EXPLORATION OF CUMULATIVE DAMAGE EVOLUTION UNDER VARIABLE AMPLITUDE FATIGUE LOADING BASED ON WÖHLER CURVE

2021 ◽  
Author(s):  
RUI MIRANDA GUEDES
Keyword(s):  
Polymer Matrix Composites ◽  
Research Work ◽  
Fatigue Loading ◽  
Cumulative Damage ◽  
Damage Functions ◽  
Simple Assumption ◽  
Variable Amplitude ◽  
Stress Levels ◽  
Miner’S Rule ◽  
Miner's Rule

How to predict the residual strength of polymer matrix composites (PMCs) after a fatigue cycle at multiple stress levels, based on the fatigue or Wöhler (S-N) curves, remains unsatisfactorily tackled. The Miner’s Rule is a widespread example of a simple way to account for damage accumulation under different fatigue cycles. Under certain combinations of stress levels, Miner’s Rule accurately predicts the lifetime of PMCs, but it fails in other cases. The reason is the simple assumption of linear cumulative damage, not accounting for sequence effects in the loading history. Several researchers have proposed modifications to Miner’s Rule. However, due to its simplicity, Miner’s Rule is still used by structural designers. Recent research work proposed compatibility conditions for fatigue damage functions in the S–N plane, leading to a simple model that fulfils those conditions contrary to the previous models, the Miner’s Rule and the Broutman and Sahu linear model. These models predict fatigue life at variable amplitude loading based on constant amplitude fatigue data. Forcibly, the analytical form of SıN influences the model lifetime predictions. Experimental data obtained in the literature serves to illustrate the models' predictions at different loading conditions. Although this work focused on composite materials, we foresaw extension to other materials.

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

2012 ◽  
Author(s):  
Y.-H. Zhang ◽  
S. J. Maddox
Keyword(s):  
Fatigue Limit ◽  
Fatigue Damage ◽  
Fatigue Testing ◽  
Full Scale ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Fatigue Design ◽  
Miner’S Rule ◽  
Miner's Rule ◽  
Loading Spectrum

In the fatigue design of steel catenary risers there are concerns regarding the fatigue damage to girth welds from low stresses, below the constant amplitude fatigue limit, in the loading spectrum and the validity of Miner’s cumulative damage rule. In both cases there is increasing evidence that current design methods can be non-conservative. These fundamental issues were addressed in a recent JIP. A key feature was development of the resonance fatigue testing rigs to enable them to test full-scale pipes under variable amplitude loading. Such tests were performed under a loading spectrum representative of that experienced by some risers, with many tests lasting over 100 million cycles to investigate the fatigue damage due to small stresses as well as the validity of Miner’s rule. However, the resonance rigs are only capable of producing spectrum loading by gradually increasing or decreasing the applied load, whereas more ‘spiky’ random load sequences may be relevant in practice. Therefore the programme also included fatigue tests in conventional testing machines on strip specimens cut from pipes to compare the two types of loading sequence. This paper presents the results of these tests, conclusions drawn and recommendations for changes to current fatigue design guidance for girth welded pipes regarding the definition of the fatigue limit, allowance for the damaging effect of low stresses and the validity of Miner’s rule.

Fatigue Design of Machine Elements Under Cumulative Damage Effect, Using Bagci’s Fatigue Failure Surface Line

1984 ◽  
Vol 106 (4) ◽  
pp. 466-475
Author(s):  
C. Bagci
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Material Properties ◽  
Cumulative Damage ◽  
Damage Effect ◽  
Stress Effect ◽  
Mean Stress ◽  
Fatigue Design ◽  
Miner’S Rule ◽  
Miner's Rule

A thorough review of the state-of-the-art of determining fatigue life of machine and structural members considering cumulative damage effect under varying stress amplitudes is given. Among the many proposed theories, Miner’s linear damage rule is seen to be as reliable as any other rule alleged to be an improvement for predicting fatigue life under cumulative damage effects. Its simplicity and amenability for easy modification have in fact been the basis for some other theories and used in design codes. In its original form, Miner’s rule, however does not account for fatigue strength reducing factors. Observing fatigue data on the effects of fatigue strength reducing factors, the article offers a modified form of the Miner’s rule to consider the effects of fatigue strength reducing factors, such as the notch, reliability, surface finish, size, and environmental factors. The mean stress effect and material properties are incorporated utilizing Bagci’s mean stress line and the S-N diagram. The safe fatigue life of a component subjected to stresses of varying magnitudes becomes Ns=df/∑i=1s(αi/10zi) where zi=A{B−log(pig/Rf)+log[1−(pi/mi)r]} in the ith block of stress range, Rf being the resultant of fatigue strength reducing factors; A, B, g are parameters defined by material properties, pi is the ratio of the basic alternating stress times the factor of safety (the failure value) to the yield strength of the material, and mi is the slope of the load line in the ith block of loading. Design charts for zi for steel and aluminum alloys for cases with and without basic mean stress for r=4 are given. Numerical examples are included. Therefore, the article offers the most general form of the Miner’s rule for designers’ use for fatigue design considering cumulative damage effect.

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

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Y.-H. Zhang ◽  
S. J. Maddox
Keyword(s):  
Fatigue Limit ◽  
Fatigue Damage ◽  
Fatigue Testing ◽  
Full Scale ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Fatigue Design ◽  
Miner’S Rule ◽  
Miner's Rule ◽  
Loading Spectrum

In the fatigue design of steel catenary risers, there are concerns regarding the fatigue damage to girth welds from low stresses, below the constant amplitude fatigue limit, in the loading spectrum and the validity of Miner's cumulative damage rule. These fundamental issues were addressed in a recent joint-industrial project (JIP). A key feature was development of the resonance fatigue testing rigs to enable them to test full-scale pipes under variable amplitude loading. Such tests were performed under a loading spectrum representative of that experienced by some risers, with many tests lasting over 100 million cycles to investigate the fatigue damage due to small stresses as well as the validity of Miner's rule. However, the resonance rigs are only capable of producing spectrum loading by gradually increasing or decreasing the applied load whereas more “spiky” random load sequences may be relevant in practice. Therefore, the program also included fatigue tests in conventional testing machines on strip specimens cut from pipes to compare the two types of loading sequence. This paper presents the results of these tests, conclusions drawn, and recommendations for changes to current fatigue design guidance for girth welded pipes regarding the definition of the fatigue limit, allowance for the damaging effect of low stresses, and the validity of Miner's rule.

Fatigue Strength Study on Different Structure Type of Hatch Corner

2011 ◽  
Vol 233-235 ◽  
pp. 2580-2583
Author(s):  
Yong He Xie ◽  
Wei Wang ◽  
Heng Zhang
Keyword(s):  
Fatigue Strength ◽  
Scale Effect ◽  
Hot Spot ◽  
Structure Type ◽  
Cumulative Damage ◽  
Hot Spot Stress ◽  
Fatigue Design ◽  
Miner’S Rule ◽  
Curve Method ◽  
Miner's Rule

The fatigue strength study of the hatch corner is carried out ,based on the S-N curve method and the assumption of the linear cumulative damage of Palmgren-Miner's rule, using the hot spot stress method. Study on the effect of the structure different type to the fatigue strength of the hatch corner is carried out through changing its construction details and thickness. By comparing, the reasonable structure is obtained, and the scale effect should be put into consideration in fatigue design.

scholarly journals Discussion of Miner’s Rule on Type 304 Austenitic Stainless Steel at 288 C in Air

2005 ◽  
Author(s):  
Makoto Hayashi
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Cumulative Damage ◽  
304 Stainless Steel ◽  
Random Loads ◽  
304 Austenitic Stainless Steel ◽  
Miner’S Rule ◽  
Cumulative Fatigue Damage ◽  
Miner's Rule ◽  
Type 304

The surface worked type 304 stainless steel exhibits an extraordinary behavior when subjected random fatigue load. In this study the effect of load history on the cumulative damage was examined. The random loads are 1) two step increasing stresses, 2) two step decreasing stresses, 3) repeated high and low step stresses, 4) repeated low and high step stresses, and 5) gradually increasing stresses. In any cases the cumulative damage calculated according to Miner’s rule remarkably exceeded 1.0, especialy for the gradually increasing stresses. In order to survey the mechanism, the elastic and plastic strain behaviors were studied. The extraordinal cumulative fatigue damage could be explained by the remarkable fatigue hardening behavir of austenitic stainless steel.

Improved Fatigue Design of SCR Modified Miner’s Rule

2019 ◽  
Author(s):  
Hans Olav Knagenhjelm ◽  
Mons Hauge ◽  
Bård Nyhus
Keyword(s):  
Carbon Steel ◽  
Stress Distribution ◽  
Fatigue Testing ◽  
Wave Spectrum ◽  
Fatigue Crack Initiation ◽  
Steel Pipe ◽  
Variable Amplitude ◽  
Fatigue Design ◽  
Miner’S Rule ◽  
Miner's Rule

Abstract The Aasta Hansteen floating production system is the first SPAR platform with steel catenary risers (SCR) at the Norwegian Continental Shelf (NCS). The water depth is 1300 msw. The weather conditions with respect to wave loading are more severe than any offshore installation completed so far. Under such environmental conditions, it is vital to verify the design of the SCR’s with respect to extreme loading and fatigue life. A fatigue verification program has been executed for ground OD welds of both clad and carbon steel riser materials. The objective was to determine the effect of weld defects in combination with the effect of variable amplitude loading using the actual fatigue stress distribution experienced by critical parts of the SCR. The stress distribution is based on the local wave spectrum and estimated from hydrodynamic analysis of the riser and the long-term wave statistics. Two clad pipes and one carbon steel pipe was exposed to rotation bending fatigue testing with artificially imposed defects. One clad pipes gave fracture after more than 1.0 × 109 cycles. The carbon steel pipe gave fracture after 4.56 × 108 cycles. A modified Miner’s summation rule is proposed for variable amplitude fatigue design. The procedure is based on a verification of variable amplitude testing against constant amplitude testing. The results indicate that load amplitudes below a fatigue limit defined at 107 cycles are not contributing significantly to fatigue crack initiation and growth from a weld defect. The proposed method suggests an engineering approach to this by a modification of the Miner’s rule for VA loading.

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