Fatigue of Stabilized SS and 316 NG Alloy in PWR Environment

2006 ◽  
Author(s):  
Jussi P. Solin
Keyword(s):  
Stainless Steels ◽  
Fatigue Tests ◽  
Test Results ◽  
Constant Amplitude ◽  
Low Oxygen ◽  
Variable Amplitude ◽  
Variable Amplitude Fatigue ◽  
Reduction Factors

Strain controlled constant and variable amplitude fatigue tests for 316NG and Titanium stabilized stainless steels in low oxygen PWR waters were performed. The stabilized steel has been plant aged for 100 000 hours. Constant amplitude test results at 0,01 Hz sinusoidal straining comply with predicted lives according to the Fen approach for both materials. Spectrum straining both in air and in environment caused predicted life reduction factors (about 3) for the stabilized steel, but for the 316NG steel spectrum straining in environment resulted to a larger reduction in life.

Corrosion Fatigue of AZ91E-T6 Cast Magnesium Alloy in a 3.5 Percent NaCl Aqueous Environment

1995 ◽  
Vol 117 (3) ◽  
pp. 293-298 ◽  
Author(s):  
R. I. Stephens ◽  
C. D. Schrader ◽  
K. B. Lease
Keyword(s):  
Fatigue Life ◽  
Magnesium Alloy ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Mean Stress ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Cast Magnesium Alloy ◽  
Cast Magnesium ◽  
Variable Amplitude Fatigue

The objective of this research was to obtain and compare constant and variable amplitude fatigue behavior of AZ91E-T6 cast magnesium alloy in both an air and 3.5 percent NaCl aqueous corrosive environment. An additional objective was to determine if commonly used models that describe fatigue behavior and fatigue life are applicable to this material and test environment. Fatigue tests included constant amplitude strain-controlled low cycle fatigue with strain ratio, R, equal to 0, −1 and −2, Region II constant amplitude fatigue crack growth with load ratio, R, equal to 0.05 and 0.5 and variable amplitude fatigue tests using keyhole notched specimens. In all fatigue tests, the corrosion environment was significantly detrimental relative to the air environment. Mean strains influenced fatigue life only if accompanied by significant mean stress. The Morrow and Smith, Watson, and Topper mean stress models provided both accurate and inaccurate fatigue life calculations. Likewise, variable amplitude fatigue life calculations using the local strain approach and based upon the formation ofal mm crack at the keyhole notch were both accurate and fairly inaccurate depending on the specific model used.

Variable Amplitude Fatigue in Relation to Highway Bridges

1980 ◽  
Vol 194 (1) ◽  
pp. 259-267 ◽  
Author(s):  
G. P. Tilly ◽  
D. E. Nunn
Keyword(s):  
Fatigue Limit ◽  
Interactive Effect ◽  
Highway Bridges ◽  
Constant Amplitude ◽  
Load Spectrum ◽  
Variable Amplitude ◽  
Load Spectra ◽  
Amplitude Data ◽  
Variable Amplitude Fatigue

With the introduction of welded construction in highway bridges it has become necessary to assess designs for fatigue. Current methods of calculating endurances involve constant amplitude data and assumption that the Palmgren-Miner law can be used to sum the damage caused by different stresses. In order to investigate the efficacy of this method laboratory tests have been conducted on representative welded connections using variable amplitude loading at endurances of up to 415 × 106 cycles. Using a Rayleigh spectrum of stresses it is shown that for endurances relevant to bridge service, the role of stresses below the constant amplitude fatigue limit is critically important. If they are ignored, calculated endurances can be many times too optimistic. An accurate allowance for the effects of low stresses can be made by representing the constant amplitude data by a curve having a higher stress exponent for stresses below the fatigue limit. At the longest endurance tested, only about 0.25 per cent of the stresses exceeded the fatigue limit and these caused 9 per cent of the calculated damage. Under an axle load spectrum, endurances were six times longer than calculated. This was found to be due to an interactive effect caused by small numbers of high stresses which effectively retard the rate of crack propagation. In practice, shapes of stress spectra differ from axle load spectra and situations in which measured stresses involve small numbers of high values are rare. In all cases, conservative endurances were estimated using the method given in the British Standard for bridge design.

Constant and Variable Amplitude Fatigue Behavior of Five Cast Steels at Room Temperature and −45°C

1984 ◽  
Vol 106 (1) ◽  
pp. 25-37 ◽  
Author(s):  
R. I. Stephens ◽  
J. H. Chung ◽  
A. Fatemi ◽  
H. W. Lee ◽  
S. G. Lee ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Room Temperature ◽  
Fatigue Behavior ◽  
Growth Behavior ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Cast Steels ◽  
Variable Amplitude Fatigue

A comprehensive fatigue program was undertaken at room temperature and −45°C (−50°F) for five representative carbon or low alloy cast steels. Constant amplitude low and high cycle axial fatigue behavior, cyclic stress-strain behavior, constant-amplitude fatigue-crack-growth behavior and variable-amplitude fatigue-crack-initiation and -growth behavior were determined. The fatigue resistance at low temperature was usually equal to or better than at room temperature except for one material under variable amplitude fatigue crack growth conditions. SEM analysis revealed similar fatigue crack growth mechanisms at both room and low temperature, even though some tests were well below the NDT temperature. Most fatigue resistance for the five cast steels was consistent with that for wrought steels. Fatigue test procedures generally developed with wrought steels were completely satisfactory for these cast steels.

scholarly journals Effects of variable amplitude loading on fatigue life

2015 ◽  
Vol 6 (3) ◽  
pp. 10 ◽  
Author(s):  
Niels Laseure ◽  
Ingmar Schepens ◽  
Nahuel Micone ◽  
Wim De Waele
Keyword(s):  
Offshore Structures ◽  
Fatigue Tests ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Industrial Sectors ◽  
Closure Mechanism ◽  
Physical Phenomena ◽  
Published Research ◽  
Variable Amplitude Fatigue ◽  
Plasticity Induced Crack Closure

This paper is a review of published research on variable amplitude loading of steels. The use of service spectra for different industrial sectors and specifically for offshore applications is first considered. Constant amplitude fatigue failure models are not representative for these applications. The JONSWAP spectrum shows potential to be used as service spectrum for offshore structures. Further investigation of variable amplitude fatigue is needed to get insight in the various phenomena linked to the variable amplitude. Observed trends in fatigue crack growth rate in variable amplitude fatigue tests on steels, such as the effects of overloads and underloads (occurring as single events, sequential events or block loadings), are discussed. Furthermore, suggestions of the underlying physical phenomena behind the load interaction effects due to variable amplitude loading are presented. It can be concluded that the plasticity induced crack closure mechanism is the most profound explanation for the acceleration effect in overloads and the retardation effect observed in underloads.

scholarly journals Experimental Study on Variable-Amplitude Fatigue of Welded Cross Plate-Hollow Sphere Joints in Grid Structures

2018 ◽  
Vol 2018 ◽  
pp. 1-15 ◽  
Author(s):  
Jin-Feng Jiao ◽  
Hong-Gang Lei ◽  
Y. Frank Chen
Keyword(s):  
Fatigue Life ◽  
Hollow Sphere ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Metallographic Analysis ◽  
Variable Load ◽  
Random Loading ◽  
Variable Amplitude ◽  
Different Types ◽  
Variable Amplitude Fatigue

The fatigue stress amplitude of the welded cross plate-hollow sphere joint (WCPHSJ) in a grid structure varies due to the random loading produced by suspending cranes. A total of 14 specimens considering three different types of WCPHSJs were prepared and tested using a specially designed test rig. Four typical loading conditions, “low-high,” “high-low,” “low-high-low,” and “high-low-high,” were first considered in the tests to investigate the fatigue behavior under variable load amplitudes, followed by metallographic analyses. The experimental and metallographic analysis results provide a fundamental understanding on the fatigue fracture form and fatigue mechanism of WCPHSJs. Based on the available data from constant-amplitude fatigue tests, the variable-amplitude fatigue life of the three types of WCPHSJs was estimated using the Miner rule and Corten-Dolan theory. Since both accumulative damage theories yield virtually same damaging results, the Miner rule is hence suggested to estimate the fatigue life of WCPHSJs.

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