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.

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.

CONSTANT AMPLITUDE SPECTRUM OF THREE COACHES TRAIN AND CYCLIC COUNTING ON PRESTRESSED CONCRETE SLEEPERS (PCS)

2015 ◽  
Vol 76 (11) ◽  
Author(s):  
Mohd Ikmal Fazlan R. ◽  
Sharul Nizam I. ◽  
Afidah A.B. ◽  
Siti Hawa H.
Keyword(s):  
Prestressed Concrete ◽  
Constant Amplitude ◽  
Counting Method ◽  
Loading Test ◽  
Freight Train ◽  
Variable Amplitude ◽  
Amplitude Data ◽  
Strain Data ◽  
Rainflow Cycle Counting ◽  
Current Loading

The raw strain data collected from Keretapi Tanah Melayu Berhad (KTMB) railway are in variable amplitude. This paper discovers how the variable amplitude data can be changed to the constant amplitude data. It is found that the raw strain data is not suitable for fatigue and strength testing on Prestressed Concrete Sleepers (PCS). Apart from that, the most suitable method in determining the numbers of cycles is Rainflow Cycle Counting Method. Through rainflow cycle counting method, the number of cycles is determined. The numbers of cycles are used to simplify the laboratory test such as fatigue and strength test for the PCS. The frequencies of dynamic loading test on the PCS are set based the numbers of cycles. The constant strain data are also converted into constant loading data using the relationship of stress-strain and loading-stress. Constant amplitude loading will again simplify the laboratory testing. The goal is to show that the designs used in PCS are appropriate based on current loading demand. Then, a comparison of constant amplitude data is made between different numbers of coaches and freight train. The maximum data from the comparison shows that the higher loadings are obtained from freight train.

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.

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.

Development of Fatigue Testing of Full-Scale Girth Welded Pipes Under Variable Amplitude Loading

2011 ◽  
Author(s):  
Yan-Hui Zhang ◽  
Stephen Maddox
Keyword(s):  
Fatigue Limit ◽  
Fatigue Damage ◽  
Fatigue Testing ◽  
Full Scale ◽  
Cumulative Damage ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Testing Procedures ◽  
Fatigue Design ◽  
Damage Rule

In service the great majority of structures and components are subjected to stresses of variable amplitude (VA). The fatigue design of welded joints in such structures is based on fatigue data obtained under constant amplitude loading, used in conjunction with a cumulative damage rule to estimate the damage introduced by cycles of varying magnitude in the service stress history. There are two major concerns with fatigue design of deepwater steel catenary risers (SCRs): the validity of cumulative damage rule and the damaging effect of stresses below the constant amplitude fatigue limit (CAFL). It is known that SCRs can experience very high numbers of low stress cycles due to vortex induced vibration (VIV) with the result that the choice of method for accounting for the fatigue damage due to stresses below the constant amplitude fatigue limit can be highly significant in terms of the estimated fatigue life. These two fundamental issues have been addressed in a recent group sponsored project. By successfully establishing a loading spectrum representative of that experienced by risers and developing the testing procedures for VA loading using the resonance testing rigs, the fatigue performance of full-scale girth welded pipes under VA loading were investigated. These loading spectra had the same peak/maximum stress histograms but different minimum stresses. Many tests lasted over 108 cycles to investigate the fatigue damage of small stresses in these spectra. This paper describes the development of the method by which fatigue testing of full-scale girth welded pipes under VA loading had been successfully performed.

Alternative Fatigue Lifetime Prediction Formulations for Variable-Amplitude Loading

2002 ◽  
Author(s):  
R. P. L. Nijssen ◽  
D. R. V. van Delft ◽  
A. M. van Wingerde
Keyword(s):  
Turbine Rotor ◽  
Rotor Blades ◽  
Lifetime Prediction ◽  
Constant Amplitude ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Amplitude Data ◽  
The Difference ◽  
Rainflow Counting ◽  
Sn Curve

Possible alternative fatigue formulations to predict lifetime under variable-amplitude loading are investigated. Test results of WISPER and WISPERX variable-amplitude tests on a material representative for wind turbine rotor blades are used. All fatigue calculations are performed using Rainflow counting of the WISPER(X) load histories and employing the Miner summation. The formulation of the SN-curve and the constant-life diagram are varied. Commonly, a log-log SN-curve is used in combination with a linear Goodman constant-life relation. However, in previous work, it was found that these formulations overestimate lifetime of specimens subjected to the variable-amplitude WISPER and WISPERX load histories. This previous work suggested that the SN-formulation be changed and also used an alternative constant-life formulation with parallel lines. These formulations and variations on them are investigated. Also, constant-amplitude data for R = 0.1 are included to construct an alternative constant-life diagram. Including R = 0.1 constant-amplitude data in the lifetime predictions for WISPER(X) seems to improve the accuracy of the calculation. The alternative constant-life formulation might remove the non-conservatism from the lifetime prediction and account for the difference in lifetime between WISPER and WISPERX.

Fatigue Life Prediction of Impacted Glass/Epoxy Composites under Variable Amplitude Loading

2004 ◽  
Vol 261-263 ◽  
pp. 1079-1084 ◽  
Author(s):  
Ki Weon Kang ◽  
Jong Kweon Kim
Keyword(s):  
Fatigue Life ◽  
Impact Damage ◽  
Fatigue Behavior ◽  
Equivalent Stress ◽  
Epoxy Composites ◽  
Constant Amplitude ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Amplitude Data ◽  
The Impact

This paper presents the fatigue behavior of plain-weave E-glass/epoxy composites with impact-induced damage under constant and variable amplitude loading. The constant amplitude fatigue life of the impacted composites can be identified through the prediction model, which was proposed on the carbon/epoxy laminates by authors. Also, the models are derived to calculate the equivalent stress of the composites under variable amplitude loading, considering the impact damage. These models allow fatigue data of the unimpacted and impacted composites under variable amplitude loading to be correlated with constant amplitude data of the unimpacted composites.

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