ◽  
Author(s):  
Wolf Reinhardt ◽  
Gary L. Stevens
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Growth Analysis ◽  
Notch Root ◽  
Stress Gradient ◽  
Fatigue Curve ◽  
Fatigue Analysis ◽  
Stress Concentrations ◽  
Notch Radius ◽  
Flaw Tolerance

To show the implications of using crack growth analysis to evaluate fatigue life, the case of a cylinder with an internal notch with a varying root radius is examined. The notch radius controls the stress gradient, where a steeper stress gradient is expected to result in slower crack growth and longer fatigue life. The notch root stress is made the same between specimens of different notch radius by scaling the applied load. As a result, the conventional fatigue analysis that calculates a fatigue usage factor from a fatigue curve based on stress at a point gives identical results for all specimens. A crack growth analysis, on the other hand, gives significantly different fatigue lives for the specimens because of the different stress gradients. On this basis of allowable fatigue life, the traditional fatigue curve-based approach is compared with the crack growth-based flaw tolerance approach. The relative conservatism of the two approaches as a function of various parameters, including stress gradient, is discussed.

Flaw Tolerance Assessment for Low-Cycle Fatigue of Stainless Steel

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Fatigue Life ◽  
Intensity Factor ◽  
Crack Growth ◽  
Loading Condition ◽  
Low Cycle Fatigue ◽  
Fatigue Curve ◽  
Fatigue Tests ◽  
Strain Intensity ◽  
Cycle Fatigue ◽  
Flaw Tolerance

According to Appendix L of the Boiler and Pressure Vessel Code Section XI, flaw tolerance assessment is performed using the stress intensity factor (SIF) even for low-cycle fatigue. On the other hand, in Section III, the fatigue damage is assessed using the design fatigue curve (DFC), which has been determined from strain-based fatigue tests. Namely, the stress is used for the flaw tolerance assessment. In order to resolve this inconsistency, in the present study, the strain intensity factor was used for crack growth prediction. First, it was shown that the strain range was the key parameter for predicting the fatigue life and crack growth. The crack growth rates correlated well with the strain intensity factor even for the low-cycle fatigue. Then, the strain intensity factor was applied to predict the crack growth under uniform and thermal cyclic loading conditions. The estimated fatigue life for the uniform cyclic loading condition agreed well with that obtained by the low-cycle fatigue tests, while the fatigue life estimated for the cyclic thermal loading condition was longer. It was shown that the inspection result of “no crack” can be reflected to determining the future inspection time by applying the flaw tolerance analysis. It was concluded that the flaw tolerance concept is applicable not only to the plant maintenance but also to plant design. The fatigue damage assessment using the design fatigue curve can be replaced with the crack growth prediction.

Environmental Effect on Fatigue Crack Initiation and Growth of Stainless Steel for Flaw Tolerance Assessment

2016 ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Growth ◽  
Correction Factor ◽  
Stress Gradient ◽  
Water Environment ◽  
Pressurized Water ◽  
Flaw Tolerance ◽  
Fatigue Life Reduction

Fatigue life can be divided into cycles of crack initiation and those in which the initiated crack grows to macroscopic size. In crack growth analysis, it is possible to consider the effect of the strain or stress gradient in the depth direction on the fatigue life. Therefore, flaw tolerance assessments allow reasonable fatigue life prediction. The fatigue life is reduced in the primary water environment of pressurized water reactor (PWR) nuclear power plants, and the correction factor Fen is used for considering the fatigue life reduction in fatigue damage assessments. To apply the flaw tolerance concept to a PWR water environment, the correction factor must be applied not to the fatigue life but to the number of cycles for crack growth. In this study, the fatigue life reduction in the PWR environment was correlated to the crack growth acceleration for a flaw tolerance assessment. The crack growth rates were obtained from fatigue life tests and crack growth tests performed in the PWR environment using Type 316 stainless steel. Then, the fatigue life was estimated by predicting the crack growth from an initial depth of 20 μm. It was concluded that a reasonable flaw tolerance assessment can be performed by using the strain intensity factor. The fatigue life reduction was successfully replaced with the crack growth acceleration.

Flaw Tolerance Assessment for Low-Cycle Fatigue of Stainless Steel

2015 ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Fatigue Life ◽  
Intensity Factor ◽  
Crack Growth ◽  
Loading Condition ◽  
Low Cycle Fatigue ◽  
Fatigue Curve ◽  
Fatigue Tests ◽  
Strain Intensity ◽  
Cycle Fatigue ◽  
Flaw Tolerance

According to Appendix L of the BPVC Section XI, flaw tolerance assessment is performed using the stress intensity factor even for low-cycle fatigue. On the other hand, in Section III, the fatigue damage is assessed using the design fatigue curve, which has been determined from strain-based fatigue tests. Namely, the stress is used for the flaw tolerance assessment, whereas the strain (Ke factor) is quoted for the design. In order to resolve this inconsistency, in the present study, the strain intensity factor was used for crack growth prediction. First, it was shown that the strain range was the key parameter for predicting the fatigue life and crack growth. The crack growth rates correlated well with the strain intensity factor even for the low-cycle fatigue. Then, the strain intensity factor was applied to predict the crack growth under uniform and thermal cyclic loading conditions. The estimated fatigue life for the uniform cyclic loading condition agreed well with that obtained by the low-cycle fatigue tests, while the fatigue life estimated for the cyclic thermal loading condition was longer. It was shown that the inspection result of “no crack” can be reflected to determining the future inspection time by applying the flaw tolerance analysis. It was concluded that the flaw tolerance concept is applicable not only to the plant maintenance but also to plant design. The fatigue damage assessment using the design fatigue curve can be replaced with the crack growth prediction.

The Use of Strain Energy and Fracture Correlation to Determine Life Expectancy for Notched Components

2009 ◽  
Author(s):  
Onome Scott-Emuakpor ◽  
Tommy George ◽  
Charles Cross ◽  
M.-H. Herman Shen
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Cross Section ◽  
Strain Energy ◽  
Notch Root ◽  
Stress Gradient ◽  
Strain Curve ◽  
Experimental Results ◽  
Cyclic Process ◽  
Notched Components

An energy-based method for predicting fatigue life of half-circle notched specimens, based on the nominal applied stress amplitude, has been developed. This developed method is based on the understanding that the total strain energy dissipated during a monotonic fracture and a cyclic process is the same material property, where the density of each can be determined by measuring the area underneath the monotonic true stress-strain curve and measuring the sum of the area within each Hysteresis loop in the cyclic process, respectively. Using this understanding, the criterion for determining fatigue life prediction of half-circle notched components is constructed by incorporating the stress gradient effect through the notch root cross-section. Though fatigue at a notch root is a local phenomenon, evaluation of the stress gradient through the notch root cross-section is essential for incorporating this method into finite element analysis minimum potential energy process. The validation of this method was carried out by comparison with both notched and unnnotched experimental fatigue life of Aluminum 6061-T6 (Al 6061-T6) specimens under tension/compression loading at the theoretical notch fatigue stress concentration factor of 1.75. The comparison initially showed a slight deviation between prediction and experimental results. This led to the analysis of strain energy density per cycle up to failure, and an improved Hysteresis representation for the energy-based prediction analysis. With the newly developed Hysteresis representation, the energy-based prediction comparison shows encouraging agreement with unnotched experimental results and a theoretical notch stress concentration value.

A Flaw Tolerance Concept for Plant Maintenance Using Virtual Fatigue Crack Growth Curve

2013 ◽  
Author(s):  
Masayuki Kamaya ◽  
Takao Nakamura
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Curve ◽  
Growth Behavior ◽  
Plant Design ◽  
Flaw Tolerance ◽  
Plant Maintenance ◽  
Crack Growth Curve

Incorporation of the flaw tolerance concept in plant design and maintenance is discussed in order to consider the reduction in fatigue life due to the high-temperature water environment of class 1 components of NPPs. The flaw tolerance concept has been included in Section XI of the ASME BPVC. The structural factor (safety factor) for the flaw evaluation is considered in the stress, whereas it was considered in the design fatigue curve in Section III of the ASME BPVC. In order to apply the flaw tolerance concept to plant design and maintenance, it is necessary to assume the crack initiation and growth behavior. In this study, first, crack initiation and growth behavior during fatigue tests was reviewed and a relationship between the crack growth and fatigue life was quantified. Then, the safety factor was considered in the crack growth curve. It was shown that the crack size could be correlated to the usage factor and the flaw tolerance concept was reasonably considered in the plant maintenance by using the proposed virtual fatigue crack growth curve.

scholarly journals Fatigue Life Prediction Based on Crack Growth Analysis Using an Equivalent Initial Flaw Size Model: Application to a Notched Geometry

2015 ◽  
Vol 114 ◽  
pp. 730-737 ◽  
Author(s):  
A.S.F. Alves ◽  
L.M.C.M.V. Sampayo ◽  
J.A.F.O. Correia ◽  
A.M.P. De Jesus ◽  
P.M.G.P. Moreira ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Life Prediction ◽  
Growth Analysis ◽  
Flaw Size ◽  
Fatigue Life Prediction ◽  
Model Application ◽  
Size Model

Constraint Effects on the Prediction of Fatigue Life of Surface Flaws

1983 ◽  
Vol 105 (3) ◽  
pp. 215-218 ◽  
Author(s):  
M. Jolles
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Stress Field ◽  
Crack Growth ◽  
Crack Closure ◽  
Growth Analysis ◽  
Crack Shape ◽  
Surface Flaws ◽  
Constraint Effects

The effects of the variation of stress field triaxiality on the prediction of the fatigue growth of semielliptic surface flaws are investigated. The concepts of crack closure are used in a fatigue growth analysis to account for constraint variation. The analysis, together with a traditional fatigue crack growth analysis which does not account for constraint variation, is used to predict flaw growth observed in experiments. Significant improvements in predicted fatigue life, as well as predicted crack shape, are obtained by accounting for the variation in constraint.

Development of New Design Fatigue Curves in Japan: Discussion of Crack Growth Behavior in Large-Scale Fatigue Tests of Carbon and Low-Alloy Steel Plates

2019 ◽  
Author(s):  
Masahiro Takanashi ◽  
Hiroshi Ueda ◽  
Toshiyuki Saito ◽  
Takuya Ogawa ◽  
Kentaro Hayashi
Keyword(s):  
Fatigue Life ◽  
Size Effect ◽  
Large Scale ◽  
Fatigue Cracks ◽  
Stress Gradient ◽  
Fatigue Curve ◽  
Fatigue Tests ◽  
Steel Plates ◽  
Low Alloy Steel ◽  
Deep Crack

Abstract In Japan, the Design Fatigue Curve (DFC) Phase 1 and Phase 2 subcommittees, which are a part of the Atomic Energy Research Committee of the Japan Welding Engineering Society, have proposed new design fatigue curves and fatigue analysis methods for carbon, low-alloy, and austenitic stainless steels. To confirm the validity of the proposed design fatigue curves, a Japanese utility collaborative project was launched, and the authors conducted fully reversed four-point bending fatigue tests for large-scale specimens of carbon steel and low-alloy steel plates. Subsequently, in a previous paper (PVP2018-84456), the authors reported that the fatigue lives determined by the best-fit curve proposed by the DFC subcommittee corresponded to those of approximately 1.5–7.0-mm-deep crack initiation in large-scale specimens. In this study, the fatigue crack initiation and propagation behavior observed in large-scale specimens was investigated by using a plastic replica and beach mark method. Similar to the case of small-sized specimens, in the large-scale specimens, multiple fatigue cracks initiated at an early stage of testing, and propagated with coalescence to penetrate the specimen width. However, no fatigue cracks were detected at the design fatigue life. Approximately 100-μm-long cracks were observed, albeit only after the specimen was subjected to a number of cycles that corresponded to approximately 3.5 times the design fatigue life. According to NUREG/CR-6909 Rev.1, the crack depths in small-sized round bar specimens at the fatigue lives, which are defined by 25%-stress-drop cycles, are reported to be approximately 3 mm. The results of the large-scale tests indicated that regardless of the specimen size, nearly the same phenomenon occurred on the specimen surface until approximately 3–4-mm-deep crack initiated. The size effect was mainly caused by the stress gradient. The finite element analysis indicated that the stress gradient in the large-scale specimen was gentle owing to the large thickness of the specimen, and the stress in the vicinity of the surface was considered to be uniform. In conclusion, the size effect was not apparent. As the same conclusion can be applied to considerably larger actual components, designers do not need to consider the size effect when designing pressure vessels or piping by using the design fatigue curve determined based on small-sized specimens.

Virtual Testing for Fracture Toughness, Fatigue Crack Growth and Fatigue Life Data Estimation of Metallic Components

2013 ◽  
Vol 577-578 ◽  
pp. 177-180
Author(s):  
Michele Pettinà ◽  
Bahram Farahmand ◽  
Filippo Berto ◽  
Frank Abdi
Keyword(s):  
Fracture Toughness ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Strain Curve ◽  
Stress Concentrations ◽  
Damage And Fracture ◽  
Data Estimation ◽  
Total Life

Evaluating fracture and fatigue life properties of structural components involves tests that are costly and time consuming. To estimate total life of engineering parts, high cycle fatigue data (S-N) for the material under study is needed. In many cases the S-N data is not available to the analyst and both the time and budget required for testing prevent engineers to meet the deadline imposed on the program. An analytical combined Progressive Damage and Fracture Mechanics based approach is proposed that estimates the S-N data for components that have stress concentrations. The proposed methodology starts from a full engineering tensile stress-strain curve of the material under study and ends up with the estimation of fracture toughness, fatigue crack growth and fatigue S-N curves.

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